Subject: [Megaco] [H.248.57, H.248.RTPMUX] RTCP port allocation rules in case of RTP transport multiplexing

From: "Schwarz, Albrecht (Albrecht)" <[email-masked]>
Date: Sun, 10 Nov 2013 14:37:30 +0000

WARNING: contains banned part

Subject: [H.248.57, H.248.RTPMUX] RTCP port allocation rules in case of RTP transport multiplexing
From: "Schwarz, Albrecht (Albrecht)" <[email-masked]>
To: Nevenka Biondic <[email-masked]>, "Kall, Jan (NSN - FI/Espoo)" <[email-masked]>, Tommy Young <[email-masked]>, "Belling, Thomas (NSN - DE/Munich)" <[email-masked]>, "LANDAIS, BRUNO (BRUNO)" <[email-masked]>, "[email-masked]" <[email-masked]>
Cc: "DRAGE, Keith (Keith)" <[email-masked]>, "[email-masked]" <[email-masked]>, "Arturo Martin De Nicolas" <[email-masked]>,박주영 <[email-masked]>, "Shaikh, Viqar A" <[email-masked]>
Date: Sun, 10 Nov 2013 14:37:30 +0000

Dear All,

the addition of SDP "a=rtcp-mux” to H.248 Iq profile (23.334/29.334) leads to RTCP port allocation rules which are not yet defined (due to the fact that Iq supports also “a=rtcp” besides the rsb property).

NOTE: Iq allows “a=rtcp” only in the H.248 RD, not in the H.248 LD, but there remains still open semantics.

Normative baseline is Table 1/H.248.57 (in case of “a=rtcp” support).

You know that the consideration of “a=rtcp-mux” is still an open action for H.248.57.

Like to recall again that there are four principal connection endpoints for RTP transport multiplexing: the LS, LD, RS and RD connection endpoints:

H.248.57/Figure 1 - Connection endpoint naming conventions - the four
RTCP ports of a bidirectional RTP/RTCP session

Please find attach an evaluation of additional support of “a=rtcp-mux”, extending Table 1/H.248.57 by additional cells.

NOTE: RFC 5761 is NOT EXPLICIT on the usage of “a=rtcp” together with “a=rtcp-mux”! It’s mentioned twice in the text. My INTERPRETATION of RFC 5761: there is an IMPLICIT assumption that the SDP Offerer/Answerer SHALL NOT use both SDP attributes together. However, a different interpretation is that the parallel usage is allowed, and the receiving side is then applying “semantic of ignore”. Both interpretations might be valid. However, would prefer rather an explicit specification.

Any comments, proposals?

Albrecht