8/13/2019 Unit 1-EC2352

1/19

Network architecture layers Physical links Channel access on links Hybrid multiple accesstechniques Issues in the data link layer - Framing

Error correction and detection

Link-level Flow

Control.

8/13/2019 Unit 1-EC2352

2/19

Computer networkComputer network is a connection of autonomous

computers and network devices for:

Resource sharing (data/devices) in an efficientmanner

Communication amongst them.

8/13/2019 Unit 1-EC2352

3/19

Bus Topologies

Mesh Topology

Star Topology Bus Topology

Ring Topology

8/13/2019 Unit 1-EC2352

4/19

Mesh Topology

8/13/2019 Unit 1-EC2352

5/19

Star Topology

8/13/2019 Unit 1-EC2352

6/19

Bus Topology

8/13/2019 Unit 1-EC2352

7/19

Ring Topology

8/13/2019 Unit 1-EC2352

8/19

OSI Model

8/13/2019 Unit 1-EC2352

9/19

Physical Layer

The physical layer coordinates the functions required to carry abit stream over a physical medium. Representation of bitsTo be transmitted, bits must be encoded

into signals, electrical or optical. The physical layer defines thetype of encoding.

Data rate

It defines the transmission rate (number of bits sentper second). Line configurationThe physical layer is concerned with the

connection of devices to the media (point-to-point or multipointconfiguration).

Physical topologyIt defines how devices are connected (mesh,

star, ring, bus or hybrid) to make a network. Transmission modeThe physical layer also defines thedirection

of transmission between two devices: simplex, half-duplex, orfull-duplex

8/13/2019 Unit 1-EC2352

10/19

8/13/2019 Unit 1-EC2352

11/19

Data Link layerThe data link layer transforms a raw transmission facility to a

reliable link. FramingThe data link layer divides the stream of bits

received into manageable data units calledframes. Physical addressingThe data link layer adds a header to

the frame to define the sender and/or receiver of the frame.

Flow control

If the receiving rate is less than thetransmission rate, the data link layer imposes a flow controlmechanism to avoid overwhelming the receiver.

Error controlThe data link layer adds reliability to thephysical layer by adding a trailer to detect and retransmit

damaged/lost frames and to recognize duplicate frames. Access controlWhen two or more devices are connected

to the same link, data link layer protocols determines whichdevice has control over the link at any given time.

8/13/2019 Unit 1-EC2352

12/19

Network Layer

The network layer is responsible for the source-to-destination delivery of a data unit called packet.

Logical addressingThe packet is identified across thenetwork using the logical addressing system provided

by network layer and is used to identify the endsystems.

RoutingThe connecting devices (routers or switches)prepare routing table to send packets to their

destination.

8/13/2019 Unit 1-EC2352

13/19

Transport Layer

The transport layer is responsible forprocess-to-process delivery ofthe entire message.

Service-point addressingIt includes a service-point address orport address so that a process from one computer communicatesto a specific process on the other computer.

Segmentation and reassemblyA message is divided into

transmittable segments, each containing a sequence number.These numbers enable the transport layer to reassemble themessage correctly at the destination and to identify/replacepackets that were lost.

Connection controlThe transport layer can be eitherconnectionless or connection oriented.

Flow control

The flow control at this layer is performed end toend.

Error controlThe error control at this layer is performedprocess-to-process. Error correction is usually achieved throughretransmission.

8/13/2019 Unit 1-EC2352

14/19

Session LayerThe session layer is the network dialog controller. It

establishes, maintains, and synchronizes the interactionamong communicating systems.

Dialog controlIt allows two systems to enter into a dialogand communication between two processes to take place ineither half-duplex / full-duplex mode.

SynchronizationThe session layer allows a process to addcheckpoints, or synchronization points, to a stream of data.For example, when checkpoints are inserted for every 100pages and if a crash happens during transmission of page

523, then only pages 501 to 523 need to be resent. Bindingbinds together the different streams that are part

of a single application. For example, audio and videostream are combined in a teleconferencing application.

8/13/2019 Unit 1-EC2352

15/19

Presentation Layer

The presentation layer is concerned with the syntax and

semantics of the information exchanged betweenpeers.

TranslationBecause different computers use differentencoding systems, the presentation layer is responsiblefor interoperability between these encoding methods.

EncryptionTo carry sensitive information, a systemensures privacy by encrypting the message beforesending and decrypting at the receiver end.

CompressionData compression reduces the numberof bits contained in the information. It is particularlyimportant in multimedia transmission.

8/13/2019 Unit 1-EC2352

16/19

Application LayerThe application layer enables the user, whether human or

software, to access the network. It provides user interface and support for services such as

electronic mail, remote file access and transfer, shareddatabase management and several types of distributedinformation services.

Network virtual terminalA network virtual terminal is asoftware version of a physical terminal, and it allows a userto log on to a remote host.

File transfer, access, and managementThis applicationallows a user to access/retrieve files in a remote host, andto manage or control files in a remote computer locally.

Mail services

This application provides the basis for e-mailforwarding and storage.

Directory servicesThis application provides distributed

8/13/2019 Unit 1-EC2352

17/19

Layers of TCP/IP architecture

8/13/2019 Unit 1-EC2352

18/19

Transmission Media- guided and

Unguided

Guided Media Unguided media

Twisted-pair Radio waves

Coaxial Micro waves

Fiber-optic cable Infrared

8/13/2019 Unit 1-EC2352

19/19