Note: Descriptions are shown in the official language in which they were submitted.
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W098/02985 PCT~S97/12045
DIGITAL COMMUNICATION SYSTEM FOR APARTMENT BUILDINGS
AND SIMILAR STRUCTURES USING EXISTING TELEPHONE WIRES
Cross Reference to Related APplications
This application references U.S. patent
applications Serial No. 08/431,270 filed April 28, 1995
entitled "VIDEO TRANSMISSION SYSTEM UTILIZING INTERNAL
RESIDENCE TELEPHONE LINES", Serial No. 08/670,216, filed
June 21, 1996, entitled "RF BROADCAST SYSTEM UTILIZING
INTERNAL TELEP~ONE LINES", Serial No. 08/816,059, filed
March ll, 1997, entitled "CABLE TELEVISION DISTRIBUTION
AND COMMUNICATION SYSTEM UTILIZING INTERNAL TELEPHONE
LINES", and Serial No. 08/814,837, filed March 11, 1997,
entitled "TWO-WAY RF COMMUNICATION AT POINTS OF
15 CONVERGENCE OF WIRE PAIRS FROM SEPARATE INTERNAL
TELEPHONE NETWORKS".
U.S. Serial No. 08/431,270, filed April 28, 1995,
entitled "VIDEO TRANSMISSION SYSTEM UTILIZING INTERNAL
RESIDENCE TELEPHONE LINES" is a continuation of Serial
20 No. 08/181,562, filed January 13, 1994, now abandoned,
which is a continuation of Serial No. 08/062,148 filed
May 14, 1993, now abandoned, which is a continuation of
Serial No. 07/688,864, filed April 19, 1991, now
abandoned, which is a continuation of Serial No.
07/379,751, filed July 14, 1989, now Patent No.
5,010,399.
U.S. Serial No. 08/670,216, filed June 21, 1996,
entitled "RF BROADCAST SYSTEM UTIL~ZING INTERNAL
TELEPHONE LINES", is a continuation of Serial No.
08/545,983, filed october 20, 1995, now abandoned, which
is a continuation of Serial No. 08/376,921, filed January
23, 1995, now abandoned, which is a continuation of
08/255,355, filed on June 8, 1994, now abandoned, which
is a continuation of application Serial No. 08/114,976,
35 filed August 31, 1993, now abandoned, which is a
continuation of application Serial No. 07/803,135, filed
. .
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- 2
December 5, 1991, now abandoned, which is a continuation-
in-part of application Serial No. 07/688,864, filed April
19, 1991 (hereinafter "U.S. patent application Serial No.
08/431,270"), now abandoned, which is a continuation of
5 application Serial No. 07/379,751, filed July 14, 1989,
now Patent No. 5,010,399.
U.S. Serial No. 08/816,059, filed March 11, 1997,
entitled "CABLE TELEVISION DISTRIBUTION AND COMMUNICATION
SYSTEM UTILIZING INTERNAL TELEPHONE LINES", is a
10 continuation of application Serial No. 08/674,117, filed
July 1, 1996, now abandoned, which is a continuation of
application Serial No. 08/545,983, filed October 20,
1995, now abandoned, which is a continuation of Serial
No. 08/376,921, filed January 23, 1995, now abandoned,
15 which is a continuation of Serial No. 08/255,355, filed
on June 8, 1994, now abandoned, which is a continuation
of application Serial No. 08/114,976, filed August 31,
1993, now abandoned, which is a continuation of
application Serial No. 07/803,135, filed December 5,
1991, now abandoned, which is a continuation-in-part of
application Serial No. 07/688,864, filed April 19, 1991
(hereinafter "U.S. patent application Serial No.
08/670,216"), now abandoned, which is a continuation of
application Serial No. 07/379,751, filed July 14, 1989,
25 now Patent No. 5,010,399.
U.S. Serial No. 08/814,837, filed March 11, 1997,
entitled "TWO-WAY RF COMMUNICATION AT POINTS OF
CONVERGENCE OF WIRE PAIRS FROM SEPARATE INTERNAL
TELEPHONE NETWORKS", which is a continuation of
30 application Serial No. 08/673,577, filed July 1, 1996,
now abandoned, which is a continuation of application
Serial No. 08/545,937, filed October 20, 1995, which is a
continuation of Serial No. 08/372,561, filed January 13,
1995, now abandoned, which is a continuation of Serial
35 No. 08/245,759 filed on May 18, 1994, now abandoned,
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-- 3
which is a continuatlon of 08/115,930, filed August 31,
1993, now abandoned, which is a continuation of
07/802,738, filed December 5, 1991 (hereinafter "U.S.
patent application serial No. 08/816,059"), now
5 abandoned, which is a continuation of 07/688,864, filed
April 19, 1991, now abandoned, which is a continuation of
Serial No. 07/379,751, filed July 14, 1989, now U.S.
Patent No. 5,010,399 (hereinafter, the "parent
application").
Backqround of the Invention
The invention relates generally to digital
communication over existing lines in residential
structures. The development and popularity of the
computer communication network called the Internet has
15 spurred much excitement. Although there are many
services provided by the Internet that people enjoy,
there is a common complaint that data does not flow
downstream (that is, towards the end user) at a rate that
is sufficient to support many of the applications that
20 are in demand.
An effort to use municipal coaxial cabling
networks to provide connections for cable TV subscribers
to the Internet has begun. New devices called "cable
modems" have enabled adaptation of these coaxial networks
25 to Internet computer communication.
The coaxial cabling in place in most localities is
installed in a "tree-and-branch" manner. This allows for
a very high downstream data rate, which is one reason why
the cabling can be used for these Internet connections.
It is very difficult, however, to use this cabling for an
upstream (that is, away from the end user) data path at
other than very low data rates. The best alternative
seems to be the use of ordinary telephone lines to
provide an upstream path. This either adds to the cost
, .. _ . . . .
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or ties up a line. Another difficulty is that cable
modems are extremely sophisticated devices and their use
will make the cable system expensive. Finally, the
coaxial wall outlets in a residence are not, in general,
5 located where connection of computers is convenient.
The municipal coaxial cabling networks represent,
unfortunately, the only existing conductive pathways that
can economically support a very high downstream
communication data rate from a central location to
lO individual residences in the surrounding areas. As a
result, there is no satisfactory solution to the problem
of inadequate downstream and upstream Internet bandwidth.
SummarY of the Invention
The present invention relates to two-way
15 communication of signals, particularly digital signals,
over telephone wires between the various residential
units in an apartment building or similar structure and a
point where the wires in the building converge, for
example, on the ground floor, while the wires continue to
20 fulfill their original function as a conductive path for
voice signals. A dedicated digital path is created, in
this manner, between each apartment unit and a
communications hub located at the point of convergence or
hub. A high capacity line connects between this hub and
25 a part of a larger network, such as the well-known
Internet. This completes the connection between the
residents upstairs and an external communications
network.
A particular advantage of the invention is that
30 the residents can share access to the high-speed line in
such a way that each resident can enjoy nearly its full
capacity. This is possible because typical residents
make short "bandwidth demands," or requests for
"dedicated" access to the line at very infrequent
CA 022628~9 1999-01-12
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intervals as, for example, a demand for one second of
access each minute. The result is that the line is
dormant and therefore fully available to the other
residents during the other 59 seconds. Ultimately, of
5 course, a resident will have to wait for access, at least
for a short period, when many other people in the same
building are also engaged in communication activities.
The invention also provides for the use of these
telephone wires to enable the tenants to concurrently
10 access video signals that are brought to the same point
of convergence. Finally, the invention includes methods
for reducing the effect that reflections in the internal
wiring can have on transmitting signals at frequencies
above voiceband. Some of these methods may be
15 particularly useful in using the telephone wiring
internal to single family homes for communication of data
and video.
This invention is partly an outgrowth of
technology presented in the parent application (Patent
20 No. 5,010,399) and the three continuations-in-part
thereof (U.S. Patent applications Serial Nos. 08/431,270,
08/670,216, 08/816,059, and 08/814,837). They are all
incorporated herein by reference.
Most of the technology disclosed in the Patent No.
25 5,010,399 and U.S. patent application Serial No.
08/431,270 relates to the transmission of telephone
signals and non-telephonic signals (such as cable
television signals, other video signals, audio signals,
data signals, and control signals) across telephone
30 wiring networks of a general nature. Many of the
elements disclosed in U.S. patent application Serial No.
08/670,216 are particularly appropriate for transmission
within typical single family residences, while the main
focus of U.S. patent application Serial No. 08/816,059 is
, . ~ . , , ., .. _
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-- 6
communication through apartment buildings and similar
structures.
This invention takes advantage of the
opportunities made available by the unused frequencies
5 that exist on the telephone wiring in apartment
buildings. In part, the invention is directed towards
the use of a wiring network internal to apartment
buildings to inexpensively establish a digital connection
between the tenants and an outside communication line.
lO By establishing such connections according to the
invention, and by connecting multiple buildings together
in a specially cooperative network, the problem of slow
data flow, described above, can be significantly reduced
at relatively low cost. This is one objective of the
15 invention. An additional objective is to provide the
digital communication capability while allowing for
simultaneous communication of video over the same
conductive pathways. A third objective is to
economically overcome some of the untoward effects that
20 splits in internal wiring have on the use of these wires
for non-telephonic communications.
Methods described in the previous applications are
extended herein. The focus of these extensions is to
provide for better communication over these wires using
25 less expensive hardware, and to provide a solution that
is less costly to install and operate. For example, the
use of the Manchester coding system and other elements of
classical Ethernet LANs (local area networks), is
extended to telephone networks, resulting in a digital
30 communications network which operates in a manner that is
virtually identical to classical Ethernet LANs. Methods
are also disclosed for using the particular data networks
described herein for the transmission of digital video
signals.
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Because the invention can also be used in single
family homes in addition to apartment buildings,
provision is made for adapting the invention for use in
those types of structures as well.
Brief DescriPtion of the Drawinq
FIG. la is an overview of a system for allowing
tenants in an MDU (multiple-dwelling unit) to access
multiple video and data sources brought to the point
where the telephone wires converge.
FIG. lb is a splitter for connecting both
voiceband and broadband signals.
FIG. lc shows the principles of the transceiver.
FIG. ld shows the processor, a principle component
of the transceiver.
FIG. 2 shows the major system components in the
wiring closet.
FIG. 3 shows the principle components of the
communications hub.
FIG. 4a is a diagram of a patch panel for
20 combining and separating multiple signals of different
varieties.
FIG. 4b is a diagram of a patch panel for
combining and separating voiceband and broadband signals.
FIG. 5 shows the principle components of a modem
25 for transmitting data in an apartment unit over active
telephone lines.
FIG. 6 is a diagram of a modem that does not load
the communication line.
FIG. 7 shows the details of the modem in FIG. 6.
FIG. 8a is a diagram showing how to use two pairs
of active internal wiring to connect a lOBaseT adapter.
FIG. ~b is a diagram showing how to use a lOBase2
adapter over a single pair.
. ~
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-- 8
FIG. 9a is a diagram showing how to connect to a
10BaseT hub over the internal wiring of a multiple
dwelling unit.
