CA1237188A - Time division switching system control arrangement and method - Google Patents
Time division switching system control arrangement and methodInfo
- Publication number
- CA1237188A CA1237188A CA000487802A CA487802A CA1237188A CA 1237188 A CA1237188 A CA 1237188A CA 000487802 A CA000487802 A CA 000487802A CA 487802 A CA487802 A CA 487802A CA 1237188 A CA1237188 A CA 1237188A
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- input
- output port
- time
- time slot
- output
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Classifications
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04Q—SELECTING
- H04Q11/00—Selecting arrangements for multiplex systems
- H04Q11/04—Selecting arrangements for multiplex systems for time-division multiplexing
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04Q—SELECTING
- H04Q11/00—Selecting arrangements for multiplex systems
- H04Q11/04—Selecting arrangements for multiplex systems for time-division multiplexing
- H04Q11/0407—Selecting arrangements for multiplex systems for time-division multiplexing using a stored programme control
Abstract
TIME DIVISION SWITCHING SYSTEM CONTROL
ARRANGEMENT AND METHOD
Abstract A method and arrangement for controlling a time division switching system including a time multiplexed switch is disclosed. The time division switching system comprises a plurality of time-slot interchange units which connect subscriber sets to the input/output ports of a time multiplexed switch. When a connection is to be established between time-slot interchange units, a central control transmits to the time multiplexed switch a path setup message defining the input/output ports to be connected and the time slot to be used for such a connection. The time multiplexed switch controller responds to the path setup messages by disconnecting existing connections through the time multiplexed switch which potentially conflict with the requested connection, then by completing the requested connection. Accordingly, the switching system operates effectively without requiring separate disconnect messages when connections through the time multiplexed switch are no longer needed.
ARRANGEMENT AND METHOD
Abstract A method and arrangement for controlling a time division switching system including a time multiplexed switch is disclosed. The time division switching system comprises a plurality of time-slot interchange units which connect subscriber sets to the input/output ports of a time multiplexed switch. When a connection is to be established between time-slot interchange units, a central control transmits to the time multiplexed switch a path setup message defining the input/output ports to be connected and the time slot to be used for such a connection. The time multiplexed switch controller responds to the path setup messages by disconnecting existing connections through the time multiplexed switch which potentially conflict with the requested connection, then by completing the requested connection. Accordingly, the switching system operates effectively without requiring separate disconnect messages when connections through the time multiplexed switch are no longer needed.
Description
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TIME DIV[SI~N SWI'rCHING ~YSTEM CONTROL
ARRANGEMENT AND METHOD
Technical Field This invention relates to time division switching systems and more particularly to methods and arrangements for controlling the switch arrangements oE such systems.
Background o~-the Invention Stored program controlled communication switching systems comprise some form oE intelligence which controls switching functions in response to a program stored in memory. Historically, such systems included a single processing entity for the control of the entire system. As technology and system design evolved, it was found desirable to separate certain routine functions from the main processing entity to save its processing time for more complex system functions and decisions. Today, systems are being designed which also separate some of the more complex system functions and decisions into several intelligent processors.
One type of modern time-division switching system comprises a plurality of tlme-slot interchange units each includin~ a processor, which is selectively interconnected by a time multiple~ed switch, sometimes called a time-shared space division switch. Such a switching system also includes a central control arrangement including a processor which determines the pattern of interconnections between the plurality of time-slot interchange units. In order to coordinate the actions of the time-slot interchange unit, the time multiplexed switch, and the central control arrangement, control messages must be exchanged. Since each control message occupies some portion of the interprocessor communication media, too many messages can reduce system real time response by causing delays in message transmission~
Similarl~, since each message requires processor real time, the individual processors can be kept from needed tasks .. , ~dP
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while receiving and transmitting mes6a~es. AccordincJly, it is important to minimize the number of control messages exchanged in the system. It is also importantt however, that each unit in a distributed processor system have enough information to enable it to properly perform its tasks. This is especially true in distributed telecommunications systems where the integrity of connections must be maintained. Thus, the portions of a distributed communications systems must be designed to operate accurately with a minimum number of required control messages.
An example of the conflict between proper operation and a potential]y large number of control messages occurs with communications between the time multiplexed switch and the central control arrangement.
The central control and time multiplexed switch must cooperate to complete connections for virtually all calls traversing the switching system. In prior art systems, the central control arrangement, when requested, transmits a message to the time multiplexed switch defining a connection between time-slot interchange units. Then, when the connection is no longer needed (a subscriber goes on-hook), a second message is transmitted directing the time multiplexed switch to remove the connection between the time-slot interchange units. If unused paths through the time multiple~ed switch are not removed, a given input port may eventually be simultaneously connected to a number of output ports and when the given input port is used to complete another connection, signals arriving at that input port may be broadcast to a number of output ports. As discussed above, prior systems transmit two control messages for each time multiplexed switch connection. The first message is used to set up the connection~ The second message is then used to remove it. In accordance with the present invention, multiple output port connections to a given input port are substantially avoided without the . necessity of disconnect orders, thus reducing , ~ .
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substantially the number of control messages exchanged between the central control arrangement and the time multiplexed switch in a time division switching system.
Similar advantages can be obtained in the interactions between time-slot interchan~e units and the central control.
Summary of _he Invention A method in accordance with the present invention of controlling connections between input and output ports of a switch arrangement, comprises tne steps of storin~ in a memory arrangement information defining a pattern of connections between the input and output ports, rea~ing from the memory arrangement, and connecting the input ports to the output ports in the pattern defined by the information so read, generating a path setup message defining one input port, one output port, and a time slot, writing into the memory arrangement information defining a pattern of connections in which the input port defined by the path setup message is not connected to any output port during the defined time slot, and writing into the memory arrangement information de~ining a pattern oE connections in which the input port and output port defined by the path setup message are connected during the defined time slot.
In accordance with one embodiment of the present invention, a time-shared space division switch is used to interconnect input/output port pairs, each of which includes an input port and an output port. Additionally, the information for controlling the connections through the time-shared space division switch is stored in such a way that the particular input port connected to a given output port during each time slot can be readily obtained. In response to a path setup message defining a first input/output port pair, a second input/output port pair, and a time slot, the control unit reads the stored information to determine which input ports are connected to the output ports of the first and second input/output port pairs. The control unit then writes into the memory ' - ~
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~;~37~L~3151 information which disconnects the input ports eound during the read operation Erom the output ports of the first and second input/output port pairs during the defined time slot, then inEormation is written into the memory which connects the defined input/output port pairs during the defined time slot. Since disconnect operations are performed in response to path setup messages, no disconnect messages need be sent to assure that multiple output ports are not conn~cted to a given input port. The avoidance o~
disconnect messages substantially reduces the message traffic between the time multiplexed switch and the central control arrangement resulting in a savings of system resources.
Brief DescriDtion of the Drawinq A more complete understanding of the present invention may be obtained from a consideration of the following description when read in conjunction with the drawing in which:
FIG. 1 is a block diagram of a system embodying the present invention;
FIG. 2 is a more detailed diagram of a time multiplexed switching unit utilized in the embodiment of FIG. 1;
FIG. 3 represents relative timing intervals within the time multiplexed switching unit;
FIGo 4 is a representation of a path setup message exchanged in the embodiment of FIG. 1;
FIG. 5 is a diagram of the data words utilized in the embodiment of FIG. 1; and FIGS. 6 through 9 represent a sequence of steps in establishing a path through the time multiplexed switch.
General Descriptlon FIG. 1 is a block diagram of a time division switching system embodyinq the present invention which is used to interconnect subscriber sets such as subscriber sets 23 thrGugh 26. The embodiment of FIG. 1 includes a .
~l23~ 8 time multiplex switchil1g unit 10 which cornprises a tlrrl~-shared space division switch having 64 input ports and 6~
output ports. The embodiment Eurther includes 31 time-slot interehange units of which representative time-slot interchange units 11 and 12 are specifically shown. Each time-slot interehange unit 11 and 12 ineludes a bidirectional time-slot interchanger. Additionally, each time-slot interchange unit 11 and 12 is eonneeted to two input ports and two output ports of time multiplex switeh unit 10. In the present embodiment, time-slot interchange unit 11 is connected to two time multiplex switch input ports via time multiplex lines 13 and 14 and to two output ports, via time multiplex lines 15 and 16.
In the description which follows, the input and output ports of time multiplex switehing unit 10 are referred to as input/output port pairs. This term is used since the source for data words to an input port of a given input/output port pair is also the destination ~or data words from the output port of that pair. As shown in FIG. 1, input/output port pair 1 is associated with time multiplex lines 13 and 15. Each time multiplex line, 13 through 16, conveys digital in~ormation in 125 microsecond frames eaeh frame comprising 256 time separated ehannels.
Accordingly, each time-slot interchange unit transmits and receives up to 512 channels o~ digital in~ormation during each 125 microseeond ~rame.
Each time-slot interehange unit is uni~uely assoeiated with a eontrol unit of whieh eontrol unit 17 is assoeiated with time-slot interchange unit 11, and eontrol unit 18 is associated with time-slot interchange unit 12.
Additionally, eaeh time-slot interehange unit is conneeted to a plurality o~ line units of whieh line units 19 through 22 are shown in FIG. 1 via individual time multiplex lines. In the present embodiment line units 19 and 20 are connected to time-slot interehange unit 11 and line units 21 and 22 are eonneeted to time-slot interchange ; unit 12. Each of the line units of the present embodiment .. .
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is connected to a number of subscriber sets of which subscriber sets 23 through 26 are shown. The exact number oE line units associated with each time-slot interchange unit and the exact number of subscriber sets associated with each line unit is determined by the number of subscribers to be served and the calling rates of those subscribers. Each line unit terminates the analog loop of the well-known type from a plurality of subscriber sets, e.g., 23 through 26, and converts call information including analog speech signals into digital data words which are transmitted to its associated time-slot interchange unit. Further, each line unit detects service requests from the subscriber sets and generates certain signaling information for those subscriber setsO The particular subscriber sets from which speech samples are taken and encoded, and the particular time multiplex channels used to transmit the resulting code between the line unit and its associated time-slot interchange unit are determined b~ the control unit of the associated time-slot interchange unit.
