CHAPTER 4: BASIC TECHNICAL KNOWLEDGE

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

1. PSTN ( Public switched telephony networks ): Allows categories I,II and III
2. ISDN ( Integrated services digital networks )
   • BRI ( basic rate ) 2B+D channes B=64kb/s transparent, isochronous,bidirectional and of low latency
   • PRI ( primary rate ) upt ot 30 BRI
3. Other Circuit Switched networks : Switched 56 in USA
4. Broadband networks
   • LAN ( Local Area Networks ), MAN ( Metropolitan area networks ) : up to category IV
   • High Bit rate WANs ( Wide area networks ) - Broad band ISDN
5. Internet ( see Chapter 6 )
6. Intranets : Usage of freely available protocol infrastructure of the Internet protocols put into a well controled enviroment ( intranet )

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