FIG. 9b is a diagram showing how to connect
5 10Base2 Adapters to a 10BaseT hub
FIG. 9c is a diagram showing how to connect
10BaseT Adapters to a 10BaseT hub using a single pair.
FIG. 10a shows a low data rate LAN that uses the
internal wires of an MDU.
FIG. 10b shows a second low data rate LAN that
uses the internal wires of an MDU.
FIG. ll shows a data communications network
established across a group of MDU buildings.
FIG. 12 shows a modulator that can transmit either
15 video or data.
Description of the Preferred Embodiments
An Overview of the SYstem
FIG. la shows the type of twisted pair network
typically found in apartment buildings and other
20 "multiple dwelling units," hereinafter referred to as
MDUs. The configuration is typical because multiple wire
pairs fan out from a point of convergence, reaching each
of the residential units in the building, which are
called local networks 411.
In most apartment buildings, each unit is served
by two or more of these wire pairs. The wiring splits
inside each unit, terminating at wall jacks at different
locations. Often, both telephones and broadband devices
connect to these jacks, the telephones communicating with
30 local exchange 475 and the broadband devices
communicating with a high-speed line 402 through
transceiver a 400. (Voice signals are expressed at
baseband using frequencies below 3 KHz. Signals whose
energy is confined to frequencies above 3 KHz, by
35 contrast, are referred to herein as broadband signals.)
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In FIG. la, telephone devices 414a, b, and c are
shown connected to one of the jacks. Each telephone
connects through a low pass filter. These jacks can
follow the design of splitter 161, shown in FI~. lb.
5 Splitter 161 includes filters which block RF energy from
transmitting between the telephone devices and the
wiring, and also provides a termination at RF frequencies
to prevent reflection of RF energy back onto the network.
FIG. la also shows a digital device, computer
10 495c, connected to the wiring through a digital
transceiver 491c. This transceiver exchanges digital
signals with a transceiver/switch 400. The basic
principles of transceiver 495c are shown in FIG. lc.
That figure shows digital transmitter 178 and digital
15 receiver 179, and how they communicate digital signals
over a network of active telephone wiring. As described
in U.S. patent application Serial No. 08/816,059,
transceiver 491c combines the functions of these two
devices together so that they transmit and receive
20 signals through the same connection to the wiring.
FIG. la shows components of the systems called
Local Network Interfaces 404a, b, and c. These represent
electronic processors connected to the wiring at a point
just before the wires reach their destination, (that is
25 the individual apartment units), and split off towards
the various terminations. Local Network Interfaces 404
are provided to assist in the communication process. An
example would be the placing of an amplifier in the
wiring closet on each floor of the building. However,
30 these interfaces are not strictly required.
Configurations can implemented where the Local Network
Interface is absent, and signals run over the wiring
directly from the convergence point to the terminations
(in the tenant's apartment) without active or passive
35 processing at any intermediate location.
~ . .
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-- 10
FIG. ld shows processor 418, which is the
principle component of transceiver 400. This is the
"nerve center" of the apartment communication system
described in U.S. patent application Serial No.
08/816,059. It applies signals onto the wires leading to
the residential units up above, receives broadband
signals applied to the wiring by the transmitters that
connect at the terminations in the local networks 411,
provides the switching necessary to direct signals to
10 their proper locations, and exchanges signals with a
high-speed communication line 402.
The following topics are covered in the next four
sections:
l. Connections at the point of convergence of the wire
15 pairs
2. The digital communications hub
3. Patch panels -- separation of voice and broadband
signals
4. Signal flow and processing in the apartment units
5. Two-way communication using one pair of wires and two
frequency bands
These sections describe the processing used to allow
individuals in a large structure to efficiently share a
high speed connection to a digital communication network.
Subsequent sections will describe much more specific
systems that provide extra functionality and economy.
1. Connections at the Point of Converqence of the Wire
Pairs. FIG. 2 illustrates the telephone connections
to an apartment building. Telephone service is typically
30 provided to tenants in apartment buildings in the
following manner. A bundle of wire pairs from the
central telephone office arrive at a patch panel 612 in
the master wiring closet in the basement of the building.
Panel 612 allows cross connection of these wires with the
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internal wires that lead from the closet upwards to
apartment units 611. An internal line is made active
when it is cross-connected to one of the outside lines
terminating in panel 612. In the US, typical apartment
5 units are served by at least two internal pairs.
Some apartment buildings include a private
telephone switch to which all tenants connect. Such a
switch, also called a PBX, is functionally identical to
the central office of the telephone company. Referring
10 to FIG. 2, it is clear that the validity of the teachings
of this invention are not affected when the "central
office" is replaced by a PBX.
To install a broadband system in a building,
broadband panel 615 is installed in the wiring closet,
15 and a "detour" through this panel is created for each
twisted pair 616 that will carry broadband signals to or
from an apartment unit. These pairs 616 exchange signals
with hub 618 through patch panel 615. In other words,
signals are added to pairs 616, transmitting in the
20 direction of the apartment units, and signals transmitted
in the opposite direction are stripped from the pairs and
transmitted to hub 618. The details of separators 613
and panel 615 are described later.
2. The Diqital Communications Hub
The functions performed by digital communication
hub 618 are a subset of the functions performed by
processor 418, in FIG. ld. Both processor 418 and hub 618
are designed to manage two-way communication with
multiple destinations in a single structure that are
30 served by twisted pairs that converge at a common point.
As described in U.S. patent application Serial No.
08/816, 059, processor 418 manages communication of
signals of all varieties, and also manages communication
between one destination and another, and between each
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- 12 -
destination and the outside communication line. Hub 618,
by contrast, manages only digital communications, between
the one destination and another, and, especially, between
one destination and an outside communication line.
The details of hub 618 is shown in FIG. 3. Hub
618 receives signals from communication line 602,
converts these signals to a time-multiplexed digital
Bitstream, separates the signal into individual
bitstreams, and applies the individual bitstreams to the
lO twisted pairs leading to the appropriate destinations.
When processing signals flowing in the reverse direction
(that is, to the line 602), hub 618 inputs digital
signals from the various telephone lines leading from
patch panel 615, time-multiplexes them together into a
high-speed Bitstream, and applies this Bitstream to
communication line 602.
Hub 618 includes interface 609. Interface 609
performs the function of exchanging signals with a high
speed communication line 602. There are many different
20 methods for performing that exchange, one of which is
frequency modulation/demodulation to separate the
frequencies of signals applied to line 602 from those
received from it. Manchester encoding could also be used
separate these frequencies.
Signal collection subsystem 607 represents the
part of hub 618 that receives digital signals at
broadband frequencies from twisted pairs 678 that lead
from broadband patch panel 615. (These pairs ultimately
lead to the individual apartment units.) Demodulators
608 represent the parts of subsystem 607 that convert the
received signals from broadband frequencies to baseband,
thereby creating a datastream of digital signals.
Processor 614 then uses time-domain multiplexing to
combine them into a single datastream that is passed to
35 interface 609. Signal distribution subsystem 603
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represents the part of hub 618 that separates a digital
Bitstream into many digital signals at lower data rates,
and applies them onto the twisted pairs leading to the
broadband patch panel 615. Processor 606 is the part of
5 subsystem 603 that separates a time-multiplexed
datastream into its individual signals. Modulators 610
represent the part of subsystem 603 that converts each of
the lower-rate digital signals to broadband frequencies
before passing them to broadband patch panel 615.
Modulators 610 and demodulators 608 may not work
by modulating a carrier wave in the classical style. A
method called Manchester coding can be used to express
digital sequences as electrical signals that will
transmit across the wiring at frequencies abo~e the
15 voiceband. Manchester codes are the same as the codes
used in standard LAN (local area network) technologies
such as Ethernet and Token Ring systems. Manchester
codes are bi-level square waves that transition at the
midpoint of every time interval used to encode a bit.
20 This transition provides timing information, and extra
transitions encode the data. Manchester coded signals do
not have energy at DC and have little energy at low
frequencies. As a result, no additional modulation of
the waveform is necessary to place the signal completely
25 above the voiceband, and the signal output by standard
LAN products can be passed directly through a hi-pass
filter onto the wiring. (Such a high pass filter is
necessary to block voiceband energy. ) These types of
signals can also be interpreted directly by the receiver
30 without classical demodulation. As a result, if
subsystems 607 and 603 are designed to send and receive
signals encoded using the Manchester method, modulators
610 actually work by converting (that is modulating)
classical square waves into bi-level square waves with a
.
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- 14 -
fixed transition pattern. Demodulators 608 work by
performing the reverse process.
Other versions of subsystems 603 and 607, which
include additional functionality, are illustrated in hub
5 618', 618a, and 618b, which are shown in Figs 9a, 10a,
and 10b of this application and described below.
3. Patch Panel 615 - SeParation of voice and broadband
siqnals
FIG. 4a shows the details of one version of patch
10 panel 615 labeled 615a. A simpler version of the patch
panel shown in FIG. 4b will be described later. The
signals outputted through the ports of hub 618 are passed
through broadband patch panel 615a, before they are
transmitted to the apartment units 611. Broadband
15 signals sent from the apartments also pass through this
panel as they flow towards hub 618. These signal
pathways are now described in greater detail.
To connect a tenant's computer to hub 618, at
least one of the pairs leading to the tenant's apartment
20 unit is detoured through panel 615a. Panel 615a is
composed of a collection of signal separators 613a, 613b
and 613c. As shown in Figs 2 and 4, broadband signals
reach one of signal separators 613 by transmitting along
pairs 616 from the tenants apartment unit or by
25 transmitting along pairs 678 leading from hub 618. Voice
signals flow through the separators from the central
office to the tenants' apartment units and back.
Separators 613 use passive processing to guide
broadband signals from pairs 616 (in FIG. 2) onto the
30 correct ones of pairs 678 (in FIG. 2), and to guide
signals transmitting in the opposite direction in a
similar manner. In doing so, they receive signals that
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transmit at different fre~uency bands on a single pair,
and separate them by applying them onto different ones of
multiple pairs. They also combine signals, at different
frequencies, from multiple pairs onto a single wire pair.
5 Different types of separators are described below.
Separator 613a is an example of a junction that
allows digital signals to flow in opposite directions on
the same wire pair. Digital signals headed downstream
(towards the tenant) pass through a coupling junction 623
10 that is internal to 613a. Junction 623 prevents
downstream signals from reversing directions by taking
the alternate path down through the junction. High pass
filter 622 is located downstream of the junction, and it
blocks the voiceband signals from flowing towards Hub
15 618. The digital signals pass though filter 622 and
continue on to the tenant's apartment. The voiceband
signals, meanwhile, reach the upstairs apartment after
passing through low pass filter 621 that blocks the
digital signals from flowing towards the central office.
In the opposite direction, digital signals applied
to the telephone wires in the tenant's apartment pass
through high pass filter 622 and through coupling
junction 623 towards demodulators 608 in Hub 618.
Ordinarily, the two digital signals must cover different
25 frequency bands in order to prevent interference while
flowing upstream and downstream on the same wire pair.
(Important exceptions to this restriction are described
later on.)
