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Introduction

A network is a group of computers and other devices, such asprinters and modems, connected to each other. This enables thecomputers to effectively share data and resources.

The concept of sharing resources over a network is callednetworking. The computers in a network can share data, messages,graphics, printers, fax machines, modems, and other hardware andsoftware resources.

Network elements

  Servers

Servers are the computers that provide the shared resources tonetwork users. There is usually only one server in a small network,but bigger networks may have more than one server.

  Clients

Clients are the computers that can access the shared networkresources provided by a server.

  Media

The computers in a network are connected to each other byhardware components, such as cables. These components are calledthe media.

  Shared data

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  File Server May Fail

Although a file server is no more susceptible to failure than any

other computer, when the files server "goes down," the entirenetwork may come to a halt. When this happens, the entire hospitalmay lose access to necessary programs and files.

  Virus Infections

If any computer system in a network gets affected by computervirus , there is a possible threat of other systems getting affected

too. Viruses get spread on a network easily because of theinterconnectivity of workstations. Such spread can be dangerous if the computers have important database which can get corrupted bythe virus.

To overcome Network Disadvantages

  Security issues and Virus Infections issues

The increase in businesses connecting their systems and using theInternet has its drawbacks. When all computers are networked, oneuser's problems may affect everyone. You should consider thegreater potential for data loss, security breaches and viruses whencreating a network.

It is important to ensure data security through regular backing upthe files, password routines, and system logs. It is important toremove access from employees who leave, otherwise they may stillbe able to access customer records.

As your data will be stored in one location on the server, physicalsecurity is very important. You should improve the quality of your

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system security to protect your business from potential virusattacks and hacking. This should include anti virus software and afirewall or software barrier.

If your staffs need to access the network while off-site, consider avirtual private network. This creates a secure link and protectsinformation sent and received.

  File Server Fail down issues

For this we can have backup fail server. When the files server "goesdown," then we can use the backup fail server. Having backup

server we can overcome this problem.

Benefits of the computer Network

In most organizations, a network offers benefits, such as datasharing and online communication that are not provided by a stand-

alone environment (An environment in which there is severalcomputers that are not connected to each other is called a stand-alone environment.). In this topic, you will identify the benefits of anetwork.

  Data sharing

The data can be easily sharable in a network so other user can

access it at any time. For example, a user working in a team wantsto share some data with the other team members. In a stand-aloneenvironment, to share the data you can verbally exchanginginformation or writing memos or putting the data on a floppy andcopying it to the machines of other members. If it network the datacan be easily made sharable in a network so that the other teammembers can access.

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A centralized data storage system enables multiple users to accessdata in different locations.

  Resource sharing

Resource sharing is also an important benefit of a computernetwork. For example, if there are four people in a family, eachhaving their own computer, they will require four modems (for theInternet connection) and four printers, if they want to use theresources at the same time. A computer network, on the otherhand, provides a cheaper alternative by the provision of resourcesharing.

In this way, all the four computers can be interconnected, using anetwork, and just one modem and printer can efficiently provide theservices to all four members. The facility of shared folders can alsobe availed by family members.

  Centralized Software Management

One of the greatest benefits of installing a network is the fact thatall of the software can be loaded on one computer (the file server).This eliminates that need to spend time and energy installingupdates and tracking files on independent computers throughoutthe building.

  Communication medium

A computer network can provide a powerful communication mediumamong people spread widely at different physical locations. It actsas a powerful communication medium when it comes to sharinginformation and resources.

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  Data Security and Management

In a business environment, a network allows the administrators tomuch better manage the company's critical data. Instead of havingthis data spread over dozens or even hundreds of small computers

in a haphazard fashion as their users create it, data can becentralized on shared servers. This makes it easy for everyone tofind the data, makes it possible for the administrators to ensure thatthe data is regularly backed up, and also allows for theimplementation of security measures to control who can read orchange various pieces of critical information.

 Speed

Sharing and transferring files within Networks are very fast.Networks provide a very rapid method for sharing and transferringfiles. The sharing of data with the other users in a stand-aloneenvironment requires physical transfer of data. This can be done bycopying the data on a floppy disk or taking a printout. This requiresmore time and is inconvenient as compared to sharing the data overa network.

Peer-to-Peer Networks

In a peer-to-peer network, there are no dedicated servers, andthere is no hierarchy among the computers. All the computers areequal and therefore are known as peers. Each computer functionsas both a client and a server.

And there is no administrator responsible for the entire network.The user at each computer determines what data on that computer

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is shared on the network. Below figure shows a peer-to-peernetwork in which each computer functions as both a client and aserver.

Computers in a peer-to-peer network are called peers. In a peer-to-peer network, all computers are considered equal; they all have thesame abilities to use the resources available on the network. Eachcomputer can function both as a client and a server. Computers arenot dedicated to function as servers. They use the network to shareresources among the independent peers. The computer whoseapplications are required by the other networked computersfunctions as a server. The other computers function as clients.Therefore, a dedicated administrator is not assigned for networkmanagement.

A peer-to-peer network is a small group of people using a network.Peer-to-peer networks members usually perform similar tasks,which necessitates the sharing of resources. The peer-to-peernetworks support 10 computers. The users in a peer-to-peernetwork are located in the same geographical area. Operatingsystems, such as Microsoft Windows 98 or Microsoft Windows XP,

can be used to set up a peer-to-peer network. Additional software isnot required because peer-to-peer networking is built into thesystems.

Another important point of peer-to-peer networks is that the usersof each computer plan and control the security of their resources.The users determine the resources on their computers, which can

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be shared on the network. The shared network resources, such asdisk space, printers or faxes, can be used by anyone who hasaccess to the network. This is possible only if the shared networkresources are not password protected. Peer-to-peer networks have

weak and intrusive security because a central server is not used toadminister and secure the network. In addition, some users maynot implement security.

A peer-to-peer network does not support a central login process.This implies that a user who logs on to one peer can access anyshared network resource, which is not controlled by a specificpassword. Peer-to-peer networks are relatively simple. Becauseeach computer functions as a client and a server, there is no needfor a powerful central server or for the other components required

for a high-capacity network. Peer-to-peer networks can be lessexpensive than server-based networks.

Peer-to-peer networks are simple and inexpensive to install andmaintain. The cost of implementing peer-to-peer networks is lowbecause a central server is not used to administer the network. Inaddition, the components for a high-capacity network are notrequired in a peer-to-peer network.

In a peer-to-peer network, the users handle administration. Thismeans that all the users need to be trained in how to share files,folders, and printers. In a peer-to-peer network, suddenly shuttingdown your computer can cause one of your colleagues to be unableto print.

Peer-to-peer networks are appropriate for environments where allthe users are located in the same geographical area and thenetwork security is not an important factor. In addition, thesenetworks are useful when the network expansion is limited.

Advantages of a peer-to-peer network:

  Less initial expense - No need for a dedicated server.

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  Setup - An operating system (such as Windows XP) already inplace may only need to be reconfigured for peer-to-peeroperations.

Disadvantages of a peer-to-peer network:

Server Based Networks

A dedicated server is one that functions only as a server and is notused as a client or workstation. Server based networks (see belowFigure) have become the standard models for networking.

In a server-based network, clients rely on the services that theserver provides, such as file storing and printing. Client computersare generally less powerful than server computers.

A server-based network using network operating system is that thenetworks are organized into domains. A domain is a collection of networks and clients that share security information. Domainsecurity and logon permissions are controlled by special serverscalled domain controllers. Users cannot access the resources of 

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servers in a domain until a domain controller has authenticatedthem.

In server-based networks, a network administrator centrallymanages the resource security. The administrator defines andmanages user access to network resources.

Another beneficial of server-based networks is central file storage.Server-based networks provide easy backup of critical data. Databackup is another useful characteristic of server based networks.

Server based networks can support a larger number of users thanpeer-to-peer networks. To support a large number of users, server-based networks use monitoring and network management tools.

Servers must perform varied and complex tasks. (See below figure)

Security is often the primary reason for choosing a server-based

approach to networking. In a server-based environment, oneadministrator who sets the policy and applies it to every user on thenetwork can manage security. (see below figure)

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Advantages of a client/server network

  Centralized - Resources and data security are controlledthrough the server.

  Security - More security then Peer-to-peer network.  Flexibility - New technology can be easily integrated into

system.  Interoperability - All components (client /server) worktogether.  Accessibility - Server can be accessed remotely and across

multiple platforms.

Disadvantages of a client/server network

  Expense - Requires initial investment in dedicated server.

  Maintenance - Large networks will require a staff to ensureefficient operation.

  Dependence - When server goes down, operations will ceaseacross the network.

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Wired Local Area Network (LAN)

It is the simplest type of network in which computers are connectedto each other by cables.

Each of the computers on the LAN is also called a node . 

A LAN is characterized by three primary attributes:

  Topology

The topology is the pattern used to connect the computers together.With a bus topology, a network cable connects each computer tothe next one, forming a chain. With a star topology, each of thecomputers is connected to a central nexus called a hub/Switch. Aring topology is essentially a bus network with the two ends joinedtogether. (You will see more about network topologies in Chapter 6)

  Medium

Four basic types of media are used in local-area networks; coaxialcable, twisted-pair wires, fiber-optic cable, And wireless.

