OSI Physical Layer

思科网络技术学院理事会 . http://www.catc.edu.cn 1

OSI Physical Layer

Network Fundamentals – Chapter 8

http://www.catc.edu.cn/

2思科网络技术学院理事会 . http://www.catc.edu.cn

Objectives Explain the role of Physical layer protocols and

services in supporting communication across data networks.- Describe the role of signals used to represent bits as a frame

as the frame is transported across the local media

Describe the purpose of Physical layer signaling and encoding as they are used in networks

Identify the basic characteristics of copper, fiber and wireless network media

Describe common uses of copper, fiber and wireless network media



Context Index

8.1 The Physical Layer – Communication Signals 8.2 Physical Signaling and Encoding: Representing Bits 8.3 Physical Media – Connecting Communication 8.4 Labs – Media Connectors



8.1 The Physical Layer – Communication Signals



8.1.1 Physical Layer - Purpose The OSI Physical layer provides the means to transport

across the network media the bits that make up a Data Link layer frame.



8.1.1 Physical Layer - Purpose The purpose of the Physical layer is to create the

electrical, optical, or microwave signal that represents the bits in each frame.



8.1.2 Physical Layer - Operation There are three basic forms of network media on

which data is represented:

－ Copper cable

－ Fiber

－ Wireless



8.1.3 Physical Layer - Standards Comparison of Physical layer standards and upper

layer standards



8.1.3 Physical Layer - Standards Standards for the Physical layer specify signal,

connector, and cabling requirements.















8.1.4 Physical Layer Fundamental Principles The three fundamental functions of the Physical layer

are:

－ The physical components

－ Data encoding

－ Signaling



8.2 Physical Signaling and Encoding: Representing Bits



8.2.1 Signaling Bits for the Media All communication from the human network becomes

binary digits, which are transported individually across the physical media.

Bits are represented on the medium by changing one or more of the following characteristics of a signal:

－ Amplitude

－ Frequency

－ Phase



8.2.1 Signaling Bits for the Media Method of signaling:

－ Non Return to Zero (NRZ) Signaling

－ Manchester Encoding

－ 4B/5B



8.2.2 Encoding – Grouping Bits One way to provide frame detection is to begin each

frame with a pattern of signals representing bits.



8.2.2 Encoding – Grouping Bits A code group is a consecutive sequence of code bits

that are interpreted and mapped as data bit patterns. Advantages using code groups include: － Reducing bit level error － Limiting energy transmitted － Distinguish data from control － Better media error detection



8.2.3 Data carrying Capacity Data transfer can be measured in three ways: － Bandwidth － Throughput － Goodput

Bandwidth Digital bandwidth measures the amount of information that

can flow from one place to another in a given amount of time.



8.2.3 Data carrying Capacity Data Throughput and Goodput



8.3 Physical Media – Connecting Communication



8.3.1 Types of Physical Media Several media characteristics defined by Physical layer

standards.



8.3.1 Types of Physical Media Several media characteristics defined by Physical layer

standards.



8.3.2 Copper Media The types of copper cabling include:

－ Coaxial cable － Twisted-pair cable · Unshielded Twisted-pair

· Shielded Twisted-pair



8.3.2 Copper Media External Signal Interference



8.3.3 Unshielded Twisted Pair (UTP) Cable The basic characteristics of UTP cable



8.3.3 Unshielded Twisted Pair (UTP) Cable UTP Cable Types － Ethernet Straight-through － Ethernet Crossover － Rollover



8.3.4 Other Copper Cable Coaxial cable



8.3.4 Other Copper Cable Coaxial cable



8.3.4 Other Copper Cable Shielded Twisted-Pair (STP) Cable



8.3.5 Copper Media Safety Types of safety issues when working with copper

cabling



8.3.6 Fiber Media Fiber Media Cable Construction



8.3.6 Fiber Media Fiber Media Cable Construction



8.3.6 Fiber Media Fiber provides full duplex communications with a cable

dedicated to each direction.



8.3.6 Fiber Media Fiber optic cables can be broadly classified into two

types: single-mode and multimode.

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8.2.7 Wireless Media Wireless media carry electromagnetic signals at radio

and microwave frequencies that represent the binary digits of data communications.



8.3.7 Wireless Media Types of Wireless Networks － Standard IEEE 802.11

－ Standard IEEE 802.15

－ Standard IEEE 802.16

－ Global System for Mobile Communications (GSM)



8.3.7 Wireless Media The Wireless LAN

In general, a wireless LAN requires the following network devices:

－ Wireless Access Point (AP) － Wireless NIC adapters



8.3.7 Wireless Media WLAN Ethernet-based standards include: IEEE 802.11a - Operates in the 5 GHz frequency band and

offers speeds of up to 54 Mbps. IEEE 802.11b - Operates in the 2.4 GHz frequency band and

offers speeds of up to 11 Mbps.

IEEE 802.11g - Operates in the 2.4 GHz frequency band and offers speeds of up to 54 Mbps.

IEEE 802.11n - The proposed standard defines frequency of 2.4 GHz or 5 GHz. The typical expected data rates are 100 Mbps to 210 Mbps with a distance range of up to 70 meters.



8.3.8 Media Connectors Common Copper Media Connectors



8.3.8 Media Connectors Correct Connector Termination



8.3.8 Media Connectors Common Optical Fiber Connectors



8.4 Labs – Media Connectors



Category 5 UTP Cable Tests Lab 8.4.1: Media Connectors Lab Activity



Summary




OSI Physical Layer

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