The relationship of subscriber sets, line units and time-slot interchange units is substantially the same for each o~ such groups of interconnected units.
Accordingly, while the description which follows relates directly to subscriber set 23, line unit 19 and time-slot interchange unit 11, it shows the relationships for all other groups of such units. Line unit 19 scans the lines connected to each subscriber set to detect requests for service. When such a request is detected, line unit 19 transmits to the control unit 17, a message indicating the request and the identity of the requesting subscriber set.
This message is transmitted to control unit 17 via a communication path 27. Ccntrol unit 17 performs the necessary translation based on the service requested, the identity of the requesting subscriber set and the available equipment, and transmits a message to line unit 19 via communication path 27 defining which of the plurality of , ~ .
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time separated channels between line unit 19 ancl time~slot interchange unit ll is to be used to transmit information from subscriber set 23 to time-slot interchange unit 11.
Based on this message, line unit 19 encodes the analog information from subscriber set 23 into digital data words and transmits the resulting data words in the assigned channel. In the present embodiment, line unit 19 also transmits in the assigned channel an indication of the DC
state, i.e., open circuit, closed circuit, of the subscriber loop associated with subscriber set 23. Each channel in the present embodiment can convey one 16-bit data wordu Each data word (FIG. 5) comprises an 8-bit PCM
data portion, a 7-bit signaling portion, and a parity bit.
The signaling portion is used to convey signaling information about the channel circuit or the subscriber set to which it is connected. For example, the A-bit of the signaling portion is used to transmit the present DC state of the associated subscriber set to the time-slot interchange unit 11.
After a time separated channel between line unit 19 and time-slot interchange unit 11 is assigned to a given subscriber set, control unit 17 detects signaling in~ormation from the subscriber set by sampling the information transmitted in the assigned channel. Such sampling operations are perEormed via a communication path 28. Control unit 17 responds to the signaling information from the subsc iber's channel, and to control messages from other control units, e.g., 18, and a central control unit 30, by controlling the time-slot interchange function of the time-slot interchange unit 11. As previously stated, each time multiplex line between a time-slot interchange unit and the time multiplex switch unit 10 has 256 channels in each 125 microsecond frame. These channels are assigned numerical designations from 1 to 256 in sequence as they occur. This sequence of channels recurs so that a given channel will be available every 125 microseconds~ The time-slot interchange ~unction takes the ~23~
data words received from the line units and place~ them in channels on the time multiplex line between ~he time-slot interchange units and the time multiplex switching unit 10 under the control of control units 17 and 18.
Time multiplex swltching unit 10 operates in recurring frarnes of time slots where each 125 microsecond frame comprises 256 time slots. During each time slot, time multiplex switching unit 10 is capable of connecting data words received at any of its 64 input ports to any of its 64 output ports in accordance with time-slot control information stored in a TMS controller 29 The pattern of connections through time multiplex switching unit 10 repeats itself every 256 time slots and each time slot is assigned a numerical designation in sequence from 1 to 256.
Accordingly, during a first time slot TS 1 the information in a channel 51) on time multiplex line 13 may be switched by time multiplex switchin~ unit 10 to an output port 64 while during the next time slot TS 2 the next channel ~2) on time multiplex line 13 may be switched to an output port 61~ Time-slot control information is transmitted to TMS
controller 29 by the central control 30 which derives this control information from control messages obtained from various control units, e.g., 17 and 18.
Central control 30 and the control units 17 and 18 exchange control messages utilizing selected channels called control channels of the time multiplex lines, e.g.l 13 through 16, between the time-slot interchange units and the time multiplex switching unit 10. In the present embodiment, each control message comprises a plurality of control words and each control channel can transmit one control word per frame of 256 time separated channels. The same channel of the two time multiplex lines associated with a given input/output port pair is predefined to be a control channel. Additionally, a given channel is used as a control channel for only one pair of time multiplex lines. For example, if channel 1 is used as a control channel on time multiplex line 13 and the associated time ~;~37~
multiplex llne 15, no other time multiplex line will use channel 1 as a control channel. During each time slot having the same numerical designation as a control channel, time mulkiplex switching unit 10 connects the data word occupying that control channel to the 64th outpu~ port and connects the 64th input port to the output port associated with the above-mentioned control channel. The following is an example of the operation oE the present embodiment when channel 1 is the control channel Eor time multiplex lines 13 and 15, and channel 2 is the control channel for time multiplex lines 14 and 16. During time slot TS 1 information in TMS controller 29 defines, among other connections, that the control word in channel 1 of time multiplex line 13 is connected to output port 64 and that the control word in channel 1 at input port 64 is connected to time multiplex line 15. Similarly, during time slot number TS 2, information in TMS controller 29 defines that the control word in channel 2 of time multiplex line 14 is connected to the output port 64 a~d that the control word in channel 2 at the input port 64 is connected to time multiplex line 16. When operating in this manner, output port 64 receives from time multiplex switching unit 10 all control words in a channel having the same numerical designation in whic~ they were transmitted to the time multiplex switch. Further, each control channel is connected to receive control words from input port 64 during the time slot ha~in~ the same numerical designation as their associated control channel Control words switched to the 64th output port are transmitted to a control distribution unit 31 which temporarily stores them in a location associated with that control channel. The association of control channels with storage locations in control distribution unit 31 identifies the source of the information stored.
Each control message from a time-slot interchange unit includes a destination portion which uniquely defines . the expected destination of the control message. Control ,i ''' ` ' ~
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distribution unit 31 lnterprets the destination portion of each control message to determine the proper destination for the control message and retransmits the message to input port 64 of time multiplex switching unit 10 in a channel having the same numerical designation as the control channel associated with the destination unit.
When operating as above described, the time-slot interchange unit 11 transmits control messages to time-slot interchange unit 12 by transmitting control words during its recurring control channel to form a control message having a destination portion identifying time-slot interchange unit 12. Control distribution unit 31 accumulates the control words, interprets the destination portion, and retransmits the message to the input port 6~
during the channel having the same numerical designation as the control channel associated with time-slot interchange unit 12. A control message can also be transmitted to the central control 30 by defining central control 30 in the des,ination portion of the control message. When this occurs, control distribution unit 31 transmits the message to central control 30 via a communication line 32 rather than returning it to the time multiplex switching unit 10.
Similarly, a message may be transmitted from central c~ntrol 30 to one o~ the time-slot interchange units by transmitting to the control distribution unit 31 a control message having a destination portion defining the particular time-slot interchange unit. This transmission is also accomplished utilizing communication link 32.
In accordance with the prior example, when a subscriber set goes off-hook, an associated control unit, e.g., 17, collects the dialed digits from that subscriber set. The control unit 17 then creates a control message including representations of the dialed digits, which message is transmitted to central control 30 via the time-multiplex switch 10 and the control distribution unit 31 asdescribed above. Central control 30 responds to the control message from control unit 17 by identifying the ~Z3'7~
time-slot interchanc3e unit, e.g./ 12, as-;ociated with the dialed digits and a common (same) idle time slot on one oE
the time-multiplex lines connecting time-slot interchange unit 12 to the time-multiplex switch 10, and one of the time-multiplex lines connecting the time-slot interchange unit 11 to the time-multiplex switch 10. When the common (same) idle time slot has been selected, central control 30 transmits a path setup message to time-multiplex switch 10 providing the necessary information for time-multiplex switch 10 to connect the input/output port pairs associated with the selected time-multiplex lines during recurrences of the selected time slot. Additionally, control messages are exchanged among the central control 30 and the control units 17 and 18 so that the selected time slot on the selected time-multiplex lines is switched by time-slot interchange units 11 and 12 to the proper subscriber sets.
When a time-slot interchange unit is informed of the time slot for an impending connection, it begins to transmit a logical 1 in the E-bit position (FIG. 5) of each data word transmitted in that time slot. Further, the time-slot interchange unit waits to receive a logical 1 E-bit in the assigned time slot from the other time-slot interchange unit. When such logical 1 E-bits are not received within a predetermined period of tilne or stop after being received, the time-slot interchange unit detecting their absence or termination transmits a control message to central control 30 indicating such. Central control 30 responds to this message b~ marking the time slot available in a translation table. No message need be sent to time multiplexed switch 10 to release the path for reasons discussed below. After a connection has been established between subscribers, the associated time-slot interchange units continue to check for logical 1 E-bits in the time slot used for the connection, as well as the on-hook/off-hook status of the associated subscriber sets. When a subscriber set goes on-hook, the associated time-slot interchange unit stops transmi~ting logical 1 E-bits in the time slot of the : ~ " ~
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communication, ancl transJnits a control message to central control 30 in~icating the completion o~ the call. Central control 30 responds to call completion messages by marking the time slot used for the connection as available for use in future connections.
FIG. 2 is a block diagram o~ a time-multiplex switch 10 embodying the present invention. Time-multiplex switch 10 includes 64 buffer arrangements, oE which buffer arrangement 50 through 52 are specifically shown. Each of the buffer arrangements, e.gO, 51, is connected to a time-slot interchange unit, e.g., 12, via a pair of time multiplex lines, e.g., 201 and 202. Buffer arrangement 50 through 52 receive data words from their associated time~
slot interchange unit and synchronize the transmission oE
those data words to the switch portions of time-multiplex switch 10 under the control of timing si~nals from a master clock circuit 53. suffer arrangements 50 through 52 also transmit data words from the switch portion of time-multiplex switch 10 back to their associated time-slot interchange unit. Each buffer arrangement 50 through 52 is connected to a fan-out circuit, e.g., 55. In the present embodiment, buffer arrangements 50, 51, and 52 are connected to fan-out circuits 5~, 55, and 56, respectively.
