4.3 - Data Link Protocols Flashcards
Data link layer protocol focuses on __________________ – which indicates where a message starts and stops, and the other parts of fields within the message
message delineation
Two Types of Data Link Layer Protocols
- Asynchronous transmission
- Synchronous transmission
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
Asynchronous transmission
Typically used on point-to-point, full-duplex circuits so that media access is not a concern
Asynchronous transmission
Each character are transmitted independently of all other characters
Asynchronous transmission
To separate the characters and synchronize transmission, a _____________ and a _____________ are put on the front and back of each individual character
start bit… stop bit
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
10
The start bit and stop bit(s) are the __________ of each other — typically the start bit is a __ and the stop bit is a __
opposite…0…1
There is no ______________ between characters because the terminal transmits the characters as soon as it is typed
fixed distance
The recognition of the start and stop of each message (called _______________) takes place for each individual character
synchronization
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
Synchronization
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
Asynchronous
The _________ bit resets the receiver’s clock so that it matches the transmitters
start
The ______________ are just the start and stop bits; the parity bit is also a control bit, but for ______________
control bits…error control
A state at logic 1
Idle state
The main problem with asynchronous transmission is its ______________, primarily due to the additional start and stop bits for every byte
high overhead
A simple formula in computing for the ratio of control bits to data bits transmitted is:
%Overhead = (Control Bits/Total Bits) * 100
%Data = 100 - %Overhead
Percent Data
ED = %Data * Data Transfer Rate (in bps)
Effective Data (ED)
All letters of data in one group of data are transmitted at one time as a block of data.
Synchronous transmission
The block of data in a synchronous transmission is called a ___________
frame
Often used in both point-to-point and multipoint circuits
Synchronous transmission
Start and end of each frame (synchronization) are established by adding synchronization characters (_____) to the start of the frame
SYN
In ___________________, the transmitter and the receiver exchange initial synchronizing information, and then continuously exchange a digital stream that keep them in lock step
synchronous transmission
Depending on the protocol, there may be anywhere from _____ to ______ SYN characters
one…eight
____________________________ is a mainframe protocol developed by IBM in 1972 that is still in use today — uses a controlled-access media protocol
Synchronous Data Link Control (SDLC)
Flag – Address – Control – Message – Frame check sequence – Flag
Synchronous Data Link Control (SDLC)
Each SDLC frame begins and ends with a special bit pattern (01111110), known as the ________
flag
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)
address field
The ______________ identifies the kind of frame that is being transmitter (information or supervisory)
control field
____________________ is used for the transfer and reception of messages, frame numbering and contiguous frames, and the like
Information frame
____________________ is used to transmit acknowledgements (ACKs and NAKs)
Supervisory frame
The ______________ is of variable length and is the user’s message
message field
The __________________________ is a 32-bit CRC code (some older versions use a 16-bit CRC)
frame check sequence field
___________________________ is a formal standard developed by the ISO often used in WANs
High-level data link control (HDLC)
Essentially the same as SDLC, except that the address and control fields can be longer
High-level data link control (HDLC)
Has several additional benefits that include:
1. Larger sliding window for continuous ARQ (acknowledgement request)
2. Uses a controlled-access media access protocol
High-level data link control (HDLC)
_____________ is a very popular LAN protocol, conceived by Bob Metcalfe in 1973 and developed jointly by Digital, Intel, and Xerox in the 1970s
Ethernet
Since then, ____________ has been further refined and developed into a formal standard called IEEE802.3ac
Ethernet
______________ uses contention media access protocol
Ethernet
_____________________ 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
Point-to-point Protocol (PPP)
