Provide trunk-to-trunk switching and usually do not connect directly to customer lines.

Provide trunk-to-trunk switching and usually do not connect directly to customer lines.

• A. Stand-alone switch
• B. Alternate routing
• C. 911 Direct Trunking
• D. Selective router

Answer: (D)

In enhanced 911 systems, the selective router is the component that handles routing calls between PSAPs using dedicated trunk circuits. It performs trunk-to-trunk switching, directing 9-1-1 calls from the originating network to the appropriate PSAP over trunk groups, rather than terminating the calls on customer lines. This setup allows the system to route a caller’s 9-1-1 request to the correct regional PSAP and to switch the call to alternate PSAPs if the primary is unavailable or congested. The call path stays on trunk networks between PSAPs, not on end-user phone lines. The other options don’t describe this cross-PSAP trunk switching role: a stand-alone switch tends to serve a single location, alternate routing concerns fallback destinations rather than the trunk-level routing between PSAPs, and 911 Direct Trunking implies direct trunks to the PSAP rather than inter-PSAP trunk switching.

In enhanced 911 systems, the selective router is the component that handles routing calls between PSAPs using dedicated trunk circuits. It performs trunk-to-trunk switching, directing 9-1-1 calls from the originating network to the appropriate PSAP over trunk groups, rather than terminating the calls on customer lines. This setup allows the system to route a caller’s 9-1-1 request to the correct regional PSAP and to switch the call to alternate PSAPs if the primary is unavailable or congested. The call path stays on trunk networks between PSAPs, not on end-user phone lines. The other options don’t describe this cross-PSAP trunk switching role: a stand-alone switch tends to serve a single location, alternate routing concerns fallback destinations rather than the trunk-level routing between PSAPs, and 911 Direct Trunking implies direct trunks to the PSAP rather than inter-PSAP trunk switching.