Note: Descriptions are shown in the official language in which they were submitted.
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CONNECTION OF SUBSCRIBER COMMUNICATION NETWORK
BASE STATION TO EXTERNAL INFORMATION NETWORK
BACKGROUND OF THE INVENTION
The present invention generally pertains to communications
systems and is particularly directed to an improvement in connecting a
subscriber communication network base station to an external
communication network having a plurality of ports.
A known prior art base station in a subscriber communication
network for communicating signals between subscriber stations and an
lo external co~munication network having a plurality of ports, includes a
communication circuit for enabling simultaneous communications between a
plurality of the ports and a plurality of subscriber stations over a
given communication channel having multiple sequentially repetitive time
slots, with predeternined time slots being assigned respectively to
predetermined subscriber stations; a remote-connection processor for
directing communications between the time slot assigned to a given
subscriber station and a given port; and an exchange for connecting the
communication circuit to the ports. The exchange includes a switch
*
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which responds to a control signal from the remote-
connection processor by physically connecting a selected
port to a selected communication channel time slot assigned
to a given subscriber station. Such a prior art base
station is described in United States Patent No. 4,675,863,
E. Paneth et al, issued on June 23, 1987.
SUMMARY OF THE INVENTION
The present invention provides an improved base
station of the type generally described above, except that
the exchange does not include such a switch. The base
station of the present invention is characterized by the
exchange including a central concentrator for directing
signals from predetermined external network ports to
predetermined sequentially repetitive time slots in a bit
stream generated by the central concentrator, and for
directing signals to predetermined external network ports
from predetermined sequentially repetitive time slots in a
bit stream received by the central concentrator; and by the
remote-connection processor directing signal transfer
between given sequentially repetitive time slots of the bit
streams and given sequentially repetitive time slots of the
communication channel.
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The base station of the present invention is further
characterized by the remote-connection processor comprising a remote
terminal concentrator for directing signals from predetermined remote
ports to predetermined sequentially repetitive time slots in a bit
stream generated by the remote concentrator and transmitted to the
central concentrator, and for directing signals to predetermined remote
ports from predetermined sequentially repetitive time slots in the bit
stream generated~ by the central concentrator; and a buffer unit
connected to the remote ports for directing signals between
predetermined remote ports and predetermined communication channel time
slots.
Because the exchange of the base station of the present
invention co~m~lnicates with the cammunication circuit by generating and
receiving bitstreams as described above, it is practical to locate the
lS exchange of the base station of the present invention remotely from the
communication circuit of the base station since the bitstream may be
transmitted between the exchange and the communication circuit over
appreciable distances by microwave.
Additional features of the present invention are described with
reference to the description of the preferred embodiment.
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BRIEF DESCRIPTION OF THE DRAWING
Figure 1 is a block diagram of a preferred embodiment of the
base station of the present invention.
Figure 2 is a block diagram of a buffer unit included in the
S buffer of the base station of Figure 1 for interfacing with a single
channel module.
Figure 3 is a state diagram illustrating normal call processing
flow in the base station of Figure 1.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The preferred embodiment of the base station of the present
invention is used in a subscriber telephone system.
Referring to Figure 1, a preferred embodiment of the base
station of the present invention includes an exchange 10, a
communication circuit 12 and a remote-connection processor 14. The
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communication circuit 12 and the remote control processor 14 are located
remotely from the exchange 10.
The exchange lO includes a two-to-four wire converter 16, a
signalling data converter 17, an echo canceller 18, and a central
5concentrator 19. The communication circuit 12 includes a plurality of
channel modules 21a, ..., 21n. Each channel module 21 includes a voice
codec unit (VCU) 23, a channel control unit (CCU) 24 and a modem 25.
The remote-connection processor 14 includes a remote concentrator 27 and
a buffer unit 28.
loReferring to Figure 2, the buffer unit 28 includes a timing
generator 30 and a channel interface module 32.
Referring again to Figure 1, the exchange 10 is connected to a
plurality of ports of a central office 35 by N pairs of lines 37. "N"
is the number of subscriber stations being served by the base station.
15Each pair of lines 37 provides a 2-wire loop appearance. Each line pair
37 is connected to both the two-to-four wire converter 16, and the
sign~lt~ng data converter 17. Unidirectional signal flow takes place on
the line pairs 38-41 on the other sides of the converters 16, 17, with
4-wire loop appearances being provided on the combination of N line
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pairs 38 and N line pairs 39. Transmitted voice signals are provided on
line pairs 38; recieved voice signals are provided on line pairs 39;
transmitted sign~ ng data is provided on line pairs 40; and received
signalling data is provided on line pairs 41.
The transmitted and received voice signals are CQ' lln~cated
between the two-to-four wire converter 16 and the central concentrator
19 through the echo canceller 18. The sign~lling data is communicated
directely between the converter 17 and the central concentrator 19.
