WIDE AREA NETWORKS - WAN
•What is a Wide Area Network?
•Brief History
•Difference between LANs and WANs
•Packet Switches in WAN
•Forming WANs
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WHAT IS A WAN ?
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A Local Area Network (LAN) can span a single building or campus,
A Metropolitan Area Network (MAN) can span a single city,
A Wide Area Network (WAN) can span sites in multiple cities, countries, continents.
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1957 ARPA(Advanced Research Projects Agency) project starts as a military research for
satellite communications, and in 1972 first public demonstration of ARPANET introduces
networks into our lives. Of many competing systems created at this time, Ethernet and
ARCNET were the most popular. Local area network technologies have become the most
popular form of computer networks. LANs now connect more computers than any other
type of network.
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The fundamental difference between a WAN and a LAN is the scalability, WANs can be
able to connect as many computers and networks as possible.
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The most popular example of WAN is the internet.
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A WAN is constructed from many switches to which individual computers connect.
Additional switches can be added as needed to connect additional sites or additional
computers.
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SWITCHES IN WANs
The basic electronic switch
used in WAN is called a packet
switch because it moves a
complete packets from one
connection to another.
 WANs are often built using
leased lines. At each end of the
leased line, a router connects
to the LAN on one side and a
hub within the WAN on the
other.
 Leased
lines can be very
expensive. Instead of using
leased lines, WANs can also be
built using less costly circuit
switching or packet switching
methods.
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WIDE AREA NETWORK PROTOCOLS
•Circuit Switch Networks
•Packet Swicth Networks
•Cell Relay Switch Networks
PSTN, ISDN, TDM
X.25, Frame Relay
ATM
WIDE AREA NETWORK PROTOCOLS
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CIRCUIT SWITCH NETWORKS
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A circuit switching network is one that establishes a fixed bandwidth circuit
(or channel) between nodes and terminals before the users may
communicate, as if the nodes were physically connected with an electrical
circuit.
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Circuit switches are actually designed for real-time audio communication. In
time, with the necessity for carrying data over distances they are used in
data transfer too.
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Circuit switches are combined through trunks
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Bandwidth allocation is not flexible
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Multiplexing techniques used in data transfers over circuit switches increases
the cost
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CIRCUIT SWITCH NETWORKS
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CIRCUIT SWITCH NETWORKS
PSTN
PSTN (Public Switched Telephone Network)
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PSTN is the conventional telephone network and it is pretty much digitalized
today.
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Today data transfer over PSTN is only used for dial-up modems.
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PSTN can only provide a maximum of 64 Kbps data transfer rate.
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In case of more bandwidth necessity ISDN is preferred over PSTN.
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It is sometimes referred to as the Plain Old Telephone Service (POTS).
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CIRCUIT SWITCH NETWORKS
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ISDN
ISDN (Integrated Services Digital Network)
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ISDN provides digitized voice and data to subscribers over conventional loop
wiring (PSTN).
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ISDN provides faster speeds than 64 kbps using PSTN. There are two types of
ISDN connection services, BRI and PRI.

BRI is formed of two 64Kbps lines which provide 128Kbps bandwidth for
subscribers. (Individual Solution)
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PRI is formed of thirty 64Kbps lines which provide 1920Kbps bandwidth for
subscribers. (Industrial solution)
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CIRCUIT SWITCH NETWORKS
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TDM
TDM (Time Division Multiplexing)
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Time-Division Multiplexing is a type of digital or analog multiplexing in which
two or more signals or bit streams are transferred apparently simultaneously
as sub-channels in one communication channel, but physically are taking
turns on the channel. So through one channel in a certain time data is
streamed to many users.
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CIRCUIT SWITCH NETWORKS
TDM (Time Division Multiplexing)
TDM is mostly used in cases where
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Continuous data transfer between two places required
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Simultaneous audio and voice transfer is required
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A fixed bandwidth is acceptable
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Security is an issue.
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TDM
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PACKET SWITCH NETWORKS
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A packet switch is a node used to build a network which utilizes the packet
switching paradigm for data communication.
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Packet switches can operate at a number of different levels in a protocol
suite; although the exact technical details differ, fundamentally they all
perform the same function: they store and forward packets.
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Packet switching is used to optimize the use of the channel capacity available
in a network, to minimize the transmission latency and to increase robustness
of communication
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PACKET SWITCH NETWORKS
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PACKET SWITCH NETWORKS
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X.25
X.25
Historical Development of X.25
Following on from ARPA's research, packet switching network standards were
developed by the International Telecommunication Union (ITU) in the form of
X.25 and related standards. The initial ITU Standard on X.25 was approved in
March 1976. The British Post Office, Western Union International and Tymnet
collaborated to create the first international packet switched network,
referred to as the International Packet Switched Service (IPSS), in 1978. This
network grew from Europe and the US to cover Canada, Hong Kong and
Australia by 1981. By the 1990s it provided a worldwide networking
infrastructure. X.25 was also commonly available for business use. There
were also the America Online (AOL) and Prodigy dial in networks and many
bulletin board system (BBS) networks such as FidoNet.
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PACKET SWITCH NETWORKS
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X.25
X.25
Historical Development of X.25
Following on from ARPA's research, packet switching network standards were
developed by the International Telecommunication Union (ITU) in the form of
X.25 and related standards. The initial ITU Standard on X.25 was approved in
March 1976. The British Post Office, Western Union International and Tymnet
collaborated to create the first international packet switched network,
referred to as the International Packet Switched Service (IPSS), in 1978. This
network grew from Europe and the US to cover Canada, Hong Kong and
Australia by 1981. By the 1990s it provided a worldwide networking
infrastructure. X.25 was also commonly available for business use. There
were also the America Online (AOL) and Prodigy dial in networks and many
bulletin board system (BBS) networks such as FidoNet.
