| When you design networks, you
need to make several key decisions concerning connectivity between
different users or groups of users in your WAN environment.
When selecting a WAN connection, you should consider the following:
- Availability -- Each method
of connectivity has characteristics inherent in its design,
usage, and implementation. For example, Frame Relay is not
available in all geographic regions.
- Bandwidth -- WAN bandwidth
is expensive, and organizations cannot afford to pay for more
bandwidth than they need. Determining usage over the WAN is a
necessary step toward evaluating the most cost-effective WAN
services for your needs.
- Cost -- WAN usage costs are
typically 80 percent of the entire Information Services budget.
When different WAN services and different service providers are
evaluated, cost is a major consideration. If, for example, you
use the line for only one hour a day, you may want to select a
dial-on-demand connection, such as an asynchronous or ISDN
connection.
- Ease of management -- Network designers are often concerned about the degree of difficulty associated with managing connections. Connection management includes both the configuration at initial startup and the ongoing configuration tasks of normal operation.
Traffic management is the capability of the connection to adjust
to different rates of traffic, regardless of whether the traffic
is steady-state or bursty in nature. Dedicated lines are often
easier to manage than shared lines.
- Application traffic -- The
application traffic may be many small packets, such as during a
terminal session; or very large packets, such as during file
transfer. A dial-on-demand connection may be the best connection
type for smaller packets. On the other hand, a packet-switched
network may be best for the higher traffic application requirements.
- Quality of service and
reliability -- How critical is the intended traffic for a link? A backup connection may be necessary.
- Access control -- A
dedicated connection may help control access, but e-commerce
cannot occur on a wide scale unless consumers access some
portion of your network.
The Figure illustrates bandwidth and
time-selection considerations (which increase cost) when determining
the best WAN technology to use. (The source of the Figure is a 1995
study done by the Forrester Research firm.) The network
administrator must determine the best WAN technology to implement
based on the amount of bandwidth and the time a user requires on the
network. As the time of use increases, WAN services associated with
a variable cost, such as dialup, tend to be less advantageous.
Likewise, as time of use decreases, WAN services associated with a
fixed cost become more advantageous.
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