Application Layer

CHAPTER 2

Announcements and Outline Administrative Items Questions?

Recap1. Introduction to Networks

1. Network Type

2. Network Layers

Today’s Outline2. Application Layer

2.1 Hardware2.2 Application Architecture (Software)2.3 Web2.4 Email

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Network Layers

Computer 1 Computer 2

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• HTTP – Hypertext Transfer Protocol

• SMTP – Simple Mail Transfer Protocol

• POP – Post Office Protocol

• IMAP – Internet Message Access Protocol

• MIME – Multipurpose Internet Mail Extensions

Acronyms of the Day

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2 Application Layer

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Application Layer

Network Layer

Transport Layer

Applications(e.g., email, web, word processing)

• The software that enables the user to perform useful work

• Application architecture• The way in which the functions of the application layer

software are spread among the clients and servers on the network

• Functions of Application Layer

What the users use

• PC • Terminal• Network Computers• Mobile Devices• Special Purpose

2.1 Hardware - Client

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Terminal

MobileTechnologies

SpecialPurpose

2.1 Hardware – Client (Special Purpose)

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What the client accesses

• PC (special purpose)• Mainframe• Clusters (aka Server Farms)• Special Purpose

2.1 Hardware – Server

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Mainframes

2.1 Hardware – Server

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From 1970’s

More Recent

Clusters

2.1 Hardware – Server

Server Clusters

Computer Cluster

Splitting the work across the client and the server

Basic Software Components:• Presentation Logic

• Application Logic

• Data Access Logic

• Data

2.2 Application Architecture

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2.2 Host (Server) Based Architecture

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CLIENT SERVER

Host becomes a bottleneck

Host upgrades typically expensive and “lumpy”

2.2 Host Based Architecture Problems

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2.2 Client Based Architecture

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CLIENT SERVER

Data traffic must travel back and forth between server and client

Example: when the client program is making a database query, the ENTIRE database must travel to the client before the query can be processed

Often the large file sizes moving across the LAN can yield a poor result in network performance

2.2 Client Based Architecture Problems

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2-Tier Architecture

2.2 Client-Server Architecture

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CLIENT SERVER

2-Tier Architecture

2.2 Client-Server Architecture

CLIENT SERVER

Classification depends on how much of the application logic resides on the client or server

Thin client: • Little or no application logic on client• Becoming popular because easier to manage, (only

the server application logic generally needs to be updated)

• The best example: World Wide Web architecture (uses a two-tier, thin client architecture)

Thick client:• All or most of the application logic resides on the

client

Thin and Thick Clients

Advantages

Disadvantages

2.2 Client-Server Architecture

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Examples of standards for Middleware: Distributed Computing Environment (DCE) Common Object Request Broker Architecture (CORBA) Open Database Connectivity (ODBC)

Middleware

Middleware

client application programs

server application programs

a standard way of translating between software from different vendors

–Manages message transfers

– Insulates network changes from the clients (e.g., adding a new server)

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Involve more than two computers in distributing application program logic 2-tier architecture

• Uses clients and servers in a balance, very popular approach in simple LANs

3-tier architecture• 3 sets of computers involved

N-tier architecture • More than three sets of computers used, more typical

across complex organizations• Allows load balancing across servers

Multi-tier Architectures

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2.2 Client-Server Architecture

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CLIENT SERVER SERVER

2.2 Client-Server Architecture

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CLIENT SERVER SERVER SERVER

Advantages

Disadvantages

2.2 Client-Server Architecture (Multi-Tier)

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Peer to Peer Architecture

• All computers can serve as a client and a server

Advantages:

Disadvantages:

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Peer to Peer Architecture

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Infrastructure Cost

Development Cost

Scalability

2.2 Criteria for Choosing Architecture

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2.2 Choosing an Architecture

 

Host-Based Client-Based Client-Server

Cost of Infrastructure

Cost of Development

Scalability

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What happens when type a web address (2-Tier Networks, Client/Server)

2.3.1 Web (How it works)

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HTTP Requests:

1. Request Line

2. Request Header

3. Request Body

2.3 Web

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HTTP Response:

1. Response Status

2. Response Header

3. Response Body

2.3 Web

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www.rexswain.com/httpview

2.3 Web (Request/Response Demo)

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How a message is sent

2.4.1 Email (2-Tier - Thick Client)

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How a message is sent offsite (e.g. email from UNCW to UNC)

2.4.1 Email (2-Tier - Thick Client)

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3-Tier Email – Off Campus

2.4.2 Email – Web Mail

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1. Header

2. Body

2.4.3 Email – SMTP Packets

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SMTP is a relatively old protocol and is text only, so how do we send attachments using text only?

MIME (Multipurpose Internet Mail Extension)

MIME example

2.4.4 Email – Sending Attachments

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A client-server program that allows real-time typed messages to be exchanged Client needs an IM client software Server needs an IM server package

Some types allow voice and video packets to be sent Like a telephone

Examples include AOL and ICQTwo step process:

Telling IM server that you are online Chatting

Instant Messaging (IM)

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How Instant Messaging Works

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Provides real time transmission of video and audio signals between two or more locations Allows people to meet at the same time in different

locations Saves money and time by not having to move people

around Typically involves matched special purpose rooms with

cameras and displays

Desktop videoconferencing Low cost application linking small video cameras and

microphones together over the Internet No need for special rooms Example: Net Meeting software on clients communicating

through a common videoconference server

Videoconferencing

2.1 Hardware2.1.1 Clients2.1.2 Servers

2.2 Application Architecture (Software)2.3 Web

2.3.1 How it works2.3.2 Requests and Responses

2.4 Email2.4.1 How it Works2.4.2 Requests and Sending Attachments

Recap – Application Layer

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• Read Chapter 3 - Physical Layer• Find out what service you currently use• What are the transmission speed?• What type of transmissions are utilized – Analog

or Digital?

Next Class

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