In separator 613b, the upstream and downstream
30 signals servicing a tenant flow over different wires
pairs. Signals transmitting upstream towards hub 618
transmit over the left pair. They encounter a simple
split in the wiring but are blocked from exiting towards
the central office by low pass filter 627 shown on one
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- 16 -
branch of the split. Instead, they continue through high
pass filter 624 and flow towards hub 618. High pass
filter 624 prevents voice band signals from transmitting
towards the hub.
Broadband signals flowing in the opposite
direction (downstream) use the second twisted pair that
services the same apartment. These signals lead from hub
618 through high pass filter 625, while telephone signals
pass, in both directions, through low pass filter 626
10 that prevents RF energy from flowing towards the central
office.
The second twisted pair passing through separator
613c also illustrates a different concept. It routes
through separator 613c which allows video signals at
15 frequencies higher than the data to flow onto the wire
pair and transmit towards the tenant. Internal to
separator 613c, the video and data signals converge at
coupler 630, which prevents either signal from flowing
back towards the opposite signal source. They continue
20 on through band pass filter 628, which blocks energy
outside of the bands occupied by the two signals
At the same time, control signals used to control
the video source are created in the tenant's apartment.
These signals are converted to electrical form and
25 transmitted onto the wiring, reaching separator 613c.
~Numerous ways of applying control signals to the wiring
are shown in the previous applications.) They flow
through the patch panel but are blocked by band pass
filter 628, passing instead through band pass filter 629
30 on the way to electronics that can receive and interpret
their information. Band pass filter 629, meanwhile,
blocks the video and digital signals from transmitting
towards these electronics.
To more clearly illustrate the signal flow through
35 separators 613b and 613c, an example of the combination
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of video, data, and control on the same wire is now
given. Assume the digital signal flowing through these
separators is an Ethernet signal with energy between 3
MHZ and 18 MHz. Assume further that a video source
5 frequency modulates a 27.5 MHz carrier, expressing the
video information between 20 MHz and 35 MHz. Because the
digital and video signals are separated in frequency by 2
MHZ, they can readily transmit on the same wire without
interference. Meanwhile, the control signal could
10 occupy, for example, the frequencies between 1.5 and 2
MHz, and also avoid interfering with those two. Bandpass
filter 629, in this case, would pass frequencies between
1.5 and 2 MHz, while bandpass filter 628 would pass
fre~uencies between 3 and 35 MHz. High pass filter 625,
15 in separator 613b, would pass all the frequencies between
1.5 and 35 MHz, because the video, data, and control
signals are not separated in that component. Low pass
filter 626 would pass only the voiceband, blocking the
three broadband signals from transmission towards the
20 central office.
FIG. 4b shows patch panel 615b, which is a simpler
version of patch panel 615. The simplicity is due to the
fact that there is no separation or combination of two
different broadband signals on the panel. Rather, the
25 separation and combination of broadband signals in
accomplished internal to hub 618 and internal to the
electronic transceiver that locates in the tenant's
apartment unit and is described below. The passive
electronics on panel 615b only separate broadband slgnals
30 from voiceband signals, and only combine a broadband
signal onto a pair that conducts a voiceband signal and
nothing else. Low pass filter 628 and high pass filter
617 are used to perform these functions, which are
described many times in the preceding applications.
35 4. Siqnal Flow and Processinq in the Apartment Units
. . .
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- 18 -
FIG. 5 shows the communication processes in the
tenant's apartment unit Modem 645a exchanges signals
between PC 646 and hub 618 through patch panel 615.
Modem 645a connects to the wiring through splitter
5 634. Within splitter 634, low pass filter 631b allows
the voiceband signals to reach the telephone, while
blocking broadband signals, thereby preventing a
telephone device from loading down broadband energy. The
digital signals transmitting between the hub 618 and the
10 modem 645a pass through high a pass filter 631a. High
pass filter 631a blocks the voicehand signals from
transmitting towards modem 645a. Splitter 634 is
similar to splitter 161 in FIG. lb but does not have the
terminator 163.
The signals arriving at the modem 645 through the
splitter 634 pass through a coupler 643 and pass through
band pass filter 640 to a digital demodulator 636. That
component converts the analog waveform of the signal into
a digital Bitstream. The resulting Bitstream reaches
20 digital diplexer 637 which sends the data to the
computer. Digital signals transmitted from the computer
646, are received by the diplexer 637 and are passed to
digital modulator 635. That device converts the digital
Bitstream to an analog waveform, which flows through band
25 pass filter 641, through coupler 643 and high pass filter
631a, and onto the internal wiring. The bandpass filters
641 and 640 prevent the analog signals passing through
coupler 643 from crossing over towards the opposite
sections of the modem.
The analog signals passing onto the internal
wiring split and transmit in two directions. If the
energy of the signal is high enough, however, sufficient
strength will appear at the one of demodulators 608, that
is the companion to modem 645 and is located in the
35 wiring closet.
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Digital modulator 635 works in coordination with
one of demodulators 608 (FIG. 3), and digital demodulator
636 works in coordination with one of modulators 610
(FIG. 3) in hub 618. The modulators use coding to
5 express digital information as analog waveforms, and the
coding procedure must be correctly interpreted by the
demodulators in order for the Bitstream to be correctly
reproduced.
Digital diplexer 637 is simply a digital device
10 that includes the means to establish two-way
communication with a port on a PC or other type of
computer. In the preferred embodiment, this diplexer
will be designed to communicate with the parallel ports
that are common to most PCs. The parallel port is a good
15 choice because it can be inexpensively added to the
computer, it can accommodate two-way digital
communication at high data rates, and digital diplexer
637 can be designed to emulate one of the many devices
that communicates through such a port in this manner.
20 Such emulation would allow the PC to use approximately
the same software that is designed to communicate with
the device being emulated.
5. Two-waY Communication Usinq One Pair and two Bands
The most common interaction on the Internet is the
25 downloading of data from a server to an end user. This
is what makes the demand on the "downstream'/ bandwidth
much higher than the demand on the "upstream" bandwidth.
There are a few applications, such as video conferencing,
where a high upstream capacity is required. Even in
30 these systems, however, the downstream data rate
requirements are likely to be much higher.
The lower upstream requirement means that the
upstream data can be expressed within a narrower
frequency band. In the invention, the narrow band makes
. . .
CA 022628~9 1999-01-12
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- 20 -
it easier to find enough spectrum on a single twisted
pair for the expression of both signals. Expressing both
the upstream and downstream signals on a single pair has
many advantages. First of all, it leaves all the
5 frequencies (that is the spectrum) on the second pair
open for other types of communication, such as the
transmission of analog video described in Patent No.
5,010,399 and in subsequent continuations in part. A
second advantage is that the path established by the
lO second wire pair is often broken at intermediate wiring
closets and at some of the telephone jacks in the
apartment unit. As a result, confining all communication
to the first path can decrease the amount of preparation
necessary to begin service to a particular unit.
15 Perhaps the most important advantage to using a single
wire pair is that communication can be conducted across
wiring where a four-conductor bundle serves an apartment
unit and all conductors are twisted together rather than
twisted in pairs. This type of wiring is sometimes
20 called "quad," and is often used to reach from the "local
wiring closet" found on the floor of each apartment
building to the individual units on that floor. Because
of the nature of the twisting, there will be very high
crosstalk between one wire pair and any second pair.
25 Effectively, this may mean that a "quad" cable includes
only one wire pair that is available for RF
communication.
An example of the expression of both the upstream
and downstream signals flowing between a single apartment
30 unit and hub 618 is now given. Assume that modulator 610
(FIG. 3) in subsystem 603 receives a Bitstream at 2 Mbs
from processor 606. Modulator 610 can then use the
common encoding scheme called frequency shift keying
(FSK) to express this Bitstream as an analog waveform
35 confined within, for example, 5-lO MHz. This signal
CA 022628~9 1999-01-12
W098/02985 PCT/US97/12045
transmits through patch panel 615b (FIG. 2) and reaches
digital demodulator 636 in modem 645 (FIG. 5). That
component recreates the 2 Mbs digital Bitstream and
passes it through digital diplexer 637 to computer 646,
5 thereby completing the downstream path. In the opposite
direction, the PC creates a Bitstream of only 1 Mbs.
This signal can also be converted to an analog waveform
using FSK, and is slow enough to be expressed in only 3
MHz of bandwidth, as between the frequencies of 1-4 MHz.
10 It can, as a result, flow between digital modulator 635
and digital demodulator 608 in subsystem 607 without
interfering with the downstream signal, because the two
do not overlap in frequency.
ImProvinq the Data (and Video) Link over the Network
15 Wirinq
Much of the foregoing discussion described
processing that is likely to be common to many systems
that meet the specific challenge of allowing individuals
in a large structure to efficiently share a high speed
20 connection to a digital communication network. Later,
more detailed systems for meeting this challenge are
described. Before that description, however, the
invention includes new methods that are useful in the
communication of high-speed data and other broadband
25 signals over telephone wires in general, and over active
internal telephone networks in particular.
1 Removinq All Reflections and Loadinqs from the Internal
Wirinq.
The Patent No. 5,010,399 and U.S. patent
30 application Serial No. 08/431,270 described the use of
low pass filters to remove the loading affects of
telephone devices that may connect to the wiring network.
As described, if all telephone devices connect through a
CA 022628~9 1999-01-12
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low pass filter, they can all continue to operate
normally and will have no affect on high-frequency
energy. These filters are shown, among other places, as
part of in splitter 161, in FIG. lb. All telephone
5 devices connected to a network of wiring can be
inexpensively filtered in this manner.
Other loadings can be caused by connection of
broadband devices that receive energy from the wiring.
In this section, a method of connecting these devices
that does not disturb the existing signal flow is
described.
Reflections are caused by open terminations and
splits in the wiring. U.S. patent application Serial No.
08/431,270 described the use of a terminator in splitter
161 to suppress reflections at the end of an open
termination. As described in that application, however,
splitter 161 can cause a substantial reduction of energy
flowing through the network if it is connected at the end
of a very short stub. An example is where the various
jacks in a network are all connected by a process known
as "daisy chaining."
Referring to FIG. 6, if one ignores, for the
moment, the wire leading from jack 642a to jack 642b, the
remaining conductive paths illustrate an example of
"daisy chaining." Note that a single wire pair leads
successively from one wall jack to the next, (that is
from 642a, to 648, to 64g,) providing a connection
opportunity at each jack. Many apartment units are
connected in such a manner. If splitter 161 were
30 connected at jack 642a, its termination would
unnecessarily drain energy from the wiring.
It is always possible to identify a straight path
leading from one "open" termination to another, and to
consider this to be the main path, or "bus," and to
35 consider all other wiring as part of a branch. In FIG.
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6, for example, it is natural to identify jack 649 as one
termination and hub 6l8 as a second termination, with
jacks 648 and 642a connected in between. The path
leading from jack 642a to jack 642b would be an example
5 of a branch. Note further that extra branches are
created if broadband transmitters and receivers connect
at intermediate jacks 642a and 648, either at the end of
a long cord or in such a way as to load the energy on the
wiring. Were a video receiver to connect at jack 642a,
lO for example, significant energy would flow towards the
receiver.
When energy encounters a branch in twisted pair
wiring, reflections can occur as a result of some energy
being reflected back towards the source. Another type of
15 reflection can occur if an "open connection" terminates
the branch. Energy reflected from an open termination
may return to the main path, but with a time delay
relative to similar signals on that path. Even when
reflected energy does not cause substantial interference,
20 energy flowing down the main path is reduced by a branch.
