Local Area NetworksLocal Area Networks

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IntroductionIntroduction

• Each day computer users use their computer for y p psending and retrieving email, scheduling meetings, sharing files, preparing reports, exchanging images, and maybe checking the g g g , y gcurrent price of an auction item on the Internet.

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

• The multiple networks required to accomplish this are the local area network (LAN), the

k (CAN) h licampus 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 usageexplosion in their usage.

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

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

• The network commonly used to accomplish thisThe 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 d t i h l d i ( i t filand 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 ideally2 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 offices’—interconnectingmodern electronic offices interconnecting workstations, word processors, shared printers, file servers, email systems, web servers and so on.

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LAN topologies and standardsLAN topologies and standards• The three most common LAN topologies are the star, ring p g , g

and bus topologies.

5/20/2015 5Figur 1. Alternative LAN topologies

Token Ring Topology

• In this topology, a “token” ( h T) i l d i th(shown as a T) is placed in the data channel and circulates around the ring, hence the gname token-ring.

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

• This technique is called token i d i b d thpassing 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(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• 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 g p grather than relying on individual computers to pass it, which improves the reliability of the network.

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network.

Bus topologyBus topology• The computers share the

media (coaxial cable) formedia (coaxial cable) for data transmission. In this topology, a coaxial cable ( ll d Thi N t) i l d(called ThinNet) is looped through each networking device to facilitate data transfer.

• However, in a bus system, all networking devices will see computer 1’s data traffic to the printer and the other devicescomputer 1’s 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.

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

Star topologyStar topology

• The most commonThe most common networking topology in today’s LANs.

• At the center of a star network is either aswitch or a hub. This connects the network devices and facilitatesdevices 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• 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 LANssometimes 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 net orkcenter 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

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gports.

mesh topologymesh topology• All networking devices

are directly connected to each other.

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

• This topology can beThis topology can be suitable for high-reliability applications but can be too costly for generaltoo 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• 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)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?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 organizationallynetwork 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 computer’s localaddress that identifies the computer s local network.

• IP network numbers are assigned by IANAIP 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 overthe 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 IPv6Basic comparison between IPv4 and IPv6

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The Classes of IPv4 NetworksThe Classes of IPv4 Networks

The Address Range for Each Class of Network

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

network?”Th f ll i d t f i d t kThe following are advantages of a wired network:

• Faster network data transfer speeds (within the LAN).• Relatively inexpensive to setup• 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 The cable connections typically require the use of

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

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expensive.

Assembling a home network Cont.

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

• User mobility• Simple installationsSimple installations• No cables

Di d t f i l t k i l dDisadvantages 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 data802.11a (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 (Wi l B) Thi t d d id d t• 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 GHzat 2.4 GHz.

• 802.11n (Wireless-N)—This is the next generation of high-speed wireless connectivity promising data transfer

t t 4 × 802 11 d (200+Mb ) It t5/20/2015 20

rates up to 4 × 802.11g speeds (200+Mbps). It operates at 2.4 GHz.

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

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

The components of a home network can include the following:the following:• Hub—This is used to interconnect networking devices.

S it h Thi i th b t h i f i t ti• Switch—This is the best choice for interconnecting networking devices.

• Network Adapter—Wired and wireless networkNetwork Adapter Wired and wireless network adapters are available. The type of network adapter used in desktop computers is called the Network Interface Card (NIC)Interface Card (NIC).

• Router—A networking device used to connect two or more networks (for example, your LAN and the Internet) ( p , y )using a single connection to your ISP.

• Access Point—Used to interconnect wireless devices and provide a connection to the wired LAN

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and provide a connection to the wired LAN.

The components of a home network can include th f ll ithe following:• Wireless router—This device uses RF to connect to the

networking devices. A wireless router typically contains a g yp yrouter, switch, and a wireless access point and is probably the most common way to interconnect wireless LANs to the ISP’s access device.

• Broadband Modem/Gateway—This describes the device used to provide high-speed data access via your cable connection or via a telephone company’s DSLcable connection or via a telephone company s DSL connection.

• Cable Modem—This device is used to make a broadband network connection from your home networkbroadband network connection from your home network to the ISP using your cable connection.

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Several issues should be considered when planning f h t k i l di th f ll ifor a home network, including the following:

• Data speed—This will be determined by whether you p y ychose to implement a wired or wireless home network.

• Cost—Implementing a high-speed wired network can be it iquite expensive.

• Ease of implementation—A wireless home network is probably the easiest to implement if the cabling andprobably the easiest to implement if the cabling and connectors for a wired network are not already installed.

• Appearance

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Reference :Reference :

• Jeffrey S Beasley “Networking”Jeffrey S. Beasley, Networking , Second Edition, Prentice Hall, 2008.

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