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Networking > Test 2 Study Guide > Flashcards

Test 2 Study Guide Flashcards

1
Q

What are the differences in phases between a virtual circuit and a datagram network?

A

A virtual circuit has a setup and teardown phase; datagram does not.

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2
Q

What network type treats each packet independently?

A

Datagram

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3
Q

Which layer is circuit switching used at?

A

The physical layer.

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4
Q

In the datagram network, do packets follow pre-set routes, or can they take any route?

A

They can take any route.

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5
Q

How does the simple parity check work?

A

A parity check happens when an extra bit is added to the last bit of a dataword. Whether or not the bit is a 1 or a 0 depends on the number of 1s in the dataword. If the number of 1s is odd, a 1 is added, making the number of 1s even. Otherwise, a zero is added.

This way, if a bit (but only one) is inverted in the dataword, the parity bit will give it away, although not which bit.

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6
Q

What is CRC?

How does CRC work?

A

CRC stands for cyclic redundancy check, wherein a code block is shifted (rotated to the left, transforming 1011000 to 0110001. Somehow, this allows for error correction.

Anyways, this thing works as follows:

The dataword has a certain number of 0s bits added on to the end of it, bringing it up to the necessary size. This is fed into a generator, which divides it by the divisor, generally 1+ the number of added 0s. The quotient is discarded, and the remainder is added on to the original dataword, creating the codeword.

When this codeword is received, a similar generator reverses the process. If the additional bits on the end of the decoded codeword are all 0s (as it was initially), all is well. A non-zero result means there was an error.

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7
Q

What is CHAP?

A

Challenge-Handshake Authentication Protocol.

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8
Q

How does CHAP work?

A

Challenge-handshake authentication protocol involves the receiver sending a challenge to the sender, who responds with a password (AKA “secret”), which is combined with the challenge and sent back for verification. Challenge-handshake authentication protocol is used in the point-to-point protocol.

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9
Q

What does PPP stand for?

A

Point-to-point protocol.

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10
Q

In PPP, what does the address field define?

A

It defines NOTHING. Since it’s point-to-point, it doesn’t need an address, it’s all 1s.

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11
Q

What is the data rate of fast ethernet?

A

100 Mbps

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12
Q

What is the data rate of gigabit ethernet?

A

1,000 Mbps

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13
Q

What is padding?

A

Padding occurs when the data field is below the minimum byte size, so extra 0s are added.

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14
Q

How would you determine if a MAC address is unicast or multicast?

A

If the 2nd bit is even, it is unicast. If the 2nd bit is odd, it’s multicast.

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15
Q

What field in PPP handles error control?

A

The FCS field handles error control in PPP.

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16
Q

In what layer does error correction for TCP/IP?

A

For TCP/IP, error correction is handled at layer four, where TCP handles retransmissions.

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17
Q

What does the protocol field do in PPP?

A

In PPP, the protocol field defines what’s being carried in the data field.

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18
Q

In the ethernet frame, what handles error correction?

A

The CRC handles error correction in CRC.

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19
Q

How do ethernet switches learn MAC addresses?

A

Ethernet switches learn MAC addresses from the source address of incoming frames.

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20
Q

Does CSMA/CD collision detection work on wireless? Why or why not?

A

Carrier-sense mulitple access / Collision detection does not work on wireless. It cannot detect collisions as it cannot look for collisions while transmitting, in addition to the hidden node problem, which occurs when an AP is out of range of another, but is still part of the network through visible APs.

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21
Q

What’s imprinted on any ethernet network adaptor?

A

A 48-bit MAC address.

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22
Q

In what layer(s) do the wired LANs operate in?

A

The bottom two layers of the TCP/IP protocol suite.

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23
Q

In what layer(s) do wireless LANs operate in?

A

They operate in the lowest two layers of the TCP/IP protocol suite.

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24
Q

What is the most secure of the wireless protocols?

A

WPA-2

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25
Q

What is contained within the address frame in PPP?

A

All 1s are contained in the address frame, due to the fact that PPP is point to point.

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26
Q

What protocols are used in LANs today that both detect and correct errors?

A

TCP and CSMA/CA

27
Q

What spectrum does 802.11g operate in?

A

It operates in the 2.4GHz spectrum

28
Q

Is 802.11g backwards-compatable with 802.11b?

A

Yes, 802.11g is backwards-compatable.

29
Q

What is a major benefit of circuit-switched networks?

A

Circuit-switched networks have very low latency; it approaches the speed of light. In circuit-switching, the channel is reserved for the full length of the transmission, and acts like a physical circuit.

30
Q

How do packets flow in a virtual-circuit network?

A

In a virtual-circuit network, packets follow a pre-determined path.

31
Q

Define “burst error”.

A

A burst error is an error that causes two or more bits in a transmission to change/invert.

32
Q

During block coding, what happens to the additional “n” bits that are added to the original “k” when the transmission is received?

A

The extra bits are discarded.

33
Q

What protocol most commonly uses CRC?

A

Ethernet

34
Q

Who solved the issue with multiple errors being ignored in checksums?

A

Addler and Fletcher.

35
Q

In the ethernet frame, how does synchronization occur?

A

Each frame opens with a series of 101010, which is used to coordinate the clock.

36
Q

What are the minimum and maximum data field sizes of each frame?

A

Ethernet: Minimum of 46 bytes, maximum of 1,500 byes.

PPP: Default max is 1,500 bytes, but can be changed in negotiation.

37
Q

How are modern ethernet networks most commonly deployed?

A

They are deployed in a star topography.

38
Q

What would you call a wireless LAN without an access point?

