Operator directed routing of connections in a digital...

Details Operator directed routing of connections in a digital... Operator directed routing of connections in a digital...

1999-05-27

2004-02-24

Chin, Wellington (Department: 2664)

Multiplex communications

Data flow congestion prevention or control

Flow control of data transmission through a network

Reexamination Certificate

active

06697329

ABSTRACT:

FIELD OF THE INVENTION
The invention generally relates to the art of establishing connections in a network; and more specifically to the establishment of a virtual circuit in an asynchronous transfer mode (ATM) network using an operator-directed routing path.
BACKGROUND OF THE INVENTION
A permanent virtual circuit (PVC) provides a bearer channel path across a network which comprises a series of bearer channel links that are interconnected by “permanent” bearer channel cross-connections established on network nodes under the direction of a central network management authority. This authority can be a human operator which decides the route and manually configures each cross-connection individually through a network management terminal interface (NMTI). Alternatively, the authority can be a network management system (NMS), which automatically selects the route through the network according to some algorithm or objective when requested by one or more human operators. The NMS is connected to each network node typically through an independent control channel and thereby automatically establishes the cross-connections.
For each PVC thus established, the central network management authority can choose a route through the network which meets criteria based on network-wide policies rather than single-element policies. One example of a network-wide routing policy is a policy of using the most efficient route through the network, for example, by minimizing the number of network nodes traversed; or by minimizing the cumulative costs of links which are traversed; or, by balancing the number of traversed nodes and the cost of the traversed links. Another example is balancing network usage across different network nodes, or the links between network node, such that no one network node or link is carrying a large proportion of all PVCs traversing the network.
This approach to establishing connections provides various benefits. For instance, since there is only one central network management authority, i.e. an expert human network operator or a powerful computer running sophisticated network management software, the cost of provisioning the authority is inexpensive relative to the overall cost of the network. In addition, whenever network management policy is changed with respect to the routing of circuits or connections, it is easy to implement the policy changes because they only need to be made in one place, in the central management authority.
This approach also has various shortcomings. One shortcoming is the relatively high cost of maintaining an exact and up-to-date picture of network conditions in the central network management authority in order to enable routing and re-routing decisions to be made with accuracy. Another shortcoming is the slow speed at which the central network management authority can re-route PVCs in the event of a network failure. This is due to the time required for the central authority to (i) become aware of the network failure, (ii) find new routes through the network for all affected PVCs which satisfy all of the various network element and network-wide criteria, and (iii) re-establish all affected PVCs along the chosen routes.
A soft permanent virtual circuit (SPVC) provides a bearer channel path across a network which comprises a series of bearer channel links that are interconnected through “switched” (i.e. on-demand) bearer channel cross-connections made across a series of network nodes. More specifically, the ingress and egress network nodes are provisioned by an operator (either through the NMTI or NMI) but the cross-connects are commissioned via signalling, like a switched virtual connection (SVC), as the SPVC is signalled and routed across the network from the ingress network node to the egress network node. An SVC is a path that is signalled from user side UNI to user side UNI whereby the route is chosen by the network nodes as the path is signalled from a source end station towards a destination end station. The individual cross-connects for the SVC path are configured and connected by call control software running on each node along the path as the path steers itself through the network using routing tables resident on each node (i.e., hop-by-hop routing) or according to a predetermined route specified in the connection request (i.e., source-routing). Thus, SPVCs are a kind of hybrid between PVCs and SVCs since SPVCs, like PVCs, are initiated by the central network management authority and require no UNI signalling between the user and the network, but, like SVCs, the cross-connects are routed through the network and maintained by the network nodes themselves.
One of the benefits of this approach to establishing connections is that SPVCs can be re-routed more efficiently because the network nodes which are closest to a network failure can quickly detect the failure and initiate the re-routing procedures. Hence, the virtual circuits can be re-established more quickly and at less cost than PVCs can be reestablished by a central network management authority. Indeed, it is estimated that SPVCs improve the cult restoration re-route performance for connections by an order of magnitude because the processing is distributed within the network rather than being centrally managed by the NMS.
The are also various disadvantages with this approach. First, it is not possible for an expert human operator to intervene and influence the network nodes to use routes for an SPVC through the network that differ from the mutes that would be automatically chosen by the network nodes, or to modify routes chosen automatically by the network nodes, for example, in order to impose routing criteria for which the network nodes have not been designed or configured. Second, due to the large number of network nodes, it is difficult and costly to employ powerful computing devices for each network node; therefore, the sophistication of the routing algorithms implemented by the network elements cannot, at reasonable expense, approach the sophistication of the routing algorithms that can be implemented by a central network management authority which comprises of a smaller number of computing devices. Third, again due to the large number of network nodes, it is difficult and costly to upgrade or reconfigure each network node whenever a network-wide policy has changed with respect to the routing and re-routing of virtual circuits, for example, when a new virtual network has been created out of available resources on many different nodes across the network, or when network management policies change with respect to the weighting of different criteria such as the number of nodes traversed versus cumulative cost of links traversed.
To further elaborate upon the disadvantages provided by both PVCs and SPVCs, consider for example, the reference network shown in
FIG. 1. A
customer wishes to connect end station or customer premise equipment (CPE)
20
from Toronto to Montreal, and purchases two (2) connections or virtual circuits
24
a
and
24
b
therebetween to ensure redundancy. If the connections
24
a
and
24
b
between Montreal and Toronto are established using SPVCs, then, since the path, i.e. intermediate nodes
28
and links
26
, of the connections are not preconfigured, a situation such as illustrated in
FIG. 1
could occur, wherein the network nodes select the shortest path between the CPEs. Thus, the paths of both connections
24
a
and
24
b
are identical, traversing node A, link
26
ag
, node G, link
26
dg
, and node D. This result would thus destroy the sought after redundancy. In order to ensure that the path of each connection does not follow a common link or share the same physical interface of the other, it is possible to provision the connections as PVCs in order to manually configure the cross-connections and predetermine the followed links. However, this strategy brings with it the above described disadvantages of PVCS, in particular, the relatively slow re-route performance of the centralized NMS in the event of a service disruption such as a failed link. For cus

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