[VoiceOps] Bad/not unique SIP Call-ID GUIDs
David_Hiers at adp.com
Mon Aug 2 11:15:08 EDT 2010
I've been yammering at vendors for years for some way to influence the callID composition. It's never caused us much trouble, but I can see where it would.
If you need uniqueness, you probably need to do it yourself. If it bugged us, we'd throw a mediator in front of the db to add a customer identifier to the callID or something. There's no problem that you can't solve with one more level of abstraction :)
<RANT> As long as "rough consensus and running code" is enough to thrill the IETF and SIP Forum, their beloved MAYs and SHOULDs will continue to drain much of the value from their product. </RANT>
CCIE (R/S, V), CISSP
ADP Dealer Services
2525 SW 1st Ave.
Portland, OR 97201
From: voiceops-bounces at voiceops.org [mailto:voiceops-bounces at voiceops.org] On Behalf Of Alex Balashov
Sent: Saturday, July 31, 2010 3:33 AM
To: voiceops at voiceops.org
Subject: [VoiceOps] Bad/not unique SIP Call-ID GUIDs
Am I the only one to run into an unusually high share of duplicate
A SIP Call-ID is supposed to be a GUID (Globally Unique Identifier),
and RFC 3261 is quite clear on just how unique it needs to be. From
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.
Use of cryptographically random identifiers (RFC 1750 ) in
the generation of Call-IDs is RECOMMENDED. Implementations
MAY use the form "localid at host". Call-IDs are case-sensitive
and are simply compared byte-by-byte.
Using cryptographically random identifiers provides some
protection against session hijacking and reduces the
likelihood of unintentional Call-ID collisions.
In theory, this means that no other SIP message series initiated by
any other UA anywhere, ever should have that same identifier.
In practice, that's a pretty tall order to absolutely logically
guarantee by algorithmic means. However, it's certainly possible to
get pretty close, from a probabilistic perspective. The use of a
highly effective cryptographic digest function coupled with time
and/or RTC-seeded pseudorandom values coupled with some sort of
host-specific values should result, in the form of a composite, in a
very unique value.
It is with this understanding in mind that pretty much all CDRs in our
least cost routing and other SIP service delivery solutions are keyed
off of the Call-ID. The Call-ID is the search key on our CDR tables,
and for a variety of logical and performance reasons has a unique
constraint on the index. Call-IDs are also used in any situation
requiring the organisation of calls into a single-key hash or tree
structure of some description.
We use them because they're the only "unique" element that
conveniently persists across all SIP messages that we would want to
logically group together, irrespectively of whether the message is a
request, a reply, whether it's an initial or an in-dialog request,
etc. They're easy to extract from the message body, and just about
anything that operates on SIP messages at a relatively low level
exposes some interface by which one can extract the Call-ID. Anything
else would rely on implementing an additional, uniform composite hash
function of some kind in many different, unrelated software components
that all utilise the same database backing, IPC, etc.
That's what they're supposed to be used for. Call-IDs are GUIDs, and
GUIDs make great keys.
Long story short, the problem I've been running into recently is that
a surprisingly high number of CDRs generated by certain customers
using our solutions are bounced by the database because of Call-ID
collisions. I think the quotation from the scrolls above quite
clearly spells out that this is singularly the fault of the UACs
involved, and while I won't name any names publicly, there are
certainly some vendors in particular on whom I have my eye.
Nevertheless, it is presenting an accounting problem for us and some
of our ITSP customers. I'd be curious to know if anyone else has run
into it, and what solutions you may have adopted to deal with it.
Alex Balashov - Principal
Evariste Systems LLC
1170 Peachtree Street
12th Floor, Suite 1200
Atlanta, GA 30309
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