FXS-to-FXO port behavior

Answered Question
Oct 11th, 2007

I don't get how an FXO port connected to an FXS port can distinguish the DNIS. Shouldn't the FXS port just apply ringing voltage to the FXO port without any DNIS passing?

Here is the scenario:

VoIPphone------(gateway)FXS----FXO(PBX)----phone

VoIP phone dials 266-XXXX. It goes over H.323 to the gateway which connects a POTS dial-peer on a FXS port. That FXS port is connected to an FXO port on a PBX. Somehow, that PBX is able to distingues what the extensions are after 266-XXXX and directly route the call. How is that possible??

------------------------------------

//gateway FXS ports

SANS-CRR01#sh voice port summ

IN OUT

PORT CH SIG-TYPE ADMIN OPER STATUS STATUS EC

============== == ============ ===== ==== ======== ======== ==

3/0/0 -- fxs-ls up dorm on-hook idle y

3/0/1 -- fxs-ls up dorm on-hook idle y

3/1/0 -- fxs-ls up dorm on-hook idle y

3/1/1 -- fxs-ls up dorm on-hook idle y

//dial-peers

dial-peer voice 111 voip

incoming called-number .

dtmf-relay h245-alphanumeric

no vad

dial-peer voice 2660 pots

destination-pattern 266

port 3/0/1

//sample call

21FF : 2955 -1328891890ms.841 +2890 +74630 pid:111 Answer 65013

dur 00:01:11 tx:3727/74540 rx:1814/35781 10 (normal call clearing (16))

IP 165.13.0.4:18390 SRTP: off rtt:321ms pl:33140/0ms lost:0/1/0 delay:60/60/70ms g729r8

media inactive detected:n media contrl rcvd:n/a timestamp:n/a

21FF : 2956 -1328891860ms.842 +2850 +75980 pid:2660 Originate 2663271

dur 00:01:13 tx:1814/50293 rx:3727/74540 10 (normal call clearing (16))

Telephony 3/0/1 (2956) [3/0/1] tx:68010/68010/0ms g729r8 noise:-67dBm acom:25dBm

I have this problem too.
0 votes
Correct Answer by Paolo Bevilacqua about 9 years 1 month ago

Hi,

the router has no problem in sending tones out of an FXS port. The same is not true for most PBXs. You can also send caller-id from the router, if the PBX is able to use it.

destination-pattern 266.... is "better" than 266 because the router will not present calls to PBX when less that 7 digits are coming from voip. Of course you can also enforce this check on the origination router.

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Overall Rating: 5 (1 ratings)
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Paolo Bevilacqua Thu, 10/11/2007 - 12:59

Hi,

DP 2660 should have destination-pattern 266....

Then router should be sending the 4 digits to pbx after it seize the line. You need to configure the pbx so that it uses them to ring t extension. You can verify this with "debug vpm signal" and "debug vtsp tone".

hope this helps, please rate post if it does!

Aaron Dhiman Thu, 10/11/2007 - 13:07

Hi, thanks for the response. The strange this is that it is working as it is configured.

My question is why does it work? If an FXS port should act as the Central Office, it should not be sending digits to the PBX right (just ring voltage)?

BTW, result of the debug is:

.Oct 11 17:06:06.958 EDT: htsp_timer_stop3 htsp_setup_req

.Oct 11 17:06:06.962 EDT: htsp_process_event: [3/0/0, FXSLS_ONHOOK, E_HTSP_SETUP_REQ]fxsls_onhook_setuphtsp_progress

.Oct 11 17:06:06.966 EDT: [3/0/0] set signal state = 0x0 timestamp = 0

.Oct 11 17:06:06.978 EDT: htsp_call_bridged invoked

.Oct 11 17:06:06.994 EDT: htsp_process_event: [3/0/0, FXSLS_WAIT_OFFHOOK, E_HTSP_VOICE_CUT_THROUGH]fxsls_waitoff_voice

.Oct 11 17:06:09.962 EDT: htsp_process_event: [3/0/0, FXSLS_WAIT_OFFHOOK, E_DSP_SIG_1100]fxsls_waitoff_offhook

.Oct 11 17:06:09.962 EDT: [3/0/0] set signal state = 0x4 timestamp = 0

.Oct 11 17:06:09.962 EDT: [3/0/0] set signal state = 0x6 timestamp = 200

.Oct 11 17:06:09.962 EDT: htsp_timer2 - 500 msec

.Oct 11 17:06:10.462 EDT: htsp_process_event: [3/0/0, FXSLS_WAIT_OFFHOOK, E_HTSP_EVENT_TIMER2]fxsls_offhook_dial htsp_dial

.Oct 11 17:06:11.302 EDT: htsp_process_event: [3/0/0, FXSLS_CONNECT, E_HTSP_VOICE_CUT_THROUGH]

.Oct 11 17:06:11.302 EDT: htsp_process_event: [3/0/0, FXSLS_CONNECT, E_HTSP_VOICE_CUT_THROUGH]u all

Thx.

Correct Answer
Paolo Bevilacqua Thu, 10/11/2007 - 13:21

Hi,

the router has no problem in sending tones out of an FXS port. The same is not true for most PBXs. You can also send caller-id from the router, if the PBX is able to use it.

destination-pattern 266.... is "better" than 266 because the router will not present calls to PBX when less that 7 digits are coming from voip. Of course you can also enforce this check on the origination router.

Paolo Bevilacqua Thu, 10/11/2007 - 15:44

I have to correct myself partially. You can use destination-pattern 266.... on the origination router. On the termination router, indeed you need 266 for the "excess digits" to be played on the FXS port.

Thanks for the nice rating and good luck!

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