[MMUSIC] RSDP directorate review of draft-ietf-avtcore-rtp-vvc-14

[Christer Holmberg <[e-mail]>]

Hi,

I have performed the SDP directorate review of draft-ietf-avtcore-rtp-vvc-14.

GEN:

In general, it is quite difficult to read and parse the SDP sections. Also, for the offer/answer procedures, we often have dedicated sub-sections for creating the offer, creating the answer, etc.

However, I will focus on things which I think are unclear.

---

Q1:

Section 7.2.1 says:

   *  The OPTIONAL parameters profile-id, tier-flag, sub-profile-id,
      interop-constraints, level-id, sprop-sublayer-id, sprop-ols-id,
      recv-sublayer-id, recv-ols-id, max-recv-level-id, max-lsr, max-
      fps, sprop-max-don-diff, sprop-depack-buf-bytes and depack-buf-
      cap, when present, MUST be included in the "a=fmtp" line of SDP.
      This parameter is expressed as a media type string, in the form of
      a semicolon-separated list of parameter=value pairs.

What does "this parameter" refer to? Do you mean "these parameters"?

---

Q2:

Section 7.2.1 says:


   *  The OPTIONAL parameter sprop-vps, sprop-sps, sprop-pps, sprop-sei,

      and sprop-dci, when present, MUST be included in the "a=fmtp" line

      of SDP or conveyed using the "fmtp" source attribute as specified

      in Section 6.3 of [RFC5576]<https://datatracker.ietf.org/doc/html/rfc5576#section-6.3>.

Why are you using the "fmtp" source attribute?

---

Q3:

Section 7.2.1 says:


      When included in

      the "a=fmtp" line of SDP, those parameters are expressed as a

      media type string, in the form of a semicolon-separated list of

      parameter=value pairs.  When conveyed in the "a=fmtp" line of SDP

      for a particular payload type, the parameters sprop-vps, sprop-

      sps, sprop-pps, sprop-sei, and sprop-dci MUST be applied to each

      SSRC with the payload type.

First, what is a "media type string"?

Second, the "fmtp" attribute is ALWAYS associated with a particular payload type, isn't it?

---

Q4:

It would be very useful to have some SDP offer/answer examples.

---

Q5:

Section 7.2.2.3 says:


      When dealing with VVC, the offerer assumes that the answerer will

      be able to receive media encoded using the configuration being

      offered.

And what if the answerer is not able to?

---

Q6:

Is there a reason why Section 7.2.2.3 is not placed before Sections 7.2.2.1 and 7.2.2.2, as it applies to both?

---

Q7:

The text says nothing (as far as I can tell) sending subsequent offers and answers within a session, and whether there are restrictions etc regarding which parameters can be modified etc.

---

Regards,

Christer