Computer Networks And Communication Systems Computer Science Essay

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A network consists of multiple computers connected using some type of interface, each having one or more interface devices such as a Network Interface Card (NIC) and/or a serial device for PPP networking. Each computer is supported by network software that provides the server or client functionality. The hardware used to transmit data across the network is called the media. It may include copper cable, fiber optic, or wireless transmission. The standard cabling used for the purposes of this document is 10Base-T category 5 ethernet cable.

This is twisted copper cabling which appears at the surface to look similar to TV coaxial cable. It is terminated on each end by a connector that looks much like a phone connector. Its maximum segment length is 100 meters.

The importance of having a computer network

1) For reliable and secure data communication.

2) To share the resources such as disk space,printers,scanners and many more physical resources.

3) To reduce the extra cost

4) To share information.


Routing or routeing is the process of selecting paths in a network along which to send network traffic. Routing is performed for many kinds of networks, including the telephone network (Circuit switching) , electronic data networks (such as the Internet), and transportation networks. This article is concerned primarily with routing in electronic data networks using packet switching technology.

In packet switching networks, routing directs packet forwarding, the transit of logically addressed packets from their source toward their ultimate destination through intermediate nodes, typically hardware devices called routers, bridges, gateways, firewalls, or switches. General-purpose computers can also forward packets and perform routing, though they are not specialized hardware and may suffer from limited performance. The routing process usually directs forwarding on the basis of routing tables which maintain a record of the routes to various network destinations. Thus, constructing routing tables, which are held in the router's memory, is very important for efficient routing. Most routing algorithms use only one network path at a time, but multipath routing techniques enable the use of multiple alternative paths.

Routing, in a more narrow sense of the term, is often contrasted with bridging in its assumption that network addresses are structured and that similar addresses imply proximity within the network. Because structured addresses allow a single routing table entry to represent the route to a group of devices, structured addressing (routing, in the narrow sense) outperforms unstructured addressing (bridging) in large networks, and has become the dominant form of addressing on the Internet, though bridging is still widely used within localized environments.

First we'll look at the main routing strategies

I. Fixed Routing

II. Flooding

III. Random Routing

IV. Adaptive Routing

Fixed routing

In this routing strategy a central database is maintained.

Single permanent route for each source to destination pair

Determine routes using a least cost algorithm.

Route fixed, at least until a change in network topology.

In this method updating new information is easy as it is to be done from a single place.But the disadvantages are each an every ip packet should be analyzed and Network traffic may increase at the central database because it has to serve lots of requests from routers.


In this scenario When an IP packet comes to a router, router will send it on all paths.

' No network info required

' Packet sent by node to every neighbor

' Incoming packets retransmitted on every link except incoming link

' Eventually a number of copies will arrive at destination

' Each packet is uniquely numbered so duplicates can be discarded

' Nodes can remember packets already forwarded to keep network load in bounds

' Can include a hop count in packets

This is a simple mechanism and most probably it will reach the destination.But the disadvantages are

1. Cusing high network traffic

2. Duplicate packets might reach the


Random Routing

When an IP packet comes to the router, it decides the path randomly and sends the IP packet in that path

' Node selects one outgoing path for retransmission of incoming packet.

' Selection can be random or round robin.

' Can select outgoing path based on probability calculation

' No network info needed.

' Route is typically not least cost nor minimum hop.

This is a simple method and it won't make unnecessary network traffic.

But in the other hand there is no guarantee that the IP packet will reach the destination.

Adaptive Routing

In this routing strategy Each router maintains a routing table.

And it can be adapted according to the network changes.

' Improved performance

' Aid congestion control

' Complex system

Here the network traffic is minimized and the best router will be selected most of the time.

The disadvantages in this method is it needs to process each IP paket,routers need to keep a routing table maintained.

Routing Methods used in Adaptive Routing

? Next hop routing

? Host specific

? Network specific

? Default routing

Routing table

In computer networking a routing table, or Routing Information Base (RIB), is a data structure in the form of a table-like object stored in a router or a networked computer that lists the routes to particular network destinations, and in some cases, metrics associated with those routes. The routing table contains information about the topology of the network immediately around it. The construction of routing tables is the primary goal of routing protocols. Static routes are entries made in a routing table by non-automatic means and which are fixed rather than being the result of some network topology 'discovery' procedure.

