1. 思科网络技术学院理事会. http://www.catc.edu.cn 1 Application Layer Functionality and Protocols Network Fundamentals – Chapter 3

2. 2 思科网络技术学院理事会. http://www.catc.edu.cn Objectives  Define the application layer as the source and destination of data for communication across networks.  Explain the role of protocols in supporting communication between server and client processes.  Describe the features, operation, and use of well-known TCP/IP application layer services (HTTP, DNS, SMTP).

3. 3 思科网络技术学院理事会. http://www.catc.edu.cn Context Index 3.1 Applications - The Interface Between the Networks 3.2 Making Provisions for Applications and Services 3.3 Application Layer Protocols and Services Examples

4. 思科网络技术学院理事会. http://www.catc.edu.cn 4 3.1 Applications - The Interface Between the Networks

5. 5 思科网络技术学院理事会. http://www.catc.edu.cn Applications – The Interface Between Human and Data Networks  it is important to know how an application is able to format, transmit and interpret messages that are sent and received across the network

6. 6 思科网络技术学院理事会. http://www.catc.edu.cn 3.1.1 OSI and TCP/IP Model  The OSI model divides the networking process into seven logical layers, each of which has unique functionality and to which are assigned specific services and protocols.

7. 7 思科网络技术学院理事会. http://www.catc.edu.cn 3.1.1 OSI and TCP/IP Model  Role of applications, services and protocols in converting communication to data that can be transferred across the data network.

8. 8 思科网络技术学院理事会. http://www.catc.edu.cn  TCP/IP application layer protocols fit roughly into the framework of the top three layers of the OSI model: Application, Presentation and Session layers. 3.1.1 OSI and TCP/IP Model

9. 9 思科网络技术学院理事会. http://www.catc.edu.cn 3.1.1 OSI and TCP/IP Model  The most widely-known TCP/IP Application layer protocols are those that provide for the exchange of user information.

10. 10 思科网络技术学院理事会. http://www.catc.edu.cn 3.1.2 Application Layer Software<  The functions associated with the Application layer protocols enable our human network to interface with the underlying data network.

11. 11 思科网络技术学院理事会. http://www.catc.edu.cn 3.1.3 User Applications, Services, and Application Layer Protocols  As mentioned previously, the Application layer uses protocols that are implemented within applications and services.

12. 12 思科网络技术学院理事会. http://www.catc.edu.cn 3.1.4 Application Layer Protocol Functions  Application layer protocols provide the rules for communication between applications.

13. 思科网络技术学院理事会. http://www.catc.edu.cn 13 3.2 Making Provisions for Applications and Services

14. 14 思科网络技术学院理事会. http://www.catc.edu.cn 3.2.1 The Client-Sever Model  In the client/server model, the device requesting the information is called a client and the device responding to the request is called a server.

15. 15 思科网络技术学院理事会. http://www.catc.edu.cn 3.2.2 Servers  Servers are repositories of information. Processes control the delivery of files to clients.

16. 16 思科网络技术学院理事会. http://www.catc.edu.cn 3.2.3 Application Layer Services and Protocols  Server processes may support multiple clients.

17. 17 思科网络技术学院理事会. http://www.catc.edu.cn 3.2.4 Peer-to-Peer Networking and Applications (p2p)  In a peer-to-peer network, two or more computers are connected via a network and can share resources (such as printers and files) without having a dedicated server.

18. 18 思科网络技术学院理事会. http://www.catc.edu.cn 3.2.4 Peer-to-Peer Networking and Applications (p2p)  A peer-to-peer application (P2P), unlike a peer-to-peer network, allows a device to act as both a client and a server within the same communication.

19. 思科网络技术学院理事会. http://www.catc.edu.cn 19 3.3 Application Layer Protocols and Services Examples

20. 20 思科网络技术学院理事会. http://www.catc.edu.cn  Most people have a hard time remembering numeric IP address. Hence, domain names were created to convert the numeric address into a simple, recognizable name. 3.3.1 DNS Services and Protocol

21. 21 思科网络技术学院理事会. http://www.catc.edu.cn 3.3.1 DNS Services and Protocol  Computer operating systems also have a utility called nslookup that allows the user to manually query the name servers to resolve a given host name.

