WO2002013465A1

WO2002013465A1 - System and method for active-active redundant cable modem service at head end

Info

Publication number: WO2002013465A1
Application number: PCT/US2001/024613
Authority: WO
Inventors: Mitchell H. Auster
Original assignee: Adc Broadband Access Systems, Inc.
Priority date: 2000-08-04
Filing date: 2001-08-06
Publication date: 2002-02-14
Also published as: AU2001281105A1

Abstract

A method and apparatus for providing continuity of service to service multiple domains of subscribers to two-way shared media telecommunications subscribers each domain served with shared upstream channels and having a dedicated service module in its normal state, where failure of one module in a multiple module platform is protected with sharing of the bandwidth of remaining functioning modules.

Description

SYSTEM AND METHOD FOR ACTIVE-ACTIVE REDUNDANT CABLE MODEM

SERVICE AT HEAD END

FIELD OF THE INVENTION

This invention relates generally to the continuous operation of cable modem termination equipment at the head end of a cable modem broadband access system.

BACKGROUND OF THE INVENTION

With the demand for downloading of large pictorial and audio files, including streaming audio and video files, as well as the advent of IP Cable Telephony, broadband access to the Internet, including access by hybrid fiber/coaxial cable (HFC) has increased rapidly. To meet this increasing demand, it is desirable to provide economical head end equipment, including Cable Modem Termination System (CMTS) interfaces, that performs reliably with minimum interruption.

Prior methods of ensuring uninterrupted service include the use of redundant standby CMTS cards or "blades" . One method utilizes one active CMTS card and one standby CMTS card for "one plus one" redundancy protection. This has the disadvantage of halving the capacity of a multiple downstream CMTS interface platform (a rack of CMTS cards or blades) as every other slot was inactive in the normal operating state.

Another prior method used an external (or internal) RF switch to redirect traffic away from the failed CMTS card to a single standby CMTS card. This added another potential failure point and required coordination with this external device .

It is desirable to minimize disruption without adding the unnecessary cost of idle standby equipment.

SUMMARY OF THE INVENTION

The problem of providing redundancy while maximizing use of expensive equipment is solved herein by providing mutual redundancy between active CMTS transceiver cards. Traffic from two service areas is simultaneously sent to a pair of active CMTS cards. In the normal state, that is, when both cards are operating correctly, card A serves area A, card B serves area B. (In HFC cable modem service, a service area typically includes approximately 1200 households passed [HHP] split between two or more fiber nodes with fiber connected to each fiber node from the headend and coaxial cable connected from each fiber node to the subscriber.) If card B fails, card A automatically takes over service of both area A and area B. Some bandwidth is lost, but service is continuous.

The invention thus enables a service provider to utilize fully the multiple downstream CMTS interface platform' s slot capacity with active CMTS card resources in the normal state, while enabling continued connectivity (at reduced bandwidth capacity) for all initially connected cable modems in the case of a failure of a single CMTS blade of a 2-blade protection set.

Although used for CMTS service, the invention has application in other two-way shared media telecommunications services such as certain types of wireless broadband systems . The present invention together with the above and other advantages may best be understood from the following detailed description of the embodiments of the invention illustrated in the drawings , wherein:

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1A is a block diagram of a two-blade redundant system according to the invention for a high-quality HFC system in normal state.

Figure IB is a block diagram of the system of Figure 1A when one blade has failed and upstream noise is low enough to allow summing of all the upstream signals .

Figure 1C is a block diagram of the system of Figure 1A when one blade has failed and upstream noise is too high to allow the second stage of summing of the upstream signals. Figure 2A is a block diagram of a two-blade redundant system according to the invention for a cable system of moderate quality in normal state.

Figure 2B is a block diagram of the system of Figure 2A when one blade has failed. Figure 3A is a block diagram of a two-blade redundant system according to the invention for a cable system of poor to moderate quality in normal state.

Figure 3B is a block diagram of the system of Figure 3A when one blade has failed and upstream noise is low enough to allow summing of the upstream signals .

