|ISDN and fax
Direct to your Desktop
BRI or PRI
Fax has come a long way. Its hard to believe that as recently
as 1966 the average transmission time for a page of simple text was six minutes. Then came
the Group 3 fax standard, and next up will be Group 4, a fully digital standard which will
introduce higher resolutions and colour faxing. Clearly the fax machine of tomorrow will
require an ISDN or leased line connection, but what about the fax devices of today? Is
there any benefit to be gained from installing digital fax hardware right now?
ISDN and fax
The first thought is that as ISDN offers significantly quicker data transmission speeds
than analogue, then fax would be the first to benefit. But, the Group 3 fax standard
allows a maximum transmission speed of 14.4kbps on a clear day with a following wind, so
whether your fax device is plugged into a humble analogue telephone line or ISDN,
youre still only sending 2 pages per minute. However, all is not bleak. ISDN
uses what is known as out-of-band signaling, and this can reduce connection time
significantly. In fact, one ISDN fax device talking to another will connect in less than a
second. Once ISDN faxing spreads, those call costs will begin to tumble and thats
not the only advantage ISDN offers.
Firstly, an ISDN connection is infinitely more reliable than any analogue line. Lower line
noise and reduced interference means that your faxes will be less likely to fail in mid
Secondly, ISDN fax hardware offers more sophisticated error reporting, so when things do
go wrong your fax server can be better informed about its retry strategy. A good fax
server product can now tell when its dialed a voice telephone line and will not
bother trying again.
Direct to your Desktop
Where ISDN really shines is in its ability to bring faxes right to the users PC.
ISDN allows the assignment of virtual extensions or fax numbers. You could conceivably
give a personal fax number to every employee in your company.
DDI (Direct Dial Inward) numbering is nothing new. Chances are you are already using it
for your company telephone system to give each user their own phone number. So why not add
a personal fax number to your corporate sales executives business cards?
Delivery of received faxes is instantaneous to the recipients desktop, streamlining
your business processes. Fax server technology also makes it possible for road users to
dial in and pick up all their fax messages at the same time they get their emails, or
The fax server can also make it childs play to assign DDI numbers to individual
users. Add the fax number to your personnel database, or LDAP-compliant email system and
have the server look it up on the fly. Ease of administration is key to the success of DDI
At present, DDI routing over ISDN is the only completely reliable medium for automatic
routing of faxes to the desktop and although it isnt cheap, prices are tumbling as a
result of tough competition in the market.
BRI or PRI
Everyone is familiar with Basic Rate ISDN (BRI). Two channels are available for faxing and
can be used for receiving faxes by DDI or sending, or both. Digital fax hardware is
available now to support one or two BRI lines for two or four lines of faxing, and your
telecomms provider will happily assign your DDI numbers across multiple BRI circuits. But
for the best bang for your buck, consider PRI. Primary Rate ISDN offers up to 30 fax lines
on a single circuit allowing you to scale up your operation at a later date. A six-line
PRI solution may look expensive at the outset, but as your fax usage grows you can simply
enable additional channels at relatively low cost, completely protecting your initial
For heavy fax users, PRI is the only way to go. With 30 fax lines in a single fax server,
well over a million fax pages can be sent or received in a month. The leading financial
institutions and law firms sending confirmations of trades, legal documents and so on are
already taking advantage of the heavy duty capabilities and reliability that is currently
only possible with a PRI-enabled fax server.
As your fax usage grows and your needs change, as new digital faxing standards appear and
ISDN becomes more widespread, you can rest assured that your fax server will meet the
challenge, delivering leading edge solutions to a technology that seems determined to
stand the test of time.
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