A data word received by the buffer arrangement in a given time slot on its associated time-multiplex line, e.g., 13, is transmitted to the connected fan-out circuit substantially simultaneously with the transmission data words received by other buffer arrangements in the same given time slot. For example, data words in time slot 3 of time-multiplex lines 202 and 13 may not be in synchronism due to different lengths of the actual time-multiplex lines themselves. However, buffer arrangements 51 and 52 operate under the control of timing signals from master clock 53 to transmit data words received in time slot 3 to their associated fan-out circuits 55 and 56 substantially simultaneously. Synchronizing buffers are well-known in the art.
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3~ 3 Fan-out circuits 5~ through 56 each have one input ~ terminal connected to an associate bufEer arrangement and 64 output terminals. E'an-out circuits receive data words from their associated bufer arrangements at t~eir input terminal and substantially simultaneously apply those data words to all 6~ of their output terminals. Time-multiplex switch 10 further includes 64 multiplex circuits of which multiplex circuits 57 through 59 are specifically shown.
Each of the multiplex circuits has ~4 input terminals and one output terminal. Multiplexers 57 through 59 operate in synchronism to connect a selected one of their input terminals once each time slot to their output terminal.
The selected input terminal, which is connected to the output terminal of each multiplexer during each time slot is defined by information stored in an associated control memory. In the present embodiment, control memories 70, 71, and 72 are associated with multiplexers 57, 58~ and 59, respectively.
As previously stated, time-multiplex switch 10 operates in repetitive 125-microsecond frames, where each frame comprises 256 time slots. Further, the pattern of connections between input and output terminals can change once each time slot. Accordingly, each control memory 70 through 72 comprises 256 addressabLe storage locationsr and one location is associated with each time slot. The master clock 53 generates a recurrin~ sequence of time slot count signals defining each time slot in the sequence in synchronism with the time slots from fan-out circuits 54 through 56. These time slot count signals are transmitted to control memories 70 through 72 via an address bus 73.
FIG. 3 is a timing diagram representing two consecutive time slots 13 and 14. Since a given frame has a duration of 125 microseconds and includes 256 time slots, each individual time slot is approximately equal to 4~8 nanoseconds. In the present embodiment, each time slot is divided approximately in half to yield two time slot portions of approximately 244 nanoseconds each. The ., .
~237~38 first time slot portion is used to read or write control memories in order to establish new connections through the time-multiplex switch. This will be described in greater detail later herein. During the second half of each tiJne slot, control memories are read un~er the control of master clock circuit 53 by applying time slot count (address) and control signals to address bus 73. It should be noted that the information read from the control memories during a given time slot is used to control the multiplexers during next time slot. Accordingly, as shown in FIG. 3, the second half of time slot 13 is utilized to read information from the location associated with time slot 14.
Time-multiplex switch 10, FIG. 2, further includes 64 latch registers of which latch registers 77 through 79 are specifically shown. ~ach latch register, e.g., 77, is connected to receive the output signals from one control memory, e.g., 70, and is connected to apply control signals to one multiplexer, e.g., 57. At the end of each time slot, the master clock 53 transmits a control pulse on conductor 80, which is connected to all of the latch registers. The latch registers in response to this control pulse, assume the state of the then present output of their associated control memory and apply this state to the associated multiplexer. The information remains in a given latch circuit until it is again changed at the end of the present time slot. Each multiplexer, e.g., 59, responds to the information stored in the latch register associated therewith, e.g., 79, to gate a data word at the input defined by the contents of the associated latch to the multiplexer output, and accordingly, to the associated synchronizing buffer arrangement, e.g., 52.
The embodiment of FIG. 2 also includes a control unit 74, which is connected to central control 30 via a transmission bus 49. Control unit 74 responds to commands received from central control 30 to control the operation of time-multiplex switch 10. The control unit 74, the .
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control memories 70 through 72, and the latch registers 77 through 79 comprise the T~S controller 29 of E'IG. 1. When central control 30 determines that a new path i5 to be established between time-slot interchange units, e.g., 11 and 12 (FIG. 1), central control transmits a path setup message (FIG. 4) to control unit 74. Each path setup message comprises four portions, each portion having its own parity bit. A first portion oE the path setup message deEines that the messa~e is a path setup message. A second portion defines the input/output port pair associated with the first of the subscribers to be connected. A third portion defines the time slot during which the connection is to be made. The input/output port pair associated with the other subscriber to the connection is de~ined by the fourth message portion.
Control unit 74 is connected to all control memories 70 through 72 by an address bus 75 and a data bus 76. These buses are used during the first half of each time slot to read and/or write information from or into the control memories, This inforn~ation is then used to control the connection of input/output port pairs through the time-multiplex switch 10. Each control memory has a unique address corresponding to the input/output port pair associated wlth that control memory. In order to read or write a given location in a given control memory, control unit 74 transmits the control memory address, the given memory location (the time slot of interest), and control signals, e.g., read-write enable signals, on address bus 75. When a memory read operation is performed, the control signals include a read indication, and the specified control memory reads the given location, and transmits that location's contents to control unit 74 on data bus 76. Similarly, when a control memory is to be written, address and control information is transmitted by control unit 74 on address bus 75 while the data to be written is transmitted to the control memory on data - bus 76.
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The Eollowing describes the actions in time-~ multiplex switch 10 when a path setup message is received by control unit 74. ~t should be remembered that a completed connection between input/output ports is bidirectional. That is, when a first input/output port pair is connected to a second input/output port pair in one direction; a connection between those input/output port pairs is also established in the reverse direction utilizing the same time slot. For purposes o~ this example, it is assumed that central control 30 has received a control message requesting a connection through time-multiplex switch 10 between subscribers connected to time-slot interchange unit 12 and time-slot interchange unit 11. Initially, central control 30 searches a translation table stored in memory and determines that the time slot 17 is available at input/output port pair 61, which is associated with time-multiplex lines 201 and 202, and at input/output port pair 1, which is associated with time-multiplex lines 13 and 15. Based on this information, central control 30 formulates a path setup message defining input/output port pairs 61 and 1, time slot 17, and that the message is a path setup message. This message is transmitted via bus 49 to control unit 74 which checks parity over all four message portions and determines i~ the message has the proper syntax. When a path setup message has a parity or syntax error, no further action is taken by control unit 74 and no error message is returned to central control 30. No error message is required due to the previousl~ described E~bit continuity check. Since no connection is established through the time multiplexed switch when a path setup message failure occurs, neither of the time-slot interchange units which were to be connected will receive logical 1 E-bits in the time slot of the connection. Accordinglyr the time-slot interchange units will transmit control messages to the central control 30 indicating a path setup failure and the time slot in which ; the failure occurred. Central control 30 responds to those ' ' :
~2371~3 messages by marking the time 510t ~or the proposed connection as available in the translation table. Although no error messages need to be returned to central control 30 in the present embodiment, it may be desirable to return some type of Eailure indication so that central control 30 can monitor system performance.
FIGS. 6 t~rough 9 are simplified diagrams oE time multiplexed switch 10 and are intended to aid in the understanding o~ the present invention. FIG. 6 represents a oattern of connections among input/output port pairs 1, Z, 25, and 61, during time slot 17. The connections shown are presently unused and are merely the remnants of past active connections. The arrangement shown in FIG. 6 includes four multiplexers, 58, 59, 87, and 89, which are respectively associated with control memories 71, 72, 88, and 90. The number drawn in brackets within the control memories represents the information stored in the location associated with time slot 17 and as such it defines the input port connected to the associated multiplexer output during time slot 17. For example, the number 1 drawn in control memory 88 represents that the output terminal of multiple~er 87 is connected to the input port of input/~utput port ~air 1 during time slot 17. It should be noted that in the ~ollowing example, input~output port pair 63 is unequipped and prior connections are re~oved by connecting output ports to the input port of input/output port 63. Although in the present example input/output port pair 63 is unequipped, it may be desirable to use it to provide idle code or as a test connection.
Time-multiplex switch 10 responds to path setup messages by disconnecting other connections to the de~ined inputjoutput port pairs during the specified time slot.
Accordingly, when control unit 74 receives a valid path setup message defining a connection between input/output port pairs 1 and ~1 using time slot 17, it must iirst locate and disconnect other possible interEering connections. Initially, control unit 74 reads control .i ~LZ~
memory 71 which is associated with input/output port pair 61 at the address corresponding to time slot 17. ~he quantity so read defines which input/output port pair is presently connected to input/output port pair 61 during time slot 17. In the present example (FIG. 6) input/output port pair 61 is presently connected to input/output port pair 2 during time slot 17. Since there is a one-to~one correspondence between input/output port pairs and control memories, the quantity so read also defines the control memory associated with the interfering input/output port pair. Accordingly, control unit 74 writes into the control memory 90 associated with input/output port pair 2 at an address corresponding to time slot 17 the identity of input/output port pair 63. Since input/output port pair 63 is unequipped, this action removes a potentially conflicting connection. FIG. 7 represents the state oE
time multiplexed switch 10 after the removal of the first conflicting connection. A~ter clearing the first interfering connection, control unit 74 reads control memory 72 associated with input/output port pair 1 at the address corresponding to time slot 17. The number 25 shown in control memory 72 (FIG. 6) indicates that input/output port pair 1 is connected to input/output port pair 25 during time slot 17. The identity o~ input/output port pair 25 is used as above described to set time slot 17 in control memory 88 to 63. FIG. 8 represents the status of time multiplexed switch 10 after writing control memory 88.
