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PPP ROHC small-CID packets


Hi. I have a question re the PPP ROHC packets that our CISCO2811 which we are using in a test enviroment as a LNS running 15.1(4)M7.


The 2811 generates ROHC packets towards the connected LAC. There is no ROHC communication in the other direction (LAC-LNS).


Initially the 2811 repeatedly sends ROHC packets of 106 bytes to the LAC which wireshark shows as "PPP ROHC small-cid (0x0003)". Then after a while all comms are sent from the LNS to LAC with packets using ROHC.


I cant find any docs showing this negotiation process for a Cisco device. Can anyone explain what the process is here re the ROHC negotiation between the 2811 (LNS) and the CPE (LAC). This usage of ROHC is not seen with all CPEs that are in use so I am trying to work out why it suddenly kicks in in this case.

After the initial ROHC packets are sent from the LNS all future comms from the LNS to the LAC have ROHC applied so I am assuming that at some point the CPE has indicated that it is capable of decompressing these or perhaps that is just taken for granted?


Any help understanding the process would be appreciated.







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