Carrier concentrator system and method
D United States Patent 3,876,838  
 Boxall Apr. 8, 1975 CARRIER CONCENTRATOR SYSTEM AND tal transmission facility having a predetermined bit METHOD rate capacity. The system comprises a central office control terminal, one or more remote terminals and an [75] Inventor&#34; Frank Boxan woodslde Cahf&#39; interconnecting digital transmission facility. The sub- [73] Assignee: Vidar Corporation, Mountain View, scribers are connected to the remove terminals by Calif. wire pairs. The control terminal interfaces with the [22] Filed Oct 26 973 central office switching machine and provides a line appearance for each subscriber connected to the re- [21] Appl. No.: 410,205 mote terminal and controls the assignment of transmission channels tO active subscribers. The system in- [52] U S Cl 179/15 179/15 179/15 Bv cludes a full access non-blocking concentration [51] hit Cl &#34;Mi 3/16 switching subsystem. The system provides for a nor- [58] Fie&#39;ld 5 EV mal mode of OperatIon where a fixed number of transl79/l 5 15 mission channels are available for assIgnment to actIve subscribers. In this mode the transmission channels operate at a fixed bit rate. When all transmission [56] References Cited channels have been assigned to subscribers, the system UNITED STATES PATENTS operates in an elastic mode which adds or deletes ad- 3,529,089 9/!970 Davis l79/l5 AL X ditional transmission channels as required by the sub- 3.59l 722 7/l97l PZIlSfl l79/l5 BA scriber traffic AS transmission hannels are added or 3.804.990 4/1974 Costa l79/l5 BW X deleted While in the elastic mode the bit rate f a Primary E.\&#39;aminerRalph D. Blakeslee [5 7] ABSTRACT A carrier telephone system useful in serving a large number of subscribers by delta modulation over a digi- CENTRAL OFFICE transmission channels changes accordingly. The carrier concentrator system and method is also useful in providing interoffice telephone trunks between a hub central office and one or more tributary offices.  
 47 Claims, 24 Drawing Figures SWITCHING MACHING SUB I SUB 64 SUB 65 SUB I28 SUB I29 SUB I92 SUB I93 SUB 256 SUB I SUB 256 3 Lu I Lu 256 Lu I Lu 64 Lu6 Lu I28 Lu I92 Lu 256 T T Lu I29 Lu I93 l4 I6 I30 13b (I30 l3d CONTROL REMOTE l9 REMOTE, REMOTE i6 I} l w REMOTE TERMI R l&#34; NAL l9 TERMINAL I6 TERMINAL &#39;9 TERMINAL 9 TERMINAL 17 21 l? ZI l7 sum cm 18 NOT (R65-|28,c)  
 INPUT BI CLOCK K 57v EXTRACTION Q5 93 SCAN m SCAN m 2 L66 6 66 m i i LL] E I I I I g I I 2% a: 5 I o m g E1 Lu (1) g E I k LL ISCAN l 8| SUB|28 O X i g A Z-WIRE E L126 2 3 C|28 sus ggglaER w 82 *3 LLI 9s 2 T w 2 w LO lD 99 Z IN? g S 83 Q I O 8 I: g 5;. 3 UJ 4 OCLE E I k O J; C r r TRAFFIC CHANGE 8 INPUTS LOGIC 6 LINE COUNTER PATENTED APR 8 i975 &#34;87 3838; SHEET C&#39;ZBF 18 q T L. 5 LO 0 I37 &#39;8&#39; o 2 2| 2)- I BLOCK 8 S-CODE I47 I FE g DETECTOR f 8 i S CHANGE g 83 g 0 C-CODE E C CLOCK REGISTER INPUT T T l INPUTS JAM 92/ LINE COUNTER CLOCK ml CLEAR 9| INPUTS 5 DECODER 3 OUTPUTS s 0) LI L256 NOTE M INPUTS (DOTTED) ARE FROM REFRAME LOGIC 1 CLOCK (3&#39; PULSE) OUTPUT l CLOCK (CPULSE) 242 F/G. 23 b BRE? )RHE EXPANSION BREAK HERE FOR EXPANSION CARRIER CONCENTRATOR SYSTEM AN METHOD BACKGROUND OF THE INVENTION This invention relates generally to a digital time division multi-channel carrier system employing concentration switching and more particularly to a carrier system having full access, non-blocking concentration switching in which the number of transmission channels is adjustable to meet traffic demand and as the number of transmission channels changes, their bit rate varies in accordance with the number of active sources. The system is particularly adaptable to subscriber carrier applications.  
