Note: Descriptions are shown in the official language in which they were submitted.
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COMMUNICATION SERVER APPARATUS AND METHOD
TECHNICAL FIELD OF THE INVENTION
This invention relates in general to data
communication, and more particularly to a communication
server apparatus and method.
BACKGROUND OF THE INVENTION
A communication server provides access to
co~munication facilities. For example, a communication
server having a bank of modems may provide subscriber
access to the modems for data communication. A
communication server may be associated with its own
dedicated communication network, or with an existing
communication network, such as the public switched
telephone network ~PSTN).
As communication networks provide greater
connectivity and access to information, there is an
increasing demand for data communication at higher rates.
One solution to provide increased data rates replaces
existing twisted pair wiring with high bandwidth media,
such as coaxial cables or fiber optic links. Other
solutions adopt improved communication techniques using
the existing hardware infrastructure. For example,
digital subscriber line (XDSL~ technology provides higher
bandwidth data service over existing twisted pair wiring.
To deliver data service to the subscriber, a
communication server may provide a dedicated or permanent
connection to its communication facilities. For example,
an existing communication server at a central office
provides enough communication facilities to
simultaneously service all PSTN subscribers. However,
all telephone subscribers may not desire data service.
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Furthermore, the subscribers that desire data service may
not simultaneously access the communication server.
SU~RY OF THE INVENTION
In accordance with the present invention, the
disadvantages and problems associated with communication
servers have been substantially reduced or eliminated.
In particular, a communication server apparatus and
method are disclosed that provide data service to a
number of subscribers using a reduced number of XDSL
communication facilities.
In one embodiment of the present invention, a
communication system includes computers located at
subscriber premises, where each computer has a first XDSL
modem to communicate information. Twisted pair
subscriber lines are coupled to the computers, and each
form a local loop. An optional splitter is remotely
located from the subscriber premises and coupled to the
local loops formed by the twisted pair subscriber lines.
The splitter splits each twisted pair subscriber line
into a twisted pair data line and a twisted pair
telephone line. A communications server coupled to the
twisted pair data lines of the splitter has a plurality
of second XDSL modems to communicate information with the
first XDSL modems using the twisted pair subscriber lines
and associated twisted pair data lines. The
communication server coupled the second XDSL modems to
selected subsets of the twisted pair data lines. The
first XDSL modems at the subscriber premises and second
XDSL modems at the communications server provide high
band with data service using the twisted pair subscriber
lines.
Important technical advantages of the present
invention include a communication server that provides
data service to a number of subscribers using a reduced
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number of XDSL communication facilities. Over-
subscription of data service is accomplished by
selectively coupling a number of twisted pair data lines
to a reduced number of XDSL modems. A controller polls
the data lines simultaneously or in succession, in groups
or individually, to determine which subscribers of the
communication system need data service. Upon detecting a
need for data service on a selected data line, the
controller directs a switch to couple the selected data
line to an available modem. The communication server may
then provide data service suitable for high bandwidth
applications, such as video-on-demand, multimedia, or
Internet access.
Another important technical advantage of the present
invention includes a communication server that provides
over-subscribed XDSL data service using the existing
infrastructure of the public switched telephone network
(PSTN). Asymmetric digital subscriber line (ADSL),
symmetric digital subscriber line (SDSL), high-speed
digital subscriber line (HDSL), very high-speed digital
subscriber line (VDSL), or other suitable XDSL technology
can provide higher bandwidth data service over existing
twisted pair wiring. These technologies may support data
service simultaneously with traditional telephone service
using a separation technique, such as frequency division
multiplexing. In one embodiment, a splitter divides each
incoming twisted pair subscriber line into a twisted pair
phone line and a twisted pair data line. The phone line
is coupled to a telephone switch to provide telephone
service and the data line is coupled to the communication
server to provide over-subscribed XDSL data service. The
communication server and splitter may be located at a
central office, remote terminal, or other point of
presence of the data service provider.
_
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Another important technical advantage of the present
invention includes the management and monitoring of XDSL
data service provided to subscribers. To accomplish
this, the communication server maintains an activity
table to determine status information on twisted pair
data lines and XDSL modems. In addition, the
communication server can track subscriber usage, monitor
subscriber information and generate billing and
demographic information. In a particular embodiment, an
activity detector disconnects a subscriber after a
predetermined period of inactivity to release a modem for
use by another subscriber.
An important technical advantage of the present
invention is the distribution of the switching function
to allow scalability of the number of supported data
lines and over-subscription of XDSL modems.
A further important technical advantage of the
present invention includes isolating the switch from the
data lines and subscriber lines. The switch can thereby
operate without constraints imposed by technical
requirements for interaction with the data lines and
subscriber lines. For example, isolation of the
switching matrix can allow CMOS switches to be used
rather than more expensive solid state relays or
mechanical relays.
Yet another important technical advantage of the
present invention includes the ability to provide a two-
wire isolated interface that can use a single switch to
couple a data line to a specific modem. The present
invention thus allows one switch per modem per data line
configuration. The isolation system of the present
invention can transform the data line impedance to an
intermediate impedance in order to increase system
performance. Other important technical advantages are
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readily apparent to one skilled in the art from the
following figures, descriptions, and claims.
BRIEF DESCRIPTION OF THE DRAWINGS
For a more complete understanding of the present
invention, and for further features and advantages,
reference is now made to the following description taken
in conjunction with the accompanying drawings, in which:
FIGURE 1 illustrates a communication system that
provides data service;
FIGURE 2 illustrates a communication server in the
communication system;
FIGURE 3 illustrates in more detail the controller
of the communication server;
FIGURE 4 illustrates in more detail the switch and
modem pool of the communication server;
FIGURE 5 illustrates in more detail the transceiver
in the controller of the communication server;
FIGURE 6 illustrates in more detail the detector in
the controller of the communication server;
FIGURE 7 illustrates an activity table used by the
controller of the communication server;
FIGURE 8 is a flow chart of a method for coupling a
data line to a modem in the communication server;
2~ FIGURE 9 is a flow chart of a method to decouple a
data line from a modem in the communication server;
FIGURE 10A illustrates another implementation of the
communication server;
FIGURE 10B illustrates in more detail a line
interface device of the communication server of FIGURE
10A;
FIGURE 10C illustrates in more detail the controller
of the communication server of FIGURE lOA;
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FIGURE lOD illustrates in more detail a detector of
the communication server of FIGURE lOA;
FIGURE lOE illustrates in more detail a modem in the
modem pool of the communication server of FIGURE lOA;
FIGURE llA illustrates in more detail an analog
filter implementation of a detector of the communication
server;
FIGURE llB illustrates in more detail a tone decoder
implementation of a detector of the communication server;
FIGURE llC illustrates in more detail a digital
signal processor implementation of a detector of the
communication server;
FIGURE 12 illustrates in more detail a digital
switching matrix implementation of the switch of the
communication server;
FIGURE 13A illustrates in more detail a frequency
multiplexing implementation of the switch of the
communication server;
FIGURE 13B is a diagram of frequencies used in the
switch of FIGURE 13A;
FIGURE 14A illustrates line interface modules and
the modem pool of a distributed switching implementation
of the communication server;
FIGURE 14B illustrates in more detail the line
interface modules and the modem pool of the communication
server of FIGURE 14A;
FIGURE 15 illustrates a functional block diagram of
one embodiment of a distributed switching implementation
of the communication server;
FIGURE 16 illustrates a block diagram of one
embodiment of a line interface module of FIGURE 15;
FIGURE 17 illustrates one embodiment of ATM based
transport communication protocols supported on the local
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loop and the network interface of the communication
server; and
FIGUREs 18A and 18B illustrate a system block
diagram for one embodiment of the communication server.
DETAILED DESCRIPTION OF THE INVENTION
FIGURE 1 illustrates a communication system 10 that
provides both telephone and data service to a subscriber
12. A station 14 is coupled to subscriber 12 using
subscriber line 16. In operation, station 14 provides
telephone service, data service, or both telephone and
data service to subscriber 12 using subscriber line 16.
Subscriber line 16 may support simultaneous telephone and
data service using twisted pair wiring.
Subscriber 12 includes a telephone 20 and a computer
22, both coupled to an interface 24. A splitter 25 is
coupled to subscriber line 16 and operates to split
subscriber line 16 into a twisted pair phone line 26 and
a twisted pair data line 28. Phone llne 26 is coupled to
telephone 20 using interface 24. Similarly, data line 28
is coupled to computer 22 using interface 24.
Subscriber 12 refers to one or more components at the
subscriber premises shown in FIGURE 1, as well as the
user of these components.
Telephone 20 is a traditional telephone transceiver,
a cordless telephone transceiver, or any other device
suitable for allowing communication over telephone line
26. Computer 22 comprises a mainframe device, mini-frame
device, server, desktop personal computer, notebook
personal computer, or other suitable computing device
having an XDSL modem 30 that communicates data using data
line 28. Modem 30 couples to other components of
computer 22 using a Peripheral Component Interconnect
(PCI) bus, an Industrial Standard Architecture (ISA) bus,
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a Personal Computer Memory Card International Association
(PCMCIA) interface, or any other suitable technology that
provides input/output capability to computer 22. The
selection and design of modem 30 for computer 22 may
depend on the type or functionality of computer 22, as
well as the data service rate supported by data line 28.
Modem 30 transmits and receives data in
communication system 10 using any suitable digital
subscriber line technology, referred to generally as
XDSL. Modem 30 also supports Ethernet, Fast Ethernet,
V.35 data protocol, frame relay, asynchronous transfer
mode (ATM), switched multi-megabit data service (SMDS),
high-level data link control (HDLC), serial line Internet
protocol (SLIP), point-to-point protocol (PPP),
transmission control protocol/Internet protocol (TCP/IP),
or any other appropriate protocol, collectively referred
to as digital protocol. For example, computer 22 may
include a network interface 31 to receive data from
station 14 or to further communicate data to a local area
network (LAN), wide area network (WAN), or other suitable
network coupled to computer 22 using link 18. In
general, modem 30 translates information between the
communication protocol supported by communication system
10 and the digital protocol supported by computer 22.
