DATA COMMUNICATIONS NETWORKS

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The word data refers to information presented in whatever f i d b th ti ti d i thform is agreed upon by the parties creating and using the data.Data communication is the exchange of data between twoData communication is the exchange of data between two devices via some form of transmission medium such as a wire cable, fiber optic or radio waves.

The effectiveness of a data communication system depends on three fundamental characteristics :

1. Delivery. The system must deliver data to the correct destination.

2 A Th t t d li th d t t l2. Accuracy. The system must deliver the data accurately.

3. Timeliness. The system must deliver the data in a timely manner

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manner.

A data communication system has five components :y p

Step 1 :Step 2 :

Step 1 :Step 2 :

Step 3 :………

Step 3 :………

P t l

Message

Protocol Protocol

Sender Receiver

Medium

Sender Receiver

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1 M Th i th i f ti (d t ) t1. Message. The message is the information (data) to be communicated (ex. Text, number, picture, sound or video).)

2. Sender. The sender is the device that sends the data message.

3. Receiver. The receiver is the device that receives the message.

4. Medium. The transmission medium is the physical path by which the message travels from sender to receiverreceiver.

5. Protocol. Protocol is a set of rules that governs data communication

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communication

Direction of Data FlowDirection of Data FlowIn telecommunications systems the transmission of information may be unidirectional or bidirectionalinformation may be unidirectional or bidirectional.

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NETWORKSNetwork is a set of devices (often referred to as nodes) ( )connected by communication links.

Most networks use distributed processing, in which a task is divided among multiple users.

A Network must be able to meet a certain number of it i Th t i t f thcriteria. The most importance of these are :

Performance : it depends on a number of factors such as the number of users the type of transmissionsuch as the number of users, the type of transmission medium, the capabilities of connected hardware and the efficiency of the software.

Reliability : it is measured by the frequency of failure.

4/1/2012 6Security : Protecting data from unauthorized access.

Physical Structure

Type of Connection

Point to point connectionPoint to point connectionWorkstation Workstation

W k t tiMainframe

4/1/2012 7Multipoint connectionWorkstationMainframe

Physical Topology

Topology

Mesh Star Bush Ringg

Mesh

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Star Topology

HubHub

Bush Topology

Cable end

Cable end

Tap Tap Tap TapDropLine

DropLine

DropLine

DropLine

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Ring Topology

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Categories of NetworksCategories of Networks

Network

Local Area Network(LAN)

Metropolitan Area Network(MAN)

Wide Area Network(WAN)

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A Local Area Network (LAN) is usually privately owned and links the devices in a single office, building, or campus.

LANs are designed to allow resources to be shared between personal computers or workstations. The resources to be shared can include hardware, software, and data.

Traditionally, LANs data rate 4 – 16 Mbps. Today, speeds are increasing and can reach 100 Mbps.

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A Metropolitan Area Network (MAN) is designed to extend over an entire city, it may be a single network (ex: cable television) or connecting a number of LANs into a larger network so that resources may be shared LAN-to-LAN as ywell as device-to-device.

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A Wid A N t k (WAN) id l di tA Wide Area Network (WAN) provides long-distance transmission of data, voice, image and video information over large geographic areas that may comprise a country, a g g g p y p ycontinent, or even the world.

When two or more networks are connected, they become , yinternetwork, or internet.

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THE INTERNETThe Internet has revolutionized many aspect of our daily lives.

The Internet is a communication system that has brought a wealth of information to our fingertips and organized it for our usefor our use.

A Brief HistoryA t k i f t d i ti d iA network is a group of connected communicating devices such as computers and printers.

An internet is two or more networks that can communicateAn internet is two or more networks that can communicate with each other. The most notable internet is the Internet, a collaboration of hundreds of thousands interconnected network

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network.

In the mid-1960s, the Advanced Research Project Agency (ARPA) i th d t t f D f (DOD) i t t d i(ARPA) in the department of Defense (DOD) was interested in finding a way to connect computers so that the researchers they founded could share their finding, thereby reducing cost and eliminating duplicate efforteliminating duplicate effort.

