2 - Phys & D.L Layer and Errors Flashcards Preview

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Flashcards in 2 - Phys & D.L Layer and Errors Deck (16)
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1
Q

P.L Responsibilities (6)

A
  • provides the physical topology of the network
  • provides the transfer medium
  • encodes data into a transmission signal
  • generarate/amplifies signal
  • detects transmission errors
  • detects arriving signal levels to sync speed and timing
2
Q

D.L.L Responsibilities (7)

A
  • constructs data frames using the format of the P.L
  • creates CRCs
  • checks for arriving errors
  • initiates and arbitrates the link to reduce interruption
  • examines arriving and passing device addr fields
  • retransmits data if error
  • ACK of frame
3
Q

Metrics of Network Performance

A
  • Latency
  • B/W
  • Throughput
4
Q

Causes of Transmission Errors

A
  • Thermal Background
  • Impulse Noise
  • Distorted frequency
  • Crosstalk
  • Reduction of dynamic range and noise
5
Q

Character Stuffing

A

Putting in a character to overcome sync problems

6
Q

Bit Stuffing

A

Lower level character stuffing with 1s and 0s

7
Q

Encoding schemes (2)

A
  • Non-return to Zero Level (NRZ-L)

- Non-return to Zero Inverted (NRZ-I), example of differential encoding

8
Q

Differential Encoding

A

Where the signal transition rather than the signal level indicates the value of each bit

9
Q

Codewords are constructed with (2)

A
  • data

- check bits

10
Q

Hamming Distance

A

The XOR between two code words

11
Q

To detect delta errors..

A

a hamming distance of (delta +1) is required

12
Q

To correct delta errors..

A

a hamming distance of (2 x delta + 1) is required

13
Q

Polynomial Codes

A

Represented by a bit string with 1 for each power represented in the polynomial, and 0 otherwise.

14
Q

When do errors go undetected?

A
E(x) - num of errors
If E(x) is divisible by G(x) then errors can go undetected
15
Q

Burst Error

A

Where the error is a number of bits than are in sequence with each other

16
Q

Types of CRCs (4)

A
  • CRC12
  • CRC16
  • CRC-CCITT
  • CRC32