Figure 3C is a block diagram of the system of Figure 3A when one blade has failed and upstream noise is too high to allow summing of the upstream signals. Figure 4A is a block diagram of a two-blade redundant system according to the invention for a cable system of poor quality in normal state.

Figure 4B is a block diagram of the system of Figure 4A when one blade has failed. Figure 5A is a block diagram of an active-active 1+2 redundant system according to the invention in normal state.

Figure 5B is a block diagram of the system of Figure 5A when one blade has failed.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

This "Active-Active 1+1 CMTS Protection Scheme" of the invention is designed to enable a service provider to utilize fully the multiple downstream CMTS interface platform's slot capacity with active CMTS resources in the normal state, while enabling continued connectivity (at -50% bandwidth capacity) for all initially connected cable modems in the case of a failure of a single CMTS blade of a 2-blade protection set. In normal operation, both blades of the two-blade set are active, each receiving the same signals, but each blade processing only a subset of the signals . In the event of a failure of one of the blades, the remaining blade in the set makes adjustments in its processing to include processing of signals that would have been processed by the failed blade. That is, signals received but formerly not applied in the second blade are applied in the event of the failure of the first blade in the set.

Depending upon the architecture and quality of the cable plant, there are several variations on the operation of this protection scheme. Following are several illustrative examples of the key variations .

Figure 1 shows a pair of Ids x 6us (one downstream port by six upstream ports) CMTS transceiver units or blades 100 and 200 serving two areas, Area A 30 and Area B 40 respectively, each with two fiber nodes (shown as groups of 600 HHP) . Generally upstream traffic is split because of the funneling effect of noise from multiple sources. The invention is useful for CMTS blades with any number of upstream receivers as well as any number of fiber nodes. The upstream (us) channels from each service area may or may not be combined onto one carrier per service area. The upstream traffic from each area is sent to a connector on both CMTS cards. In the normal state, the primary card associated with an area processes only the traffic from that area: CMTS blade 100 serves area 30, and CMTS blade 200 serves area 40. If a connector (carrier) contains multiple upstream channels, then internal circuitry replicates the signal to multiple receivers/demodulators each tuned to a distinct frequency. The upstream channels are associated with the downstream channel on that same CMTS card, transmitter 111 with receivers 121 through 126 on card 100 and transmitters 211 with receivers 221 through 226 on card 200.

In the preferred embodiment the CMTS cards 100 and 200 each have spare downstream transmitters 212 and 112, respectively, at the same frequency as the primary transmitter that it is protecting, transmitters 211 and 111, respectively. The spare downstream transmitters are initially inactive, that is, they are not transmitting any signals. The primary and secondary downstream transmitters for each area (30, 40) are respectively combined and replicated into both fiber nodes in their area. Only one transmitter (111 or 112, and 211 or -212) from each pair is active at any one time. Transmitter pairs 111/112 and 211/212 arbitrarily may be on the same or different frequencies.

In the normal state, each area (30, 40) is being served by one downstream and six upstream channels or frequencies . In the case of a failure in one of the CMTS blades, shown as the failure of card 200' in Figure IB, the still active blade 100' will be reconfigured automatically to also process the traffic coming from the area previously served by the failed CMTS blade 200. The backup downstream transmitter for the failed transmitter (112 for 111, 212 for 211) , in conjunction with a set of upstream receivers on the still active card, begins serving its associated area. Depending upon the HFC architecture and quality and the associated combining scheme, the following reconfigurations may be actuated.

In order to have the most flexibility in allocating scarce bandwidth across the aggregate of cable modems across both areas, the combined upstream signals from both areas (combined at subdomain path combiners 31 and 41 respectively for areas 30 and 40) are further combined at domain path combiner 53 and sent to a connector on both CMTS cards. If the composite noise level is sufficiently low, this summed signal is switched or connected to each of the 6 demodulators, 521 through 526 in Figure IB, reconfigured from receivers 121 through 126 in Figure 1A. This would avoid requiring cable modems or receivers to switch upstream channels . The maps served by both downstream transmitters (e.g., Ill, 212) must be common. The result would be two downstream transmitters (one serving each area) and six upstream receivers (each serving both areas) serving the combined areas.

