Centralized Automated Message Accounting
A Centralized Automated Message Accounting (CAMA) trunk is a special analog trunk
type originally developed for long-distance billing but now mainly used for emergency
call services (911 and E911 services). You can use CAMA ports to connect to a Public
Safety Answering Point (PSAP) for emergency calls. A CAMA trunk can send only outbound
automatic number identification (ANI) information, which is required by the local
public safety answering point (PSAP).
CAMA interface cards and software configurations are targeted at corporate enterprise
networks and at service providers and carriers who are creating new or supplementing
existing networks with Enhanced 911 (E911) services. CAMA carries both calling and
called numbers by using in-band signaling. This method of carrying identifying information
enables the telephone system to send a station identification number to the PSAP via
multifrequency (MF) signaling through the telephone company E911 equipment. CAMA
trunks are currently used in 80 percent of E911 networks. The calling number is needed
at the PSAP for two reasons:
■ The calling number is used to reference the Automatic Location Identification (ALI)
database to find the exact location of the caller and any extra information about the
caller that might have been stored in the database.
■ The calling number is used as a callback number in case the call is disconnected. A
number of U.S. states have initiated legislation that requires enterprises to connect
directly to the E911 network. The U.S. Federal Communications Commission (FCC)
has announced model legislation that extends this requirement to all U.S. states.
Enterprises in areas where the PSTN accepts 911 calls on ISDN trunks can use existing
Cisco ISDN voice-gateway products because the calling number is an inherent
part of ISDN.
Chapter 3: Routing Calls over Analog Voice Ports 155
Note You must check local legal requirements when using CAMA.
Calls to emergency services are routed based on the calling number, not the called number.
The calling number is checked against a database of emergency service providers
that cross-references the service providers for the caller location. When this information
is determined, the call is then routed to the proper PSAP, which dispatches services to the
caller location.
During the setup of an E911 call, before the audio channel is connected, the calling number
is transmitted to each switching point, known as a selective router, via CAMA.
The VIC2-2FXO and VIC2-4FXO cards support CAMA via software configuration.
CAMA support is also available for the Cisco 2800 Series and 3800 Series ISRs. It is
common for E911 service providers to require CAMA interfaces to their network.
Figure 3-21 shows a site that has a T1 PRI circuit for normal inbound and outbound
PSTN calls. Because the local PSAP requires a dedicated CAMA trunk for emergency
(911) calls, all emergency calls are routed using a dial peer pointing to the CAMA trunk.
Austin
PSTN
PSAP
0/0/0
T1 PRI for Standard Calls
CAMA Trunk
for Emergency
Calls
1/1/1
Figure 3-21 Configuring a CAMA Trunk
The voice port 1/1/1 is the CAMA trunk. The actual configuration depends on the PSAP
requirements. In this case, the digit 1 is used to signal the area code 312. The voice port
is then configured for CAMA signaling using the signal cama command. Five options
exist:
■ KP-0-NXX-XXXX-ST: 7-digit ANI transmission. The Numbering Plan Area (NPA),
or area code, is implied by the trunk group and is not transmitted.
■ KP-0-NPA-NXX-XXXX-ST: 10-digit transmission. The E.164 number is fully
transmitted.
■ KP-0-NPA-NXX-XXXX-ST-KP-YYY-YYY-YYYY-ST: Supports CAMA signaling with
ANI/Pseudo ANI (PANI).
■ KP-2-ST: Default transmission when the CAMA trunk cannot get a corresponding
Numbering Plan Digit (NPD) in the look-up table or when the calling number is
fewer than 10 digits. (NPA digits are not available.)
■ KP-NPD-NXX-XXXX-ST: 8-digit ANI transmission, where the NPD is a single MF
digit that is expanded into the NPA. The NPD table is preprogrammed in the sending
and receiving equipment (on each end of the MF trunk). For example: 0=415, 1=510,
2=650, 3=916
05551234 = (415) 555-1234, 15551234 = (510) 555-1234
The NPD value range is 0–3.
When you use the NPD format, the area code needs to be associated with a single digit.
You can preprogram the NPA into a single MF digit using the ani mapping voice port
command. The number of NPDs programmed is determined by local policy as well as by
the number of NPAs the PSAP serves. Repeat this command until all NPDs are configured
or until the NPD maximum range is reached.
In this example, the PSAP expects NPD signaling, with the area code 312 being represented
by the digit 1.
You could then complete the following steps to configure the voice port for CAMA
operation:
Step 1. Configure a voice port for 911 calls.
Router(config)#voice-port 1/1/1
Router(config-voiceport)#ani mapping 1 312
Router(config-voiceport)#signal cama kp-npd-nxx-xxxx-st
Step 2. Configure a dedicated dial peer to route emergency calls using the CAMA
trunk when a user dials “911.”
Router(config)#dial-peer voice 911 pots
Router(config-dialpeer)#destination-pattern 911
Router(config-dialpeer)#prefix 911
Router(config-dialpeer)#port 1/1/1
Step 3. Configure a dedicated “9911” dial peer to route all emergency calls using the
CAMA trunk when a user dials “9911.”
Router(config)#dial-peer voice 9911 pots
Router(config-dialpeer)#destination-pattern 9911
Router(config-dialpeer)#prefix 911
Router(config-dialpeer)#port 1/1/1
Step 4. Configure a standard PSTN dial peer for all other inbound and outbound
PSTN calls.
Router(config)#dial-peer voice 910 pots
Router(config-dialpeer)#destination-pattern 9[2-8].........
Router(config-dialpeer)#port 0/0/0:23
Example 3-4 shows the complete CAMA trunk configuration.
Example 3-4 CAMA Trunk Configuration
Chapter 3: Routing Calls over Analog Voice Ports 157
Router(config)#voice-port 1/1/1
Router(config-voiceport)#ani mapping 1 312
Router(config-voiceport)#signal cama KP-NPD-NXX-XXXX-ST
Router(config)#dial-peer voice 911 pots
Router(config-dialpeer)#destination-pattern 911
Router(config-dialpeer)#prefix 911
Router(config-dialpeer)#port 1/1/1
Router(config)#dial-peer voice 9911 pots
Router(config-dialpeer)#destination-pattern 9911
Router(config-dialpeer)#prefix 911
Router(config-dialpeer)#port 1/1/1
Router(config)#dial-peer voice 910 pots
Router(config-dialpeer)#destination-pattern 9[2-8].........
Router(config-dialpeer)#port 0/0/0:23