Domain Name System Computer Science at RPI域名系统在RPI计算机科学.ppt

Netprog 2002 DNS Application-layer Protocols Based on Notes by D. Hollinger Based on UNIX Network Programming, Stevens, Chapter 9 Also Java Network Programming and Distributed Computing, Chapter 3,8 Also Online Java Tutorial, Sun. Topics Issues in Protocol Design Sample Application-layer Protocols TELNET FTP DNS Application Protocol Design Think of different people/teams, working on the client and server programs. Different programming languages. Diverse hardware, operating systems. Be unambiguous, precise. Consider potential error conditions. Allow for future extensions. Leave room for additional data, meta-data. Do not replicate services provided by lower-layer protocols e.g., checksum In Summary Strive for: Interoperability Precision Extensibility Efficiency Minimality Learn by Example Many existing protocols are the result of long term collaborations. Look at existing Request for Comments (RFC) documents, specifying protocols: See /rfc.html Knock-Knock Protocol Server: “Knock knock!” Client: “Whos there?” Server: “Dexter.” Client: “Dexter who?” Server: “Dexter halls with boughs of holly.” Client: “Groan.” Java Implementation Client class KnockKnockClient.java Server class KnockKnockServer.java Protocol class KnockKnockProtocol.java Supporting multiple clients Main listener code KKMultiServer.java Protocol service thread code KKMultiServerThread.java The TELNET Protocol Reference: RFC 854 TELNET vs. telnet TELNET is a protocol that provides “a general, bi-directional, eight-bit byte oriented communications facility”. telnet is a program that supports the TELNET protocol over TCP. Many application protocols are built upon the TELNET protocol. The TELNET Protocol TCP connection data and control over the same connection. Network Virtual Terminal negotiated options Network Virtual Terminal intermediate representation of a generic terminal. provides a standard language for communication of terminal control functions. Network Virtual Terminal Negotiated Op