∙Cisco Emergency Responder can query for IP Phones through either CDP (on the Catalyst switches) or the MAC address. Since CDP is sent as a link−layer multicast and is used by the Cisco AP to determine the QoS settings for the Cisco 7920, it is not propagated up to the Catalyst switch. This means that Cisco Emergency Responder should query the Catalyst switches for the MAC addresses of the Cisco 7920 phones.
∙Cisco Emergency Responder groups devices into Emergency Response Locations (ERL) so they can be identified by a physical location (such as building, floor, or region of floor). Depending on how the power levels are configured on the Cisco APs, it is possible that the signal could propagate to floors above or below the actual AP that the Cisco 7920 is associated with. Using antennas that propagate RF signal in a more horizontal pattern helps alleviate this, but emergency personnel within a building should be made aware of this when organizing their searches for the individual or device that initiated the emergency call.
An E911 coverage policy is an individual decision that each company needs to make and adapt it to their physical locations.
It is recommended that each AP been assigned to its own ERL (or minimally grouping a couple of adjacent APs into one ERL). This has the benefit of allowing on−site, and potentially PSAP personnel, to identify that the caller is using a wireless device (by using a code or abbreviation in the Automatic Location Information (ALI) or switch port location field). This is important information for first responders because it means that adjacent floors, hallways, rooms, and even buildings may need to be searched to locate an unconscious or incapable caller. The following image is an example of the Cisco Emergency Responder's configuration Graphical User Interface (GUI):
Caveats and Limitations
Cisco − Wireless IPT Design Guide for the Cisco 7920 IP Phone