Subject: [SIP] RE: [SIPFORUM] Queries

From: Jonathan Rosenberg <[email-masked]>
Date: Sun, 26 Nov 2000 22:18:46 -0500

Once again, please direct all sip technology questions to the sip list,
[email-masked].

-----Original Message-----
>From: Naresh Kumar Agarwal [mailto:[email-masked]]
>Sent: Saturday, November 25, 2000 9:42 PM
>To: [email-masked]
>Subject: Re: [SIPFORUM] Queries
>
>
>Hi Jorgen,
>
>1. Hopefully, the following diagram should make things slightly clearer.
>
>
>SIP_CLIENT                     PROXY_LOCATOR                      SIP_PROXY
>|                                                   |
>|
>| 1)invite(client identifier, data1)       |
|
>|------------------------------------------------->|
>|
>| 2) 302 OK (SIP_PROXY_IP,data2) |
|
>|<-------------------------------------------------|
>|
>|                                                   |
>|
>| 3)invite(client identifier, data2)
|
>|--------------------------------------------------------------------------
---------------->--->|
>
>
>In this flow, data2 is something which is sent by the Proxy Locator upon
receiving the 
>invite from the SIP Client.  The Locator passes this data to the SIP Client
>but doesn't expect it to interpret it (it is intended for the destination
SIP Proxy).  But 
>at the same time, the SIP Client needs to interpret the IP address of the
SIP
>Proxy sent in the 302 OK.  

Your question came across as confusing, since there is no such thing as
"proxy locator" in the sip specifications or related documentations. This is
a redirect server.

The answer to your question, however, is yes. There is a way for the
redirect server to pass information to the client, which the client will
pass to the proxy. The client won't do anything with the data. It will be
placed in the request sent to the proxy. Of course, if this is non-standard
data, it will be meaningless to the proxy unless there is some kind of
specialized logic in the redirect server and proxy. Dangerous thing to do,
in general. If you need something from SIP thats not already there, you
should raise that issue instead of attempting non-standard extensions, which
is what this is.

ANyway, the way to send data is to encapsulate it as a header in the
redirected URL:

302 Try Here SIP/2.0
Contact: sip:user@host;maddr=proxy.me.com?newheader=foo

The client then sends an INVITE to proxy.me.com:

INVITE sip:user@host SIP/2.0
newheader: foo
From: sip:me@caller
.....

-Jonathan R.

----- Original Message ----- 
From: Jörgen Björkner 
To: [email-masked] 
Sent: Sunday, November 26, 2000 1:37 AM
Subject: RE: [SIPFORUM] Queries

Hi,
1) I am not sure that I really understand what you ask for. Could you
clarify with a small message flow diagram, since I am a but confused from
what you mean with client passing on data. 

2) I remember some discussion on the SIP list of using SIP for key exchange.
I think that the result was that there is a lot of things to think of when
designing a key interchange protocol, and therefore is it better to use one
of the already developed key exchange protocols for this purpose instead.
Although SIP provides digest authentication, but this requires a shared
secret between the parties. (Is this the right answer, should I add it to
the SIP FAQ?)

3) Yes, you can use PGP, for key distribution see answer 2)

/Jörgen
-----Original Message-----
From: [email-masked]
[mailto:[email-masked]]On Behalf Of Naresh Kumar
Agarwal
Sent: den 24 november 2000 17:49
To: [email-masked]
Subject: [SIPFORUM] Queries

Hi,

Would be grateful if any of you could help answer the following queries I
have:

1) During communication between a SIP client and a proxy locator (which is
used to find the location of a SIP proxy), is it possible for the proxy
locator to send some data (which is like a black box to the SIP client and
it does not need to interpret: something which it can simply pass on to the
SIP proxy later).  This data (black box) will be sent along with some other
data which the client might need to interpret.

Thus, what I want to find out is whether there is a SIP mechanism (some tag,
or something else) whereby a client can differentiate between data that it
needs to interpret and that it needs to simply pass on.

2) How do we do challenge in SIP?  Can we use the "challenge" mechanism for
key-exchange (for security reasons) in SIP?  If so, how?
3) I believe SIP supports PGP (Pretty Good Privacy).  In this case, how do
they actually get the key of the called-party?

Regards,

Naresh Agarwal.

---
Jonathan D. Rosenberg                       72 Eagle Rock Ave.
Chief Scientist                             First Floor
dynamicsoft                                 East Hanover, NJ 07936
[email-masked]                     FAX:   (973) 952-5050
http://www.cs.columbia.edu/~jdrosen         PHONE: (973) 952-5000
http://www.dynamicsoft.com

_______________________________________________
SIP mailing list
[email-masked]
http://lists.bell-labs.com/mailman/listinfo/sip

---

From: Billy Biggs <[email-masked]>
Date: Sun, 26 Nov 2000 23:34:33 -0600

Jonathan Rosenberg ([email-masked]):

> Anyway, the way to send data is to encapsulate it as a header in the
> redirected URL:
> 
> 302 Try Here SIP/2.0

  Picky point, but the start line should be:

  INVITE sip:user@host;maddr=proxy.me.com SIP/2.0

  Please be friendly to transparent proxies.

-- 
Billy Biggs, 3Com               Email: [email-masked]
http://www.div8.net/billy/      Phone: [email-masked]