Course Outline

NDEJJE UNIVERSITY

FACULTY OF BASIC SCIENCES AND IT

Introduction to computer networks Course Outline

Facilitator: Barungi FredTel: 0782-829965Email: barungi12@gmail.comPurpose of Module

This course introduces the concepts, design criteria, and prevailing standards used in modern distributed information systems. You will benefit by enhancing your understanding of Internet protocols and Network operating systems.

Course Outline

1. Introduction Classification of Networks

2. Numbering systems

3. Network Devices

4. Communication Models

OSI Model

TCP/IP Model

5. Bandwidth

6. Cables

7. Cable Termination Practicals

8. Adressing and Subnetting9. Wireless NetworkingAssessments

Students will undertake a coursework and an exam at the end of the semester and this will constitute 40% and 60% respectively of the total grade (100%).

Recommended Texts

INTRODUCTION

LECTURE 1A computer network is a grouping of two or more computers to share data, applications, and networked peripherals such as printers.

Types of Networks

Local area networks (LANs) link computers in the same building

LANs consist of the following components:

Computers

Network interface cards

Peripheral devices

Networking media

Network devices

LANs make it possible for businesses that use computer technology to locally share files and printers efficiently, and make internal communications possible. Some common LAN technologies are:

Ethernet

Token Ring

FDDI

wide area networks (WAN)WANs interconnect LANs, which then provide access to computers or file servers in other locations. Because WANs connect user networks over a large geographical area, they make it possible for businesses to communicate across great distances. WANs are designed to do the following:

Operate over a large geographically separated areas

Allow users to have real-time communication capabilities with other users

Provide full-time remote resources connected to local services

Provide e-mail, World Wide Web, file transfer, and e-commerce services

Some common WAN technologies are:

Modems

Integrated Services Digital Network (ISDN)

Digital Subscriber Line (DSL)

MAN

A MAN is a network that spans a metropolitan area such as a city or suburban area. A MAN usually consists of two or more LANs in a common geographic area. For example, a bank with multiple branches may utilize a MAN. Typically, a service provider is used to connect two or more LAN sites using private communication lines or optical services. A MAN can also be created using wireless bridge technology by beaming signals across public areas.

SAN

A SAN is a dedicated, high-performance network used to move data between servers and storage resources. Because it is a separate, dedicated network, it avoids any traffic conflict between clients and servers. SAN technology allows high-speed server-to-storage, storage-to-storage, or server-to-server connectivity.

Virtual private network (VPN)A VPN is a private network that is constructed within a public network infrastructure such as the global Internet. This network is said to be virtual because it links two "physical" networks (local area networks) using an unreliable connection (the Internet), and private because only computers which belong to a local area network on one end of the VPN or the other can "see" the data. A virtual private network relies on a protocol called a tunneling protocol; that is, a protocol that encrypts the data which runs from one end of the VPN to the other.Personal Area Network (PAN)The smallest type of network, a PAN simply involves connecting one person's computer to a number of devices or peripherals. Usually, all devices, such as printers, PDAs, and telephones, are within a few feet of the computer. A PAN can also refer to a connection to the internet.Network Classifications

Networks are classified as either public or private

Public NetworksInternet A global network of networks used to exchange information using the TCP/IP protocol. It allows for electronic mail and the accessing and retrieval of information from remote sources. .Private Networks

Intranet And Extranets

An intranet is a private network that is setup and controlled by an organization to encourage interaction among its members, to improve efficiency and to share information.

Information and resources that are shared on an intranet might include: organizational policies and procedures, announcements, information about new products, and confidential data of strategic value.Intranets are designed to permit access by users who have access privileges to the internal LAN of the organization.

An extranet is an extended intranet. allowing access to members of an organization, an extranet uses firewalls, access profiles, and privacy protocols to allow access to users from outside the organization.

An extranet is a private network that uses Internet protocols and public networks to securely share resources with customers, suppliers, vendors, partners, or other businesses.

Network topology

Network topology defines the structure of the network. One part of the topology definition is the physical topology, which is the actual layout of the wire or media. The other part is the logical topology, which defines how the media is accessed by the hosts for sending data. The physical topologies that are commonly used are as follows:

Bus topologyor Linear Topology: All nodes on the LAN are connected by one linear cable, which is called the shared medium. Every node on this cable segment sees transmissions from every other station on the same segment. At each end of the bus is a terminator, which absorbs any signal, removing it from the bus. This medium cable apparently is the single point of failure. Ethernet (IEEE 802.3) is the protocols used for this type of LAN.

Mesh topology: Devices are connected with many redundant interconnections between network nodes such as routers and switches. In a mesh topology if any cable or node fails, there are many other ways for two nodes to communicate. Full mesh topology occurs when every node has a circuit connecting it to every other node in a network. Partial mesh topology where some nodes are organized in a full mesh scheme but others are only connected to one or two in the network, is often used in real network to provide the reliability with less complexity.

Ring topology: Every network node has two branches connected to it and form a ring. If one of the nodes on the ring fails than the ring is broken and cannot work. A dual ring topology has four branches connected to it, and is more resistant to failures.

Star topology: The network nodes are connected to a central node, which rebroadcasts all transmissions received from any peripheral node to all peripheral nodes on the network, including the originating node. All peripheral nodes may thus communicate with all others by transmitting to, and receiving from, the central node only.

Tree topology: The network nodes are arranged as a tree, which resembles an interconnection of star networks in that individual peripheral nodes are required to transmit to and receive from one other node only and are not required to act as repeaters or regenerators. Unlike the star network, the function of the central node may be distributed.

A hybrid topology is a combination of any two or more network topologies in such a way that the resulting network does not have one of the standard forms. For example, a tree network connected to a tree network is still a tree network, but two star networks connected together exhibit hybrid network topologies. A hybrid topology is always produced when two different basic network topologies are connected.

The logical topology of a network is how the hosts communicate across the medium. The two most common types of logical topologies are broadcast and token passing.

