Pert-10 Local Area Network

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Local Area Networks

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Introduction

Each day computer users use their computer for sending and retrieving email, scheduling meetings, sharing files, preparing reports, exchanging images, and maybe checking the current price of an auction item on the Internet.

All of this requires computers to access multiple networks and share their resources.

The multiple networks required to accomplish this are the local area network (LAN), the campus area network (CAN), the metropolitan area network (MAN), and the wide area network (WAN).

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Introduction The ease of connecting to the Internet and the dramatic

decrease in computer systems cost, have led to an explosion in their usage.

Organizations such as corporations, colleges, and government agencies have acquired large numbers of single-user computer systems.

These systems may be dedicated to word processing, scientific computation, process control, or may be general-purpose computers that perform many tasks.

This has generated a need to interconnect these locally distributed computer networks.

The network commonly used to accomplish this interconnection is called a local area network (LAN), which is a network of users that share computer resources in a limited area.

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Local Area Networks (LANs) LANs emerged in the late 1980s as the most important

means of conveying data between different computers and computer peripheral devices (printer, file server,electronic mail server, fax gateway, host gateway, computer printer, scanner, etc.)within a single office, office building, or small campus.

They were originally designed as shared media (layer 2 or datalink communications media) and are ideally suited for relatively short distance, high speed data transport and have thus become the foundation for modern electronic officesinterconnecting workstations, word processors, shared printers, file servers, email systems, web servers and so on.

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LAN topologies and standards The three most common LAN topologies are the star, ring

and bus topologies.

Figur 1. Alternative LAN topologies

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Token Ring Topology

In this topology, a token (shown as a T) is placed in the data channel and circulates around the ring, hence the name token-ring.

If a user wants to transmit, the computer waits until it has control of the token.

This technique is called token passing and is based on the IEEE 802.5 Token-Ring Network standard

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Disadvantage of the token-ring system

If an error changes the token pattern, it can cause the token to stop circulating.

A failed station can cause data traffic to cease. The token-ring path must be temporarily broken

(path interrupted) if a computer or any device connected to the network is to be removed or added to the network.

A fix to this is to attach all the computers to a central token-ring hub.

Such a device manages the passing of the token rather than relying on individual computers to pass it, which improves the reliability of the network.

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Bus topology The computers share the

media (coaxial cable) for data transmission. In this topology, a coaxial cable (called ThinNet) is looped through each networking device to facilitate data transfer.

However, in a bus system, all networking devices will see computer 1s data traffic to the printer, and the other devices must wait for pauses in transmission or until it is complete before they can initiate their own transmission.

The use of a shared coaxial cable in a bus topology prevents data transmission from being very bandwidth-efficient.

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Star topology

The most common networking topology in todays LANs.

At the center of a star network is either aswitch or a hub. This connects the network devices and facilitates the transfer of data.

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Star Topology Similar to the bus topology in that all data traffic on the

LAN is being seen by all computers. The fact that the hub broadcasts all data traffic to the

devices connected to its network ports makes these devices of limited use in large networks, but hubs are sometimes still used in small, slower-speed LANs.

To minimize unnecessary data traffic and isolate sections of the network, a switch can be used at the center of a star network.

A switch stores the hardware or physical address for each device connected to its ports.

The storage of the address enables the switch to directly connect two communicating devices without broadcasting the data to all devices connected to its ports.

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mesh topology All networking devices

are directly connected to each other.

This provides for full redundancy in the network data paths but at a cost.

This topology can be suitable for high-reliability applications but can be too costly for general networking applications.

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The Ethernet LAN The networking protocol used in most modern computer

networks is Ethernet, a CSMA/CD protocol for local area networks.

CSMA/CD stands for carrier sense multiple access with collision detection.

There is a chance that two or more computers will attempt to broadcast a message at the same time; therefore, Ethernet systems must have the capability to detect data collisions (collision detection).

The information in an Ethernet network is exchanged in a packet format.

The packet provides grouping of the information for transmission that includes the header, the data, and the trailer.

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The data structure for the Ethernet frame

How are the destination and source addresses for the data determined within a LAN?

