COMPUTER NETWORKS

COMPUTER COMPUTER NETWORKSNETWORKS

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ASHWINI AVABHRAT ASHWINI AVABHRAT (01)(01)

SHWETA DESHPANDE SHWETA DESHPANDE (10)(10)

SANDEEPA GUPTA (17)SANDEEPA GUPTA (17)

NEESHA INCHODY (18)NEESHA INCHODY (18)

INTRODUCTIONINTRODUCTION

Two or more than two computer systems connected by means of a communication medium like cables is termed as a Network.

Computer Network is a communication systems, which links computers and their resources.

Computer Resources are storage devices e.g. HDD, tape drive, CDROM, MODEM,RDBMS like Oracle, MS-SQL etc and any other computing system (Mainframe, Minicomputer etc.).

BENEFITS OF A NETWORKBENEFITS OF A NETWORK

Following are the benefits of a networking which help to increase the productivity:Information SharingPrinter SharingHard Disk SharingModem SharingHardware SharingSoftware SharingService AccessEasy Back-Up ManagementSecurityCentralized Administration and Support

TYPES OF NETWORKTYPES OF NETWORK

LOCAL AREA NETWORK (LAN) : LAN connects computers that are located near each other or at the same location. A corporate network consisting of several building in a campus an example of a LAN

WIDE AREA NETWORKS (WAN—LONG HAUL NETWORKS) :WAN connects a numbers of computers which are located at a greater distance from one other or at different location.Internet is an example of WAN

The key characteristics, which are often used to differentiate between these two types of networks, are as follows:Geographic DistributionData RateError RateCommunication LinkOwnershipCommunication Cost

Note: Networks that share some of the characteristics

of both LANs and WANs are sometimes referred to as Metropolitan Area Networks (MAN). The MANs usually cover a wider geographic area than LANs. The main objective of MANs is to interconnect LANs located in a entire city or metropolitan area.

NETWORK TOPOLOGYNETWORK TOPOLOGY

It refers to the physical layout of the network, especially the location of the computers and how the cable is run between them.

The choice of the networks topology for installing a computer network depends upon a combination of factors, such as: The desired performance of the system. The desired reliability of the system. Size of the system.. Expandability of the system. Availability of communication lines. Delays involved in routing information from one node to another.

The bus topology refers to a linear arrangement of computers that are connected together by a single cable referred to as the trunk or backbone. It is often used when a network installation is small, simple or temporary.

Advantages:Simple,Reliable,Easy to use and

understand.Least amount of cable to connect

a computers.Easy to extend a bus with the help of a repeater.

BUS TOPOLOGYBUS TOPOLOGY

STAR TOPOLOGYSTAR TOPOLOGY

A star network consists of one central switch, hub or computer which acts as a router to transmit messages.

Advantages:Good PerformanceEasy to set up and to expand. Any non-centralized failure will have very

little effect on the network, whereas on a ring network it would all fail with one fault.

Disadvantages:Expensive to install Extra hardware required If the host computer fails the entire system is affected.

RING TOPOLOGYRING TOPOLOGY

A ring network is a topology of computer networks where each connected to node is two other nodes, so as to create a ring.

Advantages:Data is quickly transferred without a ‘bottle neck’. (very fast, all data traffic is in the same direction) The transmission of data is simple as packets travel in one direction only. Adding additional nodes has very little impact on bandwidth It prevents network collisions because of the media access method or architecture required.

Disadvantages:Data packets must pass through every computer between the sender and recipient therefore this makes it slower. If any of the nodes fail then the ring is broken and data cannot be transmitted successfully. It is difficult to troubleshoot the ring. Because all stations are wired together, to add a station you must shut down the network temporarily. In order for all computers to communicate with each other, all computers must be turned on.

TOKEN RINGTOKEN RING

A token ring is a type of computer network in which all the computers are arranged (schematically) in a circle. A token, which is a special bit pattern, travels around the circle. To send a message, a computer catches the token, attaches a message to it, and then lets it continue to travel around the network.

Although it is considered a more reliable system, a token ring network is slower  

  and offers less flexibility than schools and other businesses need.  In a token ring, only one computer   may send information at a time.

MEDIUM ACCESS CONTROL MEDIUM ACCESS CONTROL PROTOCOLPROTOCOL

The Medium Access Control (MAC) protocol is used to provide the data link layer of the Ethernet LAN system. It defines the access method and access control in different local area networks.