Communication system 10 includes numerous other
twisted pair subscriber lines 16 coupled to other
subscribers 12. In an exemplary embodiment, station 14
comprises a central office or other device in the public
switched telephone network (PSTN) that provides phone and
data service to a number of subscribers, with each
subscriber 12 including one or more components described
above at its premises. The subscribers and subscriber
lines in communication system 10 are referred to
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collectively in the plural as subscribers 12 and
subscriber lines 16.
Interface 24 couples phone line 26 to telephone 20,
and data line 28 to computer 22. In one embodiment,
interface 24 provides additional couplings to additional
telephones 20 and computers 22 at subscriber 12.
Splitter 25 is a passive or active splitter that divides
subscriber line 16 into phone line 26 and data line 28 of
the same type. Throughout this description, phone line
26 and data line 28 may be referred to specifically, or
collectively as part of subscriber line 16.
Subscriber line 16 couples subscriber 12 to station
14. Subscriber line 16 comprises twisted pair wiring
that is commonly installed at subscriber premises and as
the local loop in many public switched telephone networks
(PSTNs). Subscriber line 16 may be unshielded twisted
pair (UTP), shielded twisted pair (STP), or other
suitable type or category of twisted pair wiring made of
copper or other suitable material. Phone line 26 and
data line 28 associated with subscriber line 16 may be
the same or different type or category of twisted pair
wiring.
Station 14 includes an optional splitter 50 coupled
to subscriber line 16. Like splitter 25 at subscriber
12, splitter 50 at station 14 is a passive or active
splitter that divides subscriber line 16 into a twisted
pair phone line 52 and a twisted pair data line 54.
Phone line 52 and data line 54 associated with subscriber
line 16 may be the same or different type or category of
twisted pair wiring. In a particular embodiment, a
telephone switch 56 at station 14 is coupled to phone
line 52 to provide plain old telephone system (POTS)
service to subscriber 12. Telephone switch 56 also
represents other components in the PSTN or other suitable
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voice communication network, such as switches, wireline
or wireless links, satellites, microwave uplinks, and
other communication facilities to deliver telephone
service to subscriber 12.
A communication server 58 is coupled to splitter 50
using data line 54. As described in detail below,
communication server 58 manages the provisioning of data
service to subscriber 12. Communication server 58
performs off-hook detection on the local loops formed by
subscriber lines 16 to determine if subscriber 12 desires
data service. Specifically, communication server 58
couples a modem to subscriber line 16 upon detecting a
need for data service from computer 22. Communication
server 58 tracks subscriber usage, monitors subscriber
information, and generates billing and demographic
information, as described below.
The data off-hook detector in communication server
58 can use one of several methods to determine whether
subscriber 12 should be connected to an XDSL modem. The
off-hook detector may monitor direct current voltages,
electrical tones, data link frames, or any other protocol
or data sequencing ~o determine whether subscriber 12
needs data access. The off-hook detector in
communication server 58 may monitor electrical tones
generated by modem 30 while in the process of training,
notching, equalizing, or performing any other task that
puts electrical tones onto subscriber line 16 and its
associated data line 54. Communication server 58 may
also detect frames or packets. These frames or packets
could be Ethernet, ATM, HDLC, or any suitable data
communications frame format. The off-hook detector in
communication server 58 could also examine various
protocols such as TCP/IP, PPP, or any other suitable
network protocol or data stream.
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Communication server 58 multiplexes modem digital
outputs into a multiplexed digital line 62 for delivery
to a router or other network device 60. In one
embodiment, multi21exed digital line 62 carries a single
bidirectional and multiplexed signal for all subscribers
12 in communication system 10. Signals on multiplexed
digital line 62 may support any appropriate digital
protocol used by network device 60. A communication
network 64, such as a global communication network like
the Internet, is coupled to network device 60.
Communication network 64 may also include a synchronous
optical network ~SONET), a frame relay network, an
asynchronous transfer mode (ATM) network, a T1, T3, E1,
or E3 network, or any other suitable communication
network.
One important technical advantage of the present
invention is the ability to over-subscribe the XDSL
communication facilities of communication server 58 to
service an increasing number of subscribers 12 in
communication system 10. Communication server 58 may
couple to the same number and type of data lines 54 as
represented by subscriber lines 16 in communication
system 10. For example, if station 14 services one
thousand subscribers 12 using twisted pair subscriber
lines 16, then data lines 54 coupled to communication
server 58 may represent as many as one thousand twisted
pair lines.
In one embodiment, not all subscribers 12 in
communication system 10 desire access to data service
provided by communication server 58. Splitter 50 need
not provide a separate data line 54 for those
subscribers 12 that only desire phone service from
telephone switch 56. As more subscribers 12 desire
access to data service, the XDSL communication
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capabilities of splitter 50 and communication server 58
may be supplemented in a modular and cost effective
manner to meet the demand.
Communication system 10 supports data service over
subscriber lines 16 using asymmetric digital subscriber
line (ADSL), symmetric digital subscriber line (SDSL),
high-speed digital subscriber line (HDSL), very high-
speed digital subscriber line (VDSL), or any other
suitable technology that allows high rate data service
over twisted pair wiring that forms the local loops to
subscribers 12. All of these technologies are referred
to collectively as XDSL or communication protocol. In
one embodiment, subscriber line 16 and components of
subscriber 12 and station 14 support communication using
ADSL techniques that comply with ANSI standard T1.4l3.
In another embodiment, ADSL communication over subscriber
line 16 may be performed using the carrier-less amplitude
phase modulation (CAP) technique developed by AT&T
Corporation.
In an ADSL communication system, the downlink data
rate 32 from station 14 to subscriber 12 is greater than
the uplink data rate 34 from subscriber 12 to station 14.
This allows high bandwidth communication to subscriber
12, while still providing lower bandwidth communication
to station 14. ADSL communication is well-adapted for
applications, such as video-on-demand, multimedia, and
Internet access, that transfer large volumes of
information to subscriber 12 in response to shorter
requests for information. In one specific embodiment,
downlink data rate 32 is approximately 1.5 Mbps, whereas
uplink data rate 34 is approximately 750 kbps. In other
embodiments, downlink data rate 32 may be six Mbps or
more depending on the specific XDSL technology employed,
the quality and length of subscriber line 16, and the
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contribution of noise and distortion from other
components in communication system 10.
To support high bandwidth data service, local loops
formed by subscriber lines 16 may have a maximum length
imposed by the XDSL modulation technique or hardware.
For example, an existing ADSL implementation operates
over local loops of 12,000 feet or less. However, the
present invention contemplates, expects, and specifically
includes additional communication technologies that
extend the maximum length, bandwidth, and quality of
communication between subscribers 12 and station 14.
XDSL technology provides data service using existing
subscriber lines 16 without interrupting normal telephone
service. This is accomplished by a separation technique,
such as frequency division multiplexing (FDM), to
separate frequencies that provide telephone service from
those frequencies that provide data service. Dynamic
noise cancellation techniques and a guard band between
the data and phone service frequencies ensure reliable
and simultaneous access to data and phone service over
subscriber line 16. For example, subscriber 12 may
simultaneously engage in both a data communication
session using computer 22 and a voice conversation using
telephone 20.
In operation, communication system 10 provides phone
and data service to subscriber 12. Subscriber 12
accesses phone service by using telephone 20 to initiate
a call. Upon going off-hook, communication system 10
establishes a circuit between telephone 20 and telephone
switch 56 using interface 24, phone line 26, splitter 25,
subscriber line 16, splitter 50, and one of phone lines
52. Upon establishing this telephone circuit,
subscriber 12 using telephone 20 receives POTS service
from telephone switch 56.
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14
To access data service, subscriber 12 turns on
computer 22, executes a program, such as an Internet
browser, or performs some other affirmative or passive
activity that generates a request, command, data packet,
electrical tone, or other suitable information or signal
that indicates a need for data service. In one
embodiment, modem 30 repetitively transmits the need for
data service in a request interval, where the request
interval comprises the time length of the request and the
silent interval until the next request. Alternatively,
the need for data service indicated at subscriber 12 may
be based on the establishment of a closed circuit between
subscriber 12 and station 14 or on one or more analog or
digital signal transitions. Modem 30 communicates the
need to communication server 58 at station 14 using
interface 24, data line 28, splitter 25, subscriber line
16, splitter 50, and one of data lines 54.
As described in detail below, communication server
58 detects the need for data service and selects an XDSL
modem at communication server 58 to communicate with XDSL
modem 30 in computer 22. Upon establishing a modem
connection between modem 30 in computer 22 and a selected
modem in communication server 58, subscriber 12 engages
in a data communication session with communication
network 64 using network device 60. In addition,
computer 22 may function as a gateway into communication
network 10 for other devices coupled to network interface
31 using link 18.
XDSL technology allows simultaneous use of
subscriber line 16 for both phone and data service using
the existing twisted pair wiring in communication system
10. In one embodiment, splitter 50, communication server
58, and network device 60 are located at a central office
of the PSTN to provide an efficient and modular
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provisioning of XDSL data service and voice service to
subscribers 12. In a data-only embodiment, communication
server 58 and network device 60 may be located at a
central office, end office, remote terminal, private
premises, or any other location that provides a point of
presence of network 64. Splitter 50, communication
server 58, and network device 60 may be located at any
site or sites remote from subscribers 12 without
departing from the scope of the present invention.
FIGURE 2 illustrates in more detail communication
server 58. Data lines 54 associated with subscriber
lines 16 are coupled to a switch 70. In one embodiment,
each data line 54 corresponds to an associated subscriber
line 16 and its related subscriber 12. Switch 70 couples
selected data lines 54 to output lines 72 that in turn
couple to modem pool 74. The format of signals on data
lines 54 and output lines 72 is the same as the format of
signals on subscriber lines 16. For example, if
communication system 10 adopts XDSL technology, signals
on data lines 54 and output lines 72 are modulated using
XDSL techniques.
