[Kamailio-Users] rfc: xavp - extended avp

[Daniel-Constantin Mierla]

Hello,

some time ago I created a new branch in GIT named 'daniel/xavp' that 
includes code for a new pseudo-variable class 'xavp' - name being a 
shortcut to 'extended attribute value pair'. I collected some design 
details in wiki:

http://sip-router.org/wiki/devel/xavp

It is not a replacement for current AVP api implementation, although in 
the future can replace it. In the past we had couple of discussions 
about the limitations of avps which I tried to overcome. Here are some 
highlights of xavp design:

- string names only - various tests showed that having the complex 
addressing scheme with integer id and string name does not pay off 
performance gains. XAVP computes and integer id for each name that is 
used to speed up comparison

- possibility to store more data types - AVP allow string and integer 
data types. More can be handled by XAVP, including a generic data type 
where you can build your own structure and store it in the list. This is 
good for example to store custom structures for transaction lifetine -- 
right now dialog module needs to store reference to dialog structure. 
Optimizations can be done for any case of serial forking -- uri, dst 
uri, q, etc can be stored in a structure without a need to parse and 
build it from an encoded value stored in one or many avps

- possibility to group XAVPs inside another XAVP - practically is 
building lists of XAVPs. This should overcome issues with naming 
conflicts between modules - e.g., dispatacher module can group its avps 
in a list named "dispatacher", lcr module in a list named 'lcrl, then 
there can be XAVP with name 'uri' in both lists, without the risk of 
misusage. Another benefit would be reducing the number of parameters, 
right now each module exports a parameter to set the name for each AVP, 
with xavp there is need for one parameter to set the name of the list, 
then inside that list the module is free to use predefined names without 
the risk of overlapping.

- xavp having value integer or string can be used directly in config, 
whether they are in a sublist or not

Check the wiki (link above) for more. Looking forward for comments, 
suggestions and improvements.

Cheers,
Daniel

-- 
Daniel-Constantin Mierla
* SIP Router Bootcamp
* Kamailio (OpenSER) and Asterisk Training
* Berlin, Germany, Sep 1-4, 2009
* http://www.asipto.com/index.php/sip-router-bootcamp/