Broadcast topology simply means that each host sends its data to all other hosts on the network medium. There is no order that the stations must follow to use the network. It is first come, first serve. Ethernet works this way as will be explained later in the course.

The second logical topology is token passing. Token passing controls network access by passing an electronic token sequentially to each host. When a host receives the token, that host can send data on the network. If the host has no data to send, it passes the token to the next host and the process repeats itself. Two examples of networks that use token passing are Token Ring and Fiber Distributed Data Interface (FDDI). A variation of Token Ring and FDDI is Arcnet. Arcnet is token passing on a bus topology.

Fiber-distributed data interface (FDDI) is another token-passing technology that operates over a pair of fiber optic rings, with each ring passing a token in opposite directions. FDDI networks offered transmission speeds of 100 Mbps, which initially made them quite popular for high-speed networking. With the advent of 100-Mbps Ethernet, which is cheaper and easier to administer, FDDI has waned in popularity. Network architecture. The network architecture can take one of several forms, including peer-to-peer (in which each computer or node on the network has equal capabilities) and client/server (in which one node, the server, is more powerful and manages network functions for the client, or PC, devices).

PEER TO PEER NETWORKA type of network in which each workstation has equivalent capabilities and responsibilities. Computers in a peer to peer network are typically situated physically near to each other and run similar networking protocols and software.This differs from client/server architectures, in which some computers are dedicated to serving the others. Peer to peer workgroups allow sharing of files, printers and other resources equally among all of the devicesin peer-to-peer networks, each machine shares its own resources and handles its own securityaren't nearly as expensive to create, since you don't need a dedicated machine, server software, or special client licenses.The "network" consists of shared folders located on computers within the network. ADVANTAGES OF PEER TO PEER NETWORK Content and resources can be shared from both the center and the edge of the network. In client/server networking, content and resources are typically shared from only the center of the network. A network of peers is easily scaled and more reliable than a single server. A single server is subject to a single point of failure A network of peers can share its processor, consolidating computing resources for distributed computing tasks, rather than relying on a single computer, such as a supercomputer. a peer can share the file directly from its local storage rather than from a central computer in client/server model Allows the processing resources of edge computers to be utilized for distributed computing tasks. Allows local resources to be shared directly, without the need for intermediate servers. Allows efficient multipoint communication without having to rely on IP multicast infrastructure. inexpensive to set up. It uses the built in networking capabilities of Windows XP ProfessionalDISADVANTAGES OF PEER TO PEER Lack of data security Files are not centralized, so getting a back up of all critical files is more difficult. CLIENT SERVERA client server network is defined as specific type of network comprised of a single central computer acting as a server that directs multiple other computers, which are referred to as the clients. By accessing the server, clients are then able to reach shared files and information saved on the serving computer.makes it possible for multiple computers or people to interconnect and share information. In the client-server scheme, a central server handles all security and file transactions;In a client-server environment, the dedicated file server controls the level of access that client PCs have to shared resources.For example, to check your e-mail from your computer, a client program on your computer forwards your request to a server program at your Internet Service Provider (ISP). Once the server program has retrieved your e-mail, it forwards them to the client on your computer, which then allows you to read the e-mailAdvantages of client server allowing a shared database or site to be accessed or updated by multiple computers while maintaining only one control center for the action This model has an increased security, often with encryption, ensuring that the data is only available to qualified individuals.DISADVANTAGES OF CLIENT SERVER If too many different clients attempt to reach the shared network at the same time, there may be a failure or a slowing down of the connection. If the network is down, this disables access to the information from any site or clients anywhere client-server networks is the costly because server software is required It required technician to installNumbering System

LECTURE 2In networking, there are three important number systems:

Base 2 binary

Base 10 decimal

Base 16 hexadecimal Decimal numbers have 10 different placeholders, the numbers 0-9.

here's a binary number system: digits (symbols) allowed: 0, 1 base (radix): 2 each binary digit is called a BIT the order of the digits is significant

1001 (base 2) is really 1 x 2**3 + 0 x 2**2 + 0 x 2**1 + 1 x 2**0 9 (base 10)

11000 (base 2) is really 1 x 2**4 + 1 x 2**3 + 0 x 2**2 + 0 x 2**1 + 0 x 2**0 24 (base 10)Binary numbers have only two different placeholders, 0 and 1.

decimal --> binary divide decimal value by 2 (the base) until the value is 036/2 = 18 r=0 18/2 = 9 r=0 9/2 = 4 r=1 4/2 = 2 r=0 2/2 = 1 r=0 1/2 = 0 r=1 36 (base 10) == 100100 (base 2)Hexadecimal numbers have 16 different placeholders, the numbers 0-9 and the letters A-F. here's a hexadecimal number system: digits (symbols) allowed: 0-9, a-f base (radix): 16 You multiply by 16 then rise to the powers in order to change to base 10a3 (base 16)

Numbera..3

Numbering1..0

is really a x 16**1 + 3 x 16**0 160 + 3 =163 (base 10)Network Devices

LECTURE 3End-user devices that provide users with a connection to the network are also referred to as hosts. These devices allow users to share, create, and obtain information.NIC

A NIC is a printed circuit board that fits into the expansion slot of a bus on a computer motherboard, or it can be a peripheral device. It is also called a network adapter. Laptop or notebook computer NICs are usually the size of a PCMCIA card. Each individual NIC carries a unique code, called a Media Access Control (MAC) address. This address is used to control data communication for the host on the network

Modem

Short for modulator-demodulator. A modem is a device or program that enables a computer to transmit data over, for example, telephone or cable lines. Computer information is stored digitally, whereas information transmitted over telephone lines is transmitted in the form of analog waves. A modem converts between these two forms.

RepeaterA network device used to regenerate or replicate a signal. Repeaters are used in transmission systems to regenerate analog or digital signals distorted by transmission loss. Analog repeaters frequently can only amplify the signal while digital repeaters can reconstruct a signal to near its original quality.

