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© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 1Version 4.0
OSI Physical Layer
Network Fundamentals – Chapter 8
2© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
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
5© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
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.
9© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
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.
10© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
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.
14© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
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.
20© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
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.
22© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Physical Layer Signaling and Encoding
23© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Physical Layer Signaling and Encoding
24© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Characteristics & Uses of Network Media
25© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
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
26© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
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
27© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
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
28© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Characteristics & Uses of Network Media
29© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Characteristics & Uses of Network Media
30© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Characteristics & Uses of Network Media
31© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
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
32© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Characteristics & Uses of Network Media
36© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Fiber-optic cable anatomy Buffer coating
Core
Cladding
100 - 140
microns
62.5 - 125
microns
50 - 125
microns
10 - 125
microns
Single-mode MultimodeMultimodeMultimode
37© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Single and Multimode Fiber-optical connectors
ST Connector SC Connector
MultimodeSingle-Mode
38© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Fiber Optics – Compare Single and Multi Modes
39© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Characteristics & Uses of Network Media
40© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Characteristics & Uses of Network Media
41© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Characteristics & Uses of Network Media
42© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
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