School of Information TechnologySchool of Information TechnologySuranareeSuranaree University of TechnologyUniversity of Technology

204107 – Data Communication

Dr. Thara Angskun (ดร. ธรา องัสกลุ่ )E-mail: angskun@sut.ac.thTel: (044)22 4535

Schedule

Quiz [8], Chapter 9** Sun Mar 9

Final ExamFri Mar 28Quiz [10], ReviewThu Mar 20Quiz [9], Chapter 10Thu Mar 13

Quiz [6-7], Chapter 8Thu Mar 6** Sun Mar 2

Chapter 6-7Thu Feb 28

** Substitution for Makha Bucha Day (Feb 21, 2008)

CH 6: Multiplexing

Multiplexing

FDM• Frequency Division Multiplexing

• Analog multiplexing that combines signals

Guard Bands

FDM Multiplexing Process

FDM Demultiplexing Process

Example 1• Assume that a voice channel occupies a

bandwidth of 4 KHz. We need to combine three voice channels into a link with a bandwidth of 12 KHz, from 20 to 32 KHz (no guard bands). Show the configuration using FDM.

Example 1 (Cont.)

Example 2• Five channels, each with a 100-KHz bandwidth,

are to be multiplexed together. What is the minimum bandwidth of the link if there is a need for a guard band of 10 KHz between the channels to prevent interference?

Example 3• Four data channels (digital), each transmitting

at 1 Mbps, use a satellite channel of 1 MHz. Design an appropriate configuration using FDM

Example 3• Four data channels (digital), each transmitting

at 1 Mbps, use a satellite channel of 1 MHz. Design an appropriate configuration using FDM

FDM Hierarchy

Why not 2.4 MHz?

Example 4• AMPS phone company uses two bands. The

first band, 824 to 849 MHz [BW=25MHz], is used for sending; and 869 to 894 MHz is used for receiving. Each user has a bandwidth of 30 KHz in each direction. How many people can use their cellular phones simultaneously?

• Solution = 25 MHz / 30 KHz = 833.33 • (In practice: 832 channels = 42 control + 790 users)

WDM• Wavelength Division Multiplexing

• Analog multiplexing that combines optical signals

WDM Mux-Demux

TDM• Time Division Multiplexing

• Digital multiplexing that combines low-rate channels into one high-rate

Output data rate = N x Data rate of an input link

TDM Frames

Example 5• Four 1-Kbps connections are multiplexed

together. A unit is 1 bit. Find • (1) the duration of 1 bit before multiplexing [INPUT]

• 1/1,000 = 0.001 s (= 1ms)• (2) the transmission rate of the link [OUTPUT]

• 4 Kbps• (3) the duration of a time slot [OUTPUT]

• 1/4000 = 0.00025 s (= 0.25 ms = 250 µs)• (4) the duration of a frame [OUTPUT]

• 4 * 0.25 ms = 1ms

Example 6• Four channels are multiplexed using TDM. If

each channel sends 100 bytes/s and we multiplex 1 byte per channel. Find the bit rate for the link, frame size, the frame rate and the duration of a frame.

Example 7• A multiplexer combines four 100-Kbps channels

using a time slot of 2 bits. Show the output with four arbitrary inputs. What is the bit rate? What is the frame rate? What is the frame duration?

Interleaving• The process of taking a group of bits from each

input line for multiplexing

Framing Bits

Digital Signal (DS) Hierarchy

T-4DS-4

T-3DS-3

T-2DS-2

T-1DS-1T-LineService

T Lines for Analog Trans.

T-1 Frame

Empty Slots• Inefficient use of bandwidth

Synchronous vs. Statistical

Data Rate Management

Not all input links may have the same data rate.

*** ASSIGNMENT 1 ***• 1) What are Multilevel Multiplexing, Multiple-Slot Allocation and

Pulse Stuffing?

• 2) Two channels, one with a bit rate of 100 Kbps and another with a bit rate of 200 Kbps, are to be multiplexed. How this can be achieved? What is the frame rate? What is the frame duration? What is the bit rate of the link?

• 3) Question 5 [p. 119]• 4) Question 7 [p. 119]• 5) Question 8 [p. 119]

Due date: Wed Mar 5, 2008