HubA hub is a repeater, which is an OSI model device, the simplest possible. Hubs are a common connection point for devices in a network and are commonly used to connect segments of a LAN. A hub takes the incoming data packet that comes into a port and copies it out to all the other ports in the hub. It doesn't perform any filtering or redirection of data.

BridgeBridges (sometimes called "Transparent bridges") work at OSI model Layer 2. This means they don't know anything about protocols, but just forward data depending on the destination address in the data packet. This address is not the IP address, but the MAC (Media Access Control) address that is unique to each network adapter card. All computers included in the LAN must contain a network interface card (NIC). The card assigns a unique address to the machine in which it is installed. This address is called a MAC (Medium Access Control).

The bridge is the device which is used to connect two local-area networks (LANs), or two segments of the same LAN that use the same protocol.However, the only data that is allowed to cross the bridge is data that is being sent to a valid address on the other side of the bridge. No valid address, no data across the bridge. Bridges don't require programming. They learn the addresses of the computers connected to them by listening to the data flowing through them.Bridges are very useful for joining networks made of different media types together into larger networks, and keeping network segments free of data that doesn't belong in a particular segment. Only 2 networks can be linked with a bridge.

Switches

Switches are the same thing as Bridges, but usually have multiple ports with the same "flavor" connection (Example: 10/100BaseT).Switches can be used in heavily loaded networks to isolate data flow and improve performance. In a switch, data between two lightly used computers will be isolated from data intended for a heavily used server, for example. Switches are layer 2 devices. Switch can link up four, six, eight or even more networks.

RouterRouters forward data packets from one place to another, too! However routers are OSI model Layer 3 devices, and forward data depending on the Network address, not the Hardware (MAC) address. For TCP/IP networks, this means the IP address of the network interface.Routers isolate each LAN into a separate subnet, so each network adapter's IP address will have a different third "octet" (Example: 192.168.1.1 and 192.168.2.1 are in different subnets).

A router can determine the most efficient path for a packet to take and send packets around failed segments.

Gateway

Often used as a connection to a mainframe or the internet. Gateways enable communications between different protocols, data types and environments. This is achieved via protocol conversion, whereby the gateway strips the protocol stack off of the packet and adds the appropriate stack for the other side. Gateways operate at all layers of the OSI model without making any forwarding decisions.

The Differences between these devices on the network

In a hub, a frame is passed along or "broadcast" to every one of its ports. It doesn't matter that the frame is only destined for one port. The hub has no way of distinguishing which port a frame should be sent to. Passing it along to every port ensures that it will reach its intended destination. This places a lot of traffic on the network and can lead to poor network response times.

A switch, however, keeps a record of the MAC addresses of all the devices connected to it. With this information, a switch can identify which system is sitting on which port. So when a frame is received, it knows exactly which port to send it to, without significantly increasing network response times. And, unlike a hub, a 10/100Mbps switch will allocate a full 10/100Mbps to each of its ports. So regardless of the number of PCs transmitting, users will always have access to the maximum amount of bandwidth. It's for these reasons why a switch is considered to be a much better choice then a hub.

Routers are completely different devices. Where a hub or switch is concerned with transmitting frames, a router's job, as its name implies, is to route packets to other networks until that packet ultimately reaches its destination. One of the key features of a packet is that it not only contains data, but the destination address of where it's going.

PROTOCOLS

Protocol suites are collections of protocols that enable network communication from one host through the network to another host. A protocol is a formal description of a set of rules and conventions that govern a particular aspect of how devices on a network communicate. Protocols determine the format, timing, sequencing, and error control in data communication. Without protocols, the computer cannot make or rebuild the stream of incoming bits from another computer into the original format.

Protocols control all aspects of data communication, which include the following:

How the physical network is built

How computers connect to the network

How the data is formatted for transmission

How that data is sent

How to deal with errors

Key elements of a protocol are:

SYNTAC: Data format and signal levels

SEMANTICS: Control information for coordination and error handling

TIMING: Synchronization, speed matching, and sequencing

Examples of protocols:

WAN Protocol: TCP/IP

LAN Protocol: Media Access Control; Contention; Token Passing

Communication Models

LECTURE 4

OSI Model

The OSI reference model is a framework that is used to understand how information travels throughout a network. The OSI reference model explains how packets travel through the various layers to another device on a network, even if the sender and destination have different types of network media.

In the OSI reference model, there are seven numbered layers, each of which illustrates a particular network function. Dividing the network into seven layers provides the following advantages:

It breaks network communication into smaller, more manageable parts.

It standardizes network components to allow multiple vendor development and support.

It allows different types of network hardware and software to communicate with each other.

It prevents changes in one layer from affecting other layers.

It divides network communication into smaller parts to make learning it easier to understand.

In order for data to travel from the source to the destination, each layer of the OSI model at the source must communicate with its peer layer at the destination. This form of communication is referred to as peer-to-peer. During this process, the protocols of each layer exchange information, called protocol data units (PDUs). Each layer of communication on the source computer communicates with a layer-specific PDU, and with its peer layer on the destination computer

Data packets on a network originate at a source and then travel to a destination. Each layer depends on the service function of the OSI layer below it. To provide this service, the lower layer uses encapsulation to put the PDU from the upper layer into its data field; then it adds whatever headers and trailers the layer needs to perform its function. Next, as the data moves down through the layers of the OSI model, additional headers and trailers are added. After Layers 7, 6, and 5 have added their information, Layer 4 adds more information. This grouping of data, the Layer 4 PDU, is called a segment.

The network layer provides a service to the transport layer, and the transport layer presents data to the internetwork subsystem. The network layer has the task of moving the data through the internetwork. It accomplishes this task by encapsulating the data and attaching a header creating a packet (the Layer 3 PDU). The header contains information required to complete the transfer, such as source and destination logical addresses.

