Subject: [Sip] Reuse of Sip Call-Id question...

From: "Cahall, Glenn" <[email-masked]>
Date: Thu, 4 Jun 2009 10:45:33 -0600

Folks,

I work for a VoIP company, Level3 Communications, and have been doing some research on the internet about
a specific condition that has arisen here dealing with the Sip protocol.  Your names came up during my research.
Was hoping I could get some feedback about the reuse of Sip Call-Id.

We have customer UAs that are reusing the same Sip Call-Id for multiple call attempts into our network.

After reviewing the Sip RFC 3261, both myself and my team concluded that this was a clear violation of the spec.  based
on the following verbiage...

8.1.1.4 Call-ID

   The Call-ID header field acts as a unique identifier to group
   together a series of messages.  It MUST be the same for all requests
   and responses sent by either UA in a dialog.  It SHOULD be the same
   in each registration from a UA.

   In a new request created by a UAC outside of any dialog, the Call-ID
   header field MUST be selected by the UAC as a globally unique
   identifier over space and time unless overridden by method-specific
   behavior.  All SIP UAs must have a means to guarantee that the Call-
   ID header fields they produce will not be inadvertently generated by
   any other UA.  Note that when requests are retried after certain

However, some voice engineers are stating that the definition of "globally unique over time and space"  means only during the
context of a given call.  Therefore, once this context is over....Sip Call-Id can in fact be reused in the very next context.

What is your take on this?

Thanks,
Glenn E. Cahall
Sr. Architect
Level3 Communications