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Flashcards in Physical Layer Deck (23):
0

Three fundamental functions

Data encoding: converting stream of bits into a code
Signaling: the method of representing bits
Physical components: hardware and connectors

1

Bit patterns

Signals designating start and end of frame

2

Bit time

Each signal has a certain time to occupy media

3

NRZ

Signaling method suitable for slow speed data links

4

Code groups

A set of encoded symbols to represent encoded data or control info

5

Three symbols of code groups

Data symbol
Control symbols: controls transmission
Invalid symbol: not allowed on media

6

Frequent transitions

Less individual bit errors and less sync loss

7

Balancing 1s and 0s

DC balancing

8

Data transfer measured in three ways:

Bandwidth: amount of info flowing from one place to another
Throughput: measure of transfer of bits across media over time
Goodput: transfer of useable data

9

Crosstalk

Interference in the twisted pairs of wires via their magnetic field

10

Copper cable

Connects LAN devices to intermediate devices such as routers and switches

11

Coaxial cable

Consists of a copper conductor surrounded by a layer of flexible insulation

12

Uses of coaxial

Wireless and cable technologies; most widely used for transporting high radio frequency signals over wire

13

Fiber optic characteristics

Immune to electromagnetic interference; relatively low signal loss; operated at greater lengths than copper; uses glass or plastic fibers to guide light impulses from source to destination

14

Single mode optical fiber

Single ray of light emitted usually from a laser; can transmit optical pulses for very long distances; uses subscriber connector

15

Multimode fiber

Cheaper than single mode; uses Lucent and straight tip connectors; uses led to generate light pulses on the media.

16

Wireless characteristics

Carry electromagnetic signals at radio and microwave frequencies; performs well in open environments; interference from cordless phones, microwaves, other wireless devices

17

Wireless networks

802.11 wifi
802.15 wpan Bluetooth
802.16 WiMAX point to multi point topology worldwide interoperability for microwave access
Gsm

18

Wireless LAN requires

Wireless access point

Wireless NIC adapters

19

Wireless standards

802.11a 5 ghz 54 Mbps, not interoperable with 802.11b, 802.11g
802.11b 2.4 ghz 11 Mbps have longer range and can penetrate buildings better
802.11g 2.4 ghz 54 Mbps
802.11n 2.4 ghz or 5 ghz 100-200 Mbps 70 m

20

Fiber optic termination and splicing errors

Misalignment: not precisely aligned to one another
End gap: the media do not completely touch at the splice or connection
End finish: not well polished or dirt is present at termination

21

Optical time domain reflectometer

Used to test each fiber optic cable segment

22

Deliver of frames require

Physical media and associated connectors
A representation of bits in media
Encoding of data and control info
Transmitter and receiver circuitry on the network devices