Chapter 1:Introduction Computer

Networking: A Top Down Approach ,

4th edition. Jim Kurose, Keith Ross

Computer Networks

Today’s Lecture

Layered Architecture Brief description of Five Layers

Protocol Layers

Networks are complex!

• many “pieces”:

– hosts– routers– links of

various media– applications– protocols– hardware,

software

Question: Is there any way of organizing network

architecture?

Answer:

Yes possible with a layered architecture

Layering of Airline Functionality

• Airline functionality can be divided into layers, providing a frame work in which we can discuss air travel.

• At the ticketing layer and below– Airline-counter-to-airline-counter transfer of a person.

• At the gate layer– Departure-gate –to-arrival-gate transfer of a person is

accomplishedLayers: each layer implements a service

– via its own internal-layer actions– Combined with the services directly below it

ticket (purchase)

baggage (check)

gates (load)

runway (takeoff)

airplane routing

departureairport

arrivalairport

intermediate air-trafficcontrol centers

airplane routing airplane routing

ticket (complain)

baggage (claim

gates (unload)

runway (land)

airplane routing

ticket

baggage

gate

takeoff/landing

airplane routing

Why layering?Dealing with complex systems:Discuss a well defined, specific part of a

large and complex systemModularization eases maintenance,

updating of systemChange of implementation of layer’s

service transparent to rest of systeme.g. change in gate procedure doesn’t

affect rest of system

Internet Protocol Stack

To provide structure to design of network protocols, network designers organize protocols in layers

Service – says what a layer doesProtocol – says how the service is

implementedAdvantages DrawbacksWhen taken together the protocols

of various layers are called the Protocol Stack.

Internet Protocol Stack consists of Five layers

Physical, Link, Network, Transport and Application layers .

Organization of Book

Internet Protocol Stack

To provide structure to design of network protocols, network designers organize protocols in layers

Service – says what a layer doesProtocol – says how the service is

implementedAdvantages DrawbacksWhen taken together the protocols

of various layers are called the Protocol Stack.

Internet Protocol Stack consists of Five layers

Physical, Link, Network, Transport and Application layers .

Organization of Book

Internet Protocol Stack

• Application Layer:

Network applications and their application layer protocols reside.

Provides user interfaces and support for services such as e-mail, file transfer etc.

Hyper Text Transfer Protocol (HTTP)File Transfer Protocol (FTP)Session Initiation Protocol (SIP)

An application layer protocol is distributed over multiple end systems

The packets of information at the application layer is called as a message.

Internet Protocol Stack• Transport Layer:

Transports application-layer messages between application end points.

Transport layer packet is called as a segment Breaks long messages into shorter segments There are two Transport Layer Protocols Transmission Control Protocol (TCP)

Connection Oriented serviceGuaranteed delivery of application layer messagesFlow controlCongestion Control

User Datagram Protocol (UDP)Connectionless serviceNo reliability, flow control and congestion control

Internet Protocol Stack• Network Layer:

Responsible for moving network layer packets known as datagrams from one host to another.

Transport layer passes a transport layer segment and a destination address to the network layer.

Network layer includes IP ProtocolDefines the fields in the datagram as well

as how end systems and routers act on these fields

Commonly referred as IP layer.Different routing protocols.

Determine the route that datagrams take between source and destination

Internet Protocol Stack• Link Layer:

Moves a packet from one node (host or router) to the next node in the route.

Divide the stream of bits received from the network layer into manageable data units called frames.

Transforms a raw transmission facility to a reliable link.Mechanism to detect and retransmit

damaged or lost framesExample of link layer protocols include

WiFi, Ethernet etc.

Internet Protocol Stack• Physical Layer:

The job of this layer is to move the individual bits with in frames from one node to next.

Representation of bitsPhysical Layer data consists of a stream of

bits (0 or 1)To be transmitted bits must be encoded

into signals. The physical layer defines the type of encoding.

The protocol in this layer depend on the actual transmission medium of the link.

Internet Protocol Stack Application: Provides user interfaces

and support for services such as e-mail, file transfer etc. FTP, HTTP

Transport: Transports application-layer messages between application end points. Segmentation and reassembly TCP, UDP

Network: Routing of Datagrams from source to destination IP, routing protocols

Link: Move a packet from one node (host or router) to the next node in the route. Ethernet, WiFi

Physical: Move the individual bits with in frames from one node to next

Application

Transport

Network

Link

Physical