| Organizations with multiple LANs in
different geographical locations use WAN technologies to interconnect
them. When the distance between LANs becomes too great, a Wide Area
Network is needed. For instance an organization may have three
locations, Phoenix, AZ, Denver, CO and Raleigh, NC. It is not
realistic or cost effective for the organization to own all the
cabling and equipment needed to interconnect these locations and a WAN
connection is needed. The WAN's links or communication lines between locations
can be dedicated or shared. These links are leased from a service
provider such as the phone company and are not owned by the
organization whose LANs are interconnected. WANs can be worldwide
spanning thousands of miles.
Virtually every organization of any
size today has a connection to the Internet. In its simplest form a
WAN is created when a company connects its LAN to an Internet Service
Provider (ISP). There may be 100 or more users on the LAN but there is
only one WAN link to the ISP's network. Although a single LAN with an
Internet connection is technically a WAN, the term is more often used
to describe the links between two or more of an organization's LANs.
There are many WAN technologies that
can connect LANs but the link is usually provided by a T1 (Trunk 1)
connection or a fraction of a T1. A T1 connection provides 1.544 Mbps
of bandwidth, which is considered a relatively low speed connection
(compared to LANs) but it is usually adequate for Internet access or
interconnecting multiple sites. The two most common WAN connection
technologies are: dedicated T1 or shared Frame Relay. Others include
Integrated Services Digital Network (ISDN) and Asynchronous Transfer
Mode (ATM). Figure
is a summary of WAN characteristics.
In most cases there is only one WAN
link between locations, but it is possible to have more than one WAN
link for redundancy or increased performance. If there are three
locations, WAN links can be set up between each of the LANs (3 links)
as shown in Figure .
This will create multiple paths in case one of the links goes down.
Whether connecting to the Internet or
connecting multiple corporate LANs, a networking device called a
router is required. In order for an organization to connect to the
Internet, a single router is needed. If an organization wants to
connect two sites across a WAN link a router is needed at each
location.
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