The data link layer provides a service to the network layer. It encapsulates the network layer information in a frame (the Layer 2 PDU). The frame header contains information (for example, physical addresses) required to complete the data link functions. The data link layer provides a service to the network layer by encapsulating the network layer information in a frame.

The physical layer also provides a service to the data link layer. The physical layer encodes the data link frame into a pattern of 1s and 0s (bits) for transmission on the medium (usually a wire) at Layer 1.

TCP/IP

The TCP/IP model has the following four layers:

Application layer

Transport layer

Internet layer

Network access layer

Although some of the layers in the TCP/IP model have the same name as layers in the OSI model, the layers of the two models do not correspond exactly. Most notably, the application layer has different functions in each model.

The designers of TCP/IP felt that the application layer should include the OSI session and presentation layer details. They created an application layer that handles issues of representation, encoding, and dialog control.

The transport layer deals with the quality of service issues of reliability, flow control, and error correction. One of its protocols, the transmission control protocol (TCP), provides excellent and flexible ways to create reliable, well-flowing, low-error network communications.

TCP is a connection-oriented protocol. It maintains a dialogue between source and destination while packaging application layer information into units called segments. Connection-oriented does not mean that a circuit exists between the communicating computers. It does mean that Layer 4 segments travel back and forth between two hosts to acknowledge the connection exists logically for some period.

The purpose of the Internet layer is to divide TCP segments into packets and send them from any network. The packets arrive at the destination network independent of the path they took to get there. The specific protocol that governs this layer is called the Internet Protocol (IP). Best path determination and packet switching occur at this layer.

The relationship between IP and TCP is an important one. IP can be thought to point the way for the packets, while TCP provides a reliable transport.

The name of the network access layer is very broad and somewhat confusing. It is also known as the host-to-network layer. This layer is concerned with all of the components, both physical and logical, that are required to make a physical link. It includes the networking technology details, including all the details in the OSI physical and data link layers.

Some of the most commonly used application layer protocols include the following:

File Transfer Protocol (FTP)

Hypertext Transfer Protocol (HTTP)

Simple Mail Transfer Protocol (SMTP)

Domain Name System (DNS)

Trivial File Transfer Protocol (TFTP)

The common transport layer protocols include:

Transport Control Protocol (TCP)

User Datagram Protocol (UDP)

The primary protocol of the Internet layer is:

Internet Protocol (IP)

The network access layer refers to any particular technology used on a specific network.

Regardless of which network application services are provided and which transport protocol is used, there is only one Internet protocol, IP. This is a deliberate design decision. IP serves as a universal protocol that allows any computer anywhere to communicate at any time.

A comparison of the OSI model and the TCP/IP models will point out some similarities and differences.

Similarities include:

Both have layers.

Both have application layers, though they include very different services.

Both have comparable transport and network layers.

Both models need to be known by networking professionals.

Both assume packets are switched. This means that individual packets may take different paths to reach the same destination. This is contrasted with circuit-switched networks where all the packets take the same path.

Differences include:

TCP/IP combines the presentation and session layer issues into its application layer.

TCP/IP combines the OSI data link and physical layers into the network access layer.

TCP/IP appears simpler because it has fewer layers.

TCP/IP protocols are the standards around which the Internet developed, so the TCP/IP model gains credibility just because of its protocols. In contrast, networks are not usually built on the OSI protocol, even though the OSI model is used as a guide.

Although TCP/IP protocols are the standards with which the Internet has grown, this curriculum will use the OSI model for the following reasons:

It is a generic, protocol-independent standard.

It has more details, which make it more helpful for teaching and learning.

It has more details, which can be helpful when troubleshooting.

Networking professionals differ in their opinions on which model to use. Due to the nature of the industry it is necessary to become familiar with both. Both the OSI and TCP/IP models will be referred to throughout the curriculum. The focus will be on the following:

TCP as an OSI Layer 4 protocol

IP as an OSI Layer 3 protocol

Ethernet as a Layer 2 and Layer 1 technology

Remember that there is a difference between a model and an actual protocol that is used in networking. The OSI model will be used to describe TCP/IP protocols

BANDWIDTH

LECTURE 5Bandwidth is defined as the total amount of information that can flow through a network connection in a given period of time expressed in bit/s or multiples of it (kbit/s, Mbit/s etc).In radio communication ,Bandwidth is the difference between the upper and lower frequencies in a contiguous set of frequencies in radio signalingIn website hosting, the term "bandwidth" is often incorrectly used to describe the amount of data transferred to or from the website or server within a prescribed period of time, for example bandwidth consumption accumulated over a month measured in Gigabyte per month. The more accurate phrase used for this meaning of a maximum amount of data transfer each month or given period is monthly data transfer.

Consider this analogy:

Rented Water Tank = web-server that hosts your website,

Water company = hosting company where your web-server resides,

Water = files, data, images, etc. that comprise your website,

Pipe = the internet,

Quantity of water delivered = bandwidth consumption,

You = patron / visitor of your website which is hosted on aforementioned web-server.

There's a pipe that delivers water from your rented water tank to your home. As you request water, the water company delivers it to you. All the while, they are keeping track of how much water was delivered to you, during a billing cycle. You have a contract with the water company in which they agree to charge you a fixed dollar amount per billing cycle, provided you do not request more water than the allowable quantity, as defined in your contract. If you do request more water, they will not deny you ... but you will incur additional charges for the extra water requested / delivered.

It is essential to understand the concept of bandwidth when studying networking for the following four reasons:

1.Bandwidth is finite. In other words, regardless of the media used to build the network, there are limits on the capacity of that network to carry information. Bandwidth is limited by the laws of physics and by the technologies used to place information on the media. For example, the bandwidth of a conventional modem is limited to about 56 kbps by both the physical properties of twisted-pair phone wires and by modem technology. However, the technologies employed by DSL also use the same twisted-pair phone wires, yet DSL provides much greater bandwidth than is available with conventional modems. So, even the limits imposed by the laws of physics are sometimes difficult to define. Optical fiber has the physical potential to provide virtually limitless bandwidth. Even so, the bandwidth of optical fiber cannot be fully realized until technologies are developed to take full advantage of its potential.

