Re: [SAM] RG last call for draft-irtf-samrg-common-api-04
Sebastian Meiling <sebastian.meiling@haw-hamburg.de> Wed, 22 February 2012 13:48 UTC
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Date: Wed, 22 Feb 2012 14:48:12 +0100
From: Sebastian Meiling <sebastian.meiling@haw-hamburg.de>
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Subject: Re: [SAM] RG last call for draft-irtf-samrg-common-api-04
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Hi all, here some feedback on the document. In our project HAMcast we are implementing the common multicast API as part of our prototype. Lately we had some discussion in our group over the current definitions of the send and receive calls, and their error handling. At the moment error handling is quite limited and just indicates success or failure of send/recv operation. From a developers perspective this might be a little coarse, as there is no information on what to do about the error. A common problem would be the size of data (message), that an application would like to send within one send call. Using IP multicast (with standard socket API) data is send via UDP, thus message size is at least limited by UDP length field of 16 bits = 65K. But could also be limited by the OS, i.e. Linux allows to send 65K sized multicast messages, but Apple (MacOS X 10.7) has a limit of just 9K. Trying to send larger messages results in a error, e.g. "message to big". Another issues is the effective packet size on wire (MTU). Applications like video streaming often optimize their message size to fit in a single IP packet. Thereby, reducing overhead due to IP fragmentation and/or (path) MTU detection in IPv6. Though, PathMTU detection for multicast is possible, discussions in other IETF WGs (mboned) recommend to use minimal MTU of 1280 for multicast for IPv6. Note: RFC 3542 defines some additional options for the socket API, that would be useful in these cases. But our investigation shows, that these are experimental and not yet supported by most standard OS, i.e. Linux and MacOS X. However besides these IPv6 specific issues, we think that the API should be extended by calls to allow applications to detect message and MTU sizes. Further error handling should be refined for send and recv. Regards, Sebastian Am 06.02.2012 17:51, schrieb John Buford: > > This is to initiate a last call for the Common API document. > > The document and related implementation work have been presented at multiple RG meetings. > > Comments from the RG are requested to progress this document along the RFC path. > > Please review the document and provide your comments by Feb. 24. > > ID URL: http://datatracker.ietf.org/doc/draft-irtf-samrg-common-API > > Thanks, > > John > _______________________________________________ > SAM mailing list > SAM@irtf.org > http://www.irtf.org/mailman/listinfo/sam -- Sebastian Meiling +---------------------------------------+ Internet Technologies Research Group Department of Computer Science Hamburg University of Applied Sciences Berliner Tor 7, 20099 Hamburg, Germany +---------------------------------------+ Mail: sebastian.meiling@haw-hamburg.de Fon: +49 40 42875 - 8067 Fax: +49 40 42875 - 8409 Web: http://www.haw-hamburg.de/inet +---------------------------------------+
- [SAM] RG last call for draft-irtf-samrg-common-ap… John Buford
- Re: [SAM] RG last call for draft-irtf-samrg-commo… Sebastian Meiling
- Re: [SAM] RG last call for draft-irtf-samrg-commo… Matthias Waehlisch
- Re: [SAM] RG last call for draft-irtf-samrg-commo… John Buford
- Re: [SAM] RG last call for draft-irtf-samrg-commo… Matthias Waehlisch
- Re: [SAM] RG last call for draft-irtf-samrg-commo… John Buford
- Re: [SAM] RG last call for draft-irtf-samrg-commo… Matthias Waehlisch