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Each medium has its advantages and disadvantages relative to cost,speed, and expandability. Coaxial cables provide high speed and lowerror rates. Twisted-pair wires are cheaper than coaxial cables, cansustain the speeds common to most personal computers, and are

easy to install. Fiber-optic cable is the medium of choice for high-speed local-area networks. Wireless local-area networks have theadvantage of expandability. (You will see more about networkmedium in Chapter 5.2)

  Protocols

The topology and the medium used on a particular network are

specified by the protocol. (You will see more about protocolin Chapter 8).

LAN computer networks that usually cover a limited range, say,within the boundary of a building. A LAN computer network is two ormore computers that communicate with each other through somemedium.

The primary usage of local-area networks (LANs) is the sharing of hardware, software, or information, such as data files, multimediafiles, or electronic mail. Resource sharing provided by local-areanetworks improves efficiency and reduces overhead.

There are a number of ways in which nodes can communicate overa network. The simplest is to establish a dedicated link between thetransmitting and receiving stations. This technique is known ascircuit switching. A better way of communicating is to use atechnique known as packet switching, in which a dedicated path isnot reserved between the source and the destination. Data arewrapped up in a packet and launched into the network. In this way,a node only has exclusive access to the medium while it is sending apacket. During its inactive period, other nodes can transmit. Atypical packet is divided into preamble, address, control, data, anderror-check fields.

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The computers in a LAN are connected by using cables. This methodcannot be used to connect computers that are in different locations,for example, in buildings across a town or city. Therefore, a LAN isnot suitable for large businesses with offices in several locations.

Ethernet

Network architecture combines standards, topologies and protocolsto produce a working network. Currently, the most popular networkarchitecture is Ethernet. A network that follows the Ethernetarchitecture standard is known as an Ethernet network.

The first Ethernet network was introduced in 1975 by RobertMetcalfe and David Boffs at Xerox Palo Alto Research Center . Thisnetwork was designed as a 2.94 Mbps system that could connectover 100 computers on a one kilometer cable. Xerox, Intel andDigital extended the original specification to 10 Mbps. This designformed the basis for the IEEE 802.3 specification defined by theIEEE 802 committee. The IEEE 802.3 specification defines Ethernetstandards including cabling and topology alternatives.

The term Ethernet refers to the family of local-area network (LAN)

products covered by the IEEE 802.3 standard that defines what iscommonly known as the CSMA/CD protocol. This is a system whereeach computer listens to the cable before sending anything throughthe network. If the network is clear, the computer will transmit. If some other node is already transmitting on the cable, the computerwill wait and try again when the line is clear. Sometimes, twocomputers attempt to transmit at the same instant. When thishappens a collision occurs. Each computer then backs off and waitsa random amount of time before attempting to retransmit. With this

access method, it is normal to have collisions. However, the delaycaused by collisions and retransmitting is very small and does notnormally affect the speed of transmission on the network. It is oneof the most widely implemented LAN standards.

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Three data rates are currently defined for operation over opticalfiber and twisted-pair cables:

  10 Mbps-10Base-T Ethernet

  100 Mbps-Fast Ethernet

  1000 Mbps-Gigabit Ethernet

10Base-T Ethernet

10Base-T provides Manchester-encoded 10-Mbps bit-serialcommunication over two unshielded twisted-pair cables. Although

the standard was designed to support transmission over commontelephone cable, the more typical link configuration is to use twopair of a four-pair Category 3 or 5 cable, terminated at each NICwith an 8-pin RJ-45 connector (the MDI), as shown in below Figure.Because each active pair is configured as a simplex link wheretransmission is in one direction only, the 10Base-T physical layerscan support either half-duplex or full-duplex operation.

Each 10Base5 cable segment can have a maximum of 100computers. The maximum permissible distance between a computerand a transceiver is 50 meters (164 feet). The maximum total

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length of joined segments in a 10Base5 network is 2,500 meters(8,200 feet).

Fast Ethernet

To allow for an increased speed of transmission, the Ethernetprotocol has developed a new standard that supports 100 Mbps.This is commonly called Fast Ethernet.

Fast Ethernet requires the use of different, more expensive networkconcentrators/hubs and network interface cards. In addition,category 5 twisted pair or fiber optic cable is necessary.

Fast Ethernet uses the CSMA/CD access method. As 10BaseT, FastEthernet also supports star and bus topology.

Gigabit Ethernet

The most recent development in the Ethernet standard is a protocolthat has a transmission speed of 1 Gbps. Gigabit Ethernet isprimarily used for backbones on a network at this time. In thefuture, it will probably be used for workstation and serverconnections also. It can be used with both fiber optic cabling andcopper.

10-Gigabit Ethernet is under development and will likely bepublished as the IEEE 802.3ae supplement

Ethernet has survived as the major LAN technology (it is currentlyused for approximately 85 percent of the world's LAN-connected PCsand workstations) because its protocol has the followingcharacteristics:

o  Is easy to understand, implement, manage, and maintaino  Allows low-cost network implementations

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o  Provides extensive topological flexibility for networkinstallation

o  Guarantees successful interconnection and operation of standards-compliant products, regardless of 

manufacturer

Ethernet LANs consist of network nodes and interconnecting media.The network nodes fall into two major classes:

  Data terminal equipment (DTE)

o  Devices that are either the source or the destination of data frames. DTEs are typically devices such as PCs,

workstations, file servers, or print servers that, as agroup, are all often referred to as end stations.

  Data communication equipment (DCE)

o  Intermediate network devices that receive and forwardframes across the network. DCEs may be eitherstandalone devices such as repeaters, network switches,and routers, or communications interface units such asinterface cards and modems.

The current Ethernet media options include two general types of copper cable: unshielded twisted-pair (UTP) and shielded twisted-pair (STP), plus several types of optical fiber cable.

Traditionally, Ethernet uses the linear bus topology for datatransmission. Some Ethernet networks also use the star bustopology.

Bus Topology

In a bus topology, all devices on the network connect to one maincable (trunk cable). It is easy to install and configure, andinexpensive. Amplification or regeneration does not require specialequipment. If a device wants to send information must firstdetermine if the bus is being used by any other device. If no other

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device is attempting to transmit, the device sends the data. If thetrunk cable fails, all devices are affected. (You can see more aboutBus topology in Chapter 6)

Star Topology

In a star topology, each device is connected by separate cable to acentral device (hub or switch). If a cable fails it affects only the onedevice connected to the failed cable unlike the bus.

Star networks are easily expanded, easier to troubleshoot andsupport many types of cables. Passive or active hub or switch isused to connect more than two devices together in a star topology.(You can see more about Star topology in Chapter 6)

Ethernet networks can use thinnet coaxial, thicknet coaxial orunshielded twisted pair (UTP) cables. Ethernet uses basebandtransmission to transmit encoded signals over a cable.

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Ethernet is popular in the scientific and academic communitiesbecause it supports multiple protocols. Examples of the protocolssupported by Ethernet are:

o  TCP/IPo  IPXo  NetBEUIo  DLC

Ethernet breaks data down into frames. A frame is a package of information transmitted as a single unit. The length of an Ethernetframe can be between 64 and 1,518 bytes, but the Ethernet frameitself uses at least 18 bytes for control information. Therefore, thedata in an Ethernet frame can be between 46 and 1,500 bytes.

Every Ethernet frame contains control information and follows the

same basic organization. For example, the Ethernet frame used forTCP/IP contains preamble, detonation, type, CRC in addition to thedata.

o  Preamble - Makes the start of the frame o  Detonation - Specify the origin and destination addresses. o  Type - Identifies the network layer Protocol  o  CRC - Is the error checking field that determines if the

frame arrived without being corrupted. 

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Ethernet performance can be improved by dividing a crowdedsegment into two less-populated segments that are joined with abridge or a router. This reduces traffic on each segment. Since thereare fewer computers attempting to transmit on the segment, accesstime improves.

Ethernet is the most popular network architecture in use today andcan be used with most network operating systems.

o  Ethernet Featureso  Topology: Bus or Staro  Signal type: Basebando  Protocol: TCP/IP, NetBEUL, DLC

o  Access method: IEEE 802.3o  Transfer speed : 10 Mbps, 100 Mbps, 1000 Mbpso  Cable type: Thicknet, Thinnet, UTPo  Data packet format: Ethernet Frameso  Operating Systems: Can be used with most Network

operating systems

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Token Ring

The Token Ring protocol was developed by IBM in the mid-1980s.

The related IEEE 802.5 specification is almost identical to andcompletely compatible with IBM's Token Ring network. In fact, theIEEE 802.5 specification was modeled after IBM Token Ring, and itcontinues to shadow IBM's Token Ring development. Theterm Token Ringgenerally is used to refer to both IBM's Token Ringnetwork and IEEE 802.5 networks.