MAC stands for media access control. The MAC address is 6 bytes, or 48 bits, in length.

The address is displayed in 12 hexadecimal digits. The first 6 digits are used to indicate the vendor of the network interface, also called the organizationally unique identifier (OUI), and the last 6 numbers form a unique value for each NIC assigned by the vendor.

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IP (Internet Protocol) Addressing IP addressing provides a solution to worldwide

addressing through incorporating a unique address that identifies the computers local network.

IP network numbers are assigned by IANA (Internet Assigned Numbers Authority).

IP addresses are classified as either IPv4 or IPv6.

The major difference between IPv4 and IPv6 is the number of IP addresses. There are just over 4 billion IPv4 addresses. In contrast, there are over 16 billion-billion IPv6 addresses.

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Basic comparison between IPv4 and IPv6

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The Classes of IPv4 Networks

The Address Range for Each Class of Network

Cat. Hal 41

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Assembling a home network Do I want to set up a wired or wireless home

network?The following are advantages of a wired network:

Faster network data transfer speeds (within the LAN). Relatively inexpensive to setup. The network is not susceptible to outside interference.

The following are disadvantages of the wired network: The cable connections typically require the use of

specialized tools. The cable installation can be labor-intensive and

expensive.

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Assembling a home network Cont.

The advantages of a wireless network are many including the following:

User mobility Simple installations No cables

Disadvantages of a wireless network can include :

Security issues. The data transfer speed within the LAN can

be slower than wired networks.

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Wireless (Wi Fi)The most common wireless standards include :

802.11a (Wireless-A)This standard can provide data transfer rates up to 54 Mbps and an operating range up to 75 feet. It operates at 5GHz.

802.11b (Wireless-B)This standard can provide data transfer rates up to 11 Mbps with ranges of 100 to 150 feet. It operates at 2.4 GHz.

802.11g (Wireless-G)This standard can provide data transfer rates up to 54 Mbps up to 150 feet. It operates at 2.4 GHz.

802.11n (Wireless-N)This is the next generation of high-speed wireless connectivity promising data transfer rates up to 4 802.11g speeds (200+Mbps). It operates at 2.4 GHz.

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An example of a (a) wired and (b) wireless WiFi home network

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The components of a home network can include the following: HubThis is used to interconnect networking devices. SwitchThis is the best choice for interconnecting

networking devices. Network AdapterWired and wireless network

adapters are available. The type of network adapter used in desktop computers is called the Network Interface Card (NIC).

RouterA networking device used to connect two or more networks (for example, your LAN and the Internet) using a single connection to your ISP.

Access PointUsed to interconnect wireless devices and provide a connection to the wired LAN.

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The components of a home network can include the following: Wireless routerThis device uses RF to connect to the

networking devices. A wireless router typically contains a router, switch, and a wireless access point and is probably the most common way to interconnect wireless LANs to the ISPs access device.

Broadband Modem/GatewayThis describes the device used to provide high-speed data access via your cable connection or via a telephone companys DSL connection.

Cable ModemThis device is used to make a broadband network connection from your home network to the ISP using your cable connection.

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Several issues should be considered when planning for a home network, including the following:

Data speedThis will be determined by whether you chose to implement a wired or wireless home network.

CostImplementing a high-speed wired network can be quite expensive.

Ease of implementationA wireless home network is probably the easiest to implement if the cabling and connectors for a wired network are not already installed.

Appearance

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Reference :

Jeffrey S. Beasley, Networking, Second Edition, Prentice Hall, 2008.

Local Area NetworksIntroductionIntroductionLocal Area Networks (LANs)LAN topologies and standardsToken Ring TopologyDisadvantage of the token-ring systemBus topologyStar topologyStar Topologymesh topologyThe Ethernet LANSlide Number 13Slide Number 14IP (Internet Protocol) AddressingBasic comparison between IPv4 and IPv6The Classes of IPv4 NetworksAssembling a home networkAssembling a home network Cont.Wireless (Wi Fi)Slide Number 21The components of a home network can include the following:The components of a home network can include the following:Several issues should be considered when planning for a home network, including the following:Reference :