Cisco Networking Academy Chapter 4

Front 1

what is encoding

Back 1

a method of converting a stream of data bits into a predefined "code”. Codes are groupings of bits used to provide a predictable pattern that can be recognized by both the sender and the received

Front 2

Manchester encoding:

Back 2

A 0 is represented by a high to low voltage transition and a 1 is represented as a low to high voltage transition. This type of encoding is used in older versions of Ethernet, RFID and Near Field Communication.

Front 3

Non-Return to Zero (NRZ):

Back 3

This is a common means of encoding data that has two states termed “zero” and “one” and no neutral or rest position. A 0 may be represented by one voltage level on the media and a 1 might be represented by a different voltage on the media.

Front 4

What is signaling?

Back 4

The method of representing the bits is called the signaling method. The physical layer standards must define what type of signal represents a "1" and what type of signal represents a "0".

Front 5

Asynchronous Signaling

Back 5

Data signals are transmitted without an associated clock signal. The time spacing between data characters or blocks may be of arbitrary duration, meaning the spacing is not standardized.
Arbitrarily spaced time duration for signals

Front 6

Synchronous Signaling

Back 6

Data signals are sent along with a clock signal which occurs at evenly spaced time durations referred to as the bit time.

Evenly spaced time duration for signals.

Front 7

Data transfer is usually discussed in what terms?

Back 7

bandwidth and throughput

Front 8

What is bandwidth?

Back 8

The capacity of a medium to carry data. Digital bandwidth measures the amount of data that can flow from one place to another in a given amount of time.
The amount of data that is allowed by the medium to flow during a given set of time.

Front 9

What is throughput?

Back 9

The measure of the transfer of bits across the media over a given period of time.
The actual measure of data bits over a given period of time.

Front 10

What is frame encoding?

Back 10

A method for converting streams of data bits into grouping of bits-predefined.

Front 11

What is goodput?

Back 11

How much useable data is transferred over a given amount of time.

Front 12

Electromagnetic interference (EMI)

Radio frequency interference (RFI)

Back 12

EMI and RFI signals can distort and corrupt the data signals being carried by copper media. Potential sources of EMI and RFI include radio waves and electromagnetic devices such as fluorescent lights or electric motors.

Front 13

What is crosstalk?

Back 13

Crosstalk is a disturbance caused by the electric or magnetic fields of a signal on one wire to the signal in an adjacent wire.

Front 14

Unshielded twisted-pair (UTP)

Back 14

The most common networking media. UTP cabling, terminated with RJ-45 connectors, is used for interconnecting network hosts with intermediate networking devices, such as switches and routers.

Front 15

Shielded twisted-pair (STP)

Back 15

Provides better noise protection than UTP cabling. However, compared to UTP cable, STP cable is significantly more expensive and difficult to install. Like UTP cable, STP uses an RJ-45 connector.

Front 16

Category 6 cable UTP

Back 16

Used for data transmission
An added separator is between each pair of wires allowing it to function at higher speeds
Supports 1000 Mb/s - 10 Gb/s, though 10 Gb/s is not recommended

Front 17

Category 5 cable UTP

Back 17

Used for data transmission
Cat5 supports 100 Mb/s and can support 1000 Mb/s, but it is not recommended
Cat5e supports 1000 Mb/s

Front 18

Category 3 cable UTP

Back 18

Used for voice communication
Most often used for phone lines

Front 19

Ethernet Straight-Through cable

Back 19

both ends T568A or both ends T568B

connects a network host to a network device such as a switch or hub.

Front 20

Ethernet Crossover cable

Back 20

One end T568A, other end T568B

connects two network hosts
connects two network intermediary devices (switch to switch, router to router)

Front 21

Rollover cable

Back 21

Connects a workstation serial port to a router console port, using an adapter.

Front 22

Single-mode fiber (SMF)

Back 22

Consists of a very small core and uses expensive laser technology to send a single ray of light. Popular in long-distance situations spanning hundreds of kilometers

Front 23

Multimode fiber (MMF)

Back 23

Consists of a larger core and uses LED emitters to send light pulses. Specifically, light from an LED enters the multimode fiber at different angles. Popular in LANs because they can be powered by low cost LEDs. It provides bandwidth up to 10 Gb/s over link lengths of up to 550 meters.

Front 24

Fiber Straight-Tip (ST)

Back 24

An older bayonet style connector widely used with multimode fiber.

Front 25

Fiber Subscriber Connector (SC)

Back 25

Sometimes referred to as square connector or standard connector. It is a widely adopted LAN and WAN connector that uses a push-pull mechanism to ensure positive insertion. This connector type is used with multimode and single-mode fiber.