After the interfering connections have been cleared (set to input/output port pair 63), control unit 74 establishes the connections defined by the path setup message. First, control unit 74 writes into control memory 71 which is associated with input/output port pair 61 at the location corresponding to time slot 17 the quantity defining input/output port pair 1. ~ccordingly, during subsequent occurrences of time slot 17, information arriving on time-multiplex line 13 of the input/output port - pair 1, is connected to outgoing time-multiplex line 201 , 37~
via a path comprising buEfer arrangement 52, fan-out board 56, multiplexer 5~, and a buffer arrangement 51 (FIG. 2). Similarly, control unit 7~ writes into control memory 72 at the location corresponding to time slot 17 the quantity defining input/output port pair 61. During subsequent occurrences of time slot 17 data words on time-multiplex line 202 of input/output port pair 61 are connected to time-multiplex line 15 of input/output port pair 1 via a path comprising buffer arrangemen~ 51, fan-out board 55, multiplexer 59, and buffer arrangement 52 (FIG. 2). FI~. 9 represents the status of time multiplexed switch 10 when the response to the exemplary path setup message is complete. The connection as shown in FIG. 9 continues until some later connection requires the use of either multiplexer 58 or multiplexer 59 during time slot 17. Even if users of the exemplary time slot 17 terminate their communication, no disconnect message is sent to disconnect them. Performing disconnect operations as shown and described above substantially reduces the number o~ messages transmitted in a system and reduces demand on processor of the system.
It is to be understood that the above-described embodiment is merely illustrative of the principles oE the invention and that other arrangements may be devised by those skillea in the art without ~eparting ~rom the spirit and scope of the invention. For example, in the preceding description only connections between one input port and one output port are specifically described. r~he principles of the present invention apply equally well to broadcast connections where one input port is connected to a plurality of output ports. For a broadcast connection the time multiplexed switch, in response to a path setup message, first disconnects possibly conflicting paths for all of the specified output ports and then establishes the requested connection.
Further, the principles of the present invention apply equally well to interactions between time-slot : .
`
~Z3711!3~
interchange units and a central controller. In this case, the input and output ports are analagous to the tlrne-separated channels entering and leaving the time-slot interchange unit. In response to a path setup message, the time-slot interchange unit controller reads the control memories defining the pattern of connections through the time-slot interchange unit to locate potentially conflicting paths. Based on this information, the controller writes information into the control memories which removes the conflicting paths and which completes the connection re~uested by the path setup message.
,~
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- 1 ~
TIME DIV[SI~N SWI'rCHING ~YSTEM CONTROL
ARRANGEMENT AND METHOD
Technical Field This invention relates to time division switching systems and more particularly to methods and arrangements for controlling the switch arrangements oE such systems.
Background o~-the Invention Stored program controlled communication switching systems comprise some form oE intelligence which controls switching functions in response to a program stored in memory. Historically, such systems included a single processing entity for the control of the entire system. As technology and system design evolved, it was found desirable to separate certain routine functions from the main processing entity to save its processing time for more complex system functions and decisions. Today, systems are being designed which also separate some of the more complex system functions and decisions into several intelligent processors.
One type of modern time-division switching system comprises a plurality of tlme-slot interchange units each includin~ a processor, which is selectively interconnected by a time multiple~ed switch, sometimes called a time-shared space division switch. Such a switching system also includes a central control arrangement including a processor which determines the pattern of interconnections between the plurality of time-slot interchange units. In order to coordinate the actions of the time-slot interchange unit, the time multiplexed switch, and the central control arrangement, control messages must be exchanged. Since each control message occupies some portion of the interprocessor communication media, too many messages can reduce system real time response by causing delays in message transmission~
Similarl~, since each message requires processor real time, the individual processors can be kept from needed tasks .. , ~dP
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.
~237~
while receiving and transmitting mes6a~es. AccordincJly, it is important to minimize the number of control messages exchanged in the system. It is also importantt however, that each unit in a distributed processor system have enough information to enable it to properly perform its tasks. This is especially true in distributed telecommunications systems where the integrity of connections must be maintained. Thus, the portions of a distributed communications systems must be designed to operate accurately with a minimum number of required control messages.
An example of the conflict between proper operation and a potential]y large number of control messages occurs with communications between the time multiplexed switch and the central control arrangement.
The central control and time multiplexed switch must cooperate to complete connections for virtually all calls traversing the switching system. In prior art systems, the central control arrangement, when requested, transmits a message to the time multiplexed switch defining a connection between time-slot interchange units. Then, when the connection is no longer needed (a subscriber goes on-hook), a second message is transmitted directing the time multiplexed switch to remove the connection between the time-slot interchange units. If unused paths through the time multiple~ed switch are not removed, a given input port may eventually be simultaneously connected to a number of output ports and when the given input port is used to complete another connection, signals arriving at that input port may be broadcast to a number of output ports. As discussed above, prior systems transmit two control messages for each time multiplexed switch connection. The first message is used to set up the connection~ The second message is then used to remove it. In accordance with the present invention, multiple output port connections to a given input port are substantially avoided without the . necessity of disconnect orders, thus reducing , ~ .
~2371~~
substantially the number of control messages exchanged between the central control arrangement and the time multiplexed switch in a time division switching system.
Similar advantages can be obtained in the interactions between time-slot interchan~e units and the central control.
Summary of _he Invention A method in accordance with the present invention of controlling connections between input and output ports of a switch arrangement, comprises tne steps of storin~ in a memory arrangement information defining a pattern of connections between the input and output ports, rea~ing from the memory arrangement, and connecting the input ports to the output ports in the pattern defined by the information so read, generating a path setup message defining one input port, one output port, and a time slot, writing into the memory arrangement information defining a pattern of connections in which the input port defined by the path setup message is not connected to any output port during the defined time slot, and writing into the memory arrangement information de~ining a pattern oE connections in which the input port and output port defined by the path setup message are connected during the defined time slot.
In accordance with one embodiment of the present invention, a time-shared space division switch is used to interconnect input/output port pairs, each of which includes an input port and an output port. Additionally, the information for controlling the connections through the time-shared space division switch is stored in such a way that the particular input port connected to a given output port during each time slot can be readily obtained. In response to a path setup message defining a first input/output port pair, a second input/output port pair, and a time slot, the control unit reads the stored information to determine which input ports are connected to the output ports of the first and second input/output port pairs. The control unit then writes into the memory ' - ~
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~;~37~L~3151 information which disconnects the input ports eound during the read operation Erom the output ports of the first and second input/output port pairs during the defined time slot, then inEormation is written into the memory which connects the defined input/output port pairs during the defined time slot. Since disconnect operations are performed in response to path setup messages, no disconnect messages need be sent to assure that multiple output ports are not conn~cted to a given input port. The avoidance o~
disconnect messages substantially reduces the message traffic between the time multiplexed switch and the central control arrangement resulting in a savings of system resources.
Brief DescriDtion of the Drawinq A more complete understanding of the present invention may be obtained from a consideration of the following description when read in conjunction with the drawing in which:
FIG. 1 is a block diagram of a system embodying the present invention;
FIG. 2 is a more detailed diagram of a time multiplexed switching unit utilized in the embodiment of FIG. 1;
FIG. 3 represents relative timing intervals within the time multiplexed switching unit;
FIGo 4 is a representation of a path setup message exchanged in the embodiment of FIG. 1;
FIG. 5 is a diagram of the data words utilized in the embodiment of FIG. 1; and FIGS. 6 through 9 represent a sequence of steps in establishing a path through the time multiplexed switch.
General Descriptlon FIG. 1 is a block diagram of a time division switching system embodyinq the present invention which is used to interconnect subscriber sets such as subscriber sets 23 thrGugh 26. The embodiment of FIG. 1 includes a .
~l23~ 8 time multiplex switchil1g unit 10 which cornprises a tlrrl~-shared space division switch having 64 input ports and 6~
output ports. The embodiment Eurther includes 31 time-slot interehange units of which representative time-slot interchange units 11 and 12 are specifically shown. Each time-slot interehange unit 11 and 12 ineludes a bidirectional time-slot interchanger. Additionally, each time-slot interchange unit 11 and 12 is eonneeted to two input ports and two output ports of time multiplex switeh unit 10. In the present embodiment, time-slot interchange unit 11 is connected to two time multiplex switch input ports via time multiplex lines 13 and 14 and to two output ports, via time multiplex lines 15 and 16.
In the description which follows, the input and output ports of time multiplex switehing unit 10 are referred to as input/output port pairs. This term is used since the source for data words to an input port of a given input/output port pair is also the destination ~or data words from the output port of that pair. As shown in FIG. 1, input/output port pair 1 is associated with time multiplex lines 13 and 15. Each time multiplex line, 13 through 16, conveys digital in~ormation in 125 microsecond frames eaeh frame comprising 256 time separated ehannels.
Accordingly, each time-slot interchange unit transmits and receives up to 512 channels o~ digital in~ormation during each 125 microseeond ~rame.
Each time-slot interehange unit is uni~uely assoeiated with a eontrol unit of whieh eontrol unit 17 is assoeiated with time-slot interchange unit 11, and eontrol unit 18 is associated with time-slot interchange unit 12.
Additionally, eaeh time-slot interehange unit is conneeted to a plurality o~ line units of whieh line units 19 through 22 are shown in FIG. 1 via individual time multiplex lines. In the present embodiment line units 19 and 20 are connected to time-slot interehange unit 11 and line units 21 and 22 are eonneeted to time-slot interchange ; unit 12. Each of the line units of the present embodiment .. .
. -~Z~
is connected to a number of subscriber sets of which subscriber sets 23 through 26 are shown. The exact number oE line units associated with each time-slot interchange unit and the exact number of subscriber sets associated with each line unit is determined by the number of subscribers to be served and the calling rates of those subscribers. Each line unit terminates the analog loop of the well-known type from a plurality of subscriber sets, e.g., 23 through 26, and converts call information including analog speech signals into digital data words which are transmitted to its associated time-slot interchange unit. Further, each line unit detects service requests from the subscriber sets and generates certain signaling information for those subscriber setsO The particular subscriber sets from which speech samples are taken and encoded, and the particular time multiplex channels used to transmit the resulting code between the line unit and its associated time-slot interchange unit are determined b~ the control unit of the associated time-slot interchange unit.
The relationship of subscriber sets, line units and time-slot interchange units is substantially the same for each o~ such groups of interconnected units.
Accordingly, while the description which follows relates directly to subscriber set 23, line unit 19 and time-slot interchange unit 11, it shows the relationships for all other groups of such units. Line unit 19 scans the lines connected to each subscriber set to detect requests for service. When such a request is detected, line unit 19 transmits to the control unit 17, a message indicating the request and the identity of the requesting subscriber set.
