S.WENGER
Technical terms that should be known:
Bit rate Digital processing based on the exchange of the smaller information particle, called Bit
Synchronous communication : Information is received and processed by the user in the same moment that the sender
Asynchronous communication : Transfered information is stored and the receiver can reviewer later on time
Interactive communication : synchronous communication that allows inmediate response
Categories of Multimedia Communications
Category I : Bit rate transfer is low, asynchronous,unidirectional and non-interactive
examples : e-mail, FTP, WWW access
Category II : All is interactive, usually bidirectional and synchronous examples :
chat-like applications, remote control of equipment
Category III : Interactive, low bit rate ( less then 384 Kbit/s ) examples :
Low quality video-conferencing, application sharing ( WISYWIS )
Category IV : Interactive, high bit rate.
in general the tipical requirements will be more then 10 Mbit/s, low latency (100ms). No commercial typical networks is today available
Networks for multimedia communications
Protocols used :
Category I : usual Internet protocols
Category II : Internet Protocols and propietary protocols
Category III and above : H32x protocols
H320 for ISDN
B channel aggregation
Audio ( G711,722,723 ) and Video ( H.261,262,263 ) channel
H242 protocol : exchange and connection
Data channel ( generally T. 120 protocol )
H.221 protocol : multiplex audio,video and data
H230 protocol : control and indication of signals
Point to point
Multipoint could be available with H243 protocol
H324 for PSTN multimedia conferencing
H323 for packet switched networks based on Internet protocols ( The future )
Standarization not yet finished
Bandwidth on demand
Unlimited number of virtual communication channels
H.Loosely-coupled standard (H.no numered yet) will allow combined Broadcast and Multipoint conmutations
Data Compression: The Categories III and IV require data compression and coding .
Types of compression :
a) Lossless compression ( by reducing mathematical redundancy of data stream )
Still images :Huffmann, LZH, lossless Jpeg , lossless DICOM v.3
Audio : 1/2
b) Lossy compression :
Still Images : JPEG, lossy DICOM v.?
Audio: 1/10 and 1/4
Moving Images
MPEG 1 : Video and audio storage and play back
MPEG 2 : Video and audio broadcast
MPEG 3 :
MPEG 4 :
H261 to H263 Videotelefony and Videoconference 1/4000
Step 1 :
Reduce spatial and temporal resolution
YUV encoding
.Step 2 :
Interpicture prediction
Motion compensation
Step 3: Intracoding
H323 Packetized Videoconference over TCP/IP ( not yet finished )
Part or total reproduction not allow without permission
Revisado: jueves, 05 junio 1997.
Con el soporte informático y de comunicaciones
del CICEI, Universidad
de Las Palmas de Gran Canaria