Fax Attributes

Overview

The VDAC-ONE card provides real-time fax relay, compliant with ITU T.38, over IP networks. This fax capability fully supports the ITU T.30 for Group 3 facsimile transmission protocol, with speeds of up to 14.4 Kbps. To remedy network packet loss and latency issues, the VDAC-ONE card employs fax spoofing techniques and packet redundancy schemes.

With the VDAC-ONE card fax relay mode, faxes can be sent over IP using as much as 40 to 50 percent less bandwidth than the full 64 Kbps used on a traditional circuit-switched network.

The VDAC-ONE card also provides a fax bypass mode for real-time fax transmission using high-speed coders. This capability is based on a proprietary protocol that uses RTP packets to transport payloads of compressed fax transmissions, with G.726 or G.727 waveform coders operating at a rate of 32 Kbps or higher.

Important! If a matrix switchover (or switchback) occurs during fax transmission, the transmission fails.

Configurable Fax Attributes

You can configure the following fax attributes:

• Fax Type: Fax Relay or Fax Bypass

• Fax Bypass Coder Type

• Fax Payload Redundancy

Fax Type Enable

Fax Relay

The VDAC-ONE card's behavior depends upon how it is configured for detecting fax transmissions. When the host has configured a channel for Fax Relay modes and the VDAC-ONE card detects that a call is not a voice call, the codec switches from the Voice Coder mode to Answer Tone mode and then to Fax Relay mode. The packets are sent to the network as Fax Relay packets that comply with T.38. When the fax transmission ends, the channel reverts to Voice Coder mode.

Fax Bypass

The Fax Bypass feature is proprietary to the VDAC-ONE card and is supported only between VDAC-ONE cards.

When the host has configured a channel for bypass operation and a fax transmission is detected, the codec automatically switches from the current voice coder to the rate of the configured Coder Type. When the fax transmission ends, the channel reverts to Voice Coder mode.

Default: Disabled

TLV: 0x01C5 Fax Type Enable

0x00 Disable

0x01 Fax Relay

0x02 Fax Bypass

If the fax type is set to disabled (RTP not changed) then the fax goes through as a voice call. Therefore, the fax transmission might not be successful depending on the codecs used.

A PPL Event Indication of Fax Start is sent to the host regardless of the value above.

Fax Bypass Coder Type

This attribute selects the codec to be used in a fax bypass scenario. Dialogic strongly advises selecting a data rate greater than 32 kbps.

Default: G.711 µLaw

TLV: 0x01C7 Fax Bypass Coder Type

Fax Payload Redundancy

Payload redundancy is a type of protection against network packet loss. By enabling redundancy, you can configure the CSP to send redundant packets to the network. For example, when you set the redundancy level to 2, the original payload is followed by two duplicate payload. Fax redundancy is supported in relay mode only.

Default: Disabled

TLV: 0x01D2 Fax Payload Redundancy

Fax Compatibility Mode

This TLV determines the VDAC-ONE card T.38 Fax Relay Compatibility mode: Backward Compatible mode or Interoperability mode. You must choose one mode or the other, not both. The Backward Compatible mode interoperates with the fax relay mode on the previously released VDAC-ONE card software. The Interoperability mode is used primarily to facilitate interoperation with third party T.38 fax relay devices. This TLV can be configured only before or during the setup of a VDAC-ONE card call, not during an active call.

Default: Backward Compatible Mode

TLV: 0x01E1 Fax Compatibility Mode

Source T.38 Port

This TLV is used to specify the local T.38 port number for fax relay. There is no default T.38 port value for this TLV. The host must select this port number as early as possible to ensure proper fax relay operation. If this port number is not specified in time, the fax relay fails. This TLV can be set during an active call.

Default: No default

TLV: 0x01E6 Source T.38 Port

Destination T.38 Port

This TLV is used to specify the remote T.38 port number for fax relay. There is no default T.38 port value for this TLV. The host must select this port number as early as possible to ensure proper fax relay operation. If this port number is not specified in time, the fax relay will fail. This TLV can be set during an active call.

Default: No default

TLV: 0x01E7 Destination T.38 Port