Use the Switch Port Details page to assign switch ports to ERLs. This assignment allows Cisco Emergency Responder (Cisco ER) to assign the correct ERL to phones that connect to the network through the configured ports.
To support switches such as the Cisco Catalyst 3750 which have ports that can be uniquely identified by Switch ID, Module ID and Port ID combination, Cisco ER 1.2(3) uses the following port naming convention:
IfName: New field display name for port as given for the switch CLI (for example Fa1/5 or Gi2/0/1)
Port Identifier: replaces the Module ID/Port ID.
It contains {optional} <>/ {optional} <> / <>
http://www.cisco.com/en/US/docs/voice_ip_comm/cer/1_2_3/english/administration/guide/e911page.html#wp1030153