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

Bernard Aboba <bernard.aboba@gmail.com> Wed, 05 June 2019 18:04 UTC

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From: Bernard Aboba <bernard.aboba@gmail.com>
Date: Wed, 05 Jun 2019 11:04:36 -0700
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To: Paul Kyzivat <pkyzivat@alum.mit.edu>
Cc: IETF MMUSIC WG <mmusic@ietf.org>
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Subject: Re: [MMUSIC] HELP: multiple unicast addresses for layered encoding in SDP ???
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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 <pkyzivat@alum.mit.edu> wrote:

> 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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