The Signaling Port Range functionality applies to the SLB in an SLB-SBC configuration to facilitate the following behavior.

  • The SLB uses a new port from the independent signaling port range per zone, if configured, corresponding to each new initial REGISTER request received.

  • The existing behavior of SBC or SLB does not change when identifying a REGISTER request as an initial request.

  • The transport protocol (UDP or TCP) used for sending the Egress REGISTER remains based on existing procedures.

The SBC SIPSG sends the ICM to the SIPFE. The SIPFE can then direct it to the SLB through the UMS for the allocation/de-allocation of the port from the range that is specified in the SLB configuration. The SLB sends ICM to SIPCM (SLB) to manage the PORT RANGE and SIPCM will return to the SLB with the CNXID and the "Port Allocated" with a failure/success reply. The SLB returns the message with the connection ID and the PORT allocated to the SIPFE (SBC) using the UMS that sends ICM to SIPSG (SBC) with the required data to complete the process.

The Egress signaling port used during registration is used as a local port for all the Egress requests originated by that registered UE. The SLB uses the Egress signaling port in the CONTACT and VIA headers of all requests originated by that registered UE. The SLB also uses the Egress singling port in the CONTACT header of responses sent for the terminating requests towards the registered UE. This feature enables the SLB to use use the Egress signaling port (instead of SipSigPort’s PortNum configuration value) in the PATH header of the Egress REGISTER request if the SBC is configured to create the PATH header.

The SLB rejects new registration requests with an error (405) response code if no unique port is available for use as a local port on the Egress zone. On de-registration of a binding or on registration timer expiry, the SLB releases the corresponding local port on the Egress zone for re-use. The active signaling port information is replicated to stand by, and on a failover, all the active signaling ports at the time of switchover are made available on the newly active SLB instance.

For configuration details, refer to: