Multiple parameters on 'a' line: Please do help me understand

James_Renkel at James_Renkel at
Wed Jul 31 12:11:50 EDT 2002

Mario and other modem experts,

There's a subtle point that needs to be made here, and that point is
that there is a difference between SPRT being:
- used in other specific applications (e.g., FoIP) on a case by case
  basis; and
- available for general use by any application.

We (3Com / CommWorks) have no problem with SPRT being used in a
specific application such as FoIP, if the fax experts to decide to do
so. In the case of FoIP, we see the use of SPRT as valuable and support
/ encourage its use there.

We do have concerns with SPRT being made available for general use
by any application, but the packet network transport protocol
experts (i.e, the IETF) may decide to do so anyhow, if this were
proposed to them.

The core of the issue here is that we are modem experts and we have
decided to use SPRT for our application, i.e., MoIP. 3Com / Commworks
fully supports that.

But now we as modem experts, not fax experts or, more importantly,
not packet network transport protocol experts, must be careful to not
overstep our boundaries: while not precluding the fax experts and the
packet network transport protocol experts from using SPRT for their
specific or general purposes if they choose to do so, we cannot make
their decisions for them or do things in such a way that their
opportunity to make their decisions is pre-empted. 3Com / CommWorks
strongly opposes anything that would lead to this.


Mario Garakani <mgarakan at> on 07/30/2002 02:26:45 PM

Please respond to Mario Garakani <mgarakan at>

Sent by:  Mario Garakani <mgarakan at>

To:   tr301 at
cc:   tr301 at
Subject:  Re: Multiple parameters on 'a' line: Please do help me understand


We have had a couple of conversations in past TIA and ITU MoIP meetings,
Jim (3com) indicated his opinion that SPRT would be more easily adopted by
if it was known to be limited in its application.  I agree with this

However, Cisco's has indicated in all past occasions that we "should not"
SPRT to V.MoIP.  There may be other very specific areas where SPRT could be
quite useful, such as FoIP or bearer data (hdlc termination).

--- Mario

Michael_Nicholas at wrote:

> Rajesh,
> Yes, we see the similarities between FoIP and MoIP,
> but in our minds, FoIP is not the proper analogy for MoIP.
> Silence Suppression may be a better analogy of extant protocols.
> We see MoIP more as a Codec type, not a Media Type.
> If Fax is detected, MoIP can switch to FoIP as it exists if MoIP is a
> type  just as other Codec types such as G.711 or G.723 currently do.
> is not an issue.
> Rajesh, You are now proposing that SPRT will be used non-MoIP?   In
> previous meetings the issue was brought up that allowing SPRT to be used
> for non-MoIP applications would unnecessarily delay MoIP consent due to
> much longer and more rigorous IETF examination.  Cisco said then that
> would not be used for non-MoIP so that was a non-issue.  Now you are
> it an issue again.
> ---------------------- Forwarded by Michael Nicholas/MW/US/3Com on
> 07/26/2002 03:57 PM ---------------------------
> "Rajesh Kumar" <rkumar at> on 07/26/2002 03:31:37 PM
> Please respond to "Rajesh Kumar" <rkumar at>
> Sent by:  "Rajesh Kumar" <rkumar at>
> To:   tr301 at
> cc:   <bfoster at>, James Renkel/MW/US/3Com, <tr301 at>,
>       <tsg16q11 at>
> Subject:  RE: Multiple parameters on 'a' line: Please do help me
> Modem experts,
> I suggest we use an ITU FoIP precedent to resolve this MoIP issue.
> is the latest, approved version of ITU T.38. Go to Annex D which
> part of the SDP for T.38 as (copied verbatim):
> m=image 49170 udptl t38
> Mapping this into the RFC 2327 template for the 'm' line (copied
>  m=<media> <port> <transport> <fmt list>
> we may conclude that, for FoIP,  the transport protocol is 'UDPTL'  and
> media format is "T.38".
> Since FoIP and MoIP must work seamlessly for the same endpoints, we can
> postulate that "SPRT" (more accurately, UDPSPRT) is the transport
> and vxxx (based on ITU is the media format.  We can create the
> following SDP equivalent to the T.38 case:
> m=application 49345 udpsprt 100
> a=sprtmap:100 vxxx/8000
> Since SPRT can be used in non-MoIP contexts, it behooves us to separate
> attributes (protocol attributes) from vxxx attributes (media format
> attributes).
> Does this seem to be a satisfactory analogy between the FoIP and MoIP
> layers? I would think that this would be clear as crystal if we invested
> the
> effort to examine extant IETF and ITU specifications.
> Rajesh
>  | -----Original Message-----
>  | From: Michael_Nicholas at [mailto:Michael_Nicholas at]
>  | Sent: Friday, July 26, 2002 12:44 PM
>  | To: fandreas at
>  | Cc: rkumar at; bfoster at; James_Renkel at;
>  | tr301 at; tsg16q11 at
>  | Subject: Re: Multiple parameters on 'a' line: Please do help me
>  | understand
>  |
>  |
>  |
>  | Flemming,
>  | I believe the two questions are dependent on each other
>  | (SDP representation vs whether MoIP is a Codec or Media type), so
>  | Please provide us with said opinion and advice on SDP representation.
>  | Thanks in advance,
>  | Michael
>  |
>  |
>  | I'm not on the e-mail reflectors and hence haven't followed all the
>  | discussion,
>  | so I'd rather not attempt an answer that is out of context. However, I
>  | understand there is some controversy over the suggested SDP
>  | representation
>  | for
>  | these things, and I'd be happy to provide an outside opinion and
>  | advice on
>  | that.
>  |
>  | -- Flemming
>  |
>  | Michael_Nicholas at wrote:
>  |
>  | > Flemming,
>  | > Thank you for your previous comments.
>  | > Your last note hints at the basis of our current discussion.
>  | > Exactly what is V.moip?
>  | > Is it a Codec type?  Is it a Media type?  Is it an Application?
>  | > I'm not sure exactly how well you have been following V.moip
>  | development,
>  | > but I think we'd welcome an outside opinion on this.
>  | > - Mike
>  | >
>  | > >> I think this question about the exact formatting of
>  | parameters is less
>  | > >> important than some of the other differences between the
>  | such
>  | > as
>  | > >> Codec declaration, the need or lack of need for capability sets,
> and
>  | the
>  | > >> number and numbering of UDP ports.
>  | > >>
>  | > >
>  | > >I agree with that. Incidentally, I also agree that codecs should be
>  | > declared
>  | > >and there shouldn't be any unnecessary port restrictions.
>  | > >
>  | > >-- Flemming
>  |

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