IT COMPUTER NETWORKS FIFTH SEMESTER UNIT I · PDF fileIT 0305‐COMPUTER NETWORKS & FIFTH SEMESTER UNIT I ... Uses of Computer Networks ... • Peer layers communicate in the form

IT 0305‐COMPUTER NETWORKS & FIFTH SEMESTERUNIT I

J.GODWIN PONSAM & S.CHRISTOBEL DIANA

ASST.PROFESSORSRM University, Kattankulathur

112/26/2012

School of Computing, Department of IT

I.T.COMPUTER NETWORKSUNIT‐I

USES OF COMPUTER NETWORKS

NETWORK HARDWARE

NETWORK SOFTWARE

NETWORK OPERATING SYSTEM

REFERENCE MODELS

NETWORK TOPOLOGIES

12/26/20122

School of Computing, Department

Network

What is the Internet?– “network of networks”

– “collection of networks interconnected by routers”

– “a communication medium used by millions”– Email, chat, Web “surfing”, streaming media

12/26/20123


Uses of Computer Networks

• Business Applications

• Home Applications

• Mobile Users

• Social Issues

12/26/20124


Business Applications of Networks

• Resource Sharing‐ Physical Resources, Remote data access(Client server Model)

• Client/server model is applicable in an intranet

• Communication Medium‐Email, Video Conferencing, E‐commerce

12/26/20125


Business Applications of Networks(2)A network with two clients and one server.

12/26/20126


Business Applications of Networks(3)

The client‐server model involves requests and replies.

12/26/20127


Home Network Applications (2)

In peer‐to‐peer system there are no fixed clients and servers.

12/26/20128


Home Network Applications (3)

Some forms of e‐commerce.

12/26/20129


Social Issues

–Newsgroups–Employee rights Versus Employer rights

–Anonymous messages

12/26/201210


Network Hardware

• Local Area Networks

• Metropolitan Area Networks

• Wide Area Networks

12/26/201211


Classifying Networks

• Transmission Technology

• Scale

12/26/201212


Transmission Technology

Types of transmission technology

• Broadcast networks

• Point‐to‐point networks

12/26/201213


Broadcast networks

• Shares the single communication channel byall the machines

• Short Messages (Packets) sent by anymachine are received by all others

Broadcasting System allows• Addressing of a packet to all destinations byusing a special code in the address field

• Also support transmission to a subset of themachines called as multicasting

12/26/201214


Point to Point networks• Many Connections between the individual pair of machines

• Unicasting(One sender and One receiver)

• From Source to destination the packet may first visit one or more intermediate machines

• Routing algorithms are used to find the smallest path

• Large networks uses the point to point networks

12/26/201215

School of Computing, Department of IT

Scale

Classification of interconnected processors by scale.

12/26/201216


Local Area Networks

Two broadcast networks(a) Bus(b) Ring

12/26/201217


Local Area Networks(2)

• Used to connect personal computers and workstations in company officesand factories to share resources and to exchange information

• LANs are distinguished from other kind of networks by 3 characteristics1.Size,2.Transmission technology 3.topology

1.Size‐ LANs are restricted in size‐ Simplifies network management

2.Transmission Technology‐ Single cable is used to connect all machines‐ Traditional LANs run at the speed of 10‐100 mbps have low delay and

make very fewerrors

‐ Newer LANs operate at higher speeds upto hundreds of megabits/sec3. Topology

‐ Bus –Ethernet 10Mbps to 10 Gbps‐ Ring ‐FDDI 4 Mbps to 16 Mbps

12/26/201218


Local Area Networks(3)

Broadcast networks are divided dependingupon the channel allocation

1. Static– Using Round Robin algorithm discrete static time intervalsare allocated to the machines

– If any one of the machines has no message to transmit thenthe interval allocated to that machine is wasted

2. Dynamic– Centralized‐Single entity determines who goes next– No central entity ,each machine decides whether or not totransmit

