cts05collabintromay17-05.ppt
TRANSCRIPT
Collaboration Approaches for CTS05 GlobalMMCS Tutorial
CTS05 St. Louis May 17 2005
Geoffrey Fox
CTO Anabas Corporation andComputer Science, Informatics, Physics
Pervasive Technology LaboratoriesIndiana University Bloomington IN 47401
[email protected]://www.infomall.org
Material for Tutorial All talks are at
http://grids.ucs.indiana.edu/ptliupages/presentations/cts05/ Both tutorial and conference presentations (Ahmet
Uyar, Sangyoon Oh) Open source Software at
• http://www.globalmmcs.org and
• http://www.naradabrokering.org (Software Overlay Network)
• http://www.collab-ogce.org/nmi/index.jsp (Grid Portals) More information about our work
http://www.infomall.org
Tutorial Overview: 5 Sections Overview of existing audio/video systems; we are trying to
address general real-time collaboration but we A/V systems have hard technical challenges• Apply to WebEx, Placeware style shared applications as well
Grids and Web Services; current preferred approach to distributed systems but main focus asynchronous sharing; we will apply to synchronous case• Grids are “Internet-Scale Distributed Services”
Message-oriented Middleware or Software Overlay Networks; natural approach to both Grids and Collaboration spanning P2P and Server-based scalable systems; NaradaBrokering
XGSP provides Web Service (Grid) interfaces for Collaboration Finally GlobalMMCS is the collaboration environment
H.323 Introduction• Major audio-video standard but broader• “Binary” format for both “data” and “control”• Supported by many commercial vendors and used
throughout the world in commercial and educational markets
• Supports small-scale multipoint conferences• Has conference management functionality and the
call signaling functionality H.225 ~ call set-up H.245 ~ call control H.243 ~ Audio/Video multipoint control T.120 ~ Data Collaboration
H.323 Protocols• H.323 is a “framework” document that
describes how the various pieces fit together
• H.225.0 defines the call signaling and communication between endpoints (Call Signaling) and the Gatekeeper (RAS)
• Annex G/H.225.0 defines communication between Border Elements
• H.245 is the conference control protocol
Typical H.323 StackH.323
IP
UDP
RTP
RTCP
TCP/UDP TCP UDPUDP TCP
Audio
Codecs
G.711
G.723.1
G.729
..
Video
Codecs
H.261
H.263
H.264
..V.150 T.120
TCP/UDP
T.38
H.225.0
Call
Signaling
H.245H.225.0
RAS
Terminal Control and ManagementData
ApplicationsMedia Control
Multimedia Applications, User Interface
http://www.packetizer.com
H.323 Endpoint (Terminal) Architecture
Video I/O equipment
LA
N
Interface
Call Control H.225.0
H.245 Control
RAS Control H.225.0
H.225.0Layer
Video CodecH.261, H.263
System Control
Audio CodecG.711, G.722, G.723, G.728, G.729
ReceivePathDelay
Audio I/O equipment
User Data ApplicationT.120, et.
System ControlUser Interface
Scope of Rec. H.323
H.323 Architecture
Gatekeeper(security, QoS, routing etc.)
MC MPMCU
H.323 Terminal 1
H.323 Terminal 2
H.323 Terminal N
....
Packet Switch Network
H.323 MCU Responsible for managing multipoint conferences (two
or more endpoints engaged in a conference) The MCU contains
• a Multipoint Controller (MC) that manages the call signaling
• may optionally have Multipoint Processors (MPs) to handle media mixing, switching, or other media processing
H.323 Gatekeeper Admission Control Bandwidth Control Address Resolution
DNS style service for VoIP and Videoconferencing Directory Service Call routing
route the call to MCUs
H.225: Call Setup Signaling
Endpoint2Endpoint1 Gatekeeper
RAS messageCall signaling message
ARQ(1)
ACF/ARJ(2)
Setup(3)Call processing(4)
ARQ(5)
ACF/ARJ(6)
Alert(7)
Connect(8)
Open a channel
H.245 Signaling H.245 is used to negotiate capabilities and to control
aspects of the conference between two or more endpoints
Endpoint EndpointTerminal Capability Set
Terminal Capability Set
M/S Determination
M/S Determination AckM/S Determination Ack
OpenLogicChannel (OLC)OLC Confirm
SIP Initially SIP was designed to solve problems for IP
telephony. SIP basic functions
• user location resolution, • capability negotiation• call management. equivalent to the service H.225 and point to point part of H.245
The major difference from H.323• SIP was designed in a text format and took request-response
protocol style like HTTP• SIP doesn’t define the conference control procedures like
multipoint parts of H.245 and T.120.