Token Ring and IEEE 802.5 networks are basically compatible,although the specifications differ in minor ways. IBM's Token Ring

network specifies a star, with all end stations attached to a devicecalled a multistation access unit (MSAU). In contrast, IEEE 802.5does not specify a topology, although virtually all IEEE 802.5implementations are based on a star. Other differences exist,including media type (IEEE 802.5 does not specify a media type,although IBM Token Ring networks use twisted-pair wire) androuting information field size. Below figure summarizes IBM TokenRing network and IEEE 802.5 specifications.

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Token Ring Operation

  The token moves between the computers inside a logical ring.

The actual physical cable ring is through the hub. Users are apart of the ring, but they connect to the ring through the hub.

  Token Ring and IEEE 802.5 are two principal examples of token-passing networks (FDDI is the other). Token-passingnetworks move a small frame, called a token, around thenetwork. Possession of the token grants the right to transmit.

If a node receiving the token has no information to send, itpasses the token to the next end station. Each station can holdthe token for a maximum period of time.

  If a station possessing the token does have information totransmit, it seizes the token, alters 1 bit of the token (whichturns the token into a start-of-frame sequence), appends theinformation that it wants to transmit, and sends thisinformation to the next station on the ring. While theinformation frame is circling the ring, no token is on the

network (unless the ring supports early token release), whichmeans that other stations wanting to transmit must wait.Therefore, collisions cannot occur in Token Ring networks. If early token release is supported, a new token can be releasedwhen frame transmission is complete.

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  The information frame circulates the ring until it reaches theintended destination station, which copies the information forfurther processing. The information frame continues to circlethe ring and is finally removed when it reaches the sending

station. The sending station can check the returning frame tosee whether the frame was seen and subsequently copied bythe destination.

  Unlike CSMA/CD networks (such as Ethernet), token-passingnetworks are deterministic, which means that it is possible tocalculate the maximum time that will pass before any endstation will be capable of transmitting. This feature and severalreliability features, which are discussed in the section "Fault-Management Mechanisms," later in this chapter, make Token

Ring networks ideal for applications in which delay must bepredictable and robust network operation is important. Factoryautomation environments are examples of such applications.

Token Ring standard specifies a ring topology, the IBMimplementation of token ring uses the star-wired ring topology withall the computers on the network connected to a central hub.TheToken Ring protocol requires a star-wired ring using twisted pair orfiber optic cable. It can operate at transmission speeds of 4 Mbps or16 Mbps.

Token Ring networks use STP and UTP cabling, such as IBM Types1, 2 and 3 cables, to connect the network adapter cards of thecomputers to the central hub and to interconnect other hubs.

Data in a Token Ring network is transmitted in the form of frameswith start and end delimiters. The basic format of a Token Ring data

frame is showed in below figure with the descriptions of each field inthe data frame.

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o  Start and end end delimiters - Start and end of theframe. 

o   Access control - Specifies frame priority and whether it isa token of a data frame 

o  Frame control - Media Access Control information or end station information 

o  Destination and source address - Origin and destinationaddress 

o  Data - Data begin sect  o  Frame check sequence - CRC error - checking information o  Frame status - Indicates if the frame was recognized,

copied or if the destination address was available 

Token Ring is a stable architecture with the capacity to handle high-bandwidth applications, such as desktop videoconferencing andmultimedia. The right choice of equipment is the key to high-performance, scaleable Token Ring networks.

Hardware components of a Token Ring network

Hub or Switch

In a Token Ring network, the hub contains the actual ring in thenetwork. The hub of a Token Ring network is also referred to asMultistation Access Unit (MAU), MultiStation Access Unit (MSAU) orSmart Multistation Access Unit (SMAU).

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The hub is attached to individual clients and servers by cables. Thehub of a Token Ring network is a passive hub and acts as aconnection point. The internal ring converts to an external ring ateach connection point when a computer is connected.

When all the ports on a hub have computers connected to them, theToken Ring network can be enlarged by adding another hub.However, each hub must be added in such a way that it becomes apart of the logical ring.

STP or UTP cables

STP or UTP cables are required to connect the computers on aToken Ring network to a hub. Token Rings use IBM Type 1, 2 and 3cabling. Most networks use the IBM Cabling System Type 3 UTPcabling. The screen displays the cable distances relevant to a TokenRing network.

Media filters

Media filters are used in the computers that use Type 3 telephonetwisted pair cabling to convert cable connectors and reduce line

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noise. Media filters connect the token ring adapter card to astandard RJ-11/RJ-45 telephone jack.

Repeaters

Repeaters enable you to increase Token Ring cable distances. Arepeater actively regenerates and retimes the Token Ring signal toextend the distances between the hubs on the network.

Network adapter cards

Network adapter cards enable a device to be connected to theToken Ring network. Token Ring adapter cards are available in both4 Mbps and 16 Mbps models. The 16 Mbps cards accommodate anincreased frame length that requires fewer transmissions for thesame amount of data.

Token Ring cards need to be implemented carefully because aToken Ring network runs only at one of two possible speeds, 4 Mbpsor 16 Mbps. If 16 Mbps cards are used in a 4 Mbps network, they

revert to the 4 Mbps mode. However, a 16 Mbps network will notaccept the 4 Mbps cards because they cannot speed up to 16 Mbps.

Fiber optic cable

Due to the mix of data streaming, high speeds and unidirectionaldata traveling, Token Ring networks are well suited to fiber opticcable. Fiber optic cables are used in Token Ring networks to

increase the range of the network up to 10 times that possible withcopper cabling. However, fiber optic cables are more expensive thancopper cables.

ArcNET

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Attached Resource Computer Network (ArcNet) was developed byDatapoint Corporation in 1977. It is a simple, inexpensive andflexible network architecture designed for workgroup-sizednetworks.

ArcNet technology is described by the ANSI standard 878.1 andpredates the IEEE Project 802 standards. ArcNet should not beconfused with the IEEE Token Bus standard, IEEE 802.4. However,ArcNet does loosely comply to this token passing specification.ArcNet technology is described by the ANSI standard 878.1 andpredates the IEEE Project 802 standards. ArcNet should not beconfused with the IEEE Token Bus standard, IEEE 802.4. However,ArcNet does loosely comply to this token passing specification.

The token moves from one computer to another based on nodeaddresses instead of the physical location of computers. This meansthat ArcNet passes the token to the next address regardless of whether the address is on a workstation in the same room or in aseparate building.

Each computer in an ArcNet network is connected by a cable to ahub, which can be an active, a passive or a smart hub.

The standard cabling used for ArcNet is 93 ohm RG-62 A/U coaxialcable. ArcNet also supports twisted pair and fiber optic cables.

The use of star topology and cable filtering make ArcNet networksreliable. In a distributed star design, ArcNet uses passive and activehubs to control and route data tokens from one workstation to thenext. Since token passing is done at a fixed rate and collisions donot occur, ArcNet is very stable.

LocalTalk

LocalTalk is a network protocol that was developed by AppleComputer, Inc. for Macintosh computers. The method used byLocalTalk is called CSMA/CA (Carrier Sense Multiple Access with

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Collision Avoidance). It is similar to CSMA/CD except that acomputer signals its intent to transmit before it actually does so.

LocalTalk adapters and special twisted pair cable can be used toconnect a series of computers through the serial port. TheMacintosh operating system allows the establishment of a peer-to-peer network without the need for additional software. With theaddition of the server version of AppleShare software, aclient/server network can be established.

The LocalTalk protocol allows for linear bus, star, or tree topologiesusing twisted pair cable. A primary disadvantage of LocalTalk isspeed. Its speed of transmission is only 230 Kbps.

FDDI

The Fiber Distributed Data Interface (FDDI) specifies a 100-Mbpstoken-passing, dual-ring LAN using fiber-optic cable. FDDI is

frequently used as high-speed backbone technology because of itssupport for high bandwidth and greater distances than copper. Itshould be noted that relatively recently, a related copperspecification, called Copper Distributed Data Interface (CDDI), hasemerged to provide 100-Mbps service over copper. CDDI is theimplementation of FDDI protocols over twisted-pair copper wire.

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This chapter focuses mainly on FDDI specifications and operations,but it also provides a high-level overview of CDDI.

FDDI uses dual-ring architecture with traffic on each ring flowing inopposite directions (called counter-rotating). The dual rings consistof a primary and a secondary ring. During normal operation, theprimary ring is used for data transmission, and the secondary ringremains idle. As will be discussed in detail later in this chapter, theprimary purpose of the dual rings is to provide superior reliabilityand robustness. Figure shows the counter-rotating primary andsecondary FDDI rings.

FDDI uses optical fiber as the primary transmission medium, but italso can run over copper cabling. As mentioned earlier, FDDI overcopper is referred to as Copper-Distributed Data Interface (CDDI).Optical fiber has several advantages over copper media. Inparticular, security, reliability, and performance all are enhanced

with optical fiber media because fiber does not emit electricalsignals.

A physical medium that does emit electrical signals (copper) can betapped and therefore would permit unauthorized access to the datathat is transiting the medium.

