Multiplex communications – Network configuration determination – Using a particular learning algorithm or technique
Reexamination Certificate
1998-03-05
2002-01-15
Holloway, III, Edwin C. (Department: 2635)
Multiplex communications
Network configuration determination
Using a particular learning algorithm or technique
C370S254000, C370S351000
Reexamination Certificate
active
06339587
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a network management system for satisfying a request for a connection path having a specified capacity between two specified terminations and to a method of operating such a system. It is particularly concerned with a network management system for a synchronous digital hierarchy (SDH) network, but has application in other types of networks as well.
A typical digital telecommunications network for transmission of voice or data operates at a sampling rate of 8000 samples/sec; (1 per 125 microseconds). Each sample is coded as an 8-bit byte, resulting in a 64 kbit/sec bit rate. This is typically multiplexed over the network in a 32-channel frame (including one channel each for synchronisation and signalling), resulting in a transmission rate of 64×32=2,048 kbits/sec, known as a 2 Mbit system. Further multiplexing can take place by multiplexing four lower level channels into one higher level channel to produce a secondary bit rate of 8 Mbits/s, and this process can be repeated to produce tertiary (34 Mbit/s), and quaternary (140 Mbit/s) bit rates. These are not exact quadruples because of the need for an additional signalling overhead to be included.
The bit rates quoted above are those used in Europe. In other regions such as the USA and Japan, although the fundamental bit rate is the same 64 kbit/s, the samples are initially multiplexed in a 24 channel frame (rather than 32) to produce a primary bit rate of 1.544 Mbit/s, a secondary bit rate of 6.312 Mbit/s, a tertiary bit rate of 32 Mbit/s (Japan) or 45 Mbit/s (USA), and a quaternary bit rate of 98 Mbit/s (Japan) or 140 Mbit/s (USA). A network which operates at these bit rates and which has multiplexers/demultiplexers for converting from one rate to another is known as a “plesiochronous—i.e. nearly synchronous—digital hierarchy”: (PDH) network. A disadvantage of such a network is that at any point in the network at which different channels need to be separately routed, the signals have to be demultiplexed step-by-step back to a 64 kbit/s signal in order that the individual channels can be identified. This is necessary even if the channels are then to be immediately re-multiplexed up to one of the higher bit-rates for onward transmission.
The Synchronous Digital Hierarchy (SDH) is a standard which not only allows transmission at all the above bit rates to be carried, but allows individual signals to be added or extracted without demultiplexing other signals multiplexed with it. In an SDH link operating at 155 Mbit/s, the signal is divided into frames known as STM-1 frames. Each frame comprises 2430 bytes, 2349 of which are available as payload, the rest being for signalling and synchronisation. This corresponds to a payload bit rate of 150 Mbit/s.
Each 150 Mbit/s STM-1 frame consists of one or more ‘virtual containers’. There are five types:
A VC11 has a capacity of 1.7 Mbit/s and can carry one 1.5 Mbit/s primary channel according to the US or Japanese 24×64 kbit/s standard.
A VC12 has a capacity of 2.3 Mbit/s and can carry one 2 Mbit/s primary channel according to the European 30×64 kbit/s standard.
A VC2 has a capacity of 6.8 Mbit/s and can carry one 6.3 Mbit/s channel (the US/Japanese secondary level), or four VC11's or three VC12's.
A VC3 has a capacity of 50 Mbit/s, allowing it to support any of the tertiary level PDH bit rates: 32 Mbit/s (Japan), 34 Mbit/s (Europe), or 44 Mbit/s (USA). It may instead carry seven VC2's, twenty-one VC12's or twenty-eight VC11's.
A VC4 has a capacity of 150 Mbit/s, allowing it to support the quaternary PDH bit rate of 140 Mbit/s (or 98 Mbit/s in Japan), or three VC3's, twenty-one VC2's, sixty-three VC12's or eighty-four VC11's.
Mixtures of virtual containers may also be carried: for example an STM-1 frame might consist of one VC3, nine VC2's, nine VC12's and eight VC11's. The VC3 may itself contain VC11's, VC12's or VC2's (or a mixture), and the VC2's may themselves contain VC11's or VC12's.
SDH links can operate at higher bit rates. For example, in an SDH link operating at 622 Mbit/s, the signal is divided into frames known as STM-4 frames, each of which has a payload four times greater than an STM-1 frame.
SDH networks have advantages over PDH networks. In particular, the STM-1 frame includes data regarding each individual virtual container within it, which allows the channel represented by that container to be demultiplexed and routed separately at any network node without the need to dismantle the whole frame. In contrast, in a PDH network the individual channels are not identifiable and extractable without undoing each multiplexing stage in turn down to the required level, and then remultiplexing the channels not extracted for further transmission.
In an SDH network traffic capacity can be booked in advance, on request of the user. It is then necessary to meet this request by allocating a path through the network having the required capacity. The customer may have specific requirements, for example two or more independent paths may be required, sharing no individual links or nodes, to ensure that an individual failure does not result in loss of the entire booked capacity. The path allocated to the customer may then be used in any way he requires, eg to route individual calls. It should be noted that capacity management involves different requirements to the handling of individual call traffic. In particular, capacity management has to consider future requirements for capacity, and not just the real-time requirements that a call-traffic management system has to deal with. Ideally a capacity management system should also be able to provide capacity immediately, perhaps as a premium (“Just In Time”) service. Moreover, in a call traffic management system, it is normally optimal to try to spread call traffic over as many different routes as possible, to minimise interference and ensure minimum disruption if one route should fail. In capacity management, the optimum is to aggregate low capacity routes where possible, to fully load each link that is used, thereby keeping other links free. The free links can then be used if a subsequent requirement for a high-capacity link is received, without having to first re-allocate low capacity links.
The availability of connections between nodes within the network depends on a number of factors which are constantly changing. For example, equipment is taken out of service for maintenance, and re-instated afterward. This may be on a planned or emergency basis. Moreover, as capacity is allocated to one user it becomes unavailable for use by others.
In order to control the routing of transmissions through an SDH network, it is therefore necessary to allocate capacity over the network between the source and destination. Various criteria need to be addressed, such as the capacity required, the time the capacity is needed, the length of time needed, the need for robustness (addressed for example by routing part of the capacity over one path and part over another, a practice known as ‘diversity’, such that a connection is maintained, albeit at lower capacity, even should one path fail), and any variations in availability of capacity e.g. because of planned maintenance, or other users of the system.
In order to establish the routing to be taken by a transmission, the various connections to be used in the network need to be allocated and reserved. The capacity may be required immediately, or the capacity may be reserved in advance against an expected requirement.
It is possible to envisage a path-finding system in which a path is sought from first principles every time a new request for capacity is made, by analysing the network connectivity and its committed capacity, and calculating a path through it. For a complex network, such an exhaustive analysis would involve a large amount of processor power, and to explore all the possible connections would be very slow. Much of the processing could be red
British Telecommunications plc
Holloway III Edwin C.
Nixon & Vanderhye
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