12/26/201219


Metropolitan Area Networks

• MAN covers a city

• Head end initiates transmission activity

• Ex: Cable Television network,

• Internet service in unused parts of thespectrum

• Television signals and Internet fed into thecentralized head end for subsequentdistribution to peoples homes

• Cable television is not only MAN

12/26/201220


MAN

• MAN based on cable TV

12/26/201221


Wide Area Networks

• Spans a large geographical area • Contains a collection of machines indented for running user program

calles hosts or end program• They are connected using subnet• Components of Subnet

Subnets consists of 2 different components1.Tramsmission Lines –Copper wire, Optical fiber

Move bits between machines2.Swithching Elements

Used to connect 3 or more transmission LinesIt receives the message and select the outgoing lineThey are called as

1.Packed Switching nodes,2Intermediated Systems,3.Data Switching Exchanges

+

12/26/201222


Wide Area Networks(3)

Relation between hosts on LANs and the subnet.

12/26/201223


Wide Area Networks (4)

A stream of packets from sender to receiver.

12/26/201224


Network Software

• Protocol Hierarchies• Design Issues for the Layers• Connection‐Oriented and Connectionless Services• Service Primitives• The Relationship of Services to Protocols

12/26/201225


Network SoftwareProtocol Hierarchies

Layers, protocols, and interfaces.12/26/2012

26School of Computing, Department

Protocol Hierarchies (2)

To reduce the design complexity layers or levelsare usedPurpose of each layer is to offer certain servicesto the higher layer and to hides the complexityLayer n on one machine carries on aconversation with layer n on another machine.This rules and conventions used in thisconversation collectively known as the layer nprotocolA protocol is an agreement between the partieson how communication is to proceed.Peers‐The entities from the corresponding layerson different machines are called peers

12/26/201227


Protocol Hierarchies(3)

Interface defines which primitive operations and servicesthe lower layer offers to the upper one

Network Architecture –A set of layers and protocols

Protocol stack‐A list of protocols used by a certain systemone protocol per layer is called a protocol stack

No data are directly transferred from layer n on onemachine to layer n on another machine. Instead, each layerpasses data and control information to the layerimmediately below it until the lower layer is reached

Below layer1 is the physical medium through which theactual communication takes place

12/26/201228



The philosopher‐translator‐secretary architecture.

12/26/201229



Example information flow supporting virtual communication in layer 5.

12/26/201230


Design Issues for the Layers

• Addressing– Every layer needs a mechanism for identifyingsender and receiver

Rules for data transfer:– Simplex communication– Half Duplex communication– Full Duplex communication– Protocol determines the no of logical channelsthe connection corresponds to and defines theirpriorities

–Many networks provides 2 logical channels perconnection. One for normal data and another forurgent data

12/26/201231


Design Issues for the Layers(2)

• Error Control

–Many error detecting and correcting codesare known. They are useful because thephysical communication circuits are notperfect

–But both ends of the connection mustagree with on which one is being used

–Receiver must acknowledge properly tothe sender

12/26/201232



• Flow Control• How to keep a Fast sender from swamping a slow receiver

with data?• One solution is a feedback will be sent from the receiver to

sender about the receivers current situation• Another problem is to be solved is the inability of all

processes to accept the long messages. This leads todisassembling, transmitting and reassembling messages.

• When processes insist upon transmitting data in units are sosmall that sending each one separately inefficient.

• The solution is to gather small messages heading toward acommon destination into a single large message at theother side

12/26/201233



• Multiplexing–When it is expensive to set up a separateconnection for each pair of communicationprocesses the layer may decide to use the sameconnection for multiple conversation

–Multiplexing is needed in the physical layer

– For ex Where all the traffic for all connectionshas to be sent over at most a few physical circuits

• Routing–When there are multiple paths between sourceand destination then a route must be chosen

12/26/201234


Connection Types

Connection‐Oriented service– like the phone system

– a “live” connection must be established

– data is sent in “real time” and received by the other end

– the other end will respond back as data is received

– Example: a telnet connection

12/26/201235


Connection Types(2)

Connectionless Service– like the postal system

– data is packaged and sent to the destination

– no time limit is placed on the transport of the data

– each packet of data is determined to be a single messagein and of itself with no relation to other messages

12/26/201236


Connection Types(3)Quality of Service

• Some services are reliable in the sense they never lose data.

