Friday, November 16, 2012

multiplexing and multiple access

Multiplexing And Multiple Access :


Digital Communications
Difference between Multiplexing and Multiple Access
S.No.
Multiplexing
Multiple Access



1

“In telecommunications and computer networks, multiplexing is a process where multiple analog message signals or digital data streams are combined into one signal over a shared medium.”

“In telecommunications and computer networks, a channel access method or multiple access method allows several terminals connected to the same multi-point physical medium to transmit over it and to share its capacity.”


2

The multiplexed signal is transmitted over a communication channel, which may be a physical transmission medium.


A channel-access scheme is based on a multiplex method that allows several data streams or signals to share the same communication channel or physical media.




3

A device that performs the multiplexing is called a multiplexer (MUX), and a device that performs the reverse process is called a demultiplexer (DEMUX).

A channel-access scheme is also based on a Multiple access protocol and control mechanism, also known as media access control (MAC). This protocol deals with issues such as addressing, assigning multiplex channels to different users, and avoiding collisions.

4

It works on the physical layer (L1) of OSI model.

It works on the Data Link layer (L2) of OSI model.







5

Classification of multiplexing:
(w.r.t. channelization methods)

a.       Time-division multiplexing (TDM)

b.      Frequency-division multiplexing (FDM)
I.                   WDM
II.                OFDM
III.             SC-FDM








c.       Code-division multiplexing (CDM)
I.                   DSSS
II.                FHSS
III.             OFHM
IV.             MC-CDM

Classification of Multiple Access:
(w.r.t. channelization methods)

a.       TDMA
            MF-  TDMA
b.      FDMA
I.                   Wavelength division multiple access (WDMA)
II.                Orthogonal frequency division multiple access (OFDMA)
III.             Single-carrier FDMA (SC-FDMA)







c.       Code division multiple access (CDMA
I.                   Direct-sequence CDMA (DS-CDMA), based on Direct-sequence spread spectrum (DSSS)
II.                Frequency-hopping CDMA (FH-CDMA), based on Frequency-hopping spread spectrum (FHSS)
III.             Orthogonal frequency-hopping multiple access (OFHMA)
IV.             Multi-carrier code division multiple access (MC-CDMA)











6

Classification of multiplexing:
(w.r.t. Applications)
a.       Telephony
I.                   Fiber in the loop (FITL
II.                FDM in DSL

b.      Video processing
I.                   TDM

c.       Digital broadcasting
I.                   statistical multiplexing
II.                 



Classification of Multiple Access:
(w.r.t. Packet mode methods)
a.       Contention based random multiple access methods
I.                   Aloha
II.                Slotted Aloha
III.             (MACA)
IV.             (MACAW)
V.                (CSMA)
VI.             (CSMA/CD)
VII.           (CSMA/CA)
VIII.       (DCF)
IX.             (PCF)

b.      Token passing
I.                   Token ring
II.                Token bus

c.       Polling

d.      Resource reservation (scheduled) packet-mode protocols
I.                   (Dynamic TDMA)
II.                (PRMA)
III.             (R-ALOHA)


7

Example:
Cisco Frame Relay and X.25 systems are also categorized as Statistical TDMs.


Example:
Service providers can deploy Cisco-CDMA data services to track ongoing performance of their network end to end.





Synchronization in TDM system :




TDM-PAM generator

 


frame synchronization in TDM


 Advantages of TDM :

 


disadvantages of TDM

 


application of TDM


Statistical TDM

 


Statistical TDM (frame format )

 


difference in between TDM and FDM


 


comparison in FDM and synchronus TDM and statistical TDM

 


Wavelength division multiplexing (WDM)

 



working of Wavelength division multiplexing (WDM)


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