What is a Wide Area Network? Brief History Difference between LANs and WANs Packet Switches in WAN...

•What is a Wide Area Network?•Brief History•Difference between LANs and WANs•Packet Switches in WAN•Forming WANs

WIDE AREA NETWORKS – WAN

WHAT IS A WAN ?

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.

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.

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.

The most popular example of WAN is the internet.

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.


SWITCHES IN WANsThe 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.

•Circuit Switch Networks PSTN, ISDN, TDM•Packet Swicth Networks X.25, Frame Relay•Cell Relay Switch Networks ATM


CIRCUIT SWITCH NETWORKS 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.

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.

Circuit switches are combined through trunks

Bandwidth allocation is not flexible

Multiplexing techniques used in data transfers over circuit switches increases the cost


CIRCUIT SWITCH NETWORKS


CIRCUIT SWITCH NETWORKSPSTNPSTN (Public Switched Telephone

Network)

PSTN is the conventional telephone network and it is pretty much digitalized today.

Today data transfer over PSTN is only used for dial-up modems.

PSTN can only provide a maximum of 64 Kbps data transfer rate.

In case of more bandwidth necessity ISDN is preferred over PSTN.

It is sometimes referred to as the Plain Old Telephone Service (POTS).


CIRCUIT SWITCH NETWORKSISDNISDN (Integrated Services Digital

Network)

ISDN provides digitized voice and data to subscribers over conventional loop wiring (PSTN).

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)

PRI is formed of thirty 64Kbps lines which provide 1920Kbps bandwidth for subscribers. (Industrial solution)


CIRCUIT SWITCH NETWORKSTDMTDM (Time Division Multiplexing)

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.


CIRCUIT SWITCH NETWORKSTDMTDM (Time Division Multiplexing)

TDM is mostly used in cases where

Continuous data transfer between two places required

Simultaneous audio and voice transfer is required

A fixed bandwidth is acceptable

Security is an issue.


PACKET SWITCH NETWORKS A packet switch is a node used to build a network which utilizes the

packet switching paradigm for data communication.

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.

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


PACKET SWITCH NETWORKS


PACKET SWITCH NETWORKSX.25X.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.


PACKET SWITCH NETWORKSX.25X.25

X.25 is the grand father of frame relay protocol.

The general concept of X.25 was to create a universal and global packet-switched network on what was then the bit-error prone analog phone system.

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.

X.25 was developed in the era of dumb terminals connecting to host computers.

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.


PACKET SWITCH NETWORKS Frame RelayFrame Relay

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.

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.

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).


FRAME RELAY vs X.25 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 error-rates. The elimination of functions and fields, combined with digital links, enables frame relay to operate at speeds 20 times greater than X.25.

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.

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 .

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.


FRAME RELAY vs TDM Frame Relay offers flexible bandwidth, when the demand for data

transfer is irregular in delays and variable in data amount.

Frame relay has advantage cost wise and bandwidth wise if there are many connections are to be established


CELL RELAY SWITCH NETWORKS 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.

It is an unreliable, connection-oriented packet switched data communications protocol.

Cell relay transmission rates usually are between 56 kbit/s and several gigabits per second.

ATM, a particularly popular form of cell relay, is most commonly used for home DSL connections.

Cell relay is used for time-sensitive traffic such as voice and video.


CELL RELAY SWITCH NETWORKSATMATM - Asynchronous Transfer Mode 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.

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.

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).


CELL RELAY SWITCH NETWORKSATMCritique of ATM Expense

Connection Setup Latency

Cell Tax

Specification of Service Requirements

Lack of Efficient Broadcast

Complexity of QoS

Assumption of Homogenity

•Forming a WAN•Store and forward•Next-Hop forwarding•Routing In a WAN


ROUTING IN WANs


Store and Forward 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).

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.

The technique allows a packet switch to buffer a short burst of packets that arrive simultaneously.


Next-Hop Forwarding A packet switch must choose an outgoing path over which to forward

each packet.

If the packet is destined for one of the computers attached directly, switch forwards the packet to the computer.

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.

To make the choice, a packet switch uses the destination address stored in the packet.

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.


Next-Hop Forwarding


Routing in WAN

What is a Wide Area Network? Brief History Difference between LANs and WANs Packet Switches in WAN...

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