Hi I may miss some usecase here but as RoHC is (at least from my perspective) only intended for the radio links I don't see why e.g core network nodes should be affected. It is IMHO only the layers below the PDCP layer that sees the varying packet sizes and the concept of MTU does not have much meaning there. But as I said, I may miss some other usecase. BR /Ingemar
---------------------------------------------------------------------- Message: 1 Date: Mon, 18 May 2009 15:33:51 +0200 From: Magnus Westerlund <[email protected]> Subject: [Tsvwg] Path MTU discovery when having varying MTU To: TSV Area <[email protected]> Message-ID: <[email protected]> Content-Type: text/plain; charset=ISO-8859-1 This email is BCC to a number of list. Please respond to the TSV-area list. In the AD review of the documents for defining Robust Header Compression (ROHC) over IPsec: http://tools.ietf.org/wg/rohc/draft-ietf-rohc-hcoipsec/ <http://tools.ietf.org/wg/rohc/draft-ietf-rohc-hcoipsec/> I picked up on a issue that has been mentioned before but not really been dealt with. Namely the varying MTU for packets entering this tunnel. So this work is to enable so that ROHC can compress the inner IP, transport, etc headers inside an IPsec tunnel to save bandwidth that way. ROHC is a stateful compression technology which can result in that the headers being compressed can be both slightly bigger as well as much smaller. Thus the effective MTU for a particular packet inside an IPsec tunnel with ROHC varies depending on which packet in a sequence it is. This will create some issues for any path MTU discovery mechanism, where a smaller packet may result in a ICMP TOO BIG while a slightly larger packet doesn't. So I am interested in what issues you see arising with this technology and what you think should be done about it. Cheers Magnus Westerlund IETF Transport Area Director & TSVWG Chair ---------------------------------------------------------------------- Multimedia Technologies, Ericsson Research EAB/TVM ---------------------------------------------------------------------- Ericsson AB | Phone +46 10 7148287 F?r?gatan 6 | Mobile +46 73 0949079 SE-164 80 Stockholm, Sweden| mailto: [email protected] ---------------------------------------------------------------------- End of tsvwg Digest, Vol 61, Issue 62 *************************************
