Subject: [MMUSIC] HELP: multiple unicast addresses for layered encoding in SDP ???

From: Paul Kyzivat <[email-masked]>
Date: Wed, 5 Jun 2019 13:59:45 -0400

While working on rfc4566bis I discovered something I didn't know was 
there, and question:

    Multiple addresses or "c=" lines MAY be specified on a per media
    description basis only if they provide multicast addresses for
    different layers in a hierarchical or layered encoding scheme.
    Multiple addresses or "c=" lines MUST NOT be specified at session
    level.

    The slash notation for multiple addresses described above MUST NOT be
    used for IP unicast addresses.

The syntax doesn't allow the slash format for unicast addresses. But I 
didn't realize that multiple c= lines also aren't allowed. I could swear 
there have been discussions of using this.

Am I just confused? Are multiple unicast c= lines in use in the wild for 
layered encoding?

	Thanks,
	Paul

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From: Bernard Aboba <[email-masked]>
Date: Wed, 5 Jun 2019 11:04:36 -0700

Paul --

I'm not aware of multiple unicast c= lines being used for layered coding,
although there are implementations using multiple SSRCs with a single IP
address.

On Wed, Jun 5, 2019 at 10:59 AM Paul Kyzivat <[email-masked]> wrote:

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From: "Ali C. Begen" <[email-masked]>
Date: Wed, 5 Jun 2019 22:06:14 +0300

> On Jun 5, 2019, at 8:59 PM, Paul Kyzivat <[email-masked]> wrote:
> 
> Am I just confused? Are multiple unicast c= lines in use in the wild for layered encoding?

Not to my knowledge.

-acbegen