Distance Education

1
Distance Education

• TV Signals Transmission

2
Satellites

• First TV signals came from broadcast antennas
• Frequencies had to be higher than radio

3

• "kilo", "mega", and "giga" express very large
  numbers.
• "kilo" in front of a unit means 1000 of that
  unit. "Kilo is abbreviated as k. kilogram (Kg) is
  1000 grams.
• "mega" means 1 million. Mega is abbreviated as M.
  A megawatt (MW) is 1,000,000 watts.
• "giga" stands for 1 billion. It is abbreviated
  as G. gigabit (Gbit) of data is 1,000,000,000
  bits of data.

4
Satellites

• Telstar

5
Satellites

• Geosynchronous Communications Satellites
• 1963
• Covered 42 of
• The earth

6
Satellites

• Geosynchronous Communications Satellites today
  150
• 22,300 miles up

7
Satellites
8
Satellites

• Example DirecTV
• Spot beams

9
WV EDNet
Morgantown to Students via Optical Cable and
Satellite
Satellite
Health Science Center
Reduced Bandwidth (ATM)
C-band satellite uplink
C-band down link
Full bandwidth
EDNET Charleston/Institute
Site of Origin (CERC)
Receive sites
10
Videoconferencing

• Primary components
• television cameras
• monitors
• microphones
• speakers
• communications network

11
Videoconferencing

• communications network
• Coaxial cable
• Fiber optics
• ISDN
• T1
• ATM
• IP
• Satellite
• DSL and Cable Modems

12
Videoconferencing

• communications network
• Coaxial cable
• Used primarily between short distances like
  court room and jail

13
Videoconferencing CMC

• communications network
• Fiber optics
• Used mainly as intranet like within a university
• Consists of many strands of fiberglass which
  conducts and can send large quantities of
  information

14
Videoconferencing CMC

• communications network
• ISDN Integrated Services Digital Network
• voice and data are carried by bearer channels
• (B channels) bandwidth of 64 kb/s
• A data channel (D channel) 16 kb/s
• H channel is 6 B channels 384 kb/s

15
Videoconferencing CMC

• communications network
• ISDN
• Basic Rate Interface (BRI)
• 2-B channels and 1-D 144 kb/s
• Primary Rate Interface (PRI)
• 23-B and 1-D 1536 kb/s
• ISDN telephone lines and codecs use the ITU H.320
  standard
• Internet (LAN/WAN) connections and codecs use the
  ITU H.323 standard

16
Videoconferencing CMC

• communications network
• T1 - high speed digital network (1.544 mbps)
  developed by ATT
• 64Kbps 1/24 of 1 Channel DS0
• T1 1.544Mbps 24 Channels DS1
• 3.152 Mbps 2 T-1 48 Channels DS1C
• T2 6.312 Mbps 4 T-1 96 Channels DS2
• T3 44.736 Mbps 28 T-1 672 Channels DS3
• 89.472 Mbps 56 T-1 1344 Channels DS3C
• T4 274.176 Mbps 168 T-1 4032 Channels DS4

17
Videoconferencing CMC

• communications network
• ATM - Asynchronous Transfer Mode
• Also known as cell relay
• Speeds - 2.5 Gb/s in operation, 10 Gb/s in
  limited use and spanning up to 40 Gb/s in trials
• roughly 80 percent of the world's carriers use
  ATM

18
Videoconferencing CMC

• communications network
• IP
• LAN Local Area Networks
• WAN - Wide Area Networks
• MAN Metropolitan Area Networks
• Allows point-to-point between computers or codecs
• bandwidth of around 384-768kb/s is very common
• Internet bandwidth dependent

19
Videoconferencing CMC

• communications network
• DSL and Cable Modems (Broadband Services)
• DSL phone connections dedicated home to
  provider's central office using copper wire
• Residential ADSL - 1.5 Mbps
• http//www.videnet.gatech.edu/cookbook//

20
Videoconferencing CMC

• Characteristics of communications channels
• Types of signals digital and analog
• Transmission modes asynchronous and synchronous
• Direction of transmission simplex, half-duplex,
  full duplex
• Transmission rate

21
Videoconferencing CMC

• Communications equipment
• Modems
• Multiplexors
• Front-end processors
• Network interface cards

22
Videoconferencing CMC

• Wireless
• http//wireless.ittoolbox.com/default2.asp

23
References

• http//members.cotse.com/fulcrum/net_ref.htm
• http//www.anixter.com/