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The Fail-over process is using a list of servers with different priorities and preferences for load balancing and fail-over redundancy. This list is provided by the DNS server.

The decision of a first and maybe a second and maybe a third … transport destination is taken per any dialog creating client transaction ( REQUEST ) independently. There might be multiple server in use by one account for different dialogs.
Our rule is:

  • New dialog creating INVITEs (under control) of the user start with the last server.
  • Non-INIVTE dialog creating Requests (not having a user waiting for the result) start with the highest priority server, so trying a failback.
  • Once Failover/Failback was successful, the REGISTRATION process are informed to join that server.

Below you can see the mechanism available in the software 245. It can work different in previous or upcoming software versions as sometimes customer requests/improvements are implemented.

Provisioning Parameter

Via Auto-provisioning, the Fail over timer of 32 Seconds can be changed to a lower value.



x = 0-5 (Handset 1-6), % if you want to change all.

0x7d00 (=32000 decimal)Invite-Client-TA-Timeout  (default 32000ms);


x = 0-5 (Handset 1-6), % if you want to change all.

0x7d00 (=32000 decimal)Non-Invite-Client-TA-Timeout  (default 32000ms);

Example - Change the behavior for Handset 1:

<SYMB_ITEM ID="BS_VOIP_Data.astVoipProviders[0].aucI_SIP_TOUT_ICT_B_VAL" class="symb_item" value="0x7d00"/>

<SYMB_ITEM ID="BS_VOIP_Data.astVoipProviders[0].aucI_SIP_TOUT_NICT_F_VAL" class="symb_item" value="0x7d00"/>

Example 2 - Change via provisioning all handset settings with 1 parameter.

<SYMB_ITEM ID="BS_VOIP_Data.astVoipProviders[%].aucI_SIP_TOUT_ICT_B_VAL" class="symb_item" value="0x7d00"/>

<SYMB_ITEM ID="BS_VOIP_Data.astVoipProviders[%].aucI_SIP_TOUT_NICT_F_VAL" class="symb_item" value="0x7d00"/>

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