System and method for a multi-host subscriber loop

[0002] This application is a continuation of U.S. application Ser. No. 08/652,157 filed May 23, 1996, now U.S. Pat. No. 5,881,059.

[0003] This invention is related in general to the field of telecommunications systems. More particularly, the invention is related to a system and method for a multi-host subscriber loop.

[0004] Telecommunications networks have traditionally provided subscriber services by connecting them to the nearest telephone office with copper wires. Each subscriber was allocated the number of wires necessary for the type of service. The assignment of wires was dedicated to each subscriber. For example, a plain old telephone service (POTS) subscriber typically required one pair of copper wires for each telephone number.

[0005] As technology advanced, it was possible to digitally multiplex and concentrate more subscribers on a less number of copper wires. A typical example is the Digital Loop Carrier (DLC) as described in a Bellcore document TR-TSY-0008. In DLC, the telecommunications network provide service to subscribers through the support of remote subscriber terminals connected to central office terminals. The DLC technology allows a single remote terminal to be connected to a single central terminal. These remote subscriber terminals connect directly to the subscribers premise providing such services as POTS, coin, ISDN, and Wideband. The central office terminals provide connections to the local exchange switch and thus the rest of the telecommunications network. In DLC, a fixed traffic concentration not exceeding 2:1 was possible between the single central office terminal and single remote terminal.

[0006] Further technical advances have allowed multiple remote terminals to be connected to a single central terminal as in Optical Line Terminal to Optical Network Unit (OLT-ONU) configurations where a single OLT supports multiple ONUs). This is typically configured in a cascaded or dual cascaded configuration emanating from the central office terminal. For both the DLC and OLT-ONU configurations, a standard line interface is used to connect the remote terminals to their central office terminal. The control of the central office terminal and the remote terminal(s) connection is also not transparent to the network facility connecting them. Further, these configurations are disadvantageously limited to the size of the terminals and the capacity of the line connecting the terminals.

[0007] Accordingly, there is a need for multiple central office terminals to be able to be connected to multiple remote terminals to increase utilization across the network facility for concentrated traffic, whether the network facility be a copper, optical, or wireless connection.

[0008] In accordance with the present invention, a multi-host subscriber loop is provided which eliminates or substantially reduces the disadvantages associated with prior subscriber loop configurations.

[0009] In one aspect of the invention, the multi-host subscriber loop includes N central office terminals coupled to a local exchange, where one of the N central office terminals is directly coupled to all other central office terminals. M remote terminals are coupled to a plurality of telephone service subscribers. A single network facility is coupled between the M remote terminals and N central office terminals. The subscriber traffic, control information and associated signaling are concentrated onto the single network facility.

[0010] In another aspect of the invention, messages are transmitted between the remote terminals and central office terminals through the network facility. The message structure includes a plurality of time slots, where each remote terminal is assigned a predetermined number of time slots.

[0011] In yet another aspect of the invention, the time slots assigned to each remote terminal include one time slot for control, and remaining time slots being allocated to subscriber traffic.

[0012] In yet another aspect of the invention, the time slots assigned to each remote terminal include one time slot for control, one time slot for signaling, and remaining time slots being allocated to subscriber traffic.

[0013] In yet another aspect of the invention, the time slots assigned to each remote terminal are dynamically assigned to the subscribers on a per call basis depending on subscriber line conditions.

[0014] In yet another aspect of the invention, subscriber traffic bandwidth is not limited to a single time slot per subscriber. Subscriber traffic may use as many time slots as are available or necessary to accommodate the offered service, including wideband traffic.

[0015] A technical advantage of the present invention is the enhanced utilization of the network facility by concentrating subscriber traffic. Further, the control of multiple central office terminals connected to the remote terminals is advantageously transparent to the underlying network facility. The assignment of time slots to a particular subscriber may also be done dynamically on a per call basis depending on subscriber line condition. A further technical advantage is the enhancement of supported subscriber services to include wideband terminations and dynamic assignment of multiple time slots to support enhanced subscriber services.

[0016] For a better understanding of the present invention, reference may be made to the accompanying drawings, in which:

[0017] FIG. 1 is a simplified block diagram of a system for a multi-host subscriber loop constructed in according to the teachings of the present invention;

[0018] FIGS. 2A and 2B are exemplary mappings of remote terminal subscriber traffic onto one 2 Mb network facility;

[0019] FIG. 3 is a simplified block diagram of an embodiment of a multi-host subscriber loop using a radio transport connection between central office terminals and remote terminals;

[0020] FIG. 4 is an exemplary block diagram and mapping scheme for a multi-host subscriber loop using a radio transport connection between central office terminals and remote terminals; and

[0021] FIG. 5 is a block diagram of an embodiment of a multi-host subscriber loop using a radio transport connection between three central office terminals interconnected as described above and three remote terminals also interconnected in the same manner as the central office terminals.

