Cisco ATA 186/188, FXS & FAX

ATA 186 – 2 x voice ports + 1 x RJ-45 10BaseT port

ATA 188 – 2x voice ports +  2 x RJ-45 10/100BaseT port

The Cisco ATA supports two modes of fax services, in which fax signals are transmitted using the G.711 codec. It cannot support fax relay. ATA is accessed by web through http://<ipaddress_of_ata>/dev

•Fax pass-through mode—Receiver-side Called Station Identification (CED) tone detection with automatic G.711A-law or G.711µ-law switching.
•Fax mode—The Cisco ATA is configured as a G.711-only device.

Fax Pass-through Mode: Fax pass-through mode allows for maximum codec flexibility because users may set up a voice call using any voice codec, then renegotiate to a G.711 codec for the fax session. To use fax pass-through mode, first configure the Cisco ATA and supporting Cisco gateways to support the Cisco-proprietary G.711fax upspeed method. Then, disable fax relay on the far-end gateway—either for the entire gateway or for the dial peer engaged in the fax call with the Cisco ATA.

This requires configuration of two parameters at the ATA i.e. AudioMode & ConnectMode.

Audio 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.

To configure Phone 1 for Fax pass through:

0xXXXX0015 => 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

Connect Mode: 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 a value of 0x90000400.

0x90000400 => 1001.0000.0000.0000.0000.0100.0000.0000

•Bit 2,7-15 are important for Fax-pass through (made bold above)

•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.

To configure Fax pass through on the IOS gateway, follow these steps:

voice service voip
modem passthrough nse codec g711ulaw
fax rate disable  {this disables the default fax relay}



voice service voip
modem passthrough nse codec g711alaw

dial-peer voice 500 voip
incoming called-number .
destination-pattern 550
session target ipv4:
fax rate disable
codec g729r8


voice service voip
fax protocol pass-through g711ulaw

dial-peer voice 2000 voip
fax rate disable
fax protocol pass-through g711alaw

mgcp call-agent service-type mgcp version 0.1
mgcp modem passthrough voip mode nse
mgcp package-capability rtp-package
mgcp fax t38 inhibit  {disable fax relay}


Note: If you need to configure fax pass-through to work with Cisco CallManager (CCM), you must use the modem passthrough nse command. The fax protocol pass-through command does not work with CCM, which relies on NSE information.

Sample configuration for a FAX machine connected to FXS port.

Fax connected to FXS Port:

voice-port 0/1/0
cptone GB
description ### Admin Fax 0209001 ###

dial-peer voice 50 pots
description ### Admin Fax 209001 ###
destination-pattern 9001
progress_ind alert enable 8
progress_ind progress enable 8
progress_ind connect enable 8
fax rate disable
port 0/1/0


2 thoughts on “Cisco ATA 186/188, FXS & FAX

  1. Quick question on ATAs vs VG2XX:

    I am working for a telecommunications company and I have a requirement for analog lines.

    These analog lines connect to a box used to test GSM call quality and on the sites where I have ATAs, they are getting good MOS values compared to sites using VG202 or VG204s.

    Could it be the VGs that are contributing to the bad results and is there any explaining why this is the case or I might have other problems on sites where I am getting bad results.


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