Rashmi New

Networking

NETWORKING CONCEPTS AND COMPONENTS Networking is the concept of sharing resources and services. A network of computer is a group of interconnected system sharing resources and interacting using a shared communication link. Networking is nothing but the connections of two or more computers connected in a group or by cable or other media. They can share information. Networks made sharing data much easier and more efficient for user. The shared resources can be data, a printer, fax modem messages or a service such as a database or an e-mail system. The individual system must be connected through a pathway called the transmission medium i.e. used to transmit the resource or service between computers. All system on the pathway must follow a set of communication routes for data to arrive at destination and fro sending – receiving system to understand each other the rules governed by the computer communication are called protocols. 1. All networks must have following resources to share. 2. A pathway to transfer data. 3. A set of rules to govern how to communicate (protocols). The two main reasons for computer network are to provide services and to reduce equipment cost. Following are the specific region for networking:1. Sharing files. 2. Sharing printers and other devices. 3. Enabling centralized administration and security of the resource within the system. 4. Supporting network application such as e-mail and database services.

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Network components include : 1. Server – It is a powerful computer that provides services to other computer connected at network. a) File server : Stores and retriused files b) Database server : Handle user database request and responses. c) Archive server : The system i.e. used to back up and archive files on the network. d) Print server : A system that print job sends (fired) user on the networks. 2. Client – A computer that use services that a server Provides. 3. Media – It is a physical connection between the devices on the network. 4. Users – Any person that uses a client to access the resources on a network. 5. Shared resources and peripherals – These are the devices that are available to the users on the networks. Example- Printer, Storage devices.

NETWORK TOPOLOGY Ramdeobaba Institute of Computer Application

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There are three network topologies. 1> Bus Topology 2> Ring Topology 3> Star Topology

1) Bus Topology :-

N1

N2

N3

Terminator

N4

Terminator T - Connector

Fig. : Bus Topology In bus topology, all computers are connected in a linear manner. All stations are attached with appropriate hardware, interfacing directly to a linear transmission area. Bus topology is used multipoint connects. Bus network is typically used when only a few micro-computers are to be linked together. This arrangement is common in system for electronic mail or for sharing data stored on different micro-computers. Advantages : 1. Simple, reliable and easy to use. 2. Requires the least amount of cables. 3. Cheaper when compared with other topology. Disadvantages : Ramdeobaba Institute of Computer Application

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1. Can be used only in relatively small networks. 2. All computers shared the same bus. Hence, an increase in number of computers degrades the performance of the networks after a certain limit. 3. A cable break or loose connector will cause reflection and bring down the entire network.

2) Ring Topology :N1

N2 Connector

N4

N3

Fig : Ring Topology In a ring topology, each computer is connected to the next computer and last one is

connected to the first to form a ring of computer.

The physical structure is a circular topology or a close loop of point – to – point links. Ring network passes a token. There is no central file servers or computers. Messages are passed around the ring until they reach the correct destination. Token :It is a short message with the electronic address of receiver. Each network interface card is given an unique address, which is used to identify the computer on the network.

Advantages : Ramdeobaba Institute of Computer Application

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1. No signal loss as in bus topology, since the token is regenerate at each node. 2. No terminator required. Disadvantages : 1. Difficult to troubleshoot. 2. Adding and removing computers disturb the entire network. 3. Expensive when compared with other topology.

3) Star Topology :N1

N2

HUB

N3

N4

Fig : Star Topology In star topology, all the cables are run from to a centrally located device called HUB. Star topology network requires a central point of connection between media segment. These central points are referred to as a HUB. HUB’s are special repeaters that overcome the electromechanical limitations of a media. Each computer on a star network communicates with central HUB that resend the message either to all the computers or only to the destination computer.

Advantages :

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1. Easy to modify and add new computers by simply adding a new cable, without disturbing the rest of network. 2. Easy to diagnose network fault. 3. Single computer failure does not affect the network. 4. Accommodated multiple cable type (Unshielded twisted pair cable, Shielded twisted pair cables and others). 5. Ready telephone cable can be used for this type. Disadvantages : 1. Failure of the central HUB bring the entire network down.