The central concentrator 19 is a Model 1218C concentrator sold
by ITT Corp.
The central concentrator 19 directs signals from predetermined
line pairs 38-41 (which are connected to predetermined external network
ports in the central office 35) to predetermined sequentially repetitive
time slots in a bit stream generated by the central concentrator 19.
The central concentrator 19 also directs signals to predetermined
external network ports in the central office via predetermined line
pairs 38-41 from predetermined sequentially repetitive time slots in a
bit stream recieved by the central concentrator 19. The central
concentrator transmits and receives such bit streams via a microwave
antenna 43.
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These bit streams are communicated between the antenna 43 and a
microwave antenna 44 connected to the remote concentrator 27 contained
in the remote-connection processor 14. The remote concentrator 27 has a
plurality of remote ports connected to the buffer 28 by line pairs
46-49.
The remote concentrator 27 is a Model 1218S concentrator sold by
rTT Corp.
The remote concentrator 27 directs signals from predetermined
remote terminals (which are connected to predetermined line pairs 46-49)
lo to predetermined sequentially repetitive time slots in a bit stream
generated by the remote concentrator 27. The remote concentrator 27
also directs signals to predetermined remote ports from predetermined
sequentially repetitive time slots in the bit stream recieved by the
remote concentrator 27 from the central concentrator 19.
The transmitted voice signals are provided on line pairs 46; the
recieved voice signals are provided on line pairs 47; the transmitted
sign~lling data is provided on line pairs 48; and the recieved
signalling data is provided on the line pairs 49.
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The buffer 28 interfaces the remote concentrator 27 with the
communication circuit 12.
As described above, the communication circuit 12 include,s a
plurality of channel modules 21. Each channel module 21 commlnicates
with a given number of subscriber stations 51 over a given communication
channel having an assigned frequency and further having multiple
sequentially repetitive time slots. Communication between each channel
module 21 and the base stations 51 is via a microwave link between a
base station antenna 53 and antennas 54 located at each subscriber
station. Predetermined time slots are assigned to predetermined
subscriber stations 51. In the preferred embodiment, there are three
subscriber stations 51 coupled to each channel module 19 over each
discrete frequency communication channel. Each subscriber station 51
has a telephone connected thereto.
In each ~h~nn~l module 21, the VCU 23 includes a separate voice
codec (not shown~ for each subscriber station 51 and an additional codec
for comm~lnicating signalling data to and from all three subscriber
stations. The CCU 24 assigns the signals communicated through the
codecs of the VCU 23 to different time slots of the communication
r,h~nnPl assigned to the given channel module 21. These signals are
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communicated between the CCU 24 and the base station antenna 53 via the
modem 25 and additional signal conditioning components (not shown)
adapted for transmitting and recieving these signals over the discrete
communication ch~nnel at the assigned frequency. Thus, each subscriber
station ~1 communicates voice signals with the base station over its own
predetermined time slot and communicates signalling data with the base
station over a predetermined time slot that is common to all three
subscriber stations. Com~nication between the base station and the
subscriber stations is controlled by a radio control unit (RCU) software
process implemented by a microcomputer in the CCU 24.
The RCU is programmed to recognize three predetermined
subscriber stations corresponding to three predetermined line
appearances provided by the connections between the remote concentrator
27 and a given channel module 21.
lS Control processing in the RCU is organized using state machines.
Input message tokens include sign~1ling data from the remote
concentrator 27, radio control channel (RCC) messages from the
subscriber stations, and (simulated) baseband control channel (BCC)
messages.
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The state diagram, Fig. 3, illustrates the normal
call processing states and the input token (T) and the
resulting action (A) required to transit from one state to
another. The following descriptions outline some of the
state transition routines. Other routines, such as those
required for error handling, have not been described.
The following group of descriptions define some
of the RCC state transition routines which are called
whenever a RCC token is received by a CCU, whether from a
subscriber station or the remote concentrator.
Clear Call (cl call)
Current State: Active, Teardown
Token: Clear Request
Next State (RCC): RCC Idle
~-O
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Next State (CHAN): Chnl Idle
Messages:
Conc: Place circuit in idle state.
RCC: None.
CCU: Change channel (onhook) is sent to the CCU.
Actions:
This routine is invoked whenever a subscriber station
generates a Clear Request. The channel state is set to
Chnl Idle. The clear-request timer is cancelled. Whether
or not teardown was in progress, the RCU considers the
subscriber station available for another call, and returns
the RCC state to RCC Idle.
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Place Call Origination (place)
Current State: RCC Idle
Token: Call Request
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Next State (RCC): Active
Next State (CHAN): Offhk Syn Wait
Messages:
Conc: Place circuit in loop state.
RCC: Send Call Connect message to Subscriber Station.