Modems in modem pool 74 convert signals in an
appropriate XDSL communication protocol into digital data
in an appropriate digital protocol on digital lines 76.
A multiplexer 78 is coupled to digital lines 76 and
combines the signals on digital lines 76 into a fewer
number of multiplexed digital lines 62. In one
embodiment, multiplexer 78 combines information for
delivery to network device 60 using a single multiplexed
digital line 62.
A controller 80 is coupled to data lines 54 using a
link 82. Controller 80 is also coupled to switch 70 and
modem pool 74 using links 84 and 86, respectively.
Controller 80 detects a need for data service generated
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16
by subscribers 12 and communicated over subscriber lines
16 to data lines 54. In response, controller 80 using
link 84 directs switch 70 to couple a selected subset of
data lines 54 to selected output lines 72 that couple to
modems in modem pool 74. For example, controller 80 may
monitor one thousand data lines 54 to provide XDSL data
services using one hundred modems in modem pool 74.
Controller 80 also receives information from modem
pool 74 using link 86 to determine status information of
modems in modem pool 74. As digital lines 76 become
inactive for a predetermined period of time, modem pool
74 detects this inactivity and generates a timeout
indication for communication to controller 80. Upon
receiving the timeout indication, controller 80 releases
the inactive modem in modem pool 74 for later use.
In operation, communication server 58 detects a need
for data service on a selected data line 54. This need
may be indicated by current voltages, electrical tones,
data link frames, packets, or any other suitable analog
or digital protocol or data sequencing. Controller 80
detects the need using link 82 and configures switch 70
to provide a coupling between the selected data line 54
and one of the output lines 72 coupled to a selected
modem pool 74. The selected modem translates
bidirectional communication between a communication
protocol on output line 72 and a digital protocol on
digital line 76. Multiplexer 78 translates information
between digital lines 76 and one or more multiplexed
digital lines 62.
FIGURE 3 illustrates in more detail controller 80.
Data lines 54 through link 82 are coupled to polling
circuitry 100. In one embodiment, polling circuitry 100
includes a number of terminals 102 corresponding to each
data line 54. A switch 104 having a conductive probe 106
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17
contacts terminals 102 to sample the signal on the
associated data line 54. Polling circuitry 100 may
comprise electromagnetic components, such as a relay or
switch, solid state circuitry, or both. It should be
understood that the present invention embodies any
polling circuitry 100 that allows sampling, in succession
or simultaneously, one or more data lines 54.
Transceiver 108 receives a selected signal 110 from
polling circuitry 100. A detector 112 is coupled to
transceiver 108, which in turn is coupled to processor
116. Detector 112 may include a media access controller
(MAC) and associated memory to detect and store frames or
packets of an appropriate digital protocol. Detector 112
may also include less complicated circuitry to detect
current voltages, electrical tones, data bit
transmissions, or other analog or digital information
generated by transceiver 108.
Transceiver 108 and detector 112 may collectively be
represented as modem 115, as indicated by the dashed
line. Modem 115 provides an interface between the XDSL
communication protocol of communication system 10 and
processor 116. Modem 115 also includes similar
components and performs similar functions as modem 30 in
computer 22 to enable modem 30 and modem 115 to exchange
information using XDSL technology. Throughout this
discussion, the term detector may refer to detector 112
or collectively modem 115.
A processor 116 is coupled to detector 112 and
controls the overall operation of controller 80. A timer
117 is coupled to processor 116. Processor 116 is
coupled to input/output circuitry 118, which in turn is
coupled ~o switch 70 and modem pool 74 using links 84 and
86, respectively. Processor 116 is also coupled to
switch 104 of polling circuitry 100 using input/output
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18
circuitry 118. In one embodiment, processor 116 controls
the data line selection, dwell time, and other suitable
parameters of polling circuitry 100.
Processor 116 is also coupled to database 120 that
includes a program 121, an activity table 122, a line
profile table 124, and a subscriber table 126.
Database 120 stores information as one or more tables,
files, or other data structure in volatile or non-
volatile memory. All or a portion of database 120 may
reside at controller 80, within communication server 58,
within station 14, or at another location in
communication system 10. For example, several
communication servers 58 in one or more central
offices or other devices of communication system 10 can
access database 120 stored in a central location to
provide more intelligent management and provisioning of
XDSL data service in communication system 10. One or
more stations 14 may be coupled together and the
resources of their associated communication servers 58
shared using simple network management protocol (SNMP)
techniques.
Program 121 contains instructions to be executed by
processor 116 to perform the functions of controller 80.
Program 121 may reside in database 120 as shown or may be
integral to memory components in transceiver 108,
detector 112, and/or processor 116. Program 121 may be
written in machine code, pseudocode, or other appropriate
programming language. Program 121 may include modifiable
source code and other version control features that allow
modification, debugging, and enhancement of the
functionality of program 121.
Activity table 122, described in more detail below
with reference to FIGURE 7, maintains status information
on data lines 54, switch 70, and output lines 72. In
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19
particular, activity table 122 contains information on
inactive and active data lines 54, data lines 54
corresponding to current valid subscribers 16 of XDSL
data service, and the mapping performed by switch 70
between data lines 54 and output lines 72. Moreover,
activity table 122 includes information that specifies
the inactivity of a modem in modem pool 74, the status of
a data line 54 as dedicated, and any other suitable
information that enables processor 116 to monitor and
control the operation of switch 70 and modem pool 74.
Profile table 124 stores profile information on data
lines 54. This profile information reflects electrical
or physical characteristics of data line 54, its
associated subscriber line 16 and data line 28,
intervening components such as interface 24, splitter 25,
splitter 50, and polling circuitry 100, as well as any
other component or factor that effects the performance or
electrical characteristics of signals received on data
lines 54. Processor 116 may access profile table 124 and
provide profile information to transceiver 108 using link
125. Alternatively, transceiver 108 may be a more robust
and broadband device that does not need profile
information from profile table 124. Processor 116 may
also provide profile information to program XDSL modems
in modem pool 74 once a coupling is made to a selected
data line 54. The existence and complexity of profile
information in profile table 124 depends on the
requirements of transceiver 108 and XDSL modems in modem
pool 74, as well as the complexity of signals that
indicate a need for data service from subscriber 12.
Subscriber table 126 stores subscriber information
indexed by one or more identifiers of subscriber 12,
computer 22, modem 30, subscriber line 16, or other
information that associates data line 54 with a
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particular subscriber 12. Subscriber table 126 includes
subscriber connect times, session duration, session
activity, session logs, billing data, subscriber account
information, and any other suitable subscriber
information. This information may be summarized and
additional information included to generate billing and
demographic data on subscribers 12 in communication
system 10.
For example, subscriber table 126 may maintain
summary statistics on the number of subscribers 12 served
by communication server 58, the average connect time,
load factors, time-of-day connection profiles, and other
statistics to assess the communication facilities to be
deployed at communication server 58, the over-
subscription ratio that can be supported by communication
system 10, and other provisioning and management issues.
Furthermore, subscriber table 126 may combine subscriber
information from one or more communication servers 58 in
one or more stations 14 in communication system 10.
Management interface 128 is coupled to processor 116
and database 120 and allows external access to the
functionality of processor 116. Management interface 128
is also coupled to database 120, which allows
modification of program 121, as well as remote access and
modification of information in activity table 122,
profile table 124, and subscriber table 126. In one
embodiment, the telephone service provider or other
entity that operates station 14 or communication
system 10 accesses management interface 128 to provide
management and control over the operations of
controller 80 and communication server 58. For example,
the telephone service provider uses management interface
128 to access activity table 122 and/or subscriber table
126 to update the valid subscribers 12 that have access
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to communication server 58. A local or remote computer
130 is coupled to program interface 128 using an
appropriate data link 132, such as a serial RS-232 link,
to provide this management feature.
In operation, modem 30 in computer 22 indicates a
need for data service, and communicates this need to an
associated data line 54 using interface 24, data line 28,
splitter 25, subscriber line 16, and splitter 50. In one
embodiment, modem 30 transmits successive requests at a
predetermined request interval. Processor 116 accesses
activity table 122 to determine which data lines 54 to
poll, depending on the active or inactive status of the
data line 54, whether subscriber 12 corresponding to data
line 54 is a current and valid subscriber, and other
appropriate considerations. For example, activity table
122 may indicate valid and non-dedicated subscribers 12
to poll.
Polling circuitry 100 successively or simultaneously
polls one or more selected data lines 54, as directed by
processor 116, using link 82 to detect a need for data
service. For each data line 54 polled, processor 116 may
access profile table 124 in database 120 and provide
associated profile information to transceiver 108 using
link 125. Polling circuitry 100 dwells on each data
line 54 for a predetermined polling interval to detect a
need. In one embodiment, the polling interval is at
least two times a request interval of modem 30.
Upon detecting the need for data service associated
with a selected data line 54 from polling circuitry 100,
transceiver 108 may translate the information from the
selected XDSL communication protocol employed on
subscriber line 16 into digital or analog data for
detection by detector 112. A media access controller
(MAC) in detector 112 may transform serial digital data
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from transceiver 108 into a parallel digital format.
Detector 112 receives the information translated by
transceiver 108, and stores this information in a
suitable memory location for access by processor 116.
Processor 116 periodically accesses detector 112 to
determine if a need for data service has been detected.
Upon detecting a need for data service,
processor 116 accesses database 120 to determine the
availability and status of modems in modem pool 74.
Processor 116 selects an available modem from modem
pool 74. Processor 116 then directs switch 70 to make
the appropriate coupling between selected data line 54
and output line 72 coupled to the selected modem. Upon
establishing coupling between modem 30 in computer 22 at
subscriber 12 and a selected modem in modem pool 74,
controller 80 continues to monitor the remaining data
lines 54 using polling circuitry 100.
