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The IMG 2020 supports utilizing an A-Record, SRV or Service Record, or both to specify which sip server to route a call to. The determination of which record to use is configured in the DNS Servers object. DNS Queries on SRV records will be described below. SRV Records are defined in RFC 2782 and identifies the server(s) that will support a particular service. In this case the IMG 2020 will be looking for the best way to route a call to a server which employs the sip service. A Channel Group can be configured so that a query is sent to a DNS server and the DNS response would be an SRV record including all the sip servers that match the initial DNS service request. From the SRV Record the IMG 2020 will handle load balancing from the priority/weight of each server using Random number method. The final result will be that the IMG 2020 will send the outbound INVITE message to the server with highest priority/weight and attempt to connect to that SIP server. If however after a few Re-INVITES the initial SIP Server cannot be reached, an outbound INVITE will be sent to the SIP server with the next highest priority/weight. This will continue until all responses in the DNS query have been exhausted and the call will fail. Up to five DNS responses in each SRV Record are supported.
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The procedure below explains how to configure the IMG 2020 to query a DNS server using an SRV Record. Before configuring, the IMG 2020 must have an initial configuration created on it. Follow the Basic Configurations procedure before proceeding. Once all initial steps such as spans, interfaces, translations, internal routing, and IP Profiles, the IMG 2020 can be configured to accept SRV records. Follow steps below:
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Right click on the Profiles object and select New SIP Profiles. The SIP Profiles object is a parent or container object. No configuration is needed here. Refer to the SIP Profiles topic for more information on this object.
Right click on the SIP Profiles object and select New SIP Profile. The first profile that gets created is a Default SIP Profile and cannot be modified. Disregard this profile.
Right click on the SIP Profiles object and select New SIP Profile again. In the SIP Profile object that appears, either enter a name that identifies this SIP Profile or accept the default name already entered. In this example the SIP Profile was labeled DNS_SRV_Profile.
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Right click on the Dialogic object and select New External Network Elements. The External Network Elements object is a parent or container object and no configuration is needed here. Refer to External Network Elements topic for more information.
Right click on External Network Elements and select New External Gateways. The External Gateways object is a parent or container object also and no configuration is needed here. Refer to External Gateways for more information.
Right click on External Gateways and select New External Gateway. Enter a name that identifies the gateway being configured. In this example the gateway was labeled DNS_SRV_GW.
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For more information on this object, refer to the External Gateway topic.
Configure multiple gateways using the _sip._udp.jsmith.dialogic.com format in the Gateway Hostname field. For example: The 1st Gateway Host Name is _sip._udp.jsmith.dialogic.com the second gateway could be _sip._udp.jsmith1.dialogic.com and third gateway could be _sip._udp.jsmith2.dialogic.com and so on.
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The configuration above displays how to configure the SIP Profile and External SIP Gateway so that the Delayed Media feature is configured. The next step is to configure the SIP signaling stack and SIP Channel Groups. Refer to the Configure SIP (Single SIP IP) topic for a procedure on how to configure the SIP functionality.
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