Subject: Re: [AVT] Error in SRTP specs

From: "Dan Wing" <[email-masked]>
Date: Tue, 1 Jul 2008 16:34:09 -0700

> -----Original Message-----
> From: [email-masked] [mailto:[email-masked]] On 
> Behalf Of Andrei Iarus
> Sent: Monday, June 30, 2008 10:50 PM
> To: [email-masked]
> Subject: [AVT] Error in SRTP specs
> 
> Page 5 says that SRTP Framework resides between the RTP 
> application and the transport layer and that 
> "intercepts RTP packets and then forwards an equivalent SRTP packet". 
> It is not the case when the new SRTP fields are added and the 
> new packet does not fit in a UDP datagram, for example.

I don't understand that you mean; afterall, new SRTP fields would need to fit
into a UDP datagram to be sent over UDP.  A UDP datagram can be 64K bytes.

> So, probably it forwards equivalent SRTP packet(s) OR better 
> to say, it does not reside between RTP and the transport layer.

-d

_______________________________________________
Audio/Video Transport Working Group
[email-masked]
https://www.ietf.org/mailman/listinfo/avt

---

From: Magnus Westerlund <[email-masked]>
Date: Wed, 02 Jul 2008 10:50:12 +0200

Andrei Iarus skrev:
> Page 5 says that SRTP Framework resides between the RTP application and the transport layer and that 
> 
> It is not the case when the new SRTP fields are added and the new packet does not fit in a UDP datagram, for example.
> 
> So, probably it forwards equivalent SRTP packet(s) OR better to say, it does not reside between RTP and the transport layer.
> 

I think the text is in general correct, however the RTP and RTP payload 
packetization do need to be aware of the presence of SRTP for the 
session to correctly handle MTU issues. For example the scheduling 
algorithm in RTCP needs to have a correct RTCP size including lower 
layer down to IP if that is what is used to transport RTP/RTCP. That 
needs to include the fields SRTP adds.

Best regards

Magnus Westerlund

IETF Transport Area Director & TSVWG Chair
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