Chapter 4

With odd parity (assume that the parity bit (in bold) has been placed at the end of each of the following) and a 7-bit ASCII code, which of the following is incorrect?

00011011

Overhead bits are used for error checking and marking the start and end of characters and packets.

True

Undesirable stray electrical voltage can cause data communication errors.

True

The probability of detecting an error, provided that one has occurred, using cyclic redundancy checking is about:

> 99%

_______ is an effective way to prevent attenuation.

Adding repeaters or amplifiers to a circuit

The probability of detecting an error, given that one has occurred, using parity checking is about:

50%

Transmission efficiency refers to the percentage of bits transmitted without errors.

False

_______ is the process of sending a signal to a client that gives its permission to transmit or asks it to receive.

Polling

If a computer transmits a message containing "ABC" and the destination computer receives "abc" as the message, the message is corrupted.

True

Media access controls refer to the need to control when computers transmit.

True

One type of forward error correction is the Hamming code.

True

The data link layer accepts messages from the network layer and controls the hardware that transmits them.

True

The physical and data link layers of wired Ethernet have been refined over the years as a collection of standards under the IEEE 802.3 workgroup.

True

The simplest method for error correction is retransmission.

True

When we amplify the signal on an analog circuit, we also amplify any noise that is present on the circuit.

True

With roll-call polling, a server polls clients in a consecutive, pre-arranged priority list.

True

Which of the following is not a type of synchronous protocol?

VT100

____________ is not a function of a data link protocol.

Amplitude shift keying

Which of the following is not a controlled access method of media access control?

CSMA/CD

Another term for continuous ARQ is sliding window.

False

Data transmission errors are typically uniformly distributed in time.

False

With __________ ARQ, the sender immediately sends the next message or packet of data.

continuous

Gaussian noise is a special type of attenuation.

False

Impulse noise is caused by the thermal agitation of electrons.

False

In an odd parity-checking scheme, the parity bit is set to make the total number of ones in the byte (including the parity bit) an even number.

False

Most computer networks managed by a host mainframe computer use contention media access control.

False

Only the sender of a data transmission needs to be concerned about the rules or protocols that govern how it communicates with the receiver.

False

Parity checking can only detect an error when an even number of bits are switched.

False

Polling is the process of permitting all clients to transmit or receive at any time

False

The distance between repeaters or amplifiers on a telephone circuit is determined by the amount of power gained per unit length of the transmission.

False

The two categories of network errors are: lost data and delimited data.

False

With contention, a computer does not have to wait before it can transmit. A computer can transmit at anytime.

False

___________ refers to bits that have been changed, in error, from 1 to 0, or vice versa, in a data transmission.

Flipped bits

_____ has essentially replaced SDLC and offers a larger sliding window.

HDLC

____________ controls errors by detecting and correcting them at the receiving end without retransmission of the original message.

Hamming code

________can obliterate a group of bits, causing a burst error.

Impulse noise

Which of the following is true with respect to the data link layer?

It performs error detection.

________ is an effective way to prevent impulse noise, cross talk, and intermodulation noise.

Shielding wires

Token passing is a term that refers to hub polling, in which one computer starts a poll and passes it to the next computer on a multipoint circuit.

True

When the signals from two circuits combine to form a new signal that falls into a frequency band reserved for another signal, this is called intermodulation noise.

True

Calculating the actual throughput of a data communication network is:

complex because many factors affect throughput

With contention:

computers wait until the circuit is free before they send data

Controlled access MAC approaches work better in a large network with high usage.

True

Crosstalk occurs when the signal transmitted on one circuit or channel of a transmission system creates an undesired effect in another circuit or channel.

True

Cyclical redundancy check is one of the most popular polynomial error-checking schemes.

True

For effective error detection and correction, extra error detection "data" must be included with each message

True

Forward error correction is commonly used in satellite transmission.

True

HDLC is very similar to the SDLC synchronous data link protocol.

True

Errors on a network can occur:

because of noise on the line

The familiar background static on radios and telephones is called:

white noise

In general, controlled approaches:

work better than contention approaches for large networks that have high usage

Which of the following is true about roll call polling?

It typically involves some waiting because the server has to wait for a response from the polled client or terminal.

Which of the following is true about the data link protocol, SDLC:

It uses a special bit pattern called a flag at the beginning and end of every frame (or packet).

The data link layer uses the ________ to recognize the source and destination addresses.

MAC address

______ is a software-enabled technique that can change the hardcoded MAC address to any MAC address and thus overcome MAC address filtering.

MAC address spoofing

As part of the five-layer network model used in this textbook, the data link layer sits directly between:

The physical and the network layers

____________ is defined as the total number of information bits divided by the total number of bits in the transmission.

Transmission efficiency

Attenuation refers to the loss of signal strength.

True

Contention is commonly used with Ethernet local area networks.

True

ARQ means that:

a receiver that detects an error in a message simply asks the sender to retransmit the message until it is received without error

Using parity, the probability for detecting an error, given that one has occurred, is:

about 50% for either even or odd parity

The loss of power a signal suffers as it travels from the transmitting computer to a receiving computer is:

attenuation

In a _________ , more than one data bit is changed by the error-causing condition

burst error

Asynchronous transmission:

each character is transmitted independently of all other characters

When a signal is reflected back to the transmitting equipment, it is called a(n) _____

echo

Which of the following media is least susceptible to noise?

fiber optic cable

In communication protocols, _________ are used to convey the user's meaning.

information bits

If a signal with a frequency of 500 MHz combines with a another signal of 1500 MHz and they form a new signal of 2000 MHz; this is an example of:

intermodulation noise

Media access control:

is not very important in point-to-point with full duplex configuration

In ARQ, a NAK:

is sent by the recipient if the message contains an error

Synchronous transmission:

is used to transmit a "frame" or "packet" of data at a time

Which of the following is true about the data link protocol, PPP?

it is commonly used in WANs

Optical media is:

less likely to suffer from noise than electrical media

The two sublayers of the data link layer consist of the media access control sublayer and the________ .

logical link control sublayer

Which of the following is true about the data link protocol, Ethernet (IEEE 802.3)?

newer version permits jumbo frames

Cross-talk:

occurs when one circuit picks up signals in another

Which of the following is way to reduce or eliminate crosstalk on a circuit?

physically separating the cables from other communication cables

Which of the following is not an error detection method used in the data link layer?

pulse code checking

On digital circuits, we use _________ to reshape the incoming signal and prevent attenuation.

repeaters

Another term for impulse noise is:

spikes

The primary source of error in data communications is:

spikes

With __________ ARQ, the sender pauses for a response from the receiver to alter each message or packet of data.

stop and wait