The MAC layer provides an addressing mechanism called physical address or MAC address. This is a unique serial number assigned to each network adaptor, making it possible to deliver data packets to a destination within a subnetwork.

Media access control is often used as synonym to multiple access protocol, since the MAC sublayer provides the protocol and control mechanisms that are required for a certain channel access method.

CMSA/CD PROTOCOLCMSA/CD PROTOCOL

In computer networking, Carrier Sense Multiple Access With Collision Detection (CSMA/CD) is a network control protocol in which a carrier sensing scheme is used.

A transmitting data station that detects another signal while transmitting a frame, stops transmitting that frame, transmits a jam signal, and then waits for a random time interval (known as "backoff delay") before trying to send that frame again.

Ethernet is the classic CSMA/CD protocol.

WAN TECHNOLOGIESWAN TECHNOLOGIES

WAN is Wide Area Network.

A WAN is a data communications network that covers a relatively broad geographic area and that often uses transmission facilities provided by common carriers, such as telephone companies(coaxial cables) or communication satellites.

WAN uses no fixed Network Topology.

PACKET-SWITCHING PACKET-SWITCHING EXCHANGESEXCHANGES

PSEs are hardware devices (special purpose computers) dedicated to the task of data communication.

Communication channels of the network interconnect the PSEs.

A computer of a WAN only interacts with the PSE of the WAN to which it is connected for sending and receiving messages.

   A WAN of ComputersA WAN of Computers

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SWITCHING TECHNIQUESSWITCHING TECHNIQUES

The process moving data from one interface and delivering it through another interface, selecting the best paths between machines that store messages is known as switching.

There are a number of ways to perform switching:

Circuit SwitchingPacket SwitchingMessage SwitchingCell Switching

CIRCUIT SWITCHINGCIRCUIT SWITCHING

A type of communication in which a dedicated channel (or circuit) is established for the duration of a transmission.

connection-oriented networks.

Ideal for communications that require data to be transmitted in real-time or for long continuous transmission.

Used in PSTN (Public Switched Telephone Network).

ADVANTAGES :ADVANTAGES :No delay other than propagation delay.Full capacity of the circuit is available.Transmission time required to send a message can be known and guaranteed.

DISADVANTAGES :DISADVANTAGES :Additional overhead during circuit establishment and circuit disconnection.Channel bandwidths may be wasted.

PACKET SWITCHINGPACKET SWITCHING

Packet Switching techniques switch packets of data between destinations.

Each packet is then transmitted individually and can even follow different routes to its destination (Store and forward).

connectionless networks.

Used in X.25 public packet network and the internet.

ADVANTAGES :ADVANTAGES :Efficient usage of channels (Bandwidths are shared).Alternate paths may be used (Failed paths may be ignored).Suitable for small data bursty in nature.

DISADVANTAGES :DISADVANTAGES :Each packet needs to be buffered and reassembled.Inefficient for large messages.Time taken depends on the route chosen.

ROUTING TECHNIQUESROUTING TECHNIQUES

In a WAN, when multiple paths exist between the source and destination computers of a packet, any one of the path may be used.

Packets are routed to their destination as determined by a routing algorithm.

An efficient routing techniqueReduces Network Latency.Should be implementable in h/w.Should not require Global State Info.

Routing algorithms are Routing algorithms are classified based on the classified based on the following attributes :following attributes :

Place where routing decisions are made.

Time constant of the information upon which the routing decisions are based.

Control mechanism used for dynamic routing.

PLACE BASEDPLACE BASED SOURCE ROUTING :

Source computer’s PSE selects the entire path before sending the packet

HOP-BY-HOP ROUTING :Each PSE along the path decides only

the next PSE for the path.

HYBRID ROUTING :Source comps PSE specifies certain

major intermediate PSEs of the complete path and the sub paths are decided with hop-by-hop method.

TIME CONSTANT BASEDTIME CONSTANT BASED

STATIC ROUTING (Fixed or Deterministic) :

Routing tables (stored at PSEs) are set once and do not change for a very long time.

DYNAMIC ROUTING (Adaptive) :Routing tables are updated

relatively frequently, reflecting shorter term changes in the network environment.