SIP Architecture
SIP Client
SIP PROXYSERVER
SIP Client
RegistrarServer
LocationServer
RedirectServer
SIP MC SIP MP
SIP MCU
rtspd
Quick-time
GatekeeperSIPUA
SIP
H.323
RTSP
sipd
sipconfsipconf
sipumsipum
sip323sip323SIP-H.323
signaling gateway
Conferencing
Programmable SIP servers
Unified messaging
Streaming media
Hardware SIP phone
Desktop SIP clients
sipgwsipgw
PSTN
MGCPSIP-MGCP gateway
SIP-PSTN gateway
Regular telephones
A Integrated SIP Service System: CINEMAFrom Columbia University
SSipconfipconf : SIP based Centralized : SIP based Centralized conferencingconferencing
sipcsipc
http://www.cs.columbia.edu/~kns10/software/sipconfhttp://www.cs.columbia.edu/~kns10/software/sipconf
SIP323SIP323
SIP/PSTNSIP/PSTN
SIP based conferencing server SIP/SDP and RTP/RTCP Audio mixing Play-out delay algorithm Web based conference setup G.711 A and Mu law, G.721, DVI
ADPCM Multiple simultaneous
conferences
Summary of H.323/SIP Conferencing Systems
Most products are Centralized conferencing system
MCU integrates the service of media processing service and session management
Call-based
A conference call represents control connections between clients and MCUs.
Most vendors offer hardware solutions Thought as services and controllers but specialized
protocols and implementations; NOT Service-Oriented Architectures!
Access Grid I Access Grid : a large scale audio/videoconference based on a multicast
network provides the group-to-group collaborations among 150 nodes connected to
Internet 2 world wide. Use improved MBONE audiovisual tools VIC and RAT Depends upon high-speed network ( each node needs 20Mbps ) Peer to peer architecture for distribution with centralized non standard
session control (venue server) Did not develop many new capabilities but made existing public domain
software better packaged and easier to use
Access Grid II Supports multiple screens and dominates some
research communities
VRVS: Virtual Rooms VideoConferencing System
VRVS is a project from particle physics group at Caltech that extends the service of Access Grid.
VRVS builds its collaboration service on top of pure software reflector infrastructure which is a kind of software multicast. (similar to NaradaBrokering )
It is capable of supporting MBONE tools, H.323 terminal as well as QuickTime player.
It also supports shared web browsing and shared desktop (VNC).
VRVS is not an open project having few documents for their architecture and conference control framework.
Skype I Skype: p2p VoIP solution and has become a
huge success. • A Peer-to-peer overlay network for VoIP and Instant
messages developed by founders of KaZaA.• using p2p overlay (Kazaa) rather than expensive,
centralized infrastructure• Free on-net VoIP service and a fee-based off-net
SkypeOut service that allows calling to PSTN and cellular phones
• provided supplemental features like instant messaging service.
• Millions of download and on-line users in the world
Skype II Based on Kazaa Overlay network
• Unstructured p2p file sharing overlay• Overlay p2p network consisting of ordinary and
Super Nodes (SN).• Ordinary node connects to network through a Super
Node. Centralized authentication server Excellent Audio quality based on Internet Low Bit rate
Codec ILBC (http://rfc3951.x42.com/)
iLBC – MOS (Audio Quality) behavior versus percentage packet loss
Skype Architecture
Skype III Each client maintains a list of super nodes in the Host
Cache. Buddy list is local to a machine. Skype client continuously discovers and builds the list
of Skype nodes. Use a hybrid DHT and flooding mechanism to search A Super Node acts a proxy for clients and caches the
result
Skype IV Skype client listens on configured TCP and UDP ports. Uses a variant of STUN to identify the type of NAT and
firewall. Usage of TCP port 80 enables client to reach super node
even through firewalls. Call signaling is done over TCP, messages are
preferably transported over UDP. In the presence of NAT or firewalls, calls between caller
and callee are routed by an intermediate node All Skype messages are encrypted.