[0022] The preferred embodiment(s) of the present invention is (are) illustrated in FIGS. 1-5, like reference numerals being used to refer to like and corresponding parts of the various drawings.

[0023] Referring to FIG. 1, a multi-host subscriber loop system is shown, indicated generally at 10. Multi-host subscriber loop system 10 includes a central office 12 and a subscriber location 14 linked via a transport network 16. Central office 12 includes a local exchange 20 connected to a plurality of central office terminals COT_1−n22-26 via a plurality of lines 28. In domestic telephony applications, lines 28 may be 1.5 Mb lines. In international telephony applications, lines 28 may be 2 Mb lines as specified by the General aspects of Digital Transmission Systems; Terminal Equipmentsset forth by the International Telecommunication Union CCITT G.703 Physical/Electrical Characteristics of Hierarchical Digital Interfacesand G.704 Synchronous Frame Structures Used at Primary and Secondary Hierarchical Levels.

[0024] The central office terminals COT_1−n22-26 are also interconnected, where COT₁22 is directly coupled to each of the other central office terminals COT_2−n24 and 26 via lines or an internal bus 30. Lines 30 may be 2 Mb lines carrying control, signaling and subscriber traffic in a proprietary format. Central office terminals 22-26 may also be coupled directly to subscriber(s) to terminate subscriber lines. Central office terminals COT_1−n22-26 may be implemented by the Litespan-120™ manufactured by DSC Communications Corporation. Litespan-120™ is a small digital loop carrier system that provides either switch or subscriber interfaces for supporting subscriber POTS (RPOTS), VF switch interfaces (CPOTS), and 2 Mb interfaces (E1). COT₁22 is further coupled to transport network 16 and subscriber location 14 via a single 2 Mb line network facility 32. For domestic applications, network facility may be a 1.5 Mb line. The protocol of transmission on network facility 32 is described in detail below with references to FIGS. 2A and 2B. Transport network 16 is a communications link between central office location 12 and subscriber location 14 for transmission of voice, data, signaling and control information therebetween, and may be implemented by wireless, optical, or electrical transmission.

[0025] Remote terminals RT_1−m40-46 at subscriber location 14 are each preferably coupled to transport network 16 via a 2 Mb line or internal bus 50. Remote terminals RT_1−m40-46 may also be implemented with the Litespan-120™. There need not be a one-to-one correspondence between central office terminals COT_1−n22-26 and remote terminals RT_1−m40-46, and multiple central office terminals may be connected to multiple remote terminals, unlike the SLC-96 and SLC-Series 5 subscriber loop carrier systems of AT&T Bell Laboratories. Each remote terminal RT_1−m40-46 is coupled to a predetermined number of subscribers via a line 52, providing a variety of services ranging from POTS (plain old telephone service), pay phone, ISDN, wideband, etc. Accordingly, subscriber bandwidth traffic is not limited to a single time slot per subscriber.

[0026] It is further contemplated and shown in FIG. 1 that COT₁22 may also be coupled to one or more additional subscriber loops similarly constructed as transport network 16 and subscriber location 14 as described above. Furthermore, it also possible to have a single point-to-point configuration between one of the central office terminals and one of the remote terminals.

[0027] Referring to FIG. 2A, a concentrated 2 Mb frame with bearer channel, signaling, and control information mapping between the remote terminals and central office terminals is shown. According to ITU G.703 and 704, a 2 Mb network facility is to be used between the central office terminal and the remote terminal, where time slot 0 is devoted to synchronization information, and time slot 16 is devoted to common channel or channel associated signaling. The rest of the time slots may be used to carry subscriber data or bearer channels. In an embodiment of the present invention, multiple control, signaling, and bearer channels for multiple remote terminals are concentrated and mapped onto a single 2 Mb network facility 60 in a Terminal Payload Envelope (TPE) 64-68. Terminal Payload Envelope 64-68 is a general structure that may be transported across time slot structured telephone facilities. In one embodiment of the present invention as shown in FIG. 2A, the use of time slot 0 remains the same as specified in ITU G.704, and all signaling, such as channel associated signaling, for the bearer channels is carried in time slot 16. However, the remaining time slots are allocated to three remote terminals RT_1-3, for example. The maximum number of bearer channels that can be carried in the concentrated network facility is based on the grade of service of a specified number of subscribers. For example, for remote terminal RT₁, there are twenty subscribers mapped onto nine time slots (TS1-TS9); for RT₂, 28 subscribers are mapped onto six time slots (TS12-TS15, TS17-TS18); and for RT₃, 40 subscribers are mapped onto twelve time slots (TS19-TS29 and TS31). The time slots assigned to each remote terminal are dynamically allocated to the subscribers on a per call basis depending on subscriber line condition.

