COE 341 Data Computer Communications Dr Marwan AbuAmara

COE 341: Data & Computer Communications Dr. Marwan Abu-Amara Chapter 8: Multiplexing

Lecture Contents 1. 2. 3. 4. 5. 6. Introduction Multiplexing Types FDM Synchronous TDM Statistical TDM ADSL COE 341 – Dr. Marwan Abu-Amara 2

Introduction n n Multiplexing: A generic term used when more than one application or connection share the capacity of one link Objective is to achieve better utilization of resources COE 341 – Dr. Marwan Abu-Amara 3

Multiplexing Types COE 341 – Dr. Marwan Abu-Amara 4

Frequency Division Multiplexing (FDM) COE 341 – Dr. Marwan Abu-Amara 5

FDM n n n Useful bandwidth of medium exceeds required bandwidth of channel Each signal is modulated to a different carrier frequency Carrier frequencies separated so signals do not overlap (guard bands) q n e. g. broadcast radio Channel allocated even if no data COE 341 – Dr. Marwan Abu-Amara 6

FDM COE 341 – Dr. Marwan Abu-Amara 7

FDM Multiplexing Process: Time-Domain View COE 341 – Dr. Marwan Abu-Amara 8

FDM Multiplexing Process: Frequency-Domain View COE 341 – Dr. Marwan Abu-Amara 9

FDM De-Multiplexing Process: Time-Domain View COE 341 – Dr. Marwan Abu-Amara 10

FDM De-Multiplexing Process: Frequency-Domain View COE 341 – Dr. Marwan Abu-Amara 11

FDM System – Transmitter COE 341 – Dr. Marwan Abu-Amara 12

FDM System – Receiver COE 341 – Dr. Marwan Abu-Amara 13

FDM of Three Voiceband Signals COE 341 – Dr. Marwan Abu-Amara 14

Analog Carrier Systems n n n Devised by AT&T (USA) Hierarchy of FDM schemes Group q q n Supergroup q q n 60 channels FDM of 5 group signals on carriers between 420 k. Hz and 612 k. Hz Master group q n 12 voice channels (4 k. Hz each) = 48 k. Hz Range 60 k. Hz to 108 k. Hz 10 supergroups Jumbo group q 6 master groups COE 341 – Dr. Marwan Abu-Amara 15

Analog FDM Hierarchy COE 341 – Dr. Marwan Abu-Amara 16

Time Division Multiplexing (TDM) COE 341 – Dr. Marwan Abu-Amara 17

TDM n n n Data rate of medium exceeds data rate of digital signal to be transmitted Multiple digital signals interleaved in time May be at bit level or blocks Time slots preassigned to sources and fixed Time slots allocated even if no data Time slots do not have to be evenly distributed amongst sources COE 341 – Dr. Marwan Abu-Amara 18

Time Division Multiplexing COE 341 – Dr. Marwan Abu-Amara 19

TDM Frames COE 341 – Dr. Marwan Abu-Amara 20

TDM System – Transmitter COE 341 – Dr. Marwan Abu-Amara 21

TDM System – Receiver COE 341 – Dr. Marwan Abu-Amara 22

TDM Link Control n n n No headers and trailers Data link control protocols not needed for MUXed line Flow control q q n Data rate of multiplexed line is fixed If one channel receiver can not receive data, the others must carry on The corresponding source must be halted This leaves empty slots Error control q Errors are detected and handled by individual channel systems COE 341 – Dr. Marwan Abu-Amara 23

Data Link Control on TDM COE 341 – Dr. Marwan Abu-Amara 24

Framing n n n So far, no flag or SYNC characters bracketing TDM frames on the MUXed line Must provide frame synchronizing mechanism Added digit framing q One control bit added to each TDM frame n q Identifiable bit pattern used on control channel n q Looks like another channel - “control channel” e. g. alternating 0101…unlikely on a data channel Can compare incoming bit patterns on each channel with sync pattern COE 341 – Dr. Marwan Abu-Amara 25

Framing in TDM MUXed frame Four data channels C 1 2 0 3 4 C 1 2 1 3 4 C 1 0 …. . Control Channel, C 010101…. …. . A data Channel Unlikely to have 010101…. over successive frames • RX knows the size of the MUXed frame • It can check each frame bit frame-to-frame for the special pattern until it finds it • Once the position of the control channel is established, RX knows where the channel sequence starts and sync is established with TX COE 341 – Dr. Marwan Abu-Amara 26

