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Application Layer, Aplikasi P2P umum meliputi:, Dengan aplikasi P2P,…

- - - - The three application layer protocols involved in everyday work or games are:
        
        Hypertext Transfer Protocol (HTTP)
        
        browse the web
        
        Simple Mail Transfer Protocol (SMTP)
        
        digunakan untuk memungkinkan pengguna mengirim email
        
        Post Office Protocol (POP)
        
        digunakan untuk mengizinkan pengguna menerima email
    - - Example
        URL: http://www.cisco.com/index.html
    - - Developed to publish and retrieve HTML pages
      - Used for data transfer
      - Specifies a request/response protocol
      - Three common message types are GET, POST, and PUT
      - GET is a client request for data
      - POST and PUT are used to send messages that upload data to the web server
    - - Typically use an application called a Mail User Agent (email client)
      - Allows messages to be sent
      - Places received messages into the client's mailbox
      - SMTP - Send email from either a client or a server
        
        transfers mail
        
        message must be formatted properly
        
        SMTP processes must be running on both the client and server
        
        message header must have a properly formatted recipient email address and a sender
        
        uses port 25
      - POP - Receive email messages from an email server
        
        enables a workstation to retrieve mail from a mail server
        
        mail is downloaded from the server to the client and then deleted on the server
        
        uses port 110
        
        POP does not store messages
        
        POP3 is desirable for an ISP, because it alleviates their responsibility for managing large amounts of storage for their email servers
      - IMAP - Internet Message Access Protocol
        
        Another protocol that to retrieves email messages
        
        Unlike POP, when the user connects to an IMAP-capable server, copies of the messages are downloaded to the client application
        
        Original messages are kept on the server until manually deleted
      - Email client provides the functionality of both protocols within one application
  - - - A human legible name is resolved to its numeric network device address by the DNS protocol
    - - DNS server stores different types of resource records used to resolve names
      - Contain the name, address, and type of record
      - Record types are:
        
        A - an end device address
        
        NS - an authoritative name server
        
        CNAME - the canonical name for an alias; used when multiple services have the single network address but each service has its own entry in DNS
        
        MX - mail exchange record; maps a domain name to a list of mail exchange servers
      - Unable to resolve the name using its stored records, contacts other servers
      - Server temporarily stores the numbered address that matches the name in cache memory
      - Windows ipconfig /displaydns displays all cached DNS
    - - Examples top-level domains:
        
        .au - Australia
        
        .co - Colombia
        
        .com - business or industry
        
        .jp - Japan
        
        .org - non-profit organization
    - - Operating system utility called nslookup allows the user to manually query the name servers to resolve a given host name
      - Utility can be used to troubleshoot name resolution issues and to verify the current status of the name servers
    - - DHCP allows a host to obtain an IP address dynamically
      - DHCP server is contacted and address requested - chooses address from a configured range of addresses called a pool and “leases” it to the host for a set period
      - DHCP used for general purpose hosts such as end user devices, and static addressing is used for network devices such as gateways, switches, servers and printers
    - - FTP allow data transfers between a client and a server
      - FTP client is an application that runs on a computer that is used to push and pull data from a server running an FTP daemon
      - To successfully transfer data, FTP requires two connections between the client and the server, one for commands and replies, the other for the actual file transfer
- - - - Presentation layer has three primary functions:
        
        Compression of the data
        
        Encryption of the data for transmission and the decryption of data upon receipt by the destination
        
        Coding and conversion of application layer data
      - Session Layer
        
        Functions create and maintain dialogs between source and destination applications
        
        Handles the exchange of information to initiate dialogs, keep them active, and to restart sessions
    - - Domain Name Service Protocol (DNS) digunakan untuk menyelesaikan nama Internet ke alamat IP
      - Telnet adalah protokol emulasi terminal yang digunakan untuk menyediakan akses jarak jauh ke server dan perangkat jaringan
      - Bootstrap Protocol (BOOTP) adalah prekursor protokol DHCP, protokol jaringan yang digunakan untuk mendapatkan informasi alamat IP selama boot
      - Dynamic Host Control Protocol (DHCP) digunakan untuk menetapkan alamat IP, subnet mask, gateway default, dan server DNS ke host
      - Hypertext Transfer Protocol (HTTP) digunakan untuk mentransfer file yang membentuk halaman Web World Wide Web
      - File Transfer Protocol (FTP) digunakan untuk transfer file interaktif antar sistem
      - Trivial File Transfer Protocol (TFTP) digunakan untuk transfer file aktif tanpa koneksi
      - Simple Mail Transfer Protocol (SMTP) digunakan untuk transfer pesan email dan lampiran
      - Post Office Protocol (POP) digunakan oleh klien email untuk mengambil email dari server jauh
      - Internet Message Access Protocol (IMAP) adalah protokol lain untuk pengambilan email
  - - - Server
        
        Resources are stored on the server
      - Client
        
        A client is a hardware/software combination that people use directly