1. CHAPTER 2
Application Layer

2. Announcements and Outline
Administrative Items
Questions?
Recap
Introduction to Networks
Network Type
Network Layers
Today’s Outline
Application Layer
2.1 Hardware
2.2 Application Architecture (Software)
2.3 Web
2.4 2

3. Network Layers
Computer 1
Computer 2 3

4. Acronyms of the Day HTTP – Hypertext Transfer Protocol
SMTP – Simple Mail Transfer Protocol
POP – Post Office Protocol
IMAP – Internet Message Access Protocol
MIME – Multipurpose Internet Mail Extensions 4

5. 2 Application Layer Applications Application Layer Transport Layer
(e.g., , web,
word processing)
Application Layer
Transport Layer
Network Layer
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 5

6. 2.1 Hardware - Client What the users use PC Terminal Network Computers
Mobile Devices
Special Purpose 6

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

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

9. 2.1 Hardware – Server
Mainframes
From 1970’s
More Recent 9

10. 2.1 Hardware – Server
Clusters
Server Clusters
Computer Cluster

11. 2.2 Application Architecture
Splitting the work across the client and the server
Basic Software Components:
Presentation Logic
Application Logic
Data Access Logic
Data 11

12. 2.2 Host (Server) Based Architecture
CLIENT
SERVER 12

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

14. 2.2 Client Based Architecture
SERVER 14

15. 2.2 Client Based Architecture Problems
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 15

16. 2.2 Client-Server Architecture
2-Tier Architecture
CLIENT
SERVER 16

17. 2.2 Client-Server Architecture
2-Tier Architecture
CLIENT
SERVER

18. Thin and Thick Clients
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

19. 2.2 Client-Server Architecture
Advantages
Disadvantages 19

20. client application programs server application programs
Middleware
client 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)
Middleware
server application programs
Examples of standards for Middleware:
Distributed Computing Environment (DCE)
Common Object Request Broker Architecture (CORBA)
Open Database Connectivity (ODBC) 20

21. Multi-tier Architectures
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 21

22. 2.2 Client-Server Architecture22

23. 2.2 Client-Server Architecture23

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

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

26. Peer to Peer Architecture26

27. 2.2 Criteria for Choosing Architecture
Infrastructure Cost Development Cost Scalability 27

28. 2.2 Choosing an Architecture
Host-Based
Client-Based
Client-Server
Cost of Infrastructure
Cost of Development
Scalability 28

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

30. 2.3 Web
HTTP Requests:
Request Line
Request Header
Request Body 30

31. 2.3 Web HTTP Response: Response Status Response Header Response Body31

32. 2.3 Web (Request/Response Demo) 32

33. 2.4.1 Email (2-Tier - Thick Client)
How a message is sent 33

34. 2.4.1 Email (2-Tier - Thick Client)
How a message is sent offsite (e.g. from UNCW to UNC) 34

35. – Web Mail
3-Tier – Off Campus 35

36. – SMTP Packets
Header
Body 36

37. 2.4.4 Email – Sending Attachments
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 37

38. Instant Messaging (IM)
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

39. How Instant Messaging Works

40. Videoconferencing
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

41. Recap – Application Layer
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 41

42. Next Class 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? 42