Friday, November 16, 2012

multiplexing and multiple access

Multiplexing And Multiple Access :

Digital Communications

Difference between Multiplexing and Multiple Access:
Multiple Access


“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.”


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.


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.


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

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


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)


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

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)


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

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