28 Mar
2013
28 Mar
'13
5:22 p.m.
On 3/28/13 12:41 PM, Grant Bagdasarian wrote:
Do you mean "implementation" in the context
of Kamailio's implementation of SIP?
yes
If so, what if certain SIP clients implement it in a
different way and their Tag values exceed this limitation?
that depends on the application how a loss of bits affects it. With the required level of
entropy,
the impact is probably not big within a module: good enough for say correlation.
it would be more problematic if the sip_capture module tried to work with some other
module
and match the tags between them -- that would obviously fail.
if you wanted to be more deterministic with the sip_capture module and mysql data model,
you would probably have to change data types to TEXT (256 bytes) or BLOB (64k). While
these sizes are not prohibited by the spec, MTU constraints and fragmentation would
anihilate INVITEs with such Tags anyhow. Also these types have some performance penalties
associated with them.
so in summary -- it appears that while somehow esthetically suboptimal, the 64 bytes limit
is
mostly good enough.
jiri
-----Original Message-----
From: Jiri Kuthan [mailto:jiri@iptel.org]
Sent: Thursday, March 28, 2013 11:42 AM
To: Kamailio (SER) - Users Mailing List
Cc: Grant Bagdasarian
Subject: Re: [SR-Users] Tag maximum size/length
On 3/28/13 11:21 AM, Grant Bagdasarian wrote:
Hello,
Is there a maximum length/size defined for the From and To Tag?
The RFC states: “it MUST be globally unique and cryptographically random with at least 32
bits of randomness”.
Though I can’t find anything in the RFC about the maximum.
The sip_capture table stores the to_tag and from_tag in a varchar(64). Does this mean the
max is 64?
Source: https://code.google.com/p/homer/source/browse/sql/create_sipcapture.sql
Yes, that's an implementation's limitation.
-jiri