Problem with Fax

Unanswered Question
Feb 19th, 2009
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we hace installed a CUCM 0-13 with gateway configured in mode MGCP. All calls of

voice work fine, the problem is with fax. This Fax is connected a ATA186I2-A.

Next attached the configuration of gateway mgcp:

Version IOS : c2800nm-adventerprisek9-mz.124-15.T5.bin


ccm-manager fallback-mgcp

ccm-manager mgcp

no ccm-manager fax protocol cisco

ccm-manager music-on-hold

ccm-manager config server

ccm-manager config



mgcp call-agent 2427 service-type mgcp version 0.1

mgcp dtmf-relay voip codec all mode out-of-band

mgcp rtp unreachable timeout 1000 action notify

mgcp modem passthrough voip mode nse

mgcp modem passthrough voip redundancy

mgcp package-capability rtp-package

mgcp package-capability sst-package

mgcp package-capability pre-package

no mgcp package-capability res-package

no mgcp package-capability fxr-package

no mgcp timer receive-rtcp

mgcp timer nse-response t38 250

mgcp sdp simple

mgcp fax t38 inhibit

mgcp fax t38 gateway force

mgcp rtp payload-type g726r16 static

mgcp bind control source-interface GigabitEthernet0/0

mgcp bind media source-interface GigabitEthernet0/0


mgcp profile default


The fax's model is a Cannon L100 Super G3

Someone advise me a debug command to search of fax problem?

Thanks a loot!

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Overall Rating: 4 (4 ratings)
Ayodeji Okanlawon Thu, 02/19/2009 - 11:23
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    2017 IP Telephony


Usually with ATAs and G3 faxes, the problem is usually with the speed negotitation. Most G3 faxes transmit at 33.6Kbps, while the ATA can only support 14.4kbps.

Below are the recommended settings for the audio mode and conect mode:



The AudioMode parameter is a 32-bit value. The lower 16 bits apply to the Phone 1 port of the Cisco ATA and the upper 16 bits apply to the Phone 2 port of the Cisco ATA.


The following is an example of configuring the Phone 1 port of the Cisco ATA for fax pass-through mode:



This setting translates to the following bitmap:

xxxx xxxx xxxx xxxx 0000 0000 0001 0101

•Bit 0 = 1-Enables G.711 silence suppression (VAD)

•Bit 2 = 1-Enables Fax CED tone detection and switchover upon detection

•Bit 4 = 1, Bit 5 = 0-DTMF transmission method = out-of-band through negotiation

•Bit 6 = Bit 7 = 0-Hookflash transmission method = disable sending out hookflash


Note The values XXXX in the example apply to the Phone 2 port of the Cisco ATA.


To configure the same value for the Phone 2 port of the Cisco ATA, the value would be 0x0015XXXX. The configuration of one port is independent from the configuration of the other port.



The ConnectMode parameter is a 32-bit value. The parameter settings apply to both lines of the Cisco ATA. Configure ConnectMode after configuring AudioMode for fax pass-through mode. Cisco recommends you use the following ConnectMode setting to interoperate with a Cisco IOS gateway.

Recommended Setting



This setting translates to the bitmap:

1001 0000 0000 0000 0000 0100 0000 0000

Bit 2 and bits 7 through 15 are the only relevant bits for fax pass-through mode. These bits from the example are isolated below:

xxxx xxxx xxxx xxxx 0000 0100 0xxx x0xx

•Bit 2 = 0-Uses RTP payload number 126/127 for fax upspeed to G.711m-law/G.711A-law. Set this value to 1 if you want to use RTP payload number 0/8 for fax upspeed.

•Bit 7 = 0-Disables fax pass-through redundancy. Set this bit to 1 to enable redundancy. With redundancy enabled, the Cisco ATA sends each packet twice. Because of bandwidth and transmission time costs, use this option only if network quality is poor and all other gateways used in the network support this feature.

•Bits {12, 11, 10, 9, 8} = {0, 0, 1, 0, 0}-Sets the offset to NSE payload-type number 96 to 4. Setting the offset to 4 results in the Cisco ATA sending an NSE payload-type value of 100 by default. Valid offset values range from 2 to 23 (NSE payload type value of 98 to 119). Set this value to match the value for your Cisco gateways.

Most Cisco MGCP-based gateways, such as Cisco 6608, use NSE payload type 101 by default. Most Cisco H.323/SIP-based gateways use NSE payload type 100 by default.

•Bit 13 = 0-Uses G.711m-law for fax pass-through upspeed. Set this bit to 1 to use G.711A for fax pass-through upspeed.

•Bit 14 = Bit 15 = 0-Enables fax pass-through mode using the Cisco proprietary method (recommended). Set both of these bits to 1 to disable fax pass-through mode.

Secondly you need to modify your MGCP config with the following:

no mgcp fax t38 gateway force

mgcp modem passthrough voip codec g711alaw (depending on whether you use alaw/ulaw in your region). Note do not add the "redundancy" keyword at the end of the mgcp modem passthrough voip codec g711alaw.

Try again.

Nicholas Matthews Thu, 02/19/2009 - 20:08
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Can you try removing this:

mgcp modem passthrough voip redundancy

Hythim Ali El Hadad Wed, 02/25/2009 - 04:45
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Could you please add these commands

mgcp package-capability fxr-package

no mgcp fax t38 gateway force

sruizpla Wed, 02/25/2009 - 08:21
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Thanks for yours answers, I already have solved the problem. The problem was in the ATA, I have changed for other and work fine.

Thanks all and sorry for not try to change the ATA before.


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