TYPES OF NETWORK Ramdeobaba Institute of Computer Application

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1.

Local Area Network :Local area networks, generally called LANs, are privately-owned

networks. They are widely used to connect personal computers and workstations in company offices and factories to share resources (e.g. printer) and exchange information. LANs are restricted in size, which means that the worst-case transmission time is bounded and known in advance. Knowing this bound makes it possible to use certain kinds of designs that would not otherwise be possible. It also simplifies network management. Various

topologies are possible for broadcast

LAN's. Figure shows two of them. a) Bus b) Ring.

Fig. Two broadcast networks a) Bus b) Ring

LAN is a communication network that interconnects a variety of devices and provides a means for information exchange among those devices. LAN’s come in a number of different configurations. The most common are : a) Switched LANs b) Wireless LANs a) Switched LANs :The most common switched LAN is a switched Ethernet LAN, which may consist of a single switch with a number of attached devices, or a number of

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interconnected switches. Two other prominent examples are ATM LAN’s, which simply use an ATM network in a local area, and Fibre Channel. b) Wireless LANs :Wireless LAN use a variety of wireless transmission technologies and organizations. LAN is a group of computers and a network communication device interconnected with a geographically limited area such as a building or a campus. A computer communication technology is classified as a local area network if it provides a way to interconnect multiple computers across short distance. Local area networks are inexpensive, highly reliable and convenient to install and manage. Local area network are characterized by following : 1. They transfer data at high speed (higher bandwidth). 2. They exist in a limited geographical area such as a building or campus. 3. The connecting lines linking more than one computer cover a small area upto 10 km. Thus data on network does not travel long distance. 4. If one computer connected to a LAN is down, other computers can still communicate. 5. LAN permits sharing of data, hardware and software between all computers connected to it. LANs are distinguished from other kinds of networks by three characteristics: 1. their size 2. their transmission technology 3. their topology

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2.

Wide Area Network :Wide area networks generally cover a large geographical area, require

the crossing of public right-of-ways, and rely at least in part on circuits provided by a common carrier. Typically, a WAN consists of a number of interconnected switching nodes. A transmission from any one device is routed through these internal nodes to the specified destination device. These nodes(including the boundary nodes) are not concerned with the content of data; rather, their purpose is to provide a switching facility that will move the data from node to node until they reach their destination.

Fig : Relation between hosts on LAN's and the subnet

Traditionally, WANs have been implemented using one of two technologies: circuit switching and packet switching. More recently, frame relay and ATM networks have assumed major rules. Wan contains a collection of machines intended for running user programs. We follow traditional usage and call these machine hosts. The host are connected by communication subnet, or just subnet for short. The host are owned by customers (e.g. peoples personal computers), whereas the communication subnet is typically owned and operated by a telephone company or Internet service provider. The job of the subnet is to carry messages from host to host, just as the telephone system carries words from speaker to listener.

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The wide area network interconnects local area networks. A wide area network can be located entirely within a state or a country. It can be interconnected around the world. A way to build a network that connects multiple computers across a large geographic distance called wide area network. Wide area network are characterized by following : 1. They exist in an unlimited geographical area. 2. They usually interconnect multiple local area network. 3. They often transfer at low speed(lower bandwidth). 4. Connectivity and resources- Specially the transmission media usually managed by a third particular such as a telephone or a cable company. Wide area network can be further classified into two categories :a) Enterprise WAN b) Global WAN a) Enterprise WAN – An enterprise WAN connects widely separated computer resources of a single organization. b) Global WAN A global WAN interconnects network of several corporation or organization.

