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Link Layer(LL)

This describes an implementation of Link Layer which supports fragmentation and link level ARQgif . Though this was written as a part of GPRS stack implementation, it can be used independently with any other stack with minor modifications(section 4).

The default LL provided by ns has been modified to include fragmentation and acknowledged mode as options. In acked mode, currently only one MS can be supported.

The LL can be used in fragmented or unfragmented mode. This can be configured from the OTcl script. In fragmented mode, packets received from the sending Agent are segmented before sending down to the RLC and are reassembled at the other end, before being passed up to the receiving Agent. The fragment size can be set by the user. It is currently set at a default of 1500 bytes in accordance with the maximum LL PDU size specified in GPRS.

The LL can be used in acked or unacked mode. A stop-and-wait retransmit mechanism is implemented. The LL header has been modified to accommodate these changes. Presently, this implementation supports only 2 nodes in the acked mode.

In unacked mode with no fragmentation, the Link Layer functions like the default ns Link Layer.





Richa Jain (96D07007)
Tue Jul 24 22:29:53 IST 2001