If all such branches and affects are eliminated, and
terminations are added at the ends of the main path, the
transmission becomes well behaved -- signals applied to
the main path, or bus, simply split and half of the
25 energy transmits towards each termination, where it
gracefully exits the bus.
Methods to suppress reflections caused by
connection of high frequency devices and by naturally
occurring branches are now described. Referring to FIG.
6, splitter 661 is designed to allow connection of a
broadband device without causing reflection problems. It
connects to jack 648 with a zero impedance, so no
splitting or reflection of energy can occur. Signals
can be received from the main path because processor 632
35 detects the voltage variations of the signal as it flows
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- 24 -
past the wall jack, without disturbing or loading down
the signal flow. The detected signal is then amplified
and sent on to the broadband device, which is modem 645
in the case of Fig. 6. The cord that issues from
5 splitter 661 can be very long, yet it will not affect the
signal flow on the main path of the internal wiring.
Signals transmitted onto the wiring through
splitter 66~ simply flow through the zero impedance
connection, only adding to the signals on the main path.
10 These signals split, transmitting towards the
terminations at either end.
Note that splitter 661 also includes terminator
669 that connects behind high pass filter 664, at the
same point that processor 632 connects. Switch 671
15 allows one to break the connection (at high frequencies)
between this terminator and the wiring. The terminator
should not be connected when the wiring runs past a jack
in "daisy-chain" style, as it runs past jack 648 in FIG.
6. Such a connection would drain energy from the line
20 before it can flow on to jack 649 downstream.
By contrast, it is important that the terminator
be connected when splitter 661 connects to a jack at the
end of a segment of wiring, such as jack 649 in the lower
right part of FIG. 6. This connection terminates the
25 line at broadband frequencies, allowing the energy to
"exit gracefully" without causing a reflection.
Processor 632 can still detect the broadband signal
energy, if one is present, because the signal flows past
its point of connection. (Note that a similar terminator
30 is required where the internal wiring connects to hub
618, down in the wiring closet. This defines that
opposite end of the transmission "bus", and will be
discussed below.) Note that splitter 161, which is
connected at jack 649, provides the termination used in
35 FIG. 6.
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- 25 -
Now consider the issue presented when the branch
leading to jack 642b actually connects to the internal
wiring at jack 642a. This may be referred to as a
"naturaln branch, because it is not a result of
5 connecting a high frequency device to the main path.
This branch may be a wire leading to some other
part of the apartment not shown in the diagram. Because
there is nothing to prevent signal energy flowing from
hub 618 from splitting, at that branch, energy will be
10 diverted away from broadband devices that may connect at
jacks 648 and 649. Also, reflections may be created at
jack 642b, causing some energy to reflect back towards
jack 624a.
The reflections and diversion of energy can be
15 suppressed by opening the wall jack and placing low pass
filter 647 on the part of the branch nearest jack 642a.
This will make the RF signal flow behave as if there were
no branch connected at that jack. Fortunately, most such
branches are created at wall jacks, so easy access is
20 usually available to the point where the filter should
connect. Furthermore, low pass filters are made in the
form of well-known "split magnetic cores," which can be
connected to the wiring in a "snap on" manner, that is
without even making a break in the wire to connect the
25 filter.
A possible drawback to the use of low pass filter
647 in this manner is that it prevents the operation of a
broadband device at the end of the branch. A good
solution is available, however, when the internal wiring
30 consists of more than one pair, as is typical. LPF 647
will not affect the second pair, and broadband signals
can use that pair to flow towards jack 642b at the end of
the branch. A similar low pass filter (not shown),
however, must be installed along the second pair that
35 leads from jack 642a to jack 648. Placement of both
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these filters would create, effectively, two special
paths. One path would allow broadband energy to flow, on
the first wire pair, directly between hub 618 and jack
649, without any splits whatsoever, and without any
5 devices that could drain energy from the line. The
second path would allow flow of energy between jack 642b
and hub 618 in exactly the same manner.
When a second pair exists but the wiring is of the
"quad" type, where the four conductors are all twisted
10 together, the creation of two paths in this manner may
not be possible because of the likelihood of large
amounts of crosstalk. One can either tolerate the splits
created by the junction at jack 642a, or use low pass
filter 647 to simply block broadband energy from jack
642b. Yet another alternative (not shown) is to place a
sophisticated coupler at the 3-way junction. In theory,
such a junction could prevent reflections on all
branches, and allow signals to split cleanly when
crossing a junction in any direction.
The details of splitter 661 are shown in FIG. 7.
Low pass filter 663 connects directly to the internal
wiring, blocking the broadband energy from transmitting
to any telephone that may connect. Terminator 669 and
processor 632 connect behind high pass filter 664, which
25 blocks signals in the voiceband.
Switch 671 interposes between terminator 669 and
the wiring. Switch 671 is provided to defeat (that is
disconnect) the termination when needed. As described
above, the terminator should not connect when the
internal wiring runs past the jack and on to a second
location. A possible improvement is to provide an
adjustment mechanism (not shown) that can vary the
resistance that creates the termination. This will allow
the impedance to be more closely matched to the line,
35 making the suppression of reflections more certain.
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Splitter 661 is designed to be used with Modem
645, which is a slight variation on modem 645, shown
earlier. One difference is that bandpass filters 641 and
640, and coupler 643 are not included. Another
5 difference is that two wire pairs connect between modem
645 and splitter 661, and signals flow in only one
direction on each pair.
Key to processor 632 is amplifier 665. This
device detects the voltage variations created by the
10 signal on the internal wire as it flows past the wall
jack towards the termination. These variations can be
sensed through high pass filter 664, coupler 668, and
band pass filter 660. Amplifier 665 sends the
amplified signals towards demodulator 636 at a specified
15 energy level. Amplifier 665 is powered by a DC source in
modem 645, as shown in FIG. 7. The DC power is separated
from the other signals on the wire by the series of high
and low pass filters shown in the diagram.
Alternatively, amplifier 665 can be connected directly to
20 a DC power source.
In the opposite direction, signals from modulator
635 flow through amplifier 662a and band pass filter 662
to coupler 668. That junction applies 30 dB attenuation
to signals crossing towards band pass filerter (BPF) 660,
25 so it prevents amp 665 from picking up the signal from
modulator 635. The small amount of energy crossing
towards amp 665 is blocked by filter 660. Signals
continue onto the wiring and immediately split,
transmitting towards the terminator at jack 649 (FIG. 6)
30 and the terminator (described later on) at hub 618 down
in the wiring closet.
2Usinq Telephone Wirinq as a 10Base2 Bus -- Sinqle Pair,
SameBand used for Up and Downstream Flow
When reflections in the main transmission path
35 have been minimized, as provided in the previous section,
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- 28 -
modulator 635 can transmit signals within one frequency
band, and demodulator 636 can receive the signals sent
from hub 618 within the same band. The well-known
lOBase2 computer communication network sends signals
5 between stations over a single conductive path in exactly
the same manner.
Such a system can work because signals sent from
hub 618 will be terminated by splitter 161 at wall jack
649 -- they will not reflect back towards to the wiring
10 closet. As described above, signals sent from modulator
635 will also reach that termination, as well as the
termination at hub 618.
The only possibility of confusion can occur at
coupler 668. As described above, signals sent from
15 modulator 635 cannot reach demodulator 636 because
coupler 668 attenuates signals flowing along the path
from 635 to 636. (Band pass filters 662 and 660, which
were provided for extra separation, will not be effective
when signals communicate at the same frequencies.) A
20 similar mechanism allows hub 618 to send and receive
signals within the same band.
There may be several ways to implement coupler
668. An example of such a device is the "hybrid~
junction found in common telephones. (Common telephones,
25 of course, communicate signals in opposite directions
over a single pair within the same frequency bands.)
~deally, coupler 668 will include an adjustment
mechanism, so that the separation can be "tuned" to
account for minor variations in the characteristics of
30 the wiring and the electronics at the specific site.
To coordinate with modem 645, demodulator 608 and
modulator 610 must also transmit and receive signals
within the same frequency band. The same methods that
are used in splitter 661 can be used to create this
35 property in those devices.
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Transmittinq Analoq Video when Reflections and Loadinqs
are SuPPressed.
As described in the preceding applications,
transmi~sion of ordinary analog video in ordinary 6 MHz
5 AM NTSC format is possi~le over short distances of
telephone wiring such as are found in single family
homes. When transmitting NTSC video below the tunable
range, a mechanism must be provided to shift the signals
in frequency so that they again fall within the range of
10 a TV tuner. This involves extra expense, an expense that
could be saved if the signals were transmitted within
tunable channels.
But transmission over tunable channels is more
difficult because signal energy attenuates more quickly,
15 with distance, when the energy is expressed at higher
frequencies. Other factors, however, also contribute to
attenuation, and if these factors can be alleviated, the
attenuation due to transmission distance alone may not be
enough to adversely affect the picture. (The required
20 minimum thresholds for SNR and signal energy are
described in Patent No. 5,010,399 and in U.S. patent
application Serial No. 08/431,270.) In U.S. patent
application Serial No. 08/431,270, for example, the
possibility of using tunable channels is suggested as
2~ potentially feasible if the attenuatlon due to all
connected telephone devices is suppressed by low pass
filters. ~This type of attenuation is known as
"loading. a )
The methods described above, which suppress all
30 splits within the network, reduce the signal attenuation
of the digital signals described herein, but they can
also can be used to reduce the attenuation of any other
broadband signal in exactly the same manner. The
attenuation is reduced in the following ways:
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- 30 -
As described above, when a signal encounters a
split, a small amount of energy reflects back to the
source, while half of the remaining energy, in general,
transmits down one branch and half transmits down the
5 other. Assuming the target receiver is located
downstream of one of the branches, suppression of the
reflection and diversion saves slightly more than half of
the energy lost.
The attenuation due to transmission along the cord
10 connecting from a ~ack to the device is eliminated by the
affect of the amplifier ln active splitter 661.
Additionally, one of the methods disclosed in U.S.
patent application Serial No. 08/670,216 can be used, in
harmony with the methods described herein, to counter
15 attenuation in single family homes. This is the method
where video signals transmit from the source to a
repeater unit at the telephone interface, are reamplified
and transmitted along a second branch towards the video
destination. Effectively, this shortens the transmission
20 distance by as much as a factor of two.
Because these savings are substantial, these
methods can significantly increase the number of internal
networks over which transmission of analog video can
succeed within a tunable channel.
Establishinq a Common Ethernet LAN over
the Internal Wires of MDUs and other Structures
Two different types of Local Area Networks are
described in this section. Each of these networks uses
the telephone wires internal to an MDU to communicate
30 between the computers of the network and the point of
concentration located in the telephone wiring closet.
System A (the preferred embodiment) - A lOBaseT
Connection
In Each Apartment
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If there are at least two twisted pairs leading
from an apartment unit down to the wiring closet in the
basement, these pairs can, in theory, be used to connect
a 10BaseT Ethernet adapter directly to an Ethernet hub.
5 The challenge is made easier, of course, if all
reflections are removed from the two paths.