CONTROL MECHANISM CONTROL MECHANISM BASEDBASED

ISOLATED MANNER :Individual PSEs update

information in their local routing table in an isolated manner.CENTRALIZED MANNER :

Changes in the network environment,connectivity, or performance are constantly reported to one centralized PSE based on which global table is maintained.DECENTRALIZED MANNER :

Each PSE maintains a routing table and the table updates are performed by mutual interaction among the PSEs.

INTERNETWORKINGINTERNETWORKING

Interconnecting of two or more networks to form a single network is called INTERNETWORKING and the resulting network is called an INTERNETWORK (eg. Internet).

INTERNETWORKS are heterogeneous networks composed of several network segments that may differ in topology and protocol.

Goal of internetworking is to hide the details of different physical networks so that resulting internetwork functions as a single coordinated unit.

INTERCONNECTION INTERCONNECTION TECHNOLOGIESTECHNOLOGIES

Internetworking schemes provide some common point of reference for the two networks to communicate with each other. This point of reference may be High-Level protocol common to the two networks. A Device that allows interconnection of different topologies with different physical and electrical characteristics. Protocol that allows operating environment differences to be ignored

BRIDGESBRIDGES

Bridges operate at the bottom two layers of the OSI model (Physical and Data Link).

They are used to connect networks that use the same communication protocols above the data-link layer but may or may not use the same protocols at the physical and data-link layers.

ROUTERSROUTERS

Routers operate at the Network Layer of the OSI model.

They are used to connect networks with the same High Level protocols.

Routers unlike bridges only know which is the next router for the data being transferred across the network.

Routers choose the best route for data based on the info in routing table.

BROUTERSBROUTERS

Brouters are hybrid of Bridges and Routers.

They are complex,expensive and difficult to install.

They are used for connecting segments with the same high level communication protocols.

GATEWAYSGATEWAYS

Gateways are most sophisticated internetworking tools.

Gateways operate at the top three layers of the OSI model (Session, Presentation and Application).

They are used for connecting networks that are built on totally different communication architectures.

Communication Medium to Communication Medium to be usedbe used

DEPENDS ON : Location of the two networks.

Throughput desired.

OPTIONS AVAILABLE : Leased Telephone Lines Dedicated Telephone Lines

Public Data Networks Communication Satellites

Network Management Network Management TechnologiesTechnologies

Network Management is monitoring and analysis of network status and activities.They monitor Data Throughput, Node and Link Failures and other Global Occurrences on network.They report existence and cause of the problem.They should enfold all the protocols and devices on a typical heterogeneous internetwork, should be easy to use and should be intelligent.Eg. SNMP,CMIP and DME

COMMUNICATION COMMUNICATION PROTOCOLSPROTOCOLS

The term protocol is used to refer to a set of rules and conventions needed for communication between communicating parties.

Computer networks are implemented using the concept of layered protocols.

Requirements of communication protocols for network systems and distributed systems are different.

Protocols for Network SystemsProtocols for Network Systems

The OSI/ISO Reference Model

Provides a framework in which standards can be developed for the services and protocols at each layer.

It is a seven layer architecture in which a separate set of protocols is defined for each layer.

The OSI/ISO Reference The OSI/ISO Reference Model Model

 Application

Layer  

Presentation Layer

Session Layer 

Transport Layer

Network Layer  

Data Link Layer

Physical Layer 

Physical Layer: Transmits raw bit streams between two sites.

Data Link Layer:

Detects and corrects any errors in the transmitted data.

Network Layer:

Sets up logical path between two sites for communication to take place.Two popular network layer protocols are X.25 protocol and Internet Protocol.

Transport Layer:Provides site-to-site communication and hides all the details of the communication subnet from the session layer by providing network independent transport service.The two most popular protocols are TCP and UDP.

Session Layer:Provides the means by which presentation entities can organize and synchronize their dialog and manage their data exchange.

Presentation Layer:Represents message information to communicating application layer entities in a way that preserves meaning while resolving syntax differences.

Application Layer: Provides services that directly supports the end users of the network.

It is a modified reference model suitable for LANs built by IEEE.

The layers in this model are similar to those of the OSI model the only difference being that the last two layers of the reference model are modified.

