FXO to FXS one way call working only

Answered Question
Dec 11th, 2007

Hi guys, I'm sorry if this is not the right group to post this thread.

I have two 2811 running:

Cisco IOS Software, 2800 Software (C2800NM-ADVENTERPRISEK9_IVS-M), Version 12.4(2)T6, RELEASE SOFTWARE (fc3)

One router (RT_FXS) has 2 FXS ports, the other router(RT_FXO) has 2 FSX and 2 FX0 port.

The idea is to have 1 analog phones in each router, and the routers are connected using a FXO-to-FXS rj11 cross cable.

So one router (RT_fxs emulates a CO SWITCH)

The only thing that I could make work is to make calls from phone in router RT_FXO to phone in router RT_FXS

When I try to make a call from phone in router RT_FXS ( simulate a call from a CO SWITCH), the phone on the other router ring one time, then goes off-hook and 1 second latter goes on-hook, this happens without touching the phone.

Router RT_fxs has the following configuration:

voice-port 0/2/0

description FXS port connected to FXO on other router

!

voice-port 0/2/1

description FXS port connected to phone

!

dial-peer voice 2000 pots

preference 1

destination-pattern 2000

port 0/2/1

!

dial-peer voice 3000 pots

destination-pattern 3...

port 0/2/0

Router RT_fxo has the following configuration:

voice-port 0/2/1

description FXS port connected to phone

!

voice-port 0/3/0

connection plar 3000

description FXO port connected to other router

!

dial-peer voice 3000 pots

preference 1

destination-pattern 3000

port 0/2/1

!

dial-peer voice 2000 pots

destination-pattern 2...

no digit-strip

port 0/3/0

Correct Answer by smahbub about 9 years 2 months ago

I have seen an issue like this before and the usual porblem is that the cabling (or adapter) from the FXO or FXS port have more than just the "tip and ring" wired through. Please check your cables and make sure that only these two wires and conencted then test this again.

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Correct Answer
smahbub Tue, 12/18/2007 - 09:37

I have seen an issue like this before and the usual porblem is that the cabling (or adapter) from the FXO or FXS port have more than just the "tip and ring" wired through. Please check your cables and make sure that only these two wires and conencted then test this again.

nuno.pinto Fri, 12/28/2007 - 15:46

Thanks for your reply.

I already had figured it out.

I really don't know why, but I ask a coworker to make me a new cable and it just worked.

The old cable was done using a CAT5, probably that is the reason.

peternnaji Wed, 01/02/2008 - 01:52

Please can you give me the pin configuration of the FXS to FXS cable?

nuno.pinto Thu, 01/03/2008 - 01:06

I believe that what you want is the FXS-FXO cable pin.

That is very easy:

you need a phone cable (RJ11), cut one end and invert pin 2 and 3

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