If, however, the composite noise level is too high, this composite signal is not utilized. Instead, as shown, for example, in Figure 1C, the first three receivers 221' through 223' (reconfigured from 121 through 123 in Figure 1A, other permutations are possible) , along with the backup downstream transmitter 212 now serve the area 40 previously served by the failed CMTS 200', and the last three receivers 121' through 123' (reconfigured from 124 through 126 in Figure 1A) along with their original downstream transmitter 111 continue to serve their original area 30, such that now there is a pair of Ids x 3us CMTS domains within the still active card 100" (card 100 in Figure 1A reconfigured) . Since each area is now served by fewer upstream channels/receivers, this requires the cable modems on channels no longer available within its area to switch the upstream frequency on which they transmit . This would be signaled by the remaining CMTS card 100" on the downstream channel by an (Immediate) Upstream Channel Change notification message created by a code generator (not shown) . The invention implemented for a cable plant of moderate quality with upstream combining at subdomain path combiners 31 and 41 is shown in Figure 2A. This implementation does not incorporate a final domain path combining stage 53 (shown in Figure 1A) that could otherwise result in too much composite noise, thereby reducing throughput. As shown in Figure 2B, if card 200 fails, the first three receivers 221' through 223' (reconfigured from 121 through 123 in Figure 2A, other permutations are possible) , along with the backup downstream transmitter 212 now serve the area 40 previously served by the failed CMTS 200', and the last three receivers 121' through 123' (reconfigured from 124 through 126 in Figure 2A) along with their original downstream transmitter 111 continue to serve their original area 30, such that now there is a pair of Ids x 3us CMTS domains within the still active card 100" (card 100 in Figure 2A reconfigured) . Since each area is now served by fewer upstream channels/receivers, this requires the cable modems on channels no longer available within its area to switch the upstream frequency on which they transmit so that their signals will be processed by the still-active CMTS. Again, this would be signaled by the remaining CMTS card 100" on the downstream channel by an (Immediate) Upstream Channel Change notification message.

Implementation for a cable plant of poor to moderate quality, generally not using upstream combining, is shown in Figure 3A. In order to have the most flexibility in allocating scarce bandwidth across the aggregate of cable modems in each area, the upstream signals from each of areas 30 and 40 are also combined respectively at subdomain path combiners 35 and 45 and sent or switched to another connector on both CMTS cards. If the composite noise level is sufficiently low, upon failure of card 200' shown in Figure 3B, each of these summed signals is connected to three demodulators, receivers 221' through 223' (reconfigured from 121 through 123 in Figure 3A, other permutations are possible) and receivers 121' through 123' (reconfigured from 124 through 126 in Figure 2A) , respectively. Since each area is now served by fewer upstream channels/receivers, this requires the cable modems on channels no longer available within its area to switch the upstream frequency on which they transmit . Again, this would be signaled by the CMTS card 100" on the downstream channel by way of an (Immediate) Upstream Channel Change notification message. The result would be two downstream transmitters 111 and 212 (one serving each area) and six upstream receivers, three serving one area and three serving the other area.

