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Week 2 Flashcards

1
Q

What is the OSI Model?

A

The open systems interconnection reference model is a seven layer model developed to categorise the layers of communication

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2
Q

What are the seven layers of the OSI model?

A
  1. Application layer
  2. Presentation layer
  3. Session layer
  4. Transport layer
  5. Network layer
  6. Data link layer
  7. Physical layer

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3
Q

What is the physical layer responsible for?

A

The physical layer is responsible for sending bits via a wired or wireless transmission

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4
Q

What is the data link layer responsible for?

A

The data link layer puts control information in a data link layer header and at then end of the packet in a trailer (the entire message is called a frame)

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5
Q

What is the network layer responsible for?

A

The network layer is responsible for moving messages from one node to another until they reach the destination host – i.e. routing the messages

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6
Q

What is the transport layer responsible for?

A

the transport layer is responsible for transporting application layer payloads from one application to another

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7
Q

What is the session layer responsible for?

A

the session layer describes how data between applications is synched and recovered if messages don’t arrive intact at the receiving application

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8
Q

What is the presentation layer responsible for?

A

The presentation layer is responsible for reformatting, compressing and/or encrypting data in a way that the receiving application can read

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9
Q

What is the application layer responsible for?

A

the application layer describes the interface between two applications, on separate computers. The application layer protocols are used by programs that provide a service to a user and programs that provide services to the system

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10
Q

What is a payload?

A

A payload is the data that is passed between applications or utility programs and the OS

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11
Q

What are the two main transport layer protocols?

A

-TCP (Transmission Control Protocol)

-UDP (User Datagram Protocol)

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12
Q

What is involved in the encapsulation process in the transport layer?

A

Encapsulation is the process of adding a header to the data inherited from the layer above.

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13
Q

What is frequency?

A

Frequency is the number of times in a second that an electrical signal can change states. Frequency is typically measured in MHz or GHz

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14
Q

What is bandwidth?

A

Bandwidth is the amount of data that could be theoretically transmitted during a given period of time

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15
Q

What is throughput?

A

Throughput is the measure of how much data is actually transmitted during given time period

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16
Q

What is noise in the context of transmission?

A

Noise is any undesirable influence degrading or distorting signal

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17
Q

What are two common sources of noise?

A
  • EMI (electromagnetic interference)
  • Cross-talk (occurs when the signal on one wire infringes on
    adjacent wire signal)
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18
Q

What is attenuation?

A

Attenuation is the loss of a signal’s strength as it travels away from its source

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19
Q

What is latency?

A

Latency is the delay between the transmission of a signal and the receiving of the same signal.

20
Q

What is RTT?

A

RTT (round trip time) is the time for packet to go from sender to receiver, then back from receiver to sender

21
Q

What are the three types of duplex?

A
  • Full-duplex - Signals travel in both directions simultaneously
  • Half-duplex - Signals travel in both directions but only one
    direction at a time
  • Simplex - Signals travel in one direction only
22
Q

What is multiplexing?

A

Multiplexing is a form of transmission that allows multiple signals to travel simultaneously over one medium

23
Q

What are the three types of multiplexing that are used on copper lines?

A
  • TDM (Time division multiplexing) divides a channel into multiple time intervals.
  • STDM (Statistical time division multiplexing) assigns slots to nodes according to priority and need
  • FDM (Frequency Division Multiplexing) assigns different frequency bands for each communications subchannel
24
Q

What are the three types of multiplexing on fibre-optic cable?