Processor 116 can transmit status or connection
information to modem 30 in computer 22 using transceiver
108. This may be performed before, during, or after
coupling the selected modem in modem pool 74 to data line
54. For example, processor 116 may send acknowledgment
information to modem 30 that includes an indication that
a modem is or is not available, an identification of the
available modem, a time interval before modem 30 should
attempt communication with the selected modem in modem
pool 74, or any other suitable information. Furthermore,
processor 116 may access information from subscriber
table 126, such as billing and account information,
historical connection information, or other suitable
subscriber information, and transmit this information
separate to or as part of the acknowledgment information
described above.
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Processor 116 may also transmit connection
information and updated billing and subscriber
information to modem 30 at computer 22 using link 86 and
the associated XDSL modem in modem pool 74. This
information may include the length of the current
session, the current balance in the account of subscriber
12, as well as any other suitable information that
relates to the account or activity of subscriber 12 with
communication server 54. Generally, processor 116 may
communicate any suitable information stored at or made
available to controller 80 to subscribers 12 using
transceiver 108 or the associated modem in modem pool 74.
FIGURE 4 illustrates in more detail switch 70 and
modem pool 74 of communication server 58. Data lines 54
are coupled to switch 70, now shown in more detail as a
cross-bar or cross-point matrix switch. In this
particular embodiment, data lines 54 correspond to
lines 150, and output lines 72 correspond to lines 152 in
switch 70. The number of lines 150 (n) is greater than
the number of lines 152 (m). This allows switch 70 to
couple selected data lines 54 to a reduced number of
output lines 72 to provide an over-subscription of XDSL
data service in communication system 10. For example,
switch 70 couples the second of lines 150 to the last of
lines 152 by establishing connection 154. Similarly,
switch 70 couples the last of lines 150 and the first of
lines 152 by establishing connection 156.
Although switch 70 is shown in FIGURE 4 to be a
cross-bar or cross-point matrix switch, it should be
understood that any device that can couple a number of
data lines 54 to a reduced number of output lines 72 may
be used. Switch 70 may incorporate electromagnetic
components, such as relays and contacts, or may be
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24
implemented in whole or in part using one or more solid
state devices.
Modem pool 74 includes XDSL modems 160 associated
with output lines 72 from switch 70. Modems 160
translate information between an appropriate XDSL
communication protocol on output lines 72 and an
appropriate digital protocol on digital lines 76. In one
embodiment, modems 160 may be similar in construction and
operation to modem 30 at subscriber 12. A detector 162
coupled to modems 160 detects the activity of modems 160
to determine if the line has become inactive for a
predetermined interval of time. For example, if one of
the modems 160 does not display activity over a five-
minute interval, detector 162 generates a timeout
indication to notify processor 116 of the inactive modem.
Processor 116 releases or decouples the inactive modem
for later subscriber sessions. In one embodiment,
detectors 162 may include one-shot timers or other
retriggerable timers set for a predetermined time
interval to detect the inactive status of modems 160.
Detector 162 is a monitoring circuit that passes
through the digital output of modems 160 to digital
lines 76 for presentation to multiplexer 78.
Multiplexer 78 may combine signals from digital lines 76
into a single multiplexed digital line 62.
Alternatively, multiplexer 78 may employ any suitable
reduction ratio that places signals on digital lines 76
on a fewer number of multiplexed digital lines 62.
Processor 116 may directly communicate with modems
160 using link 164. For example, link 164 allows
processor 116 to program modems 160 with profile
information retrieved from profile table 124. Link 164
also supports communication between processor 116 and
selected subscribers 12 during an active subscriber
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session using modems 160. Moreover, link 164 allows
processor 116 to monitor the information received from
and transmitted to subscribers 12 during a communication
session.
In operation, switch 70 couples a selected subset of
data lines 54 to output lines 72 in response to signals
received from controller 80 using link 84. Each of the
output lines 72 is coupled to an associated modem 160
which translates the information formatted in an analog
communication protocol, such as XDSL, into an appropriate
digital signal. The digital information output from
modems 160 passes through detector 162, which monitors
the activity on the output line of modems 160. If
detector 162 senses inactivity over a predetermined
interval, a timeout indication is provided to
processor 116 using lin~ 86. Signals on digital lines 76
may be reduced to fewer multiplexed digital lines 62
using multiplexer 78.
FIGURE 5 illustrates in more detail transceiver 108
in controller 80. To receive information,
transceiver 108 includes filters and magnetics 170 to
condition the signal from selected data line 54. The
conditioned signal is provided over differential
lines 172 to analog bit pump 174. Bit pump 174 performs
the specific demodulation technique for the chosen XDSL
communication protocol. For example, bit pump 174 may
execute a discrete multi-tone demodulation (DMT) or
carrierless amplitude phase demodulation (CAP) to
demodulate an XDSL signal on differential lines 172 into
a digital stream on line 176. Logic and timing
circuitry 178 contains decode logic, timing and
synchronization circuitry, steering logic, and other
appropriate digital processing circuitry to produce a
data signal on receive data line 180 and a corresponding
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26
clock signal on clock line 182 for delivery to
detector 112 or processor 116. Detector 112 may include
a MAC to support any digital protocol or signal detection
that indicates a need for XDSL data service. The data
may be in non-return-to-zero format or any other suitable
format.
To transmit information, transceiver 108 receives a
data signal on transmit data line 184 from detector 112
or processor 116. Using the clock line 182, logic and
timing circuitry 178 digitally processes signals received
on transmit data line 184 for delivery to analog bit pump
174. Using an appropriate modulation technique, such as
DMT or CAP, analog bit pump 174 produces an analog signal
for delivery over differential lines 172 to filters and
magnetics 170 for transmission over selected data line
54.
FIGURE 6 illustrates in more detail a specific
embodiment of detector 112 that includes a MAC 113 and a
memory 114. MAC 113 is coupled to receive data line 180
and clock line 182, and translates received data from a
serial data format, such as a non-return-to-zero format,
into an appropriate parallel digital format. MAC 113
translates the data from the chosen digital protocol and
provides the data to memory 114 using data bus 190.
MAC 113 also provides an address to memory 114 using
address bus 192 to specify the location in memory 114 to
store data provided on data bus 190. In addition, MAC
113 provides a write signal to memory 114 using control
line 194.
To transmit data, MAC 113 provides a read signal to
memory 114 using control line 194, and an associated
address of the data to be read using address bus 192. In
response, memory 114 provides the requested data on data
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bus 190. MAC 113 translates the data into the selected
digital protocol for placement on transmit data line 184.
FIGURE 7 illustrates one embodiment of activity
table 122 stored in database 120 of controller 80.
Processor 116 accesses and modifies entries in activity
table 122 to direct the operation of controller 80. In
addition, management interface 128 provides external
access to activity table 122. For example, a telephone
service provider using management interface 128 can add,
delete, or otherwise modify entries in activity table 122
to maintain a listing of valid subscribers 12.
Database 120 stores some or all of the status information
shown in this exemplary activity table 122, as well as
other information that may be used by processor 116 to
direct the activities of controller 80.
Activity table 122 includes a data line column 200
that contains an address or other appropriate identifier
of data lines 54 associated with subscriber lines 16 and
their related subscribers 12. Status column 202
indicates the status of data line 54 identified in data
line column 200. For example, status column 202 may
contain one or more indications that the associated data
line 54 is inactive ~I), active tA), or dedicated (D). A
timeout column 204 indicates whether detector 162 in
modem pool 74 has detected a timeout associated with a
particular data line 54. A modem column 206 includes an
identifier of the modem 160 associated with the
corresponding data line 54.
An entry in activity table 122 corresponds to a row
that designates a selected data line 54 in data line
column 200, the status of the selected data line 54 in
status column 202, a timeout indication of the selected
data line 54 in timeout column 204, and the modem
associated with the selected data line 54 in modem column
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206. For example, entry 208 relates to data line "D1"
which is inactive. Entry 210 represents data line "D2"
which is inactive but dedicated to modem "M1." Entry 212
indicates that data line "D4" is active, coupled to modem
"M3," but a timeout indication has been detected.
Subscribers 12 indicated in status column 202 as
dedicated may be serviced by communication server 58 in a
specific way. Switch 70 in communication server 58
maintains a coupling between data line 54 corresponding
to dedicated subscriber 12 and its associated and
dedicated modem 160. In this manner, controller 80 need
not detect a need for data service or reconfigure the
couplings for data line 54 corresponding to dedicated
subscriber 12. In this manner, communication server 58
provides the option of a different class of service for a
dedicated subscriber 12 that desires uninterrupted access
to XDSL communication facilities.
FIGURE 8 is a flow chart of a method performed at
controller 80 to couple data lines 54 to modems 160 in
modem pool 74. The method begins at step 300 where
processor 116 of controller 80 loads activity table 122
from database 120 which contains an entry for each valid
subscriber 12 served by communication server 58. Using
management interface 128, a telephone service provider
may ensure that activity table 122 reflects valid
subscribers 12 by monitoring past due accounts, the
overuse of data service, successive invalid attempts to
access communication server 54, or other factors that may
cause subscribers 12 to be invalid. Processor 116
selects the first inactive and non-dedicated data line 54
indicated by the designation "I" in status column 202 of
activity table 122. Since switch 70 is configured to
continuously couple dedicated subscribers 12 to their
dedicated modems 160, processor 116 need not select an
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inactive data line 54 that is also dedicated, as
indicated by the designation "I/D" in status column 202.
Using input/output circuitry 118, processor 116
directs switch 104 of polling circuitry 100 to couple
transceiver 108 to the selected inactive and non-
dedicated data line 54 at step 304. If appropriate,
processor 116 accesses profile table 129 in database 120
and provides profile information for the selected data
line 54 to transceiver 108 using link 125 at step 306.
Processor 116 initializes timer 117 with a predetermined
polling interval at step 308.
