[SIPForum-discussion] HELP
Xavi Milà
xavi.mila at gmail.com
Fri May 16 17:05:20 UTC 2008
Inline:
On Fri, May 16, 2008 at 5:50 PM, Ashish Umrani <ashish.umrani at gmail.com>
wrote:
> I dont know if anybody answered to your satisfaction. here is my attempt.
> Mine is purely english based and less technical yet its the same that SIP
> has applied.
>
>
> Assume that Ganesh wants to talk to Ashish and we have a proxy in between.
> I am describing how will this complete process go through.
>
> Ganesh will start talking to proxy (not knowing ashish's ip proxy, is the
> only way left to Ganesh for this purpose).
> Ganesh tells proxy that he wants to talk to Ashish.
> Proxy tells ganesh that "Hang on! let me see what I can do"
>
> Proxy then tries to contact Ashish, stating that Ganesh wants to talk to
> Ashish (messages are sent to all known locations for Ashish)
> Ashish says "Ok I am ready"
>
> Proxy tells Ganesh, where about of Ashish
> Ganesh and Ashish both start talking
>
> After 5 minutes if happy talk, Ashish says Bye and tells proxy that he is
> done with conversation.
> Proxy then tell Ganesh that Ashish has ended conversation
> The call ends
>
>
> In the above mentioned scenario, the first three sentences represent a
> dialog between Ganesh and proxy.
> Complete conversation between Ganesh and Proxy is the session between
> Ganesh and Proxy
> Similarly next two sentences represent Dialog between Proxy and Ashish
> Complete conversation between Ashih and Proxy is another session
>
IMHO, In rfc3665 section "3.2. Session Establishment Through Two Proxies"
is described one scenario like the one you has explained clearly:
Alice Proxy 1 Proxy 2 Bob
| | | |
| INVITE F1 | | |
|--------------->| | |
| 407 F2 | | |
|<---------------| | |
| ACK F3 | | |
|--------------->| | |
| INVITE F4 | | |
|--------------->| INVITE F5 | |
| 100 F6 |--------------->| INVITE F7 |
|<---------------| 100 F8 |--------------->|
| |<---------------| |
| | | 180 F9 |
| | 180 F10 |<---------------|
| 180 F11 |<---------------| |
|<---------------| | 200 F12 |
| | 200 F13 |<---------------|
| 200 F14 |<---------------| |
|<---------------| | |
| ACK F15 | | |
|--------------->| ACK F16 | |
| |--------------->| ACK F17 |
| | |--------------->|
| Both Way RTP Media |
|<================================================>|
| | | BYE F18 |
| | BYE F19 |<---------------|
| BYE F20 |<---------------| |
|<---------------| | |
| 200 F21 | | |
|--------------->| 200 F22 | |
| |--------------->| 200 F23 |
| | |--------------->|
| | | |
Taking a look at every single "FX SIP message" you can see that the Call-ID
is the same for each one. This is necessary but not sufficient to say "this
is the same dialog"
From rfc3261, page 69 (Chapter 12) we can read "A dialog is identified at
each UA with a dialog ID, which consists of a Call-ID value, a local tag and
a remote tag."
An example of local or remote tag is:
From: Alice <sip:alice at atlanta.example.com
<sip%3Aalice at atlanta.example.com>>;tag=9fxced76sl
To: Bob <sip:bob at biloxi.example.com <sip%3Abob at biloxi.example.com>>
or
From: Bob <sip:bob at biloxi.example.com <sip%3Abob at biloxi.example.com>>;tag=314159
To: Alice <sip:alice at atlanta.example.com
<sip%3Aalice at atlanta.example.com>>;tag=9fxced76sl
Now, we can affirm that with the same Call-ID and the same tag (From:
or To:) there is only ONE DIALOG in the example you has provided.
Furthermore, difference between session and dialog was discussed some time
ago in this mailing list.
>
> I am not 100% sure about transaction and wont like to misguide you.
>
> Ashish
>
>
>
>
> On Fri, May 16, 2008 at 1:39 AM, Ganesh Bhattathiri <
> ganesh_bhattathiri at persistent.co.in> wrote:
>
>> Hi
>>
>>
>>
>> Can somebody tell me the difference between Dialog and session and
>> transaction?
>>
>>
>>
>> First let me tell you what I thought it was.
>>
>>
>>
>> If there is a UAC and UAS, If UAC sends a request and gets a non-100
>> response back the whole process is knows as a dialog
>>
>> And from the point of first request to the ACK sent for BYE it is a
>> session.
>>
>>
>>
>> Now if what I have said above is right then how would you differentiate a
>> request sent outside the dialog? As in doesn't that also get a response back
>> could that not be a non-100 response?
>>
>>
>>
>> Can Someone help me get this confusion cleared?
>>
>>
>>
>> Thanks again
>>
>>
>>
>> Ganesh
>>
>> _______________________________________________
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>>
>>
>
> _______________________________________________
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>
>
--
------------------------------------------------------------------------------------------------------------
| Xavier Milà
|
| Research Group on Network Technologies and Strategies (NeTS)
| Universitat Pompeu Fabra (UPF)
| Pg. de Circumval·lació 8, 08003 Barcelona, Spain
|
| phone: +34 93 542 29 06
| mailto: xavier.mila at upf.edu
| http: www.nets.upf.edu
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