Unit6_App - Application Layer 6-1 Unit 6 Application Layer...

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Unformatted text preview: Application Layer 6-1 Unit 6 Application Layer After studying this unit, you will be able to • explain the principles of application layer protocols. Application Layer 6-2 Outline of Unit 6 ¡ 6.1 Principles of network applications ¡ 6.2 Web and HTTP ¡ 6.3 File Transfer and FTP ¡ 6.4 Email and its Protocols: SMTP and POP3 ¡ 6.5 DNS Application Layer 6-3 What will you learn? Our goals: ¡ conceptual understanding of network application protocols ¢ transport-layer service models ¢ client-server paradigm ¢ peer-to-peer paradigm ¡ learn about protocols by examining popular application-level protocols ¢ HTTP ¢ FTP ¢ SMTP / POP3 / IMAP ¢ DNS Application Layer 6-4 Unit 6.1 Principles of Network Application Application Layer 6-5 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 Application Layer 6-6 Creating a network app Write programs that ¡ run on different end systems and ¡ communicate over a network. ¡ e.g., Web: Web server software communicates with browser software No need to write programs for devices in network core ¡ Network core devices do not function at app layer ¡ 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 Application Layer 6-7 Application architectures ¡ Client-server ¡ Peer-to-peer (P2P) ¡ Hybrid of client-server and P2P Application Layer 6-8 Client-server architecture server: ¡ always-on host ¡ permanent IP address ¡ server farms for scaling clients: ¡ communicate with server ¡ may be intermittently connected ¡ may have dynamic IP addresses ¡ do not communicate directly with each other Application Layer 6-9 Pure P2P architecture ¡ no always-on server ¡ arbitrary end systems directly communicate ¡ peers are intermittently connected and change IP addresses ¡ example: Gnutella ¢ an open-source P2P file-sharing application ¡ Highly scalable ¢ Demand increases but service capacity also increases ¡ But difficult to manage ¢ e.g. what happens when a client who have the only copy of an important file disconnects? Application Layer 6-10 Hybrid of client-server and P2P Napster ¡ File transfer P2P ¡ File search centralized: • Peers register content at central server • Peers query same central server to locate content Instant messaging ¡ Chatting between two users is P2P ¡ Presence detection is centralized: • User registers its IP address with central server when it comes online • User contacts central server to find IP addresses of his/her friends Application Layer 6-11 What transport service does an app need?...
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This note was uploaded on 05/01/2011 for the course ELECTRICAL EE3015 taught by Professor Albertsun during the Spring '11 term at City University of Hong Kong.

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Unit6_App - Application Layer 6-1 Unit 6 Application Layer...

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