Chapter 2 The Physical Layer 1 The lowest layer of reference model. It defines the mechanical, electrical, and timing interfaces to the network.

2 BANDWIDTH AND INFORMATION CAPACITY Bandwidth is the span of frequencies within the spectrum occupied by a signal and used by the signal for conveying information. Carrying information requires bandwidth.

N OISELESS C HANNEL : N YQUIST B IT R ATE 3 L is the number of signal levels used to represent data. Increasing the levels of a signal may reduce the reliability of the system.

N OISY C HANNEL : S HANNON C APACITY 4 where capacity is in bits/second, bandwidth is in hertz, and signal and noise powers are measured in the same physical units, such as watts. Bits are fundamental units of information. The theoretical highest data rate for a noisy channel

U SING BOTH LIMITS The Shannon capacity gives us the upper limit; the Nyquist formula tells us how many signal levels we need. 5

G UIDED T RANSMISSION D ATA Magnetic Media Twisted Pair Coaxial Cable Fiber Optics 6 W IRELESS T RANSMISSION The Electromagnetic Spectrum Radio Transmission Microwave Transmission Infrared and Millimeter Waves Lightwave Transmission

T WISTED P AIRS Category 5e UTP cable with four twisted pairs 7

C OAXIAL C ABLE A coaxial cable 8

P OWER L INES A network that uses household electrical wiring. 9

F IBER C ABLES (a) Side view of a single fiber. (b) End view of a sheath with three fibers. 10

D IGITAL S UBSCRIBER L INES (3) A typical ADSL equipment configuration. 11

F IBER T O T HE H OME Passive optical network for Fiber To The Home. 12

M ODEMS (a) A binary signal (b) Amplitude modulation (c) Frequency modulation (d) Phase modulation 13

S IGNAL E NCODING T ECHNIQUES Digital data, digital signal(Ethernet) Analog data, digital signal(PCM) Digital data, analog signal(ADSL) Analog data, analog signal(phone) 14

L INE CODING SCHEMES 15

L INE CODES 16

P OLAR (+ AND – VOLTAGES ) NRZ 17

B IPHASE Manchester Transition in middle of each bit period Transition serves as clock and data Low to high represents one High to low represents zero Used by IEEE Differential Manchester Mid-bit transition is clocking only Transition at start of a bit period represents zero No transition at start of a bit period represents one Note: this is a differential encoding scheme Used by IEEE

M ANCHESTER E NCODING 19

4.20 Effect of lack of synchronization

TQ 6. The waveform of following figure belongs to a Manchester encoded binary data stream. Determine the beginning and end of bit periods (i.e., extract clock information) and give the data sequence. 21

B IPOLAR (+, 0, - VOLTAGES ) SCHEMES 22 Alternate Mark Inversion (AMI): 1s are represented by alternating positive and negative voltages.

In mBnL schemes, a pattern of m data elements is encoded as a pattern of n signal elements in which 2 m ≤ L n. Note 23

4.24 Multilevel: 2B1Quaternary scheme, used in DSL

Multilevel: 8Binary6Ternary scheme, used in 100Base-T4 25

4.26 Figure 4.12 Multilevel: 4D-PAM5 scheme

4.27 Multitransition: MLT-3 scheme, G-bit Ethernet

4.28 Table 4.1 Summary of line coding schemes

S IMPLE C IRCUIT S WITCHED N ETWORK 29

P ACKET S WITCHED NETWORK 30