In Depth Tutorials and Information

Introducing Analog Voice Ports on Cisco IOS Routers (Routing Calls over Analog Voice Ports) Part 3

FXS Voice Port Configuration

In North America, the FXS port connection functions with default settings most of the time. The same cannot be said for other countries and continents. Remember, FXS ports look like switches to the edge devices that are connected to them. Therefore, the configuration of the FXS port should emulate the switch configuration of the local PSTN.

For example, consider an international company that has offices in the United States and England. Each PSTN provides signaling that is standard for its own country. In the United States, the PSTN provides a dial tone that is different from the dial tone in England. The signals that ring incoming calls are different in England. Another instance where the default configuration might be changed is when the connection is a trunk to a PBX or key system. In each of these cases, the FXS port must be configured to match the settings of the device to which it is connected.

In this example, you have been assigned to configure a voice gateway to route calls to a plain old telephone service (POTS) phone connected to a FXS port on a remote router in Great Britain. Figure 3-15 shows how the British office is configured to enable ground-start signaling on FXS voice port 0/2/0. The call-progress tones are set for Great Britain, and the ring cadence is set for pattern 1.

Figure 3-15 FXS Configuration Topology

The requirements for your configuration are the following:

■ Configure the voice port to use ground-start signaling.

■ Configure the call-progress tones for Great Britain.

You would then complete the following steps to accomplish the stated objectives:

Step 1. Enter voice-port configuration mode.

Step 2. Select the access signaling type to match the telephony connection you are making.

Note If you change signal type, you must execute a shutdown and no shutdown command on the voice port.

Step 3. Select the two-letter locale for the voice call progress tones and other locale-specific parameters to be used on this voice port.

Step 4. Specify a ring pattern. Each pattern specifies a ring-pulse time and a ring-interval time.

Note The patternXX keyword provides preset ring-cadence patterns for use on any platform. The define keyword allows you to create a custom ring cadence.

Step 5. Activate the voice port.

Example 3-1 shows the complete FXS voice port configuration.

Example 3-1 FXS Voice Port Configuration

FXO Voice Port Configuration

An FXO trunk is one of the simplest analog trunks available. Because Dialed Number Information Service (DNIS) information can only be sent out to the PSTN, no direct inward dialing (DID) is possible. ANI is supported for inbound calls. Two signaling types exist, loopstart and groundstart, with groundstart being the preferred method.

For example, consider the topology shown in Figure 3-16. Imagine you have been assigned to configure a voice gateway to route calls to and from the PSTN through an FXO port on the router.

Figure 3-16 FXO Configuration Topology

In this scenario, you must set up a PLAR connection using an FXO port connected to the PSTN.

The configuration requirements are the following:

■ Configure the voice port to use ground-start signaling.

■ Configure a PLAR connection from a remote location to extension 4001 in Austin.

■ Configure a standard dial peer for inbound and outbound PSTN calls.

Because an FXO trunk does not support DID, two-stage dialing is required for all inbound calls. If all inbound calls should be routed to a specific extension, (for example, a front desk), you can use the connection plar opx command. In this example, all inbound calls are routed to extension 4001.

You could then complete the following steps to configure the FXO voice port:

Step 1. Enter voice-port configuration mode.

Step 2. Select the access signaling type to match the telephony connection you are making.

Step 3. Specify a PLAR off-premises extension (OPX) connection.

Note PLAR is an autodialing mechanism that permanently associates a voice interface with a far-end voice interface, allowing call completion to a specific telephone number or PBX without dialing. When the calling telephone goes off-hook, a predefined network dial peer is automatically matched. This sets up a call to the destination telephone or PBX.

Using the opx option, the local voice port provides a local response before the remote voice port receives an answer. On FXO interfaces, the voice port does not answer until the remote side has answered.

Step 4. Activate the voice port.

Step 5. Exit voice port configuration mode.

Step 6. Create a standard dial peer for inbound and outbound PSTN calls.

Step 7. Specify the destination pattern.

Note The T control character indicates that the destination-pattern value is a variable-length dial string. Using this control character enables the router to wait until all digits are received before routing the call.

Dial-peer configuration is covered in the section, "Introducing Dial Peers."

Step 8. Specify the voice port associated with this dial peer.

Example 3-2 shows the complete FXO voice port configuration.

Example 3-2 FXO Voice Port Configuration

E&M Voice Port Configuration

Configuring an E&M analog trunk is straightforward. Three key options have to be set:

■ The signaling E&M signaling type

■ Two- or four-wire operation

■ The E&M type

As an example, consider the topology shown in Figure 3-17.

Figure 3-17 E&M Configuration Topology

In this example, you have been assigned to configure a voice gateway to work with an existing PBX system according to network requirements. You must set up a voice gateway to interface with a PBX to allow the IP phones to call the POTS phones using a four-digit extension.

The configuration requirements are the following:

■ Configure the voice port to use wink-start signaling.

■ Configure the voice port to use 2-wire operation mode.

■ Configure the voice port to use Type I E&M signaling.

■ Configure a standard dial peer for the POTS phones behind the PBX.

Both sides of the trunk need to have a matching configuration. The following example configuration shows an E&M trunk using wink-start signaling, E&M Type I, and two-wire operation. Because E&M supports inbound and outbound DNIS, DID support is also configured on the corresponding dial peer.

You could then complete the following steps to configure the E&M voice port: Step 1. Enter voice-port configuration mode.

Step 2. Select the access signaling type to match the telephony connection you are making.

Step 3. Select a specific cabling scheme for the E&M port.

Note This command affects only voice traffic. If the wrong cable scheme is specified, the user might get voice traffic in only one direction.

Also, using this command on a voice port changes the operation of both voice ports on a voice port module (VPM) card. The voice port must be shut down and then opened again for the new value to take effect.

Step 4. Specify the type of E&M interface.

Step 5. Activate the voice port.

Step 6. Exit voice port configuration mode.

Step 7. Create a dial peer for the POTS phones.

Step 8. Specify the destination pattern for the POTS phones.

Step 9. Specify direct inward dial.

Note DID is needed when POTS phones call IP Phones. In this case we match the POTS dial peer. This same dial peer is also used to call out to POTS phones.

Step 10. Specify digit forwarding all, so that no digits will be stripped as they are forwarded out of the voice port. By default, only digits matched by wildcard characters in the destination-pattern command are forwarded.