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 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}

!

H323:

voice service voip
h323
modem passthrough nse codec g711alaw