Chapter 3 Flashcards

1
Q

what is a network topology

A

a description of how a network is physically laid out and how signals travel from one device to another

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2
Q

All network designs today are based on what 4 basic physical topologies

A
  • bus
  • star
  • ring
  • point-to-point
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3
Q

What are the two categorizations of network topologies

A
  • Physical topology - the arrangment of cabling and how cables connect one device to another in a network
  • Logical topologies - the path data travels between computers on a network
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4
Q

What is physical bus topology

A

this is a continuous length of cable connecting one computer to another in a daisy-chain fashion

This is the simplest and at one time was the most common method for connecting computers

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5
Q

What are the weaknesses of physical bus topology

A
  • There’s a limit of 30 computers per cable segment
  • The maximum total length of cabling is 185 meters
  • Both ends of the bus must be terminated
  • Any break in the bus brings down the entire network
  • Adding or removing a machine brings down the entire network temporarily
  • Technologies using this topology are limited to 10 Mbps half-duplex communication since they use coaxial cabling
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6
Q

How does data travel in a physical bus

What is the term for signal travel across the medium and from device to device

A

Electrical pulses (signals) travel the cables lengths in all directions

Signal propagation

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7
Q

How does a signal stop in a physical bus?

A
  • the signal continues until it weakens to the point of fading out or until it is absorbed by a terminator
    • a terminator is an electrical component called a resistor that absorbs the signal instead of allowing it to bounce back up the wire
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8
Q

What happens to a signal if it is not terminated at the end of a wire

A

is bounces, or is “reflected”

signal bounce is the term used when electricity bounces off the end of a cable and back in the other direction

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9
Q

why can a Physical Bus only allow 30 computers, or up to 185 meters?

A
  • the signal becomes too weak and doesn’t make it to the next computer in the chain
  • As an electrical signal encounters each workstation along a daisy-chain some of its strength is absorbed by both the cabling and the connectors until the signal is eventually too weak to interpret
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10
Q

what is a Physical Star Topology

A

this is a configuration that uses a central (hub or switch) to connect computers

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11
Q

What are the advantages of a physical star topology

A
  • Much faster technologies than a bus
  • Centralized monitoring and management of network traffic are possible
  • easier network upgrades
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12
Q

what does using a central device such as in the physical star topology allow for

A

hubs and switches can include software that collects statistics about network traffic patterns and detect errors

As long as cabling and NICs support it, a star network can be easily updated by replacing the central device

If the number or workstations you need exceed the ports on the central device you can add another at any time

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13
Q

What is an extended Star topology

A

This is when several hubs or switches are connected. It’s simply an extension of a physical star.

Also sometimes referred to as a “hierarchical star”

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14
Q

What determines how data travels “logical topology” in a physical star

A

this is determined by the type of central device:

Hub = logical bus

switch = logical switching

MAU = logical ring

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15
Q

What is the disadvantage of a physical star

A

The central device represents a single point of failure. If this device fails the entire network goes down

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16
Q

What is a physical ring topology similar to and in what way

A

it’s like a bus:

Devices are daisy-chained to one another

Instead of terminating each end, the cabling is brought around from the last device back to the first device to form a ring

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17
Q

What is a physical ring topology most widely used for

What is the technology involved used for

A

to connect LANs. Uses a technology called Fiber Distributed Data Interface (FDDI)

FDDI was most often used as a “network backbone”, which is cabling used to communicate between LANs or between hubs and switches

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18
Q

How does data travel in Physical Ring Topology,

what happens if a station in the ring fails

A

Data travels unidirectionaly, if any station fails the ring ceases function and data can no longer be transferred.

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19
Q

How does FDDI transfer data

A

Fiber Distributed Data Interface

uses dual ring (data travels in both directions)

one ring failure will not break the network

Operates using fiber-optic cable at 100 Mpbs

Extended star topologies with Gigabit Ethernet has largely replaced FDDI

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20
Q

What is Point-to-Point topology

A

this is format in which data has a direct link between two devices

Mostly used in WANs

Wireless bridge

used to connect two computers

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21
Q

What is Point-to-Multipoint topology

A

also known as (PMP) this means that a central device communicates with two or more other devices

All communication goes through the central device

often used in WANs where a main office has connections to several branch offices via a router

A single connection is made from the router to a switching device that directs traffic to the correct branch office

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22
Q

What is Mesh Topology

A

this means that each device is connected to every other device in a network

the purpose of creating a mesh topology is to ensure that if one or more connections fail, there’s another path for reaching all devices on the network

Expensive due to multiple interfaces and cabling

Found in large WANs and internetworks

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23
Q

What are logical topologies

A
  • These are how data travels from computer to computer
  • They are sometimes the same as physical topology
    • In a physical bus and physical ring, the logical topology mimics the physical arrangement of cables
    • For physical star, electronics in central device determine logical topology
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24
Q

What are the three logical topologies and what are the network technologies and physical topologies associated with them?

