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WAN
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WAN stands for Wide Area Network.
Using a WAN we can perform networking for a large
area.
>
Usually a WAN is combination of Two or more LANS.
A LAN is connected to a WAN by a Gateway.
A Gateway is an interface between a LAN and a WAN.
WAN Characteristics
The WAN concept has many different applications, which
can be categorized by examining the differing characteristics
of the network environment:
Is ownership of the network public or private?
Is the network designed primarily for voice or data
traffic?
Are connections dedicated or switched?
Private:
Private network operators typically lease lines from
public network provider while maintaining control and
management of the network from their own facilities.
Most private WANs also include a separate connection
to the public WAN.
Public:
Public WAN is the presence of government regulation,
which not only dictates the telecommunications services
that are provided by public WAN operators, but also
determines how which services are subject to tariff
and at what rate.
The best example of a public WAN designed for voice
is the Public Switched Telephone Network (PSTN)
Voice:
Voice networks have several common characteristics that
are designed to meet the needs of voice traffic:
If voice transmission does not arrive in the proper
order, then it is not likely to be of any use because
it may not be understood. As a result, voice networks
are typically circuit-switched because voice requires
consistent timing to prevent jitter. In general, packet-switched
networks are not suited for voice traffic because
prioritization can cause result in delays.
Because timing restraints do not allow time to
retransmit lost or damaged information, voice networks
typically have minimal error control and no error
recovery. Fortunately, voice traffic is very forgiving
to errors.
Data:
Data is less sensitive to the timing constraints of
voice traffic. Rather, data networks are more concerned
about reliable transport of information. As a result,
data networks are typically packet-switched or cell-switched
to ensure the error control and recovery needed to ensure
a reliable transfer.
WAN Connection Types
WAN connections come in two basic flavors:
Dedicated connections are links that is reserved
for a single telecommunications purpose and available
to the user at all times.
Switched connections are general purpose links that
are available on demand and are usually paid for on
a per usage basis.
Dedicated Connections
Permanent dedicated circuits, also known as leased lines
or private lines, have the following characteristics:
Cost is high because the connection is used exclusively
for one purpose, so they are primarily used for connections
where large amounts of traffic need to be moved reliably
between two network nodes.
Call setup is not required because the connections
are point-to-point.
Connections are always available, 24 hours a day,
seven days a week.
Dedicated connections are often deployed on high-capacity
links
Common uses of dedicated connections include video conferencing,
medical data imaging, and financial wire transfers.
Switched Connections
Switched connections, also known as virtual connections,
have the following characteristics:
Cost is low because switched connections are made
on demand over shared facilities.
Switched connections are set up as needed before
information can be transmitted. The call setup might
impart a slight delay, but you only pay for what you
use.
Connections are point-to-multipoint, and routing
decisions are made dynamically along the call path.
For voice connections, routing is performed only
once per call.
For data connections, routing is more dynamic so
that each and every packet might take a different
route.
Switched connections are commonly found in the PSTN,
as well as ISDN, Frame Relay, and ATM networks.
There are three basic types of WAN switching services:
Circuit-switched networks create a dedicated
circuit, or channel, which is used for the duration
of the transmission.
Packet-switched networks separate messages
into variable-length segments and transmit them individually
across dynamically created connections.
Cell-switched networks separate messages
into fixed-length cells and transmit them individually
across routed connections that are either dynamically
or permanently created.
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