By

Jaji Nekkanti

Network Applications And Protocol Layering

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Agenda Applications

Need for Multiple Protocols

The Conceptual Layers of Protocol Software

Functionality of the Layers

ISO 7-Layer Reference Model

X.25 And its Relation to the ISO Model

The TCP/IP 5-Layer Reference Model

The Protocol Layering Principle

The Layering Principle Applied To A Network

Layering in Mesh Networks

Two Important Boundaries In The TCP/IP Model

Cross-Layer Optimizations

The Basic Idea Behind Multiplexing And Demultiplexing

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Applications

The World Wide Web

Email

Online social networking

Streaming audio and video,

Instant messaging

File-sharing

Create the applications-powerful programming platforms and new devices

such as smartphones have created new opportunities to develop applications

quickly and to bring them to a large market.

Who operate or manage networks—mostly a behind-the-scenes job, but a

critical one and often a very complex one-network operators.

Finally, there are those who design and build the devices and protocols that

collectively make up the Internet.

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Classes of Applications

Web

Presents simple interface

Users view pages full of textual and graphical objects and click on objects that

they want to learn more about, and a corresponding new page appears.

Uniform Resource Locator (URL),

For example,

http://www.cs.princeton.edu/˜llp/index.htm.

Message exchange includes up to six messages to translate the server

name(www.cs.princeton.edu) IP address (128.112.136.35)

Three messages to set up a Transmission Control Protocol (TCP) connection

between your browser and the server.

Four messages for your browser to send the HTTP “GET”

request and the server to respond with the requested page.

Four messages to tear down the TCP connection.

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Streaming audio and video

Services such as video on demand and Internet radio use this technology.

The delivery of audio and video has some important differences from

fetching a simple web page of text and images.

For example, No need to download an entire video file—a process that might

take minutes to hours—before watching the first scene.

Streaming audio and video implies a more timely transfer of messages from

sender to receiver, and the receiver displays the video or plays the audio

pretty much as it arrives.

Audio and video streams in a continuous ,skipped sounds or stalled video is

not acceptable.

By contrast, a page of text can be delivered and read in bits and pieces.

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Real-time audio and video

Tighter timing constraints than streaming applications.

Ex: Skype™ or a videoconferencing application, the interactions among

the participants must be timely.

Interactive applications usually entail audio and/or video flows in both

directions, while a streaming application is most likely sending video or

audio in only one direction.

Videoconferencing tools that run over the Internet have since the early

1990s but have achieved much more widespread in the last 2 years.

Fitting the video content into a relatively low bandwidth network, for

example, making sure that the video and audio remain in sync and arrive in

time.

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A multimedia application including videoconferencing

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Protocol layering

The Need For Multiple Protocols

Protocols allow one to specify or understand communication without

knowing the details of a particular vendor’s network hardware.

Network communication is a complex problem with many aspects:

Hardware failure

Hosts, routers

Network congestion

Networks have finite capacity

Packet delay or Packet loss

Data corruption

Electrical, magnetic interferences

HW failure

Data duplication or Inverted Arrivals

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Program translation has been partitioned into 4 sub problems identified with

software that handles each sub problem.

Compiler, assembler, link editor and loader.

Two things are clear here that:

1. It should be clear that pieces of translation software must agree on the exact

format of data passed between them.

2. The four parts of the translator form a linear sequence in which output from

the compiler becomes input to the assembler, and so on.

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The Conceptual Layers of Protocol

Software

Network

Layer n

…

Layer 2

Layer 1

Layer n

…

Layer 2

Layer 1

Sender Receiver

The modules of

Protocol SW

are on each

machine

stacked

vertically into

layers

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Functionality of the Layers

How many layers should be created ?

What functionality should reside in each layer ?

The questions are not easy to answer for several reasons:

Given a set of goals and constraints governing a particular communication

problem.

Reliable transmission.

The design of network architecture and the organization of the protocol software

are interrelated.

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ISO 7-Layer Reference Model

Service –says

what a layer

does.

Interface –says

how to access

the service.

Protocol –says

how the service

is implemented.

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X.25 And its Relation to the ISO Model

International Telecommunications Union(ITU).

In the X.25 view ,a network operates much like a telephone system.

Layers of the protocol standard specify various aspects of the network as

follows:

Physical layer:

*physical interconnection between computers and network packet

switches.

*Includes electrical characteristics of voltage and current.

Data link layer:

*specifies how data travels b/w a computer & packet switch to which it

connects.

*unit of data-frame.

* includes error detection.

* includes timeout mechanism.

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Network layer:

*Unit of data-Packets.

* includes the concepts of destination addressing and forwarding.

Transport layer:

* Unit of data-segments.

*provides end-to-end reliability.

Session layer:

*How protocol software can be organized to handle all the functionality

needed by applications programs.

*Ex: login and passwords, session and connection coordination.

Presentation layer:

* standardize the format of data that application programs send over a

network.

Application layer:

* includes application programs.

