8/14/2019 ECE-D cc3

1/53

OSI Layer Model &

8/14/2019 ECE-D cc3

2/53

- -

8/14/2019 ECE-D cc3

3/53

Encapsulation/Decapsulation

8/14/2019 ECE-D cc3

4/53

As the data flows down through the layers in,

information to the data in the form of headersor tailors.

This process of wrapping data with headers and

tailors is called encapsulation.

8/14/2019 ECE-D cc3

5/53

8/14/2019 ECE-D cc3

6/53

-- ..

International standards organisation isrespons e or a w e range o stan ar s,including many that are relevant to computer

.

In 1984 , the Open Systems Interconnection

international standard for communicationsarchitecture.

8/14/2019 ECE-D cc3

7/53

Open Systems Interconnection

Developed by the International Organization forStandardization (ISO)

Seven layers

- Application - Data link - Presentation - Physical

- Session

- Transport

- Network

8/14/2019 ECE-D cc3

8/53

OSI Model

8/14/2019 ECE-D cc3

9/53

- Layered Architecture

Peer to Peer Process Interface between Layers

Organization of the Layers

-------------------------------------------------------------- Each layer performs a subset of the required

communication functions

Layer 1,2,3-Network support layer

Layer 5,6,7-User Support Layer

Layer 4-Links the two subgroups.

8/14/2019 ECE-D cc3

10/53

..

8/14/2019 ECE-D cc3

11/53

8/14/2019 ECE-D cc3

12/53

8/14/2019 ECE-D cc3

13/53

..

8/14/2019 ECE-D cc3

14/53

Ph sical

Bottommost layerImplements an unreliable bit link

Uses synchronization bits to synchronize the receiver

Specify the modulation scheme

Mechanical

Electrical

Procedural

For activating, maintaining and deactivating the physicallink between communicating network systems

8/14/2019 ECE-D cc3

15/53

Physical Layer

Physical characteristics of interface and media Data rate Synchronization of bits

Topology Transmission Mode

8/14/2019 ECE-D cc3

16/53

Physical Layer

8/14/2019 ECE-D cc3

17/53

Data Link

Supervises transmission of packets by physical layerMeans of activating, maintaining and deactivating areliable link

Adds sequence number and CRCError detection and control

Enca sulation and Deca sulation are erformedRegulates the access to the linkHigher layers may assume error free transmission

MAC address will be added

B) Logical Link ControlCRC wi e a e

8/14/2019 ECE-D cc3

18/53

.. The data link layer is responsible for moving frames

r x .

The major duties of the data link layer are:FramingPhysical addressing:

Physical address is the MAC address, which is hard coded

into NIC and is of 48-bit represented by Hexadecimal.

00.27.AB.CC.EE.2300.27.AB-Vendor

-. .

Cmd Ipconfig/all to show the system details

Flow control Access Control

Data Link layer protocols are CSMA/CD, CSMA/CA, Tokenpassing etc.

8/14/2019 ECE-D cc3

19/53

.

8/14/2019 ECE-D cc3

20/53

Data Link Layer

8/14/2019 ECE-D cc3

21/53

.. The network layer is responsible for the source -

to- est nat on e very o a pac et poss yacross multiple networks.

,is usually no need for a network layer.

However if the two s stems are attached to differentnetworks with connecting devices between thenetworks, there is need for the network layer to

.

The major duties performed by the network

8/14/2019 ECE-D cc3

22/53

..Logical addressing:

-and represented in decimal format.

192.168.32.97

To route the packets from the source to destination in aninternetwork, the router uses network layer information.

.

Network layer protocols are IP, IPX, AppleTalk.

8/14/2019 ECE-D cc3

23/53

..

8/14/2019 ECE-D cc3

24/53

Network Layer

8/14/2019 ECE-D cc3

25/53

Transport

xc ange o a a e ween en sys ems

Multiplexes several low rate transmissions with different ServiceAccess Points (SAPs) onto one virtual circuit

Decomposes messages into packets and combines packets intomessages

Error free (Connection Oriented) In sequence

No losses

No du licates

Connectionless service no guarantee on the order of themessages (possibly with some errors)

Quality of service

8/14/2019 ECE-D cc3

26/53

Transport Layer.Transport Layer.

The transport layer is responsible for process-to-.

The major duties performed by the transport layer are:Port address:

Computers o ten running severa processes running programsat the same time:

Segmentation and reassembly:transmittable segments, each segment contains a sequencenumber.

These number enables the transport layer to reassemble themessage correc y upon arr va a e es na on an o en yand replace packets that were lost in the transmission.

8/14/2019 ECE-D cc3

27/53

..Connection Control:

he trans ort la er can be either connectionless orconnection oriented.

Flow controlError control

Transport layer 4 protocols include TCP

Transmission Control Protocol and UDP UserDatagram Protocol).

8/14/2019 ECE-D cc3

28/53

..

8/14/2019 ECE-D cc3

29/53

Reliable ProcessReliable Process--toto--ProcessProcess

..

