1 / 20

Sessions Announcements

Sessions Announcements. Bernard Rapacchi Bernard.Rapacchi@urec.cnrs.fr FINE Workshop University College, London, 1st December 1997. Finding Multimedia Sessions. MBone is used extensively for multimedia conferencing Two basics ways to locate and to participate in a multimedia session :

waylon
Télécharger la présentation

Sessions Announcements

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Sessions Announcements Bernard Rapacchi Bernard.Rapacchi@urec.cnrs.fr FINE Workshop University College, London, 1st December 1997

  2. Finding Multimedia Sessions • MBone is used extensively for multimedia conferencing • Two basics ways to locate and to participate in a multimedia session : • Advertisement : • The session is advertised, • Potential participants see the advertisement, • Then they join the session to participate. • Sessions are advertised by SAP, email, news group, web pages,… • Invitation : • Users are invited by others to participate in a session, • The session may or may not be advertised. • SIP is the invitation protocol. • The MBone equivalent to the Phone Call 2

  3. Session Directory • SDR ( MICE and MERCI Project, UCL) • Advertised session (SAP) • Invitation (quick call) (SIP) • 4 default media types : audio, video, whiteboard, text (SDP) • Version number : • 2.3a1, november 1996 • 2.4a6, july 1997, incompatible with 2.2 et 2.3 3

  4. Background • MBone site has to know : • conference ’s multicast group address • UDP ports for data stream • Medias information • Time information • … • 3 Protocols : • Session Description Protocol • Session Announcement Procotocol • Session Initiation Protocol 10

  5. SDP: Session Description Protocol • SDP is a session description protocol for multimedia sessions • Common usage is for a client to announce a conference session • Periodically multicast an announcement packet to a well known address and port (SAP) • Email and WWW Announcements • MIME content type : application/sdp • but the receiver of an announcement cannot necessarly receive the session SAP Header Text payload …………….. 11

  6. SDP : requirement • SDP serves two primary purposes • a means to communicate the existence of a session • a means to convey information to enable joining and participating • SDP includes : • Session name and purpose • Period(s) of time the session is active • The media comprising the session • Information to receive those media (adresses, ports, formats,…) • plus : • Information about the bandwith to be used • Contact information for the person responsible for the session 12

  7. SDP : Timing Information • Sessions may be bounded or unbounded in time • SDP can convey : • An arbitrary list of start and stop times bounding the session • For each bound, repeat times such as« every Wednesday at 10am for one hour » • Timing information is globally consistent, irrespective of local time zone 13

  8. SDP : more • Private sessions : • encrypting the session description • use of private announcement to convey encryption keys • Further information about a session : • SDP may inlcude additionnal pointer in the form of URI • Categorization : • to filter announcements that are of interest • Internationalization : • SDP recommends the use of the ISO 10646 character set • SDP also allows other character sets such as ISO 8859-1 14

  9. SAP : Session Announcement Protocol • SAP client announces a conference session by • periodicaly multicasting an announcement packet to a well known address and port number : • 224.2.127.254/9875 (sap.mcast.net) • With the same scope (TTL) as the session • Re-advertisement is dependent on 3 factors : • the scope (TTL) of the session • number of other sessions currently being announced • the size of your data packets 15

  10. SAP : Session Deletion • Explicit Timeout : • if current time is later than the end-time for the session • if a session deletion packet is received • specifying the version of the session to be deleted • same IP-source address • Implicit Timeout : • Session announcement message should be received periodicaly • The announcement period can be predicted by the receiver • If a session announcement message has not been received for ten times the period or half an hour then the session is deleted 16

  11. SAP : Session Modification • A pre-announced session can be modified by simply announcing the modified session description • The session itself is uniquely identified by the SDP origin field in the payload • Same rules apply for session modification as for session deletions • If cached session and modificated session do not have same authentification or IP-source addresse, the new session has to be treated as a new announcement and displayed in addition 17

  12. SIP : Session Initiation Protocol • SIP does not prescribe how a conference is to be managed • SIP can invite users to conferences by conveying the information necessary. • SIP does not allocate multicast addresses, this is done by SAP. • SIP uses a central server to manage conference and participant state and distribute state via multicast. 18

  13. SIP : Addressing • Host-specific addresses : user@host • user : is an operating system user name • host : is either a domain name having a DNS A record or a numeric network address • e.g. : • br@sylvestre.grenoble.urec.cnrs.fr • tuy@195.220.197.12 • Host independent addresses : user@location • user : may be any unambiguous name including aliases • location : domain name having an MX or A record • e.g. : • Bernard.Rapacchi@urec.cnrs.fr • SIP uses proxy servers to locate the user 19

  14. Bibliography • Internet Drafts : • draft-ietf-mmusic-sap-00.txt [19th Nov 1996] • draft-ietf-mmusic-sap-sec-01.txt [29th Jul 1997] • draft-ietf-mmusic-sdp-04.txt [2nd Sep 1997] • draft-ietf-mmusic-sip-04.txt [13rd Nov 1997] • draft-ietf-mmusic-confarch-00.txt [18th Sep 1997] • WWW sites : • http://www-mice.cs.ucl.ac.uk/merci/ • http://mirage.informatik.uni-mannheim.de/mmbook/book.html(Internetworking Multimedia, UCL Press) 20

More Related