Chapter 3 - Data Link Layer Fundamentals

Front 1

The (most complex) data unit used by Ethernet is?

Back 1

Frame

Front 2

In Ethernet, the transmitting wires are?

Back 2

1 and 2

Front 3

In Ethernet, the receiving wires are?

Back 3

3 and 6

Front 4

How would you recognize a straight-through Ethernet cable?

Back 4

Each connector would have the same colored pins in the same place.

Front 5

Why is twisted pair used for Ethernet cabling?

Back 5

Having the wires in a twisted pair reduces electrical interference.

Front 6

In UTP Ethernet, which pairs of wires are twisted together?

Back 6

Both sending wires are twisted together, as are both receiving wires.

Front 7

What does UTP stand for?

Back 7

Unshielded Twisted Pair

Front 8

What are the four functions generally performed by the Data Link Layer?

Back 8

Arbitration, Addressing, Error detection, and Identification

(note about Identification, it is unusual for a layer to be able to read the header from the layer above it. look into this)

Front 9

What is the name of the algorithm used by Ethernet for Arbitration (prevention of collisions)?

Back 9

CSMA/CD

Front 10

What does CSMA/CD stand for?

Back 10

Carrier Sense Multiple Access with Collision Detection

Front 11

What is the type of address used by the Ethernet Data Link layer?

Back 11

MAC Address

Front 12

What is the type of address used by the Frame Relay Data Link layer?

Back 12

DLCI

Front 13

What does the MAC in MAC Address stand for?

Back 13

Media Access Control

Front 14

Error detection by the Data Link layer is performed by sending additional data such as ____?

Back 14

CRC or FCS

Front 15

What does CRC stand for?

Back 15

Cyclical Redundancy Check

Front 16

What does FCS stand for?

Back 16

Frame check sequence

Front 17

T/F: The Ethernet Data Link layer performs error detection and recovery.

Back 17

F: only detection

Front 18

The data link layer's Identification function is used to determine what?

Back 18

What protocol the data received should be passed to.

Front 19

What is a reason for the Identification function of the data link layer?

Back 19

Multiple protocols being used on a computer. For instance, IPX and TCP/IP.

Front 20

In DIX Ethernet, the DIX stands for?

Back 20

DEC, Intel, Xerox

Front 21

The IEEE spec 802.3 refers to what?

Back 21

Ethernet MAC sublayer

Front 22

The IEEE spec 802.2 refers to what?

Back 22

Ethernet LLC sublayer (also Token Ring and ANSI FDDI LLC sublayers)

Front 23

Early 10BASE2 and 10BASE5 networks lacked what common features of modern Ethernet?

Back 23

Hubs, switches. (probably routers?)

Front 24

A repeater is considered to operate at what layer of the OSI model?

Back 24

Physical

Front 25

T/F: A repeater operates by amplifying the signal it receives.

Back 25

False. It interprets the bits and generates a new signal to avoid repeating noise.

Front 26

T/F: 10BASE-T allowed the use of telephone cabling to be used as an Ethernet network.

Back 26

True

Front 27

The hubs used in 10BASE-T networks functioned as ______ repeaters.

Back 27

Multiport

Front 28

Hubs used in 10BASE-T networks take the signal received on one port and do what?

Back 28

Broadcast it to every port.

Front 29

A major weakness of 10BASE5 and 10BASE2 which was fixed by 10BASE-T?

Back 29

10BASE-T star topology made it so a break at one point would not cause the entire network to go down.

Front 30

10BASE-T has a _____ physical topology, but a _____ logical topology.

Back 30

star, bus

Front 31

What is one major impact of 10BASE-T with hubs using an electrical bus topology?

Back 31

Each computer shares the bandwidth of the network. 10 computers have a total bandwidth of 10Mbps

Front 32

What type of Ethernet cable is typically used to connect a computer to a hub? (Straight-through or crossover)

Back 32

Straight-through

Front 33

Hubs generally receive and send data on the (same/opposite) pins as a PC's network card?

Back 33

Opposite

Front 34

In order to connect a PC to a PC, or a hub to a hub, you would use what type of cable?

Back 34

Crossover

Front 35

An Ethernet cable between two hubs or switches is often called a ______.

Back 35

Trunk

Front 36

Definition of half-duplex?

Back 36

once a party begins receiving a signal, it must wait for the transmitter to stop transmitting, before replying

Front 37

Definition of full-duplex?

Back 37

allows communication in both directions, and, unlike half-duplex, allows this to happen simultaneously

Front 38

Land-line telephone networks are (half or full)-duplex?

Back 38

full-duplex

Front 39

What is a duplex communication system?

Back 39

two connected devices that can communicate with one another in both directions

Front 40

What is the purpose of NIC's loopback function in detecting collisions? (in a half-duplex 10BASE-T with hubs)

Back 40

The signal is not going to be re-broadcast to the sending NIC by the hub, so the NIC loops its own signal back to its receiving wires, so if it detects a different signal as well, it can tell a collision is happening.

