FAX Method

Unanswered Question
Mar 10th, 2009


I don't know much about different Fax methods, I have a requirement to get a fax machine working that is connect to an FXS port on Cisco 2811 router, this router is a h323 GW registered to Cisco CM 6.1. The GW also terminate ISDN 2 for incoming calls and faxes once the fax is setup.

The fax communication will be more of a hairpin call type where an incoming fax comes in via the ISDN2 and terminates on the FXS port on the same router. At this stage the fax won't require to travel over the IP network.

Looking forward to your solution.


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Paolo Bevilacqua Tue, 03/10/2009 - 22:25

You do not need any special configuration beside network-clock-participate and network-clock-select for the BRI ports, and the pots DP for the FXS the port with the assigned number.

Nicholas Matthews Tue, 03/10/2009 - 22:33

Since you are using H.323 you do not need to worry about a fax over IP protocol. (If you were using MGCP it would be different.)

In this case since it is pots-to-pots, the DSPs, and thereby VOIP in general, will not be invoked and it will not require any fax configuration.


hadisharifi Tue, 03/10/2009 - 22:38

Thanks guys, the FAX number is within the DID range assigned to the ISDN2 so if I assign a four digit extension from this DID to the FXS port or pots dialpeer, will it work?

Paolo Bevilacqua Tue, 03/10/2009 - 22:45

Check with "debug isdn q931" the number that you receive from telco. Assign that number to the pots DP.

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hadisharifi Tue, 03/10/2009 - 22:53

Thanks p.bevilacqua, but the number that I receive from Telco is for the VOIP phones for this branch and I want to assign one a DN from this to the FAX.

For example:

8359 0300 to 8359 0399 and I want to assign 0350 for the FAX.

Don't I need to create a route pattern for the FAX number on the CM since this is a CM controlled GW?

Paolo Bevilacqua Tue, 03/10/2009 - 23:05

As mentioned before, just assign the number as received, to a pots DP.

Being a more specific destination-pattern, will not interfere with CMs numbers.

hadisharifi Wed, 03/11/2009 - 00:45

Thanks p.bevilacqua,

Our out going calls are via another H323 GW registered to the CM and not via the locally terminated ISDN, does this mean I will need to create a router pattern on the CM for the FAX machine connected to the FXS port?

I have configured the FXS as below however when I place a call to 85390350 the fax machine doesn't ring and I get the following.

voice-port 0/1/0

cptone AU

impedance complex1

caller-id enable

dial-peer voice 1 pots

destination-pattern 83590350

incoming called-number .


port 0/1/0

*Mar 11 17:18:54: ISDN BR0/0/0 Q931: RX <- SETUP pd = 8 callref = 0x2A

Sending Complete

Bearer Capability i = 0x8090A3

Standard = CCITT

Transfer Capability = Speech

Transfer Mode = Circuit

Transfer Rate = 64 kbit/s

Channel ID i = 0x81

Progress Ind i = 0x8583 - Origination address is non-ISDN

Calling Party Number i = 0x2183, '398373216'

Plan:ISDN, Type:National

Called Party Number i = 0xC1, '83590350'

Plan:ISDN, Type:Subscriber(local)

*Mar 11 17:18:54: ISDN BR0/0/0 Q931: TX -> CALL_PROC pd = 8 callref = 0xAA

Channel ID i = 0x89

*Mar 11 17:18:55: ISDN BR0/0/0 Q931: TX -> PROGRESS pd = 8 callref = 0xAA

Cause i = 0x8181 - Unallocated/unassigned number

Progress Ind i = 0x8188 - In-band info or appropriate now available

*Mar 11 17:19:05: ISDN BR0/0/0 Q931: TX -> DISCONNECT pd = 8 callref = 0xAA

Cause i = 0x8081 - Unallocated/unassigned number

*Mar 11 17:19:05: ISDN BR0/0/0 Q931: RX <- RELEASE pd = 8 callref = 0x2A

*Mar 11 17:19:05: ISDN BR0/0/0 Q931: TX -> RELEASE_COMP pd = 8 callref = 0xAA

hadisharifi Wed, 03/11/2009 - 04:46

Anyone else, I didn't explain myself very well when I said it was more of a hairpin call, this is true for incoming faxes but for outgoing faxes we will use a service provider who's h323 gateway is registered with our CM.

How would I set this up, do I create a router pattern on the CM pointing to the h323 GW for the fax connected to the fxs port?

