Subject: I-D ACTION:draft-song-pppext-sip-support-00.txt

From: [email-masked]
Date: Tue, 04 Jun 2002 07:44:03 -0400

A New Internet-Draft is available from the on-line Internet-Drafts directories.

	Title		: SIP server IPCP configuration option for PPP
	Author(s)	: J. Song, D. Kim
	Filename	: draft-song-pppext-sip-support-00.txt
	Pages		: 6
	Date		: 03-Jun-02
	
The Point-to-Point Protocol (PPP) [1] provides a standard method for
transporting multi-protocol datagrams over point-to-point links.  
PPP defines an extensible Link Control Protocol (LCP) for 
establishing, configuring, and testing the data-link connection; and
a family of Network Control Protocols (NCPs) for establishing and 
configuring different network-layer protocols.
This document defines the PPP IPCP configuration option that contains
a list of IPv4 addresses that can be mapped to one or more SIP
proxy servers. It is just one of the many possible mechanism to 
locate the proxy server, such as DHCP option [6] and manual 
configuration. This approach is applicable to the system using PPP 
for the link layer protocol and IP address allocaiton (ex. 3GPP2 
Packet Data network)

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From: James Carlson <[email-masked]>
Date: Tue, 4 Jun 2002 08:05:26 -0400

>   The SIP (Session Initiation Protocol) [3] is a signaling protocol 
>   used for the session invitation, modification and termination. 
>   The UAC (User Call Agent) sends a request to the callee UAC.  
>   However, the request message (INVITE) is not directly sent to the 
>   callee UAC, it rather go through proxy servers, and redirect
>   servers.  This draft is specifying one of the many possible mechanism
>   to locate the proxy server, such as DHCP option [6] and manual 
>   configuration.
[...]
>   Note : the format and behavior of these options are quoted from 
>   RFC1877 [2] for the sake of consistent implementation of PPP. 

Please do not do this.  DHCP works just fine over PPP, and it's the
appropriate mechanism for distributing application configuration
information such as SIP server addresses.  Negotiating this within
IPCP isn't the right thing to do because IPCP is part of the link
layer.  Would a SIP implementation expect to reach around IP to get
SIP server addresses from the Ethernet driver?  Or from a CLIP driver
on ATM?  Since it doesn't do that, why should it expect that same
configuration data from PPP?

In other words, with this proposal, you still need to have DHCP
distribution of these addresses on all L2 media other than PPP.  Thus,
it may as well be consistent on PPP rather than requiring a special
L2-specific mechanism.

RFC 1877 was a technical mistake and ought not be repeated.  If only
we could get rid of it ...

-- 
James Carlson, Solaris Networking         <[email-masked]>
SUN Microsystems / 1 Network Drive         71.234W   Vox +1 781 442 2084
MS UBUR02-212 / Burlington MA 01803-2757   42.497N   Fax +1 781 442 1677