Multiplex communications – Fault recovery
Reexamination Certificate
1997-07-25
2001-01-16
Ton, Dang (Department: 2732)
Multiplex communications
Fault recovery
C370S222000
Reexamination Certificate
active
06175552
ABSTRACT:
This invention relates to telecommunications networks, and in particular to an arrangement and method for providing disaster recovery in such networks.
BACKGROUND OF THE INVENTION
With the deregulation of telecommunications services, many countries are now seeing a proliferation of new operators providing both voice and data networks and who are in competition with the original ‘PTT’ or monopoly operator. Typically, the original operator has an established mainly wired network while the new operators are introducing optical fibre networks based on synchronous (SDH or SONET) rings from the exchange or switch to a street cabinet serving subscribers. At the street cabinet, a synchronous multiplexer drops out 2 Mb/s channels which are further de-multiplexed to 64 kb/s voice and/or ISDN channels which are carried to the subscribers on twisted pair copper cables. Large, e.g. corporate users may be provided with their own optical circuit from the street cabinet.
The new operators have taken subscribers from the original operators by offering enhanced services and/or lower tariffs. This has encouraged the original operators to offer similar services and tariffs in an attempt to win back lost subscribers. The new operators are acutely aware of the potential loss of their newly acquired subscribers and are becoming increasingly concerned that any risk of loss of service should be minimised. It is believed that any such loss of service for a significant period of time will result in most of the subscribers reverting back to the original operator who will almost certainly have left in place their copper connections to the subscriber premises. This loss of service may for example result from a terrorist attack or from a fire damaging a switch beyond repair, or from major damage to the optical cables connected to a switch. Although there are various schemes for providing path protection in synchronous networks, these schemes do not address the problem of the catastrophic loss of a switch. There may also be a problem where engineers are excluded from a building containing equipment for a significant period of time, e.g. as the result of a fire or an explosion, and are thus unable to effect repairs. Thus, many of the new telecommunications operators are taking a keen interest in disaster recovery plans.
The current disaster recovery plan involves the provision of a replacement switch together with its associated transmission equipment and power generators, on vehicle trailers which can be towed to a disaster area and connected into the access network at a point remote from the damaged switch. A typical arrangement requires three large trailers together with a smaller back-up power trailer housing three 120 kvA generators. Such a set up is of course costly to maintain on a largely standby basis. Also, there may well be a significant delay before the equipment can be transported to the disaster area to initiate recovery of the network.
SUMMARY OF THE INVENTION
An object of the invention is to minimise or to overcome this disadvantage.
A further object of the invention is to provide an improved system and method for effecting disaster recovery in a synchronous network.
According to a first aspect of the invention there is provided an arrangement for providing disaster recovery in a synchronous telecommunications network comprising a number of rings each incorporating a plurality of multiplexers and each coupled to a switch, the arrangement including a disaster recovery interface point providing an interface to one or more remote switches, and means responsive to failure of said switch for re-routing traffic on said synchronous rings via said disaster recovery interface point to said one or more remote switches.
According to another aspect of the invention there is provided an arrangement for providing disaster recovery in a synchronous telecommunications network comprising a number of rings each incorporating a plurality of multiplexers and each coupled to a switch via a respective master multiplexer, the arrangement including a disaster recovery interface point providing an interface to one or more remote switches, dormant master multiplexers one for each said ring and each being coupled to the disaster recovery point, means responsive to failure of said switch for activating said dormant master multiplexers as replacement master multiplexers so as to re-route traffic on said synchronous rings via said one or more remote switches.
According to another aspect of the invention there is provided a method for providing disaster recovery in a synchronous telecommunications network comprising a number of rings each incorporating a plurality of multiplexers and each coupled to a switch via a respective master multiplexer, and including a disaster recovery interface point providing an interface to one or more remote switches, the method including responding to failure of said switch by re-routing traffic from said synchronous rings to said one or more remote switches via said disaster recovery interface point.
According to a further aspect of the invention there is provided a dormant master multiplexer for a synchronous telecommunications network, the multiplexer including first and second input/output ports for receiving and transmitting synchronous traffic, an auxiliary input/output port, means for establishing communication with a master multiplexer, and means for switching traffic from a said input/output port to the auxiliary input/output port in the event of an interruption of said communication.
In a preferred arrangement, communication between the master multiplexer and the dormant master multiplexer is established over a supervisory channel. If this communication is interrupted in both directions around a ring, indicating loss of the master multiplexer, the dormant master multiplexer activates automatically to take over the ring control functions.
In this arrangement, only one fibre pair per synchronous ring is required to effect coupling to the disaster recovery interface point. Loss of interconnect fibres does not affect the main ring, and the network immediately reconfigures itself on the loss of the master multiplexer. Concentration on to STM16 can be effected at the disaster recovery interface point for instant routing to a remote alternative exchange. The entire route can be managed and monitored at all times.
In a preferred embodiment, a diverter controlled by the network manager diverts incoming calls to another switch so that there is no necessity for other system operators to amend their routing tables.
REFERENCES:
patent: 4999832 (1991-03-01), Chen et al.
patent: 5461608 (1995-10-01), Yoshiyama
patent: 5570344 (1996-10-01), Fujii
patent: 5848053 (1998-12-01), Ardon
Wehr, M. “Protection Des Reseaux De Transmission Synchrone” Communication Et Transmission, vol. 15, No. 4, Jan. 1, 1993, pp. 5-12.
Whitt, S., et al., “The Role of Sonet-Based Networks in British Telecom” International Conference on Communications, Including Supercomm Technical Sessions, Atlanta, Apr. 15-19, 1990, vol. 3, Apr. 15, 1990, Institute of Electrical Engineers and Electronics Engineers, pp. 919-923.
Parry Mark James
Unitt Brian Michael
Lee Mann Smith McWilliams Sweeney & Ohlson
Nortel Networks Limited
Ton Dang
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