Subject: [Sipping] Handling of incoming INVITE request for different MSRP session

From: <[email-masked]>
Date: Thu, 27 Apr 2006 17:36:11 +0530

Hi Garcia, Ben and all,

draft-garcia-sipping-file-transfer-mech-00.txt mandates that there
should be separate msrp session (separate m-line) for the file transfer.
But draft-ietf-simple-message-sessions-14.txt does not really
differentiate between normal chat session and file transfer session.
Also, it also does not mention the direction attribute. So User can also
have uni directional MSRP session. 

If user wants to create a session for chat and file transfer in the
single SIP INVITE. Considering the above mentioned drafts, our
understanding is that we will get two different m-lines in SDP offer for
msrp sessions. 

In such a scenario, how do we handle a case where we receive a SIP
INVITE with a SDP offer containing both types of attributes (for text
messaging and file transfer) in a single m-line? For example if we
receive an OFFER.

	v=0
      o=alice 2890844526 2890844526 IN IP4 host.atlanta.example.com
      s=
      c=IN IP4 host.atlanta.example.com
      t=0 0
      m=message 7654 TCP/MSRP *
	a=sendonly
      a=accept-types:text/plain *
      a=path:msrp://atlanta.example.com:7654/jshA7we;tcp
      a=filename:My cool picture.jpg
      a=filetype:image/jpeg
      a=disposition:inline
      a=filesize:32349
      a=icon:cid:[email-masked]
      a=hash:SHA 72245fe8653ddaf371362f86d471913ee4a2ce2e

Regards,
Amit

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---

From: Miguel Garcia <[email-masked]>
Date: Thu, 27 Apr 2006 16:49:52 +0300

Hi Amit:

As you correctly mentioned, the spirit of the file transfer draft is to 
reuse existing MSRP sessions, if they are available. But we always 
signal them in different m= lines. Notice that in the example you 
provided below there is only one m= line (for file transfer), so if you 
wanted to have chat and file transfer, you should have two m=message 
lines, one is a regular MSRP (chat), the other specific for file transfer.

So, your question... "how do we handle a case where we receive a SIP
INVITE with a SDP offer containing both types of attributes (for text 
messaging and file transfer) in a single m-line? " seems to be not 
applicable. We will have two m=message line, each one can have its own 
direction attribute if needed.

BR,

        Miguel

[email-masked] wrote:
> Simple mailing list
> [email-masked]
> https://www1.ietf.org/mailman/listinfo/simple
> 

-- 
Miguel A. Garcia           tel:+358-50-4804586
sip:[email-masked]
Nokia Research Center      Helsinki, Finland

---

From: Miguel Garcia <[email-masked]>
Date: Thu, 27 Apr 2006 17:26:01 +0300

Hi Sudha:

Inline discussion.

Sudha wrote:
> Hi all,
> Is it valid to have two m= lines in a single INVITE?

Yes, of course.

> If such is a case, Is it valid to have two MSRP sessions created for 
> each of the media line? 

yes, why not?

> As per the draft on File transfer using MSRP, 
> once the File transfer is completed, the MSRP Session associated with it 
> will be closed. So it should be apt to have 2 sessions for each of the 
> media line.

I am not sure what you mean with "2 sessions fr each of the media line". 
Each m=message represents an MSRP media stream. Both can use the same 
MSRP session (TCP connection + session-id in MSRP), but they are 
different media streams, just multiplexed over the same TCP connection 
and MSRP session.

BR,

       Miguel

> 
> Regds,
> Sudha
> 
> On Thu, 27 Apr 2006 19:19:52 +0530, Miguel Garcia 
> <[email-masked]> wrote:
> 
>> Hi Amit:
>>
>> As you correctly mentioned, the spirit of the file transfer draft is 
>> to reuse existing MSRP sessions, if they are available. But we always 
>> provided below there is only one m= line (for file transfer), so if 
>> you wanted to have chat and file transfer, you should have two 
>> m=message lines, one is a regular MSRP (chat), the other specific for 
>> file transfer.
>>
>>> have uni directional MSRP session.  If user wants to create a session 
>>> for chat and file transfer in the
>>> msrp sessions.  In such a scenario, how do we handle a case where we 
>>> receive a SIP
> --Best Regards,
> Sudha V.S

---

From: Miguel Garcia <[email-masked]>
Date: Fri, 28 Apr 2006 09:16:42 +0300

Inline discussion.

Sudha wrote:
> Hi Miguel,
> -Does "m=" lines have different port numbers?
>     If so, it would result in 2 TCP Connections and hence 2 MSRP 
> Sessions. This would naturally result in two "a=path:" attributes which 
> would complicate the message parsing.
>     else if the media lines have the same port numbers it is like 
> duplication of the previous media line and it doesnt carry any meaning.

Different m= lines will have the same port number, because they will be 
sharing the same TCP connection. There is nothing new here, the MSRP 
draft already discusses the TCP sharing in Sections 5.1 and 8.1.

What we say in our draft is that each file transfer is identified with a 
different MSRP session. We can discuss if we need to share the same 
session, but at the moment the draft says each m= line has a unique MSRP 
sessionId. Still the port number used for the TCP connection is the same.
> 
> -How to distinguish between which media line is for normal MSRP Chat and 
> MSRP File Transfer.

MSRP for File Transfer will have a file selector in the SDP. The file 
selector is described in Section 6.1 of the File Transfer draft.

> 
> -In the previous mail you had stated that,
> "Each m=message represents an MSRP media stream. Both can use the same 
> and MSRP session."

Note that sharing the same MSRP session is not correct, at least, 
according to what we have in the draft now, my apologies.

> It is possible to mutliplex MSRP Sessions(Identified by the session Id) 
> over the same TCP Connection. But I am not very clear with what you 
> meant here by "MSRP media stream". Can you please give some info on how 
> to identify the media streams in the "m=" lines.

That is probably the main point, we need a unique identifier, and that 
is the session Id in MSRP. That is the reason why the session ID has to 
be different.

BR,

         Miguel

> 
> Regds,
> Sudha.
> 
> 
> On Thu, 27 Apr 2006 19:56:01 +0530, Miguel Garcia 
>>> As per the draft on File transfer using MSRP, once the File transfer 
>>> is completed, the MSRP Session associated with it will be closed. So 
>>> it should be apt to have 2 sessions for each of the media line.
>>
>> I am not sure what you mean with "2 sessions fr each of the media 
>> line". Each m=message represents an MSRP media stream. Both can use 
>> the same MSRP session (TCP connection + session-id in MSRP), but they 
>> are different media streams, just multiplexed over the same TCP 
>> connection and MSRP session.
>>
>> BR,
>>
>>        Miguel
>>
>>
>>>  Regds,
>>> Sudha
>>>> to reuse existing MSRP sessions, if they are available. But we 
>>>> always signal them in different m= lines. Notice that in the example 
>>>> you provided below there is only one m= line (for file transfer), so 
>>>> if you wanted to have chat and file transfer, you should have two 
>>>> m=message lines, one is a regular MSRP (chat), the other specific 
>>>> for file transfer.
>>>>
>>>> INVITE with a SDP offer containing both types of attributes (for 
>>>> text messaging and file transfer) in a single m-line? " seems to be 
>>>> not applicable. We will have two m=message line, each one can have 
>>>> its own direction attribute if needed.
>>>>
>>>> BR,
>>>>
>>>>         Miguel
>>>>
>>>>
>>>>> have uni directional MSRP session.  If user wants to create a 
>>>>> session for chat and file transfer in the
>>>>> msrp sessions.  In such a scenario, how do we handle a case where 
>>>>> we receive a SIP