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Method for PCB lookup

IP.com Disclosure Number: IPCOM000109305D
Publication Date: 2005-Mar-23
Document File: 4 page(s) / 47K

Publishing Venue

The IP.com Prior Art Database


Disclosed is a method for packet context block (PCB) lookup. Benefits include improved functionality, improved performance, and improved cost effectiveness.

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Method for PCB lookup

Disclosed is a method for packet context block (PCB) lookup. Benefits include improved functionality, improved performance, and improved cost effectiveness.


              Conventionally, a packet transfer connection is associated with a connection state. After the 3-way handshake between the local and remote nodes is complete, the state is connected. The connection is ready for data transfer in either direction. A hardware-based transfer typically has a finite number of packet transfer connections that it can service in the connected state. For a received packet to be processed in the packet transfer transport layer of the network stack, the packet must be associated with a connection. The process of associating the incoming packet with a connection is called packet classification.

              Conventional PCB look-up solutions support up to 1K of offloaded connections. They are designed for 1Gb/s NIC bandwidth. They use a linear search mechanism. In the worst case, they can take up to 1024 cycles for classification. A search for 8K connections would take 8192 clock cycles, which is an unacceptable solution for 2-Gb/s and 10-Gb/s hardware accelerated connection offload processor designs. Additionally, a linear search scheme requires 48KB of internal SRAM storage (8192 x 96 bits).

General description

              The disclosed method is PCB lookup using a hash-based scheme to efficiently classify and associate a received packet across a large number of existing offloaded packet transfer connections. Each packet transfer connection is identified by the 96-bit connection-quad that contains the following fields:

•             SourceIP

•             DestinationIP

•             SourcePort

•             DestinationPort

              This identifier can have 296 unique combinations.


              The disclosed method provides advantages, including:

•             Improved functionality due to providing hash-based PCB lookup

•             Improved performance due to reducing access time by using a hash table to search for multiple connections

•             Improved performance due to using bucket frames for identifying hash collisions

•             Improved cost effectiveness due to using less SRAM storage

Detailed description

              The disclosed method uses a hashing function to map the packet transfer connection IDs over a much smaller number of unique hash indices. Because the storage space for the possible connection-quads is much larger than the unique hash indices, multiple quad combinations can be mapped to the same hash index, resulting in a has...