MODULE INETWORKING CONCEPTS

OSI MODELEstablished in 1947, the International

Standards Organization (ISO) is a multinational body dedicated to worldwide agreement on international standards.

An ISO standard that covers all aspects of network communications is the Open Systems Interconnection (OSI) model.

It was first introduced in the late 1970s.

OSI MODELOpen System:

Set of protocols that allow only 2 different systems to communicate regardless of underlying architecture

OSI model is not a protocol,but a model for designing n/w architecture

Purpose is to show how to facilitate communication b/w different systems without requiring changes to the logic of the underlying h/w or s/w

OSI model is a layered framework for design of network systems

Consist of 7 layers

OSI MODEL LAYERS

The interaction between layers in the OSI model

OSI MODELFig shows the layers involved when a

message is sent from A to BAs message travels from A to B it may pass

through many nodes and intermediate nodes usually involve only first 3 layers of OSI model

With a single machine each layer calls on services of layer just below it. Ie layer 3 provides services to layer 4 and uses services of layer2

OSI MODELBetween m/c layer x on one m/c

communicates with layer x on other m/c and that communication is governed by agreed rules called protocols

Processes on each machine that communicate at a given layer are called peer to peer processes

OSI MODELPeer to Peer Process

At physical layer communication is directIn fig device A sends stream of bits to device

B(through intermediate nodes)At higher layer communication must move down

through the layers through the layer on device A over to device B and then back up through layers

Each layer in sending device adds its own information to message it receives from the layer just above it and passes whole package to layer below it

OSI MODELPeer to Peer Process

At layer 1 the entire package is converted to a form that can be transmitted to the receiving device

At the receiving device msg is unwrapped layer by layer with each process receiving and removing the data meant for it

Eg. Layer 2 removes the data meant for it and then passes the rest to layer 3.Layer 3 removes the data meant for it and passes the rest to layer 4 and so on

OSI MODELInterface between layers

Defines the information and services a layer must provide for the layer above it

Organization of Layers7 layers belong to 3 subgroups

Layer 1,2,3 are n/w support layer deal with physical aspects of moving data from one device to other

Eg.electrical specifications,physical connector etc

OSI MODELOrganization of Layers

Layer 5,6,7.ie session presentation,application are user support layers and allow interoperability among unrelated s/w systems

Layer 4-Transport layerThis links two subgroups and ensures

that lower layer transmission is in a form that the upper layer can use

OSI MODELOrganization of LayersUpper OSI layers are commonly

implemented in s/w but lower layers are combination of h/w and s/w except physical which is mostly h/w

EXCHANGE USING OSI MODEL

EXCHANGE USING OSI MODELD7 means data unit at layer 7The process starts at application layer and

moves from layer to layer in descending sequential order

At each layer header or trailer is added to data unit

Commonly trailer is added at layer 2After data unit passes through layer 1 and

it changed to some electromagnetic signal and is transported along a physical link

EXCHANGE USING OSI MODELOn destination side signal passes to layer

1 and is transformed back into digital formThe data units then move backup through

the OSI layersAs each block reaches next high layer,

header and trailer attached to it at the corresponding sending layer are removed actions appropriate to the layer are taken

EXCHANGE USING OSI MODELWhen it reaches layer 7 the message is

again in a form appropriate to the application and is made available to the recipient

EXCHANGE USING OSI MODELEncapsulationA packet (header+data) at level 7 is

encapsulated at level6ie data portion at level N-1 carries whole

packet from level N.This is encapsulation

EXCHANGE USING OSI MODELEncapsulationA packet (header+data) at level 7 is

encapsulated at level6ie data portion at level N-1 carries whole

packet from level N.This is encapsulation

LAYERS OF OSI MODELPhysical Layer

LAYERS OF OSI MODELPhysical Layer

Deals with mechanical and electrical specifications of interface and transmission medium

Responsible for movements of individual bits from one node to next

Physical LayerPhysical LayerConcerned with

Physical characteristics of interfaces and mediumIt defines type of medium

Representation of bitsPhysical layer data consist of stream of bitsFor transmission these must be converted to

electrical or optical signalPhysical layer defines type of encoding(how

bits are changed to signal)

Physical LayerData rate

No of bits /sec is also defined by this layerSynchronization of bits

Sender and receiver must use same bit rateLine configuration

Physical layer concerned with connection of devices to media

Point-point configuration:2 devices connected through dedicated line

Multipoint configuration:a link shared among multiple devices

Physical LayerPhysical topology

This defines how devices are connected to make a n/w

These may be mesh,star,ring,bus etcTransmission mode

Physical layer defines direction of transmission between 2 devices

that may beSimplexHalf duplex Full duplex

Data Link Layer

Data Link LayerDLL

Responsible for moving frames between one hop to next

Responsibilities are 1.Framing

DLL divides stream of bits received from n/w layer to manageable data units called frames

2.Physical addressingIf frame are to be distributed to different

systems on n/w the data link layer adds a header to frame to define the sender and /or receiver of the frame

Data Link Layer2.Physical addressing

if the frame is intended for a system outside the sender’s network , the receiver address is the address of the device that connects to the n/w to the next one

3. Flow controlIf rate at which the data is absorbed by

the receiver is less than rate at which it is produced at sender the dll imposes a flow control mechanism to avoid overwhelming the receiver

Data Link Layer4.Error Control

Dll adds mechanism for to detect and retransmit damaged frame or lost frame

Also adds one mechanism to recognize duplicate frames

Error control is achieved by adding trailer to end of fame

5. Access controlWhen 2 or more devices are connected to same link dll protocols determine which device has control over link at any time

Data Link Layer4.Error Control

Dll adds mechanism for to detect and retransmit damaged frame or lost frame

Also adds one mechanism to recognize duplicate frames

Error control is achieved by adding trailer to end of fame

5. Access controlWhen 2 or more devices are connected to same link dll protocols determine which device has control over link at any time

Hop-to-hop delivery

Hop-to-hop delivery

Communication at all layer occurs between 2 adjacent nodes

To send data from A-F , 3 partial deliveries are made

1.DLL layer at A send frame to DLL layer at B2.DLL layer at B send frame to DLL layer at E3.DLL layer at E send frame to DLL layer at F

Frame from A-B has A is source address B is destination address

Frame from B-E has B is source address E is destination address

Frame from E-F has E is source address F is destination address