Troubleshooting Telephone Interfaces

Cisco IOS includes features that handle data and voice priority. Depending on user preferences, voice can take precedence over data and vice versa. Data and voice alternate on every channel. There are three options for voice priority over data: always, conditional, and never. The choice depends on the configuration, so this is the first thing to check when troubleshooting. The options are shown in the following:

 804-isdn(config-if)#isdn voice-priority 5764740 out ? always           always bump data call conditional      bump data call only if connection is not lost off              never bump data call 

The conditional option, which is the default, means that the data call will be disconnected only if the network connection can be guaranteed; that is, only if there are two data calls up to the same direction.

NOTE

Always advise the user to use POTS2 for voice if he/she is using only one phone because BRI1 is the data channel and comes up first. This way, the user can (for example) exchange data and be on a conference call simultaneously.

The next important consideration is how the line is provisioned. If it is provisioned only for data, there is no voice option. If it is provisioned for voice and data, the ring signal is usually provided by the line (the LEC's switch), but it can also be generated by the router. This should be tested or checked.

To test the ring options of the router and determine if there are any hardware issues, it is always good to have the remote user participating in the troubleshooting process. For this particular part, user participation is mandatory to make voice calls out and to hear the different signals. The following are the possible options:

 804-isdn#test pots 2 ringer ? <0-2>  Cadence number 804-isdn#test pots 2 disconnect ! Disconnect tone 

To test the tone capability of the router, the following are the command options:

 804-isdn#test pots 1 tone ?   busy           Busy Tone   call-waiting   Call Waiting Tone   dial           Dial Tone   reorder        Reorder Tone   ringback       Ringback Tone   silence        Disable Tones or ringer 

It is important to check if the line is provisioned for additional call offering (ACO). This usually means that, if you have two B channels up, the switch forwards the next call (data or voice) to the router, and the router makes a decision based on the configuration. To check if the ACO is set up on the following example (where the phone numbers are 4088535983 and 4085764741), first enter the following:

 804-isdn#debug pots csm 804-isdn#debug pots driver 

Then enter:

 804-isdn#show debugging POTS:   POTS CSM events debugging is on   POTS DRIVER debugging is on 

Then, make a voice call from 4088535983 to 4085764741, and monitor the output from the router (see Example 12-43).

Example 12-43. The Output of CSM Events and POTS Driver Debugging

 804-isdn# *Mar 22 20:41:54.525: EVENT_FROM_ISDN:dchan_idb=0x27E6F38, call_id=0x68, ces=0x2    bchan=0x0, event=0x1, cause=0x0 *Mar 22 20:41:54.525: CSM_GET_CALL_INFO_FOR_DN:forward-to-unused-port disabled      check the config ! This by default and it is correct - BY DEFAULTT *Mar 22 20:41:54.529: CSM_GET_CALL_INFO_FOR_DN:New call forwarded to port 2 ! Reporting correct because calling the second number. ! The dial-peer 1 is set up, otherwise the call will go to the first channel *Mar 22 20:41:54.529: CSM_PROC_IDLE: CSM_EVENT_ISDN_CALL, call id = 0x68,     port = 2 ! Calling the second LDN  check the dial peers *Mar 22 20:41:54.529: Calling Number:'4088535983'  Called number:'5764741' ! The numbers are correct, so Q931 provides caller ID and called party's ID *Mar 22 20:41:54.529: POTS DRIVER port=2 activate ringer: cadence=0     callerId=4088535983 *Mar 22 20:41:54.533: POTS DRIVER port=2 state=Idle drv_event=RING_EVENT *Mar 22 20:41:54.533: POTS DRIVER port=2 enter_ringing *Mar 22 20:41:54.573: POTS DRIVER port=2 CallerId Strg=032220414088535983G PCM     len=129F *Mar 22 20:41:54.573: POTS DRIVER port=2 cmd=19 *Mar 22 20:41:56.573: POTS DRIVER port=2 cmd=1A *Mar 22 20:41:57.073: POTS DRIVER port=2 cmd=1B *Mar 22 20:41:57.073: POTS DRIVER port=2 ts connect: 3 0 *Mar 22 20:42:00.573: POTS DRIVER port=2 cmd=19 *Mar 22 20:42:02.573: POTS DRIVER port=2 cmd=1A *Mar 22 20:42:06.573: POTS DRIVER port=2 cmd=19 *Mar 22 20:42:07.769: EVENT_FROM_ISDN:dchan_idb=0x27E6F38, call_id=0x68, ces=0x2    bchan=0xFFFFFFFF, event=0x0, cause=0x10 ! The caller is picking the phone *Mar 22 20:42:07.769: CSM_PROC_RINGING: CSM_EVENT_ISDN_DISCONNECTED,     call id = 0x68, port = 2 ! The caller disconnects *Mar 22 20:42:07.769: POTS DRIVER port=2 activate disconnect *Mar 22 20:42:07.773: POTS DRIVER port=2 state=Ringing drv_event=DISCONNECT_EVENT *Mar 22 20:42:07.773: POTS DRIVER port=2 cmd=1A *Mar 22 20:42:07.773: POTS DRIVER port=2 enter_idle *Mar 22 20:42:07.773: POTS DRIVER port=2 ts connect: 0 0 *Mar 22 20:42:07.777: POTS DRIVER port=2 cmd=1B *Mar 22 20:42:07.777: POTS DRIVER port=2 activate tone=SILENCE_TONE *Mar 22 20:42:07.777: POTS DRIVER port=2 state=Idle drv_event=TONE_EVENT *Mar 22 20:42:07.777: POTS DRIVER port=2 activate tone=SILENCE_TONE *Mar 22 20:42:07.781: POTS DRIVER port=2 state=Idle drv_event=TONE_EVENT 

The test proves the voice calls hit the router, if BRI2 is idle. To check if the ACO is set up, you need to bring the second channel up and test it again.

The set of voice features of ISDN can be expanded. The important point here is to have a clear understanding about how the voice features, priorities, and services are provisioned and configured. The troubleshooting needs to occur based on the expected feature performance of the ISDN service.