[SR-Users] Parallel forking call drop scenario

Koray Vatansever koray.vatansever at gmail.com
Thu Mar 24 13:38:29 CET 2022


Hi everyone,

I'm facing the following situation.

Clients are connected over TLS. Therefore there is no retransmission in
Kamailio.

How can I prevent this call drop?



+---+                             +-----------+              +-----+
               +-----+
| A |                             | Kamailio  |              | B1  |
               | B2  |
+---+                             +-----------+              +-----+
               +-----+
  |                                     |                       |
                 |
  | INVITE                              |                       |
                 |
  |------------------------------------>|                       |
                 |
  |                                     | -------------------\  |
                 |
  |                                     |-| Parallel forking |  |
                 |
  |                                     | |------------------|  |
                 |
  |                                     |                       |
                 |
  |                                     | INVITE                |
                 |
  |                                     |---------------------->|
                 |
  |                                     |                       |
                 |
  |                                     | INVITE                |
                 |
  |
|--------------------------------------------------->|
  |                                     |                       |
                 |
  |                                     |           180 Ringing |
                 |
  |                                     |<----------------------|
                 |
  |                                     |                       |
                 |
  |                                     |                       |
     180 Ringing |
  |
|<---------------------------------------------------|
  |                                     |                       |
------------------------\  |
  |                                     |                       |-| User
answers the call |  |
  |                                     |                       |
|-----------------------|  |
  |                                     |                       |
                 |
  |                                     |                200 OK |
                 |
  |                                     |<----------------------|
                 |
  |                                     |                       |
                 |
  |                              200 OK |                       |
                 |
  |<------------------------------------|                       |
                 |
  |                                     |                       |
                 |
  | ACK                                 |                       |
                 |
  |------------------------------------>|                       |
                 |
  |                                     |                       |
                 |
  |                                     | ACK                   |
                 |
  |                                     |---------------------->|
                 |
  | ------------------------------\     |                       |
                 |
  |-| Session established with B1 |     |                       |
                 |
  | |-----------------------------|     |                       |
                 |
  |                                     |                       |
                 | ----------------------------\
  |                                     |                       |
                 |-| Client changes network    |
  |                                     |                       |
                 | | LTE to Wifi or vice versa |
  |                                     |                       |
                 | | Temporary connection lost |
  |                                     | CANCEL                |
                 | |---------------------------|
  |
|----------------------------------------------X     |
  |                                     |                       |
                 | -------------------------------------------------\
  |                                     |                       |
                 |-| Reconnected with different IP                  |
  |                                     |                       |
                 | | CANCEL is missed and client continues ringing. |
  |                                     |                       |
                 | | User answers the call.                         |
  |                                     |                       |
          200 OK | |------------------------------------------------|
  |
|<---------------------------------------------------|
  |                                     |                       |
                 |
  |                              200 OK |                       |
                 |
  |<------------------------------------|                       |
                 |
  |                                     |                       |
                 |
  |                                     |                       |
             BYE |
  |
|<---------------------------------------------------|
  |                                     |                       |
                 |
  |                                 BYE |                       |
                 |
  |<------------------------------------|                       |
                 |
  | ---------------------------\        |                       |
                 |
  |-| Session terminated by B2 |        |                       |
                 |
  | | Call Drop                |        |                       |
                 |
  | |--------------------------|        |                       |
                 |
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