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Chapter2_Fall2011_IK - Chapter 2 Application Layer Last...

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2: Application Layer 1 Chapter 2: Application Layer Last Update: Oct 18, 2011
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2: Application Layer 2 Chapter 2: Application Layer Our goals: conceptual, implementation aspects of network application protocols o transport-layer service models o client-server paradigm o peer-to-peer paradigm learn about protocols by examining popular application-level protocols o HTTP o FTP o SMTP / POP3 / IMAP o DNS programming network applications o socket API
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2: Application Layer 3 Some network apps E-mail Web Instant messaging Remote login P2P file sharing Multi-user network games Streaming stored video clips Internet telephone Real-time video conference Massive parallel computing
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2: Application Layer 4 Creating a network app Write programs that o run on different end systems and o communicate over a network. o e.g., Web: Web server software communicates with browser software No software written for devices in network core o Network core devices do not function at app layer o This design allows for rapid app development application transport network data link physical application transport network data link physical application transport network data link physical
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2: Application Layer 5 Application architectures Client-server Peer-to-peer (P2P) Hybrid of client-server and P2P
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2: Application Layer 6 Client-server archicture server: o always-on host o permanent IP address o server farms for scaling clients: o communicate with server o may be intermittently connected o may have dynamic IP addresses o do not communicate directly with each other
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2: Application Layer 7 Pure P2P architecture no always on server arbitrary end systems directly communicate peers are intermittently connected and change IP addresses example: Gnutella Highly scalable But difficult to manage
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2: Application Layer 8 Hybrid of client-server and P2P Skype o voice-over-IP P2P application o centralized server: finding address of remote party: o client-client connection: direct (not through server) Instant messaging o Chatting between two users is P2P o Presence detection/location centralized: User registers its IP address with central server when it comes online User contacts central server to find IP addresses of friends
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2: Application Layer 9 Network applications: some jargon Process: program running within a host. within same host, two processes communicate using interprocess communication (defined by OS). processes running in different hosts communicate with an application-layer protocol user agent: interfaces with user “above” and network “below”. implements user interface & application-level protocol o Web: browser o E-mail: mail reader o streaming audio/video: media player
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2: Application Layer 10 Applications and application-layer protocols Application: communicating, distributed processes o e.g., e-mail, Web, P2P file sharing, instant messaging o running in end systems (hosts) o exchange messages to implement application Application-layer protocols o one “piece” of an app o define messages exchanged by apps and actions taken o
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