[SR-Users] Tag maximum size/length

[Jiri Kuthan]

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 at 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
>