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VSAT SECTION

TDM And Slotted Aloha

1)TDM(Time Division Multiplixing):-
-Time is divided into frames and frames into time slots.
-Data is transmitted as packets every packet in one time slot.
2)Slotted Aloha:-
-Based on the first come-first served.
-Time is divided into frames and frames into time slots.
-Data is transmitted as packets every packet in one time slot.
-Remote sites sends the packets randomly at any time slot and wait for acknoledge.
-If no acknoledge came (a collision happen),they wait random time and retry to send the packet again.


BOD IDU



Main IDU:-consists of
-CSC(Comman signalling channel):-which communicates with the CSC-PDC at the hub on the IB and OB channels.And also controls and takes request from the voice and data cards.
-Four voice and data cards.
Clear Channel Data Card:-
-Support synchronous data interface.
-Transmitt at rate 9.6-2,048 Kbps.
-ęContain a modem and BBP(Base band processor.
-Modulation BPSKę-QPSK.
Voice Card:-
-Support analog data interface(can be connected to your PABX or telephone).
-Since max freqquncy of voice is 4KHZ so it make sampling at rate 8KHZ or more.With 256 level of sound(8 bit each sample).So it transmit voice at rate 64Kbps and then make a data comprision for it to be with less rate.
-Support asynchronous data interface along RS-232.
-Comtains a modem and BBP.
-Modulation BPSK-QPSK.
Sub IDU:-
-Five voice and data cards.
-Dose not have CSC sine it is completly controlled by the main IDU.


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