Application Layer

Application Layer

1. Principles of Network Apps

   • Writing programs that run on different end systems and communicate with eachother over the network
     • e.g Web applications two distinct programs that communicate with each other
       • BROWSER PROGRAM running in USERS HOST, WEB SERVER PROGRAM running in the WEB SERVER HOST
   • Network core devices do not function at app layer but instead function on lower layers, specifically network layer and below
   • Examples of network apps
     • File distribution, BT, File sharing, LimeWire
     • Internet telephony
       • Skype
       • IPTV
       • PPLive
     • Email
     • Web
     • IM
     • P2P file sharing

2. Creating a Network Apps

   • No need to write software for network-core devices
     • they do not run user apps
     • Apps on end systems allow for rapid app development, propagation
   • Write programs that
     • Run on (different) end systems
     • Communicate over network, e.g web server software communicates with browser software

3. Network Application Architectures

   • App arch different from network arch (first 5 layer internet arch)
     • NAs are fixed from developers perspective
       • provides a specific set of services to applications
     • Application arch is designed by the apps developers and dictates how the apps is structured over the various end systems
   • Client server
     • Client
       • Communicates with the server
       • May be intermitently connected
       • My have dynamic IP address
       • Do not communicate directly with each other
   • p2p
   • Hybrid