Application layer

Application layer

1. Netwrok vs Application Architecture

   • Network is fixed and service orientated
   • Application fluid and dictated by app developer
     • P2P
       • No dedicated server
       • Popular for traffic intensive applications
       • Bit-torrent,skype,xunlei
       • Scalable, cost-effective(absence of servers)
       • ISP,security, incentives
     • Client-Server
       • Clients don't communicate, Servers always on with fixed IP address
       • Web, FTP, Telnet, email
       • Data centres that act as virtual server
     • Hybrid mixture of P2P and client-server
       • Instant messaging, server for iP dresses of hosts, hosts sent messages directly between themselves

2. Process to process communication

   • Transport layer protocols consideratios
     • Reliable data transfer
       • loss tolerance
     • Throughput
       • Bandwidth sensitivity
       • Elasticity
     • Timing
       • Real time app
       • Non-real time app
     • TCP vs UDP
       • SSL enhancement
       • TCP: connection orientated, reliable data transfer, congestion control
       • UDP: connectionless, unreliable data transfer, no congestion control

3. Application layer protocol

   • Decides semantics, types of messages, syntax, when/how processes can receive and send messages
   • HTTP
     • Stateless protocol
     • TCP
       • Persistent vs non-persistent connection
         • Serial allows pipelining
         • Parallel burdens server, needs to create TCP buffers and variables
     • Web
       • Web page
         • Objects
           • Base HTML file
             • URL
               • Serverhost name
                 • e.g Apache, Microsoft internet server
               • Pathname
           • JPEG image
           • Java Applet
           • Video clip
     • Inband
   • FTP
     • Out of band
     • 2 parallel connections
       • Data
         • non-persistent connection
       • Control
   • SMTP

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