<p></p>
<h3>Description</h3>
<p>After updating from 5.3.6 to 5.3.7 Kamailio is no longer increments CSeq for ACK when used together with UAC module.</p>
<p>Usage scenario:</p>
<pre>|EP1                   | Kamailio             | PBX
|    ->INVITE ->       |                      |
|    <- 407 -          |                      |
|    - ACK ->          |                      |
| -> INVITE SDP AUTH-> |                      |
|    <- 100 Trying -   |                      |
|                      | - INVITE SDP ->      |
|                      | <- 407 -             |
|                      | -> ACK ->            |
|                      | - INVITE SDP AUTH -> |
|                      | <- 100 Trying -      |
|                      | <- 200 OK -          |
|    <- 200 OK -       |                      |
|    - ACK ->          |                      |
|                      | - ACK ->             |
...
</pre>
<p>Kamailio is configured to use dialog module and calling "dlg_manage();"<br>
UAC module is used to authenticate request on the PBX.<br>
Because of the authentication against the PBX the CSeq is being incremented independently between Kamailio & PBX.<br>
ACK that is send to the PBX after 200 OK usually is CSeq + 1 from EP1 ACK message.</p>
<p>After update, Cseq is no longer incremented in ACK which cause re-transmission of 200 OK by the PBX and eventually in 30 sec PBX drops the call because 200 is not being acknowledged.</p>
<p>Dialog configured as:<br>
modparam("dialog", "dlg_flag", FLD_TRACKDLG)<br>
modparam("dialog", "track_cseq_updates", 1)<br>
modparam("dialog", "dlg_match_mode", 1)<br>
modparam("dialog", "timeout_avp", "$avp(dlgtimeout)")<br>
modparam("dialog", "default_timeout", 43200)</p>
<p>UAC configured as:<br>
modparam("uac", "reg_db_url", DBURL)<br>
modparam("uac", "reg_contact_addr", REG_CONTACT)<br>
modparam("uac", "reg_timer_interval", 10)<br>
modparam("uac", "restore_from_avp","$avp(original_uri_from)")<br>
modparam("uac", "restore_to_avp","$avp(original_uri_to)")<br>
modparam("uac", "restore_dlg", 1)<br>
modparam("uac", "auth_username_avp","$avp(auser)")<br>
modparam("uac", "auth_password_avp","$avp(apass)")<br>
modparam("uac", "auth_realm_avp","$avp(arealm)")<br>
modparam("uac", "restore_mode","manual")</p>
<h3>Possible Solutions</h3>
<p>After reverting this commit   <a class="commit-link" data-hovercard-type="commit" data-hovercard-url="https://github.com/kamailio/kamailio/commit/a973882b064c758972ce40e9ac3a83440c613be1/hovercard" href="https://github.com/kamailio/kamailio/commit/a973882b064c758972ce40e9ac3a83440c613be1"><tt>a973882</tt></a> CSeq started to update properly.<br>
"dialog: skip non-INVITE initial request for cseq update processing"</p>

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