Front 26

Fiber Lucent Connector (LC)

Back 26

Sometimes called a little or local connector, is quickly growing in popularity due to its smaller size. It is used with single-mode fiber and also supports multimode fiber.

Front 27

Standard IEEE 802.11

Back 27

Wireless LAN (WLAN) technology, commonly referred to as Wi-Fi, uses a contention or non-deterministic system with a Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA) media access process.

Front 28

Standard IEEE 802.15

Back 28

Wireless Personal Area Network (WPAN) standard, commonly known as "Bluetooth", uses a device pairing process to communicate over distances from 1 to 100 meters.
Supports speeds up to 3 Mb/s

Front 29

Standard IEEE 802.16

Back 29

Commonly known as Worldwide Interoperability for Microwave Access (WiMAX), uses a point-to-multipoint topology to provide wireless broadband access.
Provides speeds up to 1Gb/s

Front 30

IEEE 802.11a

Back 30

Operates in the 5 GHz frequency band and offers speeds of up to 54 Mb/s. Because this standard operates at higher frequencies, it has a smaller coverage area and is less effective at penetrating building structures. Devices operating under this standard are not interoperable with the 802.11b and 802.11g standards.

Front 31

IEEE 802.11b

Back 31

Operates in the 2.4 GHz frequency band and offers speeds of up to 11 Mb/s. Devices implementing this standard have a longer range and are better able to penetrate building structures than devices based on 802.11a.

Front 32

IEEE 802.11g

Back 32

Operates in the 2.4 GHz frequency band and offers speeds of up to 54 Mbps. Devices implementing this standard therefore operate at the same radio frequency and range as 802.11b but with the bandwidth of 802.11a.

Front 33

IEEE 802.11n

Back 33

Operates in the 2.4 GHz and 5 GHz frequency bands. The typical expected data rates range from 150 Mb/s to 600 Mb/s with a distance range of up to 70 meters. It is backward compatible with 802.11a/b/g devices.

Front 34

IEEE 802.11ac

Back 34

Operates in the 5 GHz frequency band providing data rates ranging from 450 Mb/s to 1.3 Gb/s (1300 Mb/s.) It is backward compatible with 802.11a/n devices.

Front 35

IEEE 802.11ad

Back 35

Also known as "WiGig". It uses a tri-band Wi-Fi solution using 2.4 GHz, 5 GHz, and 60 GHz and offers theoretical speeds of up to 7 Gb/s.

Front 36

Specifically the data link layer performs these two basic services?

Back 36

It accepts Layer 3 packets and packages them into data units called frames.

It controls media access control and performs error detection.

Front 37

Logical Link Control (LLC) of the Data Link Layer

Back 37

This upper sublayer defines the software processes that provide services to the network layer protocols. It places information in the frame that identifies which network layer protocol is being used for the frame. This information allows multiple Layer 3 protocols, such as IPv4 and IPv6, to utilize the same network interface and media.

Front 38

Media Access Control (MAC) of the Data Link Layer

Back 38

This lower sublayer defines the media access processes performed by the hardware. It provides data link layer addressing and delimiting of data according to the physical signaling requirements of the medium and the type of data link layer protocol in use.

Front 39

A router does what at each hop along the path

Back 39

Accepts a frame from a medium
De-encapsulates the frame
Re-encapsulates the packet into a new frame
Forwards the new frame appropriate to the medium of that segment of the physical network

Front 40

The data-link layer frame includes?

Back 40

Header: Contains control information, such as addressing, and is located at the beginning of the PDU.
Data: Contains the IP header, transport layer header, and application data.
Trailer: Contains control information for error detection added to the end of the PDU.

Front 41

Generic frame field types include?

Back 41

Frame start and stop indicator flags, addressing, type, control, data, and error detection

Front 42

Point-to-Point Topology

Back 42

This is the simplest topology which consists of a permanent link between two endpoints. For this reason, this is a very popular WAN topology.

Front 43

Hub and Spoke Topology

Back 43

A WAN version of the star topology in which a central site interconnects branch sites using point-to-point links

Front 44

Mesh Topology

Back 44

This topology provides high availability, but requires that every end system be interconnected to every other system. Therefore the administrative and physical costs can be significant. Each link is essentially a point-to-point link to the other node.

Front 45

Half-duplex communication

Back 45

Both devices can both transmit and receive on the media but cannot do so simultaneously.

Front 46

Full-duplex communication:

Back 46

Both devices can transmit and receive on the media at the same time. The data link layer assumes that the media is available for transmission for both nodes at any time.

Front 47

Contention-based access

Back 47

All nodes compete for the use of the medium but have a plan if there are collisions

Front 48

Controlled access

Back 48

Each node has its own time to use the medium.

