Enabling technology

Telepresence course – 2007-01-29

Johnny WidénMedia TechnologyCentre for Distance-spanning Technology (CDT)Luleå University of TechnologyLuleå, Sweden

Outline

• Human communication• Telephone based systems• Internet based systems• Mbone tools• H.323• SIP

Human communication

Face-to-face Mediated

Telephone based systems (1)

• Early communication network – the telephone network

• Circuit switched• Analog: POTS – Plain Old Telephony

System• Digital: ISDN – International

Serial Digital Network

Telephone based systems (2)

• ITU = International Telecommunication Union

• H.320 - Videoconferencing system based on ISDN

Telephone based systems (3)

• H.320 – one-to-one• Need a MCU (Multipoint Control

Unit) for many-to-many

Internet based systems (1)

• Packet switched• IP = Internet Protocol• Best effort

• Unicast one-to-one• Multicast many-to-many

Internet based systems (2) -Multicasthttp://www.cdt.luth.se/~johnny/presentations/multicast/

Internet based systems (3) -MBone

• MBone = Multicast Backbone• Unicast tunnels for multicast

Internet based systems (4) Native multicast

• States in the routers

• No single point of failure• Very hard to deploy

MBone tools

• vat – audio• rat – audio (newer)• vic – video• wb - whiteboard• sdr – directory• OthersUsed for early research. Many parameters to

tune = Limited usablity

http://www-mice.cs.ucl.ac.uk/multimedia/software/

MBone tools bundle

• Uses mainly vic and rat. Some kind of reflector and possibility to connect to SIP and H.323

• VRVS - Virtual Rooms Videoconferencing System http://www.vrvs.org/

• ISABEL http://isabel.dit.upm.es/

• More? Check with Google

MBone musical events

• June 24, 1993STD – Severe Tire Damage

• November 18, 1994Rolling Stones Live from Dallas

Refs • http://www.savetz.com/mbone/ch6.html• http://myhome.hanafos.com/~soonjp/mbone.html

mStar -> Marratech

• 1995, research at CDT (Centre for Distance-spanning Technology) at LTU started with the MBone tools

• Built chat, whiteboard, etc• Integration with Netscape• Used it ourselves extensively for meetings and learning• mVideo, mAudio, mChat, mWhiteboard, .. = m* = mStar

was a prototype• Start of Marratech 1998• Lots of effort put into underlying network performance

There is a vast difference between a prototype and a product!!

Reflectors, e-meetings managersMulticast hard to deploy

Many-to-many unicast requires a reflector or an e-meeting manager

Marratech:if multicast enabled network then

use multicastelse use unicast

H.323

• Start with the Telecommunication standard H.320 for ISDN (circuit switched)

• Adapt it to the Internet (packet switched)

... and you will get H.323• A very complicated umbrella protocol

for videoconferencing over IP

Comes from ITU – International Telecommunication Union

H.323 clients

• So far mostly used for groups sitting physically together meeting other groups sitting together

• Audio and video• Data (T.120) very seldom used

– Some times shared application with NetMeeting (Microsoft)

• New standard - H.239 for graphics

MCU –Multipoint Control Unit• Many-to-many requires an MCU –

Multipoint Control Unit• The MCU bundle all audio and all

video• I.e., only one video signal is sent to

each participant– Conferencing mode– Continuous presence mode

H.323 clients

Systems• Tandberg, Polycom, Radvision,...• The more expensive ones contains

an MCU

PC clients• VCON VPoint, DyLogic Mirial,

Polycom VX

SIP

Session Initiation ProtocolBuild directly for the Internet

Comes from IETF – Internet Engineering Taskforce

Marratech H.323 gateway

• Built on OpenH323• Current limitation

– H.261 for video– G.711 for audio

Marratech deployment

Course communication so far (1)

Marratechclient

Tandbergclient

Marratechmanager

TandbergMCU

Marratechclient Marratech

client

H.323client

H.323client

Marratechclient

Marratechclient

Marratechmanager

Course communication so far (2)

Marratechclient

Tandbergclient

Marratechmanager

TandbergMCU

Marratechclient Marratech

client

H.323client

H.323client

Marratechclient

Marratechclient

Marratechmanager

Course communication so far (1)

Marratechclient

Tandbergclient

Marratechmanager

TandbergMCU

Marratechclient Marratech

client

H.323client

H.323MCU

Marratechclient

Marratechclient

Marratechmanager

H.323client