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WAN MEDIA: Thinking Out Of The Box

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DQC Bureau
New Update

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.

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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.

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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.

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Leased lines

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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

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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.

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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.

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Upcoming Technologies

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.

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