2.Bandwidth is not free. It is possible to buy equipment for a local-area network (LAN) that will provide nearly unlimited bandwidth over a long period of time. For wide-area network (WAN) connections, it is almost always necessary to buy bandwidth from a service provider. In either case, an understanding of bandwidth and changes in demand for bandwidth over a given time can save an individual or a business a significant amount of money. A network manager needs to make the right decisions about the kinds of equipment and services to buy.

3.Bandwidth is a key factor in analyzing network performance, designing new networks, and understanding the Internet. A networking professional must understand the tremendous impact of bandwidth and throughput on network performance and design. Information flows as a string of bits from computer to computer throughout the world. These bits represent massive amounts of information flowing back and forth across the globe in seconds or less. In a sense, it may be appropriate to say that the Internet is bandwidth.

4.The demand for bandwidth is ever increasing. As soon as new network technologies and infrastructures are built to provide greater bandwidth, new applications are created to take advantage of the greater capacity. The delivery over the network of rich media content, including streaming video and audio, requires tremendous amounts of bandwidth. IP telephony systems are now commonly installed in place of traditional voice systems, which further adds to the need for bandwidth. The successful networking professional must anticipate the need for increased bandwidth and act accordingly.

Terminology in telecommunications related to bandwidth

dual-band refers to a device supporting two frequenciesused for communication. dual band wireless network equipment, some cell phones also use two bands for wireless communications. Phone that support multiple bands can connect to different types of cellular networks, helpful while roaming or traveling. Dual-band Wi-Fi network adapters likewise contain two wireless radios. These adapters can be configured to use either 802.11a via one radio, or the 802.11b/g/n family via the other, but not both.

Duplexcommunication systemis a system composed of two connected parties or devices that can communicate with one another in both directions.

Ahalf-duplexsystem provides for communication in both directions, but only one direction at a time (not simultaneously). An example of a half-duplex system is a two-party system such as a "walkie-talkie" style two-way radio, wherein one must use "Over" or another previously-designated command to indicate the end of transmission, and ensure that only one party transmits at a time, because both parties transmit on the same frequency.

Full Duplex Refers to the transmission ofdatain two directions simultaneously. For example, a telephone is a full-duplexdevicebecause both parties can talk at once.

Factors affecting bandwidth.Noise

Noise is any undesired signal in a communication circuit. Another definition calls noise unwanted disturbances superimposed on a useful signal, which tends to obscure its information content. The four most important to the telecommunication/data communication technologist are thermal noise, intermodulation noise, crosstalk and impulse noise.

Thermal noise arises from random electron motion and is characterized by a uniform distribution of energy over the frequency spectrum. Every equipment element and the transmission medium itself contribute thermal noise to a communication system if the temperature of that element or medium is above absolute zero. Whenever molecules heat above absolute zero, thermal noise will be present.

Intermodulation (IM) noise is the result of the presence of intermodulation products. If two signals of frequencies F1 and F2 are passed through a nonlinear device or medium, the result will contain IM products that are spurious frequency energy components. These components may be inside or outside the frequency band of interest for a particular device.

Crosstalk refers to unwanted coupling between signal paths. Excessive level may exacerbate crosstalk.

Impulse noise is a noncontinuous series of irregular pulses or noise "spikes" of short duration, broad spectral density and of relatively high amplitude. Impulse noise degrades telephony only marginally, if at all. However, it may seriously corrupt error performance of a data circuit. Attenuation is the loss of power a signal suffers as it travels from the transmitting device to the receiving deviceANALOGIES

Bandwidth has been defined as the amount of information that can flow through a network in a given time. The idea that information flows suggests two analogies that may make it easier to visualize bandwidth in a network. Since both water and traffic are said to flow, consider the following analogies:

1.Bandwidth is like the width of a pipe. A network of pipes brings fresh water to homes and businesses and carries waste water away. This water network is made up of pipes of different diameters. The main water pipes of a city may be two meters in diameter, while the pipe to a kitchen faucet may have a diameter of only two centimeters. The width of the pipe determines the water-carrying capacity of the pipe. Therefore, the water is like the data, and the pipe width is like the bandwidth. Many networking experts say that they need to put in bigger pipes when they wish to add more information-carrying capacity.

2.Bandwidth is like the number of lanes on a highway. A network of roads serves every city or town. Large highways with many traffic lanes are joined by smaller roads with fewer traffic lanes. These roads lead to even smaller, narrower roads, which eventually go to the driveways of homes and businesses. When very few automobiles use the highway system, each vehicle is able to move freely. When more traffic is added, each vehicle moves more slowly. This is especially true on roads with fewer lanes for the cars to occupy. Eventually, as even more traffic enters the highway system, even multi-lane highways become congested and slow. A data network is much like the highway system. The data packets are comparable to automobiles, and the bandwidth is comparable to the number of lanes on the highway. When a data network is viewed as a system of highways, it is easy to see how low bandwidth connections can cause traffic to become congested all over the network.

Measurements

In digital systems, the basic unit of bandwidth is bits per second (bps). Bandwidth is the measure of how much information, or bits, can flow from one place to another in a given amount of time, or seconds. Although bandwidth can be described in bits per second, usually some multiple of bits per second is used. In other words, network bandwidth is typically described as thousands of bits per second (kbps), millions of bits per second (Mbps), and billions of bits per second (Gbps) and trillions of bits per second (Tbps).

Throughput

Bandwidth is the measure of the amount of information that can move through the network in a given period of time. Therefore, the amount of available bandwidth is a critical part of the specification of the network. A typical LAN might be built to provide 100 Mbps to every desktop workstation, but this does not mean that each user is actually able to move one hundred megabits of data through the network for every second of use. This would be true only under the most ideal circumstances. The concept of throughput can help explain why this is so.

