DHCP option 120 (SIP Server Discovery; RFC 3361) allows SIP clients to discover a DNS (Domain Name System; RFC 103) fully-qualified domain name of a SIP server. If consistently assigned, this Location Domain can identify the client's geographical location.
The proposed way to deploy the Location Domains to the clients is to use DHCP Relay Agents with Option 82 to convey the geographical location of the clients to the DHCP server and then use Option 120 to assign the appropriate Location Domain
to the clients.
The DNS servers must also be configured so that all Location Domains resolve to the address of the SIP Registration/Location Server (i.e. TCS or central SBC). In other words, all the FQDNs are aliases for the "real" SIP Registration/Location Server domain.
Figure 1. Location Domain Discovery and Propagation (Example)
- Phone receives site specific domain name via DHCP Option 120
- Phone sends domain name as host part of To header field in SIP Register request
- DNS server resolves Location Domain to the address of Lotus Sametime Unified Telephony
- SBC does not change the domain name in the To header field
- Lotus Sametime Unified Telephony saves the domain name for each Contact in its Location Database
- Phone sends domain name as host part of From header field in SIP INVITE request
- SBC does not change the domain name in the From header field
- Lotus Sametime Unified Telephony provides the conveyed domain name to interested services
Static Location Domain Provisioning at TCS
NNI (Network-to-Network Interface) endpoints that are configured in for static registration, or NNI endpoints that do send REGISTER
requests to Lotus Sametime Unified Telephony but are unable to provide Location Domain information in SIP requests, may require an alternative means to configure a Location Domain for the endpoint. A new NNI endpoint configuration parameter allows the administrator to configure a location domain name to be used for calls via the endpoint. If this parameter is configured then it will used as the location domain and information from the SIP signalling shall not be used to determine the location domain.
A Location Domain can also be provisioned for each Media Server.
Currently those statically provisioned Location Domains are only used for CAC.
Parent topic: Subscriber Location Identification