A
  • WDM (Wavelength Division Multiplexing) carries multiple light signals simultaneously by dividing a light beam into different wavelengths or colours.
  • DWDM (Dense Wavelength Division Multiplexing) increases the number of channels provided by normal WDM
  • CWDM (Coarse Wavelength Division Multiplexing) lowers cost by spacing frequency bands wider apart to allow for cheaper transceiver equipment.
25
What are twisted pair cables?
Twisted-pair cables are cables that consist of four colour-coded insulated copper wire pairs.
26
What are the two types of twisted-pair cable?
- Shielded twisted pair (STP) Wires are individually insulated and may be surrounded by a metallic substance shielding (foil) and have high noise resistance but are more expensive - Unshielded twisted pair (UTP) Wires are not surrounded by a metallic substance. Cheaper than STP but worse noise reisistance
27
What are the two methods of inserting wires into R-45 plugs?
- TIA/EIA 568A - TIA/EIA 568B There is no functional difference between the two standards, just ensure that the same standard is used on every RJ-45 plug and jack
28
What is a fibre-optic cable?
A fibre-optic cable is a cable that contains a one or more glass or plastic fibres at its centre (core). Data is transmitted via a pulsing light sent from a laser or an LED
29
What benefits does fibre-optic cabling offer over copper cabling?
- Extremely high throughput - Very high noise resistance - Excellent security - Able to carry signals for longer distances
30
What are the drawbacks of fibre-optic cabling?
- More expensive than twisted pair cable - Requires special equipment to splice
31
What is SMF fibre-optic cabling?
Single mode fibre (SMF) consists of a narrow core (8-10 microns in diameter). Laser-generated light travels over one path, reflecting very little. The light does not disperse as the signal travels. - Can carry signals for many miles before repeating is required - SFM is rarely used for shorter connections due to high cost - The internet backbone depends on SMF
32
What is MMF fibre-optic cabling?
Multimode fibre (MMF) contains a core with a larger diameter than a single mode fibre (usually 50 or 62.5 microns) - Laser or LED generated light pulses travel at different angles through MMF - Signals traveling over MMF experience greater attenuation than single-mode fibre - Common uses include: - Cables connecting routers, switches, and servers on the backbone of the network. - Cables to connect a desktop workstation to the network.
33
What fire suppression systems are usually found in data centres?
- Emergency alert system - Portable fire extinguishers (use class C for electrical fires) - Emergency power-off switch
34
What are the 7 troubleshooting steps?
1. Identify problem 2. Establish theory of probable cause 3. Test theory to determine cause 4. Establish plan of action 5. Implement solution or escalate the problem 6. Verify full functionality 7. Document findings, actions, outcomes
35
What do the three LED status indicator lights indicate?
1. A steady light indicates connectivity 2. A blinking light indicates activity 3. A red or amber light might indicate a problem
36
What does a tone and probe kit do?
Tone and probe kits (Which include tone generators and tone locators) are used to determine where wired pairs terminate (cannot be used to determine cable characteristics)
37
What does a multimeter do?
1. Measures voltage to verify a cable is conducting electricity 2. Checks for the presence of noise 3. Tests for short or open circuits in the wire
38
What does a cable continuity tester do?
Tests whether a cable carries a signal to destination
39
What does a cable performance tester do?
1. Measures distance to a connectivity device, termination point, or cable fault 2. Measures attenuation 3. Measures NEXT (near end cross-talk) 4. Measures termination resistance and impedance 5. Issue pass/fail ratings for Cat 3-7 standards 6. Store and print results or save to a computer database 7. Graphically depict attenuation and cross-talk
40
What does an OPM do?
An OPM measures the amount of light power transmitted on a fibre-optic line
41
What is the fastest ethernet standard?
100GBASE-T
42
What is ESD?
ESD is electrostatic discharge which can damage sensitive electronic components.
43
What are the two types of damage static electricity can cause?
- Catastrophic failure - destroyed beyond use - Upset failure - shorten the life of a component
44
What is the maximum segment length for twisted pair cables?
100 metres
45
What are the three types of cross talk?
- Alien cross-talk occurs between two cables - Near end cross-talk (NEXT) occurs near the source - Far end cross-talk (FEXT) occurs at the far end
46
What are amplifiers used for?
Amplifiers are used to boost analogue signals, but they also boost any noise that effected the analogue signal as well.

1402 (10 decks)

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