Such an arrangement is shown in FIG. 8a, which
shows the electronics in the apartment unit Low pass
filters 647, 647a, and 647b confine the high frequencies
10 along the dedicated path between hub 618' and powered
splitter 691 which connects at ~ack 648. There are no
reflections along this path because there are no splits.
(In FIG. 8b, Filters 647, 647a, and 647b provide
filtering on each of the two pairs.)
Note that the cord connecting powered splitter 691
to jack 648 need not be short. That is because the
technology, described in the last section, is not used
for the solution which is shown in FIG. 8a and 9a. In
particular, the broadband devices do not connect to the
20 wiring in the style of a bus.
Ordinarily, a 10BaseT Ethernet adapter only
requires an ordinary two-pair connection to a hub, so
long as the length does not exceed 100m and the wiring
meets certain specifications. In this case, however,
25 several problems may arise. These problems and their
corresponding solutions (shown in FIG. 8a) are described
below.
Voice signals are on the line. High pass filters
692a are provided to block to the voiceband.
~ A telephone device can load down the energy. Low
pass filter 692b is provided to block high
frequencies from those devices.
There may not be a good match between the
impedance of the line and that of the adapter. Impedance
35 matcher (IM) 694a corrects for these types of mismatches
.
CA 022628~9 1999-01-12
W O 98~ 98~ PCTrUS97/12045
on the wire pair over which signals arrive at the
adapter. Impedance matching and balancing (IMB)
circuitry 694b corrects for similar mismatches on the
opposite pair, and also balances the signal across the
5 two leads of the line before applying it to the wiring.
IM units 694a and 694b should be manually adjustable, so
that the impedance matching can be conveniently and
correctly established upon installation.
The wiring may attenuate the signal more than the
10 Ethernet spec allows, and higher frequencies may
attenuate more, vis-à-vis the lower frequencies, than is
allowed under spec. (This relative attenuation
difference is also called "tilt.") Amplifier/equalizer
695a corrects for tilt on the first wire pair, and 695b
15 provides gain and corrects for impending tilt by "pre-
emphasizing" the signal that is about to be applied to
the second pair.
It may be noted that broadband devices cannot
connect to either of jacks 649, 642a, or 642b, because
20 broadband energy does not reach those jacks. This is
necessary to reduce splits, and while this is somewhat
limiting to the tenant, powered splitter 691 can be
removed and connected at either of the other jacks to
operate in the same way. All that is required is to
25 shift the position of low pass filters 647, 647a and/or
647b. (For example, connecting powered splitter 691 at
jack 649 would require LPF 647b to be disabled, and for
all telephones that connected to jack 648 to be filtered.
Connecting powered splitter 691 at jack 642a would
30 require LPF 647b to connect near jack 642a, along the
path towards jack 648.) Special wall jacks that include
such low-pass filters and allow a user to easily enable
or disable them would allow a user to quickly perform
this shift. Methods for designing these jacks will be
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- 33 -
clear to those skilled in the art of building connectors
and switches for twisted pair systems
[Line Powered Devices. Nearly all telephone
devices have excess DC power made available to them by
5 the telephone system that establishes the communication.
The public switched telephone system (PSTN) is no
exception. This allows devices connected to the wiring
network to derive power through that connection, as many
ordinary telephones derive power for illumination of
10 their dial pads. While there are severe legal
restrictions on the power that can be derived from the
PSTN, such restrictions do not apply to systems driven by
PBX electronics, or similar devices. Deriving power for
powered splitter 691 will eliminate the need for a
15 separate power supply and will reduce the amount of
wiring required to complete all connections.
In FIG. 8a, DC power supply 691a is shown
connected behind low pass filter 692b. (Power will be
available at that point, but not behind filters 692.)
20 Those skllled in the art will be able to design 691 so
that it can derive power for the operation of amplifiers
695. This concept can be extended further, allowing the
network to supply power for the lOBaseT adapters, or
other devices that connect to powered splitter 691 at
25 port 691b. Yet another good solution is to use an empty
pair to make power available throughout the network. If
such a pair is available, this may be the best
alternative.]
The electronics in the wiring closet are shown in
30 FIG. 9a. The major components in this diagram are
Ethernet Switching Hub 618', bridge transceiver 609a,
rectangle switch 699, and patch panel 615b.
(The diagram also includes PBX/voice concentrator
698a, voice-ethernet link 698c, and backup telephone link
35 698b. These devices are used to join the voice traffic
.. . . ..
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- 34 -
to the data traffic on a common external line. Except
for that important function, they do not play a role in
the systems described herein.)
Bridge transceiver 609a can be any device that:
5 connect to a group of devices connected together
according to a local area network standard, such as the
lOBase2 Ethernet standard, and can connect to a
communications line that ties into the Internet to
exchange signals with that line, and either performs the
l0 addressing functions necessary to direct signals to the
correct destinations on the local area network, or
coordinates with devices that perform such addressing.
In the preferred embodiment, bridge transceiver
609a is one half of an Ethernet Bridge transceiver pair.
15 Together with the companion pair, it constitutes what is
known as an Ethernet Bridge.
When connected to a group of computers (or other
digital devices) that are connected together according to
the Ethernet local area network (LAN) standard, a bridge
20 gives the local network the property of being an
"ethernet segment." The segment is composed of the
computers or other digital devices that connect to this
LAN.
The bridge connects to a second LAN, which also
25 becomes an ethernet segment. The dataflow between the
two can be increased by adding an extra bridge
transceiver pair as an additional link between each of
the two segments. One property of the bridge is that
data applied by one station that is destined for a second
30 station on the same LAN does not flow across the bridge.
(The LAN connected to bridge transceiver 609b is shown in
FIG. ll and the manner in which these two ethernet
segments coordinate is described later on.)
An example of a remote bridge is the BestLan2
35 bridge which is carried in the catalog of the well-known
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- 35 -
Black Box Corporation. The BestLan2 bridge consists of
two companion transceivers. As described, one
transceiver connects to one Ethernet segment, and the
second connects to a different segment. They allow 2
5 million bits per second to flow from one segment to
another. If a second BestLan bridge is established, of
course, the data rate connecting the two segments becomes
4 Mbs.
Switching hub 618' is a common Ethernet lOBaseT
10 switching hub. It has a multiple number of lOBaseT ports
through which Ethernet adapters can connect via two
twisted pair wires. Typically, it also has one port for
establishing a connection to a lOBase2 bus. In the
preferred embodiment, it connects to bridge transceiver
15 609a via this port. (Voice-Ethernet Link 698c may also
connect to this lOBase2 bus.) Hub 618' exchanges signals
with line 602 through that connection. All other
connections to hub 618' are through standard lOBaseT
twisted pair ports.
The lOBaseT adapters in the apartment units
connect, ultimately, to the lOBaseT ports on hub 618'.
These connections are made through patch panel 615b,
shown in the upper left. The filters on patch panel 615b
are the same as those on patch panel 615a, and they
25 provide the same filtering. (Panel 615b includes
rectangular switch 699, which is not part of panel 615a
and is described below.)
Signals transmit between the lOBaseT adapters and
hub 618' by transmitting through high pass filters 617
30 and powered splitter 691. The effect of 617 and 691 is
to adapt the wiring so that this communication functions,
for all practical purposes, exactly like lOBaseT hubs
that are used in a more recognizable system.
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The switching property of hub 618' protects the
privacy of the individual tenants. Without this
property, all signals flowing through hub 618' are
transmitted to all of the connected lOBaseT adapters.
5 While the lOBaseT adapters are normally set to intercept
only data tagged with their address, overriding that
protection is not difficult.-- leaving open the
opportunity for monitoring a neighbor's communication.
When switching is provided, signals flow only to their
10 intended destinations.
Rectangular switch 699 is provided to economize on
the number of ports that must be included on hub 618'.
In theory, the number of required ports is equal to the
maximum number of users that may connect at any one time.
15 Because this is likely to be far less than the total
number of users that subscribe, that is that have the
ability to connect, one need not include one port for
each subscriber. As a result, the number of ports on hub
618' can correspond to the maximum number of users that
20 one may expect at any one time. This will correspond to
the number of ports on the input to switch 699. The
dimensionality of the output, on the other hand, should
be equal to the total number of subscribers. Clearly,
some mechanism of controlling switch 699 is required, and
25 it is clear that one can be developed by those skilled in
the art of switching and control. For example, a cross
point switching circuit could be used as the rectangular
switch.
Amplifier/equalizer section 699a is provided to do
30 the following at each port of hub 618':
boost the power of the signals transmitted out
through the port
apply pre-emphasis to the transmitted signals to
compensate for impending tilt
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tightly balance the transmitted signals across the
twisted pairs
match the impedance of the port to the
transmission line
equalize the signals input by the port, thereby
compensating for spectral tilt, and
increase the energy level of the input signals.
These functions extend the distance over which hub
618' and the lOBaseT adapters can reliably communicate.
10 Note that it is most efficient to perform these processes
before the dimensionality is expanded by rectangular
switch 699.
Focusing now on the voice processing, PBX/voice
concentrator 698a intercepts all voice traffic in the
15 building, and converts it to a coded Bitstream. This
data is applied, via voice/Internet link 698c, to the
lOBase2 LAN that connects hub 618' to bridge transceiver
609a. The data is addressed for "PSTN" link 673, shown
in FIG. 11 and described later on.
In the event of the failure of this link,
telephone communications would be suspended. Telephone
backup 698b is provided to ensure emergency connections.
Backup 698b can be any telephone link that is activated
"on-demand" and makes the telephones in the building
25 active.
System B - Using a lOBase2 Adapter over an Empty
Pair. Consider FIG. 8b, where modem 645a represents an
ordinary Ethernet lOBase2 card. This figure will
illustrate a method of using this common adapter to
30 establish an Ethernet hAN by connecting computers to the
network hub over internal wiring. In particular, this
method is attractive when there is at least one
"inactive" twisted pair leading from the apartment unit
down to the wiring closet.
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Establishing such a capability is important
because there may be situations where external factors,
such as warranty contracts on PBX systems, prevent the
connection of external devices to active wiring. (When
5 no PBX is present, warranties are not an issue but
governmental regulations are. Fortunately, the low pass
filters 628 can be made to block any energy that might be
in violation. These regulations, and the filters
necessary to meet them, are described in U.S. patent
10 application Serial No. 08/816,059 and the Patent No.
5,010,399.)
[The lOBase2 adapter connects to adapter 661a,
which is an optional device. Adapter 661a is only needed
when the communication is to be conducted over an active
15 twisted pair. The pair in question is assumed to be
inactive, at the outset of this discussion, and
description of adapter 661a is deferred.]
Low pass filters 647 and 647a block broadband
frequencies at two of the paths leading away from jac~
642a. As a result, signals transmit directly between
modem 645 and hub 618 and do not split at jack 642a or
anyplace else. (Note that the cord connecting to modem
645 cannot cause a split because it is part of the main
transmission path. The technology, described above, that
25 prevents connecting cords from creating splits is not
required in the examples of 8b and 9b.) Thus, the wiring
between the two devices acts as a standard lOBase2 bus,
so long as a termination is provided at modem 645a (as
indicated by the circled T in figure 8a, and also at hub
30 618.)