Routing tables are generally not used directly for packet forwarding in modern router architectures; instead, they are used to generate the information for a smaller forwarding table which contains only the routes which are chosen by the routing algorithm as preferred routes for packet forwarding, often in a compressed or pre-compiled format that is optimized for hardware storage and lookup. The remainder of this article will ignore this implementation detail, and refer to the entire routing/forwarding information subsystem as the "routing table".

Routing Table update Methods

? Connected

(Once the router is connected to the network its interfaces are given IP addresses)

? Static

(Administrator can manually give routing table records)

? Dynamic

(Using some protocols (set of rules) routing tables are updated automatically

routing protocols

A routing protocol is a protocol that specifies how routers communicate with each other, disseminating information that enables them to select routes between any two nodes on a computer network, the choice of the route being done by routing algorithms. Each router has a priori knowledge only of networks attached to it directly. A routing protocol shares this information first among immediate neighbors, and then throughout the network. This way, routers gain knowledge of the topology of the network.

? Routing Protocols allow routers to dynamically advertise and learn routes, determine which routes are available and which are the most efficient routes to a destina

Interior routing protocols

Interior Gateway Protocols (IGPs) exchange routing information within a single routing domain. A given autonomous system can contain multiple routing domains, or a set of routing domains can be coordinated without being an Internet-participating autonomous system. Common examples include:

' IGRP (Interior Gateway Routing Protocol)

' EIGRP (Enhanced Interior Gateway Routing Protocol)

' OSPF (Open Shortest Path First)

' RIP (Routing Information Protocol)

' IS-IS (Intermediate System to Intermediate System)

? In this assignment we'll mainly look in to IGRP and RIP protocols.

IGRP (Interior Gateway Routing Protocol)

Interior Gateway Routing Protocol (IGRP) is a distance vector interior routing protocol. It is used by routers to exchange routing data within an autonomous system.

IGRP was created in part to overcome the limitations of RIP (maximum hop count of only 15, and a single routing metric) when used within large networks. IGRP supports multiple metrics for each route, including bandwidth, delay, load, MTU, and reliability; to compare two routes these metrics are combined together into a single metric, using a formula which can be adjusted through the use of pre-set constants. The maximum hop count of IGRP-routed packets is 255 (default 100), and routing updates are broadcast every 90 seconds (by default).

RIP (Routing Information Protocol)

The Routing Information Protocol (RIP) is a dynamic routing protocol used in local and wide area networks. As such it is classified as an interior gateway protocol (IGP). It uses the distance-vector routing algorithm.

RIP has also been adapted for use in IPv6 networks, a standard known as RIPng (RIP next generation) protocol, published in RFC 2080 (1997).

Comparison RIP/IGRP

This section compares IGRP with RIP. This comparison is useful because RIP is used widely for purposes similar to IGRP. However, doing this is not entirely fair. RIP was not intended to meet all of the same goals as IGRP. RIP was intended for use in small networks with reasonably uniform technology. In such applications it is generally adequate.

The most basic difference between IGRP and RIP is the structure of their metrics. Unfortunately this is not a change that can simply be retrofitted to RIP. It requires the new algorithms and data structures present in IGRP.


A network switch or switching hub is a computer networking device that connects network segments.

The network switch plays an integral part in

most modern Ethernet local area networks (LANs).

Switches may operate at one or more layers of the OSI model, including data link, network, or transport (i.e., end-to-end). A device that operates simultaneously at more than one of these layers is known as a multilayer switch.

The TCP/IP Protocol Suite

The TCP/IP protocol suite, also referred to as the Internet

protocol suite, is the set of communications protocols that

implements the protocol stack on which the Internet and most

commercial networks run. It is named after the two most

important protocols in the suite: the Transmission Control

Protocol (TCP) and the Internet Protocol (IP).

Transmission Control Protocol

In the TCP/IP protocol suite, TCP is the intermediate layer between IP below it, and an application above it. Using TCP,applications on networked hosts can establish reliable connections to one another. The protocol guarantees in-orde delivery of data from the sender to the receiver.

Basic Protocol Operation

The Transmission Control Protocol is connection-oriented,

meaning user data is not exchanged between TCP peers until a

connection is established between the two end points. This

connection exists for the duration of the data transmission.