Why is Skype so successful? Better voice quality excellent audio codec, fancy echo cancellation algorithm Global IP Sound ( iLBC audio codec ) Ability to work behind firewalls and NAT Ease of use ( quite simple UI ) based on IM metaphor P2P style without centralized MCU any peer that has enough resource can be selected to host
the mixing service limited the number of participants in a conference ( at most
4 which is common for private social meetings ) use p2p overlay to discover resources and route packets
But they are simply not good enough! Although all of these systems have advantages, they are not sufficient for building
more advanced and integrated collaboration systems: SIP : very limited supported for conference control H.323 :
AV collaboration and T.120 are not well integrated. the AV communication services and T.120 overlay networks don’t have very good
scalability.H.323 and T.120 are designed in a relative complicated OSI model. It is not easy to
understand and develop in their APIsMost H.323 and SIP conferencing products are based on centralized MCU
Access Grid : heavily depends on multicast service and limited number of uni-cast bridge servers in the Internet 2• No way to be deployed in current Internet
VRVS : No clear way to generalize Skype : Most promising
• use their own propriety protocols and can’t interoperate with other legacy VoIP clients such as H.323 and SIP
• only support small-scale audio conferencing ( at most 4-party ) and have no video service
What’s the ideal videoconferencing system I A unified, scalable, robust “overlay” network is needed to
support AV and data group communication over heterogeneous networking environments• go through firewall and NAT • provide group communication service in whatever unicast and multicast
networks • offer reliable data delivery in whatever loss network• to be configured as P2P or distributed server-based overlay to provide
differential services for VIP and regular users• Publish-Subscribe collaboration mechanism natural for centralized and P2P
modes A service-oriented architecture for hosting media processing
service and session control service• More scalable than centralized MCU• Support various style of conferencing ( massive scale of broadcasting as well
as medium size of private social meetings )• Service providers can be highly distributed and p2p ~ Skype p2p audio mixing• Scalable service discovery based on p2p search • Customized media filters for different clients ( PC, PDA, … )
What’s the ideal videoconferencing system II
A core conference control mechanism is required for establishing and managing the multi-point conference• Complete conference control service like T.124 (Generic
Conference Control) in T.120 framework
• more flexible facilities to describe application sessions and entities ( role-based, XML )
• Integrate different AV sessions ( H.323 , SIP, Access Grid, RealStreaming … )
Introduce a common AV signaling protocol to interoperate different AV collaboration endpoints
Simply regard these bridging gateways as “add-on services”
Global-MMCS is one approach to the ideal conferencing solution
NaradaBrokering as “software overlay”
• Group communication
• Service discovery
• Skype and VRVS also are based on similar idea XGSP is Web Service compatible conferencing framework
• Service management
• Conference control
• Common AV signaling protocol Publish-Subscribe as collaboration mechanism
• Easy to support new applications Services with SOA as components
• Codec conversion or video mixing are separate services
• Grids are high performance large scale sevices
H.323 SIPIETF
Access GridVRVS Global-MMCS
ConferenceManagement supported No supported supported supported
Overlay NetworkEnvironment
Internet / ISDNFirewall transversalunder the support of VPN
No
Need multicast support ,No firewall tunneling
Reflector InfrastructureSoftware Multicast
Publish/Subscribe Firewall & NAT transversal(VPN optional)
Data Collaboration
Limited: T.120 whiteboard, File
FTP No
Limited to ( PowerPoint,
Chat )
Limited to ( Shared browsing and VNC )
allows fullintegration of all tools
Floor Control
Mechanism
H.243T.120
NoUnder
developmentNo No
Chairman based Flexible role setting
Scalability Not good Not good Good Good Good
Support heterogeneous clients No No No
H.323,MBONE
H.323, SIP, MBONE, RealPlayer, PDA, Cell Phone
Community-To-CommunityCollaboration
No No No No Yes
Comparison of Global-MMCS with Competitive Systems