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In addition, fiber is immune to electrical interference from radiofrequency interference (RFI) and electromagnetic interference(EMI). Fiber historically has supported much higher bandwidth(throughput potential) than copper, although recent technological

advances have made copper capable of transmitting at 100 Mbps.Finally, FDDI allows 2 km between stations using multimode fiber,and even longer distances using a single mode

FDDI defines two types of optical fiber: single-mode and multimode.A mode is a ray of light that enters the fiber at a particular angle.Multimode fiber uses LED as the light-generating device, whilesingle-mode fiber generally uses lasers.

Below figure depicts single-mode fiber using a laser light source and

multimode fiber using a light emitting diode (LED) light source.

FDDI specifies the physical and media-access portions of the OSIreference model. FDDI is not actually a single specification, but it isa collection of four separate specifications, each with a specificfunction. Combined, these specifications have the capability toprovide high-speed connectivity between upper-layer protocols such

as TCP/IP and IPX, and media such as fiber-optic cabling.

The FDDI frame format is similar to the format of a Token Ringframe. This is one of the areas in which FDDI borrows heavily fromearlier LAN technologies, such as Token Ring. FDDI frames can beas large as 4,500 bytes. Figure shows the frame format of an FDDIdata frame and token.

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o  Preamble - Gives a unique sequence that prepares eachstation for an upcoming frame. 

o  Start delimiter - Indicates the beginning of a frame. o  Frame control - Indicates the size of the address. o  Destination address - Origin and destination address o  Source address - Identifies the single station that sent 

the frame. o  Frame check sequence (FCS) - CRC error - checking o  End delimiter - End of the frame. o  Frame status - Identifies whether the frame was

recognized and copied by a receiving station. 

Ethernet Network Interface Card (NIC)

A network card (network adapter, network interface card, NIC,Ethernet adapter etc.) is a piece of computer hardware designed toallow computers to communicate over a computer network. It is anOSI model layer 2 item.

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Every network card in the world has a unique 48-bit serial numbercalled a MAC address, which is written to ROM carried on the card.Every computer on a network must have a card with a unique MACaddress. The IEEE is responsible for assigning MAC addresses to the

vendors of network interface cards, which means that two cardssharing the same MAC address is impossible.

Whereas network cards used to be expansion cards to plug into acomputer bus, most new computers have a network interface builtinto the motherboard, so a separate network card is not requiredunless multiple interfaces are needed or some other type of networkis used.

The card implements the electronic circuitry required to

communicate using a specific physical layer and data link layerstandard such as Ethernet or token ring. This provides a base for afull network protocol stack, allowing communication among smallgroups of computers on the same LAN and large-scale networkcommunications through routable protocols, such as IP.

  There are four techniques used for transfer of data, the NICmay use one or more of these techniques.

  Polling is where the microprocessor examines the status of theperipheral under program control.

  Programmed I/O is where the microprocessor alerts thedesignated peripheral by applying its address to the system'saddress bus.

  Interrupt-driven I/O is where the peripheral alerts themicroprocessor that its ready to transfer data.

 DMA is where the intelligent peripheral assumes control of thesystem bus to access memory directly.

A network card typically has a twisted pair and BNC sockets wherethe network cable is connected, and a few LEDs to inform the user

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of whether the network is active, and whether or not there is databeing transmitted on it.

The Network Cards are typically available in 10/100/1000 Mbit/s.This means they can support a transfer rate of 10 or 100 or 1000Mbit/s.

Network Cables

Cable is the medium through which information usually moves fromone network device to another. There are several types of cablewhich are commonly used with LANs. In some cases, a network willutilize only one type of cable, other networks will use a variety of cable types. The type of cable chosen for a network is related to the

network's topology, protocol, and size. Understanding thecharacteristics of different types of cable and how they relate toother aspects of a network is necessary for the development of asuccessful network.

The following sections discuss the types of cables used in networks.

Chapter 5.2.1: Twisted Pair

Chapter 5.2.2: Coaxial cables

Chapter 5.2.3: Fiber Optic Cable

Ethernet Switches

An Ethernet Switch is a LAN interconnection device which operatesat the data link layer (layer 2) of the OSI reference model. A switch

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is fundamentally similar to a bridge , but usually supports a largernumber of connected LAN segments and has a richer managementcapability. A network switch is a computer networking device that connectsnetwork segments. It uses the logic of a Network bridge but allowsa physical and logical star topology. It is often used to replacenetwork hubs. A switch is also often referred to as an intelligent hubor switching hub.

As a frame comes into a switch, the switch saves the originatingMAC address and the originating port in the switch's MAC addresstable. The switch then selectively transmits the frame from specificports based on the frame's destination MAC address and previous

entries in the MAC address table.

If the destination MAC address is unknown a broadcast address or(for simpler switches) a multicast address the switch simplytransmits the frame out of all of the connected interfaces except theincoming port.

If the destination MAC address is known, the frame is forwardedonly to the corresponding port in the MAC address table.

If the destination port is the same as the originating port, the frameis filtered out and not forwarded.

Routers

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A router is an Intermediate System (IS) which operates at thenetwork layer of the OSI reference model. Routers may be used toconnect two or more IP networks , or an IP network to an internetconnection.

A router consists of a computer with at least two network interfacecards supporting theIP protocol . The router receives packets fromeach interface via a network interface and forwards the receivedpackets to an appropriate output network interface. Receivedpackets have all link layer protocol headers removed, andtransmitted packets have a new link protocol header added prior totransmission.

The router uses the information held in the network layer

header (i.e. IP header) to decide whether to forward each receivedpacket, and which network interface to use to send the packet. Mostpackets are forwareded based on the packet's IP destinationaddress , along with routing information held within the router in arouting table. Before a packet is forwarded, the processor checksthe Maximum Transfer Unit (MTU) of the specified interface.

Packets larger than the interface's MTU must be fragmented by therouter into two or more smaller packets. If a packet is receivedwhich has the Don't Fragment (DF) bit set in the packet header , the packet is not fragmented, but instead discarded. In this case,an ICMP error message is returned to the sender (i.e. to the originalpacket's IP source address) informing it of the interface's MTU size.This forms the basis for Path MTU discovery (PMTU) . 

The routing and filter tables resemble similar tables in link layerbridges and switches. Except, that instead of specifying linkhardware addresses ( MAC addresses ), the router table sepcifynetwork ( IP addresses ).

The routing table lists known IP destination addresses with theappropraite network interface to be used to reach that destiantion.A default entry may be specified to be used for all addresses notexplicitly defined in the table. A filter table may also be used toensure that unwanted packets are discarded. The filter may be usedto deny access to particular protocols or to prevent unauthorised

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access from remote computers by discarding packets to specifieddestination addresses.

A router forwards packets from one IP network to another IPnetwork. Like other systems, it determines the IP network from thelogical AND of an IP address with the associated subnetworkaddress mask.

One execption to this rule is when a router receives an IP packet toa network broadcast address. In this case, the router discards thepacket. Forwarding broadcast packet can lead to severe storms of packets, and if uncontrolled could lead to network overload.

Routers are often used to connect together networks which use

different types of links (for instance an HDLC link connecting a WANto a local Ethernet LAN ). The optimum (and maximum) packetlengths (i.e. the maximum transmission unit (MTU) ) is different fordifferent types of network. A router may therefore uses IP toprovide segmentation of packets into a suitable size for transmissionon a network.

ained together, usually within a telecommunications closet, which

connects incoming and outgoing lines of a LAN or othercommunication, electronic or electrical system.

In a LAN , the patch panel connects the network's computers toeach other and to the outside lines that enable the LAN to connectto the Internet or another WAN. Connections are made with patchcords.

The patch panel allows circuits to be arranged and rearranged by

plugging and unplugging the patch cords.

Switch rack

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A rack which can accommodate the Ethernet switch and patchpanel, and usually this located on the common place for all thecomputers.

Wall pallets

The wall outlet will be like a plug point which connects the internal

and external wiring, and the wall outlet is mostly used for securethe internal cables.

Firewall

A firewall protects networked computers from intentional hostileintrusion that could compromise confidentiality or result in datacorruption or denial of service. It may be a hardware device or asoftware program running on a secure host computer. In eithercase, it must have at least two network interfaces, one for thenetwork it is intended to protect, and one for the network it isexposed to.

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  Hardware Firewall : Hardware firewall providing protection to aLocal Network

  Firewall Software : Computer running firewall software toprovide protection

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A firewall sits at the junction point or gateway between the twonetworks, usually a private network and a public network such asthe Internet. The earliest firewalls were simply routers. The termfirewall comes from the fact that by segmenting a network into

different physical subnetworks, they limited the damage that couldspread from one subnet to another just like firedoors or firewalls.

A firewall examines all traffic routed between the two networks tosee if it meets certain criteria. If it does, it is routed between thenetworks, otherwise it is stopped.

A firewall filters both inbound and outbound traffic. It can alsomanage public access to private networked resources such as hostapplications. It can be used to log all attempts to enter the private

network and trigger alarms when hostile or unauthorized entry isattempted.

Firewalls can filter packets based on their source and destinationaddresses and port numbers. This is known as address filtering.Firewalls can also filter specific types of network traffic. This is alsoknown as protocol filtering because the decision to forward or rejecttraffic is dependant upon the protocol used, for example HTTP, ftpor telnet. Firewalls can also filter traffic by packet attribute or state.

