© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 1Version 4.0

OSI Physical Layer

Network Fundamentals – Chapter 8

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What Will we Learn from chapter 8?

Physical layer protocols and services in supporting communication across data networks

The role of signals used to represent bits as a frame transported across the local media

The purpose of Physical layer signaling and encoding used in networks

Basic characteristics of copper, fiber and wireless network media

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Physical Layer Protocols & Services

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Physical Layer Protocols & Services

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OSI Model – PDU– protocol - hardware

Layer 7 data

Layer 6 data

Layer 5 data

Layer 4 segments TCP,UDP

Layer 3 packets IP routers

Layer 2 frames MAC hubs, bridges, switches

Layer 1 bits amplifiers, repeaters

*PDU – Protocol Data Unit (may contain control information) Layers 1 thru 4.

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Physical Layer Protocols & Services

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Physical Layer Protocols & Services

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Physical Layer Protocols & Services

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Modulation

A technique for processing signals in which two waves are combined to produce a wave that possesses characteristics of both and can be decoded to separate these characteristics.

Information wave - the wave containing the signal you want to transmit.

Carrier wave - the wave that is modulated, and whose properties are constant and known to both the sender and receiver.

Guided waves - waves that are bound to a carrier wave’s frequency.

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Modulation

Modulator - the device that imposes the message signal on the carrier signal at the transmission end.

Demodulator - separates the message from the carrier signal at the receiving end.

Modem - a device used to convert digital into analog signals and analog into digital signals.

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Modulation

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Amplitude Modulation

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Amplitude Modulation

t =>

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Frequency Modulation

A method of modulation in which the frequency of the carrier signal is modified by the addition of the message signal.

Frequency shift keying (FSK) - when FM signals are converted into digital signals, the differing frequencies are conveyed as either 0s or 1s.

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Frequency Modulation

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Frequency Modulation

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Phase Modulation

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Phase Modulation

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Phase Modulation

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Pulse Code Modulation (PCM)

The process of converting analog signals into digital signals

Sampling - the first step in converting analog signals to digital signals is to measure the amplitude of an analog signal at multiple instants.

The higher the sampling rate, the more closely the digital signal resembles the original analog signal.

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Pulse Code Modulation (PCM)

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Physical Layer Signaling and Encoding

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Physical Layer Signaling and Encoding

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Characteristics & Uses of Network Media

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10 base 2 and 10 base 5 are terms used to describe coaxial cables.

10 is the speed 10 mbpsbase- signaling(baseband)

2 or 5 denotes the max length that can be used. 200 meters or 500

10base 2 – 10base 5

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10base-T – 100base-T – 1000base-T

1xxx base T used to describe twisted pair cabling

1xxx is the speed in mbpsbase- signaling (baseband)

The T stands for twisted pair

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For Gigabit Ethernet, industry offerings include these types of wiring:

• 1000BASE-SX (a short laser wavelength on multimode fiber optic cable for a maximum length of 550 meters)

• 1000BASE-LX/LH (a long wavelength for a "long haul" fiber optic cable for a maximum length of 10 kilometers)

• 1000BASE-ZX (an extended wavelength single-mode optical fiber for up to 100 kilometers)

• 1000BASE-CX (two pairs of 150-ohm shielded twisted pair cable for a maximum length of 25 meters)

• 1000BASE-T (four pairs of Category 5 unshielded twisted pair cable for a maximum length of 100 meters)

Fiber

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Characteristics & Uses of Network Media

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Characteristics & Uses of Network Media

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Characteristics & Uses of Network Media

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Characteristics & Uses of Network Media

Shielded twisted pair (two pair)

Outer Jacket

Braided shield

Foil shield

Twisted Pairs

Unshielded twisted pair (four pair)

Twisted Pair

Plastic insulation

Outer Jacket

Outer Jacket

Overall shield

Twisted Pair

ScTP (a hybrid UTP) shielded

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Characteristics & Uses of Network Media

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Fiber Optics

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Fiber Optics

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Coaxial cable anatomy

A

CD

B

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Fiber-optic cable anatomy Buffer coating

Core

Cladding

100 - 140

microns

62.5 - 125

microns

50 - 125

microns

10 - 125

microns

Single-mode MultimodeMultimodeMultimode

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Single and Multimode Fiber-optical connectors

ST Connector SC Connector

MultimodeSingle-Mode

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Fiber Optics – Compare Single and Multi Modes

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Characteristics & Uses of Network Media

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Characteristics & Uses of Network Media

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Characteristics & Uses of Network Media

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What Did I Learn from chapter 8?

Physical layer protocols and services in supporting communication across data networks

The role of signals used to represent bits as a frame transported across the local media

The purpose of Physical layer signaling and encoding used in networks

Basic characteristics of copper, fiber and wireless network media

43© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public

OSI Physical Layer

NextEthernet