If a need for data service has not been detected by
transceiver 108 at step 312, then processor 116 checks
timer 117 at step 314. If the polling interval monitored
by timer 117 has not expired at step 314, then processor
116 again determines if a need has been detected at step
312. However, if the polling interval monitored by timer
117 has expired at step 314, processor 116 selects the
next inactive and non-dedicated data line 54 as indicated
in status column 202 of activity table 122 at step 316,
and returns to step 304.
If a need for data service is detected at step 312,
the associated information may be further processed by
detector 112 and placed in memory for access by processor
116 at step 318. Before, during, or after step 318,
transceiver 108, detector 112, and/or processor 116 may
validate the need for data service. Validation may be
performed at a low level, such as a verification of the
checksum or detection of an incomplete transmission, or
at a higher level, such as a verification of an
identifier, password, or other security information that
provides access to communication server 58. Validation
contemplates any level of validation or security
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handshake that confirms that the received need is valid
and accepted by controller 80.
Upon selecting an unused modem at step 332,
processor 116 generates a command that directs switch 70
to couple the selected data line 54 to the selected
modem 160 at step 333. Processor 116 may communicate
status or connection information to subscriber 12 using
transceiver 108 or the selected modem 160 at step 334.
Processor 116 updates activity table 122 at step 336 to
indicate that the selected data line 54 is now active and
that the selected modem 160 is now being used. Processor
116 directs activity detector 162 to initialize the
inactivity interval for the selected modem 160 at step
338. Processor 116 then selects the next inactive and
non-dedicated data line 54 in activity table 122 at
step 316, and returns to step 304.
FIGURE 9 is a flow chart of a method for monitoring
and decoupling modems 160 due to inactivity. It should
be understood that the methods described with reference
to FIGURES 8 and 9 may be performed simultaneously or in
alternative succession by processor 116 to couple and
decouple data lines 54 with modems 160. The method
begins at step 400 where processor 116 loads activity
table 122 which contains an entry for each valid
subscriber 12 served by communication server 58.
Processor 116 selects a first active and non-dedicated
data line 54 as indicated by the designation "A" in
status column 202 of activity table 122 at step 402.
Since switch 70 is configured to maintain a coupling
between dedicated subscribers 12 and their dedicated
modems 160, processor 116 need not select an active data
line 54 that is also dedicated, as indicated by the
designation "A/D" in status column 202.
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Processor 116 retrieves timeout status for modem 160
associated with the selected active data line 54 from
detector 162 using link 86 and input/output circuitry 118
at step 404. Processor 116 determines if a timeout has
occurred for the selected active data line 54 at
step 408. If a timeout has not occurred, processor 116
selects the next active and non-dedicated data line 54 as
indicated in status column 202 of activity table 122 at
step 410, and returns to step 404.
If a timeout has occurred at step 408, processor 116
may communicate status or connection information to
subscriber 12 associated with the selected active data
line 54 using transceiver 108 or the associated modem 160
at step 412. Processor 116 generates a command to direct
switch 70 to decouple the active data line 54 from its
associated modem 160 at step 414. Processor 116 updates
activity table 122 at step 416 to indicate that data line
54 is now inactive and that the associated modem 160 is
available for another subscriber session.
FIGURE lOA illustrates another implementation of
communication server 58 in communication system 10.
Communication server 58 of FIGURE lOA provides switching
at an isolated four-wire interface. As shown in FIGURE
lOA, data lines 54 are coupled to and received by a
plurality of line interface units 500. Each line
interface 500 provides an analog interface, line driver
and transformer for processing signals on data lines 54.
Each line interface unit 500 is coupled to a switching
matrix 502 and communicates with switching matrix 502
across a transmit data pair 504 and a receive data pair
506. Each line interface unit 500 operates to interface
between transmit data pair 504 and receive data pair 505
and twisted pair data line 54.
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In the implementation of FIGURE lOA, a detector 508
is coupled to each receive data pair 506. Each detector
508 operates to detect a request for service on the
associated receive data pair 506 and, upon detection,
provides a signal to controller 80 indicating a request
for service. Detector 508 is shown in more detail in
FIGURE lOD, and implementations of detectors are shown in
more detail in FIGURES llA, llB and llC. It should be
understood that other implementations can combine polling
with multiple detectors to reduce the number of inputs to
controller 80 and to reduce the number of detectors. For
example, FIGURE 3 shows an implementation using polling
circuitry 100 that can be used with the detector in the
communication server embodiment of FIGURE lOA.
As shown, switching matrix 502 is coupled to a modem
pool 510 and communicates with modem pool 510 across
transmit data pairs 512 and receive data pairs 514.
Transmit data pairs 512 and receive data pairs 514
contain a number of pairs equal to the number of modems
in modem pool 510. As described above, modems in modem
pool 510 convert signals in an appropriate XDSL
communication protocol into digital data in an
appropriate digital protocol on digital lines 76.
Multiplexer 78 is then coupled to digital line 76 and
provides a multiplexed digital line output 62. Also as
described above, controller 80 provides switch control
signals 84 to switching matrix 502 and communicates modem
selection and control information 86 with modem pool 510.
In operation, each detector 508 detects a request
for service on the associated receive data pair 506 and
informs controller 80 that a request for service has
occurred. Controller 80 then checks which modems in
model pool 510 are assigned and which data lines 54 are
valid. Controller 80 assigns a modem from modem pool 510
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to the requesting data line 54 using switching matrix 502
to connect the associated receive data pair 506 and
transmit data pair 504 to the appropriate receive data
pair 514 and transmit data pair 512.
A technical advantage of providing switching at a
four-wire interface within communication server 58 is
that switching matrix 502 is isolated from data lines 54
and subscriber lines 16 by transformers in line interface
unlts 500. Because of this isolation, switching matrix
502 can operate without constraints imposed by technical
requirements for interaction with data lines 54 and
subscriber lines 16. For example, the isolation of
switching matrix 502 allows CMOS switches to be used
rather than more expensive solid state relays or
mechanical relays.
FIGURE lOB illustrates in more detail line interface
device 500 of communication server 58 of FIGURE lOA.
Line interface device 500 includes a line protection
circuit 520 that is coupled to and receives data line 54.
Line protection circuit 54 operates to ensure that
activity down stream in communication server 58 does not
affect the integrity of data line 54. Line protection
circuit 520 is coupled to a magnetics/hybrid unit 522.
Magnetics/hybrid unit 522 can comprise a transformer and
operates to interface between the data line and an
internal transmit data pair 524 and receive data pair
526. Magnetics/hybrid unit 522 also isolates the four-
wire interface provided by internal receive data pair 526
and transmit data pair 524 from data line 54.
A line receiver 528 receives receive data pair 526
and drives signals to a receive filter 530. The output
of receive filter 530 is receive data pair 506 which is
coupled to switching matrix 502 as shown in FIGURE lOA.
Similarly, transmit data pair 504 is coupled to a
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34
transmit filter 532 which provides signals to a cable
driver 534. Cable driver 534 then drives signals on
transmit data pair 524 to magnetics/hybrid unit 522.
FIGURE lOC illustrates in more detail controller 80
of communication server 58 where a plurality of detectors
provide indications of a request for service. Controller
80 of FIGURE lOC includes processor 116 and input/output
circuitry 118 as discussed above with respect to FIGURE
3. Controller 80 also includes a scanner or processor
interrupt circuit 540 which receives the request for
service indications from detectors 508 and provides a
scanner output or processor interrupt to processor 116.
This allows the outputs of a number of detectors 508 to
be sampled to provide an appropriate signal to processor
116 when a request for service has been detected. As
mentioned above, it should be understood that selection
of the number of detectors and the amount of polling can
be made as appropriate for the desired application. In
one implementation, scanner or processor interrupt
circuit 540 comprises a gate array having logic circuitry
for generating appropriate interrupt signals to processor
116.
FIGURE lOD illustrates in more detail a detector 508
of communication server 58. As shown, detector 508
includes a receiver circuit 550 and a service request
detector 552. Receiver circuit 550 is coupled to a
receive data pair 506 and provides an output to service
request detector 552. Service request detector 552 then
operates to identify a request for service. Upon
detection, service request detector 552 provides a signal
indicating a request for service to controller 80. For
ADSL systems (e.g., CAP and DMT), the request for service
can be an initial tone that is a pure sinusoid or a
modulated sinusoid. Three implementations of a detector
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508 are illustrated in more detail in FIGURES llA, llB
and llC and described below.
FIGURE lOE illustrates in more detail a modem 560 in
modem pool 510 of communication server 58. Modem 560 is
analogous to modem 108 of FIGURE 5 with filters and
magnetics 170 removed. Modem 560 includes a bit pump 174
which communicates with switching matrix 502 across
receive data pair 526 and transmit data pair 524. Modem
560 does not need to include filters and magnetics 170
because of the functions provided by line interface units
500 to create the four-wire interface described above.
Bit pump 174 and logic and timing circuitry 178 otherwise
operate as discussed with respect to FIGURE 5.
Conceptually, the implementation of FIGURE lOA moves the
function of filters and magnetics 170 of modem 108 to
line interface units 500 to isolate switching matrix 502
from data lines 54.
FIGURE llA illustrates in more detail an analog
filter implementation of a detector 508 of communication
server 58. Detector 508 of FIGURE llA detects the tone or
modulated tone using an analog filter circuit tuned to
the distinct frequency used to transmit a subscriber
request for service. Detector 508 comprises a
differential receiver 570 that is coupled to an
associated receive data pair 506. Differential receiver
570 is coupled to and provides a signal to a band pass
filter 572. Band pass filter 572 is coupled to a gain
device 574 which is coupled to a signal processing
circuit 576. The output of signal processing circuit 576
is coupled to a rectifier circuit 578 which is coupled to
a low pass filter 580. The output of low pass filter 580
is then provided as one input to a voltage comparator
582. The other input to voltage comparator 582 is
connected to a reference voltage 584.
