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Multiple Access Protocol
ผศ. ดร. อนั�นัต์ ผลเพิ่ �มAsst.Prof.Anan Phonphoem, Ph.D.
[email protected]://www.cpe.ku.ac.th/~anan
Computer Engineering DepartmentKasetsart University, Bangkok, Thailand
Multiple access protocols
Random Access Evolution
MAMultiple access
CSMACarrier sense
Multiple access
CSMA/CDCarrier sense
Multiple accessCollision detect
CSMA/CACarrier sense
Multiple accessCollision avoidance
ALOHA Network
ALOHA protocol
Collision in CSMA
Collision
Cisco: CCNA
Persistent strategy
CSMA/CD
CSMA/CD animation
CSMA/CD
CRS
collision
CRS
CRS
CRS
defer
defer
X
Y
Z
Modified from Lucent Slide
CSMA/CA
DCF - CSMA/CA
defer
CRS
CRS
defer
defer
CRS CRS
defer
X
Y
Z
Modified from Lucent Slide
Multiple access protocols
Reservation access method
Poll – Select
Token passing
Token passing procedure
Token Ring animation
Multiple access protocols
Channelization
Cellular Access Technologies Frequency Division Multiple Access
(FDMA) Time Division Multiple Access
(TDMA) Code Division Multiple Access
(CDMA)
FDMA
Mainly used in Analog System
Bandwidth is divided into channels
Voice channel uniform BW range
Not efficiency
TDMA
Bandwidth is just one channel that is timeshared
30 KHz wide, 7.6 ms long (3 time slots)
3 times capacity over Analog
Operate in 800 MHz (IS-54) & 1900 MHz (IS-136)
GSM Global System for Mobile communications TDMA Use encryption security 900 MHz & 1800 MHz (Asia-Europe) 1900 MHz (US. – not compat. with above) International support by changing
Subscriber Identification Module (SIM) card
CDMA One channel carries all
transmissions simultaneously
Spread spectrum Data spread out Each call unique
sequence code Need accurate time stamp 800 MHz and 1900 MHz 8-10 times over Analog
CDMA
Chip sequence
Encoding rules
CDMA Multiplexer
CDMA Demultiplexer