This message is transmitted to control unit 17 via a communication path 27. Ccntrol unit 17 performs the necessary translation based on the service requested, the identity of the requesting subscriber set and the available equipment, and transmits a message to line unit 19 via communication path 27 defining which of the plurality of , ~ .
,, 3~
time separated channels between line unit 19 ancl time~slot interchange unit ll is to be used to transmit information from subscriber set 23 to time-slot interchange unit 11.
Based on this message, line unit 19 encodes the analog information from subscriber set 23 into digital data words and transmits the resulting data words in the assigned channel. In the present embodiment, line unit 19 also transmits in the assigned channel an indication of the DC
state, i.e., open circuit, closed circuit, of the subscriber loop associated with subscriber set 23. Each channel in the present embodiment can convey one 16-bit data wordu Each data word (FIG. 5) comprises an 8-bit PCM
data portion, a 7-bit signaling portion, and a parity bit.
The signaling portion is used to convey signaling information about the channel circuit or the subscriber set to which it is connected. For example, the A-bit of the signaling portion is used to transmit the present DC state of the associated subscriber set to the time-slot interchange unit 11.
After a time separated channel between line unit 19 and time-slot interchange unit 11 is assigned to a given subscriber set, control unit 17 detects signaling in~ormation from the subscriber set by sampling the information transmitted in the assigned channel. Such sampling operations are perEormed via a communication path 28. Control unit 17 responds to the signaling information from the subsc iber's channel, and to control messages from other control units, e.g., 18, and a central control unit 30, by controlling the time-slot interchange function of the time-slot interchange unit 11. As previously stated, each time multiplex line between a time-slot interchange unit and the time multiplex switch unit 10 has 256 channels in each 125 microsecond frame. These channels are assigned numerical designations from 1 to 256 in sequence as they occur. This sequence of channels recurs so that a given channel will be available every 125 microseconds~ The time-slot interchange ~unction takes the ~23~
data words received from the line units and place~ them in channels on the time multiplex line between ~he time-slot interchange units and the time multiplex switching unit 10 under the control of control units 17 and 18.
Time multiplex swltching unit 10 operates in recurring frarnes of time slots where each 125 microsecond frame comprises 256 time slots. During each time slot, time multiplex switching unit 10 is capable of connecting data words received at any of its 64 input ports to any of its 64 output ports in accordance with time-slot control information stored in a TMS controller 29 The pattern of connections through time multiplex switching unit 10 repeats itself every 256 time slots and each time slot is assigned a numerical designation in sequence from 1 to 256.
Accordingly, during a first time slot TS 1 the information in a channel 51) on time multiplex line 13 may be switched by time multiplex switchin~ unit 10 to an output port 64 while during the next time slot TS 2 the next channel ~2) on time multiplex line 13 may be switched to an output port 61~ Time-slot control information is transmitted to TMS
controller 29 by the central control 30 which derives this control information from control messages obtained from various control units, e.g., 17 and 18.
Central control 30 and the control units 17 and 18 exchange control messages utilizing selected channels called control channels of the time multiplex lines, e.g.l 13 through 16, between the time-slot interchange units and the time multiplex switching unit 10. In the present embodiment, each control message comprises a plurality of control words and each control channel can transmit one control word per frame of 256 time separated channels. The same channel of the two time multiplex lines associated with a given input/output port pair is predefined to be a control channel. Additionally, a given channel is used as a control channel for only one pair of time multiplex lines. For example, if channel 1 is used as a control channel on time multiplex line 13 and the associated time ~;~37~
multiplex llne 15, no other time multiplex line will use channel 1 as a control channel. During each time slot having the same numerical designation as a control channel, time mulkiplex switching unit 10 connects the data word occupying that control channel to the 64th outpu~ port and connects the 64th input port to the output port associated with the above-mentioned control channel. The following is an example of the operation oE the present embodiment when channel 1 is the control channel Eor time multiplex lines 13 and 15, and channel 2 is the control channel for time multiplex lines 14 and 16. During time slot TS 1 information in TMS controller 29 defines, among other connections, that the control word in channel 1 of time multiplex line 13 is connected to output port 64 and that the control word in channel 1 at input port 64 is connected to time multiplex line 15. Similarly, during time slot number TS 2, information in TMS controller 29 defines that the control word in channel 2 of time multiplex line 14 is connected to the output port 64 a~d that the control word in channel 2 at the input port 64 is connected to time multiplex line 16. When operating in this manner, output port 64 receives from time multiplex switching unit 10 all control words in a channel having the same numerical designation in whic~ they were transmitted to the time multiplex switch. Further, each control channel is connected to receive control words from input port 64 during the time slot ha~in~ the same numerical designation as their associated control channel Control words switched to the 64th output port are transmitted to a control distribution unit 31 which temporarily stores them in a location associated with that control channel. The association of control channels with storage locations in control distribution unit 31 identifies the source of the information stored.
Each control message from a time-slot interchange unit includes a destination portion which uniquely defines . the expected destination of the control message. Control ,i ''' ` ' ~
~2371~B
distribution unit 31 lnterprets the destination portion of each control message to determine the proper destination for the control message and retransmits the message to input port 64 of time multiplex switching unit 10 in a channel having the same numerical designation as the control channel associated with the destination unit.
When operating as above described, the time-slot interchange unit 11 transmits control messages to time-slot interchange unit 12 by transmitting control words during its recurring control channel to form a control message having a destination portion identifying time-slot interchange unit 12. Control distribution unit 31 accumulates the control words, interprets the destination portion, and retransmits the message to the input port 6~
during the channel having the same numerical designation as the control channel associated with time-slot interchange unit 12. A control message can also be transmitted to the central control 30 by defining central control 30 in the des,ination portion of the control message. When this occurs, control distribution unit 31 transmits the message to central control 30 via a communication line 32 rather than returning it to the time multiplex switching unit 10.
Similarly, a message may be transmitted from central c~ntrol 30 to one o~ the time-slot interchange units by transmitting to the control distribution unit 31 a control message having a destination portion defining the particular time-slot interchange unit. This transmission is also accomplished utilizing communication link 32.
In accordance with the prior example, when a subscriber set goes off-hook, an associated control unit, e.g., 17, collects the dialed digits from that subscriber set. The control unit 17 then creates a control message including representations of the dialed digits, which message is transmitted to central control 30 via the time-multiplex switch 10 and the control distribution unit 31 asdescribed above. Central control 30 responds to the control message from control unit 17 by identifying the ~Z3'7~
time-slot interchanc3e unit, e.g./ 12, as-;ociated with the dialed digits and a common (same) idle time slot on one oE
the time-multiplex lines connecting time-slot interchange unit 12 to the time-multiplex switch 10, and one of the time-multiplex lines connecting the time-slot interchange unit 11 to the time-multiplex switch 10. When the common (same) idle time slot has been selected, central control 30 transmits a path setup message to time-multiplex switch 10 providing the necessary information for time-multiplex switch 10 to connect the input/output port pairs associated with the selected time-multiplex lines during recurrences of the selected time slot. Additionally, control messages are exchanged among the central control 30 and the control units 17 and 18 so that the selected time slot on the selected time-multiplex lines is switched by time-slot interchange units 11 and 12 to the proper subscriber sets.
When a time-slot interchange unit is informed of the time slot for an impending connection, it begins to transmit a logical 1 in the E-bit position (FIG. 5) of each data word transmitted in that time slot. Further, the time-slot interchange unit waits to receive a logical 1 E-bit in the assigned time slot from the other time-slot interchange unit. When such logical 1 E-bits are not received within a predetermined period of tilne or stop after being received, the time-slot interchange unit detecting their absence or termination transmits a control message to central control 30 indicating such. Central control 30 responds to this message b~ marking the time slot available in a translation table. No message need be sent to time multiplexed switch 10 to release the path for reasons discussed below. After a connection has been established between subscribers, the associated time-slot interchange units continue to check for logical 1 E-bits in the time slot used for the connection, as well as the on-hook/off-hook status of the associated subscriber sets. When a subscriber set goes on-hook, the associated time-slot interchange unit stops transmi~ting logical 1 E-bits in the time slot of the : ~ " ~
~37~
communication, ancl transJnits a control message to central control 30 in~icating the completion o~ the call. Central control 30 responds to call completion messages by marking the time slot used for the connection as available for use in future connections.
FIG. 2 is a block diagram o~ a time-multiplex switch 10 embodying the present invention. Time-multiplex switch 10 includes 64 buffer arrangements, oE which buffer arrangement 50 through 52 are specifically shown. Each of the buffer arrangements, e.gO, 51, is connected to a time-slot interchange unit, e.g., 12, via a pair of time multiplex lines, e.g., 201 and 202. Buffer arrangement 50 through 52 receive data words from their associated time~
slot interchange unit and synchronize the transmission oE
those data words to the switch portions of time-multiplex switch 10 under the control of timing si~nals from a master clock circuit 53. suffer arrangements 50 through 52 also transmit data words from the switch portion of time-multiplex switch 10 back to their associated time-slot interchange unit. Each buffer arrangement 50 through 52 is connected to a fan-out circuit, e.g., 55. In the present embodiment, buffer arrangements 50, 51, and 52 are connected to fan-out circuits 5~, 55, and 56, respectively.
A data word received by the buffer arrangement in a given time slot on its associated time-multiplex line, e.g., 13, is transmitted to the connected fan-out circuit substantially simultaneously with the transmission data words received by other buffer arrangements in the same given time slot. For example, data words in time slot 3 of time-multiplex lines 202 and 13 may not be in synchronism due to different lengths of the actual time-multiplex lines themselves. However, buffer arrangements 51 and 52 operate under the control of timing signals from master clock 53 to transmit data words received in time slot 3 to their associated fan-out circuits 55 and 56 substantially simultaneously. Synchronizing buffers are well-known in the art.
