Method and apparatus for classifying IP data

What is this patent about?

’173 is related to the field of packet-switched networking and specifically addresses the challenges of maintaining Quality of Service (QoS) in environments utilizing source routing. In standard IP networking, routers typically prioritize or manage traffic based on the destination address found in the primary IP header. However, when source routing is employed—allowing a sender to specify a path through specific intermediate nodes—the destination field in the IP header is overwritten with the address of the next hop rather than the ultimate recipient. This creates a visibility gap for resource reservation protocols like RSVP, which may fail to apply the correct traffic policies because they cannot identify the true end-to-end session.

The underlying idea behind ’173 is to shift the classification logic from the transient destination address in the IP header to the permanent final destination address embedded within the source routing extension headers. By forcing the router to look deeper into the packet structure—specifically targeting the tail end of the routing list—the system ensures that the packet is mapped to its reserved resources regardless of how many intermediate hops it must traverse. This insight allows the network to maintain a consistent traffic control state for a specific flow, even as the visible destination address in the outer header changes at every hop along the source-defined path.

The claims of ’173 focus on a method and apparatus for classifying IP data by extracting routing information from specific sub-fields within the packet header. The independent claims describe receiving data that includes a list of intermediate nodes and performing classification based on an entry within that header rather than the standard destination field. This mechanism is specifically applied to both IPv4 and IPv6 architectures, targeting the Loose/Strict Source and Record Route (LSRR/SSRR) options in the former and the Type 0 routing header in the latter. The scope covers the logic required to identify when source routing is active and redirect the classifier to the final address in the list.

In practice, the invention functions as a diagnostic check performed by the router's processor during the initial packet inspection phase. If the router detects that the source routing has not yet been fully consumed—indicated by a pointer in IPv4 or a non-zero segments left field in IPv6—it bypasses the standard destination field. Instead, it calculates the offset for the very last address in the routing data field. This final address is then used as the key for the RSVP session lookup, ensuring the packet receives the specific bandwidth or latency guarantees previously negotiated between the source and the ultimate destination.

This approach differs from prior solutions that often failed to provide QoS for source-routed packets until they reached the final leg of their journey. By integrating the final destination address into the classification flow at every intermediate node, the invention prevents the 'misclassification' that occurs when a router mistakes an intermediate hop for the session endpoint. Furthermore, the system extends this logic to PATH refresh messages, allowing intermediate routers to store and propagate source routing states, thereby maintaining stable resource reservations across the entire network fabric.