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In operation, detector 508 operates to detect a tone
or modulated tone that indicates a request for service on
recelve data pair 506. Differential receiver 570
produces a voltage output which is filtered by band pass
filter 572 and provided to gain device 574. Gain device
574 then amplifies the signal and provides it to signal
processing circuit 576. The signal processing circuit
576 processes or demodulates the XDSL signals generated
at the customer location that indicate a request for data
service. Signal processing circuit 476 provides the
signal to rectifier circuit 578 that outputs the signal
to low pass filter 580. Low pass filter 580 filters low
frequency noise to provide a DC voltage as an input to
voltage comparator 582. Voltage comparator 582 compares
that DC voltage with reference voltage 584 and outputs a
logic high when the DC voltage is greater than reference
voltage 584. Reference voltage 584 is set so that voltage
comparator 582 signals a request for service only when
the appropriate tone or modulated tone is present on
receiver data pair 506.
It should be understood that detector 508 of FIGURE
llA, as well as those of FIGURES llB and llC, can be
connected to polling circuit 100 of FIGURE 3 or other
polling circuits to reduce the number of detectors
required or to scan the outputs of the detectors. The
number of lines that can be polled by a single polling
circuit is generally limited by the amount of time that
is required by the detector to reliably detect the
subscriber request for service.
FIGURE llB illustrates in more detail a tone decoder
implementation of detector 508 of communication server
58. Detector 508 comprises a differential receiver 590
that is coupled to receive data pair 506 and provides an
output to a band pass filter 592. Band pass filter 592
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is coupled to a gain device 594 which provides an output
to a signal processing circuit 596. The signal
processing circuit 576 processes or demodulates the XDSL
signals generated at the customer location that indicate
a request for data service. The output of signal
processing device 596 is then coupled to a tone decoder
circuit 598. Tone decoder integrated circuit 598
provides an output to controller 80 indicating a request
for service upon detection.
In one implementation, tone decoder circuit 598
comprises an integrated circuit, and specifically is an
LMC567 tone decoder available from NATIONAL
SEMICONDUCTOR. In this implementation, tone decoder
circuit 598 includes a phase locked loop detector for
identifying the tone or modulated tone that indicates a
request for service. The phased locked loop detects when
the received tone or modulated tone matches the signaling
frequency, and the tone detector circuit responds ~y
signaling a request for service.
FIGURE llC illustrates in more detail a digital
signal processor implementation of detector 508 of the
communication server 58. Detector 508 of FIGURE llC
comprises a polling circuit 600 that is coupled to a
plurality of receive data pairs 506. Polling circuit
selects each receive data pair 506 and connects it to a
line receiver 602. Line receiver 602 is coupled to a
filter 604 which is coupled to an analog/digital
converter 606. Analog/digital converter converts the
signal to a digital signal and provides an output to a
digital signal processor 608. Upon detection, digital
signal processor provides a request for service
indication to controller 80.
In the implementation of FIGURE llC, polling
circuitry 600 connects line receiver 602, filter 604,
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38
analog/digital converter 606 and digital signal processor
608 to each line in succession. Digital signal processor
608 reads the data from the analog/digital converter 606
and demodulates or detects the request for service. The
dwell time for polling circuitry 600 can be set, for
example, such that detector 508 can poll the lines in
less than half the duration of the subscriber request for
service tone or modulated tone. The number of lines that
can be polled by a single digital signal processor 608 is
then determined by the amount of time required for
digital signal processor 608 to reliably perform the
detection algorithm and the duration of the tone
described above.
Digital signal processor 608 is programmable to
detect the subscriber request for service tone or
modulated tone using an appropriate tone detection
algorithm or demodulation algorithm. One advantage
provided by the detector implementation of FIGURE llC is
this programmability of the algorithm within digital
signal processor 608.
It should be understood that the tones used to
indicate service in the above description of FIGURES llA,
llB, and llC, may be the tone used in standard non-
switched applications of XDSL modems, or may be
additional tones added specifically to facilitate
detection in switching.
FIGURE 12 illustrates in more detail a digital
switching matrix implementation of communication server
58. The implementation of FIGURE 12 is appropriate for
both a two-wire and four-wire interface to provide
digital switching of the modem connections.
Communication server 58 of FIGURE 12 includes line
interface components and data off-hook detection units
610 that interface with subscriber lines 54 and detect
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39
subscriber requests for service. Request for service
indications are then provided to controller 612 for
controlling the modem connections.
Each line interface and detection unit 610 is
coupled to an associated analog/digital and
digital/analog converter 614. Converters 614 are in turn
connected to parallel/serial and serial/parallel
converters 616. Converters 616 are coupled to a digita~
multiplexer 618 which operates under control of
controller 612 to connect converters 616 to assigned
modems in modem pool 620. Modems in modem pool 620 are
coupled to a network interface/multiplexer 622 and can be
implemented using digital signal processors. As shown,
network interface/multiplexer 622 is coupled to and
communicates with controller 612. This allows network
interface/multiplexer 622 to know which modems and lines
are active without having to monitor the communication
traffic on the lines.
In operation, incoming communications are converted
to digital words by converters 614 and then converted to
serial bit streams by converters. The serial bit streams
are connected to an assigned modem by digital multiplexer
618. The modems in modem pool 620 then communicate with
network interface/multiplexer 622. For outgoing
communications, the process is reversed. Serial bit
streams from the modems are converted to parallel words
and then to analog signals for transmission on data lines
54. This digital switching implementation of
communication server 58 can be advantageous for switching
of higher frequency XDSL communications.
FIGURE 13A illustrates in more detail a frequency
multiplexing implementation for switching modem
connections in communication server 58. This frequency
multiplexing implementation could be appropriate for
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being located at a cable operator as well as a central
office of a telephone network. As shown, data lines 54
are coupled to receiver/buffers 630 and transmit/buffers
632. Data off-hook detectors 634 are coupled to the
output of receiver/buffers 630 and provide request for
service indications to controller 636. For each data
line 54, communication server 58 includes a frequency
agile modulator 638 and a frequency agile demodulator
640. Each modulator 638 operates to modulate an incoming
analog signal at a selectable frequency. In the
illustrated embodiment, the frequency is set to one of a
plurality of frequencies, fl to fN, equal in number to
the number of available modems. Similarly, each
demodulator 640 operates to demodulate at a selectable
frequency where the frequency is set to one of the
plurality of frequencies, fl to fN. Associated
modulators 638 and demodulators 640 are set to operate at
the same frequency.
Modulators 638 provide signals to and demodulators
640 receive signals from a mixer 642. Mixer 642 mixes
the signals from modulators 638 and provides the combined
signal to demodulators 644. Each demodulator 644
operates to demodulate the incoming signal at one of the
frequencies, fl to fN, as designated by controller 636.
Each demodulator 644 is coupled to and provides the
demodulated signal to an associated modem 648 in the
modem pool. By designating the appropriate frequency,
controller 636 effectively connects an assigned a modem
648 to a data line 54.
Outgoing signals are processed in an analogous
manner. Each modem 648 provides outgoing analog signals
to an associated modulator 646 designated to operate at
the same frequency as the associated demodulator 644.
Modulators 646 modulate the analog signal and provide the
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41
modulated signal to mixer 642. Mixer 642 combines the
modulated signals and provides the combined signal to
each demodulator 640. Demodulators 640 demodulate the
combined signal to recover the appropriate analog signal
at their selected frequency and provide the demodulated
analog signal to transmit/buffers 632 for transmission.
In this manner, modems 648 are connected to data lines
540 by modulating and demodulating signals at one of the
frequencies, fl to fN.
FIGURE 13B is a diagram of frequencies, fl to fN,
used in the implementation of FIGURE 13A. This results
in each of the modems, ml to mN, being assigned to one of
the frequencies, fl to fN, based upon the frequency for
the connected data line 54, as shown. In order to
connect a data line 54 to a assigned modem 648,
modulators 644 and demodulators 646 are designated to
operate at the frequency of the modulator 638 and
demodulator 640 for that data line 54.
FIGURE 14A illustrates line interface modules ~LIM)
650 and modem pool 652 of a distributed switching
implementation of communication server 58. A controller
653 is coupled to line interface modules 650 and to modem
pool 652. As shown, a plurality of line interface
modules 650 are coupled to the data lines and to modem
pool 652. Each line interface module 650 is operable to
detect a request for service on the data lines and to
connect each of the data lines it receives to each modem
in modem pool 652. Controller 653 operates to select a
modem from modem pool 652 in response to a detected
request for service. Controller 653 then directs the
appropriate line interface module 650 to connect the
requesting data line to the selected modem. In the
illustrated implementation, each line interface module
650 receives N data lines and includes switches to
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42
connect the N data lines to any of the M modems in modem
pool 652. In this manner, the switching function is
distributed across line interface modules 650 and is
scalable as support for more data lines is added. In
addition, although a two-wire interface is shown, the
architecture of FIGURE 14A can be used at a two-wire or
four-wire interface.
Line interface modules 650 allow switching
capabilities to be scalable with the desired number of
modems and over-subscription. As an example, one
implementation has four data lines connected to each line
interface module 650 and thirty-two modems in modem pool
652. For a 10:1 over-subscription, this implementation
would use 80 line interface modules 650 for connecting
320 data lines to the 32 modems in modem pool 652. In
order to double the number of supported data lines,
another 80 line interface modules 650 could be added
along with another 32 modems. On the other hand, if a
5:1 over-subscription for 32 modems is desired, 40 line
interface modules 650 would be used to service 160 data
lines.
FIGURE 14B illustrates in more detail line interface
modules 650 and modems 660 in modem pool 652. As shown,
each line interface module 650 includes a plurality of
line interface units 654 that receive one of the N tip
and ring data lines. Each line interface device 654
includes magnetics 656 and a plurality of switches 658.