8/14/2019 ECE-D cc3

30/53

8/14/2019 ECE-D cc3

31/53

Supervises the control of dialogues betweenapplications (two computers)

a ogue sc p ne

Sets up the connection prior to exchange of

information between the machinesInserts synchronization points

Grouping

ecovery

8/14/2019 ECE-D cc3

32/53

..

he session layer defines how to establish, maintainingand terminates session between two communication

hosts. he ma or duties of the session la er are:

SynchronizationDialog control:

Session la er determines that which role is to be la ed at angiven time by a host. Duplex: Two-way simultaneous. Half-Duplex: Two-way alternate.

S mp ex: One-way. Session layer protocols are SQL, ASP(AppleTalk SessionProtocol), Remote Procedure Call (RPC), X Windowys em.

8/14/2019 ECE-D cc3

33/53

..

8/14/2019 ECE-D cc3

34/53

Defines the data formatDefines coding and conversion functions

Common Data Representation

Data compression

Encryption Conversion of Characters

Examples:

MPEG

ASCII JPEG

8/14/2019 ECE-D cc3

35/53

.. The presentation layer ensures that the information

readable by the application layer of another system.

The major duties of the presentation layer are: orma convers on:

Convert message from one format into another format .

Compression. ompress e message o a e ess an w on etransmission media and less time for transmission.

Encryption:

others. Provides security to the message.

Protocols of the resentation la er are JPEG MPEGASCII etc.

8/14/2019 ECE-D cc3

36/53

..

8/14/2019 ECE-D cc3

37/53

Application

This layer is closest to the user

Means for applications to access OSI environment

r v w r rv r y

Determines the identity and availability of

communication partners and determines if sufficientresources are available to start program to programcommunication

Exam les of a lication la er rotocols:

Telnet SMTP

SNMP

8/14/2019 ECE-D cc3

38/53

8/14/2019 ECE-D cc3

39/53

Summary of the Layers.Summary of the Layers.

8/14/2019 ECE-D cc3

40/53

Developed by the US Defense Advanced

esearc ro ect gency or ts pac et

switched network (ARPANET)

se y e g o a n erne

No official model but a working one.

pp ca on ayer

Transport layer

Network access layer

Ph sical la er

8/14/2019 ECE-D cc3

41/53

Physical interface between data transmission

ev ce e.g. computer an transm ss on

medium or network

arac er s cs o ransm ss on me um

For activating, maintaining and deactivating the

systems

Data rates

8/14/2019 ECE-D cc3

42/53

Also called as host to host network la er

Exchange of data between end system andnetwork

Destination address provision

In l h LAN n WAN hn l iland all the details contained in the OSI physicaland data-link layers

Invoking services like priority

8/14/2019 ECE-D cc3

43/53

Defines a packet and an addressing scheme Transfers the data between the Internet la er and the

Network access layers

The purpose of the Internet layer is to select the best paththrough the network for packets to travel

The main protocol that functions at this layer is InternetProtocol (IP)

Internet Protocol: Connectionless, best effort delivery routing of.looks for a path to the destination. It is an unreliable protocol. Itdoes not perform error checking and correction

Internet Control Message Protocol: Provides control and messaging

Reverse Address Resolution Protocol: Determines the IP addresswhen the MAC address is known

Systems may be attached to different networks Routing functions across multiple networks and remote hosts

Implemented in end systems and routers

8/14/2019 ECE-D cc3

44/53

The transport layer provides transport services from the

Logical connection between the endpoints of the network, thesending host and the receiving host

End to End control rovided b slidin windows and reliabilitin sequencing numbers and acknowledgements

Also defined as end to end connectivity between host

applications Reliable delivery of data Ordering of delivery

TCP and UDP

Sending segments from one end device to another end device TCP only

Establishing end to end operations F ow contro provi e y s i ing win ows Reliability provided by sequence numbers and acknowledgements

8/14/2019 ECE-D cc3

45/53

Support for user applications

Handles high level protocols

e.g. FTP, HTTP, NFS (Network File Server),SMTP, SNMP, Telnet (Terminal Emulation), TFTP(Trivial File Transfer Protocol), DNS (Domain

8/14/2019 ECE-D cc3

46/53

8/14/2019 ECE-D cc3

47/53

Usual transport layer is Transmission Control Protocol

e a e connec on

Connection em orar lo ical association between entities in different

systems

TCP PDU

Includes source and destination port (c.f. SAP)

Identify respective users (applications)

onnec on re ers o pa r o por s

TCP tracks segments between entities on eachconnection

8/14/2019 ECE-D cc3

48/53

Alternative to TCP is User Datagram Protocol

Not guaranteed delivery

No preservation of sequence

No protection against duplication

Minimum overhead Adds port addressing to IP

8/14/2019 ECE-D cc3

49/53

8/14/2019 ECE-D cc3

50/53

Level in architecture at which entity is named

Unique address for each end system (computer)and router

Network level address

IP or internet address (TCP/IP)

e wor serv ce access po n or

Process within the system

r u r

Service access point or SAP (OSI)

8/14/2019 ECE-D cc3

51/53

8/14/2019 ECE-D cc3

52/53

TCP/IP and the OSI Model

8/14/2019 ECE-D cc3

53/53

C / a d t e OS ode