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PACKET SWITCH NETWORKS
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X.25
X.25
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X.25 is the grand father of frame relay protocol.
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The general concept of X.25 was to create a universal and global packetswitched network on what was then the bit-error prone analog phone system.
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Much of the X.25 system is a description of the rigorous error correction
needed to achieve this, as well as more efficient sharing of capital-intensive
physical resources.
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X.25 was developed in the era of dumb terminals connecting to host
computers.
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It was developed before the OSI Reference Model or the equivalent Network
Access Layer of the DoD protocol model, and its functionality does not map
precisely to either model.
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PACKET SWITCH NETWORKS
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Frame Relay
Frame Relay
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Network providers commonly implement frame relay for voice and data as an
encapsulation technique, used between local area networks (LANs) over a
wide area network (WAN).

Frame Relay provides flexible bandwidth over WANs and considerably costs
less than leased lines. Frame relay has its technical base in the older X.25
packet-switching technology, designed for transmitting analog data such as
voice conversations.
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Unlike X.25, whose designers expected analog signals, frame relay offers a
fast packet technology, which means that the protocol does not attempt to
correct errors.
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CIR in a Frame relay network is the average bandwidth for a virtual circuit
guaranteed by an ISP to work under normal conditions. Above the CIR, an
allowance of burstable bandwidth is often given, known as the Excess
Information Rate (EIR).
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FRAME RELAY vs X.25
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The design of X.25 aimed to provide error-free delivery over links with high
error-rates. Frame relay takes advantage of the new links with lower errorrates. The elimination of functions and fields, combined with digital links,
enables frame relay to operate at speeds 20 times greater than X.25.
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X.25 specifies processing at layers 1, 2 and 3 of the OSI model, while frame
relay operates at layers 1 and 2 only. This means that frame relay has
significantly less processing to do at each node, which improves throughput
by an order of magnitude.
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X.25 prepares and sends packets, while frame relay prepares and sends
frames. X.25 packets contain several fields used for error and flow control,
none of which frame relay needs. The frames in frame relay contain an
expanded address field that enables frame relay nodes to direct frames to
their destinations with minimal processing .
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X.25 has a fixed bandwidth available. It uses or wastes portions of its
bandwidth as the load dictates. Frame relay can dynamically allocate
bandwidth during call setup negotiation at both the physical and logical
channel level.
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FRAME RELAY vs TDM
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Frame Relay offers flexible bandwidth, when the demand for data transfer is
irregular in delays and variable in data amount.
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Frame relay has advantage cost wise and bandwidth wise if there are many
connections are to be established
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CELL RELAY SWITCH NETWORKS
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In telecommunications, cell relay refers to a method of statistically
multiplexing fixed-length packets, i.e. cells, to transport data between
computers or kinds of network equipment.
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It is an unreliable, connection-oriented packet switched data communications
protocol.
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Cell relay transmission rates usually are between 56 kbit/s and several
gigabits per second.
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ATM, a particularly popular form of cell relay, is most commonly used for
home DSL connections.
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Cell relay is used for time-sensitive traffic such as voice and video.
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CELL RELAY SWITCH NETWORKS
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ATM
ATM - Asynchronous Transfer Mode
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ATM is a cell relay, packet switching network and data link layer protocol
which encodes data traffic into small (53 bytes; 48 bytes of data and 5 bytes
of header information) fixed-sized cells.
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ATM provides data link layer services that run over Layer 1 links. This differs
from other technologies based on packet-switched networks (such as the
Internet Protocol or Ethernet), in which variable sized packets (known as
frames when referencing layer 2) are used.
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ATM is a connection-oriented technology, in which a logical connection is
established between the two endpoints before the actual data exchange
begins. ATM uses ATM specific switches(label switching).
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CELL RELAY SWITCH NETWORKS
Critique of ATM
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Expense
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Connection Setup Latency
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Cell Tax
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Specification of Service Requirements
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Lack of Efficient Broadcast
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Complexity of QoS
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Assumption of Homogenity
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ATM
ROUTING IN WAN
•Forming a WAN
•Store and forward
•Next-Hop forwarding
•Routing In a WAN
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ROUTING IN WANs
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Store and Forward
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The store operation occurs when a packet arrives: the I/O hardware inside
the packet switch places a copy of the packet in the switch’s memory and
informs the processor that a packet has arrived. (using interrupter
mechanism).
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The forward operation occurs next. The processor examines the packet,
determines over which interface it should be sent, and starts the output
hardware device to send the packet.
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The technique allows a packet switch to buffer a short burst of packets that
arrive simultaneously.
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Next-Hop Forwarding
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A packet switch must choose an outgoing path over which to forward each
packet.
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If the packet is destined for one of the computers attached directly, switch
forwards the packet to the computer.
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If the packet is destined for a computer attached to another packet switch,
the packet must be forwarded over one of the hi-speed connections that
leads to the switch.
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To make the choice, a packet switch uses the destination address stored in
the packet.
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A packet switch does not keep complete information about how to reach all
possible destinations. Instead a switch has information about the next place
(hop) to send a packet.
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Next-Hop Forwarding
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Routing in WAN
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Routing in WAN
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