In the illustrated implementation, magnetics 656 includes
a transformer that receives tip and ring lines of the
associated data line. As shown in FIGURE 14B, a T line
is then provided to a plurality of switches 658 for
connecting the T line to one of M outgoing lines. As
shown, the M outgoing lines are equal in number to the
number of modems 660 in modem pool 652. Then outputs of
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43
each line interface device 654 are connected together so
that line interface module 650 has one output line for
each modem 660 in modem pool 652 in addition to one
output for the R lines. It should be understood that
this can be implemented differentially using a pair of
switches to switch the modem to the data line, rather
than a single switch and a common R line, to enable
switching R lines as well.
Modem pool 652 includes a plurality of modems 660 of
which only the front-end portion are shown. Each modem
660 receives two lines from line interface modules 650
using magnetics 662. Because of magnetics 656 and
magnetics 662, the switching and connections between line
interface devices 654 and modems 660 are isolated from
the data lines and from the back-end of modems 660. In
one implementation, the connections between line
interface modules 650 and modems 660 are accomplished on
th~ back plane of a telecommunications chassis, and the
line interface modules 650 and modems 660 are implemented
as cards that plug into the back plane. In this
implementation, a controller communicates with line
interface modules 650 and modems 660 to control switching
connections to modems 660.
In general, the communication server of the present
invention detects a request for data transport service
from a subscriber's XDSL modem, XDSL transceiver unit or
other customer premises equipment as well as, for
example, from a central office multiplexer. The detected
request for service is then used to switch into
connection an XDSL transceiver unit located at the
central office, remote terminal or other local loop
termination point providing, for example, a point of
presence for an information service provider ~ISP) or
corporate network. The request-for-service detection
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44
mechanism allows a large pool of subscribers to be served
by a smaller pool of XDSL transceiver units, thereby
providing the basis for a cost-effective, massively
deployable XDSL service. The request for service
detection also makes fault tolerance possible since no
subscriber is required to be dependent upon any specific
XDSL transceiver unit in the pool.
FIGURE 15 illustrates a functional block diagram of
one embodiment of a distributed switching implementation
of the communication server, indicated generally at 700.
For clarity, one set of line interface modules 702 and
POTS filter modules 704 are shown. Larger or smaller
numbers of line interface modules and POTS filter modules
can be used. In addition, POTS filter modules 704, which
can provide the splitting function for voice and data
traffic, are optional equipment and are not typically
used when the communication server services terminated
twisted pair data lines. Communication server 700 also
includes line power modules ~LPMs) 706 for powering line
interface modules 702 and LIM control modules (LCs) 708
for controlling the line interface modules 702.
Communication server 700 further includes XDSL
transceiver units (xTU-C's) 710, system controllers (SCs)
712, and network interface modules (NIs) 714. In
addition, communication server 700 can include expansion
units 716.
A number of data buses within communication server
700 are shown in FIGURE 15. Communication server 700 of
FIGURE 15 operates through the use of four major bus
systems on a backplane of communication server 700: an
analog switching bus 718, a digital serial bus 720,
serial management buses 722, and a power bus (not shown
in FIGURE 15). Each of these buses can support
redundancy and fault tolerance. In addition, an analog
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test bus (ATB) can be present for optional analog path
testing, a protect bus can be present to allow l:15 or
l:31 equipment protection for l:l deployments, and a busy
bus can be used to distribute a busy indication to the
line interface modules 702.
In one embodiment, the communication server consists
of a multiplexer chassis, one or more optional POTS
filter chassis, and one or more optional line interface
module (LIM) chassis. In this embodiment, XDSL lines
that carry a combined POTS/XDSL signal from the customer
premises, can be terminated in a POTS filter shelf, which
is a passive unit capable of accepting, for example, up
to twenty POTS filter modules 704. These POTS filter
modules 704 can contain lightning and power cross
protection as well as passive filters which split out any
analog POTS connections to the Public Switched Telephone
Network (PSTN). Four lines, for example, can be
terminated by each POTS module 704, giving the POTS
filter shelf a maximum capacity, for example, of 80
subscriber terminations. As mentioned above, where the
XDSL lines do not carry both POTS and XDSL signals, the
POTS modules 704 are not used.
Wire pairs carrying XDSL service, whether
originating from the subscriber or coming from the POTS
filter shelf, can then be connected to line interface
modules 702. Line interface modules 702 can reside, for
example, either in a multiplexer chassis or in a separate
LIM chassis. The multiplexer chassis can be capable of
supporting up to eight LIM chassis, for a maximum
capacity of 640 subscriber lines, or l0:l
oversubscription. The LIM chassis can accept, for
example, up to twenty line interface modules 702, with
each module 702 terminating four subscriber lines, giving
the LIM chassis a capacity of eighty subscribers (at l0:l
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46
oversubscriptlon). The line interface modules 702 can
contain line isolation circuitry, digital service request
detection circuitry, and an analog switching matrix which
performs the concentration of lines to the pool of
available XDSL transceiver units 710.
The XDSL signals from the line interface modules 702
can be connected to XDSL transceiver units via analog
switching bus 718. The multiplexer chassis can support,
for example, up to thirty two XDSL transceiver unit
modules 710, with each module 710 containing two XDSL
transceiver units, for a total of sixty four XDSL
transceiver units. The XDSL transceiver units can be
organized in two pools of thirty-two terminations each.
Each transceiver can be connected to analog swltching bus
718 carrying XDSL signals from the line interface modules
702. Each XDSL port on line interface modules 702 can be
connected to one of the thirty two XDSL transceiver units
in the assigned pool using a set of analog switches
resident on the line interface modules 702.
Two network interface (NI) modules 714 can be
provided in the multiplexer chassis, allowing a redundant
network interface to be installed if desired. The XDSL
transceiver unit modules 710 can be connected to the
network interface modules 714 via redundant digital
serial point-to-point buses 720, carrying ATM cells on
synchronous duplex lines. The network interface modules
714 can statistically multiplex cells to and from XDSL
transceiver unit modules 710 in a cell switch
architecture. The network interface modules 714 can also
processes network signaling data.
Two slots can be provided for system controller (SC)
modules 712. One system controller module 712 can be
designated as the primary module, and the other system
controller module 712 can be installed for redundancy.
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The System controller modules 712 can contain a processor
which manages the multiplexer chassis and LIM chassis.
Each line interface module 702 and XDSL transceiver unit
module 710 can communicate with the System controller
module 712 over dual redundant serial management buses
722 for configuration information and to report status.
The System controller modules 712 also can provide, for
example, both Ethernet and RS-232 management interfaces
which can run either SNMP or TL1 protocols respectively.
Further, the System controller modules 712 can contain
power supply circuitry providing bus bias voltage as well
as provide alarm contacts and alarm cut-off functions.
The multiplexer chassis can further contain two
expansion unit (EX) slots. Expansion unit units 716 in
those slots can be used for a variety of different
functions. The expansion unit units 716 can have access
to the network interface modules 714 through redundant
high-speed serial buses. A separate line power module
(LPM) 706 can be used to power line interface modules 702
when they are located in the multiplexer chassis. Line
power modules 706 can be placed, for example, in any
universal slot and can be redundantly deployed. Further,
all modules in communication server 700 can be "hot"
insertable. A separate bias supply, generated by the
System controller modules 712 or LIM control modules 708,
can be used to bias bus logic and allow hitless insertion
of all modules in the system. Auto detection of newly
inserted modules can then be supported by the System
controller modules 712.
Analog switching bus 718 ~ASB) is a shared switching
bus to which all line interface modules 702 have access.
Analog switching bus 718 can consist of individual two-
wire connections from the line interface modules 702 to
ports for the XDSL transceiver units on modules 710. The
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48
XDSL lines from the customer premises equipment ~CPE) are
connected to analog switching bus 718 using a matrix of
analog switches on respective line interface modules 702.
These switches allow each port of line interface modules
702 to be connected to, for example, any one of thirty-
two two-wire connections to XDSL transceiver units on
modules 710. Sixty four XDSL line terminations, for
example, can be supported in the multiplexer chassis in
the form of two pools of thirty-two terminations each.
Analog switching bus 718 connections can be provided
internally on the multiplexer chassis backplane for line
interface modules 702 located in the multiplexer chassis.
For the LIM chassis, analog switching bus 718 connections
can be provided via cable assemblies from the LIM chassis
to the multiplexer chassis. The analog switching bus 718
cables can be "daisy-chained" for multiple ~IM chassis,
as opposed to direct connections from each ~IM chassis to
the multiplexer chassis, to minimize connectors and
cabling.
Digital serial bus 720 provides a path from XDSL
transceiver units on modules 710 to network interface
modules 714. Each XDSL transceiver unit port can drive
two serial data and transmit/receive clock buses towards
network interface modules 714, one bus for each network
interface module 714, for redundancy. Each network
interface module 714 can also drive two serial data buses
towards the XDSL transceiver unit ports, and each XDSL
transceiver unit can be programmed for which bus to
receive by system controller 712.
Serial management bus (SMB) 722 can c~nsist of two
buses. Each redundant system controller 712 can drive
and operate one of buses 722. The serial management bus
722 can be used to manage all modules on the multiplexer
chassis and LIM chassis backplanes. The bus electrical
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49
format can be TTL on the multiplexer chassis backplane
and LIM chassis backplane and can be multipoint RS485
from system controllers 712 to LIM controller modules 708
via external cabling. The serial management bus 722 can
be an asynchronous bus and can carry a heartbeat message
sent on the serial management bus 722 by the system
controller modules 712. The other modules can be
programmed to automatically switch to the alternate
serial management bus 722 if the heartbeat signal is not
received. Two control signals issued by the system
controller module 712 can be used to determine whether
the primary or secondary serial management bus 722 should
be used.
