In this section:

Related articles:

 Overview

The SBC Core provides a preconditions support feature to reserve network resources as a preventative measure to minimize chances of session failure due to lack of resources before alerting the called party. This prevents a "ghost ring" where the called party is alerted before the call is set up.

The SBC Core supports preconditions interworking functionality only when one leg of a call supports preconditions and other does not. The SBC supports preconditions functionality on either of the legs (egress or ingress). With this feature, preconditions interworking is decided based on the precondition profile configuration, present in the Common IP Attributes of the IP Signaling Profile (IPSP).

This feature supports ISUP-SIP and SIP-SIP preconditions interworking, and provides transparency by dropping/adding of preconditions attributes between supporting or non-supporting peers. The preconditions are configured from the SBC at the SIP Trunk Group level using the parameters “preconditions” (for incoming requests) and “transmitPreconditions” (for outgoing requests).

The SBC Core completes the ingress preconditions when the call terminates at the PSX script. Users can configure the list of script names (in the psxScriptProfile) for which the SBC performs ingress preconditions interworking. The ingress preconditions trigger when one of the configured script names matches with the PSX returned script name. The script execution continues after the ingress preconditions are met.

Note

The SBC allows a maximum of three script names to be configured.

The configurable script name is the same as the script name that PSX returns.

The pemInterworking flag inhibits sending the P-Early Media header in the first 18x response for the ingress preconditions interworking scenario.

For additional details, refer to Reserving Network Resources.

The following is an example of ingress preconditions interworking: 

Creating the SMM  Profile

To create a SMM profile to select SMM rule based ingress IPTG, enter the following command:

% set profiles signaling sipAdaptorProfile Add_CRLF rule 1
% set profiles signaling sipAdaptorProfile Add_CRLF rule 1 criterion 1 type message message messageTypes request methodTypes INVITE condition exist
% set profiles signaling sipAdaptorProfile Add_CRLF rule 1 criterion 2 type header header name NNI value Japan condition exist
% set profiles signaling sipAdaptorProfile Add_CRLF rule 1 action 1 type variable 
% set profiles signaling sipAdaptorProfile Add_CRLF rule 1 action 1 operation storeIpTg
% set profiles signaling sipAdaptorProfile Add_CRLF rule 1 action 1 from type value value SBX_TG_SIP
% set profiles signaling sipAdaptorProfile Add_CRLF rule 1 action 1 to type variable variableValue var1
% set profiles signaling sipAdaptorProfile Add_CRLF state enabled
commit

 Attaching the SMM Profile

To attach the SMM profile to ingress prefix based IPTG, enter the following command:

% set addressContext default zone ZONE1 sipTrunkGroup NGRESS_TG signaling messageManipulation inputAdapterProfile Add_CRLF

Creating the Preconditions Profiles

Note
  • If Preconditions interworking is configured as “Use UPDATE”, configure the Allow UPDATE flag as well.
  • If Preconditions interworking is configured as “Use UPDATE” but a 183 from the peer does not have UPDATE in the Allow header, the SBC will not send an UPDATE and does not take any other action, thus a call timeout timer generates to terminate the call.
  • Do not set Preconditions to "Required" for interworking scenarios.

  • During an ingress precondition interworking sceanario, if the remote precondition is met in PRACK, the SBC will be able to process it and send the INVITE towards egress.

Ingress IPSP

 To create the preconditions profile in ingress IPSP, enter the following command:

% set profiles signaling ipSignalingProfile INGRESS commonIpAttributes preconditions State enable
% set profiles signaling ipSignalingProfile INGRESS commonIpAttributes preconditions SupportIfEgressIPTG disable
% set profiles signaling ipSignalingProfile INGRESS commonIpAttributes preconditions StrengthMandatoryPolicy enable
% set profiles signaling ipSignalingProfile INGRESS commonIpAttributes preconditions StrengthMandatoryPriority 12
% set profiles signaling ipSignalingProfile INGRESS commonIpAttributes preconditions StrengthOptionalPolicy disable
% set profiles signaling ipSignalingProfile INGRESS commonIpAttributes preconditions StrengthOptionalPriority 1
% set profiles signaling ipSignalingProfile INGRESS commonIpAttributes preconditions UPDATEPreconditionsPolicy enable
% set profiles signaling ipSignalingProfile INGRESS commonIpAttributes preconditions UPDATEPreconditionsPriority 1
commit

 Egress IPSP

 To create the preconditions profile in egress IPSP, enter the following command:

% set profiles signaling ipSignalingProfile EGRESS commonIpAttributes preconditions State enable
% set profiles signaling ipSignalingProfile EGRESS commonIpAttributes preconditions SupportIfEgressIPTG disable
% set profiles signaling ipSignalingProfile EGRESS commonIpAttributes preconditions StrengthMandatoryPolicy disable
% set profiles signaling ipSignalingProfile EGRESS commonIpAttributes preconditions StrengthMandatoryPriority 20
% set profiles signaling ipSignalingProfile EGRESS commonIpAttributes preconditions StrengthOptionalPolicy disable
% set profiles signaling ipSignalingProfile EGRESS commonIpAttributes preconditions StrengthOptionalPriority 1
% set profiles signaling ipSignalingProfile EGRESS commonIpAttributes preconditions UPDATEPreconditionsPolicy disable
% set profiles signaling ipSignalingProfile EGRESS commonIpAttributes preconditions UPDATEPreconditionsPriority 2
commit

 Attaching the Ingress and Egress IPSPs to the Trunk Groups

 To attach the ingress IPSP to the ingress Trunk Group, enter the following command: 

% set addressContext default zone ZONE1 sipTrunkGroup INGRESS_TG policy signaling ipSignalingProfile INGRESS 
commit

To attach the egress IPSP to the egress Trunk Group, enter the following command:

% set addressContext default zone ZONE1 sipTrunkGroup EGRESS_TG policy signaling ipSignalingProfile EGRESS 
commit