\
3~ 3 Fan-out circuits 5~ through 56 each have one input ~ terminal connected to an associate bufEer arrangement and 64 output terminals. E'an-out circuits receive data words from their associated bufer arrangements at t~eir input terminal and substantially simultaneously apply those data words to all 6~ of their output terminals. Time-multiplex switch 10 further includes 64 multiplex circuits of which multiplex circuits 57 through 59 are specifically shown.
Each of the multiplex circuits has ~4 input terminals and one output terminal. Multiplexers 57 through 59 operate in synchronism to connect a selected one of their input terminals once each time slot to their output terminal.
The selected input terminal, which is connected to the output terminal of each multiplexer during each time slot is defined by information stored in an associated control memory. In the present embodiment, control memories 70, 71, and 72 are associated with multiplexers 57, 58~ and 59, respectively.
As previously stated, time-multiplex switch 10 operates in repetitive 125-microsecond frames, where each frame comprises 256 time slots. Further, the pattern of connections between input and output terminals can change once each time slot. Accordingly, each control memory 70 through 72 comprises 256 addressabLe storage locationsr and one location is associated with each time slot. The master clock 53 generates a recurrin~ sequence of time slot count signals defining each time slot in the sequence in synchronism with the time slots from fan-out circuits 54 through 56. These time slot count signals are transmitted to control memories 70 through 72 via an address bus 73.
FIG. 3 is a timing diagram representing two consecutive time slots 13 and 14. Since a given frame has a duration of 125 microseconds and includes 256 time slots, each individual time slot is approximately equal to 4~8 nanoseconds. In the present embodiment, each time slot is divided approximately in half to yield two time slot portions of approximately 244 nanoseconds each. The ., .
~237~38 first time slot portion is used to read or write control memories in order to establish new connections through the time-multiplex switch. This will be described in greater detail later herein. During the second half of each tiJne slot, control memories are read un~er the control of master clock circuit 53 by applying time slot count (address) and control signals to address bus 73. It should be noted that the information read from the control memories during a given time slot is used to control the multiplexers during next time slot. Accordingly, as shown in FIG. 3, the second half of time slot 13 is utilized to read information from the location associated with time slot 14.
Time-multiplex switch 10, FIG. 2, further includes 64 latch registers of which latch registers 77 through 79 are specifically shown. ~ach latch register, e.g., 77, is connected to receive the output signals from one control memory, e.g., 70, and is connected to apply control signals to one multiplexer, e.g., 57. At the end of each time slot, the master clock 53 transmits a control pulse on conductor 80, which is connected to all of the latch registers. The latch registers in response to this control pulse, assume the state of the then present output of their associated control memory and apply this state to the associated multiplexer. The information remains in a given latch circuit until it is again changed at the end of the present time slot. Each multiplexer, e.g., 59, responds to the information stored in the latch register associated therewith, e.g., 79, to gate a data word at the input defined by the contents of the associated latch to the multiplexer output, and accordingly, to the associated synchronizing buffer arrangement, e.g., 52.
The embodiment of FIG. 2 also includes a control unit 74, which is connected to central control 30 via a transmission bus 49. Control unit 74 responds to commands received from central control 30 to control the operation of time-multiplex switch 10. The control unit 74, the .
3~8~
control memories 70 through 72, and the latch registers 77 through 79 comprise the T~S controller 29 of E'IG. 1. When central control 30 determines that a new path i5 to be established between time-slot interchange units, e.g., 11 and 12 (FIG. 1), central control transmits a path setup message (FIG. 4) to control unit 74. Each path setup message comprises four portions, each portion having its own parity bit. A first portion oE the path setup message deEines that the messa~e is a path setup message. A second portion defines the input/output port pair associated with the first of the subscribers to be connected. A third portion defines the time slot during which the connection is to be made. The input/output port pair associated with the other subscriber to the connection is de~ined by the fourth message portion.
Control unit 74 is connected to all control memories 70 through 72 by an address bus 75 and a data bus 76. These buses are used during the first half of each time slot to read and/or write information from or into the control memories, This inforn~ation is then used to control the connection of input/output port pairs through the time-multiplex switch 10. Each control memory has a unique address corresponding to the input/output port pair associated wlth that control memory. In order to read or write a given location in a given control memory, control unit 74 transmits the control memory address, the given memory location (the time slot of interest), and control signals, e.g., read-write enable signals, on address bus 75. When a memory read operation is performed, the control signals include a read indication, and the specified control memory reads the given location, and transmits that location's contents to control unit 74 on data bus 76. Similarly, when a control memory is to be written, address and control information is transmitted by control unit 74 on address bus 75 while the data to be written is transmitted to the control memory on data - bus 76.
., ~23~
The Eollowing describes the actions in time-~ multiplex switch 10 when a path setup message is received by control unit 74. ~t should be remembered that a completed connection between input/output ports is bidirectional. That is, when a first input/output port pair is connected to a second input/output port pair in one direction; a connection between those input/output port pairs is also established in the reverse direction utilizing the same time slot. For purposes o~ this example, it is assumed that central control 30 has received a control message requesting a connection through time-multiplex switch 10 between subscribers connected to time-slot interchange unit 12 and time-slot interchange unit 11. Initially, central control 30 searches a translation table stored in memory and determines that the time slot 17 is available at input/output port pair 61, which is associated with time-multiplex lines 201 and 202, and at input/output port pair 1, which is associated with time-multiplex lines 13 and 15. Based on this information, central control 30 formulates a path setup message defining input/output port pairs 61 and 1, time slot 17, and that the message is a path setup message. This message is transmitted via bus 49 to control unit 74 which checks parity over all four message portions and determines i~ the message has the proper syntax. When a path setup message has a parity or syntax error, no further action is taken by control unit 74 and no error message is returned to central control 30. No error message is required due to the previousl~ described E~bit continuity check. Since no connection is established through the time multiplexed switch when a path setup message failure occurs, neither of the time-slot interchange units which were to be connected will receive logical 1 E-bits in the time slot of the connection. Accordinglyr the time-slot interchange units will transmit control messages to the central control 30 indicating a path setup failure and the time slot in which ; the failure occurred. Central control 30 responds to those ' ' :
~2371~3 messages by marking the time 510t ~or the proposed connection as available in the translation table. Although no error messages need to be returned to central control 30 in the present embodiment, it may be desirable to return some type of Eailure indication so that central control 30 can monitor system performance.
FIGS. 6 t~rough 9 are simplified diagrams oE time multiplexed switch 10 and are intended to aid in the understanding o~ the present invention. FIG. 6 represents a oattern of connections among input/output port pairs 1, Z, 25, and 61, during time slot 17. The connections shown are presently unused and are merely the remnants of past active connections. The arrangement shown in FIG. 6 includes four multiplexers, 58, 59, 87, and 89, which are respectively associated with control memories 71, 72, 88, and 90. The number drawn in brackets within the control memories represents the information stored in the location associated with time slot 17 and as such it defines the input port connected to the associated multiplexer output during time slot 17. For example, the number 1 drawn in control memory 88 represents that the output terminal of multiple~er 87 is connected to the input port of input/~utput port ~air 1 during time slot 17. It should be noted that in the ~ollowing example, input~output port pair 63 is unequipped and prior connections are re~oved by connecting output ports to the input port of input/output port 63. Although in the present example input/output port pair 63 is unequipped, it may be desirable to use it to provide idle code or as a test connection.
Time-multiplex switch 10 responds to path setup messages by disconnecting other connections to the de~ined inputjoutput port pairs during the specified time slot.
Accordingly, when control unit 74 receives a valid path setup message defining a connection between input/output port pairs 1 and ~1 using time slot 17, it must iirst locate and disconnect other possible interEering connections. Initially, control unit 74 reads control .i ~LZ~
memory 71 which is associated with input/output port pair 61 at the address corresponding to time slot 17. ~he quantity so read defines which input/output port pair is presently connected to input/output port pair 61 during time slot 17. In the present example (FIG. 6) input/output port pair 61 is presently connected to input/output port pair 2 during time slot 17. Since there is a one-to~one correspondence between input/output port pairs and control memories, the quantity so read also defines the control memory associated with the interfering input/output port pair. Accordingly, control unit 74 writes into the control memory 90 associated with input/output port pair 2 at an address corresponding to time slot 17 the identity of input/output port pair 63. Since input/output port pair 63 is unequipped, this action removes a potentially conflicting connection. FIG. 7 represents the state oE
time multiplexed switch 10 after the removal of the first conflicting connection. A~ter clearing the first interfering connection, control unit 74 reads control memory 72 associated with input/output port pair 1 at the address corresponding to time slot 17. The number 25 shown in control memory 72 (FIG. 6) indicates that input/output port pair 1 is connected to input/output port pair 25 during time slot 17. The identity o~ input/output port pair 25 is used as above described to set time slot 17 in control memory 88 to 63. FIG. 8 represents the status of time multiplexed switch 10 after writing control memory 88.
After the interfering connections have been cleared (set to input/output port pair 63), control unit 74 establishes the connections defined by the path setup message. First, control unit 74 writes into control memory 71 which is associated with input/output port pair 61 at the location corresponding to time slot 17 the quantity defining input/output port pair 1. ~ccordingly, during subsequent occurrences of time slot 17, information arriving on time-multiplex line 13 of the input/output port - pair 1, is connected to outgoing time-multiplex line 201 , 37~
via a path comprising buEfer arrangement 52, fan-out board 56, multiplexer 5~, and a buffer arrangement 51 (FIG. 2). Similarly, control unit 7~ writes into control memory 72 at the location corresponding to time slot 17 the quantity defining input/output port pair 61. During subsequent occurrences of time slot 17 data words on time-multiplex line 202 of input/output port pair 61 are connected to time-multiplex line 15 of input/output port pair 1 via a path comprising buffer arrangemen~ 51, fan-out board 55, multiplexer 59, and buffer arrangement 52 (FIG. 2). FI~. 9 represents the status of time multiplexed switch 10 when the response to the exemplary path setup message is complete. The connection as shown in FIG. 9 continues until some later connection requires the use of either multiplexer 58 or multiplexer 59 during time slot 17. Even if users of the exemplary time slot 17 terminate their communication, no disconnect message is sent to disconnect them. Performing disconnect operations as shown and described above substantially reduces the number o~ messages transmitted in a system and reduces demand on processor of the system.
