Difficulty with sending faxes
The support of sending faxes over VoIP is still limited. The existing voice codecs are not designed
for fax transmission. An effort is underway to remedy this by
defining an alternate IP-based solution for delivering Fax-over-IP,
namely the T.38 protocol. Another possible solution to overcome
the drawback is to treat the fax system as a message switching
system which does not need real time data transmission - such
as sending a fax as an email attachment (see Fax) or remote printout
(see Internet Printing Protocol). The end system can completely
buffer the incoming fax data before displaying or printing the
fax image.