Subject: help on SIP headers

From: jimmy Zhang <[email-masked]>
Date: Thu, 30 Mar 2000 18:38:23 -0800

Since I am pretty new to SIP, please forgive me for asking naive
questions, such as
the following one.

   In the specificiation, both "to" and "from" fields require the sip
address to be in
the form of either "sip:[email-masked]" or "anonymous
<sip:[email-masked]>".
But I just collected some sample messages in which both "to" and "from"
headers were
in different looks, e.g. "to: isbn:2983792873" and "From:
http://www.cs.columbia.edu". Just
wondering if anyone could explain, in the case that they are both
valid,  why http URL would
be allowed in the From or To headers? Also, aside from "isbn", what are
other possible
prefixes allowed?

thanks,

--

Jimmy zhang ([email-masked])

Software Engineer