The IEEE 802 LAN Reference The IEEE 802 LAN Reference ModelModel

Application Layer

Presentation Layer

Session Layer

Transport Layer

Network Layer

Data Link Layer

Physical Layer

Logical-Link Control Layer

Medium-Access

Control Layer 

Physical Layer 

Relationship between the Relationship between the IEEE 802 LAN MODEL & OSI MODELIEEE 802 LAN MODEL & OSI MODEL

The physical layer defines interface protocols for the four types of media that are commonly used in LANs : baseband,broadband,fiber optics and twisted pair.

The medium-access-control layer deals with medium access control protocols for LANs.

The logical-link-control layer contains the IEEE 802.2 standard.

Protocols for Distributed Protocols for Distributed SystemsSystems

Requirements for distributed systems

TransparencyClient-server based communicationGroup communicationSecurityNetwork managementScalability

The Versatile Message The Versatile Message TransportTransport

Protocol (VMTP)Protocol (VMTP)

It is a transport protocol designed for distributed operating systems that has special features to support request/response behavior between a client and one or more server processes.Entities are identified by 64 bit identifiers.It provides selective retransmission mechanism.It uses a rate-based flow control mechanism

The Fast Local Internet The Fast Local Internet Protocol (FLIP)Protocol (FLIP)

It is a connectionless protocol designed to support transparency, group communication, secure communication and easy network management.

The following FLIP properties helps to achieve the efficiency requirements for distributed systems.

FLIP identifies entities called network service access points (NSAPs)

FLIP uses a one way mapping between the “private” address, used to register an endpoint of a network connection, and the “public” address used to advertise the endpoint.

FLIP routes messages based on NSAP.

FLIP uses a bit in the message header to request transmission of sensitive messages across trusted networks.

ATM NETWORKSATM NETWORKS

FEATURESFEATURES

Enables high-bandwidth distributed applications.Provides high transmission speeds for local and wide-area networks and services.Supports circuit switching and packet switching.[CELL SWITCHING]Uses the concept of virtual networking to pass traffic between 2 locations.Supports multi-casting.Enables use of single network to efficiently transport a wide range multimedia data.It is flexible since it grants access to bandwidth

BASIC CONCEPTSBASIC CONCEPTS

Fundamental types of network traffic-CBR & VBR.

Connection oriented technology.

Cell Switching technology is based on the digital packet switching technology which relays and routes traffic over virtual path by means of an address contained within the packet.

In ATM, a virtual path is essentially a bundle of virtual channels that can be multiplexed together.

ATM Protocol Reference ATM Protocol Reference ModelModel

Other layers not specified in ATM protocol reference model

ATM Adaptation Layer (AAL)

ATM Layer

Physical Layer

PHYSICAL LAYERPHYSICAL LAYER

By carrying cells as a synchronous data stream.

By carrying cells in the payload portion of an externally framed transmission.

SONET (Synchronous Optical NETwork).

ATM LAYER ATM LAYER

Generic Flow Control (GFC)Virtual Path Identifier (VPI)Virtual Circuit Identifier (VCI)Payload Type Identifier (PTI)Cell Loss Priority (CLP) Field Header Error Control (HEC) Field

4 bits

48 bits8 bits

16 bits

3 bits

1 bit

8 bits

Payload area

Header area

GFC

VPI VCIPTI

CLP

HEC

Payload

ATM CELL FORMATATM CELL FORMAT

ATM ADAPTATION LAYERATM ADAPTATION LAYER

Responsible for providing different types of services to different types of traffic according to their specific requirements.It packages various kinds of user traffics into 48-byte cells, together with the overhead.Four service classes defined by the ITU:

CLASS A: Applications having delay sensitive & CBR traffic & are connection oriented.CLASS B: Applications having delay sensitive & CBR traffic & are connection oriented.CLASS C: Applications having delay sensitive & CBR traffic & are connection oriented.CLASS D: Applications having delay sensitive & CBR traffic & are connection oriented.

Four service classes defined by the ITU:CLASS A: Applications having delay sensitive & CBR traffic & are connection oriented. It uses AAL1 protocol.CLASS B: Applications having delay sensitive & VBR traffic & are connection oriented. It uses AAL2 protocol.CLASS C: Applications that are not delay sensitive &VBR traffic & are connection

oriented. It uses AAL3/4 or AAL5 protocol.CLASS D: Applications that are not delay sensitive &VBR traffic & are not connection oriented. It uses AAL3/4 or

AAL5 protocol.

ATM NETWORKSATM NETWORKS

ATM SWITCH

ATMSWITCH

ATMSWITCH

Host Computers

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