Bachelor of Computer Applications (Part-III)

1. Introduction: Network Definition, Basic components of a network, network types and topologies, Uses of computer networks, network architecture. Transmission Media: Coaxial cable, twisted pair cable, fibre optics & satellites. OSI referable model, TCP/IP references model, comparison of OSI and TCP reference model.

2. Introduction to Analog and Digital Transmission: Telephone system, Modems, Types of modems, pulse code modulation. Transmission & Switching: Multiplexing, circuit switching packet switching, hybrid switching, ISDN service transmission.

3. Local Area Network Protocols: CSMA Protocols, BRAP, MLMA, IEEE standards 602, Token Bus, Token Ring, FDDI.

4. Data Link Layer Design Issues: Services provided to Network layer framing, error control, flow control, link management. Error detection & correction, Elementary Datalink Protocols.

5. Design Issues of Network Layer: Services provided to transport layer, routing, connection, internet & world wide web.

6. Network Security and Privacy: Brief Introduction to Cryptography. 7. Network Services: File transfer, Access & Management, Electronic

Mail, Remote logic

Unit 1

1. Introduction: Network Definition, Basic components of a network, network types and topologies, Uses of computer networks, network architecture. Transmission Media: Coaxial cable, twisted pair cable, fibre optics & satellites. OSI referable model, TCP/IP references model, comparison of OSI and TCP reference model.

Networking

• A computer network is a group of interconnected computers. Networks may be classified according to a wide variety of characteristics.

• In the world of computers, networking is the practice of linking two or more computing devices together for the purpose of sharing data. Networks are built with a mix of computer hardware and computer software.

Network Classification

• The following list presents major categories used for classifying networks.

• Local Area Network (LAN),

• Wide Area Network (WAN),

• Metropolitan Area Network (MAN).

Connection method/ Transmission Media

Computer networks can also be classified according to the hardware technology that is used to connect the individual devices in the network such as:

• Coaxial cable• Twisted pair cable• Fibre optics• satellites • Ethernet,• Wireless LAN.

Optical Fiber

• An optical fiber (or fibre) is a glass or plastic fiber that carries light along its length. Fiber optics is the overlap of applied science and engineering concerned with the design and application of optical fibers. Optical fibers are widely used in fiber-optic communications, which permits transmission over longer distances and at higher data rates ("bandwidth"), than other forms of communications. Fibers are used instead of metal wires because signals travel along them with less loss, and they are immune to electromagnetic interference. Optical fibers are also used to form sensors, and in a variety of other applications.

Coaxial cable

Coaxial cable is a cable consisting of an inner conductor, surrounded by a tubular insulating layer typically made from a flexible material with a high dielectric constant, all of which is then surrounded by another conductive layer (typically of fine woven wire for flexibility, or of a thin metallic foil), and then finally covered again with a thin insulating layer on the outside. The term coaxial comes from the inner conductor and the outer shield sharing the same geometric axis. Coaxial cables are often used as a transmission line for radio frequency signals.

Coaxial cable

Twisted pair cable

Twisted pair cable

Twisted pair cabling is a form of wiring in which two conductors (two halves of a single circuit) are wound together for the purposes of canceling out electromagnetic interference (EMI) from external sources; for instance, electromagnetic radiation from unshielded twisted pair (UTP) cables, and crosstalk between neighboring pairs. Twisting wires decreases interference because the loop area between the wires (which determines the magnetic coupling into the signal) is reduced. In

Fibre optics

Fibre optics

• An optical fiber (or fibre) is a glass or plastic fiber that carries light along its length. Fiber optics is the overlap of applied science and engineering concerned with the design and application of optical fibers. Optical fibers are widely used in fiber-optic communications, which permits transmission over longer distances and at higher data rates (a.k.a "bandwidth"), than other forms of communications. Fibers are used instead of metal wires because signals travel along them with less loss, and they are immune to electromagnetic interference. Optical fibers are also used to form sensors, and in a variety of other applications.

satellites

• In the context of spaceflight, a satellite is an object which has been placed into orbit by human endeavor. Such objects are sometimes called artificial satellites to distinguish them from natural satellites such as the Moon.

Ethernet :Ethernet uses physical wiring to connect devices. Often deployed devices are hubs, switches, bridges, and/or routers.

Wireless LAN: Wireless LAN technology is designed to connect devices without wiring. These devices use radio waves as transmission medium.

Network topology

• Network Topology signifies the way in which devices in the network see their logical relations to one another. The use of the term "logical" here is significant. That is, network topology is independent of the "physical" layout of the network. Even if networked computers are physically placed in a linear arrangement, if they are connected via a hub, the network has a Star topology, rather than a Bus Topology. In this regard the visual and operational characteristics of a network are distinct; the logical network topology is not necessarily the same as the physical layout.

Network topology

Computer networks may be classified according to the network topology upon which the network is based, such as:

• Bus network,• Star network,• Ring network,• Mesh network,• Star-bus network,• Tree or Hierarchical topology network.