If the composite noise level is too high, the composite signals from summers 35 and 45 are not utilized. Rather, as shown in Figure 3C, one of the first three receivers, receiver 221' is fed from connector 43 from the area 40 originally associated with the failed CMTS card 200', and the other two receivers 222' and 223' fed from the other connector 44 from the area 40 originally associated with the failed CMTS card 200', while one of the second three receivers, receiver 121' is fed from connector 33 from area 30, and the other two receivers 122' and 123' are fed from the other connector 34 from area 30. This results in a pair of Ids x 3us CMTS domains within the still active card 100". Some set of cable modems will now be sharing one upstream channel rather than three, while another set will be sharing two rather than three; therefore subscribers may experience one- to two-thirds the throughput as before. Since each area is now served by fewer upstream channels/receivers, this requires the cable modems on channels no longer available within its area to switch the upstream frequency on which they transmit. Once more, this would be signaled by the CMTS card 100" on the downstream channel with an (Immediate) Upstream Channel Change notification message. An implementation for a cable plant of poor quality, not using upstream combining, is shown in Figure 4A. In the normal state, three upstream channels/frequencies are shared by each of four subsets of cable modems in the two service areas and presented by connectors 33 and 34 to receivers 121 through 123 and receivers 124 through 126 respectively in card 100 and by connectors 44 and 43 to receivers 221 through 223 and receivers 224 through 226 respectively in card 200. In this implementation, with the failure of card 200' in Figure 4B, one of the first three receivers of card 100'", receiver 221' (reconfigured, for example, from receiver 123 in Figure 4A) , is fed from one connector 44 from the area 40 originally associated with the failed CMTS card 200', and the other two receivers 222' and 223' fed from the other connector 43 from the area 40 originally associated with the failed CMTS card 200', while one of the remaining three receivers, receiver 123' (reconfigured, for example, from receiver 126 in Figure 4A) is fed from connector 34 from area 30, and the other two receivers, receivers 121 and 122, are fed from the other connector 33 from area 30. This results in a pair of Ids x

3us CMTS domains within the still active card 100'". Some set of cable modems will now be sharing one upstream channel rather than three, while another set will be sharing two rather than three; therefore subscribers may experience one- to two-thirds the throughput as before. Since each area is now served by fewer upstream channels/receivers, this requires the cable modems on channels no longer available within its area to switch the upstream frequency on which they transmit. Again, this would be signaled by the CMTS card 100'" on the downstream channel with an (Immediate) Upstream Channel Change notification message.

Depending upon the specific HFC architecture and plant quality, techniques from each variation could be combined to maximize flexibility and resource utilization. The invention can be applied advantageously to an Active- Active 1+2 CMTS protection scheme. This would be used when a CMTS card normally has two active CMTS (DOCSIS/HFC) domains corresponding to two active downstream transmitters such as a 2 x (1 x 3) CMTS blade. With Active-Active 1+2, there are three cards in the protection group, e.g., A, B and C domains of households passed with Al, A2, Bl, B2 , Cl and C2 as the subdomains associated with a particular node. Card A would protect Bl and C2 , card B would protect Cl and A2 , and card C would protect Al and B2. In this manner, if any one of the three cards fails, all of its associated cable modems would still have connectivity.

One implementation of this scheme is shown in schematic form in Figures 5A and 5B, where the broken lines show standby alternative connections and Figure 5B shows the configuration upon failure of card B. In this scheme, each card has two transmitters and six receivers. Upon the failure of card B, transmitter 111 and receivers 121-123 in card A perform double duty as transmitter 411 and receivers 421-423 serving one subdomain of A households passed and one subdomain of B households passed. Transmitter 312 and receivers 324-326 in card C perform double duty as transmitter 512 and receivers 524-526 serving one subdomain of C households passed and the other subdomain of B households passed.

Other implementations, including, but not limited to, application to other two-way shared media telecommunications systems such as certain wireless broadband systems, are possible without departing from the basis of the invention in using active mutual protection or redundancy.

Claims

What is claimed is:

1. A process for providing continuous broadband service to subscribers divided into at least two service domains and sharing multiple communications channels, said process comprising the steps of: a) providing service from a head end facility to each of said service domains through transceiver units each of which is normally dedicated to one of said service domains; and b) when one of said dedicated transceiver units fails, providing service from said head end facility to at least a portion of the domain normally served by said failed transceiver through another transceiver unit that continues to serve at least a portion of the domain to which it is normally dedicated.

