Multiplex communications – Pathfinding or routing
Reexamination Certificate
1997-06-09
2001-11-06
Chin, Wellington (Department: 2664)
Multiplex communications
Pathfinding or routing
C370S236000, C370S238000, C370S255000, C370S400000, C379S220010
Reexamination Certificate
active
06314092
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to identifying a path between a selected first node and a selected second node in a communications network to provide routing in the network.
RELATED ART
Over recent years communications companies have increasingly provided their customers with an improved quality of service and an improved range of services due to the introduction of digital communications equipment. Thus the equipment that is found within network interconnection sites (trunk exchanges) and local service exchanges is largely digital. However, the connection between local service exchanges and network interconnection sites may consist of a variety of different technologies including copper coaxial cable, fibre optic cable, radio links and satellite links.
In order to take advantage of changing demands placed on a communications network, for example the changes in communications traffic density that occur throughout a daily cycle, digital communications equipment may be controlled to divert customer services dynamically, so taking advantage of the most economical route that may be available at a particular time during the day. Networks are known where diversion of communications traffic is performed automatically according to algorithms encoded at processor sites within each communications node.
A call made from a point A in a communications network to a point B in the same communications network may be made over a plurality of different paths. It is important for the particular path that is chosen to be that which is most economical at the time when the service is in use. A method is known where a service request message is distributed throughout the nodes of a system so that each intermediate node between points A and B receives the request message and transfers it on to every node to which it is connected. At some point, the node to which point B is connected will receive the request message. The first such message received will have encoded within it all the nodes through which it has passed on its journey from point A to B. Several messages will then arrive at the node nearest to point B subsequently; however, these will have arrived later in time and thus the list of nodes encoded within a request message received after a first request message describes a route which took longer to transmit the request message from the caller at A to the receiver at B. This is a typical example of how a network may effectively provide dynamic re-routing of calls and communications services with a high degree of efficiency. Other similar and more advanced methods for dynamic routing of communications services in a network are known, and are the subject of much current research.
A known disadvantage of this type of network is that the behaviour of the network under certain critical conditions can become unpredictable and even chaotic, possibly resulting in catastrophic failure of an entire communications network for a period of time. The network is difficult to simulate because the degree of complexity embodied by large numbers of distributed nodes taking part in dynamic routing can only be approximated roughly by a mathematical model.
A further disadvantage of this type of network is that a large proportion of the nodes within a communications network have to conform to a particular specification, i.e. hardware and software must precisely match the requirements for a particular type of node, and thus the phased introduction of this type of network is more difficult than the phased introduction of communications nodes which are monitored by one or several central network monitoring sites.
Centralised network monitoring requires considerable computing resources in order to ensure that efficient routing and re-routing of calls is performed dynamically, however. The restrictions imposed by the need to monitor a communications network centrally have typically resulted in the use of simple re-routing algorithms such as swapping services to predetermined less efficient routes when the most efficient route for a service is close to saturation of its channel capacity.
A further use for re-routing, whether in the distributed or centrally monitored type, is to circumvent cable failures. In a passive, centrally monitored network when a line failure is detected it is a common practice to re-route services over predetermined alternative paths.
In addition to dynamic routing requirements within an operational communications network, large industrial users of a communications network, for example a petroleum company or a bank, may require a direct digital connection between different company sites. In order to provide such a direct link, the communications provider will design an optimal route through the existing communications network taking advantage of the various technologies that may be available concerning the customer's needs. For a high reliability connection, a customer may specify that no radio links are to be used. Alternatively, the customer may specify that two lines should be provided over completely different routes, so that failure of one line for whatever reason is unlikely to coincide with failure of a second line.
Mixed technology communications networks may include communications nodes that may not be reconfigured by remote monitoring computers. In this event, the design of an optimal routing between geographically distinct customer sites frequently requires co-ordination between personnel and resources from a number of communications operators, or between divisions of a single larger communications provider. This results in a large degree of co-ordination and administration during the evaluation and design of the route. Furthermore, as there may be a number of different possible ways of providing a route between a given pair of customer sites, problems may arise when dealing with different company divisions along the route which may feel the need to compete against each other.
At a local level a particular type of route, for example coaxial cable, may appear to provide an advantage over other types of route, for example radio links. When seen within the context of the overall route, however, what may have been an advantage at a local level may turn out to be a disadvantage within the route as a whole. This may be due to the type of connections which may be made subsequently to the coaxial cable. Due to the cost of the administrative design process, it may not be cost efficient to perform an additional iteration of the design process, resulting in the provision of a route that is more expensive than that which may have theoretically been achieved.
SUMMARY OF THE INVENTION
According to a first aspect of the present invention there is provided a method of identifying preferred paths for traffic in a communications network, said paths having transmission links and reconfigurable switching nodes, comprising steps of; processing a first set of data relevant to paths starting from a first node to providing communication towards a second node; processing a second set of data relevant to paths starting from said second node to provide communication towards said first node; and comparing said sets of data to establish whether further steps to identify said preferred path should start from said first node or from said second node.
Preferably, said first set of data and said second set of data includes a number of potential links which could form part of a preferred path. Said comparison step may consist of comparing said number of links connected to each of said first node and said second node, such that the node having the fewer number of links is selected as starting node.
In a preferred embodiment, the further steps consist of a heuristic procedure to identify a third node connected via a link to either said first node or to said second node. Preferably, the third node may be treated as a new first node if connected to said first node or treated as a new second node if connected to said second node, whereafter the method is repeated to identify a preferred path betwe
British Telecommunications public limited company
Chin Wellington
Nixon & Vanderhye P.C.
Phan M.
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