Subject: Question about SIP protocol

From: [email-masked] (Pradeep Malhotra)
Date: Mon, 7 Jun 1999 18:39:04 -0700

Hi,
	I have a fundamantal question on a telephonic call estblishment over
	internet using SIP. SIP is used by ite user (call control etc..) to		
	establish the session between the called and the calling party. After
	the session establishment the user may require a UDP port to send voice
	packets (using RTP protocol). Which UDP port should be used for
	this purpose? Is this negotiated during the session establishment
	using SIP?
	
	Your help is appreciated..
	
regards,
pradeep

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From: Jonathan Rosenberg <[email-masked]>
Date: Mon, 07 Jun 1999 23:16:22 -0400

>         this purpose? Is this negotiated during the session establishment

This is accomplished with the session description protocol (SDP),
rfc2327. SDP describes codecs, port numbers, and media streams for a
session. SDP is carried in SIP message to describe the session the
called party is being asked to join. See annex B of SIP (rfc2543), which
describes the usage of SDP in SIP. It describes how to format the SDP to
convey port numbers and the like.

-Jonathan R.
-- 
Jonathan D. Rosenberg                       Lucent Technologies
Member of Technical Staff                   101 Crawfords Corner Rd.
High Speed Networks Research                Holmdel, NJ 07733
FAX: (732) 834-5379                         Rm. 4C-526
EMAIL: [email-masked]
URL: http://www.cs.columbia.edu/~jdrosen

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From: Igor Slepchin <[email-masked]>
Date: Tue, 08 Jun 1999 00:31:41 -0400

Media session description (including port numbers) should normally be
listed in INVITE/response message body. All SIP implementations are
required to support SDP (RFC 2327) media descriptions (Content-type is
application/sdp) but other types are possible. See Appendix B of RFC2543
for details on using SDP with SIP.

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Igor Slepchin