2. A process for providing continuous broadband service to subscribers divided into at least two service domains and sharing multiple upstream communications channels, said process comprising the steps of: a) for each service domain, applying transmissions on each upstream channel to multiple receivers in a transceiver unit in a head end facility dedicated to the service domain; and b) when one of said dedicated transceiver units fails, applying said upstream transmissions to multiple receivers in a remaining transceiver unit.

3. The process of claim 2 wherein step (a) further comprises combining said upstream transmissions towards said head end facility from the service domain.

4. The process of claim 2 wherein step (b) further comprises combining said upstream transmissions from the domain served by the failed transceiver unit and the domain served by said remaining transceiver.

5. The process of Claim 2 further comprising the step, when said dedicated transceiver units fails, of providing transmissions downstream from said head end facility to the domain normally served by said failed dedicated transceiver unit through a transmitter in said remaining transceiver unit.

6. A process for providing continuous broadband service to subscribers divided into at least two service domains and sharing multiple upstream communications channels, said process comprising the steps of: a) separately, for each service domain, applying transmissions on each upstream channel to multiple receivers in a transceiver unit in a head end facility dedicated to the service domain; and b) when one of said dedicated transceiver units fails, (i) assigning a subset of the multiple receivers in a remaining transceiver unit to serve the domain previously served by the failed transceiver unit; (ii) applying transmissions on each upstream channel from the domain served by the failed transceiver unit to said subset of receivers ; and (iii) applying transmissions on each upstream channel from the domain served by said remaining transceiver unit to other receivers in said remaining transceiver unit.

7. The process of claim 6 wherein step (a) further comprises combining said upstream transmissions towards said head end facility from the service domain.

8. The process of claim 6 wherein step (b) further comprises combining said upstream transmissions from the domain served by said failed transceiver unit and the domain served by said remaining transceiver.

9. The process of claim 6 wherein step (b) further comprises combining transmissions on each upstream channel from the domain served by said remaining transceiver unit .

10. The process of Claim 6 wherein the channels are frequency channels and further comprising the step, when said dedicated transceiver unit fails, of assigning a subset of frequency channels for transmission upstream from the domain previously served by the failed transceiver unit and a non- intersecting subset of frequency channels for transmission upstream from the domain served by the remaining transceiver unit .

11. The process of Claim 6 further comprising the step, when said dedicated transceiver unit fails, of providing transmissions downstream from said head end facility to the domain normally served by said failed dedicated transceiver unit through a transmitter in said remaining transceiver unit.

12. A process for providing continuous broadband service to subscribers divided into at least two service domains, each further subdivided into at least two service subdomains, and sharing multiple upstream communications channels, said process comprising the steps of: a) separately, for each service subdomain, (i) applying transmissions on each upstream channel to a unique subset of multiple receivers in a transceiver unit in the head end facility dedicated to the service subdomain; and b) when one of said dedicated transceiver units fails, (i) reassigning a subset of the multiple receivers in a remaining transceiver unit to serve the domain previously served by the failed transceiver unit; (ii) applying transmissions on each upstream channel from the subdomain served by the failed transceiver unit to said reassigned subset of receivers; and (iii) and applying transmissions on each upstream channel from the subdomain served by said remaining transceiver unit to other receivers in said remaining transceiver unit.

13. The process of claim 12 wherein step (a) further comprises combining transmissions on each upstream channel towards the head end facility from the service subdomain.

14. The process of claim 12 wherein step (b) further comprises combining transmissions on each upstream channel from the subdomain served by the failed transceiver unit.

15. The process of claim 12 wherein step (b) further comprises combining transmissions on each upstream channel from the domain served by said remaining transceiver unit.

16. The process of Claim 12 wherein the channels are frequency channels and each of said subdomains within a service domain is assigned a non-intersecting subset of frequencies, said process further comprising the step, when said dedicated transceiver unit fails, of assigning a subset of frequency channels for transmission upstream from the domain previously served by the failed transceiver unit and a non-intersecting subset of frequency channels for transmission upstream from the domain served by the remaining transceiver unit.

