RFC2327SDPSession Description Protocol.docx

RFC2327SDPSession Description Protocol.docx

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RFC2327SDPSessionDescriptionProtocol

　NetworkWorkingGroupM.Handley

RequestforComments:

2327V.Jacobson

Category:

StandardsTrackISI/LBNL

April1998

SDP:

SessionDescriptionProtocol

StatusofthisMemo

ThisdocumentspecifiesanInternetstandardstrackprotocolforthe

Internetcommunity,andrequestsdiscussionandsuggestionsfor

improvements.Pleaserefertothecurrenteditionofthe"Internet

OfficialProtocolStandards"（STD1）forthestandardizationstate

andstatusofthisprotocol.Distributionofthismemoisunlimited.

CopyrightNotice

Copyright（C）TheInternetSociety（1998）.AllRightsReserved.

Abstract

ThisdocumentdefinestheSessionDescriptionProtocol,SDP.SDPis

intendedfordescribingmultimediasessionsforthepurposesof

sessionannouncement,sessioninvitation,andotherformsof

multimediasessioninitiation.

ThisdocumentisaproductoftheMultipartyMultimediaSession

Control（MMUSIC）workinggroupoftheInternetEngineeringTask

Force.Commentsaresolicitedandshouldbeaddressedtotheworking

group'smailinglistatconfctrl@isi.eduand/ortheauthors.

1.Introduction

OntheInternetmulticastbackbone（Mbone）,asessiondirectorytool

isusedtoadvertisemultimediaconferencesandcommunicatethe

conferenceaddressesandconferencetool-specificinformation

necessaryforparticipation.Thisdocumentdefinesasession

descriptionprotocolforthispurpose,andforgeneralreal-time

multimediasessiondescriptionpurposes.Thismemodoesnotdescribe

multicastaddressallocationorthedistributionofSDPmessagesin

detail.Thesearedescribedinaccompanyingmemos.SDPisnot

intendedfornegotiationofmediaencodings.

2.Background

TheMboneisthepartoftheinternetthatsupportsIPmulticast,and

thuspermitsefficientmany-to-manycommunication.Itisused

extensivelyformultimediaconferencing.Suchconferencesusually

havethepropertythattightcoordinationofconferencemembershipis

notnecessary;toreceiveaconference,auseratanMbonesiteonly

hastoknowtheconference'smulticastgroupaddressandtheUDP

portsfortheconferencedatastreams.

Sessiondirectoriesassisttheadvertisementofconferencesessions

andcommunicatetherelevantconferencesetupinformationto

prospectiveparticipants.SDPisdesignedtoconveysuchinformation

torecipients.SDPispurelyaformatforsessiondescription-it

doesnotincorporateatransportprotocol,andisintendedtouse

differenttransportprotocolsasappropriateincludingtheSession

AnnouncementProtocol[4],SessionInitiationProtocol[11],Real-

TimeStreamingProtocol[12],electronicmailusingtheMIME

extensions,andtheHypertextTransportProtocol.

SDPisintendedtobegeneralpurposesothatitcanbeusedfora

widerrangeofnetworkenvironmentsandapplicationsthanjust

multicastsessiondirectories.However,itisnotintendedto

supportnegotiationofsessioncontentormediaencodings-thisis

viewedasoutsidethescopeofsessiondescription.

3.GlossaryofTerms

Thefollowingtermsareusedinthisdocument,andhavespecific

meaningwithinthecontextofthisdocument.

Conference

Amultimediaconferenceisasetoftwoormorecommunicatingusers

alongwiththesoftwaretheyareusingtocommunicate.

Session

Amultimediasessionisasetofmultimediasendersandreceivers

andthedatastreamsflowingfromsenderstoreceivers.A

multimediaconferenceisanexampleofamultimediasession.

SessionAdvertisement

Seesessionannouncement.

SessionAnnouncement

Asessionannouncementisamechanismbywhichasession

descriptionisconveyedtousersinaproactivefashion,i.e.,the

sessiondescriptionwasnotexplicitlyrequestedbytheuser.

SessionDescription

Awelldefinedformatforconveyingsufficientinformationto

discoverandparticipateinamultimediasession.

3.1.Terminology

Thekeywords"MUST","MUSTNOT","REQUIRED","SHALL","SHALLNOT",

"SHOULD","SHOULDNOT","RECOMMENDED","MAY",and"OPTIONAL"inthis

documentaretobeinterpretedasdescribedinRFC2119.

4.SDPUsage

4.1.MulticastAnnouncements

SDPisasessiondescriptionprotocolformultimediasessions.A

commonmodeofusageisforaclienttoannounceaconferencesession

byperiodicallymulticastinganannouncementpackettoawellknown

multicastaddressandportusingtheSessionAnnouncementProtocol

（SAP）.

SAPpacketsareUDPpacketswiththefollowingformat:

|--------------------|

|SAPheader|

|--------------------|

|textpayload|

|//////////

TheheaderistheSessionAnnouncementProtocolheader.SAPis

describedinmoredetailinacompanionmemo[4]

ThetextpayloadisanSDPsessiondescription,asdescribedinthis

memo.Thetextpayloadshouldbenogreaterthan1Kbyteinlength.

IfannouncedbySAP,onlyonesessionannouncementispermittedina

singlepacket.

4.2.E