Throughput refers to actual measured bandwidth, at a specific time of day, using specific Internet routes, and while a specific set of data is transmitted on the network. Unfortunately, for many reasons, throughput is often far less than the maximum possible digital bandwidth of the medium that is being used. The following are some of the factors that determine throughput:

Internetworking devices

Type of data being transferred

Network topology

Number of users on the network

User computer

Server computer

Power conditions

The theoretical bandwidth of a network is an important consideration in network design, because the network bandwidth will never be greater than the limits imposed by the chosen media and networking technologies. However, it is just as important for a network designer and administrator to consider the factors that may affect actual throughput. By measuring throughput on a regular basis, a network administrator will be aware of changes in network performance and changes in the needs of network users. The network can then be adjusted accordingly.Cable specifications

LECTURE 6Cables have different specifications and expectations pertaining to performance:

What speeds for data transmission can be achieved using a particular type of cable? The speed of bit transmission through the cable is extremely important. The speed of transmission is affected by the kind of conduit used.

What kind of transmission is being considered? Will the transmissions be digital or will they be analog-based? Digital or baseband transmission and analog-based or broadband transmission are the two choices. How far can a signal travel through a particular type of cable before attenuation of that signal becomes a concern? In other words, will the signal become so degraded that the recipient device might not be able to accurately receive and interpret the signal by the time the signal reaches that device? The distance the signal travels through the cable directly affects attenuation of the signal. Degradation of the signal is directly related to the distance the signal travels and the type of cable used.

Some examples of Ethernet specifications which relate to cable type include:

10BASE-T

10BASE5

10BASE2

10BASE-T refers to the speed of transmission at 10 Mbps. The type of transmission is baseband, or digitally interpreted. The T stands for twisted pair.

10BASE5 refers to the speed of transmission at 10 Mbps. The type of transmission is baseband, or digitally interpreted. The 5 represents the capability of the cable to allow the signal to travel for approximately 500 meters before attenuation could disrupt the ability of the receiver to appropriately interpret the signal being received. 10BASE5 is often referred to as Thicknet. Thicknet is actually a type of network, while 10BASE5 is the cabling used in that network.

10BASE2 refers to the speed of transmission at 10 Mbps. The type of transmission is baseband, or digitally interpreted. The 2, in 10BASE2, represents the capability of the cable to allow the signal to travel for approximately 200 meters, before attenuation could disrupt the ability of the receiver to appropriately interpret the signal being received. 10BASE2 is often referred to as Thinnet. Thinnet is actually a type of network, while 10BASE2 is the cabling used in that network.

Coaxial cable

Coaxial cable consists of a hollow outer cylindrical conductor that surrounds a single inner wire made of two conducting elements. One of these elements, located in the center of the cable, is a copper conductor. Surrounding the copper conductor is a layer of flexible insulation. Over this insulating material is a woven copper braid or metallic foil that acts as the second wire in the circuit and as a shield for the inner conductor. This second layer, or shield reduces the amount of outside electro-magnetic interference. Covering this shield is the cable jacket.

Fibre Optic

Every fiber-optic cable used for networking consists of two glass fibers encased in separate sheaths. One fiber carries transmitted data from device A to device B.The second fiber carries data from device B to device A. The fibers are similar to two one-way streets going in opposite directions. This provides a full-duplex communication link. Just as copper twisted-pair uses separate wire pairs to transmit and receive, fiber-optic circuits use one fiber strand to transmit and one to receive. Typically, these two fiber cables will be in a single outer jacket until they reach the point at which connectors are attached.

Until the connectors are attached, there is no need for twisting or shielding, because no light escapes when it is inside a fiber. This means there are no crosstalk issues with fiber. It is very common to see multiple fiber pairs encased in the same cable. This allows a single cable to be run between data closets, floors, or buildings. One cable can contain 2 to 48 or more separate fibers. With copper, one UTP cable would have to be pulled for each circuit. Fiber can carry many more bits per second and carry them farther than copper can.

Usually, five parts make up each fiber-optic cable. The parts are the core, the cladding, a buffer, a strength material, and an outer jacket.

The core is the light transmission element at the center of the optical fiber. All the light signals travel through the core. A core is typically glass made from a combination of silicon dioxide (silica) and other elements.

Surrounding the core is the cladding. Cladding is also made of silica but with a lower index of refraction than the core. Light rays traveling through the fiber core reflect off this core-to-cladding interface as they move through the fiber by total internal reflection.

Surrounding the cladding is a buffer material that is usually plastic. The buffer material helps shield the core and cladding from damage. There are two basic cable designs. They are the loose-tube and the tight-buffered cable designs.

The strength material surrounds the buffer, preventing the fiber cable from being stretched when installers pull it. The material used is often Kevlar, the same material used to produce bulletproof vests.

The final element is the outer jacket. The outer jacket surrounds the cable to protect the fiber against abrasion, solvents, and other contaminants. The color of the outer jacket of multimode fiber is usually orange, but occasionally another color.

For LANs, coaxial cable offers several advantages. It can be run longer distances than shielded twisted pair, STP, and unshielded twisted pair, UTP, cable without the need for repeaters. Repeaters regenerate the signals in a network so that they can cover greater distances. Coaxial cable is less expensive than fiber-optic cable, and the technology is well known. It has been used for many years for many types of data communication, including cable television.

STP cable

Shielded twisted-pair cable (STP) combines the techniques of shielding, cancellation, and twisting of wires. Each pair of wires is wrapped in metallic foil. The four pairs of wires are wrapped in an overall metallic braid or foil. It is usually 150-Ohm cable. As specified for use in Ethernet network installations, STP reduces electrical noise within the cable such as pair to pair coupling and crosstalk. STP also reduces electronic noise from outside the cable, for example electromagnetic interference (EMI) and radio frequency interference (RFI). Shielded twisted-pair cable shares many of the advantages and disadvantages of unshielded twisted-pair cable (UTP). STP affords greater protection from all types of external interference, but is more expensive and difficult to install than UTP.

