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Community Member

Physical Connections FXO and FXS


I am new to the voice technology. In fact this is my first.

My customer has a 3640 at his HO. He plans to buy 1750V for his two remote sites. He also plans to use VoFr. He wants to connect two phones each at the remote sites to his PBX. The PBX is at his HO.

I have suggested that he use 4 FXO ports at the HO and 2 FXS ports at each of the two remote sites so that he can extend his PBX extension to the remote.

Physically PBX-------FXO-------FRAME RELAY-------FXS-------TELEPHONE.

Is this correct? what is required from the PBX vendor?

Is there any other way that this requirement can be met(Not VOIP)?

Is it possible to physically connect

PBX------FXS------FRAME RELAY------FXS-------TELEPHONE ?If so how do you configure? and what is required from the PBX vendor?


Cisco Employee

Re: Physical Connections FXO and FXS

If you want a true OPX extension, such that you can send hookflash *and* other supplemental signalling, then you'll want to use what Cisco calls "connection trunk" from FXO to FXS:

If you don't need to pass supplemental signalling, then you can do FXS to FXS and use either connection trunk or connection plar:

(connection plar does now support hookflash when configuring hookflash relay)

The advantage of plar is that the call is not active until someone tries to dial the remote extension. With connection trunk the call is up all the time.

From the PBX vendor you will just need them to provide either FXS or FXO ports, depending on which scenario you decide on.

Additionally, I would reccomend strongly that you use 1751Vs and not 1750Vs due to the memory limitation in the 1750s.



Community Member

Re: Physical Connections FXO and FXS

Thanks Clay.

Will Check out the combinations for VoFr as well

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