Front 49

Carrier sense multiple access with collision detection (CSMA/CD)

Ethernet

Back 49

The end device monitors the media for the presence of a data signal. If a data signal is absent and therefore the media is free, the device transmits the data. If signals are then detected that show another device was transmitting at the same time, all devices stop sending and try again later

Front 50

Carrier sense multiple access with collision avoidance (CSMA/CA)

802.11 Wireless

Back 50

The end device examines the media for the presence of a data signal. If the media is free, the device sends a notification across the media of its intent to use it. Once it receives a clearance to transmit, the device then sends the data

Front 51

Ethernet frame header fields

Back 51

Start Frame field: Indicates the beginning of the frame.
Source and Destination Address fields: Indicates the source and destination nodes on the media.
Type field: Indicates the upper layer service contained in the frame.

Front 52

FCS Frame Check Sequence

Frame Trailer

Back 52

This field is used for error checking. The source calculates a number based on the frame's data and places that number in the FCS field. The destination then recalculates the data to see if the FCS matches. If they don't match, the destination deletes the frame.

Front 53

Ethernet Frame Fields

Back 53

preamble, destination address (MAC address), source address (MAC address), type, data or payload, frame check sequence (FCS)

Front 54

Point to Point Protocol (PPP) Frame Fields

Back 54

Flag, address, control, protocol, data, frame check sequence (FCS)

Front 55

When is a wired connection preferred to a wireless connection by an end-user device?

Back 55

when the end-user device will run an application that requires a dedicated connection to the network

Front 56

What is the function of the Logical Link Control (LLC), data-link sublayer?

Back 56

to identify which network layer protocol is being used
The data link layer accepts Layer 3 packets and packages them into data units that are called frames.

Front 57

What is the purpose of the physical link control field in a data link layer header?

Back 57

to establish the media link

Front 58

What is a characteristic of a WAN hub-and-spoke topology?

Back 58

The branch sites are connected to a central site through point-to-point links.​

Front 59

An administrator measured the transfer of usable data across a 100 Mb/s physical channel over a given period of time and obtained 60 Mb/s. Which kind of measurement did the administrator obtain?

Back 59

goodput

Goodput is the measure of usable data transferred over a given period of time. It is the throughput minus traffic overhead for establishing sessions, acknowledgments, and encapsulation.

Front 60

What describes a characteristic of the frame header fields of the data link layer?

Back 60

All data link layer protocols encapsulate the Layer 3 PDU within the data field of the frame. However, the structure of the frame and the fields that are contained in the header vary according to the protocol.

Front 61

What is the correct color order of wire when terminating a cable by the T568B standard?

Back 61

Whit/orange, orange, white/green, blue, white/blue, green, white/brown, brown

Front 62

Which two engineering organizations define open standards and protocols that apply to the data link layer?

Back 62

International Organization for Standardization (ISO)

International Telecommunication Union (ITU)

Front 63

Which two factors influence the method that is used for media access control?

Back 63

how data is generated by end devices applications

how nodes share the media

Front 64

What is are true of the deterministic access method?

Back 64

The throughput is predictable.

Devices take turns transmitting

Front 65

A network administrator notices that some newly installed Ethernet cabling is carrying corrupt and distorted data signals. The new cabling was installed in the ceiling close to fluorescent lights and electrical equipment. Which two factors may interfere with the copper cabling and result in signal distortion and data corruption?

Back 65

EMI

RFI

Front 66

How is the magnetic field cancellation effect enhanced in UTP cables?

Back 66

by increasing and varying the number of twists in each wire pair

Front 67

What is true concerning physical and logical topologies?

Back 67

Logical topologies determine the media access control method used.

Front 68

What are two reasons for physical layer protocols to use frame encoding techniques?

Back 68

To distinguish data bits from control bits

To identify where the frame starts and ends

Front 69

A network administrator is designing the layout of a new wireless network. Which three areas of concern should be accounted for when building a wireless network?

Back 69

Security

Coverage Area

Interference

Front 70

As data travels on the media in a stream of 1s and 0s how does a receiving node identify the beginning and end of a frame?​

Back 70

The transmitting node inserts start and stop bits into the frame.

Front 71

Which layer of the OSI model is responsible for specifying the encapsulation method used for specific types of media?

Back 71

data-link

Front 72

Why are two strands of fiber used for a single fiber optic connection?

Back 72

They allow for full-duplex connectivity.

Front 73

A network administrator is required to upgrade wireless access to end users in a building. To provide data rates up to 1.3 Gb/s and still be backward compatible with older devices, which wireless standard should be implemented?

Back 73

802.11ac

Front 74

What are two characteristics of 802.11 wireless networks?

Back 74

They use CSMA/CA technology.

Collisions can exist in the networks.

Front 75

What is one main characteristic of the data link layer?

Back 75

It shields the upper layer protocol from being aware of the physical medium to be used in the communication.