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48 Chapter 3: Assembling and Cabling the WAN Components

Has future growth been taken into account?

Will the selected WAN components support an upgrade, or will a new component be
necessary?

Choosing WAN Equipment

Once the goals of the network have been decided on, the hunt for proper equipment begins.
Choosing the equipment that goes into each site is always an interesting endeavor. Vendors are
contacted, and sales personnel visit and relentlessly tell you that their equipment is the best.
Wisely, the decision is made to go with Cisco products (as if there were ever a doubt).

Obviously, the needs of each individual site in Figure 3-2 vary. The next few sections focus on
each site and its unique technological requirements.

Central Site Router Selection

The central site is usually the corporate office site and is also usually the largest of the sites.
With this distinction comes the need for more diverse capabilities with regard to WAN
connectivity. Many times, multiple technologies must be supported at this site, and all facets of
the network must be supported. In addition, each of the branch offices connects back to the
central site, and remote and/or mobile users need to be able to connect through telephone lines
to the network.

All of these needs must be supported from the central site. To do so, you must simultaneously
deploy a number of technologies, such as Frame Relay, ISDN BRI/PRI (T1 or E1), asynchronous
modems, network authentication, serial connections, bandwidth issues, and the list goes on.
Many times the solution involves a combination of the options listed here, and then some.

For serial connections as well as T1/E1 PRI, you should know that inside of North America, the
customer (that is, your company) is responsible for providing a CSU/DSU for the installation
of the network. For BRI connections, the customer must provide the NT1. Outside of North
America, however, these devices are generally telco-provided.

The issue of the point of demarcation (demarc) arises when setting up the central site. The
demarc is the point at which responsibility for the line changes from the telco to customer or
vice versa.

The demarc is placed in the section of the premises at which the telephone equipment is
installed. Many times, however, this is not the desired location of the router, so a choice must
be made. Should you have the demarc extended, or extend it yourself? Usually, it's much easier
(although slightly more expensive) to have the telco installer extend the demarc for you. On the
customer side of the demarc, the devices installed are known as customer premises equipment
(CPE). Extending the point of responsibility transfer saves you a great number of headaches.