It is to be understood that the above-described embodiment is merely illustrative of the principles oE the invention and that other arrangements may be devised by those skillea in the art without ~eparting ~rom the spirit and scope of the invention. For example, in the preceding description only connections between one input port and one output port are specifically described. r~he principles of the present invention apply equally well to broadcast connections where one input port is connected to a plurality of output ports. For a broadcast connection the time multiplexed switch, in response to a path setup message, first disconnects possibly conflicting paths for all of the specified output ports and then establishes the requested connection.
Further, the principles of the present invention apply equally well to interactions between time-slot : .
`
~Z3711!3~
interchange units and a central controller. In this case, the input and output ports are analagous to the tlrne-separated channels entering and leaving the time-slot interchange unit. In response to a path setup message, the time-slot interchange unit controller reads the control memories defining the pattern of connections through the time-slot interchange unit to locate potentially conflicting paths. Based on this information, the controller writes information into the control memories which removes the conflicting paths and which completes the connection re~uested by the path setup message.
,~
' ~:
Claims (13)
1. In combination a switch arrangement comprising a plurality of input ports, and a plurality of output ports;
memory means for storing control information defining a pattern of connections between said input and said output ports;
means for reading said control information from memory means and for connecting said input and said output ports in accordance with said defined pattern of connections;
means for generating path setup messages defining a connection between a specified one of said input ports and a specified one of said output ports; and control means responsive to said path setup messages for writing into said memory means control information defining a pattern of connections in which no output port is connected to said specified input port and then for writing into said memory means control information defining a pattern of connections in which said specified input port is connected to said specified output port.
memory means for storing control information defining a pattern of connections between said input and said output ports;
means for reading said control information from memory means and for connecting said input and said output ports in accordance with said defined pattern of connections;
means for generating path setup messages defining a connection between a specified one of said input ports and a specified one of said output ports; and control means responsive to said path setup messages for writing into said memory means control information defining a pattern of connections in which no output port is connected to said specified input port and then for writing into said memory means control information defining a pattern of connections in which said specified input port is connected to said specified output port.
2. In combination a time-shared space division switch comprising a plurality of input/output port pairs each comprising one input and one output port;
memory means for storing information defining a plurality of patterns of connections between said input ports and said output ports, each pattern of connections being associated with one of a plurality of time slots;
connection control means for periodically reading a pattern of connections from said memory means and for connecting said input and said output ports in accordance with the pattern of connections so read;
means for generating a path setup message requesting a connection between a first input/output port pair and a second input/output port pair during a defined time slot; and control means responsive to said path setup messages for writing into said memory means information defining a pattern of connections in which no output port is connected to the input ports of said first and said second input/output port pairs during said defined time slot and then for writing into said memory means information defining a pattern of connections in which the input port of said first input/output port pair is connected to the output port of said second input/output port pair during said defined time slot and in which the input port of said second input/output port pair is connected to the output port of said first input/output port pair during said defined time slot.
memory means for storing information defining a plurality of patterns of connections between said input ports and said output ports, each pattern of connections being associated with one of a plurality of time slots;
connection control means for periodically reading a pattern of connections from said memory means and for connecting said input and said output ports in accordance with the pattern of connections so read;
means for generating a path setup message requesting a connection between a first input/output port pair and a second input/output port pair during a defined time slot; and control means responsive to said path setup messages for writing into said memory means information defining a pattern of connections in which no output port is connected to the input ports of said first and said second input/output port pairs during said defined time slot and then for writing into said memory means information defining a pattern of connections in which the input port of said first input/output port pair is connected to the output port of said second input/output port pair during said defined time slot and in which the input port of said second input/output port pair is connected to the output port of said first input/output port pair during said defined time slot.
3. The combination in accordance with claim 2 wherein said memory means stores information defining the input port connected to each output port during each time slot; and said control means comprises means responsive to said path setup message for reading said memory means to determine when the output port of said first input/output port pair is connected to the input port of a third input/
output port pair during said defined time slot and for writing into said memory means information defining a pattern of connections which does not connect the output port of said third input/output port pair to the input port of said first input/output port pair during said defined time slot.
output port pair during said defined time slot and for writing into said memory means information defining a pattern of connections which does not connect the output port of said third input/output port pair to the input port of said first input/output port pair during said defined time slot.
4. The combination in accordance with claim 2 wherein said time-shared space division switch comprises a plurality of multiplexers equal in number to the number of output ports, each of said multiplexers having a plurality of input terminals and one output terminal;
means for connecting each of said input ports to one input terminal of each of said multiplexers;
means for connecting each of said output ports to a unique one of said output terminals; and wherein said memory means comprises a plurality of storage locations, a predetermined number of which are associated with each output port, each storage location defining the input port connected to the associated output port during one time slot.
means for connecting each of said input ports to one input terminal of each of said multiplexers;
means for connecting each of said output ports to a unique one of said output terminals; and wherein said memory means comprises a plurality of storage locations, a predetermined number of which are associated with each output port, each storage location defining the input port connected to the associated output port during one time slot.
5. The combination in accordance with claim 4 wherein the information stored in the storage location associated with the output port of said first input/output port pair for the defined time slot identifies the input port of a third input/output port pair; and said control means comprises means responsive to said path setup message for reading the information stored in the storage location associated with the output port of said first input/output port pair for said defined time slot and means, responsive to the identity of said input port of said third input/output port pair read by said means for reading, for writing into the storage location associated with the output port of said third input/output port pair information which does not define the input port of said first input/output port pair.
6. The combination in accordance with claim 5 wherein said connection control means comprises means for generating a sequence of time-slot count signals at the rate of one time-slot count signal per time slot, each time-slot count signal defining one time slot;
means operative during each time slot for reading from said memory means information defining the input ports connected to all of said output ports for the time slot currently defined by said time-slot count signals; and means for transmitting signals defining the input port connected to each of said output ports to the multiplexers associated therewith.
means operative during each time slot for reading from said memory means information defining the input ports connected to all of said output ports for the time slot currently defined by said time-slot count signals; and means for transmitting signals defining the input port connected to each of said output ports to the multiplexers associated therewith.
7. A time division switching system comprising a time-shared space division switch comprising a plurality of input/output port pairs each comprising one input and one output port;
a plurality of time slot interchange means each connected to at least one of said input/output port pairs;
memory means for storing information defining a plurality of patterns of connections between said input ports and said output ports each pattern of connections being associated with one of a plurality of time slots;
connection control means for periodically reading a pattern of connections from said memory means and for connecting said input and said output ports in accordance with the pattern of connections so read;
means for generating a path setup message requesting a connection between a first input/output port pair and a second input/output port pair during a defined time slot; and control means responsive to said path setup messages for writing into said memory means information defining a pattern of connections in which no output port is connected to the input ports of said first and said second input/output port pairs during said defined time slot and then for writing into said memory means information defining a pattern of connections in which the input port of said first input/output port pair is connected to the output port of said second input/output port pair during said defined time slot and in which the input port of said second input/output port pair is connected to the output port of said first input/output port pair during said defined time slot.
a plurality of time slot interchange means each connected to at least one of said input/output port pairs;
memory means for storing information defining a plurality of patterns of connections between said input ports and said output ports each pattern of connections being associated with one of a plurality of time slots;
connection control means for periodically reading a pattern of connections from said memory means and for connecting said input and said output ports in accordance with the pattern of connections so read;
means for generating a path setup message requesting a connection between a first input/output port pair and a second input/output port pair during a defined time slot; and control means responsive to said path setup messages for writing into said memory means information defining a pattern of connections in which no output port is connected to the input ports of said first and said second input/output port pairs during said defined time slot and then for writing into said memory means information defining a pattern of connections in which the input port of said first input/output port pair is connected to the output port of said second input/output port pair during said defined time slot and in which the input port of said second input/output port pair is connected to the output port of said first input/output port pair during said defined time slot.
8. The time division switching system in accordance with claim 7 wherein said memory means stores information defining the input port connected to each output port during each time slot; and said control means comprises means responsive to said path setup message for reading said memory means to determine when the output port of said first input/output port pair is connected to the input port of a third input/output port pair during said defined time slot and for writing into said memory means information defining a pattern of connections which does not connect the output port of said third input/output port pair to the input port of said first input/output port pair during said defined time slot.
9. The time division switching system in accordance with claim 7 wherein said time-shared space division switch comprises a plurality of multiplexers equal in number to the number of output ports, each of said multiplexers having a plurality of input terminals and one output terminal;
means for connecting each of said input ports to one input terminal of each of said multiplexers;
means for connecting each of said output ports to a unique one of said output terminals; and wherein said memory means comprises a plurality of storage locations, a predetermined number of which are associated with each output port, each storage location defining the input port connected to the associated output port during one time slot.
means for connecting each of said input ports to one input terminal of each of said multiplexers;
means for connecting each of said output ports to a unique one of said output terminals; and wherein said memory means comprises a plurality of storage locations, a predetermined number of which are associated with each output port, each storage location defining the input port connected to the associated output port during one time slot.
10. The time division switching system in accordance with claim 9 wherein the information stored in the storage location associated with the output port of said first input/output port pair for the defined time slot identifies the input port of a third input/output port pair; and said control means comprises means responsive to said path setup message for reading the information stored in the storage location associated with the output port of said first input/output port pair for said defined time slot and means, responsive to the identity of said input port of said third input/output port pair read by said means for reading, for writing into the storage location associated with the output port of said third input/output port pair information which does not define the input port of said first input/output port pair.