17. The process of Claim 12 further comprising the step, when said dedicated transceiver unit fails, of providing transmissions downstream from said head end facility to the domain normally served by said failed dedicated transceiver unit through a transmitter in said remaining transceiver unit.

18. A process for providing continuous broadband service to subscribers divided into at least two service domains, each further subdivided into at least two service subdomains, and sharing multiple upstream communications channels, said process comprising the steps of: a) separately, for each service subdomain, (i) applying said transmissions on each upstream channel towards a head end facility from the service subdomain to a unique subset of multiple receivers in a transceiver unit in the head end facility dedicated to the service subdomain; and b) when one of said dedicated transceiver units fails, (i) reassigning non-intersecting subsets of the multiple receivers in a remaining transceiver unit to serve each of the subdomains previously served by the failed transceiver unit and each of the subdomains served by the remaining transceiver unit; and, for each said subdomain for which a subset is assigned, (ii) and applying transmissions on each upstream channel from said subdomain to its assigned subset of receivers .

19. The process of claim 18 wherein step (a) further comprises combining transmissions on each upstream channel towards said head end facility from the service subdomain.

20. The process of claim 18 wherein step (b) further comprises combining transmissions on each upstream channel from said subdomain.

21. The process of Claim 18 wherein the channels are frequency channels and each of said subdomains within a service domain is assigned a non-intersecting subset of frequencies, said process further comprising the step, when said dedicated transceiver unit fails, of assigning non- intersecting subsets of frequency channels for transmission upstream from each of the subdomains previously served by the failed transceiver unit and each of the subdomains served by the remaining transceiver unit .

22. The process of Claim 21 further comprising the step, when said dedicated transceiver unit fails, of providing transmissions downstream from said head end facility to the domain normally served by said failed dedicated transceiver unit through a transmitter in said remaining transceiver unit.

23. A process for providing continuous broadband service to subscribers divided into at least three service domains and sharing multiple communications channels, said process comprising the steps of: a) providing service from a head end facility to each of said service domains through transceiver units each of which is normally dedicated to one of said service domains; b) when one of said dedicated transceiver units fails, providing service from said head end facility to at least a portion of the domain normally served by said failed transceiver through at least two transceiver units that continue to serve at least a portion of the domains to which they are normally dedicated.

24. A process for providing continuous broadband service to subscribers divided into at least three service domains, each further subdivided into at least two service subdomains, and sharing multiple upstream communications channels, said process comprising the steps of: a) separately, for each service subdomain, applying transmissions on each upstream channel to at least one of multiple receivers in a transceiver unit in a head end facility dedicated to the service subdomain; and b) when one of said dedicated transceiver units fails, (i) reassigning a subset of the multiple receivers in each of at least two of the remaining transceiver units to serve at least one of the subdomains previously served by the failed transceiver unit; (ii) applying said transmissions to said reassigned subset of receivers; and (iii) applying said transmissions to receivers in said remaining transceiver units.

25. The method of claim 24 wherein step (a) further comprises combining transmissions on each upstream channel towards said head end facility from the service subdomain.

26. The method of claim 24 wherein step (b) (ii) further comprises combining transmissions on each upstream channel from each of at least one of the subdomains served by the failed transceiver unit.

27. The method of claim 24 wherein step (b) (iii) further comprises combining transmissions on each upstream channel from at least one of the subdomains served by said at least two remaining transceiver units .

28. The process of Claim 24 wherein unique subsets of multiple receivers in each transceiver unit are assigned to each of the subdomains in each service domain and wherein the step of reassigning receivers, when said dedicated transceiver unit fails, assigns one of said unique subsets of receivers in a different remaining transceiver unit to each of the subdomains previously served by the failed transceiver unit.

29. The process of Claim 24 further comprising the step, when said dedicated transceiver unit fails, of providing transmissions downstream from said head end facility to the domain normally served by said failed dedicated transceiver unit through a transmitter in one of said remaining transceiver units .

