Re: [AVT] WGLC comments on draft-ietf-avt-ports-for-ucast-mcast-rtp-11: Part 6: Resend behavior

> -----Original Message-----
> From: avt-bounces@ietf.org [mailto:avt-bounces@ietf.org] On Behalf Of Magnus Westerlund
> Sent: Friday, January 14, 2011 6:09 PM
> To: IETF AVT WG; draft-ietf-avt-ports-for-ucast-mcast-rtp@tools.ietf.org
> Subject: [AVT] WGLC comments on draft-ietf-avt-ports-for-ucast-mcast-rtp-11: Part 6: Resend behavior
> 
> Hi,
> 
> In Section 4, there is some statement about resending. I want to come to
> some conclusion on this topic that was brought up before.
> 
> The basic issue is the question on how one detects packet loss for RTCP.
> There is no other mechanism than detecting lack of response / action
> from the corresponding peer.

Indeed and that is what we do.

> The issue I have is that the RTT + server delay in responding can easily
> be many times the minimal sending interval that RTCP configure to serve

Hmm, why unless you have an awfully slow server? If the server is really that slow, then I guess the system has more major issues than just losing the token request messages.

> even 1 mbit/s stream. Thus the formulation in the draft:
> 
> "When a client sends a
>    Port Mapping Request or Token Verification Request message but it
>    does not receive a response back from the server (either a Port
>    Mapping Response or Token Verification Failure message), it MAY
>    resend its request by following the timer rules defined for RTCP
>    feedback messages in Section 3.5 of [RFC4585] as a good practice."
> 
> Might not be sufficient. Because the issue is how one detects the packet
> loss and how quickly the packet is considered lost.

Well, we cannot say "wait X seconds before you ask again" unless you wanna propose a value of X.

I understand this is not perfect but I don’t think there exists anything better than the rules we have in place. Re-using them is easy for implementation as well.

BTW, the same problem exists with NACKs or other RTCP packets that can actually create a lot of traffic. Ours is merely a corner case IMO.

-acbegen

> Cheers
> 
> Magnus Westerlund
> 
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