THE WHATIS.COM WORD-OF-THE-DAY March 25, 2002 Real-Time Transport Protocol ______________ TODAY'S SPONSOR: VeriSign - The Value of Trust
FREE E-COMMERCE SECURITY GUIDE Is your e-business built on a strong, secure foundation? Find out with VeriSign's FREE White Paper, "Building an E-Commerce Trust Infrastructure." Learn how to authenticate your site to customers, secure your web servers with 128-Bit SSL encryption, and accept secure payments online. Click here: http://WhatIs.techtarget.com/r/0,,2592,00.htm?VeriSign ______________ TODAY'S WORD: Real-Time Transport Protocol See our definition with hyperlinks at http://searchnetworking.techtarget.com/sDefinition/0,,sid7_gci812019,00.html The Real-Time Transport Protocol (RTP) is an Internet protocol standard that specifies a way for programs to manage the real-time transmission of multimedia data over either unicast or multicast network services. Originally specified in Internet Engineering Task Force (IETF) Request for Comments (RFC) 1889, RTP was designed by the IETF's Audio-Video Transport Working Group to support video conferences with multiple, geographically dispersed participants. RTP is commonly used in Internet telephony applications. RTP does not in itself guarantee real-time delivery of multimedia data (since this is dependent on network characteristics); it does, however, provide the wherewithal to manage the data as it arrives to best effect. RTP combines its data transport with a control protocol (RTCP), which makes it possible to monitor data delivery for large multicast networks. Monitoring allows the receiver to detect if there is any packet loss and to compensate for any delay jitter. Both protocols work independently of the underlying Transport layer and Network layer protocols. Information in the RTP header tells the receiver how to reconstruct the data and describes how the codec bit streams are packetized. As a rule, RTP runs on top of the User Datagram Protocol (UDP), although it can use other transport protocols. Both the Session Initiation Protocol (SIP) and H.323 use RTP. RTP components include: a sequence number, which is used to detect lost packets; payload identification, which describes the specific media encoding so that it can be changed if it has to adapt to a variation in bandwidth; frame indication, which marks the beginning and end of each frame; source identification, which identifies the originator of the frame; and intramedia synchronization, which uses timestamps to detect different delay jitter within a single stream and compensate for it. RTPC components include: quality of service (QoS) feedback, which includes the numbers of lost packets, round-trip time, and jitter, so that the sources can adjust their data rates accordingly; session control, which uses the RTCP BYE packet to allow participants to indicate that they are leaving a session; identification, which includes a participant's name, e-mail address, and telephone number for the information of other participants; and intermedia synchronization, which enables the synchronization of separately transmitted audio and video streams. Compressed RTP (CRTP), specified in RFC 2509, was developed to decrease the size of the IP, UDP, and RTP headers. However, it was designed to work with reliable and fast point-to-point links. In less than optimal circumstances, where there may be long delays, packet loss, and out-of-sequence packets, CRTP doesn't function well for Voice over IP (VoIP) applications. Another adaptation, Enhanced CRPT (ECRPT), was defined in a subsequent Internet Draft document to overcome that problem. RELATED TERMS: real time http://searchsolaris.techtarget.com/sDefinition/0,,sid12_gci214344,00.html unicast http://searchnetworking.techtarget.com/sDefinition/0,,sid7_gci213249,00.html multicast http://searchnetworking.techtarget.com/sDefinition/0,,sid7_gci212610,00.html User Datagram Protocol http://searchwebmanagement.techtarget.com/sDefinition/0,,sid27_gci214157,00.html Voice over IP http://searchnetworking.techtarget.com/sDefinition/0,,sid7_gci214148,00.html ______________________ SELECTED LINKS: The IETF provides the Real-Time Transport Protocol RFC. http://www.ietf.org/rfc/rfc1889.txt The Audio/Video Transport Working Group maintains an RTP Frequently-Asked Questions list. http://www.cs.columbia.edu/~hgs/rtp/faq.html SearchNetworking offers "Best Web Links about Voice/Data Convergence." http://searchnetworking.techtarget.com/bestWebLinks/0,289521,sid7_tax3a3,00.html ______________________ QUIZ #23 | Firewalls How much do you really know about this useful set of related programs? 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Full conference benefits at: http://ad.doubleclick.net/clk;4012996;5058249;p?http://www.securityconf.com/html/registration.htm ______________________________ RECENT ADDITIONS AND UPDATES [1] picofarad per meter http://whatis.techtarget.com/definition/0,,sid9_gci812011,00.html [2] Nyquist Theorem http://whatis.techtarget.com/definition/0,,sid9_gci812005,00.html [3] coulomb per centimeter squared http://whatis.techtarget.com/definition/0,,sid9_gci811193,00.html [4] optical disc http://searchstorage.techtarget.com/sDefinition/0,,sid5_gci811276,00.html [5] data preprocessing http://searchdatabase.techtarget.com/sDefinition/0,,sid13_gci810056,00.html ____________________________________________________________________ ::::::::::::::::::: WHATIS.COM CONTACTS ::::::::::::::::::: LOWELL THING, Site Editor ([EMAIL PROTECTED]) ____________________________________________________________________ MARGARET ROUSE, Assistant Editor ([EMAIL PROTECTED]) ___________________________________________________________________ :::::::::::::::::::: ABOUT THIS NEWSLETTER ::::::::::::::::::::: Created by TechTarget (http://www.techtarget.com) TechTarget - The Most Targeted IT Media Copyright 2002, All Rights Reserved. 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