Subject: [Megaco] 14bTD411 RTCP Port Allocation ? Clarification of usage

From: [email-masked]
Date: Wed, 20 Jun 2007 13:36:18 +0200

Hi Wayne & Jerker,

your CR is related to the usage of gm/rsb property. I'd like to make some
comments in advance, also because the semantical clarifications for this
property are subject of Draft ITU-T Rec. H.248.57, which is discussed in
ITU-T Q.3/16 in parallel to WG3 next week.

Comment 1:
Sentence: "The MG must follow the port allocation rules as defined in
clause 11/RFC 3550, which results in the allocation of a contiguous port
pair for RTP and RTCP within a single stream."
=> contiguous port value allocations are not mandated by clause 11/RFC
3550, thus the 2nd half of the sentence should include a MAY
The port allocation rules are one difference between RFC 1889 and RFC 3550,
and we refer to RFC 3550.

Comment 2:
Sentence: "In line with the recommendations of RFC 3605, non-contiguous
RTCP port numbers (identified via the a=rtcp media attribute) shall not be
used by the BGW in its LD."
=> is this not contradicting and against the purpose of RFC 3605? RFC 3605
is used for non-contiguous port allocations!?

Comment 3:
Wayne, as you mentioned last week, we got now two (different?) semantical
interpretations concerning RFC 3605 usage together with gm/rsb:
Common to both semantics is: rsb property takes precedence over RFC 3650,
right?
Difference: port allocation rules!

Semantic 1: Draft H.248.57, clause 5.6
   If the MGC sets the rtcph/rsb property to "ON", when the MG is requested
   to allocate/de-allocate a port for an RTP stream, a consecutive port for
   the associated RTCP flow is automatically allocated/de-allocated.
   If the MGC sets the rtcph/rsb property to "OFF", then only a single port
   is allocated to the RTP stream and no RTCP flow exists for the stream.
   The setting of the rtcph/rsb property takes precedence over any values
   set in the local and remote descriptors with regards to port allocation
   for RTP streams. E.g. rtcph/rsb takes over a=rtcp:<port> defined in
   RFC3605.

      => port allocation rule: rsb = ON -> consecutive port allocation,
      independent of a=rtcp specification

Semantic 2: CR 14bTD411
      => port allocation rule: rsb = ON -> port allocation dependent of
      a=rtcp specification

I don't got any strong view about the two semantics. H.248.57 is reflecting
gm v1 specification ("consecutive ports"), but perhaps a too strict
interpretation of the original TS 102 333 text ("which isn't mentioning RFC
3605 at all") in my understanding.

Do see two possibilities:
a) new package semantic: rsb=ON, but a=rtcp takes precedence for
non-contiguous port allocations
b) current package semantic: make rsb optional in a profile, in order to
allow semantics for omitted rsb property and present a=rtcp

Comments?
Albrecht

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---

From: [email-masked]
Date: Wed, 20 Jun 2007 13:54:36 +0200

Like to open a separate discussion concerning SDP usage of the "number of
ports" qualifier:

 m=<media> <port>/<number of ports> <proto> <fmt> ...

The "number of ports" qualifier (RFC 4566) is also used by RFC 3605.

Any opinions about impact on port allocation rules when used together with
rsb property?
(Assumption is a mapping of a "set of flows" on a single H.248 Stream. I do
supposse that the H.248 LD/RD may use such "m=" lines ...)

Albrecht

                      Albrecht.Schwarz@alcate                                                                                               
                      l-lucent.de                     To:      "Wayne Cutler (CV/ETL)" <[email-masked]>, "Jerker Zetterlund      
                                                      (TN/EAB)" <[email-masked]>                                            
                      20.06.2007 13:36                cc:      [email-masked], [email-masked]                                    
                                                      Subject: [Megaco] 14bTD411 RTCP Port Allocation ? Clarification of usage              

Hi Wayne & Jerker,

Comment 1:

Comment 2:

Comment 3:

Semantic 2: CR 14bTD411

Comments?
Albrecht