A
  • Bus
    • Ethernet
      • bus or star
    • Wireless LANs
      • star
  • Ring
    • Token ring
      • Star
    • FDDI
      • Ring
  • Switched
    • Ethernet
      • Star
25
What are example of LAN technologies
Ethernet, 802.11 wireless, Token Ring
26
What are examples of WAN technologies
Frame relay, FDDI, ATM
27
What is an unshielded twisted pair
an unshielded twisted pair or (UTP) is: The most common media type in LANs made up of 4 pairs of copper wires each twisted together Comes in numbered categories
28
What is Fiber-optic cabling
Fiber-optic cabling uses thin strands of glass to carry pulses of light long distances and at high data rates
29
What is Coaxial Cable
this is obsolete as a LAN medium but it is used as the network medium for internet access via cable modem
30
What are the two ways network technologies can use media to transmit signals
Baseband - sends digital signals in which each bit of data is represented by a pulse of electricity or light. Sent at a single fixed frequency and no other frames can be sent along with it Broadband - uses analog techniques to encode binary 1s and 0s across a continuous range of values. Signals flow at a particular frequency and each frequency represents a channel of data
31
Ethernet is the ___ \_\_\_ LAN technology Easy to install and support with a ___ \_\_\_ factor supports a broad range of speeds: 10 ___ to 10 \_\_\_ Can operate in physical ___ or physical ___ and logical ___ or ___ \_\_\_ topology Most NICs/hubs/switches can operate at multiple speeds: 10/100/1000 Underlying technology is the same
Ethernet is the most popular LAN technology Easy to install and support with a low cost factor supports a broad range of speeds: 10 mbps to 10 Gbps Can operate in physical bus or physical star and logical bus or switched local topology Most NICs/hubs/switches can operate at multiple speeds: 10/100/1000 Underlying technology is the same
32
What is Ethernet 2 frame type
frame type used by TCP/IP TCP/IP has become the dominant network protocol in LANs so supporting multiple frame types has become unnecessary
33
What are ethernet frames composed of
Destination MAC, Source MAC, Type, Data, FCS
34
What is Carrier Sense Multiple Access with Collision Detection (CSMA/CD)
* Carrier Sense - Listen before send - must hear silence * Multiple Access - If two or more stations hear silence, multiple stations may transmit at the same time * Collision Detection - If two or more stations transmit, a collision occurs and is detected by the NIC; all stations must retransmit
35
What is a collision domain
The extent to which signals in an ethernet bus topology network are propagated is called a collision domain
36
What does the term "best-effort delivery system" mean when referring to Ethernet
* Like the post-office; you hope it gets there but there is no acknowledgement either way * Network protocols and applications ensure delivery * Only collisions are automatically retransmitted
37
Ethernet detects damaged frames, how does this occur
There is an error checking code in a frame's trailer called a Cyclic Redundancy Check (CRC) Uses CRC to determine that data is unchanged If a frame is detected as damaged, it is discarded with no notification
38
Ethernet on hubs works only in what mode
Half duplex
39
How are Ethernet standards expressed
* XBaseY * X designates speed of transmission * Y specifies type of media (T = twisted pair, FX = fiber optic)
40
Describe the following Ethernet Standard: 10BaseT
* uses two of the four wire pairs * Runs over category 3 or higher UTP cabling * Highly susceptible to collisions and is obsolete
41
Describe the following Ethernet Standard: 40 Gigabit and 100 Gigabit Ethernet
Very high cost is still prohibitive Adoption has been slow Fiber-optic cabling is primary medium Although there are provisions to use special copper assemblies over short distances
42
What is 802.11 wireless networking also referred to as can be found in most towns and in those cases it is called what?
Wireless Fidelity (Wi-Fi) a hotspot
43
what are the two modes in which Wi-Fi can operate
* Infrastructure - use central access point (AP) * Ad hoc - no central device; data travels from device to device like a bus * sometimes called peer-to-peer mode
44
what is the Wi-Fi access method
sending station can't hear if another station begins transmitting so they cannot use the CSMA/CD access method that ethernet uses Wi-Fi devices use carrier sense multiple access with collision avoidance (CSMA/CA) uses request-to-send/clear-to-send (RTS/CTS) packets and acknoledgements With this extra "chatter" actual throughput is essentially cut in half
45
Describe the following type of signal interference: Absorption
Solid objects absorb radio signals, causing them to attenuate (weaken)
46
Describe the following type of signal interference: Refraction
The bending of a radio signal as it passes from a medium of one density through a medium of a different density
47
Describe the following type of signal interference: Diffraction
the altering of a wave as it tries to bend around an object
48
Describe the following type of signal interference: Reflection
Occurs when a signal hits a dense, reflective material, resulting in signal loss
49
Describe the following type of signal interference: Scattering
When a signal changes direction in unpredictable ways, causing a loss in signal strength
50
What is signal-to-noise ratio
* the amount of noise compared with the signal strength * Noise can come from equipment, other wireless devices, and other wireless networks
51
What is throughput
The actual amount of data transferred - not counting erros and acknowledgements
52
what is goodput
Actual application-to-application data transfer speed
53
What is overhead
Packet frame headers, acknowledgements, and retransmissions
54
What are Wi-Fi encryption protocols
Wired equivalent privacy (WEP), Wi-Fi Protected Access (WPA), and WPA2 Not all devices support all three protocols Older devices might only support WEP and/or WPA
55
What are the physical and logical topologies for a Token Ring network?
They have a Star Physical topology with a ring logical topology
56
How does a Token Ring Network operate?
* A token is passed along the network * Only the station with the token can transmit * Frames are acknowledged and token is released * no collisions * Obsolete
57
What is Fiber Distributed Data Interface Technology topology, speed, cabling and so on
This uses a physical and logical ring topology uses a token passing method with dual rings for redundancy Transmits at 100 mbps and can include up to 500 nodes over a distance of 60 miles uses only fiber optic cable Obsolete on new networks
58
What are the 4 primary physical topologies
bus star ring point-to-point
59
What are the 3 primary logical topologies
bus, ring, switched