*Ex: E-mail, File transfer programs.

The TCP/IP 5-Layer Reference Model

Application

Transport

Internet

Network Interface

Physical

Messages or Streams

Transport Protocol Packets

IP Packets

Network-Specific Frames

Functionality

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Layer 5: Application

Users invoke application programs that access services available across a TCP/IP.

Application programs may send,sequence of individual messages or a continuous stream of data.

Layer 4: Transport

Provide communication from one application to another.

Provides reliable delivery of data.

Layer 3: Internet

Handles communication from one computer to another.

Defines uniform format of packets forwarded across networks of different technologies and rules for forwarding packets in routers.

Layer 2: Network Interface

Responsible for accepting IP packets and transmitting them over a specific network.

Defines formats for carrying packets in hardware frames

Layer 1: Physical

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Protocol 1

Protocol 2

Protocol 3

Interface 1Interface 2

Interface3

IP Module

A realistic view of protocol software with multiple network interfaces and

multiple protocols

Software Organization

Application

Transport

Internet

Network

interface

Physical

Hardware

app1 app3 app4 app5 app6app2

Network3Network2Network1

Conceptual Layers

Conceptual layers of protocols needed in computers and routers to

transfer a message from an application on computer A to an application

on computer B.

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Transpor

t

Internet

Net Iface

Transpor

t

Internet

Net Iface

Net1 Net2 Net3

Internet

Net Iface

Internet

Net Iface

Send

er

Receiv

er

Computer

A

Computer BRouter

1

Router

2

Locus of Intelligence

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In the original telephone network , all the intelligence was located in phone

switches. Ex: a microphone , earpiece & a mechanism used to dial.

By contrast, the TCP/IP protocols require attached computers to run transport

protocols and applications as well as layer 3 and layer2 protocols.

The fundamental concept is:

* TCP/IP protocols place much of intelligence in hosts – routers in the

Internet forward packets , but do not participate in higher-layer services.

The Protocol Layering Principle

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Layered protocols are designed so that layer N at the destination receives

exactly the same object sent by layer N at the source.

The layering principle offers:

Protocol design independence:

* A protocol designers can focus on the message exchange for a given layer

with the assurance that lower layers will not alter the message.

* The key idea is that a transport protocol can be designed independent of

other protocols.

Definition of the end-to-end property:

* We say a protocol is end-to-end if and only if the layering principle applies

between the original source and ultimate destination.

* Other protocols are classified as machine-to-machine.

The Layering Principle Applied To A Network

Application

Transport

Internet

Network Interface

Host A Host B

Application

Transport

Internet

Network Interface

Physical net

Identica

l

messag

eIdentica

l

packet

Identical

IP packet

Identica

l

Frame

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Layering in a tcp/ip internet environment

Application

Transport

Internet

Network Interface

Host A Host B

Application

Transport

Internet

Network Interface

Physical net1

Identica

l

messag

eIdentica

l

packet

Identical

IP packet

Identica

l

Frame

22 Physical net2

Identica

l

Frame

Network Interface

Internet Identical

IP packet

Router R

Layering in Mesh Networks

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Protocol 1Protocol 2

Protocol 3

Interface 1Interface 2

Interface3

IP Module

Point-To-Point

forwarding

Transport

Internet

Network Interface

Intranet Sublayer

Conceptual Layers Software Organization

Application

Physical hardware

app1 app2app3 app4 app5 app6

Network1 Network3

Two Important Boundaries In The TCP/IP Model

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Application

Transport

Internet

Network

interface

Physical

Hardware

Conceptual Layers

Software outside the operating system

Software inside the operating system

Only Internet addresses used

Physical addresses used

Application programs and all protocol software from the internet layer

upward use only Internet addresses; addresses used by the network hardware

are isolated at lower layers.

Protocol

addresses

boundary

Operating

system

boundary

Cross-Layer Optimizations

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Designer divides complex problem into subproblems and solve each one

independently. But the software that results from strict layering can be

extremely inefficient.

To optimize transfer, the transport layer should choose the largest packet size

that will allow one packet to travel in one network frame.

Strict layering will prevent the transport layer from optimizing transfers.

Implementers relax the strict layering scheme when building protocol software.

When allocating packet buffers, transport layer protocols can use the

information to optimize processing by leaving sufficient space for headers that

will be added by lower-layer protocols.

Similarly, lower-layer protocols often retain all the headers on an incoming

frame when passing the frame to higher-layer protocols.

The Basic Idea Behind Multiplexing And Demultiplexing

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Demultiplexing

Based on Frame type

IP Module

ARP Module

RARP Module

Frame arrives

Illustration of frame demultiplexing that uses a type field in the frame

header .Demultiplexing is used with most networks,including Ethernet

and Wi-Fi.

Illustration of demultiplexing incoming IP packets based on the type field

in the IP header

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IP Module

Datagram arrives

TCP ProtocolUDP Protocol

ICMP Protocol