Configuring the POTS (Telephone) Interfaces

Plain old telephone service (POTS) functionality refers to the use of the voice capabilities of the ISDN routers. The ringer equivalent number (REN) consists of a number and a letter that indicates the frequency response of that telephone's ringer. The term telephone port refers to the physical port on the router back panel. The telephone interface refers to a logical interface that you have to configure to make an analog telephone, fax, or modem connected to the router port (phone 1 and 2) work properly as touch-tone devices.

The set of configuration commands related to the configuration of the physical ports includes the country, resistance of the line, dialing method, disconnect supervision, encoding, and ringing frequency. Most of the default settings are for the U.S. The first thing to check in the global configuration mode of the router is who is providing the tones and how the following command is set up:

 804-isdn(config)# pots tone-source {local | remote} 

This command sets who supplies dial, ring back, and busy tones for telephones, fax machines, or modems connected to a Cisco IOS-based ISDN router. The keywords are as follows:

• local (by default) Specifies that the router supplies the tones

• remote Specifies that the ISDN switch supplies the tones

Specifically for supplying the dial tone, another global configuration command is available with same local and remote options:

 804-isdn(config)#pots dial-tone {local | remote} 

In the global configuration command, another command specifies the delay after which a telephone port can be rung after a previous call is disconnected:

 804-isdn(config)#pots distinctive-ring-guard-time milliseconds 

The milliseconds argument is the number of milliseconds of the delay and ranges from 0 to 1000. The default depends on the chosen country.

You can connect multiple devices (analog telephones, fax machines, and modems) to a router telephone port. The number you can connect depends on the REN of the telephone port (five) or the REN of each device that you plan to connect. If you have five devices and all of them have REN 1, you can connect all of them to the POTS port.

Creating Dial Peers

Dial peers determine the routing of incoming calls to the telephone ports. You can create a total of six dial peers for the two telephone ports. Example 11-9 lists some of the relevant Cisco IOS Software configuration commands.

Example 11-9. A Common Procedure for Dial Peers Configuration

 ! This command sets up a tag number (1 to 6): 804-isdn(config)#dial-peer voice tag pots ! This command assigns a local directory number: 804-isdn(config-dial-pe)#destination-pattern ldn ! The number of the port is defined using the following command: 804-isdn(config-dial-pe)#port port-number ! The following command disables  call waiting (optional): 804-isdn(config-dial-pe)#no call-waiting ! This command (optional) sets a custom ring.  Any call coming to that port will ! use that ring. The cadence-number can be 0,1, or 2: 804-isdn(config-dial-pe)#ring cadence-number 

The configuration is displayed if you type show dial-peer voice 5, as shown in Example 11-10.

Example 11-10. Displaying the Configuration of dialer-peer 5

 804-isdn#show dial-peer voice 5 VoiceEncapPeer5         tag = 5         destination-pattern = '3335555'         voice-port = 2         ring cadence = 0         call-waiting disabled         forward_to_unused_port disabled 

The local directory number (LDN) must be associated with a service profile identifier (SPID). If you do not assign LDN to both SPIDs, you cannot make voice calls simultaneously. If the dial peers are not created, all voice calls are routed to port 1. To ensure you allow incoming and outgoing voice calls under a BRI interface, configure the following command:

 804-isdn(config-if)#isdn incoming-voice modem 

The simple configurations enable the basic POTS functionality of the voice portion of ISDN service. There are some advanced features, and their number is continuously changing and growing. Some of them are discussed in the next paragraph.

Advanced Telephone Features

This section provides coverage of some of the more advanced features provided by Cisco IOS Software-based ISND configuration, including the following:

• Setting voice priority

• Enabling supplementary phone services

ISDN Voice Priority

The voice priority feature of IOS handles the data and voice priority. Depending on the user preferences, voice could take precedence over data and vice versa. There are three options:

• Always Always bumps the data call if an outgoing or incoming voice call is initiated.

• Conditional (by default) Voice call bumps data call only if the user has two data connections in the same direction; otherwise, the calling party receives a busy signal.

• Never/Off Voice callers always receive a busy signal.

In Cisco 700 series routers, a set of commands handles the process, as displayed in Example 11-11.

Example 11-11. Voice Priority Settings for 77x Router

 776-isdn>SET VOICEPRIORITY INCOMING INTERFACE PHONE1 CONDITIONAL 776-isdn>SET VOICEPRIORITY OUTGOING INTERFACE PHONE1 CONDITIONAL 776-isdn>SET CALLWAITING INTERFACE PHONE1 ON 776-isdn>SET VOICEPRIORITY INCOMING INTERFACE PHONE2 ALWAYS 776-isdn>SET VOICEPRIORITY OUTGOING INTERFACE PHONE2 ALWAYS 776-isdn>SET CALLWAITING INTERFACE PHONE2 ON 776-isdn>SET CALLTIME VOICE INCOMING OFF 776-isdn>SET CALLTIME VOICE OUTGOING OFF 776-isdn>SET CALLTIME DATA INCOMING OFF 776-isdn>SET CALLTIME DATA OUTGOING OFF 

The result of this configuration for a Cisco 700 series router is displayed in Example 11-12.

Example 11-12. Verifying Voice Priority Settings on the 776 Router

 776-isdn>show voice Interface     VoicePriority   VoicePriority    Call     Directory    Ring               In              Out             Waiting    Number     Cadence  PHONE1       CONDITIONAL    CONDITIONAL      ON      5764740  PHONE2        ALWAYS          ALWAYS           ON      5764741  DOV           N/A             N/A              N/A  UNSPECIFIED   N/A             N/A              N/A 

For IOS-based routers, the commands are

 804-isdn#isdn voice-priority ldn {in | out}{always | conditional | off} 

The pots dialing-method {overlap | enblock} command affects the way you receive a busy signal. With the overlap option, you hear a fast busy signal. With enblock, you initially hear a dial tone followed by a busy signal.

If you cannot make the configuration settings work correctly, it's possible that the LEC is blocking voice calls, the line was provisioned without additional call offering (ACO), or the router is rejecting voice calls due to an incorrect configuration.

Supplementary Phone Services

Cisco supports some supplementary phone services that are available in Cisco IOS Software. Use of these services is possible, but not mandatory; it depends on the way the line is provisioned. Some of the phone services might include the following, depending on the LEC settings:

• Call holding and retrieving By default, this option is set to **number,number #, but it depends on the LEC settings.

• Call waiting By default, it is enabled with no call-waiting. To disable it, enter **number,number#.

• Three-way call conferencing If the LEC switch type is NI1 or DMS-100 custom, you can activate this feature by using isdn conference-code range, where range is 0 to 999 and the default is 60.

• Call transfer To use this feature, you must request it when you order the line. The feature can then be activated with the command isdn transfer-code range, where range is 0 to 999 and the default code is 61.

• Call forwarding This feature must also be requested from the LEC when you order the line. There are four ways of forwarding available in Cisco routers:

  - Call forwarding unconditional (CFU) forwards all incoming calls unconditionally to another telephone number.

  - Call forwarding no reply (CFNR) forwards incoming calls that are not answered within a defined period to another telephone number.

  - Call forwarding busy (CFB) forwards incoming calls that get a busy signal to another telephone number. The LEC must provide a number for each forwarding feature such as #number#.

  - Call forwarding variable (CFV) is available only in the U.S. for NI1 ISDN switch types, and can be turned on or off using numbers provided by the LEC.