Front 41

What are two things which have improved Ethernet performance, relating to the reduction of collisions?

Back 41

LAN switching and full-duplex Ethernet

Front 42

What does the term "collision domain" mean?

Back 42

The set of devices for which their frames could collide.

Front 43

How do switches differ from hubs?

Back 43

They treat each individual port as a separate bus.

Front 44

What are memory buffers in switches used for?

Back 44

To hold incoming frames in case more than one is sent at a given time on the same bus, they can be sent in turn and the devices do not have to re-transmit.

Front 45

Switches operate at which layer of the OSI model?

Back 45

Data Link

Front 46

Hubs operate at which layer of the OSI model?

Back 46

Physical

Front 47

Hubs interpret data in what unit?

Back 47

Bit

Front 48

Switches interpret data in what unit?

Back 48

Frame

Front 49

What part of the original Ethernet specification made half-duplex communication a necessity?

Back 49

Having all computers on the same bus.

Front 50

What device made full-duplex Ethernet possible? How?

Back 50

Ethernet switches replacing hubs

Eliminated collisions / need for CSMA/CD

Front 51

T/F: CSMA/CD is not used in Full-Duplex Ethernet

Back 51

True

Front 52

In order for Full-Duplex operation to work, the NIC must _______ its loopback circuitry.

Back 52

Disable

Front 53

MAC addresses can also be known as?

Back 53

Burned-in Address (BIA), Universally Administered Addresses (UAA), LAN addresses, or Ethernet addresses

Front 54

What does the term "group address" refer to in the context of Ethernet?

Back 54

addresses which identify more than one LAN interface card

Front 55

What are the two general categories of Ethernet group addresses?

Back 55

Broadcast address
AND
Multicast address

Front 56

What is the value of the "Broadcast address"

Back 56

FFFF.FFFF.FFFF

Front 57

What does the "Broadcast address" signify to the LAN?

Back 57

Every device on the LAN should process the frame.

Front 58

Multicasting over Ethernet is supported by which protocol?

Back 58

IP

Front 59

What is the significance of
0100.5exx.xxxx

??

Back 59

It is the format of the MAC address used for multicasting.

Front 60

Ethernet framing defines what?

Back 60

How a string of binary numbers is interpreted.

Front 61

The IEEE 802.3 spec limits the data portion of a frame to ______ bytes?

Back 61

1500 bytes

Front 62

DSAP stands for?

Back 62

Destination Service Access Point

Front 63

What is the purpose of DSAP?

Back 63

It identifies the type of protocol header which follows the (Ethernet) Data-Link header.

Front 64

Where is the DSAP located?

Back 64

In the Ethernet Data-Link header.

Front 65

Why was the SNAP field introduced?

Back 65

They ran out of possible DSAP codes.

Front 66

Which DSAP value signifies that a SNAP field follows the 802.2 header?

Back 66

AA

Front 67

Where is the SNAP field located in an Ethernet frame?

Back 67

After the standard 802.2 header, before the data.

Front 68

What does SNAP stand for?

Back 68

Subnetwork Access Protocol

Front 69

What does SSAP stand for?

Back 69

Source Service Access Point

Front 70

The "Type" field from the original Ethernet specification was replaced by ________ and then by _______

Back 70

SSAP + DSAP, SNAP

Front 71

T/F: Ethernet + TCP/IP requires the use of SNAP headers.

Back 71

True

Front 72

Why does Ethernet + TCP/IP require the use of SNAP headers?

Back 72

There is no DSAP value for TCP/IP.

Front 73

Which function is performed by the FCS field in the Ethernet frame?

Back 73

Error-detection.

Front 74

The only type of Ethernet which does not use DSAP or SNAP is?

Back 74

DIX Ethernet

Front 75

IEEE spec 802.3u defines what standard?

Back 75

Fast Ethernet

Front 76

Fast Ethernet operates at what speed?

Back 76

100Mbps

Front 77

Autonegotiation in 802.3u Ethernet refers to?

Back 77

Devices deciding between 10Mbps and 100Mbps, and between half and full duplex.

Front 78

The IEEE spec 802.3z defines what?

Back 78

Gigabit Ethernet over optical cabling.

Front 79

The IEEE spec 802.3ab defines what?

Back 79

Gigabit Ethernet over electrical cabling.

Front 80

T/F Gigabit Ethernet retains the option to use CSMA/CD

Back 80

True

Front 81

True/False: Ethernet uses the same headers and trailers over 10Mbps, 100Mbps, and 1Gbps

Back 81

True

Front 82

What is the size of the SNAP field?

Back 82

2 bytes

Front 83

What is the size of the DSAP and SSAP fields?

Back 83

1 byte each

Front 84

What is the size of a MAC address?

Back 84

6 bytes

Front 85

Which part of a MAC address identifies the manufacturer of the device?

Back 85

The first half

Front 86

What does OUI stand for?

Back 86

Organizationally Unique Identifier

Front 87

What is the meaning of OUI? (not what it stands for)

Back 87

The part of a MAC address which is unique to the manufacturer of the device.