• Reliability is achieved by receiving acknowledgement fromthe receiver. But ack introduces a delay

• Delays introduced by acknowledgements are unacceptablefor some applications (Ex: Digitized voice traffic, videotraffic)

• Unreliable connectionless services is called as DatagramService

• When the convenience of not having to establish aconnection to send one short message is desired but thereliability is required then the Acknowledged datagramservice will be used.

• Request reply service is commonly used to implementcommunication in the client server model

12/26/201237


Connection Types(4)

Six different types of service.

12/26/201238


Service Primitives

• Set of primitives available to a user processto access the service

• Primitives tell the service to perform someaction

• These calls a trap to kernel mode whichturns control of the machine over to theoperating system to send necessary packets

• Primitives for connection oriented serviceare different from those connectionlessservice

12/26/201239


Service Primitives

• Five service primitives for implementing a simple connection‐oriented service.12/26/2012


Relationships of services to protocols

• Service is a set of primitives that a layerprovides to the layer above it

• Protocol is a set of rules governing theformat and meaning of the frames, packetsor messages that is exchanged by peerentities within a layer

• Entities use protocols in order to implementtheir service definitions

12/26/201242


Relationships of services to protocols(2)

The relationship between a service and a protocol.

12/26/201243


Reference Models

• The OSI Reference Model

• The TCP/IP Reference Model

• A Comparison of OSI and TCP/IP

12/26/201244


Reference Models (2)

The TCP/IP reference model.

12/26/201245


Reference Models (3)

Protocols and networks in the TCP/IP model initially.

12/26/201246


Definitions• Corresponding or peer layers on different computers talk with each

other to achieve communication between the computers.• Inter‐layer interface allows communication between adjacent layers.

Interfaces specifies what information and services a layer mustprovide for the layer above. Such design provides modularity andenables different layer implementations as long as interface remainsthe same.

• Peer layers communicate in the form of formatted blocks of data andobey a set of communication rules known as protocol.

• The data block exchanged between peer layers is called a protocoldata unit (PDU).

• Each layer’s PDU consists of data and header or trailer informationwhich is encapsulated within the PDU of the lower layers. At thesource node, layer N, treats PDU from layer N‐1 and data andattaches its own headers/trailers to it. Layer N+1 treats PDU fromlayer N and data and attaches its own headers/trailers to it, and soon. The process is reversed, the header/trailer is removed, at thedestination.

12/26/201247


Definitions

12/26/201248


Definitions

12/26/201249


Definitions: summaryISO – International Standards OrganizationOSI – Open Systems Interconnection (model)PDU – Protocol Data Unit

– Bit stream, frame, packet, segment message, and data stream.Peers – layers that located on the same level and communicateLayer – software that performs well defined functionsInterface – a point of access between the adjacent layersSAP – service access pointService – layer N uses services from layer N‐1 and provides services to

layer N+1. Services between adjacent layers expressed in terms ofprimitives and parameters. Primitives: request, indication, response,and confirm. Parameters carry date for specification of requestedservices. There are two types of services confirmed and unconfirmed.

NOTE: Headers are added to the data at layers 6, 5, 4, 3, and 2. Trailers areusually added only at layer 2.

12/26/201250


Physical Layer

Physical characteristics of interface and mediaRepresentation of bitsData/transmission rateBit synchronization

Line configuration (point-to-point, multipoint, etc)Physical topology (star, mesh, ring, bus, etc)Transmission mode (simplex, half-duplex, full-duplex)

The physical layer coordinates the functions required to carry a bit stream over a physical medium and is concerned with the following:

–transmission of raw bits over a communication channel.