A

An ad-hoc network.

39
Q

What was the speed of the first 802.11 wireless standard?

A

1 to 2 Mbps.

40
Q

What makes the 802.11n network more effective?

A

It uses multiple antenna to increase bandwidth, can use either the 2.4 GHz or 5 GHz spectrum, and can use 40MHz channels instead of the standard 20MHz to increase bandwidth. Max theoretical speed of up to 600 Mbps

41
Q

What is stored in the “type” section of the ethernet frame?

A

It serves the same role as the protocol field in the Datagram protocol, defining the contents of the frame.

42
Q

How do signals travel in a cicruit-switched network?

A

They all travel along the same route.

43
Q

Is CSMA/CD is necessary in a switched ethernet environment?

A

These days CSMA/CD is not generally not needed on switched networks and is turned off as part of the auto-negotiation process that configures the line speed and duplex parameters. Most switches are of the store-and-forward type and neither A nor B talk directly to C. Instead each machine will simultaneously send their packets to the switch, which will store both of them in its internal memory. When each packet has been received in full and checked for validity they will be forwarded on to the destination port. In the event that two packets need to be sent through the same port they will be queued up and sent one after the other. This is what would happen with the packets from A and B that were sent at the same time.

The exception is quite rare these days and that is with hardware that only supports half duplex communication.

44
Q

Do most desktops have a half- or a full-duplex network card?

A

Most have a full-duplex card.

45
Q

What are two types of forward error correction?

A

Two types are XOR and chunk interleaving.

XOR simply adds a large amount of redundant data to each packet, allowing for reconstruction should one get damaged.

Chunk interleaving occurs when each packet is split divided evenly among a certain number of packets, and then reconstructed from those packets at the receiver. That way, if one packet is lost, only a small part of each packet is lost, instead of a whole packet.

In multimedia, there’s “compounding”, where each frame contains a high resolution packet and a low resolution packet of the frame before, so that if one is lost, the low is put in its place.

46
Q

What is an example of a still-used circuit-switched network?

A

Telephone system.

47
Q

What are the advantages of a virtual-circuit network, and why aren’t they useful much anymore?

A

The VCN simplified routing inside of networks, but added complexity in return. Nowadays, it’s not helpful as most routers are very fast with very low latency, so latency due to routing is a non-issue.

48
Q

Can wireless LAN be accurately called wireless ethernet? Why or why not?

A

Yes, it can, simply because it still uses the ethernet standard and MAC addresses.

49
Q

What is CSMA? What are the versions of CSMA? What does ACK refer to?

A

Carrier sense multiple access, a MAC protocol. In CSMA, the sender “listens” to the medium before attempting to transmit, so as to ensure nothing is transmitting as well that could cause a collision. There are two versions, CD and CA.

CD refers to collision detection. In this variant, the transmission is terminated as soon as a collision is detected (the medium is monitored during transmission), which shortens the amount of time between retries.

CA stands for Collision Avoidance, where when the channel is noticed to be in-use, the transmission is deferred for a random interval.

50
Q

What phyiscal medium were used for Ethernet 10/2 and 10/5?

A

Coaxial cable.

51
Q

What is the physical media used for moden ethernet (10/T, 100/TX, 1000/TX, etc)?

A

CAT5 cable.

52
Q

What physical media is used for gigabit ethernet?

A

Fiber optic cabling.

53
Q

If you were laying out the network for a new business, would you invest in a 10 Gbps network connection for each workstation? Why or why not?

A

You would not, because the wide majority of common business uses on a network would come nowhere near using even half of a 10Gbps connection, not unless there was a great deal of bandwidth-intensive tasks, like moving large files often.

54
Q

What are the most common causes of CRC errors?

A

Generally, most CRC errors are caused either by a bad NIC port on the sender or the reciever, or a faulty cable.

55
Q

If a workstation is generating a good number of CRC errors, but the user claims to not have noticed any issues, what’s happening there?

A

Each CRC error is a dropped frame, and yes, ethernet is not a “reliable” protocol, but the upper layers generally are, specifically TCP, are registering the dropped frames and having them retransmitted.

56
Q

Why does 10 Gbps internet not have CSMA/CA features?

A

This is because it’s only full duplex and only used in switched environment, therefore it’s a point-to-point link, and is operating in full duplex. No need!

57
Q

What are the three wireless LAN protocols, from least to most secure?

A

WPA

WEP

WEP-2

58
Q

What is the purpose of an ethernet bridge?

A

Primarily, it seperates collision domains, but it also, technically, raises bandwidth. The bridge splits the network up into smaller networks, with the bridge acting as a, well, bridge. Dividing the network up in this way means less of it needs to be shared at once.

59
Q

If you were implemented a wired network in a home office, what speed of connection would you use?

A

For very basic transfers and whatnot, 100 Mbit would be enough, but gigabit is standard.

60
Q

Just know that full-duplex ethernet is the norm. No real question here.

A
61
Q

Where might you find a PPP connection these days?

A

Dial-up internet and/or DSL.

62
Q

Name two protocols that operates at the data link layer.

A

PPP and Ethernet.

63
Q

What dose CSMA stand for? With CD / CA?

A

CSMA stands for “Carrier Sense Multiple Access”. This is where a sender must listen to its medium before it can send.

CA stands for “Collision Detection”. This is a form of CSMA where the transmission is termintated upon the detection of a collision.

CD stands for “Collision Avoidance”. This is when, upon attempting to transmit and either finding the medium in-use or detecting a collision, the sender waits a random interval before attempting to send again.

Networking (15 decks)

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