Application Layer CHAPTER 2

Announcements and Outline  Administrative Items  Questions? Recap 1.Introduction to Networks 1.Network Type 2.N etwork Layers Today’s Outline 2.Application Layer 2.1 Hardware 2.2 Application Architecture (Software) 2.3 Web

3 Network Layers Computer 1Computer 2 3

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 4

2 Application Layer 5 Application Layer Network Layer Transport Layer Applications (e.g., , 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 6

Terminal Mobile Technologies Special Purpose 2.1 Hardware – Client (Special Purpose) 7

What the client accesses PC (special purpose) Mainframe Clusters (aka Server Farms) Special Purpose 2.1 Hardware – Server 8

Mainframes 2.1 Hardware – Server 9 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 11

2.2 Host (Server) Based Architecture 12 CLIENTSERVER

Host becomes a bottleneck Host upgrades typically expensive and “lumpy”    2.2 Host Based Architecture Problems 13

2.2 Client Based Architecture 14 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 15

2-Tier Architecture 2.2 Client-Server Architecture 16 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 19

Examples of standards for Middleware:  Distributed Computing Environment (DCE)  Common Object Request Broker Architecture (CORBA)  Open Database Connectivity (ODBC) 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) 20

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 21

2.2 Client-Server Architecture 22 CLIENT SERVER

2.2 Client-Server Architecture 23 CLIENT SERVER

Advantages   Disadvantages   2.2 Client-Server Architecture (Multi-Tier) 24

Peer to Peer Architecture All computers can serve as a client and a server Advantages: Disadvantages: 25

Peer to Peer Architecture 26

Infrastructure Cost Development Cost Scalability 2.2 Criteria for Choosing Architecture 27

2.2 Choosing an Architecture Host-BasedClient-BasedClient-Server Cost of Infrastructure Cost of Development Scalability 28

What happens when type a web address (2-Tier Networks, Client/Server) Web (How it works) 29

HTTP Requests: 1.Request Line 2.Request Header 3.Request Body 2.3 Web 30

HTTP Response: 1.Response Status 2.Response Header 3.Response Body 2.3 Web 31

2.3 Web (Request/Response Demo) 32

How a message is sent (2-Tier - Thick Client) 33

How a message is sent offsite (e.g. from UNCW to UNC) (2-Tier - Thick Client) 34

3-Tier – Off Campus – Web Mail 35

1.Header 2.Body – SMTP Packets 36

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 – Sending Attachments 37

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 ICQ Two step process:  Telling IM server that you are online  Chatting Instant Messaging (IM)

How Instant Messaging Works

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 Hardware Clients Servers 2.2 Application Architecture (Software) 2.3 Web How it works Requests and Responses How it Works Requests and Sending Attachments Recap – Application Layer 41

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 42