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To be able to FAX with TBB, you need to do the following:

•Set your FAX device to 9600 baud. Higher rates are not "officially" supported by TBB.

•Set your TBB Web Portal - Options - Call Quality to "High Bandwidth Voice / Best Quality"

TBB Faxing is only supported officially at 9600 baud since there are technical limits related to bandwidth and jitter. However, depending on the quality of each user's LAN and ISP connection, TBB faxing can work at 14400 or more (some users report using this successfully).

Following is "snickerdo"'s tip that helped him and others with faxing more than one page:

Put a DSL filter on your fax machine. Yes, a plain ol' filter used for the same DSL that Bell sells. They can be purchased for about $5, or you can get them for free if you have a Sympatico DSL High Speed account. In other words, place a DSL filter on the Line 1 port of the gateway, and split it from there as needed.

A DSL filter is meant to remove the DSL signal from a phone line. However, used in this way with the DVG, it probably removes high frequency noise due to jitter (etc), from the fax line, thus perhaps making it more stable.

If you have trouble with FAXING, run the Primus VoIP Test. At the end of the test, provide the ticket # to Primus TBB Technical Support who can sometimes help to resolve the issue.


A Primus comment on Faxing:

Note that faxing is considered a best effort service over IP. (IP itself is considered best effort). With the nature of the underlying protocols and codecs supported by most major VoIP providers, it's currently very susceptible to packet loss.

T.30 (which is the PSTN faxing standard) is very sensitive to errors and contains a lot of error correction mechanisms. With RTP using UDP as a transport packetloss is considered a behavior of the protocol and the Internet. Running at a codec like G.711u allows for a full 64KBps channel, but it's blind to any of the error corrections provisioned by T.30. That is to say, IP is blind to those error mechanisms, not either end of the PSTN. This is why longer faxes tend to fail over congested links. (Which can be argued as all links)

An ITU standard called T.38 allows VoIP carriers to transport this T.30 PSTN signaling transparently across an IP transport while adhering to error corrections provisioned by T.30. Primus is currently in the process of testing this. There is no ETA, but it is in the works.



Feedback received on this FAQ entry:
  • Is there an update for this Primus comment on faxing? Does Primus use T.38 at present? How can we find the answer to this?

    2012-01-07 14:16:01



Expand got feedback?

by canoe See Profile
last modified: 2005-10-17 23:44:30