Bus Topology

• A bus topology connects computers along a single or more cable to connect linearly as figure 1. A network that uses a bus topology is referred to as a "bus network" which was the original form of Ethernet networks

Ring Topology

Ring Topology

• Each computer in the ring examines all messages, passes them on if they are not the destination node. If no computer accepts a message, it returns to the sender, which removes it from the ring.

• All clients have equal access to data. This gives even performance under heavy demand conditions.Difficult to add another host to the ring.

Start Topology

Star Topology

• All signals are directed through the central hub.

• Reduces risk of failure. Expanding the network is simple. Managing the network is centralised. If the hub breaks down, the system fails.

Hybrid Topology

Hybrid Topology

• A series of star topologies with the hubs connected by a bus trunk (the backbone of the network).

• Network expansion is simple. If one client fails, the entire network does not fail. If one hub fails, all connections to that hub fail, although other hubs continue to function.

Mesh Topology

• Mesh topologies are networks in which many paths connect computers.

• This redundancy allows the system to continue if some connections fail. However, multiple connections are expensive.

Types of networks

Below is a list of the most common types of computer networks in order of scale:

• Local Area Network (LAN)

• Wide Area Network (WAN)

• Metropolitan Area Network (MAN)

Local Area Network (LAN)

• A network covering a small geographic area, like a home, office, or building. Current LANs are most likely to be based on Ethernet technology. For example, a library may have a wired or wireless LAN for users to interconnect local devices (e.g., printers and servers) and to connect to the internet.

Wide Area Network (WAN)

A WAN is a data communications network that covers a relatively broad geographic area (i.e. one city to another and one country to another country) and that often uses transmission facilities provided by common carriers, such as telephone companies. WAN technologies generally function at the lower three layers of the OSI reference model: the physical layer, the data link layer, and the network layer

Metropolitan Area Network (MAN)

• A Metropolitan Area Network is a network that connects two or more Local Area Networks or Campus Area Networks together but does not extend beyond the boundaries of the immediate town/city. Routers, switches and hubs are connected to create a Metropolitan Area Network.

Internetwork • Two or more networks or network segments connected using devices, such

as a router. Any interconnection among or between public, private, commercial, industrial, or governmental networks may also be defined as an internetwork.

• In modern practice, the interconnected networks use the Internet Protocol. There are at least three variants of internetwork, depending on who administers and who participates in them:

• Intranet • Extranet • Internet

• Intranets and extranets may or may not have connections to the Internet. If connected to the Internet, the intranet or extranet is normally protected from being accessed from the Internet without proper authorization. The Internet is not considered to be a part of the intranet or extranet, although it may serve as a portal for access to portions of an extranet.

Intranet

• An intranet is a set of networks, using the Internet Protocol and IP-based tools such as web browsers and file transfer applications, that is under the control of a single administrative entity. That administrative entity closes the intranet to all but specific, authorized users. Most commonly, an intranet is the internal network of an organization. A large intranet will typically have at least one web server to provide users with organizational information.

Extranet

• An extranet is a network or internetwork that is limited in scope to a single organization or entity but which also has limited connections to the networks of one or more other usually, but not necessarily, trusted organizations or entities (e.g. a company's customers may be given access to some part of its intranet creating in this way an extranet, while at the same time the customers may not be considered 'trusted' from a security standpoint).

Internet• The Internet is a specific internetwork. It consists of a worldwide

interconnection of governmental, academic, public, and private networks based upon the networking technologies of the Internet Protocol Suite. The Internet is also the communications backbone underlying the World Wide Web (WWW). The 'Internet' is most commonly spelled with a capital 'I' as a proper noun, for historical reasons and to distinguish it from other generic internetworks.\

• Participants in the Internet use a diverse array of methods of several hundred documented, and often standardized, protocols compatible with the Internet Protocol Suite and an addressing system (IP Addresses) administered by the Internet Assigned Numbers Authority and address registries. Service providers and large enterprises exchange information about the reachability of their address spaces through the Border Gateway Protocol (BGP), forming a redundent world-wide mesh of transmission paths.

Basic Hardware Components in Networking

All networks are made up of basic hardware building blocks to interconnect network nodes, such as:

• Network Interface Cards (NICs),• Bridges,• Hubs,• Switches, and• Routers

Repeater

• A repeater is an electronic device that receives a signal and retransmits it at a higher level or higher power, or onto the other side of an obstruction, so that the signal can cover longer distances without degradation. In most twisted pair ethernet configurations, repeaters are required for cable runs longer than 100 meters away from the computer .

Network Interface Cards (NICs)

• A network card, network adapter or NIC (network interface card) is a piece of computer hardware designed to allow computers to communicate over a computer network. It provides physical access to a networking medium and often provides a low-level addressing system through the use of MAC addresses. It allows users to connect to each other either by using cables or wirelessly.

Bridges• A network bridge connects multiple network segments. Bridges do

not promiscuously copy traffic to all ports, as hubs do. Once the bridge associates a port and an address, it will send traffic for that address only to that port. Bridges do send broadcasts to all ports except the one on which the broadcast was received.

