WAN Basics
Transmission Options or WAN Services
There are a number of transmission options
available today. They fall either into the analog or digital
category. Next let’s take a brief look at each of these
transmission types.
POTS Using Modem Dialup
Analog modems using basic telephone service
are asynchronous transmission-based, and have the following
benefits:
- Available everywhere
- Easy to set up
- Dial anywhere on demand
- The lowest cost alternative of any wide-area
service
Integrated Services Digital Network (ISDN)
ISDN is a digital service that can use asynchronous
or, more commonly, synchronous transmission. ISDN can transmit
data, voice, and video over existing copper phone lines. Instead
of leasing a dedicated line for high-speed digital transmission,
ISDN offers the option of dialup connectivity—incurring
charges only when the line is active.
ISDN provides a high-bandwidth, cost-effective solution for
companies requiring light or sporadic high-speed access to
either a central or branch office.
ISDN can transmit data, voice, and video over existing copper
phone lines.
Instead of leasing a dedicated line for high-speed digital
transmission, ISDN offers the option of dialup connectivity
—incurring charges only when the line is active.
Companies needing more permanent connections should evaluate
leased-line connections.
- High bandwidth
- Up to 128 Kbps per basic rate interface
- Dial on demand
- Multiple channels
- Fast connection time
- Monthly rate plus cost-effective, usage-based
billing
- Strictly digital
ISDN comes in two flavors, Basic Rate Interface
(BRI) and Primary Rate Interface (PRI). BRI provides two “B”
or bearer channels of 64 Kbps each and one additional signaling
channel called the “D” or delta channel.
While it requires only one physical connection, ISDN provides
two channels that remote telecommuters use to connect to the
company network.
PRI provides up to 23 bearer channels of 64 Kbps each and
one D channel for signaling. That’s 23 channels but
with only one physical connection, which makes it an elegant
solution- there’s no wiring mess (PRI service typically
provides 30 bearer channels outside the U.S. and Canada).
You’ll want to use PRI at your central site if you plan
to have many ISDN dial-in clients.
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