4.3 - Data Link Protocols

Question 1

Data link layer protocol focuses on __________________ – which indicates where a message starts and stops, and the other parts of fields within the message

Answer 1

message delineation

Question 2

Two Types of Data Link Layer Protocols

Answer 2

1. Asynchronous transmission
2. Synchronous transmission

Question 3

Often referred to as start-stop transmission because the transmitting computer can transmit a character (or byte) whenever it is convenient, and the receiving computer will accept that character

Answer 3

Asynchronous transmission

Question 4

Typically used on point-to-point, full-duplex circuits so that media access is not a concern

Answer 4

Asynchronous transmission

Question 5

Each character are transmitted independently of all other characters

Answer 5

Asynchronous transmission

Question 6

To separate the characters and synchronize transmission, a _____________ and a _____________ are put on the front and back of each individual character

Answer 6

start bit… stop bit

Question 7

For example, in asynchronous transmission if we are using a 7-bit ASCII with even parity, the total transmission is _____ bits for each character: 1 start bit, 7 bits for the letter, 1 parity bit, 1 stop bit

Answer 7

10

Question 8

The start bit and stop bit(s) are the __________ of each other — typically the start bit is a __ and the stop bit is a __

Answer 8

opposite…0…1

Question 9

There is no ______________ between characters because the terminal transmits the characters as soon as it is typed

Answer 9

fixed distance

Question 10

The recognition of the start and stop of each message (called _______________) takes place for each individual character

Answer 10

synchronization

Question 11

The process in which the receiver looks at the digital signal at the appropriate times to detect the proper transition from one energy level to another

Answer 11

Synchronization

Question 12

This type of transmission is often used in situations when characters may be generated at random intervals, such as when a used types at a terminal

Answer 12

Asynchronous

Question 13

The _________ bit resets the receiver’s clock so that it matches the transmitters

Answer 13

start

Question 14

The ______________ are just the start and stop bits; the parity bit is also a control bit, but for ______________

Answer 14

control bits…error control

Question 15

A state at logic 1

Answer 15

Idle state

Question 16

The main problem with asynchronous transmission is its ______________, primarily due to the additional start and stop bits for every byte

Answer 16

high overhead

Question 17

A simple formula in computing for the ratio of control bits to data bits transmitted is:

Answer 17

%Overhead = (Control Bits/Total Bits) * 100

Question 18

%Data = 100 - %Overhead

Answer 18

Percent Data

Question 19

ED = %Data * Data Transfer Rate (in bps)

Answer 19

Effective Data (ED)

Question 20

All letters of data in one group of data are transmitted at one time as a block of data.

Answer 20

Synchronous transmission

Question 21

The block of data in a synchronous transmission is called a ___________

Answer 21

frame

Question 22

Often used in both point-to-point and multipoint circuits

Answer 22

Synchronous transmission

Question 23

Start and end of each frame (synchronization) are established by adding synchronization characters (_____) to the start of the frame

Answer 23

SYN

Question 24

In ___________________, the transmitter and the receiver exchange initial synchronizing information, and then continuously exchange a digital stream that keep them in lock step

Answer 24

synchronous transmission

Question 25

Depending on the protocol, there may be anywhere from _____ to ______ SYN characters

Answer 25

one...eight

Question 26

____________________________ is a mainframe protocol developed by IBM in 1972 that is still in use today --- uses a controlled-access media protocol

Answer 26

Synchronous Data Link Control (SDLC)

Question 27

Flag -- Address -- Control -- Message -- Frame check sequence -- Flag

Answer 27

Synchronous Data Link Control (SDLC)

Question 28

Each SDLC frame begins and ends with a special bit pattern (01111110), known as the ________

Answer 28

flag

Question 29

The ______________ identifies the destination -- length is usually 8 bits but can be set to 16 bits (computers on the same network must use the same length)

Answer 29

address field

Question 30

The ______________ identifies the kind of frame that is being transmitter (information or supervisory)

Answer 30

control field

Question 31

____________________ is used for the transfer and reception of messages, frame numbering and contiguous frames, and the like

Answer 31

Information frame

Question 32

____________________ is used to transmit acknowledgements (ACKs and NAKs)

Answer 32

Supervisory frame

Question 33

The ______________ is of variable length and is the user's message

Answer 33

message field

Question 34

The __________________________ is a 32-bit CRC code (some older versions use a 16-bit CRC)

Answer 34

frame check sequence field

Question 35

___________________________ is a formal standard developed by the ISO often used in WANs

Answer 35

High-level data link control (HDLC)

Question 36

Essentially the same as SDLC, except that the address and control fields can be longer

Answer 36

High-level data link control (HDLC)

Question 37

Has several additional benefits that include: 1. Larger sliding window for continuous ARQ (acknowledgement request) 2. Uses a controlled-access media access protocol

Answer 37

High-level data link control (HDLC)

Question 38

_____________ is a very popular LAN protocol, conceived by Bob Metcalfe in 1973 and developed jointly by Digital, Intel, and Xerox in the 1970s

Answer 38

Ethernet

Question 39

Since then, ____________ has been further refined and developed into a formal standard called IEEE802.3ac

Answer 39

Ethernet

Question 40

______________ uses contention media access protocol

Answer 40

Ethernet

Question 41

_____________________ protocol was developed in the early 1990s and is often used in WANs --- designed to transfer data over a point-to-point circuit but provides an address so that it can be used on multipoint circuits

Answer 41

Point-to-point Protocol (PPP)