WAN media is an alternative
available for carrying your
customer’s valuable and heavy WAN traffic. The most common choices are
standard telephone lines, digital communications lines, and permanent leased
lines. Other less common options are fiber links, and various wireless
alternatives such as cellular, microwave and even satellite transmission. Let’s
look at the most common alternatives.
WAN communication protocols are collections of procedures,
data formats and rules used to describe how data could be transmitted over a WAN
link. The most common of these protocols are X.25, Frame Relay, PPP and SNA. The
communication protocol is the common language on the WAN. Again, we’ll
overview these alternatives.
The key to choosing the optimal WAN medium and communication
protocol is to understand the specific requirements of the application it must
support. Here are some issues that need to be considered:
1. What is the application? LAN-LAN connectivity often
requires permanent high bandwidth connections. Remote access requires an
intermediate-speed dial-up connection, while LAN access to SNA hosts is
typically used for mission critical applications requiring extremely reliable
but lower-speed connections.
2. How many locations are involved and where are they?
Certain media and communication protocols become more or less cost-effective
depending on how meshed the network is, and how far apart offices are. Depending
on where a branch is located, the existing communications infrastructure may
only permit certain WAN media and communication protocols to be used
3. What are the traffic patterns? Only certain networks can
handle bursty LAN traffic. Also, the cost of some services varies with usage,
making these alternatives overly expensive for high traffic links. Moreover,
usage fees may vary according to the time the link is used; for example, costs
may increase during business hours, which would be impractical for certain
applications
Answers to the above questions should help narrow the choice
of WAN media and communication protocols.
Leased lines
Leased lines continue to remain one of the most popular
choices for large corporations, especially in North America. Because a leased
line is a permanent link between two sites, it can be used for LAN-LAN
connections or LAN-SAN host connections. It is suitable for carrying any
communication protocol. Leased lines offer excellent performance for these
applications. Leased lines support transmission speeds ranging from 19.2 Kbps to
T3 (45 MBPS) and pricing is generally bandwidth and distance sensitive.
Fiber links
Fiber links are based on fiber optic cables, which conduct
light with extremely high efficiency. The great advantage with fiber cable over
conventional wire cables is the substantial weight and size savings and much
greater bandwidth. Although fiber is not yet in wide use in people’s homes or
offices, it is used for special applications such as metropolitan area networks.
Fiber links can be used to transport various communication protocols. Fiber is
generally more expensive than the media alternatives discussed so far.
Wireless media (Microwave and satellite)
Microwave and satellite are closely related because both are
all wireless. In both cases, data is transmitted via high frequency radio
signals from origin to a central relay station or satellite. These media are
delay sensitive and best used for "one to many" applications such as
distribution of financial market information. Because of inconsistent
reliability and high expense, these media are not well suited to LAN-LAN or LAN-SNA
applications. Again, these media can be used to transport a variety of
communication protocols.
Upcoming Technologies
ADSL
One promising technology is Asymmetric Digital Subscriber
Line (ADSL). It was developed to allow high bandwidth applications to be
delivered to homes (video on demand, Internet) using existing unshielded twisted
pair wiring. When available, ADSL will allow high bandwidth in one direction and
low bandwidth in the other. It uses signal encoding, compression, and modulation
techniques and can support various configurations of data rates depending on the
length of wire to be traversed. A typical ADSL configuration supports a
downstream delivery rate of 6 MBPS and an upstream rate of 64 Kbps up to a
distance of 12,000 feet.
SDSL
Symmetric Digital Subscriber Line (SDSL) is based on the same
technology as ADSL. However, as the name suggests, it offers equal bandwidth in
both directions and is better suited for applications such as video-conferencing
and high-speed remote LAN access. A typical configuration will support data
rates of 2 MBPS in each direction.
Cable modems
Another promising technology is cable modems that will allow
connection of personal computers to high bandwidth cable TV coax cables. The
good news about this technology is that tremendous bandwidth’s (up to 30 or 40
MBPS) will be attainable. The bad news is that this technology is not widely
available today and there are no industry standards for interoperability. Also,
unless the local cable company connects to the public telephone network, users
won’t be able to access sites not supported by the cable company.
WAN Communication Protocols
Wide Area Network communication protocols can seem like a
complex subject. However, two insights can help users of WAN services better
understand the technologies:
l Any WAN media can be used to transport any WAN
communication protocol.
l Any WAN communication protocol can be encapsulated in any
other WAN communication protocol.
A note of caution regarding communication protocols and
encapsulation; if you need to mix and match protocols on your WAN, do so with
care. Be careful to use only open protocol and encapsulation standards.
Following is a brief overview of the most common communication protocols in use
today.
V Srivathsan is Business Development Manager, Eicon Technology Corporation.