XDSL transceiver unit modules 710 provide local loop
termination for XDSL service. Each module 710 can
support, for example, two XDSL connections to line
interface modules 702. In this case, each module 710 can
include two XDSL transceiver subsystems, two sets of
digital serial data bus interfaces which connect to the
network interface modules 714, and a microcontroller and
serial management bus interface for configuration and
control. The digital serial buses 720 between each XDSL
transceiver unit module 710 and the redundant network
interface modules 714 can carry demodulated data to the
network interface modules 714 and digital data from the
network interface modules 714 to be modulated. Data can
be, for example, in the form of ATM cells or HDLC-framed
packets, and the serial bus can consist of transmit and
receive clock and data pairs to each network interface
module 714. Each XDSL transceiver unit port on the
modules 710 can be programmed by the system controller
module 712 for which network interface bus to receive
~i.e. which network interface module 714 is active). The
microcontroller on the XDSL transceiver unit module 710
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can be used to manage communications with the system
controller module 712 and to control the XDSL
terminations. Rate adaptive decisions, provisioning,
performance monitoring, and other control functions can
be performed by the microcontroller.
In the illustrated embodiment, system control module
712 is responsible for overall control of the
communication server and for gathering of status
information. Two system controller modules 712 can be
provided for redundancy. In a redundant configuration,
the two system controller modules 712 communicate with
each other over a dedicated communications bus for
sharing database information, self-checking, and on-
line/offline control. Data requiring persistent storage,
such as provisioning, performance statistics and billing
information, can be stored on the system controller
module 712 in non-volatile memory. Performance
monitoring information can be collected for the network
interface modules 714 and for each XDSL line, including
information from remote customer premises equipment
units.
Network interface modules 714 provide a high-speed
connection for aggregated data traffic from the XDSL
transceiver units. The network interface modules 714
connect to the XDSL transceiver unit modules 710 via
point-to-point serial data buses 720. A high-speed
serial interface to subtend host modules (SHMs) can also
be provided. In one embodiment, two types of network
interface modules 714 are supported: DS3/OC-3 ATM and DS1
ATM. A DS1 Frame Relay interface may also be provided.
An OC3/DS3 ATM network interface can support ATM cell
traffic at the XDSL transceiver unit interface, and
either a 155 Mbit single-mode optical ATM User-Network
Interface or a DS3 75 ohm coaxial interface on the
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network side. A DS1 ATM network interface can support
ATM cell traffic at the XDSL transceiver unit interface,
and a 1.544 Mbps DS1 ATM user-network interface on the
network side. A DS1 Frame Relay network interface can
support a 1.544 Mbit unchannelized DS1 Frame Relay port.
The subtend host module (SHM) is an expansion unit
716 that allows ATM data from multiple multiplexer
chassis to be aggregated before being presented to the
switched data network, using a technique caIled
subtending. This technique provides full utilization of
the ATM switch ports in the network. The subtend host
module can contains six DS1 interfaces, and can be used
to subtend one to six remote communication servers. The
subtend interface can essentially be six DS1 UNI
interfaces containing ATM cells, from the remote
communication server. DS1 is terminated by the subtend
host module and remote cells are sent to the network
interface over individual and aggregate 10 Mbit serial
connection. Each subtend host module has a serial
interface to both network interface modules 714,
providing full redundancy. Cell delineation is performed
on the network interface 714, and cells are forwarded to
the switching matrix in the same manner as cells from the
XDSL transceiver unit interfaces.
Line interface module 702 can contain, for example,
intra-office line protection/termination, XDSL start tone
detection, test bus access, busy bus access, and
switching for four XDSL connections. Line interface
modules 702 can be located either in the multiplexer
chassis for smaller system configurations, or in an LIM
- chassis for large configurations. A pair of lines from
the POTS filter chassis can be routed to each line
interface module 702 through the backplane for each
interface. The shared analog switching bus 718 between
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the line interface modules 702 and the XDSL modem pool
carries the switched signal from each active line to an
XDSL transceiver unit. Service request detection
circuitry detects the presence of start tones generated
by the customer premises equipment (CPE) and signals the
LIM controller 708 or system controller 712 through the
serial management bus 722.
FIGURE 16 illustrates a block diagram of one
embodiment of line interface module 702 of FIGURE 15. As
shown, line interface module 702 includes a plurality of
intra-office protection circuits 730 that receive a two-
wire interface for XDSL communications. Intra-office
protection circuits 730 are coupled to an analog switch
matrix 732. Analog switch matrix 732 connects selected
~5 intra-office protection circuits 730 to XDSL transceiver
units. In the illustrated embodiment, analog switch
matrix 732 connects each of four intra-office protection
circuits 730 to one of thirty-two XDSL transceiver
units. Line interface module 702 further includes a
microcontroller 734 and a start tone detect circuit 736.
In this embodiment, analog switch matrix 732 is used to
connect each intra-office protection circuit 730 to start
tone detect circuit 736 in succession to identify a
request for service.
The LIM control modules (LCMs) 708 are responsible
for receiving service request detect information from the
line interface modules 702, configuring the analog
switching matrix 732 under control of the system
controller module 712, generating a busy signal for all
line interface modules 702 in the chassis, and providing
power for the line interface modules 702. One LIM
control module 708 can be designated as a primary and
another as a redundant back-up. For connection
initiation, the LIM control module 708 can poll the line
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interface modules 702 to identify any pending service
request detection events. The LIM control module 708 can
then notify the system controller module 712, which in
turn selects an available XDSL transceiver unit. The
system controller module 712 then instructs the line
interface module 702 to configure the analog switching
matrix 732 to connect the requesting port to the selected
XDSL transceiver unit. Connection termination
notification is provided by the XDSL transceiver unit
module 710 to the system controller module 712 upon
detecting loss of carrier at the XDSL facility. The
system controller module 712 then signals the LIM control
module 708 to disconnect the line interface module 702
from the XDSL transceiver unit by clearing the switching
matrix connection. Power for the line interface modules
702 can also be provided by the LIM control module 708.
FIGURE 17 illustrates one embodiment of ATM based
transport communication protocols supported on the local
loop and the network interface of the communication
server. Loop protocols refers to the data encapsulation
protocols which reside on the local loop interface. It
should be recognized that standards bodies are currently
formulating a strategy on local loop protocols and the
communication server is intended to support various
protocol models with minimal hardware impact. PPP over
ATM is one implementation for the disclosed communication
server architecture. As shown in FIGURE 17, the hardware
can consist of a communication server 740 that
interconnects a network router 742 and computing devices
744 with an access server 746 for an Internet service
provider (ISP) or corporate network 74~.
In this implementation, supported protocols are
carried over ATM cells. The communication server 740
then becomes an ATM multiplexer switching ATM cells from
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54
the low speed XDSL ports to the high speed network
interface port. The communication server 740 network
interface can perform this switching independently of the
underlying adaptation protocol. All cells can be
indiscriminately switched. Specific support for MLl,
ML3/4, ML5, OAM, and raw cell formats also can be
incorporated into the network interface switching
element. RFC1577 compatible IP over ML is a protocol
that can be supported over the ATM layer of the XDSL
loop. Point to point PVC or SVC connections can be
established between the router 742 or device 744 at the
customer premise and the access server 746 at the home
network. PPP can be used to encapsulate IP, IPX, or
Ethernet frames over ATM from the customer premises
equipment across the XDSL link to the communication
server 740. PPP over ML5 can be encapsulated using
RFC1483 guidelines. SNAP/LLC headers can be used to
distinguish PPP traffic from other possible traffic
types.
The use of PPP allows many protocol encapsulations,
including IP and IPX, and bridging using RFC1638. PPP
can be carried through the ATM network to the access
server 746 located at the corporate or ISP gateway.
Authentication can then be performed between the customer
premises and the service network using PPP authentication
services such as the Password Authentication Protocol
(PAP) and the Challenge ~andshake Authentication Protocol
~CHAP). In this scenario, PPP packets from remote users
are transported to the ISP or corporate network 748 for
authentication, thus freeing a network provider from
authenticating each user to various network destinations.
PPP also has the advantage of being relatively protocol
independent and may be the wrapper for many networking
protocols. In addition, Ethernet bridging may be
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supported through the use of ATM Forum LAN Emulation
(LANE). LANE allows the bridging of multiple remote
users to the home LAN over ATM.
FIGUREs 18A and 18B illustrate a system block
diagram for one embodiment of the communication server.
As shown, the communication server of FIGUREs 18A and 18B
includes a plurality of line interface modules (LIMs) 750
and a plurality of ADSL transceiver units 752
interconnected by dual analog buses 754. ADSL
transceiver units 752 are connected to serial buses 756.
Each line interface module 750 includes intra-office
protection circuits 758, hybrid circuits 760, switch 762
and detect circuit 764. Each ADSL transceiver circuit
752 includes an ADSL chipset 766 (i.e., CAP or DMT) for
each transceiver channel, serial bus drivers 768 and
other devices 770 (microcontroller, flash RAM).
Redundant OC3/DS3 ATM network interface units 772 are
connected to ADSL transceiver units 752 by serial buses
756. Each network interface unit 772 includes a
plurality of ATM cell delineation circuits 774 connected
to ATM cell switch fabric 776. The switch fabric 776 is
controlled by OAM/signaling cell access unit 778 and
processor 780. A DRAM 782 and a flash memory 784 provide
memory space for processor 780. A physical interface 786
and a line interface unit 788 are connected to switch
fabric 776 and provide the physical DS3 connection.
Redundant system controllers 790 each include serial
drivers 792 connected to a processor 794. Relay driver
circuits 796 are connected to processor 794 and to alarm
relays 798. Receiver circuits 800 also are connected tc
processor 794 and are connected to OPTO circuits 802.
Processor 794 has memory 804 and flash memory 806 provide
memory space for processor 794. Processor 794 is further
connected to Ethernet interface 808 and to serial
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56
interface 810. System controller 790, network interface
772, ADSL transceiver units 752, and line interface
modules 750 operate generally as described above to
accomplish the functions of the communication server.
Although the present invention has been described
with several embodiments, a myriad of changes,
variations, alterations, transformations, and
modifications may be suggested to one skilled in the art,
and it is intended that the present invention encompass
such changes, variations, alterations, transformations,
and modifications as fall within the spirit and scope of
the appended claims.
