Chapter 10: Application Layer

Chapter 10: Application Layer

1. Class Activity – Application Investigation

   • Network Applications
     • Make communication in the workplace easier
     • Affect the amount of work completed on a daily basis
     • Reduce data communications time and costs

2. Application Layer

   • The application layer is closest to the end user.

3. Presentation and Session Layer

   • The presentation layer has three primary functions
     • Formatting, or presenting, data at the source device into a compatible form for receipt by the destination device
     • Compressing data in a way that can be decompressed by the destination device
     • Encrypting data for transmission and decrypting data upon receipt

4. TCP/IP Application Layer Protocols

   • The TCP/IP application protocols specify the format and control information necessary for many common Internet communication functions.

5. Client-Server 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.

6. Peer-to-Peer Networks

   • In the peer-to-peer (P2P) networking model, the data is accessed from a peer device without the use of a dedicated server.

7. Peer-to-Peer Applications

   • A P2P application allows a device to act as both a client and a server within the same communication

8. Common P2P Applications

   • With P2P applications, each computer in the network running the application can act as a client or a server for the other computers in the network running the application.
     • eDonkey
     • G2
     • BitTorrent
     • Bitcoin

9. Hypertext Transfer Protocol and Hypertext Markup Language

   • When a web address or uniform resource locator (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.

10. HTTP and HTTPS

    • HTTP is a request/response protocol.
      • GET
        • A client request for data. A client (web browser) sends the GET message to the web server to request HTML pages.
      • POST
        • Uploads data files to the web server such as form data.
      • PUT
        • Uploads resources or content to the web server such as an image.

11. Email Protocols

    • One of the primary services offered by an ISP is email hosting. To run on a computer or other end device, email requires several applications and services

12. SMTP Operation

    • SMTP message formats require a message header and a message body.

13. POP Operation

    • POP is used by an application to retrieve mail from a mail server. With POP, mail is downloaded from the server to the client and then deleted on the server. This is how POP operates, by default.

14. IMAP Operation

    • IMAP is another protocol that describes a method to retrieve email messages.

15. Domain Name Service

    • In data networks, devices are labeled with numeric IP addresses to send and receive data over networks.

16. DNS Message Format

    • The DNS server stores different types of resource records used to resolve names.
      • A
        • An end device IPv4 address
      • NS
        • An authoritative name server
      • AAAA
        • An end device IPv6 address (pronounced quad-A)
      • MX
        • A mail exchange record

17. DNS Hierarchy

    • The DNS protocol uses a hierarchical system to create a database to provide name resolution.

18. The nslookup Command

    • When configuring a network device, one or more DNS Server addresses are provided that the DNS client can use for name resolution.

19. Dynamic Host Configuration Protocol

    • The Dynamic Host Configuration Protocol (DHCP) for IPv4 service automates the assignment of IPv4 addresses, subnet masks, gateways, and other IPv4 networking parameters.

20. DHCP Operation

    • As shown in the figure, when an IPv4, DHCP-configured device boots up or connects to the network, the client broadcasts a DHCP discover (DHCPDISCOVER) message to identify any available DHCP servers on the network.

21. File Transfer Protocol

    • FTP is another commonly used application layer protocol.
      • The client establishes the first connection to the server for control traffic using TCP port 21, consisting of client commands and server replies.
      • The client establishes the second connection to the server for the actual data transfer using TCP port 20.