• Bridges come in three basic types:

• Local bridges: Directly connect local area networks (LANs) • Remote bridges: Can be used to create a wide area network (WAN)

link between LANs. Remote bridges, where the connecting link is slower than the end networks, largely have been replaced by routers.

• Wireless bridges: Can be used to join LANs or connect remote stations to LANs.

Hubs

• A hub contains multiple ports. When a packet arrives at one port, it is copied to all the ports of the hub for transmission. When the packets are copied, the destination address in the frame does not change to a broadcast address. It does this in a rudimentary way, it simply copies the data to all of the Nodes connected to the hub.

Switches

• A switch is a device that performs switching. Specifically, it forwards and filters (chunk of data communication) between ports (connected cables). This is distinct from a hub in that it only forwards the datagrams to the ports involved in the communications rather than all ports connected. Strictly speaking, a switch is not capable of routing traffic based on IP address which is necessary for communicating between network segments or within a large or complex LAN. Some switches are capable of routing based on IP addresses but are still called switches as a marketing term. A switch normally has numerous ports with the intention that most or all of the network be connected directly to a switch, or another switch that is in turn connected to a switch.

Routers

• Routers are networking devices that forward data packets between networks using headers and forwarding tables to determine the best path to forward the packets. Routers also provide interconnectivity between like and unlike media . They use preconfigured static routes, status of their hardware interfaces, and routing protocols to select the best route between any two subnets. A router is connected to at least two networks, commonly two LANs or WANs or a LAN and its ISP's network.

Routers

• Interconnect dissimilar subnetworks– Provide a link between networks– Provide for routing and delivery of data between processes on

end systems attached to different networks– Do not require modifications of architecture of subnetworks

• Must accommodate differences among networks– Addressing schemes– Maximum packet sizes– Interfaces– Reliability 

• Satisfied by internetworking protocol implemented in all end systems and routers– IP

Network architecture

Network architecture In computing, network architecture is the design of a computer network. In telecommunication, the term network architecture has the following meanings:

• The design principles, physical configuration, functional organization, operational procedures, and data formats used as the bases for the design, construction, modification, and operation of a communications network.

• The structure of an existing communications network, including the physical configuration, facilities, operational structure, operational procedures, and the data formats in use.

• It outlines the products and services required in data communication networks.

OSI referable model

• The Open Systems Interconnection Basic Reference Model (OSI Reference Model or OSI Model) is an abstract description for layered communications and computer network protocol design. It was developed as part of the Open Systems Interconnection (OSI) initiative. In its most basic form, it divides network architecture into seven layers which, from top to bottom, are the Application, Presentation, Session, Transport, Network, Data-Link, and Physical Layers. It is therefore often referred to as the OSI Seven Layer Model.

• A layer is a collection of conceptually similar functions that provide services to the layer above it and receives service from the layer below it. For example, a layer that provides error-free communications across a network provides the path needed by applications above it, while it calls the next lower layer to send and receive packets that make up the contents of the path

OSI referable model

OSI referable model

OSI referable model

OSI Layers

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An Exchange Using the OSI Model

Physical Layer

Physical Layer

Provides physical interface for transmission of information.

Defines rules by which bits are passed from one system to another on a physical communication medium.

Covers all - mechanical, electrical, functional and procedural - aspects for physical communication.

Such characteristics as voltage levels, timing of voltage changes, physical data rates, maximum transmission distances, physical connectors, and other similar attributes are defined by physical layer specifications.

Data Link Layer

Data Link Layer

Data link layer attempts to provide reliable communication over the physical layer interface.

Breaks the outgoing data into frames and reassemble the received frames.Create and detect frame boundaries.Handle errors by implementing an acknowledgement and retransmission scheme.Implement flow control.Supports points-to-point as well as broadcast communication.Supports simplex, half-duplex or full-duplex communication.

Data Link Layer Example

Network Layer

Network Layer

Implements routing of frames (packets) through the network.

Defines the most optimum path the packet should take from the source to the destinationDefines logical addressing so that any endpoint can be identified. Handles congestion in the network.Facilitates interconnection between heterogeneous networks (Internetworking).The network layer also defines how to fragment a packet into smaller packets to accommodate different media.

TCP/IP references model

• Developed by the US Defense Advanced Research Project Agency (DARPA) for its packet switched network (ARPANET)

• Used by the global Internet• No official model but a working one.

– Application layer– Host to host or transport layer– Internet layer– Network access layer– Physical layer

TCP/IP references modelApplication Layer

Application programs using the networkTransport Layer (TCP/UDP)

Management of end-to-end message transmission,error detection and error correction

Network Layer (IP)Handling of datagrams : routing and congestion

Data Link LayerManagement of cost effective and reliable data delivery,

access to physical networks

Physical LayerPhysical Media

Comparison of OSI & TCP/IP Models

TCP/IP Model

comparison of OSI and TCP reference model.