lect-04 - Application Layer 1 ECE/CS438 Communication...

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Unformatted text preview: Application Layer 1 ECE/CS438 Communication Networks Application Layer Protocols: HTTP, FTP, DNS Sept. 9, 2011 Lecture notes derived Jim Kurose and Larry Peterson slides. Application Layer 2 Objectives Our goals: conceptual, implementation aspects of network application protocols Interaction with transport layer client-server paradigm peer-to-peer paradigm learn about protocols by examining popular application-level protocols DNS SMTP / POP3 / IMAP HTTP Overlay networks Peer to peer applications Application Layer 3 Application architectures Client-server Peer-to-peer (P2P) Hybrid of client-server and P2P Other classifications Traditional Applications Multimedia Applications Infrastructure Services Overlay Networks Application Layer 5 Client-server archicture 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 Pure P2P architecture not always on server arbitrary end systems directly communicate peers are intermittently connected and change IP addresses example: Gnutella Highly scalable But difficult to manage Application Layer 7 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/location centralized: User registers its IP address with central server when it comes online User contacts central server to find IP addresses of buddies Application Layer 8 App-layer protocol defines Types of messages exchanged, eg, request & response messages Syntax of message types: what fields in messages & how fields are delineated Semantics of the fields, ie, meaning of information in fields Rules for when and how processes send & respond to messages Public-domain protocols: defined in RFCs allows for interoperability eg, HTTP, SMTP Proprietary protocols: eg, KaZaA Application Layer 9 Internet apps: application, transport protocols Application e-mail remote terminal access Web file transfer streaming multimedia Internet telephony Application layer protocol SMTP [RFC 2821] Telnet [RFC 854] HTTP [RFC 2616] FTP [RFC 959] Proprietary, RTP (e.g. RealNetworks) proprietary (e.g., Dialpad) Underlying transport protocol TCP TCP TCP TCP TCP or UDP typically UDP Application Layer 10 Web and HTTP First some jargon Web page consists of objects Web page consists of base HTML-file which includes several referenced objects Object can be HTML file, JPEG image, Java applet, audio file, Each object is addressable by a URL Example URL: www-courses.cs.uiuc.edu/~ece438/pic.gif host name path name Application Layer 11 HTTP overview HTTP: hypertext transfer protocol Webs application layer...
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lect-04 - Application Layer 1 ECE/CS438 Communication...

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