[AVTCORE] Comments on draft-singh-avt-mprtp-01

[Wangyekui <[e-mail]>]

Hi Varun, all,

I have some comments on draft-singh-avt-mprtp-01, for discussion.


-          First of all, I think this draft initiated a very useful work. For example, today, many mobile operators have deployed dual-plane IP bearer networks, wherein a multipath version of RTP can be used for real-time communications such as voice- and video-over-IP services. BTW, you may want to mention this in the introduction section.



-          The draft specifies the negotiation of multiple paths is through upgrading from a single-path session and using in-band signaling (i.e. RTP header extension) for indication of additional paths. Would it be better to negotiate the use of one or more of the available paths out-of-band (i.e. using SDP)? One problem with in-band negotiation is that, if the initial path happens to be broken, then even the session setup would fail. Another problem is that in-band information may get lost (and when it happens the negotiation would fail).



-          In some cases, it may be useful to use multiple paths concurrently, for improved throughput. In some other cases, it may be more desirable to use only a subset of available paths at any time instance. For example, in mobile networks using dual-plane IP bearer, typically the better-performing path is used, while the other path is kept there for fast fallback when the path being used has problem. Therefore, it would be desirable if signaling of such a capability/preference is possible.



-          Finally, it would be useful if it is possible to indicate more path specific information when advertising paths (or "interfaces" as used in the draft), e.g., which of the two planes in a network using dual-plane IP bearer. It might be sufficient if there is a hook specified to enable backwards compatible extensions when the potential multipath RTP standard is used in the future by application system standards.

BR, YK