Re: [MMUSIC] [rtcweb] Updating JSEP and BUNDLE: Semantics of same port in multiple m- lines

[Roman Shpount <[e-mail]>]

Chirster,

This is exactly the language I have remembered. So, it is not explicitly
prohibited but the behavior is undefined.
_____________
Roman Shpount


On Thu, Jan 28, 2021 at 4:26 AM Christer Holmberg <
[e-mail]> wrote:

> This is the test from Section 5.14 of RFC 4566:
>
>
>
>       “The semantics of multiple "m=" lines using the same transport
>
>       address are undefined.  This implies that, unlike limited past
>
>       practice, there is no implicit grouping defined by such means and
>
>       an explicit grouping framework (for example, [18]) should instead
>
>       be used to express the intended semantics.”
>
>
>
> ([18] refers to the SDP grouping framework defined in RFC 5888)
>
>
>
>
>
> This is the corresponding (slightly modified) text from Section 5.12 of
> RFC 8866:
>
>
>
>      “This document gives no meaning to assigning the same media address
>
>       to multiple media descriptions.  Doing so does not implicitly
>
>       group those media descriptions in any way.  An explicit grouping
>
>       framework (for example, [RFC5888]) should instead be used to
>
>       express the intended semantics.  For instance, see [RFC8843].”
>
>
>
> (RFC 8843 is BUNDLE)
>
>
>
>
>
> So, again, it is ok to use the same port in multiple m- lines, if the
> semantics is defined, and if the participants support that semantics.
>
>
>
> When you send an initial INVITE, from a standards viewpoint, you don’t
> know whether the participants in the path support that semantics.
>
>
>
> Regards,
>
>
>
> Christer
>
>
>
>
>
>
>
> *From:* mmusic <[e-mail]> *On Behalf Of *Christer Holmberg
> *Sent:* torstai 28. tammikuuta 2021 1.26
> *To:* Roman Shpount <[e-mail]>
> *Cc:* Magnus Westerlund <magnus.westerlund=[e-mail]>rg>;
> [e-mail]
> *Subject:* Re: [MMUSIC] [rtcweb] Updating JSEP and BUNDLE
>
>
>
> Hi,
>
>
>
> >Can you or anyone else provide the reference to the document which
> prohibits using the same port in multiple m= lines?
>
>
>
> It is not prohibited, but the SDP spec says that the semantics is
> undefined.
>
>
>
> Now, in BUNDLE we can define semantics for usage of multiple m= lines, and
> BUNDLE endpoints would support that semantics.
>
>
>
> The problem is if you send an initial INVITE that reaches a non-BUNDLE
> endpoint. There is no way to know how that endpoint will process the offer,
> and we have seen that the offer gets rejected (in different ways).
>
>
>
> Regards,
>
>
>
> Christer
>