30. The process of Claim 28 further comprising the step, when said dedicated transceiver unit fails, of providing transmissions downstream from said head end facility to each of the subdomains normally served by said failed dedicated transceiver unit through a transmitter associated with the subset of receivers reassigned to that subdomain.

31. A process for providing continuous broadband service to subscribers divided into three service domains, each further subdivided into two service subdomains, and sharing multiple upstream communications channels, said process comprising the steps of: a) separately, for each service subdomain, applying said combined transmissions to one of two non-intersecting subsets of receivers in a transceiver unit in a head end facility dedicated to the service subdomain; and b) when one of said dedicated transceiver units fails, continuing service under step (a) for each of the two remaining transceiver units, and, for each of the subdomains that it previously served, (i) reassigning one subset of the multiple receivers in each of the two remaining transceiver units to serve said subdomain previously served by the failed transceiver unit; and (ii) and applying said transmissions to said reassigned subset of receivers .

32. The process of claim 31 wherein step (a) further comprises combining transmissions on each upstream channel towards said head end facility from the service subdomain.

33. The process of claim 31 wherein step (b) further comprises combining transmissions on each upstream channel from said subdomain previously served by the failed transceiver unit.

34. The process of Claim 31 further comprising the step, when said dedicated transceiver unit fails, of providing transmissions downstream from said head end facility to each of the subdomains normally served by said failed dedicated transceiver unit through a transmitter associated with the subset of receivers reassigned to that subdomain.

35. A system for providing continuous broadband service to subscribers in multiple domains sharing multiple communications channels, said apparatus comprising multiple transceiver units each of which is normally dedicated to one of said service domains, where under circumstances in which one of said dedicated transceiver units fails, at least one of the remaining transceiver units is shared by continuing to service at least a portion of the service domain to which it is normally dedicated and also serving at least a portion of the service domain normally served by the failed transceiver unit.

36. The system of Claim 35 wherein a switch is provided to switch from normal connection of one of said service domains to its dedicated transceiver unit to said shared transceiver unit upon failure of its dedicated transceiver unit.

37. Apparatus for providing continuous broadband service to subscribers divided into at least two service domains and sharing multiple upstream communications channels, said apparatus comprising: a) at least two transceivers units each containing multiple receivers and each normally providing dedicated service to one of said service domains; b) switches adapted to connect a communication path from a service domain normally to the transceiver unit dedicated to its service and, upon failure of one transceiver unit, to a remaining transceiver unit.

38. The apparatus of Claim 37 wherein said transceiver units each further comprises two transmitters, one of which serves the domain served by the transceiver unit that it protects .

39. The apparatus of Claim 37 further comprising, for each said domain and connected to said switches, combiners of the upstream communication paths from each subdomain of said domain.

40. The apparatus of Claim 39 further comprising a combiner of upstream communication paths from the domains served by the failed transceiver unit and the remaining transceiver unit and wherein said switches include switches adapted to connect the output of said subdomain path combiners to said domain path combiner.

41. The apparatus of Claim 39 further comprising switches connecting the outputs of said subdomain path combiners to non-intersecting subsets of receivers in a remaining transceiver unit upon failure of the protected unit.

42. The apparatus of Claim 41 further comprising a code generator to reassign upstream channels used by subscribers in said subdomains.

43. The apparatus of Claim 39 further comprising switches connecting said subdomain paths alternatively to non- intersecting subsets of receivers in dedicated transceiver units and, upon failure of the protected unit, to non- intersecting subsets of receivers in a remaining transceiver unit.

44. The apparatus of Claim 43 further comprising a code generator to reassign upstream channels used by subscribers in said subdomains .

45. A process for providing continuous broadband service to subscribers sharing multiple upstream communications channels to a first transceiver unit and a second transceiver unit that are paired, comprising the steps of: a) receiving transmissions from each upstream communications channel at both said first and said second transceiver units; b) dividing said transmissions into two sets, a first set to be processed by said first transceiver unit and said second set to be processed by said second transceiver unit; and c) processing said first set of transmissions in said second transceiver unit in the event of a failure of said first transceiver.