The processing in the wiring closet is nearly
identical to the processing shown in FIG. 9a. The only
difference is in the electronics, shown in FIG. 9b, that
connect between hub 618' and switch 699. In FIG. 9b, no
35 high pass filters are required because the line is not
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active. Instead, Media converters 679a and baluns 679b
are interposed between the switch and the hub. The
baluns 679b convert the path from a single twisted pair
to a single coax, which is the natural media for 10Base2.
5 The converters 679a , which are available as inexpensive,
off-the-shelf devices, perform the exact coordination
necessary for 10Base2 devices to connect to 10BaseT hubs.
In particular, the coax media of 10Base2 is replaced with
two twisted pair wires, and coordination of the different
10 collision detection schemes of the two systems is
provided. Preferably, they would also include the
amplification and equalization functions embodied in
amp/equalizer 699a.
It remains to show how to adapt the 10Base2
15 collision detection system to operate over a twisted pair
that conducts voiceband signals. This is not
straightforward because the 10Base2 adapters coordinate
to avoid detections by signaling each other at DC.
Specifically, the 10base2 adapter creates a "DC offset'~
20 on the bus to signal its intention to transmit. Other
adapters sense this and react accordingly.
To adapt the collision detection system of 10Base2
adapters, adapter 661a includes means (not shown) to
provide the following:
Block DC signals with a low pass filter.
Provide impedance matching between the twisted
pair wires and the coax port of the 10Base2 adapter.
Detect the DC offset from 645a, create a tonal
frequency in response, and apply the tone to the line.
Detect tones applied to the line by a similar
adapter connected to hub 618. Create a DC offset at the
connection to 645 in response to these tones.
The media converters, 679a, shown in FIG. 9b must
be adapted to recognize that collision detection is
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signaled by a tone and not a DC offset, and to react
accordingly.
System C - lOBaseT & lOBase2 Adapters that use a
single twisted pair as a Bus. ~The preferred embodiment
5 for single family homes.) Referring to Figs 6 and 7
assume that modem 645b is a standard Ethernet lOBaseT
card. (Functionally, this assumption is sound, because
modem 645b connects to a PC and exchanges signals through
two twisted pairs.) Because all reflections from the
10 wiring are suppressed, the 10 Mbs Manchester code
signals, created by 645b, will transmit, in the style of
a bus, over the single pair to which splitter 661
connects. These signals transmit towards the terminators
at jack 649 and at hub 618.
Note that lOBaseT cards use Manchester codes to
communicate both their data signals and their collision
detection signals. As a result, both of these signals
will transmit across the bus between jack 649 and hub
618.
It remains to show how these signals would
coordinate with a lOBaseT switching hub. (A lOBaseT hub
is the best choice for hub 618 because it is the only
inexpensive piece of hardware that performs the switching
functions necessary to protect privacy.) The electronics
25 in the wiring closet are nearly the same as those shown
in FIG. 9a. The only differences are shown in FIG. 9c.
That figure shows how diplexers 679c replace
amp/equalizer 699a. Also, a termination is provided
between each diplexer and hi pass filter 617.
Diplexers 679c connect to detect signals without
loading the bus. These signals are passed to the twisted
pair providing input to a port on the lOBaseT hub.
Signals issued by the hub are picked up from the second
pair by the diplexers, and applied to the bus, ultimately
35 reaching lOBaseT adapter 645a in the apartment unit. In
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the preferred embodiment, diplexers 679c also perform the
a~plification/equalization ordinarily provided by 699a.
It is noted that, where privacy is not a concern,
use of a 10BaseT hub is not required. This has major
5 implications for use in single family homes. In
particular, multiple 10BaseT adapters can connect, each
through splitter 661, to a "bus" created from the
internal wiring in the manner shown in FIG. 6 and
described above. These adapters will then communicate
10 with each other over this bus without the aid of a hub --
just as 10Base2 cards communicate over a stretch of
coaxial cable. Each adapter will all receive all data
signals and collision signals applied by each of the
other cards -- exactly as if they had been connected to a
15 lOBaseT hub.
For example, referring to FIG. 6, assume 645b is a
10BaseT adapter, and assume a second 10BaseT adapter is
connected (through a second splitter 661) to jack 642a.
If a low pass fllter is connected between hub 618 and
20 jack 642a, and terminator 669 in the second splitter 661
is connected, the "bus" will reach between jack 642a and
the termination at jack 649. The two lOBaseT cards will
be able, at that point, to freely communicate across this
stretch of wiring. Were other jacks available along the
25 bus, additional 10baseT adapters could connect and
communicate in the same manner.
It is further noted that 10Base2 adapters can
connect directly to a bus, without the aid of splitter
661, and no reflections will occur if the connecting cord
30 is not too long. (One way to do this is to connect a
"pocket-style" 10Base2 adapter to a wall jack using a
very short cord, and use a long cord to connect to the
parallel port on a PC.) In order that the collision
signaling work properly, however, the twisted pair that
35 serves as the bus must be empty -- it cannot be used for
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telephone communications. If these conditions are met,
the lOBase2 adapters will communicate as they do over
standard coaxial cables.
Networks for Wirinq that will Not SuPPort 10 Mbs.
As described above, the wiring in some apartment
buildings is not of sufficiently reliable quality for
support of 10 Mbs communication. The factor of
communication reliability, however, trades off directly
with communication data rate, so these problems can be
10 addressed by establishing lower data rate communications
over the apartment wires.
In the following two sections, two systems for
establishing such communications are described. The
major advantage of these designs are that they require
15 relatively inexpensive electronics, they allow all
tenants in the building to share access to one or more
high speed lines, and they guarantee the privacy of all
who use the system.
In both systems, it is suggested that a data rate
20 of 2 Mbs between the basement and each tenant be used.
While this rate is significantly less than 10 Mbs, the
data rate may be limited below 10 Mbs by other factors.
Also, the advantage of the extra 8 Mbs may be that the
user can download a graphic in .2 seconds instead of 1
25 second, a difference that may not be appreciated.
SYstem A - Ethernet AdaPters are Used for Routinq.
The first system is now described in terms of the
major components shown earlier. Hub 618a, which differs
from hub 618 only in that its description is more
30 detailed, is shown in FIG. lOa. Hub 618a consists of
bridge transceiver 609a, bus 619, and modems 650a.
The function of bridge transceiver 609a, in this
system, is the same as the function it played in the
system described above. Specifically, bridge transceiver
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609a can be any device that: can connect to a group of
devices connected together according to a similar LAN
(local area network) standard, such as the lOBase2
Ethernet standard, and can connect to a communications
5 line that ties into the Internet to exchange signals with
that line, and either performs the addressing functions
necessary to direct signals to the correct destinations
on the LAN, or coordinates with devices that perform such
addressing.
In the preferred embodiment, bridge transceiver
609a is one half of an Ethernet Bridge transceiver pair.
Together with its companion pair, bridge transceiver
609b, it constitutes what is known as an Ethernet bridge,
and the LAN in the wiring closet is called an Ethernet
15 Segment. These concepts were described in greater detail
above.
Modems 650a include modulators and demodulators
that apply signals on to the twisted pairs and recover
signals transmitting from the apartment units up above.
20 They correspond to modulators 610 and demodulators 608,
shown in FIG. 3. (It is noted that, together with bus
619, which is described below, modems 650a perform the
same processing as subsystems 603 and 607, described
above.)
Modems 650a and bridge transceiver 609a connect to
bus 619, and can apply data to and recover data from that
bus. Data applied to the bus transmits to all other
devices connected to the same bus. Communication is
therefore established between all devices that connect to
30 bus 619. In the preferred embodiment, the common lOBase2
standard governs communication across thls bus.
Bus 619 connects the modems together into an
Ethernet LAN. (As described above, this LAN also becomes
an Ethernet network "segmentn when bridge transceiver
35 609a connects to its companion transceiver.) Bus 619 can
, . ~
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follow the standard of the common lOBaseT hubs, the
lOBase2 bus, or similar mechanisms. In the case of
lOBase2, the "hub" is simply a thin coaxial cable, or
bus, that is terminated at both ends. The digital
5 stations on the network connect to the bus through a high
impedance, picking up the signals without disturbing or
otherwise loading down the flow of signal energy.
Signals applied to the bus transmit to both ends, where
their energy is removed by the terminators.
There is one modem for each tenant that subscribes
to the service provided by the system described in this
section. Part of each modem 650a is Ethernet NIC 653,
which does processing equivalent to a Network Interface
Card, or NIC. A NIC is the common piece of electronics
15 that connects between computers and a network hub or bus.
Each NIC senses all the signals flowing across the bus,
and selects only those that are tagged with the same
"address" that is encoded on the NIC. These signals are
passed to the data bus of the computer. In summary, a
20 NIC provides the processing necessary to exchange signals
between the computer bus (to which it connects) and the
network bus (or hub) while protecting the privacy of
others on the network.
While providing a two-way communication path, a
25 typical NIC also uses the computer's processing power to
manage some of the processing it (the NIC) conducts.
Microprocessor 654 is included in modem 650a for this
specific purpose. This eliminates the need for NIC 653
to make use of a processor in a large computer. (Such a
30 need would significantly increase the cost of the hub.)
A design for hub 618a whereby one microprocessor 654
performs this function for several of modems 650a would
be preferred.
The signals recovered by the NIC are passed to
"first in first out," (FIFO) queue 655, hereinafter
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referred to as FIFO 655. That device is a digital buffer
and matches the speed at which data flows across the
network with the speed of the data flowing between the
modem and the subscriber. FIFO 655 can be implemented by
5 well-known electronic circuits.
The focus now moves to the question of how fast
modem 650a should pass data to its associated computer.
If a common Ethernet technology is used, 10 million bits
per second (Mbs) will flow across the network. But the
10 maximum data rate is more likely to be limited by remote
bridge 609a, and bridges become very expensive when they
are called on to accommodate a very high data rate.
Because of the availability of relatively inexpensive
wireless bridges, such as the BestLan2, that communicate
15 at 2 Mbs, a data rate of 2 Mbs link to the tenant may be
a good choice.
Data flows across an Ethernet LAN, however, in
bursts of 10 Mb/s, even if data arrives at the network at
a slower speed. As a result, NIC 653 must pass data
20 downstream at a rate of 10 Mbs. Under those
circumstances, NIC 653 will fill the buffers of FIFO
queue 655 at the rate of 10 Mbs, but only in relatively
short "bursts." The buffers must be emptied, or read
out, at the rate of 2 Mbs, and the capacity of the buffer
25 will determine the possibility of an overflow. Clearly,
the buffers should be large enough to make such
possibility very small.
The FIFO operates under control of MPU 654 and
its buffers are read out towards modulator 657. That
30 device expresses the digital energy as a waveform
confined to frequencies above the voiceband, and passes
it to broadband patch panel 615. Various methods, such
as QPSK (quadrature phase shift keying) or the Manchester
coding described earlier, can be used to encode the
35 information at frequencies above the voiceband.
. .
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The analog waveform created by modulator 657 is
passed through band pass filter 658 and coupler 651 and
onto the twisted pair leading through broadband panel
615 and towards the tenant's apartment.