A firewall cannot prevent individual users with modems from diallinginto or out of the network, bypassing the firewall altogether.Employee misconduct or carelessness cannot be controlled byfirewalls. Policies involving the use and misuse of passwords anduser accounts must be strictly enforced. These are managementissues that should be raised during the planning of any securitypolicy but that cannot be solved with firewalls alone.

OSI Layer

OSI (Open Systems Interconnection) is a standard description or"reference model" for how messages should be transmitted betweenany two points in a telecommunicationnetwork. Its purpose is to

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guide product implementers so that their products will consistentlywork with other products.

The reference model defines seven layers of functions that takeplace at each end of a communication. Although OSI is not alwaysstrictly adhered to in terms of keeping related functions together ina well-defined layer, many if not most products involved intelecommunication make an attempt to describe them in relation tothe OSI model. It is also valuable as a single reference view of communication that furnishes everyone a common ground foreducation and discussion. Developed by representatives of majorcomputer and telecommunication companies beginning in 1983, OSIwas originally intended to be a detailed specification of interfaces.Instead, the committee decided to establish a common reference

model for which others could develop detailed interfaces that in turncould become standards. OSI was officially adopted as aninternational standard by the International Organization of Standards ( ISO ). Currently, it is Recommendation X.200 of theITU-TS.

The main idea in OSI is that the process of communication betweentwo end points in a telecommunication network can be divided intolayers, with each layer adding its own set of special, related

functions. Each communicating user or program is at a computerequipped with these seven layers of function. So, in a givenmessage between users, there will be a flow of data through eachlayer at one end down through the layers in that computer and, atthe other end, when the message arrives, another flow of data upthrough the layers in the receiving computer and ultimately to theend user or program.

The actual programming and hardware that furnishes these sevenlayers of function is usually a combination of the

computer operating system , applications (such as your Webbrowser), TCP/IP or alternative transport and network protocols,and the software and hardware that enable you to put a signal onone of the lines attached to your computer.

OSI divides telecommunication into seven layers. The layers are intwo groups. The upper four layers are used whenever a message

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passes from or to a user. The lower three layers (up to the networklayer) are used when any message passes through the hostcomputer. Messages intended for this computer pass to the upperlayers. Messages destined for some other host are not passed up to

the upper layers but are forwarded to another host.

The seven layers are:

1. Layer 7: The application layer2. Layer 6: The presentation layer3. Layer 5: The session layer4. Layer 4: The transport layer

5. Layer 3: The network layer6. Layer 2: The data-link layer

7. Layer 1: The physical layer

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Layer 7: The application layer

The application layer is the seventh level of the seven-layer OSImodel. It interfaces directly to and performs common applicationservices for the application processes; it also issues requests tothe presentation layer . 

The common application layer services provide semantic conversionbetween associated application processes. Note: Examples of 

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common application services of general interest include the virtualfile, virtual terminal , and job transfer and manipulation protocols.

Examples:

  FTP

  DNS

  SNMP

  SMTP gateways

  Web browser

  Network File System (NFS)

  Telnet and Remote Login (rlogin)

  X.400

  FTAM

  Database software

  Print Server Software

Layer 6: The presentation layer

The presentation layer is the sixth level of the seven layer OSImodel. It responds to service requests from the applicationlayer and issues service requests to the session layer . 

The presentation layer concerns itself not only with the format andrepresentation of actual user data, but also with data structure usedby programs. Therefore, the presentation layer negotiates datatransfer syntax for the application layer.

The presentation layer is responsible for the delivery and formattingof information to the application layer for further processing or

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display. It relieves the application layer of concern regardingsyntactical differences in data representation within the end-usersystems. Note: An example of a presentation service would be

the conversion of anEBCDIC -coded text file to an ASCII -coded file.

The idea of the application layer should be able to point at the datato be moved, and the Presentation layer will deal with therest. Encryption is typically done at this level too, though it can bedone at the application , session , transport , or network layer ;each having its own advantages and disadvantages. Anotherexample is representing structure, which is normally standardised atthis level, often by using XML . As well as simple pieces of data, likestrings, more complicated things are standardised in this layer. Twocommon examples are 'objects' in object-oriented programming , 

and the exact way that streaming video is transmited.

In many widely used applications and protocols, no distinction ismade between the presentation and application layers. Forexample, HTTP , generally regarded as an application layer protocol,has presentation layer aspects such as the ability to identifycharacter encodings for proper conversion, which is then done in theapplication layer.

Examples: 

  AFP, AppleShare File Protocol

  LPP, Lightweight Presentation Protocol

  NCP, NetWare Core Protocol

  NDR, Network Data Representation

  XDR, eXternal Data Representation

  X.25 PAD, Packet Assembler/Disassembler Protocol

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Layer 5: The session layer

The session layer is level five of the seven level OSI model. Itresponds to service requests from the presentation layer and issuesservice requests to the transport layer .

The Session layer provides the mechanism for managing thedialogue between end-user application processes. It provides foreither full duplex or half-duplex operation and establishescheckpointing, adjournment, termination, and restart procedures.

The Session layer is typically completely unused, but it does have afew places where it is useful. The idea is to allow information ondifferent streams, perhaps originating from different sources, to be

properly combined. In particular, it deals with synchronizationissues, and ensuring nobody ever sees inconsistent versions of data,and similar things.

One application which is fairly intuitively clear is web conferencing . Here, we want to make sure that the streams of audio and videomatch up - or in other words, that we do not have lipsync problems.We may also want to do "floor control" - ensuring that the persondisplayed on screen and whose words are relayed is the oneselected by the speaker, or by some other criteria.

Another big application is in live TV programs, where streams of audio and video need to be seamlessly merged from one to theother so that we do not have half a second of blank airtime, or half a second when we transmit two pictures simultaneously.

Examples:

  ADSP, AppleTalk Data Stream Protocol

  ASP, AppleTalk Session Protocol

  NetBIOS, Network Basic Input Output System

  PAP, Printer Access Protocol

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  PPTP, Point-to-Point Tunnelling Protocol

  RPC, Remote Procedure Call Protocol

  RTP, Real-time Transport Protocol

  RTCP, Real-time Transport Control Protocol

  SMPP, Short Message Peer-to-Peer

  SCP, Secure Copy Protocol

  SSH, Secure Shell

Layer 4: The transport layer

In computing and telecommunications , the transport layer is layerfour of the seven layer OSI model. It responds to service requestsfrom the session layer and issues service requests to the networklayer.

The transport layer provides transparent transfer of data betweenhosts. It is usually responsible for end-to-end error recovery andflow control, and ensuring complete data transfer. In the Internet

protocol suite this function is most commonly achieved by theconnection oriented Transmission Control Protocol (TCP).The datagram -type transport,User Datagram Protocol (UDP),provides neither error recovery, nor flow control, leaving these tothe application .

The purpose of the Transport layer is to providetransparent transfer of data between end users, thus relieving theupper layers from any concern with providing reliable and cost-effective data transfer.

The transport layer usually turns the unreliable and very basicservice provided by the Network layer into a more powerful one.There is a long list of services that can be optionally provided at thislevel. None of them are compulsory, because not all applicationswant all the services available.

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Some can be wasted overhead, or even counterproductive in somecases:

  Connection-Oriented 

This is normally easier to deal with than connection-less models, sowhere the Network layer only provides a connection-less service,often a connection-oriented service is built on top of that in theTransport layer.

 Same Order Delivery 

The Network layer doesn't generally guarantee that packets of datawill arrive in the same order that they were sent, but often this is adesirable feature, so the Transport layer provides it. The simplestway of doing this is to give each packet a number, and allow thereceiver to reorder the packets.

  Reliable Data 

The underlying network may well be noisy, and the data receivedmay not always be the same as the data sent. The Transport layercan fix this: typically by providing a checksum of the data whichdetects if there has been a glitch of some kind. Of course, error freeis impossible, but it is possible to substantially reduce the numbersof undetected errors. This layer may also retransmit packets whichhave gone missing en route.

  Flow Control 

The amount of memory on a computer is limited, and without flowcontrol a larger computer might flood a computer with so muchinformation that it can't hold it all before dealing with it. Nowadays,

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this is not a big issue, as memory is cheap while bandwidth iscomparatively expensive, but in earlier times it was more important.Flow control allows the receiver to say "Whoa!" before it isoverwhelmed. Sometimes this is already provided by the network,

but where it is not, the Transport layer may add it on.

  Byte Orientation 

Rather than dealing with things on a packet-by-packet basis, theTransport layer may add the ability to view communication just as astream of bytes. This is nicer to deal with than random packet sizes,however, it rarely matches the communication model which will

normally be a sequence of messages of user defined sizes.

  Ports 

Ports are essentially ways to address multiple entities in the samelocation. For example, the first line of a postal address is a kind of port, and distinguishes between different occupants of the samehouse. Computer applications will each listen for information on

their own ports, which is why you can use more than one network-based application at the same time.

