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Tuesday, July 28, 2015

About new variables in Kamailio v4.3

Each new major version of Kamailio brings a new set of configuration file variables, which adds to the existing long list (see Pseudo-Variables Cookbook), enabling more flexibility or making easier to approach some specific needs.

v4.3 introduced as well several new variables, here we touch few of them.

$var(name) is an old variable, storing the value in private memory, being persistent per process. It is very fast when used in operations (no looking needed), therefore popular across config files. One of its property is that the initial value is 0 (no need to initialize it explicitly) and setting it to $null results in resetting it to value 0.

Requested by community, a new variable class $vn(name) was introduced in v4.3 by pv module, which has the properties of $var(name), but it holds ‘null’. Setting it to 0 requires explicit assignment ‘$vn(name) = 0′ and setting it to ‘$null’ no longer resets the value to 0, but to ‘null’.

The pv module added $sbranch(key), a class of variables that allows to manage all the attributes of outgoing branches, including the first branch corresponding to request URI. It is like a temporary container where to store the attributes before pushing them to the branches. A set of three functions come to help in these operations: sbranch_set_ruri(), sbranch_append() and sbranch_reset(). An use case that is possible now can be setting the Path of a branch (next hops till final destination), including the one for R-URI branch.

Related to XAVP variables, a function named xavp_explode_params() can be now used to take the names and values of a parameters string and add them as XAVPs.

The rr module introduced variables to get the direction of the request – $rdir(name) will return ‘downstream’ if request is from caller to callee and ‘upstream’ if the request is from callee to caller.$rdir(id) is the variant to return 1 for ‘downstream’ and 2 for ‘upstream’. From the same module come $fti and $tti – the From and To tags as for the initial INVITE transaction, no matter of direction for the request. For example, using in config (e.g., as htable key) the dialog 3-tuple identifier (call-id, from-tag, to-tag) is now simpler, no need to care anymore about the direction of the request.

Presence or other IMS modules are among the components introducing new variables, you can see the full list of variables available for Kamailio v4.3 at:
What is new in v4.3 is summarized at:
Enjoy the summer!

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