Modem 650a also receives signals sent from the
tenant's apartment. These signals are applied by modem
645a, as shown in FIG. 6. They transmit through
broadband panel 615, through coupler 651 and band pass
filter 652 in modem 650a. They are blocked from
10 modulator 657 by band pass filter 651 and by
directionality of the coupler, while filter 652 blocks
signals from 657 from flowing towards demodulator 656.
It is noted that band pass filter 658, 652 and coupler
651 perform filtering and signal separation that is
15 equivalent to that performed by signal separator 613a.
Demodulator 656 converts the received signals to
digital logic form. Finally, this data is applied to the
NIC card in the same manner that a PC would pass signals
to that card. This completes the communication circuit
20 in the wiring closet because any further transmission of
the signals is accomplished according to common Ethernet
standards.
As described above, modem 645a communicates, in
the preferred embodiment, with the tenant's PC through a
25 common parallel port. An advantage of using the
parallel port can be seen by envisioning modem 650a and
modem 645 working together in a common enclosure. Modem
650a connects to a common lOBase2 Ethernet network, and
modem 645a connects to a parallel port on a PC. As such,
30 the combination of the two devices is equivalent to what
are known as "pocket Ethernet Adapters." Those devices
are small electronic boxes that connect to a parallel
port on a PC and also to an Ethernet. As a result of the
similarly of the inputs and outputs, modem 645 can be
35 designed to emulate these adapters, and the same software
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used to drive the adapters can be used to accommodate the
system described herein.
System 2 - Usinq a PC Bus and Software for Routinq.
FIG. 10b shows Hub 618b, which is an alternative
5 to Hub 618a. Like hub 618a, hub 618b includes one modem
(shown in FIG. 10b as modem 650b) for each subscribing
tenant. Hub 618b also includes bridge transceiver 609a.
The main difference between the two is embodied in the
way data from bridge transceiver 609a reaches the input
10 of each modem. This mechanism is now described.
Referring to FIG. 10b, data from the Internet
reaches bridge transceiver 609a over line 602, and
continues on to microprocessing unit (MPU) 670. Data
destined for the Internet transmits in the opposite
15 direction. In the preferred embodiment, the physical
connection between bridge transceiver 609a and MPU 670
adheres to the Ethernet lOBase2 LAN standard, and the
protocols of communication also adhere to standards
established for Ethernet LANs. Other types communication
20 links may also suffice.
It is noted that a second bridge transceiver can
simply connect to the 10Base2 LAN in the ordinary manner.
This will double the data rate between the MPU and the
Internet. If more bridge transceivers connect in this
25 manner, the factor limiting the data rate in the wiring
closet may ultimately become the 10 Mbs of the 10Base2
link, rather than the aggregate data rate of bridge
transceivers.
In the preferred embodiment, data reaching MPU 670
30 includes a tag that determines which of the tenants is
targeted as the final destination. Using software, MPU
670 must interpret this tag, and apply the associated
signals onto logical data bus 681 in such a way as to
direct them to the appropriate destination. Circuitry
35 that implements such a communication bus is well known.
.. .. .
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Furthermore, a particular MPU, Motorola xxx, is already
designed to conduct the type of communication described
herein, adding an economy to this system.
Modems 650b connect to bus 681 and allow data to
5 flow in each direction. This exchange of data is managed
by digital diplexer 684. That device is similar in
function to digital diplexer 637, described above.
The function of modems 650b is nearly identical
to modems 650a. Both exchange data with the
10 communication bus, and relay that data to the modems in
the tenants apartments. As can be seen from Figs 10a and
10b, both use the same arrangement of modulators and
passlve filtering and coupling to create the data-over-
voice function.
One difference in function is that modem 650b must
include hardware to recognize data addresses. That
function is performed by NIC 653 under control of MPU
654. When modems 650b are used, this function is
performed in software by MPU 670.
Connectinq Small Offices that are Located in the
Buildinq.
The system described herein gives each subscriber
shared access to a high capacity line. This capability
can be useful for individual residents in an apartment
25 building, but it can also by attractive to small
businesses. In particular, when many different small
businesses share a common building, some may find that
the cost for level of service provided by this system is
one that is attractive to them. These businesses may
30 choose to subscribe and locate modem 645a on the desktops
of workers with a requirement to access the Internet.
To be sure, a common PBX switch is installed in
many such offices, and this device may interrupt the
continuity of a twisted pair path reaching between the
35 basement wiring and a desktop. A high frequency bypass
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is required to reach the desktop in such a configuration.
(This bypass is not shown in this application, but an
example is shown in figure 5 of Patent No. 5,010,399.)
Many such offices, howe~er, have a LAN that
5 connects the computers used by several of the workers,
and may desire to provide the workers with access to line
602 over this LAN. This can be accomplished by
connecting the office LAN to the 10Base2 network in the
basement by using a network bridge, such as the bridges
10 described above.
A network bridge can be implemented by a variety
of products. Some of the products, such as the V.35
bridges that appear in the catalog of the Black Box
Corporation, consist of transceiver pairs. Such a
15 connection is shown in FIG. 10a, where Ethernet Bridge
transceiver 659 connects to the Ethernet LAN established
in the basement, and the companion transceiver connects
to the network LAN established in the office. When such
a connection is made, the networks become Ethernet
20 segments relative to each other.
Privacy issues are solved automatically. Data
destined for the tenants does not reach the office LAN
because bridge 659, which follows Ethernet standards,
does not allow traffic for other destinations to flow
25 onto the connected segment. Data destined for the office
LAN cannot be intercepted by the tenants because the NIC
cards are set to block data that is not tagged for
transmission to the tenant. Data destined for the
Internet (via high capacity line 602) will be blocked
30 from both the tenants and the office LAN by the same
provisions.
The CaPacitY of the APartment Internet System
One benefit of connecting computers as described
earlier is that each computer can communicate digital
35 data with any other computer in the bullding. A more
,
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important benefit, which is the focus of this invention,
is that each tenant can communicate with the well-known
Internet at a relatively high data rate.
There are two data rates internal to the system
5 disclosed herein that will have a big affect on the rate
experienced by the users. The first is the rate at which
signals communicate from the Internet Connection to hubs
618', 618a, or 618b, located in the wiring closet. The
second is the rate at which signals communicate between
10 these hubs and modems 645a (or 645b) in the apartment
units.
The proper rates for these links will depend on
many factors. There are several characteristics of this
system, however, that are common to all implementations,
15 and can help in determining the optimal data rate. Some
of these characteristics are described below.
When line 602 communicates at 2 Mbs, there is no
immediate reason for modems 650 and modems 645, which
determine the data rate internal to the building, to
20 communicate at a higher speed. Valid reasons for
implementing a higher data rate are a) to allow for
future expansion, b) economy -- some higher data rate
devices, such as Ethernet devices, are actually less
expensive, and c) the ability to use the link for
25 compressed digital video.
Because of the Internet's "stop-start~ nature, a
shared connection functions most efficiently when a large
part of its capacity can be focused, that is "burst" upon
a single user. When the connecting link can focus in
30 this manner, a request for bandwidth can be quickly
satisfied and the user examines the data while the
bandwidth of the connection is dedicated to satisfying
requests of other users in the pool. Until the requests
for a "burst" are so numerous as to overlap and
35 concentrate at a single moment in time, every user feels
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as if he or she enjoys the full bandwidth of the
connecting link.
The data rate of the connection to the Internet is
limited by remote bridge 609a, which, in the preferred
5 embodiment, provides a data rate of approximately 2 Mbs.
Extra bridges can be added to create a simple increase in
this data rate, that is doubling the number of bridges
increases the rate of connection to the Internet by a
factor of 2.
Many experts believe that the most common
experience of an Internet user will be one that proceeds
according to this sequence: a) the Internet "refreshes
the user's screen," b) the user examines the screen, c)
the user makes certain decisions, d) the Internet reacts
15 by refreshing to create a new screen, and e) the cycle
begins again. When the newly created screen consists
largely of graphics rather than text (alphanumerics)
refresh of the screen can be very time consuming. It is
this phenomenon that has created a large demand for an
20 increase in the rate at which users can access the
Internet.
Using compression methods, approximately 1 million
bits are required to fill a computer screen. Meanwhile,
the tenant must, presumably, inspect each screen for at
25 least a number of seconds. Because 2 Mbs can refresh a
screen in approximately .5 seconds, a doubling in
capacity will lower the "wait" time by .25 seconds, which
will lower the "advance" from one screen to another by
only a small fraction. While there are other uses for
30 the Internet that do not involve advancing from screen to
screen, this particular type of use is very common, so an
increase in data rate may not be significantly
appreciated.
Because a user advancing through screens draws
35 data from the shared line for only a few seconds each
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minute, several users can be added before even a very
small decrease in service is perceived by the existing
users. Also, only a fraction of the total number of
subscribing tenants may be actively using the system at
any given time.
As a result of the foregoing, it is suggested that
2 Mbs is sufficient until the number of subscribing
tenants in the building exceeds between 25-50. A second
bridge should be added when the number increases beyond
10 that.
It can be shown, mathematically, that the
efficiency of the system increases when the number of
users sharing access increases while the "quality of
service" remains the same. For example, let the "quality
of service" be defined by the percentage of times that a
user who requests y seconds of access must wait more
than x seconds for such access, (where x is a fixed
threshold.) Under those conditions, a doubling of
capacity, that is bandwidth, results in an increase in
20 the maximum number of users (that can enjoy at least the
same "quality of service") by a factor well above 2 and
possibly approaching 4. In other words, the efficiency
of bandwidth sharing has increased.
Standard motion pictures can be expressed as a
25 compressed digital Bitstream with a data rate of 1.5 Mbs,
and a data rate of 6 Mbs can be used to express any NTSC
video signal whatsoever. Transmission of compressed
digital video signals, however, requires the source to
feed a steady stream of data to the receiver, and such a
30 capability cannot typically be provided by the systems in
Figs 6-10. The next section describes how to make the
communication link between modems 650 and modems 645
provide a path for the digital video signals generated by
the systems disclosed in U.S. patent application Serial
35 No. 08/816,059.
CA 022628~9 1999-01-12
W O 98~'~29~S PCT~US97/12045
Providinq Multiple APartment Buildinqs with Shared Access
and a Common Router
As described above, when one the systems described
in Figs 6-10 is installed in a given apartment building,
5 it creates a LAN among the computers of the tenants in
that building. In the preferred embodiment, this network
follows the well-known Ethernet LAN standards. ~In FIG.
8b, to be precise, only a small Ethernet LAN connects at
the root of the electronics -- that is between bridge
10 transceiver 609a and MPU 670. Data moving beyond MPU 670
to the individual tenants is shared by means other than
LAM technology.)
According to these standards, many such networks
can be connected to a master network using devices known
15 as Ethernet bridges. The result is that all the
computers in all the buildings are actually part of the
same large network. (The LAN in the basement of a single
building is referred to as an "Ethernet segment,~ and the
larger network is composed of many of these different
20 segments.)
A device called a router is re~uired to provide
Internet access to the computers on an Ethernet network.
One router can suffice for each network, even networks
that are composed of many different segments. Because
25 routers are relatively expensive, there is a significant
advantage to connecting (the networks installed in)
several buildings so that they become separate Ethernet
segments of a single common network, allowing one router
to serve them all.