3) Metropolitan Area Network :As the name suggests, a MAN occupies a middle ground between LANs and WANs. Interest in MANs has come about as a result of a recognition that the traditional point-to-point and switched network techniques used in WANs may be inadequate for the growing need of organizations. While frame relay and ATM promise to meet a wide range of high-speed needs, there is a requirement now for Ramdeobaba Institute of Computer Application

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both private and public networks that provide high capacity at low costs over a large area. A number of approaches have been implemented, including wireless networks and metropolitan extensions to Ethernet. The primary market for MANs is the customer that has high capacity needs in a metropolitan area. A MAN is intended to provide the required capacity at lower cost and greater efficiency than obtaining an equivalent service from the local telephone company. The term metropolitan is referred to as city i.e. it covers a city. The best known example of a MAN is the cable television network available in many cities. This system grew from earlier community antenna systems used in areas with poor over-the-air television reception. In this early systems, a large antenna was placed on top of a nearby hill and signal was then piped to the subscribers’ houses. Starting when the Internet attracted a mass audience, the cable TV network operators began to realize that with some changes to the system, they could provide two-way Internet service in unused parts of the spectrum. To a first approximation, a MAN might look something like the system shown in fig. below. In this figure we see both television signals and Internet being fed into the centralized head end for subsequent distribution to people’s homes. This network covers a large geographic area limited within a city or a town. It provides a communication between different business house or bank branches located at different area.

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Fig: A Metropolitan area network based on cable TV

Characteristics : 1. The scope of network covers a large geographic area including different branches of a particular bank in a metropolitan city. 2. Since it connect different location, the set up is comparatively complex as compared to LAN. 3. It has ability to connect various LAN’s in the city.

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PROTOCOLS The networking protocol starts the communication process between computers. A protocol is a set of rule created for the process of communication with another computer or with an operating system. Protocol exists at several levels in the OSI communication model. Network protocol govern the way actual transmission is handled. In the world of networking and data communication, different types of computer communicate with each other with the help of different protocols. A protocol is a set of rules or convention that govern the generation, formatting, control and interpretation of information i.e. transmitted through a network or i.e. stored in a database. Basically, a protocol defines what is communicated, how it is send, when it is transmitted. Syntax, semantics, and timing are the key protocol elements. Syntax describes the order structure or format of the data. Semantics refers to the meaning of a structured block of bits. Timing describes when data should be send and at what rate. REFERENCE MODELS : There are two important network architectures :1) OSI reference model. 2) TCP/IP reference model.

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THE OSI REFERENCE MODEL The OSI model helps computer communicate with other computers over different networks without any error and allows systematic reduction of complexity. In 1977,the ISO developed the OSI model for computer communication. The OSI model can be used to understand the complex interaction that take place between various devices on a network. The OSI model is a theoretical model. It does not function in the communication process. The appropriate hardware and software do the actual work. The models simply define which protocol will handle those task. The protocols associated with the OSI model are rarely used any more, the model itself is actually quite general and valid, and the features discussed at each layer are very important. The OSI model is shown in fig. This model is based on a proposal developed by the International Standards Organization (ISO) as a first step toward international standardization of the protocols used in the various layers by Day and Zimmermann in 1983. It was revised in 1995 by Day. This model is called the ISO OSI (Open Systems Interconnection) Reference Model because it deals with connecting open systems - that is, systems that are open for communication with other systems. It is called the OSI model in short. The OSI model breaks down the task of communication into seven independent function performed by seven independent layers. Each layer talk to the neighbouring layer. It is a model for understanding and designing a network architecture i.e. flexible and robust. Those seven layers are:1> The Physical Layer 2> The Data Link Layer 3> The Network Layer 4> The Transport Layer 5> The Session Layer 6> The Presentation Layer 7> The Application Layer Ramdeobaba Institute of Computer Application

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Fig: The OSI reference model

The principles that were applied to arrive at these seven layers is summarized as follows : 1. A layer should be created where a different abstraction is needed. 2. Each layer should perform a well-defined function. 3. The function of each layer should be chosen with an eye toward defining internationally standardized protocols. 4. The layer boundaries should be chosen to minimize the information flow across the interfaces. 5. The number of layers should be large enough that distinct functions need not be thrown together in the same layer out of necessity and small enough that the architecture does not become unwieldy.

