Mapping a remote FXO ports to a local IP Phone

Unanswered Question
May 23rd, 2008

We have two call manager express routers (2801 and 2811) connected through a WAN Connection. The 2801 router is acting as a voice gateway at the head office and connects 10 FXO ports to a Leagcy PBX. No IP Phones are connected with the 2801.

The 2811 has 10 IP Phones connected. We want to be able to have an FXO Line dedicated to each IP Phone at the remote site. Incoming calls are being routed to the Remote CME by using the connection plar xxxx command on the head office voice port accordingly.

The problem is with Outgoing calls from the IP Phones. We want that the same FXO port is used everytime that we want to access an outside line. This is so that users at the head office will know who is calling them and also we need this for the callback function on the legacy PBX to work properly.

I am achieving this result currently by specifying voice translation rules on the remote CME. A different set of rule is applied to every ephone so the before the number is passed to the Head office CME, a number (unique to the ephone) is appended to the number dialed and then it is passed to the Head CME. The head CME then has dial peers configured for every possible appended number which in turn strips this appended number and passes the digits to the appropriate voice port.

This is working fine, however I am feeling this solution a bit too dirty and too complicated, simply to map always the same FXO port to an ephone. I am also not happy with the fact the when you dial a number, you will see the extra appended number on the display of the IP Phone.

Is there a more clean and easy way to achieve what I require. Maybe using the Head Router as an MGCP gateway will be an idea?

Thanks alot,

Alex

I have this problem too.
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Paolo Bevilacqua Fri, 05/23/2008 - 08:36

Hi, what you're doing is correct. There is a configuration alternative, you setup COR so that on the remote router, cor rules direct the call out to the proper line. This had the advantage of not having any numbering massaging.

Hope this helps, please rate post if it does!

aseychell Fri, 05/23/2008 - 23:26

Hi,

Thanks for your reply. I never used COR. Do COR apply also when the call is not originated from the local router?

Perhaps you could suggest a sample config. it would be greatly appreciated.

Thanks again

aseychell Fri, 05/23/2008 - 23:49

Hi again,

I am searching a bit further and as I said in my previous reply, COR is always applied on the same router. For me to use COR, I would have to set up the COR Incoming statement on the ephone, then Corlist outgoing on the voice port. This would work but in my case these two statements will be specified on two different router which will surely not work.

Do you think that the answer-address on the dial-peer of the Head router will do the job. I mean the Head call manager will always receive the ANI number from the Remote call manager no?

Thanks

Paolo Bevilacqua Sat, 05/24/2008 - 00:10

Hi, yes you would set the cor statement in the remote router with answer-address, under the incoming DP.

aseychell Sun, 05/25/2008 - 09:32

But with the answer-address I would not need COR anymore then? When you say incoming DP, as far as I know incoming will refer to the voice-port, and so for the port to initiate the call, the incoming dial-peer will be a dynamic one, as I only have the outgoing DP set up on the router.

Kapil Atrish Sun, 05/25/2008 - 10:36

hi,

put answer-address on your outgoing POTS dial-peer on 2801. Call-control logic should route calls based on ANI correctly out to preferred fxo which is under pots DP.

thanks,

inner_silence

Paolo Bevilacqua Sun, 05/25/2008 - 10:43

No. Incoming DP is a voip one. There is no such thing as a dynamic DP. You will have as many incoming and outgoing DP pairts as ports, each one with a different cor tagging, but with the same destination-patter.

aseychell Mon, 05/26/2008 - 06:26

Hi,

Thanks for trying to help but I think that I am not making myself clear enough. First of all I read that the answer-address in an outgoing dial-peer is the second preference, the first being the destination-pattern command.

Second of this, I cannot do a cor on the remote router only (where the IP Phones are plugged) as the voice ports (FXO) are at the head office. It would not make sense to put COR tagging on the outgoing DP at the Remote router as it will only restrict which DP is used by which ephone. The DP at the Remote Router will still not be able to differentiate between a voice port and another on the Head Office Router.

Thanks again

AS

Paolo Bevilacqua Mon, 05/26/2008 - 06:41

Hi,

About you first doubt, the incoming voip DP has no destination-pattern, so answer-address is the decisive selector.

For your second one, that is not a problem. If you want the IP phones connected to the remote router to be able to use the "reserved" FXO port, you do not configure any corlist for ephone-dn. Using preferences, you can do so that the reserved port is used as a "last resort".

If you do not want them to ever be able use the port, you configure an incoming corlist for ephone-dn or ephone-dn-template.

I understand this configuration is not straightforward, but it works once you command the concepts that regulate DP selection in presence of equel destination-pattern and COR.

aseychell Mon, 05/26/2008 - 06:56

This is getting a bit long :)

Here is my Incoming DP on the Head router:

dial-peer voice 3000 voip

service session

destination-pattern 37..

session protocol sipv2

session target ipv4:172.16.20.253

dtmf-relay rtp-nte

codec g729br8

dial-peer voice 8 pots

description ** FXO Extension 2093 **

destination-pattern 1[1,2]...

port 0/0/2

forward-digits 4

!

dial-peer voice 9 pots

description ** FXO Extension 2093 **

destination-pattern 13[0,1,2,3,4,5,6,8,9]..

port 0/0/2

forward-digits 4

!

dial-peer voice 7 pots

description ** FXO Extension 2093 **

destination-pattern 10........

port 0/0/2

forward-digits 9

This is one set of DP at the Remote Router:

voice translation-rule 1

rule 1 /^2/ /12/

rule 2 /^1/ /11/

rule 3 /^0/ /10/

rule 4 /^31/ /131/

rule 5 /^32/ /132/

rule 6 /^33/ /133/

rule 7 /^34/ /134/

rule 8 /^35/ /135/

rule 9 /^36/ /136/

rule 11 /^39/ /139/

rule 12 /^30/ /130/

voice translation-profile 3701

translate called 1

dial-peer voice 12 voip

destination-pattern [1-9]3[0-6,8,9]..

session protocol sipv2

session target ipv4:172.16.10.36

dtmf-relay rtp-nte

codec g729br8

!

dial-peer voice 10 voip

destination-pattern [1-9][1,2]...

session protocol sipv2

session target ipv4:172.16.10.36

dtmf-relay rtp-nte

codec g729br8

!

dial-peer voice 11 voip

destination-pattern [1-9]02.......

session protocol sipv2

session target ipv4:172.16.10.36

dtmf-relay rtp-nte

codec g729br8

It appends a number (1) to al lthe numbers outgoing from ephone 1 passes it to 172.16.10.36 (Head Router). The Head router has a destination-pattern on each DP so that it matches the appended 1 number. It then forwards to the voice-port.

Maybe this will clarify the scenario a bit better.

Thanks for your help.

Kapil Atrish Thu, 05/29/2008 - 07:38

If following works:

dial-peer voice 7 pots

description ** FXO Extension 2093 **

answer-address (CCM IP Phone Ext)

port 0/0/2

Thanks,

inner_silence

aseychell Thu, 05/29/2008 - 07:52

Hi,

No that wont work. I tried it already. Don't know why but it doesnt. I know that first preference is destination-pattern then second is answer-address. In this case answer-address is the only try so it should work but no it doesnt.

However thanks for your help. I think I will leave it like it currently is, ie. adding / stripping digits to the number.

AS

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