How many voice FXOs can the cisco 2821 Router support?

Answered Question
Jul 3rd, 2008

Good day all.

Please i need to know how many fxo cards can the 2821 cisco router support. The router has two HWIC cards that can support 2 4-voice port FXS/FXOs and an extension module (EM-HDA-8FXS) that specifically supports 8-fxs voice connections. Is there module that can handle FXOs? or can the same card handle both FXS and FXO connections? I hope i'm making sense here.

Regards,

Obinna.

I have this problem too.
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Correct Answer by Paolo Bevilacqua about 8 years 5 months ago

You can use the NM-HD-2V in any type of NM slot. The PVDM2-16 is a DSP module installed on said NM.

Note that when router is FXO and PBX is FXS, most likely you won't be able to do single stage dialing from PBX extensions to destinations reached via the router. Meaning you will have to wait for router dialtone, then dial the actual destination. This is called two-stage dialing and is quite inconvenient.

So, if you cannot use ISDN BRI or PRI, the only workaround to the above, is to use a mix of FXS and FXO ports. Router and PBX will use their respective FXO port for outgoing calls, FXS for incoming.

This allows for single-stage dialing in both directions.

Thanks for the nice rating and good luck!

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Paolo Bevilacqua Thu, 07/03/2008 - 09:16

Hi, dense configurations of FXO are very expensive and cumbersome on routers.

The theoretical maximum is 4 x 4FXO in the VWIC slots, plus 8 x 4FXO in the network module slots, hosted on 4 x NM-HD-xx, plus the adegaute number of PVDM2-xx to support all the voice ports.

You will find that because of that, it is more convenient to insist with telco for a T1/E1 connection, or if they are unable to deliver that, use a channel bank to present the lines as E1/T1 to the router.

Also remember that FXO lines present a lot of problem for telephony projects, much lower voice quality, no DID, lack of sure disconnect supervision, etc.

Hope this helps, please rate post if it does!

richnam Thu, 07/03/2008 - 09:31

Thank you very much for your reply.

At the moment i have 3 x 4port voice card on the VWIC slots. I have a Gigabit WIC card on the last HWIC. I am asking; is it possible for me to use the NME-X slot or the EVM Slot to support additional 1 x 4port FXO voice module and if i can, what type of NME-X or EVM module do i need.

Regards,

Obinna.

Paolo Bevilacqua Thu, 07/03/2008 - 09:50

Hi, you can add either:

1 x EVM-HD, plus 2 x EM-6FXO, PVDM2 resources as needed. This will also require an RJ21 cable to RJ11 patch panel.

or

1 x NM-HD-2V, plus 2 x VIC2-4FXO, plus PVDM2-16. This solution presents the voice ports directly as RJ11.

But as mentioned before, dense configuration of FXO are complicated and expensive, and you should evaluate migrating to PRI instead.

As an appreciation to those providing answers, please rate useful posts with the scrollbox below!

richnam Thu, 07/03/2008 - 10:07

Thanks alot.

I am interested in the 1 x NM-HD-2V module. Is this suppose to be used in the NME-X slot or the EVM slot? Is the PVCM2-16 a part of the VIC or is a seperate resource? The folks that need this service do not have a PRI or E1 card on the PABX.

Regards,

Obinna.

Correct Answer
Paolo Bevilacqua Thu, 07/03/2008 - 10:19

You can use the NM-HD-2V in any type of NM slot. The PVDM2-16 is a DSP module installed on said NM.

Note that when router is FXO and PBX is FXS, most likely you won't be able to do single stage dialing from PBX extensions to destinations reached via the router. Meaning you will have to wait for router dialtone, then dial the actual destination. This is called two-stage dialing and is quite inconvenient.

So, if you cannot use ISDN BRI or PRI, the only workaround to the above, is to use a mix of FXS and FXO ports. Router and PBX will use their respective FXO port for outgoing calls, FXS for incoming.

This allows for single-stage dialing in both directions.

Thanks for the nice rating and good luck!

richnam Thu, 07/03/2008 - 10:29

Thank you very much. I really appreciate this.

Regards,

Obinna.

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