- From: Magnus Westerlund <magnus.westerlund@ericsson.com>
- Date: Fri, 29 Apr 2011 09:26:31 +0200
Harald Alvestrand skrev 2011-04-27 14:42: >>> >>> I'm happy to change this, but I'd like solid data to base the decision on. >> Wouldn't it be possible to abstract this away for the web developer? I.e. the send method should, like for WebSockets, not have a max size. Instead the sending UA would be responsible for chopping up (the receiving UA for re-assembling) the message into packets not larger than the minimum path MTU. Depending on the UA (and how integrated with the IP stack of the device it is) different levels of implementation sophistication could be used (e.g. max 576 byte, or select 576/1280 depending on IP version, or even using MTU path discovery to find out max size). > Yes, we could reimplement UDP's defragmentation mechanism at the higher > level. > There is no fragmentation mechanism at UDP level. Either one uses IP level fragmentation which has issues when it comes to NAT and F/W traversal or you implement something on top of UDP. I think one do need to consider the need for a Path MTU discovery mechanism. If one has framing and sequencing of data parts, then one can consider to implement a application level PMTU discovery mechanism. I think one do needs to consider at least enabling tie in to lower layer MTU mechanisms. As you already raised there is no lower limit on IPv4 packet size other than that IPv4 fragments with any payload needs to be 56 bytes or so. 576 is a more realistic lower limit but still pretty darn small. In general I think people should review RFC 5405 "Unicast UDP Usage Guidelines for Application Designers" which is very applicable to this discussion. It does discuss a number of issue of doing things on top of UDP. http://www.rfc-editor.org/rfc/rfc5405.txt Cheers Magnus Westerlund ---------------------------------------------------------------------- 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: magnus.westerlund at ericsson.com ----------------------------------------------------------------------
Received on Friday, 29 April 2011 00:26:31 UTC