11. The time division switching system in accordance with claim 10 wherein said connection control means comprises means for generating a sequence of time-slot count signals at the rate of one time-slot count signal per time slot, each time-slot count signal defining one time slot;
means operative during each time slot for reading from said memory means information defining the input ports connected to all of said output ports for the time slot currently defined by said time-slot count signals; and means for transmitting signals defining the input port connected to each of said output ports to the multiplexers associated therewith.
means operative during each time slot for reading from said memory means information defining the input ports connected to all of said output ports for the time slot currently defined by said time-slot count signals; and means for transmitting signals defining the input port connected to each of said output ports to the multiplexers associated therewith.
12. The method of controlling connections between the input and output ports of a switch arrangement in time slots of fixed duration comprising the steps of storing in a memory arrangement information defining patterns of connections between said input and output ports;
periodically reading information from said memory arrangement and connecting said intput ports and said output ports in the pattern defined by the information so read;
generating a path setup message defining one input port, one output port, and a time slot;
writing into said memory arrangement information defining a pattern of connections in which the input port defined by said path setup message is not connected to any output port during the time slot defined by said path setup message; and after the performance of the preceding writing step writing into said memory arrangement information defining a pattern of connections in which the input and output ports defined by said path setup message are connected during the time slot defined by said path setup message.
periodically reading information from said memory arrangement and connecting said intput ports and said output ports in the pattern defined by the information so read;
generating a path setup message defining one input port, one output port, and a time slot;
writing into said memory arrangement information defining a pattern of connections in which the input port defined by said path setup message is not connected to any output port during the time slot defined by said path setup message; and after the performance of the preceding writing step writing into said memory arrangement information defining a pattern of connections in which the input and output ports defined by said path setup message are connected during the time slot defined by said path setup message.
13. In a time division switching system comprising a time-shared space division switch having a plurality of input/output port pairs each input/output port pair comprising one input and one output port, the method comprising the steps of storing in a memory arrangement information defining a plurality of patterns of connections between said input and said output ports, each pattern of connections being associated with one of a plurality of time slots;
periodically reading a pattern of connections from said memory arrangement and connecting said input ports and said output ports in the pattern of connections defined by the information so read;
generating a path setup message requesting a connection between a first input/output port pair and a second input/output port pair during a defined time slot;
writing into said memory arrangement information defining a pattern of connections in which no output port is connected to the input ports of said first and said second input/output port pairs during the time slot defined by said path setup message; and after the performance of the preceding writing step writing into said memory arrangement information defining a pattern of connections in which the input port of said first input/output port pair is connected to the output port of said second input/output port during the time slot defined by said path setup message and in which the input port of said second input/output port pair is connected to the output port of said first input/output port pair during said defined time slot.
periodically reading a pattern of connections from said memory arrangement and connecting said input ports and said output ports in the pattern of connections defined by the information so read;
generating a path setup message requesting a connection between a first input/output port pair and a second input/output port pair during a defined time slot;
writing into said memory arrangement information defining a pattern of connections in which no output port is connected to the input ports of said first and said second input/output port pairs during the time slot defined by said path setup message; and after the performance of the preceding writing step writing into said memory arrangement information defining a pattern of connections in which the input port of said first input/output port pair is connected to the output port of said second input/output port during the time slot defined by said path setup message and in which the input port of said second input/output port pair is connected to the output port of said first input/output port pair during said defined time slot.
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US06/641,449 US4621357A (en) | 1984-08-16 | 1984-08-16 | Time division switching system control arrangement and method |
| US641,449 | 1996-04-30 |
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| US4792948A (en) * | 1985-08-08 | 1988-12-20 | Data General Corporation | Distributed switching architecture |
| CA1254981A (en) * | 1986-02-18 | 1989-05-30 | Lester Kirkland | Communications switching system |
| DE3772311D1 (en) * | 1986-09-29 | 1991-09-26 | Siemens Ag | METHOD FOR OPERATING INTERFACE CIRCUITS BETWEEN A CENTRAL PART AND DECENTRAL PARTS OF A SUBSCRIBER CONNECTION ASSEMBLY OF A DIGITAL TIME-MULTIPLEX TELECOMMUNICATION NETWORK. |
| US4866708A (en) * | 1987-10-28 | 1989-09-12 | American Telephone And Telegraph Company, At&T Bell Laboratories | Communication channel ownership arrangement |
| US4805166A (en) * | 1987-10-28 | 1989-02-14 | American Telephone And Telegraph Company, At&T Bell Laboratories | Switch path reservation arrangement |
| US4882699A (en) * | 1988-09-19 | 1989-11-21 | International Business Machines Corp. | Communications network routing and management system |
| US4993016A (en) * | 1989-05-08 | 1991-02-12 | At&T Bell Laboratories | Network control arrangement for processing a plurality of connection requests |
| US4991168A (en) * | 1989-05-08 | 1991-02-05 | At&T Bell Laboratories | Concurrent multi-stage network control arrangement |
| US5115425A (en) * | 1990-05-31 | 1992-05-19 | At&T Bell Laboratories | Switching system reliability |
| US5119366A (en) * | 1990-12-14 | 1992-06-02 | At&T Bell Laboratories | Call processing method for distributed switching |
| EP0507452B1 (en) * | 1991-03-06 | 1999-06-02 | Fujitsu Limited | Fault tolerant communication control processor |
| JPH05252228A (en) * | 1992-03-02 | 1993-09-28 | Mitsubishi Electric Corp | Data transmitter and its communication line management method |
| EP0622927B1 (en) * | 1993-03-04 | 1997-06-04 | Mitsubishi Denki Kabushiki Kaisha | Data transmission apparatus and a communication path management method therefor |
| CA2128835C (en) * | 1993-08-03 | 1999-04-06 | Daniel F. Daly | Modular digital recording logger |
| JPH0758718A (en) * | 1993-08-17 | 1995-03-03 | Fujitsu Ltd | Line setting device for maintenance-dedicated leased line of signal transmission equipment |
| JPH0787046A (en) * | 1993-09-16 | 1995-03-31 | Fujitsu Ltd | Line setting phase adjustment device for synchronous multiplex communication |
| US5521912A (en) * | 1994-12-20 | 1996-05-28 | At&T Corp. | Time slot shifter enhances data concentration |
| US5862136A (en) * | 1995-07-07 | 1999-01-19 | Northern Telecom Limited | Telecommunications apparatus and method |
| US5936942A (en) * | 1996-08-29 | 1999-08-10 | Lucent Technologies Inc. | Communication of alarm information within a telecommunication switching system |
| US6775372B1 (en) | 1999-06-02 | 2004-08-10 | Dictaphone Corporation | System and method for multi-stage data logging |
| US6252946B1 (en) * | 1999-06-08 | 2001-06-26 | David A. Glowny | System and method for integrating call record information |
| US6252947B1 (en) * | 1999-06-08 | 2001-06-26 | David A. Diamond | System and method for data recording and playback |
| US6246752B1 (en) * | 1999-06-08 | 2001-06-12 | Valerie Bscheider | System and method for data recording |
| US6249570B1 (en) * | 1999-06-08 | 2001-06-19 | David A. Glowny | System and method for recording and storing telephone call information |
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| US6869644B2 (en) * | 2000-10-24 | 2005-03-22 | Ppg Industries Ohio, Inc. | Method of making coated articles and coated articles made thereby |
| US20020141386A1 (en) * | 2001-03-29 | 2002-10-03 | Minert Brian D. | System, apparatus and method for voice over internet protocol telephone calling using enhanced signaling packets and localized time slot interchanging |
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| BE791282A (en) * | 1971-11-13 | 1973-05-14 | Int Standard Electric Corp | CONTROL METHOD FOR CENTRAL-CONTROLLED TEMPORAL TELECOMMUNICATION SYSTEM |
| US4038497A (en) * | 1975-05-12 | 1977-07-26 | Collins Arthur A | Hardwired marker for time folded tst switch with distributed control logic and automatic path finding, set up and release |
| GB1567477A (en) * | 1976-10-01 | 1980-05-14 | Danray Inc | Digital switching for telephone communication systems |
| US4296492A (en) * | 1979-12-26 | 1981-10-20 | Bell Telephone Laboratories, Incorporated | Continuity verification arrangement |
| FR2513470B1 (en) * | 1981-09-18 | 1986-02-21 | Cit Alcatel | GROUP OF TERMINAL UNITS FOR DIGITAL AUTOMATIC SWITCHES |
| US4484323A (en) * | 1982-06-14 | 1984-11-20 | At&T Bell Laboratories | Communication arrangements for distributed control systems |
| EP0115486A1 (en) * | 1982-07-29 | 1984-08-15 | Western Electric Company, Incorporated | Time multiplex switch for time division switching systems |
| GB2125254B (en) * | 1982-07-30 | 1985-10-23 | Plessey Company The | Telecommunications digital switchblock |
| US4484324A (en) * | 1982-08-23 | 1984-11-20 | At&T Bell Laboratories | Control information communication arrangement for a time division switching system |
| US4520477A (en) * | 1983-06-27 | 1985-05-28 | At&T Bell Laboratories | Control information communication arrangement for a time division switching system |
| US4543651A (en) * | 1983-09-12 | 1985-09-24 | At&T Bell Laboratories | Duplicated time division switching system |
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1984
- 1984-08-16 US US06/641,449 patent/US4621357A/en not_active Expired - Lifetime
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1985
- 1985-06-25 JP JP60503146A patent/JP2582749B2/en not_active Expired - Lifetime
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- 1985-06-25 WO PCT/US1985/001218 patent/WO1986001361A1/en active IP Right Grant
- 1985-06-25 DE DE8585903559T patent/DE3577963D1/en not_active Expired - Fee Related
- 1985-07-30 CA CA000487802A patent/CA1237188A/en not_active Expired
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1986
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| WO1986001361A1 (en) | 1986-02-27 |
| JP2582749B2 (en) | 1997-02-19 |
| JPS61503068A (en) | 1986-12-25 |
| KR920010220B1 (en) | 1992-11-21 |
| EP0190198A1 (en) | 1986-08-13 |
| DE3577963D1 (en) | 1990-06-28 |
| EP0190198B1 (en) | 1990-05-23 |
| KR870700256A (en) | 1987-05-30 |
| US4621357A (en) | 1986-11-04 |
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