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# Chapter 2 The Physical Layer - PowerPoint PPT Presentation

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

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The lowest layer of reference model. It defines the mechanical, electrical, and timing interfaces to the network.

Chapter 2 The Physical Layer

BANDWIDTH AND INFORMATION CAPACITY mechanical, electrical, and timing interfaces to the network.

Bandwidthis the span of frequencies within the spectrum occupied by a signal and used by the signal for conveying information.

Carrying information requires bandwidth.

Noiseless Channel: Nyquist Bit Rate mechanical, electrical, and timing interfaces to the network.

L is the number of signal levels used to represent data.

Increasing the levels of a signal may reduce the reliability of the system.

Noisy Channel: Shannon Capacity mechanical, electrical, and timing interfaces to the network.

The theoretical highest data rate for a noisy channel

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.

Using both limits mechanical, electrical, and timing interfaces to the network.

The Shannon capacity gives us the upper limit;

the Nyquist formula tells us how many signal levels we need.

Guided Transmission Data mechanical, electrical, and timing interfaces to the network.

• Magnetic Media

• Twisted Pair

• Coaxial Cable

• Fiber Optics

WirelessTransmission

• The Electromagnetic Spectrum

• Microwave Transmission

• Infrared and Millimeter Waves

• Lightwave Transmission

Twisted Pairs mechanical, electrical, and timing interfaces to the network.

Category 5e UTP cable with four twisted pairs

Coaxial Cable mechanical, electrical, and timing interfaces to the network.

A coaxial cable

Power Lines mechanical, electrical, and timing interfaces to the network.

A network that uses household electrical wiring.

Fiber Cables mechanical, electrical, and timing interfaces to the network.

(a) Side view of a single fiber.

(b) End view of a sheath with three fibers.

Digital Subscriber Lines (3) mechanical, electrical, and timing interfaces to the network.

Fiber To The Home mechanical, electrical, and timing interfaces to the network.

Passive optical network for Fiber To The Home.

Modems mechanical, electrical, and timing interfaces to the network.

(a) A binary signal

(b) Amplitude modulation

(c) Frequency modulation

(d) Phase modulation

Signal Encoding Techniques mechanical, electrical, and timing interfaces to the network.

• Digital data, digital signal(Ethernet)

• Analog data, digital signal(PCM)

• Analog data, analog signal(phone)

Line coding schemes mechanical, electrical, and timing interfaces to the network.

Line codes mechanical, electrical, and timing interfaces to the network.

Polar (+ and – voltages) NRZ mechanical, electrical, and timing interfaces to the network.

Biphase mechanical, electrical, and timing interfaces to the network.

• 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 802.3

• 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 802.5

Manchester Encoding mechanical, electrical, and timing interfaces to the network.

Effect of lack of synchronization mechanical, electrical, and timing interfaces to the network.

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.

Bipolar (+, 0, - voltages) schemes Manchester encoded binary data stream. Determine the beginning and end of bit periods (i.e., extract clock information) and give the data sequence.

Alternate Mark Inversion (AMI): 1s are represented by alternating positive and negative voltages.

Note Manchester encoded binary data stream. Determine the beginning and end of bit periods (i.e., extract clock information) and give the data sequence.

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

Multilevel: 2B1Quaternary scheme, used in DSL Manchester encoded binary data stream. Determine the beginning and end of bit periods (i.e., extract clock information) and give the data sequence.

Multilevel: 8Binary6Ternary scheme, used in 100Base-T4 Manchester encoded binary data stream. Determine the beginning and end of bit periods (i.e., extract clock information) and give the data sequence.

Figure 4.12 Manchester encoded binary data stream. Determine the beginning and end of bit periods (i.e., extract clock information) and give the data sequence. Multilevel: 4D-PAM5 scheme

Multitransition: MLT-3 scheme, G-bit Ethernet Manchester encoded binary data stream. Determine the beginning and end of bit periods (i.e., extract clock information) and give the data sequence.

Table 4.1 Manchester encoded binary data stream. Determine the beginning and end of bit periods (i.e., extract clock information) and give the data sequence. Summary of line coding schemes

Simple Circuit Switched Network Manchester encoded binary data stream. Determine the beginning and end of bit periods (i.e., extract clock information) and give the data sequence.

Packet Switched network Manchester encoded binary data stream. Determine the beginning and end of bit periods (i.e., extract clock information) and give the data sequence.