On the Internet there are a variety of Transport services, but thetwo most common are TCP and UDP. TCP is the more complicated,providing a connection and byte oriented stream which is almosterror free, with flow control, multiple ports, and same orderdelivery. UDP is a very simple 'datagram' service, which provideslimited error reduction and multiple ports. TCP stands forTransmission Control Protocol, while UDP stands for User DatagramProtocol. Other options are the Datagram Congestion ControlProtocol(DCCP) and Stream Control Transmission Protocol (SCTP).

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Some things, such as connection orientation can be implemented ateither Transport or Network layer. The idea is that the Networklayer implements whatever set of options is easiest: for someunderlying networks it is easiest to implement connectionless

communication, while for others it is easiest to implementconnection oriented communication. The Transport layer uses thissimplest set of options to implement whatever combinations of options are actually desired.

Examples:

  AEP, AppleTalk Echo Protocol

  ATP, AppleTalk Transaction Protocol

  DCCP, Datagram Congestion Control Protocol 

  FCP, Fiber Channel Protocol

  FCIP, Fiber Channel over TCP/IP

  TCP, Transmission Control Protocol

Layer 3: The network layer

The network layer is level three of the seven level OSI model. Itresponds to service requests from the transport layer and issuesservice requests to the data link layer. 

The network layer addresses messages and translates logical

addresses and names into physical addresses. It also determinesthe route from the source to the destination computer and managestraffic problems, such as switching , routing , and controlling thecongestion of data packets. In essence, the network layer isresponsible for end to end (source to destination) packet delivery,whereas the data link layer is responsible for node to node (hop tohop) packet delivery.

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The network layer provides the functional and procedural means of transferring variable length data sequences from a source to adestination via one or more networks while maintaining the qualityof service requested by the transport layer. The Network layer

performs network routing, flow control , networksegmentation /desegmentation, anderror control functions.Thenetwork layer deals with transmitting information all the way fromits source to its destination - transmitting from anywhere, toanywhere.

Here are some things that the network layer needs to address:

i. Network connection-oriented or connectionless 

The OSI Network Layer protocol can be either connection-oriented,or connectionless. The TCP/IP Internet Layer (equivalent to OSI'sNetwork Layer) supports only the connectionless Internet Protocol(IP).

ii. Global Addresses

Everybody in the network needs to have a unique address whichdetermines who they are. This address will normally be hierarchical,so you can be "Fred Murphy" to Dubliners, or "Fred Murphy, Dublin "to people in Ireland , or "Fred Murphy, Dublin , Ireland " to peopleanywhere in the world. On the internet, these addresses are knownas IP Numbers.

iii. Forward a message

This is of particular interest to mobile applications, where a usermay rapidly move from place to place, and it must be arranged thathis messages follow him. Version 4 of the Internet Protocol ( IPv4 )doesn't really allow for this, though it has been hacked somewhat

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since its inception. Fortunately, the forthcoming IPv6 has a muchbetter designed solution, which should make this type of applicationmuch smoother.

Examples

  IP/IPv6, Internet Protocol 

  IPSec, Internet Protocol Security 

  IPX, Internetwork Packet Exchange

  X.25, Packet Level Protocol

  DDP, Datagram Delivery Protocol 

Layer 2: The data-link layer

The data link layer is layer two of the seven-layer OSI model. Itresponds to service requests from the network layer and issuesservice requests to the physical layer. This is the layer whichtransfers data between adjacent network nodes in a wide area

network or between nodes on the same local areanetwork segment . The data link layer provides the functional andprocedural means to transfer data between network entities andmight provide the means to detect and possibly correct errors thatmay occur in the Physical layer.

Examples of data link protocols are Ethernet f or local area networksand PPP , HDLC andADCCP f or point-to-point connections.

The data link is all about getting information from one place to a

selection of other places. At this layer one does not need to be ableto go everywhere, just able to go somewhere else. So in socialcontact, one needs to know at least one other person, but notnecessarily know Fred, Bob, or James.

The data link provides data transfer across the physical link. Thattransfer might or might not be reliable; many data link protocols do

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not have acknowledgments of successful frame reception andacceptance, and some data link protocols might not even have anyform of checksum to check for transmission errors. In those cases,higher-level protocols must provide flow control, error checking, and

acknowledgments and retransmission.

In some networks, such as IEEE 802 local area networks, the datalink layer is split into MAC and LLC sublayers; this means thatthe IEEE 802.2 LLC protocol can be used with all of the IEEE 802MAC layers, such as Ethernet, Token Ring , IEEE 802.11 , etc., aswell as with some non-802 MAC layers such as FDDI.

Other data link layer protocols, such as HDLC, are specified toinclude both sublayers, although some other protocols, suchas Cisco HDLC , use HDLC's low-level framing as a MAC layer incombination with a different LLC layer.

  Logical Link Control Sublayer 

The uppermost sublayer is Logical Link Control (LLC). Thissublayermultiplexes protocols running atop the data link layer, andoptionally provides flow control, acknowledgment, and error

recovery.

  Media Access Control Sublayer 

The sublayer below it is Media Access Control (MAC). Sometimesthis refers to the sublayer that determines who is allowed to accessthe media at any one time (usually CSMA/CD ). Other times it refersto a frame structure with MAC addresses inside, specially speakingabout ethernet over switches.

Examples:

  ARCnet

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  ATM

  Controller Area Network (CAN)

  Ethernet

  Fiber Distributed Data Interface (FDDI)

  Frame Relay

  IEEE 802.2 (provides LLC functions to IEEE 802 MAC layers)

  IEEE 802.11 wireless LAN 

  LocalTalk 

  Multiprotocol Label Switching (MPLS)

  Point-to-Point Protocol (PPP)

  Token ring

  And most forms of serial communication. 

Layer 1: The physical layer

The physical layer is level one in the seven level OSImodel of computer networking. It performs services requested bythe data link layer. This level refers to networkhardware , physicalcabling or a wireless electromagnetic connection . It also deals withelectrical specifications, collision control and other low-levelfunctions.

The physical layer is the most basic network layer, providing onlythe means of transmitting raw bits. The shapes of the electricalconnectors , which frequencies to broadcast on, and similar low-level things are specified here. An analogy of this layer in a physicalmail network would be a specification for various kinds of paper andink.

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The major functions and services performed by the physical layer are:

  Establishment and termination of a connection to

a communications medium. 

  Participation in the process whereby the communicationresources are effectively shared among multiple users,e.g., contention resolution and flow control. 

  Conversion between the representation of digitaldata in user equipment and the corresponding signalstransmitted over a communications channel . 

Examples:

  EIA standards: RS-232, RS-422, RS-423, RS-449, RS-485

  ITU Recommendations: see ITU-T

  DSL

  ISDN

  T1 and other T-carrier links, and E1 and other E-carrier links

  10BASE-T, 10BASE2, 10BASE5, 100BASE-TX, 100BASE-FX, 100BASE-T, 1000BASE-T,1000BASE-SX and other varietiesof Ethernet

TCP/IP

Transmission Control Protocol/Internet Protocol (TCP/IP) is anindustry standard protocol stack that is used for communicationbetween Windows based computers. TCP/IP is designed forcommunication across large-scale networks. The tasks involved inusing TCP/IP in the communication process are distributed betweenprotocols that are organized into four distinct layers of the TCP/IP

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stack. Each protocol in the TCP/IP stack has a distinct role in thecommunication process. During the communication process, manyapplications may be in communication at the same time. TCP/IP hasthe ability to differentiate one application from another. TCP/IP

identifies an application on one computer and then moves the datafrom that application to an application on another computer.

TCP/IP Activities

The TCP/IP communication process is initiated using an applicationon the source computer that prepares the data to be transmitted ina format that an application on the destination computer can read.

This is similar to writing a letter in a language that the recipient canunderstand. Then the data is associated with the destinationapplication and computer, much like how you address a letter to arecipient and household. The address of the destination computer isthen added to the data, just as the address of the recipient isspecified on the letter. After these activities are performed, the dataand additional information, including a request for confirmation of its delivery, are sent over the network to the destination.

The network medium used for transmitting the data is independentof the above activities, just as the means of transport that transfersthe letter from one post office to another is independent of theletters content or address.

TCP/IP Protocol:

  Transmission Control Protocol (TCP)  User Datagram Protocol (UDP)  Internet Protocol (IP)  Internet Control Message Protocol (ICMP)  Internet Group Management Protocol (IGMP)  Address Resolution Protocol (ARP)  TCP/IP Utilities

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Transmission Control Protocol (TCP)

Transmission Control Protocol (TCP) is a required TCP/IP standard

protocol that provides a reliable, connection-oriented data deliveryservice between only two computers. Such a communication isknown as a unicast. In connection oriented communication, theconnection must be established before data can be transmittedbetween the two computers.

After the connection is established, data is transmitted over thissingle connection only. Connection-oriented communication is alsoreferred to as reliable communication because it guarantees the

delivery of the data at the destination. On the source computer, TCPorganizes the data to be transmitted into packets. On thedestination computer, TCP reorganizes the packets to recreate theoriginal data.