UTP cableUnshielded twisted-pair cable (UTP) is a four-pair wire medium used in a variety of networks. Each of the 8 individual copper wires in the UTP cable is covered by insulating material. In addition, each pair of wires is twisted around each other. This type of cable relies solely on the cancellation effect produced by the twisted wire pairs, to limit signal degradation caused by EMI and RFI. To further reduce crosstalk between the pairs in UTP cable, the number of twists in the wire pairs varies. Like STP cable, UTP cable must follow precise specifications as to how many twists or braids are permitted per foot of cable.

TIA/EIA-568-A contains specifications governing cable performance. It calls for running two cables, one for voice and one for data, to each outlet. Of the two cables, the one for voice must be four-pair UTP. CAT 5 is the one most frequently recommended and implemented in installations today.

Unshielded twisted-pair cable has many advantages. It is easy to install and is less expensive than other types of networking media. In fact, UTP costs less per meter than any other type of LAN cabling. However, the real advantage is the size. Since it has such a small external diameter, UTP does not fill up wiring ducts as rapidly as other types of cable. This can be an extremely important factor to consider, particularly when installing a network in an older building. In addition, when UTP cable is installed using an RJ-45 connector, potential sources of network noise are greatly reduced and a good solid connection is practically guaranteed. There are disadvantages in using twisted-pair cabling. UTP cable is more prone to electrical noise and interference than other types of networking media, and the distance between signal boosts is shorter for UTP than it is for coaxial and fiber optic cables.

When communication occurs, the signal that is transmitted by the source needs to be understood by the destination. This is true from both a software and physical perspective. The transmitted signal needs to be properly received by the circuit connection designed to receive signals. The transmit pin of the source needs to ultimately connect to the receiving pin of the destination. The following are the types of cable connections used between internetwork devices.

A LAN switch is connected to a computer. The cable that connects from the switch port to the computer NIC port is called a straight-through cable.

Two switches are connected together. The cable that connects from one switch port to another switch port is called a crossover cable.

The cable that connects the RJ-45 adapter on the com port of the computer to the console port of the router or switch is called a rollover cable.

Cable Practicals

LECTURE 7The TIA/EIA 568-A standard which was ratified in 1995, was replaced by the TIA/EIA 568-B standard in 2002 and has been updated since. Both standards define the T-568A and T-568B pin-outs for using Unshielded Twisted Pair cable and RJ-45 connectors for Ethernet connectivity. The standards and pin-out specification appear to be related and interchangeable, but are not the same and should not be used interchangeably.

T-568B Straight-Through Ethernet Cable

Both the T-568A and the T-568B standard Straight-Through cables are used most often as patch cords for your Ethernet connections. If you require a cable to connect two Ethernet devices directly together without a hub or when you connect two hubs together, you will need to use a Crossover cable instead.

PRACTICALS

Ethernet Cable Instructions:

Pull the cable off the reel to the desired length and cut. If you are pulling cables through holes, its easier to attach the RJ-45 plugs after the cable is pulled. The total length of wire segments between a PC and a hub or between two PC's cannot exceed 100 Meters (328 feet) for 100BASE-TX and 300 Meters for 10BASE-T.

Start on one end and strip the cable jacket off (about 1") using a stripper or a knife. Be extra careful not to nick the wires, otherwise you will need to start over.

Spread, untwist the pairs, and arrange the wires in the order of the desired cable end. Flatten the end between your thumb and forefinger. Trim the ends of the wires so they are even with one another, leaving only 1/2" in wire length. If it is longer than 1/2" it will be out-of-spec and susceptible to crosstalk. Flatten and insure there are no spaces between wires.

Hold the RJ-45 plug with the clip facing down or away from you. Push the wires firmly into the plug. Inspect each wire is flat even at the front of the plug. Check the order of the wires. Double check again. Check that the jacket is fitted right against the stop of the plug. Carefully hold the wire and firmly crimp the RJ-45 with the crimper.

Check the color orientation, check that the crimped connection is not about to come apart, and check to see if the wires are flat against the front of the plug. If even one of these are incorrect, you will have to start over. Test the Ethernet cable.

Adressing and Subnetting

LECTURE 8DNS Server Provides host name resolution by translating host names to IP addresses (forward lookups) and IP addresses to host names (reverse lookups).

DHCP Server Provides automatic IP addressing services to clients configured to use dynamic IP addressing. IP

IP" stands for Internet Protocol, so an IP address is an Internet Protocol address. What does that mean? An Internet Protocol is a set of rules that govern Internet activity and facilitate completion of a variety of actions on the World Wide Web. Therefore an Internet Protocol address is part of the systematically laid out interconnected grid that governs online communication by identifying both initiating devices and various Internet destinations, thereby making two-way communication possible.Internet Protocol Address

Internet Protocol Address (or IP Address) is an unique address that computing devices use to identify itself and communicate with other devices in the Internet Protocol network. Any device connected to the IP network must have an unique IP address within its network. An IP address is analogous to a street address or telephone number in that it is used to uniquely identify a network device to deliver mail message, or call ("view") a website. An IP address is written in "dotted decimal" notation, which is 4 sets of numbers separated by period each set representing 8-bit number ranging from (0-255). An example of IPv4 address is 216.3.128.12, which is the IP address assigned to topwebhosts.org.Subnetmask A Subnet mask is a 32-bit number that masks an IP address, and divides the IP address into network address and host address. Subnet Mask is made by setting network bits to all "1"s and setting host bits to all "0"s. Within a given network, two host addresses are reserved for special purpose. The "0" address is assigned a network address and "255" is assigned to a broadcast address, and they cannot be assigned to a host.