Pulse Stuffing n Problem - Synchronizing data sources q n n Clocks in different sources drifting Data rates from different sources not related by simple rational number Solution - Pulse Stuffing q q q Outgoing data rate (excluding framing bits) higher than sum of incoming rates Stuff extra dummy bits or pulses into each incoming signal until it matches local clock Stuffed pulses inserted at fixed locations in frame and removed at demultiplexer COE 341 – Dr. Marwan Abu-Amara 27

TDM of Analog and Digital Sources COE 341 – Dr. Marwan Abu-Amara 28

Digital Carrier Systems n n Hierarchy of TDM (similar to FDM) USA/Canada/Japan use one system ITU-T use a similar (but different) system US system based on DS-1 format q q q Multiplexes 24 PCM voice channels Each frame has 8 bits per channel plus one framing bit 193 bits per frame (24 ch. 8 bits per ch. + 1 framing bit = 193 bits per frame) COE 341 – Dr. Marwan Abu-Amara 29

DS Signals COE 341 – Dr. Marwan Abu-Amara 30

DS & T Lines Rates Service Line DS-1 T-1 Rate (Mbps) 1. 544 DS-2 T-2 6. 312 96 DS-3 DS-4 T-3 T-4 44. 736 274. 176 672 4032 COE 341 – Dr. Marwan Abu-Amara Voice Channels 24 31

Digital Carrier Systems n For voice each channel contains one word of digitized data (PCM, 8000 samples per second) q q n Data rate 8000 x 193 = 1. 544 Mbps Five out of six frames have 8 bit PCM samples Sixth frame is 7 bit PCM word plus signaling bit Signaling bits form stream for each channel containing control and routing info Same format for digital data q 23 channels of data n q n 7 bits per frame plus indicator bit for data or systems control 24 th channel is sync DS-1 can carry mixed voice and data signals COE 341 – Dr. Marwan Abu-Amara 32

DS-1 Transmission Format (8000 x 7 bits = 56 kbps) COE 341 – Dr. Marwan Abu-Amara 33

T 1 Due to 1 framing bit Per frame COE 341 – Dr. Marwan Abu-Amara 34

T 1 Frames COE 341 – Dr. Marwan Abu-Amara 35

E 1 E-1 Rate (Mbps) 2. 048 E-2 8. 448 120 E-3 E-4 34. 368 139. 264 480 1920 E Line COE 341 – Dr. Marwan Abu-Amara Voice Channels 30 36

Mixed Data n n DS-1 can carry mixed voice and data signals 24 channels used No sync byte Can also interleave DS-1 channels q DS-2 is four DS-1 giving 6. 312 Mbps COE 341 – Dr. Marwan Abu-Amara 37

SONET/SDH n n n Synchronous Optical Network (ANSI) Synchronous Digital Hierarchy (ITU-T) Compatible Utilize the large channel capacity of optical fibers Signal Hierarchy q q Synchronous Transport Signal level 1 (STS-1) or Optical Carrier level 1 (OC-1) n Frame of 810 octets every 125 ms: 51. 84 Mbps Carry DS-3 or group of lower rate signals (DS 1, DS 1 C, DS 2) plus ITU-T rates (e. g. 2. 048 Mbps) Multiple STS-1 combined into STS-N signal ITU-T lowest rate is 155. 52 Mbps (STM-1) COE 341 – Dr. Marwan Abu-Amara 38

SONET/SDH Frame Format COE 341 – Dr. Marwan Abu-Amara 39

Statistical TDM n n In Synchronous TDM many slots are wasted Statistical TDM allocates time slots dynamically based on demand Multiplexer scans input lines and collects data until frame is full Data rate on line lower than aggregate rates of input lines COE 341 – Dr. Marwan Abu-Amara 40

Statistical TDM COE 341 – Dr. Marwan Abu-Amara 41

Statistical TDM Frame Formats COE 341 – Dr. Marwan Abu-Amara 42

Performance n n Output data rate less than aggregate input rates May cause problems during peak periods q q Buffer inputs Keep buffer size to minimum to reduce delay COE 341 – Dr. Marwan Abu-Amara 43

Buffer Size and Delay n Increasing utilization increases q q n Buffer size delay Utilization > 0. 8 is undesirable COE 341 – Dr. Marwan Abu-Amara 44

ADSL n n ADSL is an asymmetric communication technology designed for residential users; it is not suitable for businesses The existing local loops can handle bandwidths up to 1. 1 MHz ADSL is an adaptive technology. The system uses a data rate based on the condition of the local loop line Use the following as a rule of thumb q XYZ km XYZ Mbps COE 341 – Dr. Marwan Abu-Amara 45

ADSL Hardware COE 341 – Dr. Marwan Abu-Amara 46

ADSL Frequency Bands COE 341 – Dr. Marwan Abu-Amara 47

DMT COE 341 – Dr. Marwan Abu-Amara 48