12/26/201251


Data Link Layer

FramingPhysical Addressing

Flow ControlError ControlAccess Control

The data link layer deals with transformation of the raw data (bits) into a line free of transmission errors for the network layer and delivery of data between two systems within same network. Its responsibilities include:

12/26/201252


Hop-to-hop delivery

12/26/201253


Hop‐by‐Hop

Process A

Process B

12/26/201254


Network LayerThe network layer is responsible for source-to-destination delivery of a packet, possibly across multiple links. Its primary responsibilities are Logical Addressing and Routing.

12/26/201255


Source-to-Destination delivery

12/26/201256


Transport LayerThe transport layer is responsible for process-to-process delivery of an entiremessage. It accepts data from the session layer, splits it into smaller units tobe passed to the network layer and ensures that all of them arrive correctly atthe other end. Its other responsibilities are:Service-point addressing (ports)

Segmentation and re-assemblyConnection control (connection-oriented or connectionless)Flow ControlError Control

12/26/201257


End‐to‐End

Process A

Process B

12/26/201258


Transport Layer: Reliable Data Delivery

12/26/201259


Session LayerThe session layer is a dialog controller. It establishes, maintains, and synchronizes interaction between communication systems. Its responsibilities include: Dialog Control (half-duplex or full-duplex)SynchronizationToken management

12/26/201260


Session Layer– Service 1 –Manage dialog control‐allows traffic togo in both directions at the same time

– Service 2‐Token Management‐It is necessary forsome protocols that both sides do not attemptsame operation at same time

– It provides tokens that are exchanged

– The side which holds the token can performoperation

– Synchronization‐A way to insert checkpoints intothe stream so that after a crash only the datatransferred after the last checkpoint have to berepeated

12/26/201261


Presentation LayerThe presentation layer is concerned with data representation, i.e. syntaxand semantics of the information exchange between two systems. Ittranslates computer data representation into the network standardrepresentation format and back. Its responsibilities include:

TranslationEncryptionCompression

12/26/201262


Application LayerThe application layer enables the user to access the network. It provides user interface and support for such services as: e-mail, remote file access and transfer, etc. Its responsibilities include:

Network Virtual TerminalFile transfer, access, and managementMail serviceDirectory services

12/26/201263


Summary of Layers

12/26/201264


TCP/IP Protocol Suite

TCP/P protocol architecture consists only of five layers (in some books only 4):

Physical LayerNetwork Access LayerInternet LaterTransport Layer (host-to-host)Application layer

12/26/201265


Physical and Data Link Layers

Physical and Data Link Layers perform the same functions as the physical and data link layers in OSI model.

Physical layer is responsible for physical interface between transmission devices.Data link layer is responsible for accessing the network.

TCP/IP Model does NOT have a specific Data Link protocol or Physical medium assigned to it. TCP/IP model supports most of the standard and proprietary protocols.

12/26/201266


Network LayerNetwork Access Layer deals with the data exchange between the end systems and the underlying network. Network access layer is also concerned with the routing data across a single network.

Network Layer is also known as (inter-network layer) supports Internet Protocol (IP) and corresponding supporting protocols: ARP, RARP, ICMP, IGMP.

Internet Protocol (IP) – is an unreliable and connectionless protocol that provides best-effort services. IP delivers data in the form of datagrams (or packets), each transported separately and possibly over different routes. The datagrams may arrive out of order and duplicated. IP does not keep track of routes and provides no facilities for ordered and reliable data delivery.

12/26/201267


Network LayerAddress Resolution Protocol (ARP) – provides translation of IP addresses into physical addresses.

Reverse Address Resolution Protocol (RARP) – allows discovery of IP addresses based on the physical addresses (e.g. during device boot time).

Internet Control Message Protocol (ICMP) – a protocol that provides a mechanism to notify the sender about various problems with the datagram.

Internet Group Message Protocol (IGMP) – a protocol that provides facilities for delivering data to multiple recipients or a group of recipients.

12/26/201268


Transport LayerTransport layer contains functionality for reliable/unreliable, ordered/unordered, etc. data transmission between end hosts only (source and destination).