Basic SubnettingSubnetting is the process of breaking down an IP network into smaller sub-networks called "subnets." Each subnet is a non-physical description (or ID) for a physical sub-network Uses of Subnetting Subnets are created to limit the scope of broadcast traffic, to apply network security measures, to separate network segments by function, and/or to assist in resolving network congestion problems.., A subnet is usually composed of a network router, a switch or hub, and at least one hostCalculations will be done in classWireless Networking

Lecture 9

Wireless network is a network set up by using radio signal frequency to communicate among computers and other network devices. Sometimes its also referred to as WiFi network or WLAN. WiFi Technology is a standard of communication among wireless devices and computers all over the world. Wi-Fi is wireless technology which enable connection between two or more devices wirelessly for data sharing purposes . I It is wireless networking which is based on IEEE 802.11 standards. it enabled file transferring from server to clients without wires, networking cards, hubs and other important networking related hardware. Using Wi-Fi internet connection can be shared among computers with minimum usage of hardware, WLAN cards enable feature of wireless networking among devices, wireless routers help to broadcast wireless networking signals in given area. The uses of the Wi-Fi Technology contain any type of WLAN product support any of the 802.11 together with dual-band, 802.11a, 802.11b. Wi-Fi Technology is through accessible hot Spots like Home, Office, Airports, Hotels, Railway stations, Restaurants Wireless products The product used by Wi-Fi Technology are Wireless access points which make possible and fast access to your priorities , Wireless adapters makes it more sufficient for wok, Wireless routers make traffic clean and quick, Wireless network bridges which enable links, allow PC card, Express Card, USB, Card bus, mini-PCI and PCI, Handhelds and PDAs and expand range of wireless repeater.Wireless standards In 1997, the Institute of Electrical and Electronics Engineers (IEEE) created the first WLAN standard. They called it 802.11 Unfortunately, 802.11 only supported a maximum network bandwidth of 2 Mbps - too slow for most applications. For this reason, ordinary 802.11 wireless products are no longer manufactured. 802.11b IEEE expanded on the original 802.11 standard in July 1999, creating the 802.11b specification. 802.11b supports bandwidth up to 11 Mbps 802.11b uses the same unregulated radio signaling frequency (2.4 GHz) as the original 802.11 standard. 802.11b gear can incur interference from microwave ovens, cordless phones, and other appliances using the same 2.4 GHz range. However, by installing 802.11b gear a reasonable distance from other appliances, interference can easily be avoided. Pros of 802.11b - lowest cost; signal range is good and not easily obstructed Cons of 802.11b - slowest maximum speed; home appliances may interfere on the unregulated frequency band 802.11a While 802.11b was in development, IEEE created a second extension to the original 802.11 standard called 802.11a. Because 802.11b gained in popularity much faster than did 802.11a, some folks believe that 802.11a was created after 802.11b. In fact, 802.11a was created at the same time. Due to its higher cost, 802.11a is usually found on business networks whereas 802.11b better serves the home market. 802.11a supports bandwidth up to 54 Mbps and signals in a regulated frequency spectrum around 5 GHz. This higher frequency compared to 802.11b shortens the range of 802.11a networks. The higher frequency also means 802.11a signals have more difficulty penetrating walls and other obstructions. Because 802.11a and 802.11b utilize different frequencies, the two technologies are incompatible with each other. Some vendors offer hybrid 802.11a/b network gear, but these products merely implement the two standards side by side (each connected devices must use one or the other). Pros of 802.11a - fast maximum speed; regulated frequencies prevent signal interference from other devices Cons of 802.11a - highest cost; shorter range signal that is more easily obstructed 802.11g In 2002 and 2003, WLAN products supporting a newer standard called 802.11g emerged on the market. 802.11g attempts to combine the best of both 802.11a and 802.11b. 802.11g supports bandwidth up to 54 Mbps, and it uses the 2.4 Ghz frequency for greater range. 802.11g is backwards compatible with 802.11b, meaning that 802.11g access points will work with 802.11b wireless network adapters and vice versa. Pros of 802.11g - fast maximum speed; signal range is good and not easily obstructed Cons of 802.11g - costs more than 802.11b; appliances may interfere on the unregulated signal frequency 802.11n The newest IEEE standard in the Wi-Fi category is 802.11n. It was designed to improve on 802.11g in the amount of bandwidth supported by utilizing multiple wireless signals and antennas (called MIMO technology) instead of one. When this standard is finalized, 802.11n connections should support data rates of over 100 Mbps. 802.11n also offers somewhat better range over earlier Wi-Fi standards due to its increased signal intensity. 802.11n equipment will be backward compatible with 802.11g gear. Pros of 802.11n - fastest maximum speed and best signal range; more resistant to signal interference from outside sources Cons of 802.11n - standard is not yet finalized; costs more than 802.11g; the use of multiple signals may greatly interfere with nearby 802.11b/g based networks. How WIFI works Wi-Fi uses a frequency of 2.4 to 2.4835 gigahertz, which is also common microwaves and cordless telephones. A Wi-Fi connection works through a transmitting antenna, which is usually connected to a DSL or cable Internet connection. The antenna on the router will then beam radio signals through a specific range. Another antenna, which is on the laptop or personal computer, receives the signal.

The wireless signal typically has a range of 300 feet. The connection speeds gets slower as the distance between the computer and the router increases A wireless access point connects a group of wireless devices to a wired Local Area Network, or LAN connection. The wireless access point then relays data between the connected devices. Before a device can connect to a Wi-Fi network, a wireless adapter will need to be present. Wireless adapter can connect to devices using PCI or miniPCI, USB, Cardbus, ExpressCard, and PC card. Once the device has a wireless adapter, you will need a wireless router to relay the signal to your adapter. The wireless router is connected to the high-speed modem with an Ethernet cable. Once the wireless router is connected, you should be able to receive a wireless signal as long as there is a wireless adapter on the device you wish to connect.

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