Can I send and receive fax with VoIP ?
Generally yes, however, it is not guaranteed so you may want to ask your provider and test, if possible at all ahead of time.
Most protocols used in faxing were written with the intent of sending signals over traditional phone circuits using sounds, which were then turned back into data by the receiving fax machine. This type of communication expects a constant, steady transmission of ordered data without any loss.
In a VoIP Internet world, voice is compressed and converted into packets that travel independently, some may arrive out of order, and some may be lost/discarded without any noticeable voice degradation. This, however poses problems for traditional fax transmissions.
You may want to make the following changes:
- slow down the fax machine transmission speed (baud rate)
- turn off or disable ECM (error correction mode), a default setting of many fax machines.
- try enabling "overseas" mode
- try placing a DSL filter in reverse position between the line and the fax machine
- use a non-compressed VoIP codec - use G711 codec if possible. This is a non-compressed codec (as opposed to G729, which uses compression and may cause problems with faxes). Some providers have a "bandwidth saver" setting that corresponds to a compressed codec.
- ask your VoIP provider for fax settings - for example, Ooma users can dial *99 or *98 before the fax number.
You can test faxing using the HP test fax service by sending a one page fax to the following number (you should get a response fax sent back to you within 5 minutes):