Paolo Bevilacqua Wed, 03/11/2009 - 08:00

Hi, it's very strange that the call for which you took the trace didn't go to the FXS port. Can you send output of "show dialplan number 83590350" ?

hadisharifi Wed, 03/11/2009 - 15:30

Hi, here is the output for the show dialplan number:

Macro Exp.: 83590350


peer type = voice, information type = voice,

description = `"Melbourne 3G office Fax Machine"',

tag = 1, destination-pattern = `83590350',

answer-address = `', preference=0,

CLID Restriction = None

CLID Network Number = `'

CLID Second Number sent

CLID Override RDNIS = disabled,

source carrier-id = `', target carrier-id = `',

source trunk-group-label = `', target trunk-group-label = `',

numbering Type = `unknown'

group = 1, Admin state is up, Operation state is up,

Outbound state is up,

incoming called-number = `.', connections/maximum = 0/unlimited,

DTMF Relay = disabled,

URI classes:

Destination =

huntstop = disabled,

in bound application associated: 'DEFAULT'

out bound application associated: ''

dnis-map =

permission :both

incoming COR list:maximum capability

outgoing COR list:minimum requirement

Translation profile (Incoming):

Translation profile (Outgoing):

incoming call blocking:

translation-profile = `'

disconnect-cause = `no-service'

advertise 0x40 capacity_update_timer 25 addrFamily 4 oldAddrFamily 4

type = pots, prefix = `',

forward-digits default

session-target = `', voice-port = `0/1/0',

direct-inward-dial = enabled,

digit_strip = enabled,

register E.164 number with H323 GK and/or SIP Registrar = TRUE

fax rate = system, payload size = 20 bytes

supported-language = ''

Time elapsed since last clearing of voice call statistics never

Connect Time = 333179, Charged Units = 0,

Successful Calls = 0, Failed Calls = 2, Incomplete Calls = 0

Accepted Calls = 32, Refused Calls = 19,

Last Disconnect Cause is "10 ",

Last Disconnect Text is "normal call clearing (16)",

Last Setup Time = 49667804.

Matched: 83590350 Digits: 8


Paolo Bevilacqua Wed, 03/11/2009 - 20:39

All is good so far, maybe you want to enable debug voip dialpeer and debug vpm signal in addition to isdn debug, to see what's going on here.

hadisharifi Wed, 03/11/2009 - 21:03

Hi, attached is the debug output of the two commands, I also tried a test call from the router and it failed as well.

csim err csimDisconnected recvd DISC cid(126)

csim: loop = 1, failed = 1

csim: call attempted = 1, setup failed = 1, tone failed = 0

How would I setup the outgoing faxes? Since all our outgoing calls are via a service provider and the calls from this router will have an IP part.


Paolo Bevilacqua Wed, 03/11/2009 - 21:21

From the debug, you have FXO, not FXS. Check you "show diag".

You cannot have the fax working with an FXO port.

For the outgoing calls, ask ITSP if they support T.38.

hadisharifi Wed, 03/11/2009 - 21:34

Thanks, I am getting this checked out now.

This is the setup:

Branch office has a 2811 ISR, it has an ISDN2 for incoming calls which will also be used for failover for outgoing calls.

This router is a H323 GW registered to CM6 and there is also a SP H323 GW registered to the CM for all our outgoing calls and the faxes from this branch office will have to take this path.

hadisharifi Wed, 03/11/2009 - 21:58

You mean on the CM or the local router which is registered to the CM as h323 GW? The GW has a voip DP pointing to the CM which has a RP pointing to the ITSP.

Paolo Bevilacqua Wed, 03/11/2009 - 22:29

The voip DP for CM should have a destination-pattern for extensions.

Make another one like .T and the GW will be able to go to ITSP without using CM at all.

hadisharifi Wed, 03/11/2009 - 22:40

Thanks for your help p.bevilacqua,

As you said in your earlier post that I should ask the ITSP if they support T.38, do I still need to configure a fax protocol to the ITSP?

This is the first time I am trying this hence why asking so many questions.


hadisharifi Thu, 03/12/2009 - 21:59

Hi p.bevilacqua, There was an FXO and it has been replaced with an FXS, I can make calls in and out, however when trying a fax call it doesn't go through.

There is VOIP DP 100 pointing to the CM for destination pattern 0.T, this is the DP get used by the FAX call as I don't have another DP, you suggested that I created a DP pointing to the ITSP but how will this get used over the existing voip one since they both will have a destination pattern of 0.T and if I do create a new one won't this get used by the VOIP phones?

If I don't specify anything regarding the fax configuration, will the Cisco fax protocol get negotiated.


Paolo Bevilacqua Thu, 03/12/2009 - 23:03

Hi, you also need network-clock-participate and select for the isdn ports. The change destination-pattern to match extensions and add another DP. Use codec g.711 to ITSP and hopefully fax will work

hadisharifi Thu, 03/12/2009 - 23:16

I have already got network-clock-participate wick 0, I also have the following DP.

dial-peer voice 100 voip

destination-pattern .T

modem passthrough nse codec g711alaw

session target ipv4: "This is the CM"

incoming called-number .

fax-relay ecm disable

fax rate disable

Paolo Bevilacqua Thu, 03/12/2009 - 23:32

Add network-clock-select 1 ...

change destination pattern to match the CM extensions as close as possible.

hadisharifi Thu, 03/12/2009 - 23:36

I know what you are saying that I change this DP to be more specific but what about SRST? If I create a less specific like a 0.T pointing the ITSP what is going to happen to the SRST in case of WAN failure?

Paolo Bevilacqua Fri, 03/13/2009 - 09:36

Actually what I'm saying is more specific DP like 4... pointing to CM, less specific like 0T pointing to ITSP.


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