  Digital time division multiplex communication systems for transmitting information from a plurality of sources from one location over a digital transmission medium to another location have included a dedicated transmission channel for each of the information sources. Each of the transmission channels serves to carry digital information representative of the information to be transmitted. In such systems the channels are arranged in groups or frames with each channel occupying a time slot in a frame. One or more additional time slots may be provided to carry framing and control information.  
  The number of channels which can be accommodated in any digital transmission medium is determined by the bit rate capacity of the transmission medium and the channel bit rate required to obtain the desired transmission quality. Thus, with dedicated channels, the number of information sources which can be accommodated is limited to the number of transmission channels. To overcome this limitation, so-called concentration type communication systems have been developed. In such systems, the number of information sources which can be accommodated exceeds the number of transmission channels available. Control means assign the transmission channels to the information sources on demand. When all available transmission channels are in use, the system cannot accommodate additional information sources and additional service requests are denied.  
  Below this ultimate limit, there may be a traffic restriction due to the characteristics of the concentrator switch. Unless the switch is non-blocking, it may be impossible for a requesting information source to access an avilable transmission channel because of congestion within the switch due to existing traffic. Thus, the ultimate traffic capacity is achieved only when the concentration switch is a non-blocking switch, which permits any requesting information source to access any available transmission channel, regardless of the existing traffic pattern.  
  Digital time division multiplex communication systems have been widely applied in the telephone industry for transmitting messages from one location to another. One particular application of such systems has been in rural subscriber carrier systems where a central office serves a large number of rural subscribers. Originally wire pairs connected the central office to each of the subscribers. However, when distances became sufficiently long to make the cost of wires uneconomical, multi-channel digital message transmission systems were employed. The early systems used one transmission channel dedicated to each subscriber whereby the number of subscribers were limited by the fixed bit rate rate. More modern systems economize by concentrator switching which serves a large number of subscriber channels on a smaller number of transmission channels. Such systems have a fixed number of transmission channels and can only accept traffic up to the system limit and then deny service to additional subscribers. If the concentration switch is not of the non-blocking type, the traffic capacity of the systems is less than the ultimate capacity determined by the total number of transmission channels.  
 OBJECTS AND SUMMARY OF THE INVENTION It is a general object of the present invention to provide an improved digital time division multiplex information transmission system.  
  It is another object of the present invention to provide an improved delta modulation multi-channel carrier system.  
  It is a further object of the present invention to provide a carrier system which automatically adds and subtracts transmission channels responsive to service requests whereby the number of active transmission channels corresponds to the number of active sources.  
  It is a further object of the present invention to provide a digital time division multiplex subscriber carrier system which operates over a transmission medium having a fixed bit rate in which the system automatically adds and subtracts transmission channels responsive to service requests by subscribers so that the number of transmission channels corresponds to the number of active subscribers and the bit rate and quality for each transmission channel varies with the number of active subscribers.  
  It is still another object of the present invention to provide an improved full access, non-blocking concentration switching system.  
  It is still a further object of the present invention to provide a delta modulation multi-channel subscriber carrier system in which a large number of subscribers are served over a transmission medium having a fixed bit rate byconcentrating a large number of subscriber channels into a smaller number of transmission channels transmitting at bit rates corresponding to the number of active subscribers.  
  The foregoing and other objects of the invention are achieved by a carrier system providing time division multiplex transmission between a control terminal connected to the central office and one or more remote terminals. The system includes means for scanning the status of the source lines at the remote terminals and the line appearances at the central office to determine when a source has become active or idle, and then automatically adding or deleting a transmission channel to accommodate the change in active sources. The carrier system is particularly useful where the sources are subscribers but is also useful where the sources are interoffice trunks.  
 BRIEF DESCRIPTION OF THE DRAWINGS FIG. .1 is a schematic block diagram showing a subscriber carrier system incorporating the invention.  
 FIG. 2 illustrates a typical message frame.  
 FIG. 3 is a diagram of a remote terminal line unit.  
 FIG. 4 is a diagram of a control terminal line unit.  
 FIG. 5 is a block diagram of the control terminal.