Subject: [MMUSIC] POF/PAN: Length of mid values

From: Christer Holmberg <[email-masked]>
Date: Tue, 22 Oct 2013 18:12:22 +0000

Hi,

The draft currently says that the length of the mid value must be at least 32 randomly chosen characters. AFAIK, the only reason is to prevent that two endpoints would choose the same mid value.

However, as I indicated in another reply, there might be cases where e.g. a BUNDLE group contains LOTS of m- lines (read: mid values), which means we could end up with really long SDP message bodies - just because of the mid values.

Wouldn't it be possible to simply assign e.g. a 1 character mid value prefix to the Offerer and the Answerer? That would ensure that they don't assign the same mid value to an m- line, because at least the prefix would always be different.

Regards,

Christer

---

From: Martin Thomson <[email-masked]>
Date: Tue, 22 Oct 2013 15:31:04 -0700

On 22 October 2013 11:12, Christer Holmberg
<[email-masked]> wrote:
> Wouldn't it be possible to simply assign e.g. a 1 character mid value prefix
> to the Offerer and the Answerer?

That would be possible iff you could derive that from the original
context consistently, but I'm not sure that this is possible in SIP
given 3PCC and all the crazy shit that goes on there.

---

From: Paul Kyzivat <[email-masked]>
Date: Tue, 22 Oct 2013 23:05:56 -0400

> given 3PCC and all the crazy shit that goes on there.

I thought about that too.

We *could* say that if there is a middle box that turns offers into 
answers, it also has to fix up the resulting mess. It would, in 
principle, know enough to do it. Boxes that do that already have to fix 
up other stuff.

Or we could define an O/A negotiation for the prefixes. That would still 
require a middle box to do some fixup, but it would be simpler.

Or, as I suggested earlier, we could derive a prefix from other stuff in 
the offer and answer that is likely to result in unique prefixes for the 
two sides. And just ban POF/PAN if it doesn't. (In that case another O/A 
could probably resolve it.)

	Thanks,
	Paul

---

From: Christer Holmberg <[email-masked]>
Date: Wed, 23 Oct 2013 03:35:37 +0000

Hi,

Yed, the prefix could also be negotiated, e.g. using a new 'midpref' attribute.

Regards,

Christer

Sent from my Sony Ericsson Xperia arc S

Paul Kyzivat <[email-masked]> wrote:

        Thanks,
        Paul
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