User Datagram Protocol (UDP)

User Datagram Protocol (UDP) is a transport layer protocol that

identifies the destination application in network communications.UDP provides a connectionless packet delivery service that offersfast but unreliable, best-effort delivery of the data.

UDP does not require an acknowledgment for the data received anddoes not attempt to retransmit data that is lost or corrupted. Thismeans that less data is sent, but neither the arrival of packets northe correct sequencing of delivered packets is acknowledged orguaranteed.

UDP is used by applications that transmit data to multiplecomputers by using broadcast or multicast transmissions. It is alsoused for transmitting small amounts of data or data that is not of high importance. Example uses of UDP include multicastingstreaming media, such as during a live videoconference, and

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broadcasting a list of computer names, which are maintained forlocal communication.

To use UDP, the source application must supply its UDP portnumber as well as that of the destination application. It is importantto note that UDP ports are distinct and separate from TCP ports,even though some of them use the same numbers.

Internet Protocol (IP)

Internet Protocol (IP) helps to identify the location of the destinationcomputer in a network communication. IP is a connectionless,

unreliable protocol that is primarily responsible for addressingpackets and routing them between networked computers. AlthoughIP always attempts to deliver a packet, a packet may be lost,corrupted, delivered out of sequence, duplicated, or delayed.

However, IP does not attempt to recover from these types of errorsby requesting retransmission of the data. Acknowledging thedelivery of packets and recovering lost packets is the responsibilityof a higher-layer protocol, such as TCP, or of the application itself.

Activities Performed by IP

You can visualize IP as the mailroom of the TCP/IP stack, wherepacket sorting and delivery take place. The packets are passeddown to IP by UDP or TCP from the transport layer or passed upfrom the network interface layer.

The primary function of IP is to route the packets until they reach

their destination. Each packet includes the source IP address of thesender and the destination IP address of the intended recipient.These IP addresses in a packet remain the same throughout thepackets journey across a network.

If IP identifies a destination address as an address from the samesegment, it transmits the packet directly to that computer. If the

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destination IP address is not on the same segment, IP must use arouter to send the information. IP is also responsible for ensuringthat a packet does not remain on the network forever by limitingthe number of networks across which the packet can travel.

This is done by assigning a Time to Live (TTL) number to everypacket. A TTL specifies the maximum length of time that the packetcan travel on the network before being discarded.

Internet Control Message Protocol (ICMP)

Internet Control Message Protocol (ICMP) provides troubleshooting

facilities and error reporting for undeliverable packets. With ICMP,computers and routers that use IP communication can report errorsand exchange limited control and status information. For example, if IP is unable to deliver a packet to a destination computer, ICMPsends a Destination Unreachable message to the source computer.

Although the IP protocol is used to move data across routers, ICMPreports errors and control messages on behalf of IP. ICMP does notattempt to make IP a reliable protocol, because ICMP messages areunacknowledged and therefore unreliable. It only attempts to report

errors and provide feedback on specific conditions. Although thismay not seem effective, it is much more efficient than usingbandwidth to acknowledge each ICMP message.

Internet Group Management Protocol (IGMP)

Internet Group Management Protocol (IGMP) is a protocol thatmanages the membership lists for IP multicasting in a TCP/IPnetwork. IP multicasting is a process by which a message istransmitted to a select group of recipients, known as a multicastgroup. IGMP maintains the list of members who subscribe to eachmulticast group.

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All of the members of a multicast group listen for IP traffic directedto a specific multicast IP address and receive the packets sent tothat IP address. However, because multicasting involves multiplecomputers, the packets are sent using the unreliable UDP protocol,

which does not guarantee the delivery of the packets to themulticast group.

When multiple computers need to access information, such asstreaming media, an IP address reserved for multicasting is used.Routers that are configured to process multicast IP addresses pickup this information and forward it to all subscribers of the multicastgroup associated with the multicast IP address.

Address Resolution Protocol (ARP)

Located in the Internet layer of the TCP/IP suite, Address ResolutionProtocol (ARP) performs address resolution for outgoing packets.Address resolution is the process by which IP addresses are mappedto MAC addresses. The network adapters use the MAC address todetermine if a packet is meant for that computer. Without the MACaddress, the network adapters do not know if they are to pass thedata to a higher layer for further processing. As the outgoingpackets in the IP layer are being readied for transmission on thenetwork, the source and destination MAC addresses must be added.

ARP Cache

ARP stores a table containing IP addresses and their correspondingMAC addresses. The area of memory where this table is stored isreferred to as the ARP cache. The ARP cache for any computercontains the mappings for only computers and routers that resideon the same segment.

Physical Address Resolution

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ARP compares every outbound packets destination IP address withthe ARP cache to determine the MAC address to which the packetwill be sent. If there is a matching entry, the MAC address isretrieved from the cache. If not, ARP broadcasts a request for the

computer owning the IP address in question to reply with its MACaddress.

Next, the computer with the corresponding IP address adds theinitial computers MAC address to its cache and then replies with itsown MAC address. When an ARP reply is received, the ARP cache isupdated with the new information and the packet can then be sent.

If the packet is going to another segment, ARP resolves the MACaddress for the router responsible for that segment, rather than

resolving the address for the final destination computer. The routeris then responsible for either finding the MAC address of thedestination or forwarding the packet to another router.

Network Wiring

There are several types of wiring schemas available. So, we have toconsider more appropriate schema for our network. EIA/TIA 568AStandard and 568A and 568B Wiring Schemes are most popularwiring standard CAT 5e wiring.

568A Standard:

The purpose of EIA/TIA 568A was to create a multiproduct,multivendor, standard for connectivity. Prior to the adoption of thisstandard, many "proprietary" cabling systems existed. This wasvery bad for the consumer. Among other things, the standard setthe minimum requirements for category-5E cable and hardware.The 568 "standard" is not to be confused with 568A or 568B wiringschemes, which are themselves, part of the "568A standard".

568A & 568B Wiring Schemes:

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When we refer to a jack or a patch panel's wiring connection, werefer to either the 568A, or 568B wiring scheme, which dictates thepin assignments to the pairs of cat 5E cable. It is very important tonote that there is no difference, whatsoever, between the two

wiring schemes, in connectivity or performance when connectedform one modular device to another (jack to Patch panel, RJ-45 toRJ-45, etc.), so long as they (the two devices) are wired for thesame scheme (A or B). The only time when one scheme has anadvantage over the other, is when one end of a segment isconnected to a modular device, and the other end to a punch block.In which case, the 568A has the advantage of having a morenatural progression of pairs at the punch block side.

The Category 5 E standard is now officially part of the 568Astandard.

Category 5e Cable Unshielded Twisted Pair

Category 5 (CAT5) cabling is good, solid cable for 100-Mbps LANs.The Category 5 standard has been around since 1991, so it's wellestablished. You'll find existing Category 5 installations everywhere.If you still have a lot of 10-Mbps equipment, CAT5 cabling will serveyour needs. It also handles 100-Mbps Fast Ethernet transmissionsvery well.

Category 5e: The improved Category 5

Category 5e (CAT5e), also known as Enhanced Category 5, wasratified in 1999. It's an incremental improvement designed to

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enable cabling to support full-duplex Fast Ethernet operation andGigabit Ethernet.

The main differences between Category 5 and Category 5e can befound in the specifications. The performance requirements havebeen raised slightly in the new standard (see the Buyer's Guidebelow).

Like CAT5, CAT5e is a 100-MHz standard, but it has the capacity tohandle bandwidth superior to that of CAT5. With theseimprovements, you can expect problem-free, full-duplex, 4-pairEthernet transmissions over your CAT5e UTP.

COLOR-CODE STANDARDS

Here are the diagrams:

Note that the TX (transmitter) pins are connected to corresponding

RX (receiver) pins, plus to plus and minus to minus. And that youmust use a crossover cable to connect units with identicalinterfaces.

If you use a straight-through cable, one of the two units must, ineffect, perform the cross-over function.

Two wire color-code standards apply: EIA/TIA 568A and EIA/TIA568B. The codes are commonly depicted with RJ-45 jacks as follows(see below figure from the front of the jacks):

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Network Cabling Tools

Modular Plug Tool

We need a modular crimping tool during the cabling of the twistedpair and RJ 45 connectors. It's a tool in a shape of pliers which willsecurely crimp RJ-45 connectors. Even though the crimper hascutters, which we use to cut cables and individual wires, andperhaps stripes the outer jacket.

UTP Stripping Tool

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This tool works neat and produces good finishing; as well this tool isused to cut cables and individual wires.

Diagonal Cutters

This tool is used for easier to cut the cable off at the reel and to finetune the cable ends during the process of assembling.

Crimping the twisted pair Cables

1. Pull the cable off the reel to the desired length and cut (seebelow figure).

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2. Stripe one end of the cable with the stripper. This is about rightto strip a little over 1/2" of the cover off the cable. Turn thestripper about one turn or so. Once scored, you should be able totwist the end of the jacket loose and pull it off with one hand whileholding the rest of the cable with the other.

3. Examine the wires for nicks. Cut off the end and start over if we

see any. We may have to adjust the blade with the screw at thefront stripper. Cable diameters and jacket thicknesses vary.

