[Speechsc] MRCP and mixed IPv4/IPv6 environments

["Wyss, Felix" <[e-mail]>]

The examples in the most recent draft (draft-ietf-speechsc-mrcpv2-24.txt) use only IPv4 address types.  There is no mention of IPv6, let alone how MRCP should be used in mixed IPv4/IPv6 environments.  I think that should be addressed in the RFC, at a minimum with some examples and/or discussion to provide guidance to implementers.  This seems especially important as the introduction of the "a=cmid" co-media attribute adds another dimension to the media negotiation.

As an example, I took a synthesizer sample from the current draft and tried to come up with an offer/answer exchange in a mixed environment with alternate address type semantics (RFC#4091).  I am assuming here that the offerer allows the answerer to accept a different address type for MRCP and RTP by listing both stream identifiers of the IP4 and IP6 RTP streams as two separate "a=cmid" attributes.  Thus, the answerer could elect to use IPv6 for MRCP and IPv4 for RTP:


Offer:

v=0
o=sarvi 2890844526 2890844526 IN IP6 2001:DB8::4
s=-
a=group:ANAT 1 2
a=group:ANAT 3 4
m=application 9 TCP/MRCPv2 1
c=IN IP4 192.0.2.12
a=setup:active
a=connection:new
a=resource:speechsynth
a=cmid:3
a=cmid:4
a=mid:1
m=application 9 TCP/MRCPv2 1
c=IN IP6 2001:DB8::1
a=setup:active
a=connection:new
a=resource:speechsynth
a=cmid:3
a=cmid:4
a=mid:2
m=audio 49170 RTP/AVP 0
c=IN IP4 192.0.2.12
a=rtpmap:0 pcmu/8000
a=recvonly
a=mid:3
m=audio 49170 RTP/AVP 0
c=IN IP6 2001:DB8::1
a=rtpmap:0 pcmu/8000
a=recvonly
a=mid:4


Example Answer 1 (IPv6 for MRCP, IPv6 for RTP):

v=0

o= 2890842808 2890842808 IN IP6 2001:DB8::5
s=-
m=application 0 TCP/MRCPv2 1
c=IN IP4 0.0.0.0
a=mid:1
m=application 32416 TCP/MRCPv2 1
c=IN IP6 2001:DB8::2
a=setup:passive
a=connection:new
a=channel:32AECB234338@speechsynth
a=cmid:4
a=mid:2
m=audio 0 RTP/AVP 0

c=IN IP4 0.0.0.0
a=mid:3

m=audio 48260 RTP/AVP 0
c=IN IP6 IN IP6 2001:DB8::2
a=rtpmap:0 pcmu/8000
a=sendonly
a=mid:4


Example Answer 2 (IPv6 for MRCP, IPv4 for RTP):

v=0

o= 2890842808 2890842808 IN IP6 2001:DB8::5
s=-
m=application 0 TCP/MRCPv2 1
c=IN IP4 0.0.0.0
a=mid:1
m=application 32416 TCP/MRCPv2 1
c=IN IP6 2001:DB8::2
a=setup:passive
a=connection:new
a=channel:32AECB234338@speechsynth
a=cmid:3
a=mid:2
m=audio 48260 RTP/AVP 0

c=IN IP4 192.0.2.11
a=rtpmap:0 pcmu/8000
a=sendonly
a=mid:3

m=audio 0 RTP/AVP 0
c=IN IP6 ::
a=mid:4


Does that seem like an appropriate interpretation?

Thanks,
Felix Wyss
Interactive Intelligence, Inc.