16 February 2003 [email protected] TU/e Computer Science, System Architecture and...

16 February 2003 [email protected]/e Computer Science, System Architecture and Networking

1

Communication media

Thanks to A. Tanenbaum


2

Fourier Coefficients

11

)2sin()2cos(2

1)(

n

n

n

n nftbnftac

tg

T

T

n

T

n

dttgT

c

dtnfttgT

b

dtnfttgT

a

0

0

0

)(2

)2cos()(2

)2sin()(2


3

Bandwidth-Limited Signals

A binary signal and its root-mean-square Fourier amplitudes.

(b) – (c) Successive approximations to the original signal.


4

Bandwidth-Limited Signals (2)

(d) – (e) Successive approximations to the original signal.


5

Twisted Pair

(a) Category 3 UTP.(b) Category 5 UTP.


6

Coaxial Cable

A coaxial cable.


7

Fiber Optics

(a) Three examples of a light ray from inside a silica fiber impinging on the air/silica boundary at different angles.

(b) Light trapped by total internal reflection.


8

Fiber Optic Networks

A fiber optic ring with active repeaters.


9

Fiber Optic Networks (2)

A passive star connection in a fiber optics network.


10

The Electromagnetic Spectrum

The electromagnetic spectrum and its uses for communication.


11

Politics of the Electromagnetic Spectrum

The ISM bands in the United States.


12

The Local Loop: Modems, ADSL, and Wireless

The use of both analog and digital transmissions for a computer to computer call. Conversion is done by the modems and codecs.


13

Data transmission

Receiver needs to know about sender• duration of each bit• length of elements in bits• duration of a frame


14

Modems

(a) A binary signal

(b) Amplitude modulation

(c) Frequency modulation

(d) Phase modulation


15

Bit encoding(1)

Asynchronous data transmission

Used for• character oriented devices• large indeterminate intervals between characters

receiver resynchronizes with sender on start and stop bits

polarity of stop bit different from polarity of start bit

1 0 0 1 0 0 1 0Stopbit(s)

Startbit


16

Bit encoding(2)

(a) Binary encoding, (b) Manchester encoding, (c) Differential Manchester encoding.


17

Modems (2)

(a) QPSK.

(b) QAM-16.

(c) QAM-64.


18

Frequency Division Multiplexing

(a) The original bandwidths. (c) The multiplexed channel.

(b) The bandwidths raised in frequency.


19

Wavelength Division Multiplexing

Wavelength division multiplexing.


20

Time Division Multiplexing

The T1 carrier (1.544 Mbps).


21

Time Division Multiplexing (2)

Delta modulation.


22

Time Division Multiplexing (3)

Multiplexing T1 streams into higher carriers.


23

Code Division Multiple Access (CDMA)

Every single bit Xor with individual Walsh code1 bit is extended to 64 or 128 chipsConsequence 64 (128) more bits transmitted

Walsh codes are orthogonalSo assume two codes A and B then A.B = 0


24

Code Division Multiple Access (CDMA) (2)

Example, two stations with Walsh codes A and BA: -1 -1 -1 1 1 -1 1 1B: -1 -1 1 -1 1 1 1 -1

A and B both transmit 1, Xor with Walsh codeAddition of signals then gives S = -2 -2 0 0 2 0 2 0 S.A = (2+2+0+0+2+0+2+0)/8 = 1 S.B = (2+2+0+0+2+0+2+0)/8 = 1


25

Wireless coding

Direct Sequence Spread Spectrum (DSSS) basis for CDMAFrequency Hopping Spread Spectrum (FHSS)


26

Advanced Mobile Phone System

(a) Frequencies are not reused in adjacent cells.

(b) To add more users, smaller cells can be used.


27

Multiple Access Protocols

a) ALOHA

b) Carrier Sense Multiple Access Protocols

c) Collision-Free Protocols

d) Limited-Contention Protocols

e) Wavelength Division Multiple Access Protocols

f) Wireless LAN Protocols


28

Dynamic Channel Allocation

a) Terminals

b) Single Channel

c) Collision

d) Continuous time vs slotted time

e) Carrier sense or not


29

Pure ALOHA

In pure ALOHA, frames are transmitted at completely arbitrary times.


30

Pure ALOHA (2)

Vulnerable period for the shaded frame.


31

Pure ALOHA (3)

Throughput versus offered traffic for ALOHA systems.


32

Persistent and Nonpersistent CSMA

Comparison of the channel utilization versus load for various random access protocols.


33

Collision detection interval

Collision detection can take as long as 2 .


34

CSMA with Collision Detection

CSMA/CD can be in one of three states: contention, transmission, or idle.


35

Collision-Free Protocols

The basic bit-map protocol.


36

Collision-Free Protocols (2)

The binary countdown protocol. A dash indicates silence.


37

Limited-Contention Protocols

Acquisition probability for a symmetric contention channel.


38

Adaptive Tree Walk Protocol

The tree for eight stations.


39

Wireless LAN protocols

(a) The hidden station problem.(b) The exposed station problem.


40

Wireless LAN Protocols (2)

The MACA protocol. (a) A sending an RTS to B.

(b) B responding with a CTS to A.


41

Wireless Lan Protocol: CSMA/CA

The use of virtual channel sensing using CSMA/CA.


42

Wireless LAN Protocol: CSMA/CA (2)

A fragment burst.


43

Ethernet MAC Sublayer Protocol

Frame formats. (a) DIX Ethernet, (b) IEEE 802.3.


44

Ethernet Performance

Efficiency of Ethernet at 10 Mbps with 512-bit slot times.


45

IEEE 802.2: Logical Link Control

(a) Position of LLC. (b) Protocol formats.


46

The 802.11 Protocol Stack

Part of the 802.11 protocol stack.


47

The 802.11 MAC Sublayer Protocol (4)

Interframe spacing in 802.11.


48

The 802.11 Frame Structure

The 802.11 data frame.


49

Bluetooth Architecture

Two piconets can be connected to form a scatternet.


50

Bridges from 802.x to 802.y (2)

The IEEE 802 frame formats. The drawing is not to scale.

16 February 2003 [email protected] TU/e Computer Science, System Architecture and...

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