In 1967, ARPA presented its idea for ARPANET (a small network of connected computers) at an Association for Computing Machinery (ACM) meeting.

In 1969, ARPANET was a reality. Four nodes (UCLA, ACSB, Utah Univ. and SRI) were connected via interface message processor ) g p(IMP) to form a network and the software called Network Control Protocol (NCP) provided communication between the host.

In 1972 Vint Cerf and Bob Kahn both of whom were part of theIn 1972, Vint Cerf and Bob Kahn, both of whom were part of the core ARPANET group, collaborated on what they called the Internetting Project. This produced Transmission Control Protocol (TCP) include concepts such as encapsulation, the datagram and

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( ) p p , gthe function of gateway.

Shortly thereafter, the TCP was split into two protocols: Transmission Control Protocol (TCP) and Internetworking Protocol (IP). The IP would handle datagram routing while the TCP would be responsible for g ghigher level function such as segmentation, reassembly, and error detection.

Th i t t ki t l b k TCP/IPThe internetworking protocol became known as TCP/IP.

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Fi ARPANET A hit t D b 19694/1/2012 18

Figure. ARPANET Architecture, December 1969

4/1/2012 19Figure. ARPANET Architecture, July 1976

From ARPANET to NSFNETBy 1985, the ARPANET was heavily utilized and burdened with congestion. In response, the National Science Foundation initiated phase 1 development of theScience Foundation initiated phase 1 development of the NSFNET.In its earliest form, in 1986, the NSFNET created a more distributed, three-tiered network architecture. This architecture connected campuses and research organizations to regional networks which in turnorganizations to regional networks, which in turn connected to a main backbone network linking six nationally funded supercomputer centers.By 1991, data traffic had increased tremendously, which necessitated upgrading the NSFNET's backbone network service to T3 (45 Mbps) links.

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( p )

From ARPANET to NSFNETAs late as the early 1990s the NSFNET was still reserved forAs late as the early 1990s, the NSFNET was still reserved for research and education applications, and government agency backbones were reserved for mission-oriented purposes.Commercial and general-purpose interests were clamor ring for g p p gnetwork access, and Internet service providers (ISPs) were emerging to accommodate those interests, defining an entirely new industry in the process.In the United States go ernment agenc net orks interconnected atIn the United States, government agency networks interconnected at Federal Internet eXchange (FIX) points on both the east and west coasts.Commercial network organizations had formed the CommercialCommercial network organizations had formed the Commercial Internet eXchange (CIX) association, which built an interconnect point on the west coast. At the same time, 13 ISPs around the world, particularly in Europe and Asia, had developed substantial i f t t d ti itinfrastructures and connectivity.the NSFNET to be the International Connections Manager (ICM), responsible for providing connectivity between the U.S., European, and Asian networks NSFNET was decommissioned in April 1995

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and Asian networks. NSFNET was decommissioned in April 1995.

The Internet TodayyThe Internet today is not a simple hierarchical structure. It is made up of many wide and local area networks p yjoined by connecting devices and switching station.

Today's Internet infrastructure is a move from a core network (NSFNET) to a more distributed architecture operated by commercial providers such as UUNET, Qwest, Sprint, and thousands of others, connected via Q est, Sp t, a d t ousa ds o ot e s, co ected amajor network exchange points, as well as direct network interconnections.

The Internet today is run by private companies, not the government.

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4/1/2012 23The General Structure of Today's Internet

The contemporary backbone of the Internet is a p ycollection of service providers that have connection points called POPs (points of presence) over multiple regions. POP is p ) p gcommonly referred to as national providersTo enable customers of one provider to reach customers connected to another provider trafficcustomers connected to another provider, traffic is exchanged at public Network Access Points (NAPs) or via direct interconnections.Th NSP (N k S i P id )The term NSP (Network Service Provider) was traditionally used to refer to backbone network providers.

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p

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