TCP connections have three phases:

1. Connection establishment

2. Data transfer

3. Connection termination

The Internet Protocol

The Internet Protocol (IP) is a data-oriented protocol used for

communicating data across a network. It is a best effort protocol;it does not guarantee delivery. It also makes no guarantee as to the correctness of the data it transports. Transmission using IP may result in duplicated packets and/or packets out-of-order. All of these contingencies are addressed by an upper layer protocol

(For example, TCP) for applications that require reliable delivery.

Virtual LAN

A virtual local area network, virtual LAN or VLAN, is a group of hosts with a common set of requirements that communicate as if they were attached to the same broadcast domain, regardless of their physical location. A VLAN has the same attributes as a physical local area network (LAN), but it allows for end stations to be grouped together even if they are not located on the same network switch. LAN membership can be configured through software instead of physically relocating devices or connections.

? VLAN has a switched network that

is logically segmented

? Each switch port can be assigned

to a VLAN

? Ports that do not belong to that

VLAN do not share these broadcasts

Technologies able to implement VLANs are

' Asynchronous Transfer Mode (ATM)

' Fiber Distributed Data Interface (FDDI)

' Ethernet

' Fast Ethernet

' Gigabit Ethernet

' 10 Gigabit Ethernet

As we have seen there are significant advances in the field of networks in the form of VLAN's which allow the formation of virtual workgroups, better security, improved performance, simplified administration, and reduced costs.

Spanning Tree Algorithm


STP is a Data Link Layer protocol. The Spanning Tree Protocol (STP) ensures a loop-free topology for any bridged Ethernet local area network. The basic function of STP is to prevent bridge loops and ensuing broadcast radiation. Spanning tree also allows a network design to include spare (redundant) links to provide automatic backup paths if an active link fails, without the danger of bridge loops, or the need for manual enabling/disabling of these backup links.

How STP works

I. Elects a root bridge

II. Elects a root port for Each non root bridge

III. Elects a designated bridge for LAN segment

IV. Elects a designated port for each designated bridge

By using STP we can stop frames looping infinitely.It makes the LAN usable.


' Network does not actively take advantage of some of the redundant links because they are blocked

' Some users' traffic travels a seemingly longer path through the network because a shorter physical path is blocked.

The Internet Protocol (IP)

The Internet Protocol (IP) is the principal communications protocol used for relaying datagrams(packets) across an internetwork using the Internet Protocol Suite. Responsible for routing packets across network boundaries, it is the primary protocol that establishes the Internet.

The first major version of IP, now referred to as Internet Protocol Version 4 (IPv4) is the dominant protocol of the Internet, although the successor, Internet Protocol Version 6 (IPv6) is in active, growing deployment worldwide.

? With everyone talking about the pressing need to switch from IPv4 to IPv6, few people ask what should be an obvious question: what about IPv5?

The story of IPv5 dates all the way back to 1979, when a group of engineers created the Internet Stream Protocal (ST). It was created to transmit video, audio, and simulations over the Internet. IPv5 gained some following at places like IBM, Apple, and Sun, but never really saw the light of day. Regardless of its popularity, the protocol was given the designation IPv5 and as a result, the next generation Internet protocol couldn't take the name and is thus called IPv6.

Real Time Streaming Protocol

The Real-Time Streaming Protocol (RTSP) establishes and controls either a single or several time-synchronized streams of continuous media such as audio and video.

The protocol is used for establishing and controlling media sessions between end points. Clients of media servers issue VCR-like commands, such as play and pause, to facilitate real-time control of playback of media files from the server.

' RTSP provides an extensible framework to enable controlled, on-demand delivery of real-time data, such as audio and video, using the Transmission Control Protocol (TCP) or the User Data Protocol (UDP).

Functions of RTSP

' Provides for on-demand access of multimedia items such as stored real-time audio/video files, live real-time feeds, or stored non-real-time items.

' Allows interoperability between client-server multimedia products from multiple vendors.

' Provides for control and delivery of real-time media and associated events between a media server and large numbers of media clients.

' Addresses key concerns of Internet content-providers and users - quality of service, efficiency of delivery, rights management, and measurement. It also provides a underpinning for developing the richest possible streaming multimedia applications

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