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Now, we will discuss each layer of the model in turn, starting at the bottom layer. Actually, the OSI model itself is not a network architecture because it does not specify the exact services and protocols to be used in each layer. It just tells what each layer should do. However, ISO has also produced standards for all the layers, although these are not part of the reference model itself. Each one has been published as a separate international standard. 1> The Physical Layer The physical layer is the lowest layer of the model and is responsible for sending bits (Binary digits) physically from one computer to another. This layer deals with only the physical characteristics of the network and with transmitting and receiving transmission signals. It defines the physical and electrical details such as what 1 and 0 represent, how data will synchronize and when the network interface may or may not transmit the data. The devices in physical layers are : i) HUB’s ii) Connectors iii)Cable iv) Multiplexer The physical layer is concerned with transmitting raw bits over a communication channel. The design issues have to do with making sure that when one side sends a one bit, it is received by the other side as a one bit, not as a zero bit. Typical questions here are : i) How many volts should be used to represent a one and how many for a zero. ii) How many nanoseconds a bit lasts. iii) Whether transmission may proceed simultaneously in both directions.

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iv) How the initial connection is established and how it is torn down when both sides are finished. v) How many pins the network connector has and what each pin is used for. The design issues here largely deal with mechanical, electrical, and timing interfaces, and the physical transmission medium, which lies below the physical layer. 2> The Data Link Layer The data link layer is responsible for ensuring error free and reliable transmission of data to the immediate link. It accepts packets from the network layer, packages the information into data units called frames and send them to the physical layer for transmission. The data link layer at control information such as frame type and segmentation information to the data being send. This layer provides error free transfer of frame from one computer to another. It also request fro retransmission of frame in case of disturbance in the transmission. The devices in data link layer are: ii)

Bridges

ii) Intelligent HUB’s The main task of the data link layer is to transform a raw transmission facility into a line that appears free of undetected transmission errors to the network layer. It accomplishes this task by having the sender break up the input data into data frames (typically a few hundred or a few thousand bytes) and transmit the frame sequentially. If the service is reliable, the receiver confirms correct receipt of each frame by sending back an acknowledgement frame. Another issue that arises in the data link layer(and most of the higher layers as well) is how to keep a fast transmitter from drowning a slow receiver in data. Some Ramdeobaba Institute of Computer Application

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traffic regulation mechanism is often needed to led the transmitter know how much buffer space the receiver has at the moment. Frequently, this low regulation and the error handling are integrated. Broadcast networks have an additional issue in the data link layer: how to control access to the shared channel. A special sub layer of the data link layer, the medium access control sub layer deals with this problem. 3> The Network Layer The network layer is responsible for setting up an appropriate routine of data throughout network. It also forwards the packet when the link between the two networks is not direct link but has one or more intermediate link for the transport. Network layer helps the transport layer and layer above it to send packet without being concern about whether the destination is adjacent or away. Network layer uses devices like a router and get way. The network layer controls the operation of the subnet. A key design issue is determining how packets are routed from source to destination. Routes can be based on static tables that are “wired into” the network and rarely changed. They can also be determined at the start of each conversation, for example, a terminal session (e.g., a login to a remote machine). Finally they can be highly dynamic, being determined a new for each packet, to reflect the current network load. If too many packets are present in the subnet at the same time, they will get in one another’s way, forming bottlenecks. The control of such congestion also belongs to the network layer. More generally, the quality of service provided (delay, transit time, jitter, etc.) is also a network layer issue. When a packet has to travel from one network to another to get its destination, many problems can arise. The addressing used by the second network can be different from the first one. The second one may not accept the packet at all because Ramdeobaba Institute of Computer Application

