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Link Layer Flashcards

(46 cards)

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1
Q

4 layers of TCP/IP, top to bottom

A

Application
Transport
Internet
Link

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2
Q

Network Layer works with what format of data?

A

Packets

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3
Q

Link Layer works with what format of data?

A

Frames

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4
Q

Physical Layer works with what format of data?

A

Bits

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5
Q

What 3 things make up a Network Layer packet?

A

IP + TCP + Data

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6
Q

What part of a packet is considered the payload?

A

Anything that comes after the header

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7
Q

What are Encoding Systems used for?

A

Transmitting bits from Physical to Link Layer

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8
Q

The Link Layer has 3 main functions.
What is the first function, relating to data transmission?

A

Transmitting frames over physical media

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9
Q

The Link Layer has 3 main functions.
What is the second function, relating to receiving frames?

A

Receive frames, unframe them, pass the datagram upwards

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10
Q

The Link Layer has 3 main functions.
What is the third function, relating to errors?

A

Detect and handle errors

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11
Q

What 2 things might the Link Layer do, when it detects an error in a packet?

A

1) Handle the error
2) Drop the packet

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12
Q

The Link Layer has Flow Control. Flow Control has 2 features.
What is the first feature, relating to speed?

A

Flow Control moderates the speed of data being sent

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13
Q

The Link Layer has Flow Control. Flow Control has 2 features.
What is the second feature, relating to the sender?

A

Flow Control can ask the sender for more data

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14
Q

Link Layer offers how many types of acknowledgements?

A

3 types

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15
Q

Link Layer offers 3 types of acknowledgements.
1) C___, No ____
2) A___, C___ S___
3) A___, C___ O___ S___

A

1) Connectionless, No Acknowledgments
2) Acknowledged, Connectionless Service
3) Acknowledged, Connection Orientated Service

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16
Q

Link Layer offers “Connectionless, No Acknowledgments” type of acknowledging.
What is this type ideal for?

A

Low error rate networks
(e.g. wired, Ethernet)

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17
Q

Link Layer offers “Acknowledged, Connectionless Service” type of acknowledging.
What is this type ideal for? Why?

A

Wi Fi
Wi Fi can be unreliable so best to acknowledge

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18
Q

Link Layer offers “Acknowledged, Connection Orientated Service” type of acknowledging.
What is this type ideal for? Why?

A

Long delay, unreliable links (e.g. Satellite)
Best to establish connection before sending over unreliable link

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19
Q

In regards to ACK Strategies and Protocols, what does ARQ stand for?

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A

Automatic Repeat reQuest

20
Q

What are 3 ACK Strategies/Protocols?
1) ⛔
2) ⏪
3) 🔁

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A

1) ⛔ Stop and Wait ARQ
2) ⏪Go Back N ARQ
3) 🔁Selective Repeat ARQ

21
Q

What are the 3 steps of Stop and Wait ARQ?

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A

1) Send frame
2) Wait for ACK
3) Send next
(No ACK if frame lost or damaged)

22
Q

What is a negative of Stop and Wait ARQ?

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A

Waiting takes time, so Stop and Wait is slow

23
Q

Waiting takes time, so Stop and Wait ARQ is slow.
What can be done to improve speed?

Study These Flashcards
A

Pipelining: Send multiple frames before receiving ACK

24
Q

What are the 3 steps of Go Back N ARQ?

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A

1) Label each frame with numbers in sequence
2) Send many frames at the same time
3) Wait for ACK and repeat from 1
(Resend any frames for which ACK not received)

25
In Go Back N ARQ, I send packets 1, 2, 3, 4 and 5. I receive ACKs for 1 and 2, but not 3. What packets do I resend?
3, 4 and 5. In Go Back N ARQ, you resend any packets starting from the one with no ACK onwards.
26
In Go Back N ARQ, I send the packets 1, 2, 3, 4 and 5 I receive ACKs for 1 and 2, but not 3 What do I resend?
3, 4 and 5 Go Back N ARQ resends missed ACK packet and the ones after it
27
Selective Repeat ARQ is the same as Go Back N ARQ, but what is the 1 thing it does differently?
Only resends packets that it did not receive ACK for.
28
Link Layer can detect errors. What are the 2 methods used by the layer to detect errors?
1) Parity Bit 2) CRC (Cyclic Redundancy Check)
29
CRC is a value calculated by ___ and ___, the values are ___ to detect errors in data
CRC is a value calculated by sender and reciever, the values are compared to detect errors in data
30
If there is an error in a Wired Ethernet, what is likely to be the cause?
A damaged cable
31
What does MAC stand for?
Media Access Protocol
32
What does MAC manage (4 things)?
MAC manages how you access a physical medium Manages channels, frequencies and collisions
33
Which layer is MAC a part of?
Link Layer
34
MAC has a mechanism for sending ___ to/from ___ layers
MAC has a mechanism for sending frames to/from physical layers
35
Wi Fi has ___ 👨‍👩‍👧‍👦bandwidth Ethernet has ___ 🙍 bandwidth
Wi Fi has shared bandwidth Ethernet has dedicated bandwidth
36
Wi Fi has different ___ 📺
Wi Fi has different frequencies (channels)
37
Why does Wi Fi have different frequencies? (Hint: Bandwidth)
Minimise contention for the shared bandwidth
38
What does Wi Fi not guarantee on its channels?
Wi Fi does not guarantee uninterrupeted connection on its channels
39
Ethernet used to be a shared medium. What did Ethernet use to ensure only one sender was transmitting at any one time?
CSMA/CD Carrier Sense Multiple Access w/ Collision Detection
40
What are the 5 steps of CSMA/CD? 1) 👂 2) if 🗣️ 🫸 3) 🗣️ 4) 📨, if 🗣️⛔ 5) ⌚, then try again
1) 👂= Listen for busy 2) if 🗣️ 🫸= If busy, wait 3) 🗣️= When free, talk 4) 👂📨, if 💥⛔ = Listen while sending. If collision stop 5) ⌚, then try again = Random delay then try again
41
Why doesn't Wi Fi use CSMA/CD?
Wi Fi cannot send and receive (listen) at the same time, which is needed in CSMA/CD
42
What does Wi Fi use instead of CSMA/CD?
CSMA/CA Carrier Sense Multiple Access w/ Collision Avoidance
43
How does Wi Fi's CSMA/CA differ from Ethernet's CSMA/CD?
Instead of listening to transmission, wait for ACK from Access Point to know if frame was successfully sent.
44
Wi Fi, instead of listening to transmission, waits for ACK from Access Point to know if frame was successfully sent. What sort of request does it send and ACK does it receive?
Wi Fi can send RTS, and receive CTS, before sending frame
45
The Link Layer's job, in summary, is reliable data transfer between two ___ ___ (Essentially local packet transfer)
The Link Layer's job, in summary, is reliable data transfer between two connected nodes (Essentially local packet transfer)
46
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