Another economy available to large networks is the
shared use of a computer called an Internet
workstation. Such a computer can be useful in improving
the convenience and power available to users accessing
the Internet over a network. A single computer,
CA 022628~9 1999-01-12
W098/02985 PCT~S97/12045
- 54 -
moreover, can be useful to any of the users on any
segment of the network.
A system of connecting the network segments
installed in multiple apartment buildings is now
5 described. In addition to the economy of a single router
and a single Internet workstation, this system will enjoy
the added advantage, described above, of having all
segments share the same connection into the Ethernet.
(This advantage was described earlier in terms of several
lO individual users sharing access to the same high-speed
line. The same principles apply when several network
segments share the same port of access.)
Referring to FIG. ll, a group of bridge
transceivers 609b are located together with router 672
15 and port 670. Port 670 is a port providing a fixed rate
of access into the Internet. It connects to router 672,
which connects to bus 675, which is a simple lOBase2
Ethernet bus. The bridge transceivers 609b also connect
to the same bus. Bridge transceivers 609b and router
20 672 are co-located with port 670. Such a location is
commonly referred to as a "point of presence.'~
Internet workstation 686a and PSTN 686b also
connect to this bus. The workstation provides the
economy described above. PSTN Link 686b communicates
25 with PBX/Voice Concentrator 698a, shown in FIG. 9a.
Those devices cooperate to connect the telephones in each
apartment (of the group of apartments) to a common port
of the public switched telephone network.
The connections described above establish a
30 network among router 672, the transceivers 609b, the
Internet workstation and the PSTN link. lO Mbs can flow
across this network when common Ethernet standards are
used. Data flows between the Internet and this network
via port 670 and router 672. Router 672 processes the
35 data as it is applied to the network. It follows well
CA 022628~9 1999-01-12
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- 55 -
established protocols for communicating between Ethernet
networks and the Internet. In particular, it examines
the addressing information associated with the data, and
alters that information so that it can be understood by
5 the bridges and the network interface cards (also known
as network adapters,) that are connected to the network.
A group of apartment buildings is shown at the top
of FIG. ll. Bridge transceiver 609a is installed in the
basement of each of these buildings, as well as the other
lO electronics shown in Figs 9-lO. At the point of
presence, each of transceivers 609b is the dedicated
companion of one of bridge transceivers 609b installed in
the basement of one of the apartment buildings. (More
than one of bridge transceivers 609a may be connected to
15 the network segment in the basement wiring closet of any
given building, so long as it has a dedicated companion
transceiver at the point of presence. Systems where the
transceivers are not pairwise dedicated are also
possible.) The link between each transceiver pair
20 connects the network in the corresponding building
together with the network at the point of presence,
making the network in the building an individual
"segment" of this larger network. The following results
are now established:
Any piece of data sent from port 670 is processed
by router 672. After processing, the data will be
targeted for one of the tenants in one of the buildings.
(In the system described in FIG. lOb, router 672 directs
data only so far as the correct buildings. Routing
30 performed by MPU 670 computes the final address that is
used to direct the data to the correct tenant.)
This data will be input by the one of Ethernet
transceivers 609b that connects to the LAN at the point
of presence. The data will be passed across to the
.
CA 022628~9 1999-01-12
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- 56 -
companion Ethernet transceiver 609a. It will not flow to
other buildings.
The Ethernet transceiver 609a will apply the data
to the access sharing system inside the building. The
5 data will be recognized by hub 618' (or by modem 650a or
modem 650b) and directed to the correct tenant.
Data transmitted from a tenant and destined for
the Internet will be interpreted by the bridge
transceiver 609a in the building of that tenant. This
10 data will be relayed back to the point of presence, where
it will be received by the companion bridge transceiver
609b. It will then flow across bus 675 to router 672,
where its address will be processed and passed to the
Internet through port 670.
In the preferred embodiment, data will flow from
the Internet, through port 670, through the router, onto
the bus 675 and will be received by one of bridge
transceivers 609b. This data will flow at a rate of 10
Mbs. Data will flow between bridge transceivers 609b and
609a at a rate of 2 Mbs, and these bridges follow the
BestLAN system, referenced above. (The aggregate data
rate reaching a building can be increased by providing
extra bridging.) The considerations governing the rates
at which data flow internal to the buildings were
25 discussed earlier.
Assuming there are 10 buildings, if each building
connected directly to the Internet, rather than through a
shared connection, its demands could be completely
satisfied by a dedicated 2 Mbs connection. In that
situation, 10 buildings would require at most 20Mbs of
access. Because of the efficiency, described above,
where several network segments share the same port of
access, a port of significantly less than 20Mbs will
provide exactly the same level of service as would be
35 provided if each segment enjoyed the dedicated 2 Mbs
CA 022628~9 1999-01-12
W O 98~9~S PCT~US97/12045
connection. Assuming, as before, between 25-50
subscribers for each 2 Mbs connection, implies that
approximately 400 subscribers could feel they enjoy a 2
Mbs access from a port whose capacity is less than 20Mbs.
5 These numbers translate to 50 Kbs per customer,
indicating that shared access provides a very substantial
efficiency.
When there are only a very small number of
subscribers in an apartment building, one may not be able
10 to justify the cost of dedicating bridge transceivers
609a and 609b to such a building. In this case, the
network segment established by transceiver 609a can be
broadened by connecting extra buildings. In particular,
a bridge can connect the network segment in the "under-
15 subscribed" building to a neighboring building. If theneighboring building is nearby, the cost of the bridge
may be significantly less than the cost of the 609 pair,
and total number of subscribers in the two buildings can
justify the cost of the link to the Point of Presence.
20 This type of "doubling" is illustrated by the apartment
building shown in the upper left of FIG. 11.
Providing for Transmission of Digital Video
Recent advances in compressed digital video have
increased the number of video signals that reach
subscribers in digital form. In particular, signals
received by 18-inch satellite dishes, called DSS signals,
are received in this form, and the US telephone companies
have announced plans to deliver their programming in
digital form via microwave technology.
In U.S. patent application Serial No. 08/816,059,
many methods were described for allowing tenants in
apartment buildings to access video sources, that provide
many programs brought to the basement wiring closet via
one or more hi-capacity paths. Using these systems,
35 tenants would send a control signal down to the
CA 022628~9 1999-01-12
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- 58 -
electronics in the wiring closet. This signal would
indicate which of the programs should be sent to the
tenant's apartment unit, and the basement electronics
would respond accordingly. Part of the system that
5 brought the signals to the tenants required, of course, a
digital link between the basement and the apartment unit
up above.
In this invention, such digital links are provided
between modem 650a and modem 645a. To use these links to
10 communicate compressed digital video, however, a
mechanism of transmitting the data streams to modem 650a
must be provided. Applying these signals directly to the
network established by bus 619 is not a solution because
the network cannot guarantee transmission of a datastream
15 at a minimum steady rate, a characteristic required for
digital video transmission.
Referring to FIG. lOa, it is seen that two
communication lines connect to FIFO 655: the line
connecting to NIC 653, and a line from digital video
20 source 655a. Source 655a can be provided, in
coordination with a path for control signals, by many of
the systems described in U.S. patent application Serial
No. 08/816,059. MPU 654 controls FIFO 655, enabling it
to input digital signals from either NIC 653 or source
25 655a. If digital signals are input from the video source
rather than NIC 653, there is no reason for interruptions
of the datastream, and the digital signals can flow
steadily to the PC up in the tenant's apartment.
Electronic hardware is available, such as the well-known
30 MPEG hardware, that can provide a PC with the capability
of displaying compressed digital video on common PC
monitors.
A Transmit/Receive Pair that can Communicate either Data
or Analoq Video
CA 022628~9 1999-01-12
W03~ 29$5 PCT~S97/12045
- 59 -
U.S. patent application Serial No. 08/816,059
described circuitry for transmitting analog video signals
over twisted pair wiring using FM methods. As described
therein, these signals can communicate over a single
5 twisted pair wire at the same time as digital signals, so
long as different frequency bands are used for each. In
configurations where two twisted pairs serve the end
user, FM video can transmit over one pair and digital
signals over the second.
Because of the recent and very large increase in
interest in communications, there has been an increase in
the demand for new paths that bring data and/or video to
end users. When communicating over internal telephone
wiring according to the methods disclosed in this
15 application and its predecessors, transmission over the
final link reaching the end user typically requires a
different transmit/receive pair for each type of signal.
As a result, an efficiency can be obtained when one
transmit/receiver pair can manage communication of
20 signals of two or more different types.
A method is now disclosed for a transmit/receive
pair that can communicate both analog video and digital
signals. The transmit/receive pair works on FM
principles. Conceptually, an FM transmit/receive pair
25 will treat any input waveform in the same manner --
whatever waveform is input by the transmitter will be
reproduced as output at the receive end. The only
consideration is that the bandwidth of the input be
within the range of the devices.
As a result of the property that FM
transmit/receive pairs are essentially transparent to the
nature of their input, the same transmit/receive pairs
described in U.S. patent application Serial No.
08/431,270 can be used to communicate a digital Bitstream
35 as well as an analog video signal. An example of how
. . .
CA 022628~9 1999-01-12
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- 60 -
these devices would react to digital and analog input is
shown in FIG. 12.
An example of the time varying behavior of an
ordinary NTSC video signal, expressed at baseband, is
5 shown in the left most diagram of the top row in FIG. 12.
The waveform looks arbitrary, but its spectrum, shown in
the diagram to the right, indicates that its energy is
confined below 4.5 MHZ. As in classic frequency
modulation, the time varying amplitude of the input
10 waveform is used to create time-varying alterations in
the frequency of a carrier, shown at the right. This
carrier, which oscillates at 25 MHZ when no input is
applied, travels over 20 MHZ of spectrum, between 15 MHZ
and 35 MHZ, when reacting to the video information
15 supplied at its input. This motion provides an encoded
expression of the video information. The FM receiver at
the receive end will interpret this motion to reconstruct
the signal on the left.
A bi-level square wave produced by digital logic
20 is shown on the left side of the lower row. High levels
represent ones and low levels represent zeros. If the
data rate is at or below 2 Mbs, most of its spectrum will
be confined below 4.5 MHZ, as shown in the middle
diagram. In response to the movement between high and
25 low levels, the frequency of the 25 MHZ carrier changes
between approximately 17.5 MHZ and 32.5 MHZ. The
spectrum of the transmitted signal is shown on the right,
concentrated at the 17.5 and 32.5 extremes but spread
about them so that the entire spectrum is largely
30 confined to the same channel as is shown in the top row.
The motion of the carrier between the two frequency
extremes is detected by the receiver and used to
reproduce the square wave at the receive end.
The foregoing represents an example of how the
35 same transmit/receive pair can be used to communicate
CA 02262859 1999-01-12
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- 61 -
either a digital Bitstream or an analog video signals,
whichever is fed at its input. As a result of this
economy, there may be good reason to use such pairs as
the components of the digital network described above.
5 They would perform the functions, embodied in modulators
610, 657, and demodulators 636, that expressed the
digital bitstreams as waveforms on the wiring, and the
reverse.
What is claimed is :
,, ..... ,, . = .. . . ...