22. 22 思科网络技术学院理事会. http://www.catc.edu.cn 3.3.1 DNS Services and Protocol  The DNS server stores different types of resource records used to resolve names. These records contain the name, address, and type of record.

23. 23 思科网络技术学院理事会. http://www.catc.edu.cn 3.3.1 DNS Services and Protocol  A hierarchy of DNS servers contains the resource records that match names with addresses.

24. 24 思科网络技术学院理事会. http://www.catc.edu.cn 3.3.2 WWW Service and HTTP  When a web address (or URL) is typed into a web browser, the web browser establishes a connection to the web service running on the server using the HTTP protocol.

25. 25 思科网络技术学院理事会. http://www.catc.edu.cn 3.3.2 WWW Service and HTTP  In response to the request, the HTTP server returns code for a web page.

26. 26 思科网络技术学院理事会. http://www.catc.edu.cn 3.3.2 WWW Service and HTTP  The browser interprets the HTML code and displays a web page.

27. 27 思科网络技术学院理事会. http://www.catc.edu.cn 3.3.2 WWW Service and HTTP  Entering ‘http://www.cisco.com’ in the address bar of a web browser generates the HTTP ‘GET’ Message.

28. 28 思科网络技术学院理事会. http://www.catc.edu.cn 3.3.3 E-mail Services and SMTP/POP Protocols  Clients send e-mails to a server using SMTP and receive e-mails using POP3.

29. 29 思科网络技术学院理事会. http://www.catc.edu.cn 3.3.3 E-mail Services and SMTP/POP Protocols  E-mail Server – MTA  The mail Transfer Agent process governs e-mail handling between servers and servers.

30. 30 思科网络技术学院理事会. http://www.catc.edu.cn 3.3.3 E-mail Services and SMTP/POP Protocols  E-mail Server – MDA  The mail Delivery Agent process governs delivery of e- mail between servers and clients.

31. 31 思科网络技术学院理事会. http://www.catc.edu.cn 3.3.3 E-mail Services and SMTP/POP Protocols  SMTP is used to forward e-mail.  POP is used to deliver e-mail.

32. 32 思科网络技术学院理事会. http://www.catc.edu.cn 3.3.4 FTP  FTP was developed to allow for file transfers between a client and a server.

33. 33 思科网络技术学院理事会. http://www.catc.edu.cn 3.3.5 DHCP  The Dynamic Host Confirmation Protocol (DHCP) service enables devices on a network to obtain IP addresses and other information from a DHCP server.

34. 34 思科网络技术学院理事会. http://www.catc.edu.cn 3.3.5 DHCP  The DHCP server maintains a pool of IP addresses and leases an address to any DHCP-enabled client when the client is powered on.

35. 35 思科网络技术学院理事会. http://www.catc.edu.cn 3.3.6 File Sharing Services and SMB Protocol  SMB is a client-server, request-response protocol. Servers can make their resources available to clients on the network.

36. 36 思科网络技术学院理事会. http://www.catc.edu.cn 3.3.6 File Sharing Services and SMB Protocol  A file may be copied from PC to PC with Windows Explorer using the SMB protocol.

37. 37 思科网络技术学院理事会. http://www.catc.edu.cn 3.3.7 P2P Services and Gnutella Protocol  With P2P applications based on the Gnutella protocol, people can make files on their hard disks available to others for downloading.

38. 38 思科网络技术学院理事会. http://www.catc.edu.cn 3.3.7 P2P Services and Gnutella Protocol  Many P2P applications do not use a central database to record all the files available on the peers.

39. 39 思科网络技术学院理事会. http://www.catc.edu.cn 3.3.8 Telnet Services and Protocol  Telnet provides a way to use a computer, connected via the network, to access a network device as if the keyboard and monitor were directly connected to the device.

40. 40 思科网络技术学院理事会. http://www.catc.edu.cn 3.3.8 Telnet Services and Protocol  Telnet is a client/server protocol and it specifies how a VTY session is established and terminated.

41. 41 思科网络技术学院理事会. http://www.catc.edu.cn Summary

42. 42 思科网络技术学院理事会. http://www.catc.edu.cn