Subject: Re: H.323 with ATM

From: Abhishek Singh <[email-masked]>
Date: Wed, 21 Apr 1999 07:11:40 -0700 (PDT)

Hi Eric,

There is work going on in the ATM Forum and it is
called RMOA(realtime multimedia over ATM). Seems
pretty good way for H.323 transport over ATM. Not
aware of SIP efforts though.

cheers
Abhishek

--- Eric Ho <[email-masked]> wrote:
> Hi,
> 
> Could anyone please advise how VoIP is going to run
> over ATM
> (i.e., what kind of encapsulation or native ATM)?
> 
> Thanks in advance!
> 
> eh
> 
> 
>  
> 
>
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---

From: Henning Schulzrinne <[email-masked]>
Date: Wed, 21 Apr 1999 10:18:44 -0400

> aware of SIP efforts though.
This topis doesn't really belong here, but to answer the question:

There is no particular need to specify how SIP works with ATM, as it
works just fine either with ATM transport for media or for sending SIP
across (say) AAL5. The only minor item to be settled is how to represent
ATM addresses in SDP. Presumably, H.332-for-ATM will have to solve that
problem.

-- 
Henning Schulzrinne   http://www.cs.columbia.edu/~hgs

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From: "ronald h. davis" <[email-masked]>
Date: Wed, 21 Apr 1999 11:17:09 -0500

> ATM addresses in SDP. Presumably, H.332-for-ATM will have to solve that

the simple answer to h.323 over atm is to say that any ip over atm
mechanism can be used (classical ip over atm, mpoa, &c.).  in this
way, atm is invisible to h.323.  however, annex c of h.323 goes further
to define a method of carrying media channels directly over atm without
the udp/ip overhead (i.e. rtp over aal 5).

maybe you could fill us in, but i'm going to assume that there is no
such specification for sip and therefore sip over atm uses ip over atm
methods.

--
  __  ______  __  / __/ |       lucent technologies, naperville il, usa
_/ (_(_) / (_(_/_/_(_/  .       [email-masked]
author of "atm for public networks" published by mcgraw-hill
     http://www.amazon.com/exec/obidos/ASIN/0071344764

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---

From: Henning Schulzrinne <[email-masked]>
Date: Wed, 21 Apr 1999 12:55:32 -0400

> such specification for sip and therefore sip over atm uses ip over atm

That is incorrect. As discussed in more technical detail in the SIP FAQ
or various papers, SIP as a *signaling* protocol runs over any
packet-based medium (or indeed, any digital bit stream), even without
the presence of IP or UDP. As a protocol, it also doesn't care whether
the media streams use IP, ATM, or PSTN (see the PINT WG for details).
Thus, one possible approach is to run SIP over UDP/IP and voice over
ATM, as that avoids having to set up a VC just for signaling.

You'll run into timeout problems, but you could send SIP by carrier
pigeon, bottle mail, Tanenbaum's tape-in-station-wagon transport
protocol or FedEx.

Since SIP does not depend on RTP (it does not specify a complete
application scenario as H.323 does), it could just as easily set up on
RMOA connection across ATM, with the caveat of SDP naming conventions
being needed.

This should really move to mmusic...
-- 
Henning Schulzrinne   http://www.cs.columbia.edu/~hgs

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