over IP is alive and kicking
fax still relevant in today's e-mail dominated world?
G B Kumar, General
Manager, Internet Solutions Group and Business Development,
Intel thinks fax over IP may be the next big booster
for this dying technology
fax still relevant in today's e-mail dominated world?
Scan through an IP telephony analyst report from the
likes of Probe Research or Frost and Sullivan and
you'll see that IP fax has tremendous upside and presents
a formidable business opportunity. It's not quite
there yet, as real time fax today is not part and
parcel of a typical Internet telephony service providers
Actually, a small percentage of today's IP telephony
calls drop off because they connect non-voice tones
which the gateways don't understand (meaning a customer
is either trying to fax or use a modem). So is fax
alive and kicking, or is it at death's door? And what
does all this mean for IP telephony?
answer the first question, let's consider the perspective
from a US office. I remember just a few years ago
sending and receiving several faxes a day. Today,
I still send and receive faxes but now it's only a
couple of times a week. Why even that many faxes,
you may ask? Because I still send faxes to submit
my forms for speaking engagements at trade-shows.
Companies like TMC, which sponsors the Internet Telephony
Conference and Expo, want my signature to show I'm
committed to that event. I also sometimes fax documents
to other company offices with my notes scribbled on
them, since it's often faster than editing a document
online. It's also more convenient to edit a hard copy
when travelling. Plus, I frequently receive faxes
from my company's offices and customers in the Pacific
Though e-mail is my primary means of communication,
the fact that I'm still using fax drives a point:
faxing is still alive and kicking and is important
for the point of view of a full IP telephony solution.
In this context, we're talking about real-time fax
service that fulfills users' expectations of walking
up to a fax machine, sending a fax, and having a piece
of paper simultaneously come out of a receiving machine
at the destination phone number. The bottom linenext-generation
service providers and IP centric enterprise communication
systems need to ensure that this type of fax capability
is part of their infrastructure solution.
way of going about implementing fax over IP is by
using standards formalized by the ITU (International
Telecommunications Union). The ITU has developed two
different standards addressing fax over IP. These
standards were incorporated in commercial systems
in the second half of 1999. The first standard, T.37,
is used mainly for store-and-forward faxing. It merely
defines the format in which fax is to be delivered
as an e-mail attachment. The second standard, T.38,
defines the protocol for real-time delivery of fax
over IP (FoIP).
With T.37, the fax is sent over IP as e-mail attachment
and delivered to the destination over the public switched
telephony network (PSTN) by the gateway closest to
the destination. While T.37 allows for cost savings
through toll arbitrage, from a user's perspective
it is a store and forward model and is not real time.
You can't immediately receive confirmation that the
fax was successfully delivered. Although a sender
might claim a fax "has been sent," the T.37
model doesn't let you automatically assume a confirmation
of delivery has been sent. If an en route e-mail server
happened to be down (perhaps due to some worm or virus
attack), the confirmation wont go through.
To satisfy the need for real-time FoIP, it's possible
to use the G.711 coder to transmit the fax. The problem
here is very high bandwidth usage. Unlike voice transmission
where the penalty is just human discomfort; jitter,
packet loss or latency can all cause a fax machine
to immediately terminate a call. The world is still
learning traffic engineering for multimedia transport
over IP. In some locations, the bandwidth is extremely
limited making network problems virtually impossible
Any real-time protocol over IP that bridges the call
path must meet requirements of the T.30 protocol (the
protocol for standard fax calls over PSTN). The T.30
protocol has very stringent requirements. For example,
signals are exchanged every 75ms. To solve this problem,
ITU-T Study Group 8 developed the T.38 protocol. Transporting
a fax using T.38 takes only a half-duplex channel
and 14.4 kbps plus
packet overhead. Transporting a fax using the G.711
a full duplex 64 kbps plus packet overhead.
T.38 is modeled as a smart T.30 interpreter. It executes
extensive training, signaling, and data exchange with
T.30 to determine the line quality on a PSTN network.
This is meaningless with a packet network, since the
IP packets can take any available route. Gateways
at each end execute full T.30 for communication with
fax machines. However, all the data is not transferred
over IP. While the fax machine sends the entire CNG/CED-type
tones for signaling, the gateways using T.38 only
exchange octets that indicate whether they've succeeded
or failed at detecting tones.
Essentially, the two gateways only exchange simple
results such as confirming success or failure, and
only transmit the pages intended for delivery.
focus is slowly shifting to developing V.34 extensions
to protocols in order to allow 33.6 kbps fax transmission
over IP. More research is being done in alternative
call control models such as SIP and H.248, as well
as on standardizing techniques
for switching from voice to fax and
vice versa for both H.323 and
So is fax still alive and kicking? Yes. And it will
continue to be important for IP telephony. As standards
evolve the picture will become clearer.
G B Kumar is General Manager, Internet Solutions Group
and Business Development, Intel. The views express
in this column are the author's own.