Multiplex communications – Diagnostic testing – Determination of communication parameters
Reexamination Certificate
1999-03-18
2003-08-26
Kizou, Hassan (Department: 2662)
Multiplex communications
Diagnostic testing
Determination of communication parameters
C370S254000, C709S238000
Reexamination Certificate
active
06611499
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a technique for determining the availability of a router-based connectionless network for transporting packets from individual data sources to various data destinations.
BACKGROUND ART
Present day data networks typically comprise routers that route data packets over one or more links between individual sources and destinations of data, each typically comprising a customer's computer. Successful routing of data packets requires that at least one logical path (a collection of one or more physical links inter-connected by routers) exist in the network between the source and destination for each packet. For that reason, each router maintains data, in the form of a routing table, that identifies different destinations and the links that router enjoys to those destinations in the network. Using the knowledge of the data destinations in its routing table, each router can determine the identity of the downstream router (or next hop) that should receive a packet in accordance with the destination of that packet specified in its header. Assuming the network possesses sufficient physical redundancy (e.g., multiple routers and multiple links), the network can dynamically redefine paths using protocols such as the Border Gateway Protocol (BGP) or Open Shortest Path First (OSPF) protocol, in case of a router or link failure. The use of such protocols ensures that no one router or link failure disrupts the flow of packets between a particular data source and destination.
Entities that maintain data networks of the type described above strive for high reliability. To that end, such entities seek to maximize the network availability, which is defined as the ratio of the actual service time to scheduled service time. Heretofore, network managers monitored network availability by monitoring the availability of individual network routers and their associated links, that is the ratio of the actual router and link operating time to the scheduled operating time. Unfortunately, attempting to approximate network availability based on router and link availability does not provide an accurate measure of availability in a connectionless network because packets travel across multiple dynamically defined paths and typically cross a number of individual routers and their associated links. A failure of one or more routers often will not effect the network's ability to route a packet from a particular source to a particular destination, since in that case an alternate path may exist.
Another approach to establishing network availability is to launch a prescribed packet (e.g., a “ping”) to a particular destination and then await a response. While this method affords a more accurate method of monitoring performance, active monitoring in this manner is impractical for large networks because the number ingress-egress path combinations increases by the factor n x (n−1) where n is the total number of ingress and egress points. Moreover, not every ingress and egress point is accessible to permit such active monitoring.
Thus, there is need for a technique for providing accurate monitoring of the availability of a data network irrespective of its size.
BRIEF SUMMARY OF THE INVENTION
Briefly, the present invention provides a technique for determining the availability of a connectionless network that includes routers for routing data from different sources (e.g., source networks) to different destinations (e.g., destination networks) across paths comprised of one or more links. Network availability is determined by first identifying all potential destinations of data. In other words, all network endpoints are established. Next, the routing table in each router is examined to determine whether a route exists through the network to each destination endpoint. If a route exists, then a path between the endpoints is presumed available. The network availability is established by comparing the available paths within the network to the total number of endpoint pairs. Thus, for example, if a path exists to every destination endpoint, the network is fully available. In contrast, the availability of the network is diminished by the unavailability of paths to destination endpoints.
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AT&T Corp.
Kizou Hassan
Pezzlo John
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