Alternatives can be explored for how to represent the information provided by SDP, but the enumeration and testing of potential endpoints within an offer-answer exchange is at the core of ICE (RFC 5245), and is also a potential means for demonstrating media authorization. If the Javascript limitations on enumeration of physical or logical addresses can't be overcome, we might have to live with server reflexive and relayed endpoint identifiers (assuming that server reflexive and relayed endpoint identifiers don't trigger similar concerns). Replacing addresses with names could be done prior to the offer/answer exchange but this might introduce vulnerabilities (e.g. voice hammer attacks based on DNS cache poisoning). Date: Wed, 2 Feb 2011 16:09:48 -0800 From: harald@alvestrand.no To: rtc-web@alvestrand.no Subject: Re: [RTW] [dispatch] Does RTC-WEB need to pick a signaling protocol? On 02/02/11 11:19, Henry Sinnreich wrote: Message body Is there some understanding on the list on how the IP addresses in SDP can be reconciled with the USAF RFC 3424? Nit: UNSAF, not USAF. http://www.rfc-editor.org/rfc/rfc3424.txt “...a process whereby some originating process attempts to determine or fix the address (and port) by which it is known - e.g. to be able to use address data in the protocol exchange, or to advertise a public address from which it will receive connections. There are only heuristics and workarounds to attempt to achieve this effect; there is no 100% solution. Since NATs may also dynamically reclaim or readjust translations, "keep-alive" and periodic re- polling may be required. Use of these workarounds MUST be considered transitional in IETF protocols, and a better architectural solution is being sought. The explicit intention is to deprecate any such workarounds when sound technical approaches are available.” In our case, the answer that has proved workable is called STUN. Obviously there is much more dead stuff in SDP besides using the misleading IP addresses, but this seems to be a deep architectural flaw. There were some early attempts to do SDPng and we know today much more: http://tools.ietf.org/html/draft-ietf-mmusic-sdpng-07 Why not replace SDP, since it deals only with a/v codec negotiation with a more general, standards based metadata approach? For example including Web conferencing displays and UI control capabilities. Of course such a new approach must be easily mapped to the existing global SIP VoIP infrastructure. Or are the no “sound technical approaches” available at all? I'm all in favour of replacing SDP, but would not like to require that before we can produce any output from this group. Justin's idea of sorting out what information we need and specifying how that maps into SDP (just like is currently done by Jingle) might be a reasonable approach that can allow us to not fossilize SDP's misfeatures forever. Harald _______________________________________________ RTC-Web mailing list RTC-Web@alvestrand.no http://www.alvestrand.no/mailman/listinfo/rtc-web