4. Spread and arrange the pairs roughly in the order of the desiredcable end

5. Untwist the pairs and arrange the wires in the order of thedesired cable end. Flatten the end between thumb and forefinger.Trim the ends of the wires so they are even with one another. It isvery important that the untwisted end be slightly less than 1/2"

long.

If it is longer than 1/2" it will be out-of-spec and susceptible tocrosstalk. If it less than slightly less than 1/2" it will not be properlyclinched when RJ-45 plug is crimped on. Flatten again. Thereshould be little or no space between the wires.

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6. Hold the RJ-45 plug with the clip facing down or away from you.Push the wire firmly into the plug. Looking through the bottom of the plug, the wire on the far left side will have a white background.

The wires should alternate light and dark from left to right. Thefurthest right wire is brown. The wires should all end evenly at thefront of the plug.

7. Hold the wire near the RJ-45 plug with the clip down and firmlypush it into the left side of the front of the crimper. Hold the wire inplace squeeze the crimper handles quite firmly. The crimper pushestwo plungers down on the RJ-45 plug. One forces what amounts toa cleverly designed plastic plug/wedge onto the cable jacket andvery firmly clinches it. The other seats the "pins," each with twoteeth at its end, through the insulation and into the conductors of their respective wires.

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8. Test the crimp. If done properly an average person will not beable to pull the plug off the cable with the bare hands.

9. Prepare the other end of the cable so it has the desired end andcrimp.

10. If both ends of the cable are within reach, hold them next toeach other and with RJ-45 clips facing away. If the plugs are wired

correctly, and they are identical, it is a straight-thru cable. If theyare wired correctly and they are different, it is a crossover cable.

Windows Server 2003 Operating Systems

Windows Server 2003 operating systems take the best of Windows2000 Server technology and make it easier to deploy, manage, anduse. The result: a highly productive infrastructure that helps makeyour network a strategic asset for your organization. As of March28, 2005 , all Windows Server 2003 operating systems ship with

Windows Server Service Pack 1 (SP1). Windows Server 2003 SP1provides enhanced security, increased reliability, and a simplifiedadministration to help enterprise customers across all industries.

Windows Server 2003 includes all the functionality customers needtoday from a Windows Server operating system to do more withless, such as security, reliability, availability, and scalability. Inaddition, Microsoft has improved and extended the Windows serveroperating systems to incorporate the benefits of Microsoft .NET forconnecting information, people, systems, and devices.

Windows Server 2003 is a multipurpose operating system capable of handling a diverse set of server roles, depending on your needs, ineither a centralized or distributed fashion.

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Some of these server roles include:

• File and print server.

• Web server and Web application services.

• Mail server.

• Terminal server.

• Remote access and virtual private network (VPN) server.

• Streaming media server.

Installing Server 2003 Standard Edition

To successfully install Windows server 2003 standard edition, it isvery important that you assess the system, document it, plan theinstallation, and then methodically follow through with your plan.

  Insert the Server 2003 Standard Edition CD ROM and click theapplicable Install Windows button.

  To install windows from across a network, launch thewinnt32.exe program on the network drive containing the

windows setup files,and then proceed within setup normally.

  Choose new Installation (Advanced) from the Installation Typebox and then click Next to perform a clean install of Windows.following window will be appears

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  Read the licensee agreement, choose the I accept ThisAgreement option, press F8 to continue

  On the next screen you are asked to choose the disk and

partition on which you want to install windows appears

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  After you finish modifying the partition, select the partition onwhich you want to install windows and press enter.

  If you choose to create new partition, you are prompted toformat the partition using either the NTFS or FAT file system,using either a quick format or full format, Choose the NTFSQuick format if you know the disk has not bad sectors orhistory of file corruption, otherwise choose NTFS full Formatand press enter

  Setup confirms the choice of partition and gives you the optionof converting the partition to NTFS if it's not an NTFS partitionalready. If you want to reformat the hard drive, choose theNTFS Quick format option if you know the disk has no badsector or history on file corruption, otherwise choose NTFS fullformat and press enter

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  Press ENTER to format

  Formatting

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  Setup checks the hard disk for error and then copies the

appropriate files into the newly created Windows folder. AfterSetup finishes copying files, it prompts you to remove anyfloppy or CD -ROM and then it restart the system and startsthe windows Setup Wizard

  Windows setup wizard

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  The setup Wizard detects and configures the devices installedon the computer/If Setup can not properly detected a device,it display a Device Configuration dialog box for manualconfiguration of the device.

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  After the hardware is detected, you are prompted to configurethe regional settings, if you haven't already. These settingsaffect such factors as keyboard layout and how dates andcurrency values are displayed. Configure this option as

appropriate and then click next

  Type the name of the person the computer is to be registeredunder as well as the organization

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  Type the product key if you haven't already, and then clicknext

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  Choose the licensing mode in the next window, either PerServer or Per Seat. If you choose Per Server, Specify howmany CALs(Certificate Authority License) you purchased

  Type the name of the computer in the computer Name textBox. The computer name can contain the numbers zero to

nine, uppercase and lowercase letters, and hyphen character.The must be DNS compatibility with per-Windows XP clients.

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  Review the date, and time zone information, make anynecessary correction, and then click next to configure yournetwork settings

  Select custom setting . And then click next

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  Choose the typical Settings option to install the followingcommonly used networks protocols and services. Clients forMicrosoft Networks, File And Printer Sharing fro MicrosoftNetworks, and Transmission Control Protocol/ Internet Protocolconfigured to use DHCP

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  Highlight the TCP/IP and click properties. In the followingwindow.

  In the following window enter the required under the 'General'tab and click ok in the following window.

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  In the Workgroup or Domain window enter the name of ourworkgroup or domain.

  Setup will finish copying

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  Setup will then finish the installation and reboot windowsserver 2003.

  After Setup restarts your computer, you see the standardwindows logon screen.

File Server

Many people mistake file servers for a high-end storage system, butin reality, file servers do not need to possess great power or super

fast computer specifications. A form of disk storage that hosts fileswithin a network File servers do not need to be high-end but musthave enough disk space to incorporate a large amount of data.

File servers generally offer some form of system security to limitaccess to files to specific users or groups. In a confidentialorganizations like the Hospital has lot of details of many numbers of patients.

These are hierarchical views of the computing environment which

treat users, directories, computers, applications and files as distinctbut related entities on the network and grant access based on useror group credentials.In many cases, the directory service spansmany file servers, potentially hundreds for large organizations. Inthe past, and in smaller organizations, authentication can take placedirectly to the server itself.

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Installing File Server

  Select the File Server and click next

  This wizard will guide us to give the limit and warning disk

space for new user. click next

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  Here this wizard ask us to keep index service to the folders ornot select yes and click next

  This wizard gives the summary of the service click next.

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  Then the share folder wizard will be appears. click next

  Select a folder path to implement the file server and click next

  In the Name, Description, and settings dialog box, type ashare name and a description of the Folder's contents

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  Click change to set weather and how the contents of the folderare available for offline use.

  Set the permission for the shared and click finish

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  click Close

Printer servers

A computer in a network that controls one or more printers isknown as the print server. It is either part of the network operatingsystem or an add-on utility that stores the print-image output fromusers' machines and feeds it to the printer one job at a time. Thecomputer and its printers are known as a "Print Server" or a fileserver with "print services."

Printer servers are computers that manage the communicationbetween printers and the clients' computers that want to print tothe printers.

Printers can be connected to the print server by networkconnection, with parallel or serial port connection, or via a UniversalSerial Bus or IEEE 1394 (Fire wire or iLink) connection. Although

USB printers and old parallel printers are popular among consumersand can be connected to the Windows server 2003 print server,easier to locate, and reduce the amount of processing power usedon the print server.

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Implementing VPN

VPN is an external link and simply an extension of private network.Virtual Private Networks (VPN) technology uses private encryptedtunneling, allowing networking of remote workers, branch officelocations, and central corporate sites without dedicated physicalcircuits.

VPN offers companies a safe, inexpensive means of using theInternet to access their internal networks.

Installing VPN

  Installing VPN, go to configure your server wizard and selectRemote Access / VPN server as in figure 10.5.1

Figure 10.5.1: Server Role 

  Figure 10.5.1 wizard helps to connect Remote Access /VPNenable remote clients to connect the network through eitherdial up connection or VPN security connection, click next willshow the summarize selection wizard of the VPN server access

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Figure 10.5.2: Summary of Selection 

  Click next to change our selection and continue installation,then the following new wizard will appear. This Routing andRemote Access Server Setup Wizard will help you to connectyour clients' remote, click next

Figure 10.5.3: Welcome 

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  Figure 10.5.4 help to configuration the services select customconfiguration and click next then the following Figure 10.5.5will display

Figure 10.5.4: Configuration 

  From Figure 10.5.5 select VPN access and LAN routing and

click next

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Figure 10.5.5: Custom Configuration 

  Complete the Routing and Remote Access Server Setup Wizardwill be display and click finish.

Figure 10.5.6: Complete 

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  After few minutes the wizard will give the message thatRemote Access and VPN access were successfully set up thisserver as remote access, click finish.