Subject: RE: LL1, LL23

From: Stuart Cheshire <[email-masked]>
Date: Mon, 3 Mar 2003 21:27:31 -0800

Christian Huitema wrote:

>Consider now a host using an address passing application, such as
>for example VoIP using SIP. The host has just one interface. When
>the application wants to set up a VoIP call, it reads the IP
>address of the interface, and document it in the SDP payload of a
>SIP message; the peer will then send RTP packets to that address.
>If the interface has several addresses, the host needs to pick
>one; if the application is not LL aware and the interface has both
>an LL address and a routable address, the application is likely to
>pick at random. The SIP packet will often travel beyond the local
>link; if the application placed the LL address in the RTP payload,
>the VoIP call will fail. This failure will not happen if the host
>did not configure an LL address.

I think a lot of these concerns can be easily answered by simply 
implementing the APIs intelligently.

If naive applications ask the OS for its address list and then simply use 
the first address in the list, then the OS should arrange to give the 
"best" address first to accomodate these naive applications.

Also, this problem is not unique to LL.

If a laptop computer has an Ethernet interface with address 157.54.12.81 
and a wireless interface with address 10.0.0.2, then there is still the 
question of which address to put in the SIP packet. This is not a new 
problem.

Stuart Cheshire <[email-masked]>
 * Wizard Without Portfolio, Apple Computer, Inc.
 * www.stuartcheshire.org