CCU: Send Change Channel (OFFHOOK).
Actions:
This routine is invoked when a Subscriber Station is in the RCC
Idle state and the RCU receives a Call Request token. A Change Channel
message with an Offhook status is sent to the CCU, and a Call Connect
message is sent to the Subscriber Station. The channel state of the
allocated frequency is set to Offhk Syn Wait, and the RCC state is set
to Active.
- Subscriber Stati~n Call Accept (s accp)
Current State: Page
Token: Call Accept
Next State (RCC): Active
Next State (CHAN): Ring Syn Wait
Messages:
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Conc: Place circuit in loop state.
RCC: Send Call Connect message.
CCU: Send Change Channel (RING).
Actions:
This routine is invoked when the RCU receives a Call
Accept token from a Subscriber Station that is in the Page
state. The page timer is cancelled. A Change Channel
message with Ring status is sent to the CCU, and a Call
connect message is sent to the Subscriber Station. The
channel state is set to Ring Syn Wait, and the RCC state is
set to Active.
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Subscriber Station Page (s_page)
Current State: RCC Idle
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Token: Incoming Ring
Next State (RCC): Page
Next State (CHAN): No state change
Messages:
Conc: None.
RCC: Send a Page message if the Subscriber Station.
CCU: None
Actions:
If an Incoming Ring token is received from the
concentrator while the Subscriber Station is in the RCC
Idle state, then this routine is invoked. The line
appearance is mapped to a predetermined Page message, which
is then transmitted to the appropriate Subscriber Station.
A timer is set in case the Subscriber Station does not
respond to the page. The RCC state is set to Page.
The following group of descriptions define some of the
channel state transition routines which are called whenever
a token is received from a CCU.
16
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Subscriber Station Ring Trip (rng_offhk)
Current State: Syn Ring, Ring Syn Wait
Token: Sync Offhook
Next State (RCC): No state change
Next State (CHAN): Syn Offhk
Messages:
Conc: None.
RCC: None.
CCU: Send Change Channel (OFFHOOK) to the CCU.
Actions:
This routine is activated when a Subscriber Station is
in the ring state and either in or out of synchronization,
and the RCU receives
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a message that the Subscriber Station is now in synchronization and has
transitioned to Offhook. Normally, when a Sync Offhook token is
received, the Subscriber Station is already in synchronization. The CCU
is sent a Change Channel message with Offhook status, and the channel
state is changed to Syn Offhk.
Subscriber Station Sync Offhook (syn offhk)
Current State: Offhk Syn Wait
Token: Sync Offhook
Next State (RCC): No state change
lo Next State (CHAN): Syn Offhk
Messages:
Conc: None.
RCC: None.
CCU: None.
Actions:
This routine generates no messages, it only causes a change in
channel state to Sync Offhk.
Subscriber Station Sync Ring (syn ring)
Current State: Ring Syn Wait
Token: Sync Ring
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Next State (RCC): No state change
Next State (CHAN): Syn Ring
Messages:
Conc: None.
RCC: None.
CCU: None.
Actions:
This routine changes the channel state to Syn Ring.
The buffer 28 is connected to the remote ports of the remote
lo concentrator 27 via line pairs 46-49 and to the ~h~nnel modules 21 of
the communication circuit 14 via lines 57 for directing the transmitted
and recieved voice signals between the predetermined remote ports of the
remote concentrator 27 and the predetermined communication channel time
slots assigned to predetermined subscriber stations 51. The subscriber
stations 51 are located remotely from the base station.
The buffer 28 includes a separate buffer unit, as shown in
Figure 2, for interfacing with each channel module 21 in the
communication circuit 12. The timing generator 30 provides the channel
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interface module 32 with a clock signal CLK and four gate signals Gate
0, Cate 1, Gate 2, Gate 3 for defining four sequentially repetitive time
slots in the assigned communication ch~nnel.
The transmitted voice signal line pairs 46, the received voice
signal line pairs 47, and the the signalling data line pairs 48, 49 are
connected between the remote ports of the concentrator 27 and the
channel interface module 32.
The channel interface module 32 provides the clock and gate
signals to the channel module 27 for defining the time slots assigned by
the CCU 24.
The channel interface module 32 is connected to the VCU 23 in
the corresponding channel module 21 in a predetermined manner for
directing communications between line pairs 46, 47 carrying transmitted
and received voice signals associated with a given subscriber station
and a codec in the VCU 23 having the predetermined communication channel
time slot assigned by the CCU 24 to the given subscriber station. The
channel interface module is further connected to the VCU 23 for
directing the signalling data between the signalling data line pairs 48,
49 and the the voice codec in the VCU having the common time slot
~,o
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assigned by the CCU 24 for communicating signalling data ~or all three
subscriber stations associated with the given channel module.
~l
