### Description

After updating from 5.3.6 to 5.3.7 Kamailio is no longer increments CSeq for ACK when used together with UAC module.

Usage scenario: <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>

Kamailio is configured to use dialog module and calling "dlg_manage();" UAC module is used to authenticate request on the PBX. Because of the authentication against the PBX the CSeq is being incremented independently between Kamailio & PBX. ACK that is send to the PBX after 200 OK usually is CSeq + 1 from EP1 ACK message.

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.

Dialog configured as: modparam("dialog", "dlg_flag", FLD_TRACKDLG) modparam("dialog", "track_cseq_updates", 1) modparam("dialog", "dlg_match_mode", 1) modparam("dialog", "timeout_avp", "$avp(dlgtimeout)") modparam("dialog", "default_timeout", 43200)

UAC configured as: modparam("uac", "reg_db_url", DBURL) modparam("uac", "reg_contact_addr", REG_CONTACT) modparam("uac", "reg_timer_interval", 10) modparam("uac", "restore_from_avp","$avp(original_uri_from)") modparam("uac", "restore_to_avp","$avp(original_uri_to)") modparam("uac", "restore_dlg", 1) modparam("uac", "auth_username_avp","$avp(auser)") modparam("uac", "auth_password_avp","$avp(apass)") modparam("uac", "auth_realm_avp","$avp(arealm)") modparam("uac", "restore_mode","manual")

### Possible Solutions

After reverting this commit a973882b064c758972ce40e9ac3a83440c613be1 CSeq started to update properly. "dialog: skip non-INVITE initial request for cseq update processing"