Weight-based contacts call termination distribution

[marcocapetta]

Description

Implement a new TM logic to distribute calls to contacts belonging to the same subscriber similar to the weight mechanism that is used in lcr module. This mechanism should support primary/backup, load-sharing or a combination of both.

Expected behavior

Currently, with the existing serial forking using q-value:

• if the q-values are different, the devices will ring serially but always in the same order
• if the q-values are equals, the devices will ring in parallel

With the new mechanism, instead, I have to be able, for example, to register 2 devices and send:

• the 50% of the call to device 1 and then to device 2 as a backup
• the 50% of the call to device 2 and then to device 1 as a backup

Possible Solutions

A possible approach is to extend the existing load_contact function and re-use the q-value as a weight.
For example:

• contact 1 has Q value 1
• contact 2 has Q value 0.5
• contact 3 has Q value 0.5
• contact 4 has Q value 0
  Then kamailio distributes the calls using the following proportion:
  Q : total_Q = call_prob : 100
  So:
• contact 1 has probability to ring of 50% (1 * 100 / 2)
• contact 2 has probability to ring of 25% (0.5 * 100 / 2)
• contact 3 has probability to ring of 25% (0.5 * 100 / 2)
• contact 4 has probability to ring of 0 (0 * 100 / 2) but it is used as backup option if all other contacts fail

This should solves the limitations of serial forking and allows to achieve equal or predictable weight-based call termination distribution.

[miconda]

The related PR was merged.