S1 C3 Application Layer Functionality and Protocols

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The Presentation layer // Tao ra mot cau truc va dinh dang chung cua thong tin

  • Coding and conversion // Ma hoa
  • Compression //Nen du lieu
  • Encryption //Ma hoa (bao mat)

The Session Layer

  • Create and maintain dialogs between source and destination applications. // Khoi tao va duy tri cac phien ket noi giua ung dung nguon va dich
  • Handles the exchange of information to initiate dialogs, keep them active, and to restart sessions that are disrupted or idle for a long period of time.

Application Layer Protocols and Services

  • Domain Name System (DNS) – TCP/UDP Port 53
  • Hypertext Transfer Protocol (HTTP) – TCP Port 80
  • Simple Mail Transfer Protocol (SMTP) – TCP Port 25
  • Post Office Protocol (POP) – UDP Port 110
  • Telnet – TCP Port 23
  • Dynamic Host Configuration Protocol – UDP Port 67
  • File Transfer Protocol (FTP) – TCP Ports 20 and 21

The Client-Server Model

  • Client: device requesting // yeu cau
  • Server: device responding // dap ung


  • Peer-to-Peer Networking: two or more computers are connected via a network and can share resources (such as printers and files) without having a
    dedicated server.
  • Peer-to-Peer Applications: allows a device to act as both a client and a server within the same communication. In this model, every client is a server and every server a client. Both can initiate
    a communication and are considered equal in the communication process.