Configure Fax Relay

Applies to version(s): v2.7.

This is the list of fax Options. To view the list of fax options, in the Web Portal, select Profile, in the navigation menu followed by Fax/Modem Relay.

Fax Relay

Options	Description
Enable Fax Relay	This option is the global option telling if faxes (Passthrough or T38) will be relayed or not.
Detection Mode	This option contains one of the following mode: Standard, Use relay mode on any tone or Always Relay. Standard: Fax tones and T.38 re-invites will trigger fax relay mode. Modem tones and passthrough re-invites will trigger passthrough mode, though fax detection will still continue. Use relay mode on any tone: Both fax and modem tones will immediately cause switch to the chosen relay mode (without going to passthrough first for modem tones). Always relay: Calls are directly invited using the specified relay mode, without waiting for any fax/modem tone. This improves performance when the calls are known to always be fax or modem (e.g. when connecting with a fax server).
Relay Mode	This option is to choose which mode of fax will be used. This option contains one of the following mode: T.38 or Passthrough. T.38: This relay mode is used for faxes modulated in IP. Passthrough: Fax passthrough encodes fax traffic with in a G.711 (ulaw or alaw) voice codec and sends it across the VoIP network as a voice call. In this mode, echo cancellers are disabled, there's a fixed jitter buffer and there's no Voice Activity Detection.
Modem vs. Fax distinction timeout	This option is the time we wait after we got the CED, to get V21 flags. This is to avoid to send a SIP re-invite in passthrough and few ms after, when we realize it's a faxes, send another SIP re-invite in T38. Since CED is both for modem and faxes, we have the choice to wait a few ms before taking the "final" decision. The best choice depends on the setup. In general, 0ms will work fine. If the endpoint is T.38, then the option "Always Relay" will override the "Modem vs. Fax distinction timeout". Otherwise, 500ms will save a re-invite, but takes longer to switch to passthrough if the final result is modem.
Fax tones detection duration	This option is the maximum time (in seconds) to listen for FAX tones. After that delay, FAX tones are ignored. This avoids false FAX detection later in the call when a sound in an audio conversation has frequencies very similar to a FAX tone. Default time is 30 seconds. Can be set to 0 to keep fax detection enabled throughout the entire call.
Enable early Fax/Modem tone detection	This option is used to detect longer fax tones (CED and CNG) faster. Fax tones will be reported at the beginning of the detection instead of waiting to validate the tone duration before reporting. The drawback is that it increases the chance of detecting false positive, since these fax tones are single frequency tone and can appear frequently in an audio conversation. We suggest to keep this option turned off to avoid these false positives.
Enable switching to fax relay upon CNG tone	This option indicates if the detection of a CNG tone will trigger a switch to fax relay mode. We recommend to leave this option enabled for faster switch to fax in most setup. Note: this option works only if the sender Fax is on TDM (this option will do nothing if the sender fax is on SIP).

T.38 Params

Options	Description
Use V.34	This option activates support for V.34 faxes. By using that option, faxes can be transferred at speed up to 33.6 Kbps. If disabled, only V.17 faxes will be supported (transfer speed up to 14.4 Kbps). Before using this option, you also need to enable V.34 Globally on each Telecom unit: Hardware -> TB00xxxx [Edit] -> Advanced Parameters -> Enable V.34 fax After this has been done, a restart of the Telecom unit is required: Status Tab -> Reboot adapter -> Yes [Apply States]
Max bitrate	This option is used to limit the maximum bitrate of faxes. By default, faxes will try to train at maximum bitrate. If a Failure to Train (FTT) happens, the bitrate will be reduced again and again. This option is used when you want to specify the maximum bitrate. By using that option, faxes transmission can complete in less time since unnecessary training sequences will be skipped.
Fill bit removal	This option is used to remove inserted fill bits in Phase C for non-ECM data. We suggest to leave this option unchecked.
TCF transfer mode	Transfer training in T.38 or generate locally the Training Confirmation. We suggest to leave this option at Transferred (default option).
Redundancy Count	This option indicates how many times each fax control frame will be sent. Note that this only applies to fax control frame. It does not apply to fax page data.
Transmission level (-1dBm unit)	This option is to adjust the transmission level to the TDM network. Valid values are between 0 and -15dBm, inclusive.

Modem/Fax Passthrough Params

Options	Description
Detection type	This option is used to detect if a call will be in passthrough mode. Possible values are: None, Silence Suppression Off and G711 Only. "None" means no Passthrough will be triggered whatever the SPD is. "G711 only" means if there's only G711 codecs (ulaw and/or alaw), this call will be treated as a passthrough call. This is true when sending or receiving SDP. "Silence Suppression Off" means when receiving an SIP invite, if the SDP contains the attribute "a=silenceSupp:off - - - -", it will be treated as a Passthrough call. When sending SIP invite for a passthrough call, the same attribute will be used. This option works if there's only G711 codecs in the list of supported media. So this option is a bit less resrictive than "G711 only"
Codec	This option specifies which codec will be used for fax passthrough. By nature, fax passthrough MUST be a non-compressed codec so you can choose between PCMU or PCMA. Note that when a switch to passthrough is initiated by the remote endpoint, our gateway will always use the same codec as the peer.
Jitter Buffer Depth	This option is to specify what will be the size of the fixed Jitter Buffer when in passthrough mode.
Use NSE	This option is to specify what method will be used to switch to Passthru. NSE is a way to swith using RTP events instead of SIP re-INVITE.

References

• Wikipedia article
• NSE