IP is host-to-host protocolTCP or UDP are process-to-process protocols

User Datagram Protocol (UDP) – provides simple process-to-process data delivery, without any guarantees. UDP carries only port addresses, checksum, and packet length information and provides connectionless service

Transport Control Protocol (TCP) – provides reliable, ordered delivery of data segments between the processes using connection-oriented service model

Stream Control Transmission Protocol (SCTP) – combines good features of TCP and UDP to provide data delivery for new often multimedia applications such as VoIP. Dr. Paul Amer from University of Delaware is one of the SCTP developers.12/26/2012


Application LayerApplication layer contains logic for support of various user applications. It is equivalent to the combined session, presentation, and applications layers of the OSI model.

HTTP

12/26/201270


Comparing OSI and TCP/IP Models

Concepts central to the OSI model

• Services‐ what the layer does, howentities above it access it or howthe layer works

• Interfaces‐ Tells the processesabove it how to access it

• Protocols‐ Use any protocols itwants to as long as it gets the jobdone

12/26/201271


Comparing OSI and TCP/IP Models

• TCP IP model did not clearly distinguish between service, interface andprotocol

• Only services offered by the internet layer are send ip packet and receiveip packet

• But protocols in the OSI model are hidden than in the TCP/IP model andcan be replaced as technology changes

• OSI model was not biased towards one particular set of protocols

• TCP/IP reverse : protocols came first and model was really just adescription of the existing protocols

• TCP/IP wont fit to any other protocol stacks

• OSI model supports both connectionless and connection orientedcommunication in the network layer but only connection orientedcommunication in the transport layer

• TCP/IP model has only one mode in network layer(connectionless), butsupports both connection oriented and connectionless in the transportlayer

12/26/201272


Network topologies

12/26/201273


Network topologies

• Bus topology

• Ring topology

• Star topology

• Fully connected topology

• Mesh topology

12/26/201274


Bus Topology

Prototype of the Ethernet Standard

• Characteristics:

– A central cable (coaxial cable)

– Lines to the attached stations

– Decentralized structure (stations with equalstanding)

– All attached stations are affected bydisturbance at the central cable

12/26/201275


RING Topology

• One token "moves" in the circle (Ring structure ofthe network)

• • If the token is "free", then the station can attacha network package

12/26/201276


RING Topology

12/26/201277


STAR Topology

There is a central element

– Originally the HUB

– More intelligent is the SWITCH

• Used with

– Twisted‐Pair‐Wiring

– Fast and Gigabit‐Ethernet

• central structure

• steering element

12/26/201278


STAR Topology

12/26/201279


Fully Connected Topology

a direct link between all stations

• n stations n(n‐1)/2 direct links

( number of connections grows

exponentially with number of stations )

• multiple data paths

• Used in …

– military applications

– the file sharing protocol:

BitTorrent 12/26/201280


Fully Connected Topology

12/26/201281


MESH Topology

Route data between stations

• Route reconfiguration around broken orblocked paths

Mesh networks are self‐healing

• Concept for …

– wireless and wired networks

provide an inexpensive “internal” infrastructure

– Mesh network whose stations are allconnected with each other

F ll d k12/26/2012


Disclaimer

The contents of the slides are solely for the purpose of teaching students at SRM University. All copyrights and Trademarks of organizations/persons apply even if not specified explicitly.

12/26/2012School of Computing, Department 83

bibliography

• Andrew S. Tanenbaum, Computer Networks,Fourth Edition, Prentice Hall of India, 2003

• 2. Cisco Network Fundamentals – CCNAExploration Companion Guide, PearsonEducation , 2008


Review questions

• 1. List the functionality of the network Layer?

• 2. What is the difference between Connection oriented and Connectionless Service?

• 3. Define SAP

• 4. List the types of network topologies

• 5. What is the difference between full duplex and half duplex communication

• 6. List the functionality of the transport layer

• 7. What is the difference between error control and flow control?

• 8. List the protocols used in transport Layer


Documents

IT COMPUTER NETWORKS FIFTH SEMESTER UNIT I · PDF fileIT 0305‐COMPUTER NETWORKS & FIFTH SEMESTER UNIT I ... Uses of Computer Networks ... • Peer layers communicate in the form