WAN channel is created by linking together

WAN stands for ‘Wide Area Network’
and spans across a large geographic area, connecting multiple smaller networks together
such as LANs and MANs and can use telephone lines, fibre optic cables or
satellite links. This allows computers to communicate with each other while in
different locations. The best example of a WAN is the internet. A WAN can
either be public through the internet, or private with the use of leased lines
and many businesses use WANs connected different headquarters and offices

Circuit Switching

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This is a type of
switching method where a dedicated channel for communication is established between
two points within a network for the duration of the session. This is connection
oriented, meaning a connection must be established between the two points
before the channel can be created and any data sent. The most common use of
circuit switching is in traditional telephone systems, where the dedicated
channel is created by linking together phone lines into one single path between
the two points. While the channel is in use, no one else can use the physical
links involved. Circuit switching has three phases Circuit Establishment, Data
Transfer and Circuit Disconnect.

Packet Switching


Packet Switching was created to combat
the issue that arose with circuit switching. It works by taking the data that
is to be sent and breaks it down into smaller chunks called packets then sent
to the destination. Each packet is given a given a header section that
contains: destination address, source address, total number of pieces and
sequence number. There are two types of packet switching Connectionless Packet
Switching and Connection-Oriented Packet Switching. In Connectionless Packet
Switching, also known as datagram switching, each packet is transmitted individually
and may take different routes to the destination, once all packets have arrived
they are then reorganised in to the correct order, so the data can be read. If
Connection- Oriented Packet Switching is used, then a predetermined route is
made and all the packets are sent across this in order sequentially. This is
also known as virtual circuit switching.

Cell Switching


Cell Switching is a high-speed
switching technology that is commonly used in Asynchronous Transfer Mode (ATM)
networks. It is similar to Packet Switching but uses fixed length packets known
as cells. Due to the cells being fixed size it is more predictable and reliable
at transferring video, voice and data. Because Cell Switching is a
connection-oriented packet switched network it also has similar features to
circuit switching but uses virtual circuits instead of a physical circuit. The
virtual circuits in cell switching can either be configured as Switched Virtual
Circuits (SVC) or Permanent Virtual Circuits (PVC).



General Routing Algorithms

Distance Vector


This is one of the two major routing
protocols used to send packets over a network. It uses the Bellman-Ford algorithm
to calculate the shortest routing paths. Distance Vector Routing relies on
routers sharing their routing tables with neighbours periodically as routers
using this protocol can only see addresses in its own interface and are unable
to see the full network topology. To calculate paths for routing, two factors
are used:

Distance: How many hops it will take to reach
the destination

Vector: Direction of the next hop to reach the

The path with the shortest hops is
then considered the best path. Distance Vector Routing is better for smaller
networks as it doesn’t scale well with larger networks, it is also easy to
configure though it can be susceptible to routing loops and count to infinity

Link State


This is the other major routing
protocol used in packet switching networks. Link State differs from Distance Vector
as routers using Link State are able to see the full network topology. This is
achieved by each router gathering routing information about itself and the
devices connected to its interface and the state of those links known as
Link-State advertisements(LSAs). Once this information is gathered it is send
to all other routers on the network using multicasting until all router have an
identical database of the network. Then each router individually uses the
Dijkstra algorithm to find its own shortest/best paths. If the state of a link
changes then a single LSA is sent out. Link State is less prone to routing
loops, converges quicker and is more scalable, though it can be more complex to
setup and use more CPU power and memory.

Congestion Control


Use of Fair Queuing




Other Algorithms to Prevent Congestive Collapse


Addressing and Routing with IP


Logical Addressing


Subnet Masks


PTO Switched Services


Circuit Switched Services



PSTN stands for
Public switched telephone Network and is the global network of the public
telephone systems. It is an advancement from the first telephone system when two
telephones had to be connected over a copper wire to communicate, now the
copper wire from individual telephones are connected to a local telephone
exchange. It was originally created to provide analogue voice communication but
now is a mostly digital system that integrates mobile phone technology and provides
most of the internet with the long-distance infrastructure needed for communication
across countries and continents by sharing the circuits.



ISDN stands for Integrated Services Digital Network and is
an international standard for digital transmission of voice, video, and data
over ordinary copper based telephone lines. It can support a 64 Kbps data rate
transfer. There are two types of ISDN:

Basic Rate Interface (BRI) – has two 64 Kbps Bearer
(B) Channels for data and one Delta (D) channel for signalling and control information

Primary Rate Interface (PRI) – has either 23 (U.S.)
or 30 (E.U.) B channels and one D channel

It was an improvement over dial-up as it allowed two connections
to be made on the same line, letting users use the internet and make a phone call
simultaneously. Other advantages to ISDN are it’s faster to connect to calls, it
is more reliable at sending data, and channels can be joined for faster
transfer speeds.