Determining and maintaining hop-count for switched networks

• Main Authors: BOIVIE; RICHARD H, FELDMAN; NANCY KAREN, VISWANATHAN; ARUN, WOUNDY; RICHARD M
• Format: Patent
• Language: English
• Published: 10.10.2000
• Edition: 7
• Subjects: ELECTRIC COMMUNICATION TECHNIQUE; ELECTRICITY; SELECTING; TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHICCOMMUNICATION

This invention discloses a way to map IP or similar routing information onto a technology that uses label switching and swapping, such as ATM, without the need to change the network paradigm. This allows a network to continue to function and appear as a standard IP network, but with much higher performance. One of the requirements of IP networks is to decrement the IP packet Time-To-Live (TTL) field on each hop it traverses. Currently, switched packets within an ATM like network cannot decrement the TTL. This invention can decrement packet TTLs appropriately by maintaining a hop-count per each switched path. This hop-count maintains the total number of hops a packets would have traversed, had it been forwarded in the IP hop-by-hop model, rather than through the ATM like switched path. Before forwarding a packet on a switched path, an ingress ISR decrements the TTL by the hop-count. In this way, at the switched path exit point, the TTL is the same as if it had been forwarded by IP. If the decrement value is greater than or equal to the TTL of the packet, the packet may be forwarded hop-by-hop; in this situation, the packet will be discarded at the correct IP node, rather than being switched through the ATM like network. This hop-count is calculated by virtue of the fact that each switched path is initiated by the egress node, and the establish (or set-up) message traverses the network hop-by-hop until each ingress node is reached. The switched path establishment message includes a hop-count field, which is incremented at each node that processes the establishment message. Thus, at the ingress node, the received hop-count is equal to the total number of hops to the egress point.