SIP Retransmission Timeout Critical Request

Overview

 

Sometimes, the following warning entry related to Session Initiation Protocol (SIP) extension appears in the logs:

[28/May/2019 20:39:58] Asterisk: SIP retransmission timeout for host 192.168.93.115:44814 (timeout=32000ms, reqmethod=SUBSCRIBE, method=NOTIFY, from=sip:1503@sip.test.local:5060, callid=0_2246883871@192.168.0.54, seqno=117, type=Critical Request).

This article provides information related to the SIP workflow and this warning.

 

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Information

 

This warning message indicates that the SIP (Session Initiation Protocol) extension is no longer responding to the subscribe event, and it will be considered not available to the server for that specific event. This is normal behavior on SIP.

It does not mean that the server will not send calls to this extension, the calls will be sent to the last known IP that the extension was registered if the REGISTER is timed out.

The following diagram represents the typical workflow of the SUBSCRIBE messages:

                          +-------------+
                          |    init     |<-----------------------+
                          +-------------+                        |
                                 |                           Retry-after
                           Send SUBSCRIBE                    expires
                                 |                               |
                                 V          Timer N Fires;       |
                          +-------------+   SUBSCRIBE failure    |
             +------------| notify_wait |-- response; --------+  |
             |            +-------------+   or NOTIFY,        |  |
             |                   |          state=terminated  |  |
             |                   |                            |  |
   ++========|===================|============================|==|====++
   ||        |                   |                            V  |    ||
   ||  Receive NOTIFY,    Receive NOTIFY,             +-------------+ ||
   ||  state=active       state=pending               | terminated  | ||
   ||        |                   |                    +-------------+ ||
   ||        |                   |          Re-subscription     A  A  ||
   ||        |                   V          times out;          |  |  ||
   ||        |            +-------------+   Receive NOTIFY,     |  |  ||
   ||        |            |   pending   |-- state=terminated; --+  |  ||
   ||        |            +-------------+   or 481 response        |  ||
   ||        |                   |          to SUBSCRIBE           |  ||
   ||        |            Receive NOTIFY,   refresh                |  ||
   ||        |            state=active                             |  ||
   ||        |                   |          Re-subscription        |  ||
   ||        |                   V          times out;             |  ||
   ||        |            +-------------+   Receive NOTIFY,        |  ||
   ||        +----------->|   active    |-- state=terminated; -----+  ||
   ||                     +-------------+   or 481 response           ||
   ||                                       to SUBSCRIBE              ||
   || Subscription                          refresh                   ||
   ++=================================================================++

 

For further information, refer to RFC 6665 that details the notification of SIP events.

 

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Configuring Additional SIP Interface Details in Kerio Operator

 

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