Specifying the default telephony gateway

When transferring or placing outbound calls with tel: URI destinations, you must specify a default SIP telephony gateway to send calls. The Telephony Session service uses this gateway to build the To address of the new call for the transfer. An example of a tel: URI is <transfer dest=”tel:1234”/>.

You don’t need to specify a default gateway for sip: URI destinations since these already specify a gateway in the destination string. An example of a sip: URI is <transfer dest=”sip:1234@GW1:5070”/>.

ts.APSIPGatewayList

On the Advanced tab of the Telephony Session service, edit the ts.APSIPGatewayList service property and enter the hostname:[port] for the telephony gateway. The hostname can be a name or IP address. The default port is 5060. The value matches the gateway specified in the incoming sip: URI. For example, if the From header of the incoming call were sip:4444@GW1, you would enter GW1 for hostname.

You can also enter multiple gateways as a comma-separated list, for example, GW1, GW2, 10.100.0.0:5070. The Telephony Session service uses the incoming call’s gateway if present in the list. For all other cases—outbound dialing, calls without ANI information, or calls where the gateway is not listed—it uses the first gateway in the list.

For example, say you set ts.APSIPGatewayList to GW1,GW2,GW3:5070. A call comes in from sip:2472@GW2. The Telephony Session service finds GW2 in the list and uses that gateway to transfer the call.

Say the call came in from GW5, which is not in the list. The Telephony Session service uses GW1, the first one in the list, to transfer the call.

When not set, this service property defaults to an empty string. The Management Station generates an alarm if the transfer destination string is a tel: URI and you failed to provide a default gateway.

Redirecting calls

When the Telephony Session service places a call, the destination endpoint might redirect the call to a different endpoint. To do so, it returns a 3xx message with a new destination endpoint address for redirecting the call. You can control call redirection with these service properties:

  • ts.APSIPRedirectsUseGatewayList—When set to TRUE (default), the Telephony Session service looks for the gateway of the new destination endpoint address in the list specified by ts.SIPGatewayList. If found, it redirects the call to that address. If not found, it fails to redirect the call.
  • ts.APRedirectsMaxCount—Specifies the number of times the Telephony Session service attempts to redirect the call before giving up. The default is 3.