[0028] Note that the control information for each remote terminal may be mapped onto any time slot within the time slots allocated for the remote terminal. Alternatively, certain time slots may be designated to carry control information for a certain number of remote terminals. For example, time slots 10, 20, and 30 may be designated to carry control information if system 10 includes three remote terminals.

[0029] Referring to FIG. 2B, an alternate embodiment of concentration and mapping of remote terminal bearer channel is shown. In this mapping scheme, TS16 is used for bearer channel data, and control and signaling associated with each remote terminal are carried in two time slots allocated to each remote terminal. For example, for RT₁, TS1-TS8 are allocated for bearer channels and TS9 and TS10 are allocated for control and signaling, respectively. Similarly for RT₂, TS11-TS16 are allocated for bearer channels, and TS17 and TS18 are allocated for control and signaling, respectively. For RT₃, TS19-TS29 are allocated for bearer channels, and TS30 and TS31 are allocated for control and signaling, respectively. In this exemplary concentration and mapping scheme, the control and signaling are carried in the last two time slots allocated to each remote terminal. Alternatively, the control and signaling information may be allocated to the first two time slots, or any two time slots therein.

[0030] Although not shown, the present multi-host subscriber loop is also applicable to other subscriber loop standards, such as the 1.5 Mb subscriber loop more commonly used in the United States. In the 1.5 Mb format, each frame has twenty-four time slots including one framing bit, the 193rd bit. The twenty-four time slots may be similarly allocated to transmit Terminal Payload Envelope 64-68 as described above. In this concentration and mapping scheme, the framing 193rd bit is not required for COT/RT control or to synchronize the subscriber signal state as the signaling can be carried in its own time slot. This allows the subscriber channel use of the full 64 Kbs per assigned time slot.

[0031] Referring to FIG. 3, a multi-host subscriber loop system 70 having a central office location 72 coupled to a subscriber location 74 with a wireless transport network 76 implementation of a transport network 16 in FIG. 1 is shown. At central office location 72, a plurality of central office terminals COT_1−n78 are coupled to a local exchange 79 by lines 80. Central office terminals 78 are connected, where COT₁is directly coupled to all other central office terminals COT_2−nvia lines 82. COT₁is also linked to network transport 76 via a 2 Mb line having the concentration and mapping set forth in FIGS. 2A and 2B and described above.

[0032] An exemplary transport network 76 as shown in FIG. 3 employs a wireless technology for transmitting traffic, control, and signaling information between central office location 72 and subscriber location 74. Transport network 76 includes a modem and RF radio 86 using spread spectrum code division multiple access (SS-CDMA) technology for transmitting data over the air to a plurality of subscriber terminals (ST) 90 at subscriber locations 74. Multiple subscriber terminals 92-96 may be coupled to each remote terminal 100-104, which depends on the concentration level of the subscriber traffic onto the radio link. Subscriber terminals 92-96 are coupled to respective remote terminals 100-104 via 2 Mb proprietary lines 106, with each line carrying Terminal Payload Envelopes 64-68.

[0033] FIG. 4 shows additional details. In the exemplary configuration shown in FIG. 4, three central office terminals COT_1-3110-114 are coupled to three remote terminals RT_1-3100-104 through a wireless transmission medium 76. Central office terminal COT₁110 includes three 2 Mb/s interfaces 120-124 to modem and RF radio 86, COT₂112, and COT₃114, respectively. Similarly, COT₂112 and COT₃114 each includes a 2 Mb/s interface 126 and 128 for interfacing with COT₁110.

[0034] In operation, 2 Mb span 84 connected between radio and modem 86 and COT₁110 has an exemplary concentrated format shown as E1_CT140 in FIG. 4, and as shown in FIGS. 2A and 2B as Terminal Payload Envelope 64-68. COT₁receives subscriber traffic, control, and signaling information from radio and modem 86, which is in the concentrated format, removes information associated with RT₁, and passes on information associated with RT₂to COT₂and information associated with RT₃to COT₃. If time slot 16 is used for signaling, COT₁may process the received Terminal Payload Envelope to the extent that it becomes deframed and synchronized to all other subscriber signaling. If time slot 16 is not used for signaling, COT₁does not process RT₂and RT₃bearer, signaling, and control channels in anyway, but merely passes on the information to the destination central office terminal. Upon receipt of the concentrated message, COT_1-3then looks for control, signaling channels in the predetermined time slots, and bearer channels in the remaining time slots, and process the information and data accordingly.

[0035] At the subscriber side, the exemplary configuration in FIG. 4 shows E1_CTis received by subscriber terminals 130-134 and the appropriate Terminal Payload Envelopes are separated and received by the respective remote terminals as one E1_CSand multiple E1_ST. Four subscriber terminals can support two bearer channels and their associated signaling, or bearer information only, an exemplary format of which is shown as E1_ST142. Alternatively, E1_ST142 may carry only bearer channels. Subscriber terminal 134 is designated as the control link carrier for carrying one bearer channel and the associated signaling and a control channel, an exemplary format of which shown as E1_CS144. Alternatively, E1_CSmay carry only control information or control and signaling only. For both E1_STand E1_CSthe exemplary format uses TS1 for a subscriber channel and TS2 as either the second bearer channel or the control channel. The associated signaling may be carried in TS16 of E1_STand/or E1_CS. The remaining time slots are unused. The concentrated messages E1_CSand E1_STare used to help set up the call path through the wireless transmission medium in transport network 76. In the exemplary configuration shown, nine bearer channels are carried by five subscriber terminals 90, all of which are coupled to RT₁. In the instance where subscriber terminal 134 fails, the E1_CScarrying the control channel is routed to another subscriber terminal to minimize the number of out-of-service subscribers on RT₁. Accordingly, an E1_CTis composed of a plurality of Terminal Payload Envelopes 64-68, with each Terminal Payload Envelope consisting of one E1_CSand one or more E1_STat remote terminal 74.

[0036] Because the control and signaling channels may occupy any time slot in the 2 Mb signal transmitted between central office terminals and remote terminals, both terminals are provisioned in advance during system initialization as to the location of control and signaling channels, the number of bearer channels, and the allocation of time slots. Dynamic reassignment of control and signaling channels during remote terminal failure conditions as described above are also established. Furthermore, the central office terminals and remote terminals support special commands that allow craft or management provisioning of channel allocations. Databases (not shown) may be created to maintain the provisioning information in non-volatile memory. The database stores details of the multi-host subscriber loop configuration including the number of central office terminals located on a given radio link, the number of bearer channels associated with each central office terminals, and the mapping of the 2 Mb format, etc.

[0037] FIG. 5 shows another connection configuration of a multi-host subscriber loop 140 of the present invention. Subscriber loop 140 includes a central office 142 and a subscriber location 144 linked with a wireless network facility. Central office 142 includes a radio 146 coupled to a first central office terminal COT₁148, which is directly coupled to central office terminals COT₂150 and COT₃152. Each of the central office terminals COT_1-3148-152 is then coupled to a local exchange 154.

[0038] Subscriber location 144 also includes a radio 160 in communication with radio 146 of central office 142, and three remote terminals RT_1-3162-166. Remote terminals RT_1-3162-166 are coupled together in a similar manner as central office terminals COT_1-3: RT₁162 is coupled directly to each one of the other remote terminals RT₂and RT₃164 and 166. Accordingly, the E1_CTmessage format shown in FIG. 4 may be used in both the connection between radio 146 and COT₁148 as well as the connection between radio 160 and RT₁162. Further, RT₁162 processes data, control, and signaling associated with its subscribers and passes on information associated with other subscribers to RT₂and RT₃, respectively, in a similar manner as central office terminals COT_1-3using Terminal Payload Envelopes 64-68 shown in FIGS. 2A and 2B.

[0039] It is worthwhile to summarize the distinctive features of the present invention:

[0040] 1. Multiple central office terminals are coupled to multiple remote terminals via a single network facility.

[0041] 2. The number of central office terminals need not equal to the number of remote terminals.

[0042] 3. Transport network 16 may connect the central office terminals to the remote terminals by a wireless, optical, or electrical transmission medium.

[0043] 4. The remote terminal data, control, and signaling may be mapped to the 2 Mb message format in a number of ways, whether using TS16 for signaling or not; similarly the mapping of subscriber traffic, control, and signaling to the 1.5 Mb message format is also flexible.

[0044] 5. The control channels for each remote terminal may be mapped to a fixed location within time slots allocated to a remote terminal, or to any predetermined time slot.

[0045] 6. The time slots assigned to each remote terminal may be dynamically allocated to the subscribers on a per call basis.

[0046] 7. The control and signaling channels of Terminal Payload Envelopes 64-68 may be reassigned when needed for failure conditions.

[0047] 8. Subscriber traffic bandwidth may freely extend across a plurality of possible predetermined available time slots without regard for time slot sequence or quantity.

[0048] 9. Terminal Payload Envelopes 64-68 provide a flexible structure to convey subscriber traffic, signaling, and control between central office terminals and remote terminals without regard of the transport facility format.

[0049] The above list is not intended to be exhaustive, but serves to highlight some of the inventive features of the present invention.

[0050] Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made therein without departing from the spirit and scope of the invention as defined by the appended claims.