Re: [rtcweb] Reasons (not?) to multiplex audio with video
Ross Finlayson <finlayson@live555.com> Tue, 26 July 2011 20:55 UTC
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References: <4E123C54.10405@jdrosen.net> <8785C0A3-31E5-44D7-8557-3BEEE4F95E3D@skype.net> <4E2D5C5D.6060402@alvestrand.no>
Date: Tue, 26 Jul 2011 16:55:32 -0400
To: rtcweb@ietf.org
From: Ross Finlayson <finlayson@live555.com>
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Subject: Re: [rtcweb] Reasons (not?) to multiplex audio with video
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When I first started thinking about the 'multiplexing' question, I tended to support Colin's point-of-view. Carrying audio and video on separate ports gives a system more flexibility, is compatible with existing implementations (including mine :-), and is in line with long-standing assumptions about the use of the SSRC, RTCP etc. But over time I have become increasingly sympathetic to Jonathan's arguments - especially regarding NAT traversal - in particular, setup time, use of resources (# of ports), and failure modes. We have to assume that many, if not most users of RTCWEB systems will be on unsophisticated, heavily NATed IPv4 home (or hotel, or coffee shop etc.) networks. As IPv4 addresses become scarcer, this situation will likely only get worse. However, as someone noted (in the context of "security") during today's RTCWEB session, we're not the first people to be designing a (hopefully) widely-deployed consumer-oriented peer-to-peer A/V chat system. There are several existing systems out there, so it might be instructive to look at how they address the 'media multiplexing' issue - in particular: 1/ Apple's "FaceTime". OK, this is not browser-based (although with a bit of work it probably could have been), but it does use RTP. Is it using separate ports for audio and video (and two more for RTCP)? If so, has NAT traversal been a problem, and would it have been beneficial to have been able to reduce the number of ports used? (Is Dave Singer on this mailing list?) 2/ Facebook's new video chat. OK, this uses Skype, and thus presumably not RTP (at least, not now). But does this multiplex audio+video on a single port? (And if so, did this help motivate Jonathan's point-of-view?) 3/ Google Plus "Hangouts". Similar question to 1/. 4/ Any others (whether RTP-based or not)? -- Ross Finlayson Live Networks, Inc. http://www.live555.com/
- [rtcweb] Fwd: I-D Action: draft-rosenberg-rtcweb-… Jonathan Rosenberg
- Re: [rtcweb] Fwd: I-D Action: draft-rosenberg-rtc… Henry Sinnreich
- Re: [rtcweb] Fwd: I-D Action: draft-rosenberg-rtc… Cullen Jennings
- Re: [rtcweb] Fwd: I-D Action: draft-rosenberg-rtc… Randell Jesup
- Re: [rtcweb] Fwd: I-D Action: draft-rosenberg-rtc… Matthew Kaufman
- [rtcweb] Reasons not to multiplex audio with vide… Harald Alvestrand
- Re: [rtcweb] Reasons not to multiplex audio with … Emil Ivov
- Re: [rtcweb] Reasons not to multiplex audio with … Harald Alvestrand
- Re: [rtcweb] Reasons not to multiplex audio with … Randell Jesup
- Re: [rtcweb] Fwd: I-D Action: draft-rosenberg-rtc… Colin Perkins
- Re: [rtcweb] Reasons not to multiplex audio with … Emil Ivov
- Re: [rtcweb] Fwd: I-D Action: draft-rosenberg-rtc… Colin Perkins
- Re: [rtcweb] Reasons not to multiplex audio with … Muthu Arul Mozhi Perumal (mperumal)
- Re: [rtcweb] Reasons not to multiplex audio with … Matthew Kaufman
- Re: [rtcweb] Reasons not to multiplex audio with … Muthu Arul Mozhi Perumal (mperumal)
- Re: [rtcweb] Reasons not to multiplex audio with … Harald Alvestrand
- Re: [rtcweb] Reasons not to multiplex audio with … Matthew Kaufman
- Re: [rtcweb] Fwd: I-D Action: draft-rosenberg-rtc… Jonathan Lennox
- Re: [rtcweb] Reasons not to multiplex audio with … Jonathan Lennox
- Re: [rtcweb] Reasons not to multiplex audio with … Muthu Arul Mozhi Perumal (mperumal)
- Re: [rtcweb] Reasons (not?) to multiplex audio wi… Ross Finlayson
- Re: [rtcweb] Reasons (not?) to multiplex audio wi… Matthew Kaufman
- Re: [rtcweb] Reasons (not?) to multiplex audio wi… Harald Alvestrand
- Re: [rtcweb] Reasons (not?) to multiplex audio wi… Bala Pitchandi
- Re: [rtcweb] Reasons (not?) to multiplex audio wi… Aron Rosenberg