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it is too large. The protocols may differ, and so on. It is up to the network layer to overcome all these problems to allow heterogeneous networks to be interconnected. In broadcast networks, the routine problem is simple, so the network layer is often thin or even nonexistent. 4> The Transport Layer The transport layer ensure that packets are delivers error free in a sequence, with no losses and duplication. The transport layer breaks large message from the session layer into packets to be send in the destination computer and reassembled packets into their origin form to be presented to the session layer. The transport layer sends an acknowledgement to the originator for packets that are received. The basic function of the transport layer is to accept data from above, split it up into smaller units if need be, pass these to the network layer, and ensure that the pieces all arrive correctly at the other end. Furthermore, all this must be done efficiently and in a way that isolates the upper layer from the inevitable changes in the hardware technology. The transport layer also determines what type of service to provide to the session layer, and ultimately, to the users of the network. The most popular type of transport connection is an error-free point-to-point channel that delivers messages or bytes in the order in which they were sent. However, other possible kinds of transport service are the transporting of isolated messages, with no guarantee about the order of delivery, and the broadcasting of messages to multiple destinations. The type of service is determined when the connection is established. As an aside, an error-free channel is impossible to achieve; what people really mean by this term is that the error rate is low enough to ignore in practice. The transport layer is a true end-to-end layer, all the way from the source to the destination. In other words, a program on the source machine carries on a Ramdeobaba Institute of Computer Application

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conversation with a similar program on the destination machine, using the message headers and control messages. In the lower layers, the protocols are between each machine and its immediate neighbors, and not between the ultimate source and destination machines, which may be separated by many routers. The difference between layers one through three, which are chained, and layers four through seven, which are end-to-end, is illustrated in above fig. 5> The Session Layer The session layer is responsible for requesting a logical connection to be established for the communication process. This shared connection is called a session. This layer provides for data synchronization between user’s task by placing checkpoint so that, in the event of a network failure only the data send after the point of failure needs to be resent. Services such as name, look up, security, allowing two programs to find each other and establishing the communication link are also provided by this layer. This layer controls the dialogue between two processes, determine who can transmit and who can receive at what point of time during the communication. The session layer allows users on different machines to establish sessions between them. Sessions offer various services, including dialog control(keeping track of whose turn it is to transmit), token management (preventing two parties from attempting the same critical operation at the same time), and synchronization (checkpointing long transmissions to allow them to continue from where they were after a crash)

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6> The Presentation Layer The presentation layer translates or format data to adapt to the needs of the application layer and node at both the receiving and the sending ends of communication process. The presentation layer does the protocol conversions, data translation, formatting, compression, encryption, and character set conversion. It also interprets graphics command. Unlike lower layers, which are mostly concerned with moving bits around, the presentation layer is concerned with the syntax and semantics of the information transmitted. In order to make it possible for computers with different data representations to communicate, the data structures to be exchanged can be defined in an abstract way; along with a standard encoding to be used ”on the wire.” The presentation layer manages these abstract data structures and allows higher level data structures(e.g., banking records), to be defined and exchanged. 7> The Application Layer The application layer is the topmost layer of the OSI model and provide user access to the network. It provided services that directly support user application such as database access e-mail and file transfer. It allows application on one computer to communicate with application on other computer as though the application were on the same computer. The application layer contains a variety of protocols that are commonly needed by users. One widely-used application protocol is HTTP(Hyper Text Transfer Protocol), which is the basis of World Wide Web. When a browser wants a Web page, it sends the name of the page it wants to the server using HTTP. The server then sends the page back. Other application protocols are used for file transfer, electronic mail, and network news. Ramdeobaba Institute of Computer Application

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CONTENTS Sr. No. 1 2

Particulars Networking concepts and components Network Topology

Page No. 1 3

 Bus Topology  Ring Topology 3

 Star Topology Types of Network

7

 LAN  WAN 4 5

 MAN Protocols The OSI reference model  The Physical Layer  The Data link Layer  The Network Layer  The Transport Layer  The Session Layer  The Presentation Layer  The Application Layer

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