Transcript Exercises Chapter 7 Data Link Control Protocol 课后
Computer Networking
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CHAPTER 7 DATA LINK CONTROL PROTOCOL
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Online lecture Department of Computer Networking Application
Chapter 7 Data Link Control Protocol
7.1 INTRODUCTION
A set of rules that define the
messages
between computers or between computers and people is called a
.
are necessary so that all of the devices on the network are operating by the same set of rules and are able to communicate with each other.
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Chapter 7 Data Link Control Protocol 7.2 DATA LINK PROTOCOLS FUNCTIONS
Character identification and framing
Message identification The DTE must separate
the characters on
the communications line into messages
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Chapter 7 Data Link Control Protocol 7.2 DATA LINK PROTOCOLS FUNCTIONS
The part of a protocol consisting of the rules that specify the way the receiving terminal signals the sending terminal if it has received data correctly, how and under what
the line will be turned around, and whether the receiving terminal can accept more data is called line control.
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Chapter 7 Data Link Control Protocol 7.2 DATA LINK PROTOCOLS FUNCTIONS
The part of the protocol consisting of rules specifying what happens when an error is detected, what to do if communications suddenly and
unexplainably cease , and the way communications are reestablished
broken is called error control .
after they are
The part of a protocol consisting of rules for ending the communications under normal and abnormal
is called termination .
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Chapter 7 Data Link Control Protocol
7.3 DESIRABLE ATTRIBUTES OF DATA LINK PROTOCOLS
The ability of data terminal equipment
(DTE) to be able to transmit and receive any bit pattern as data is called transparency .
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Chapter 7 Data Link Control Protocol
7.3 DESIRABLE ATTRIBUTES OF DATA LINK PROTOCOLS
The protocol allow the transmission of data from any data coding system.
The protocol should use as few characters as possible to control the data transmission so that most of
can be used for actual data transmission.
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Chapter 7 Data Link Control Protocol
7.4 PROTOCOL IMPLEMENTION A data link protocol is implemented
by transmitting
certain bit patterns or characters on the communications
circuit.
7.5 PREDETERMINED COMMUNICATIONS PARAMETERS
Predetermined communication parameters are those
that are set manually by switches or specified as parameters in software.
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Chapter 7 Data Link Control Protocol
When two stations on a circuit transmit at the same
occurs.
There are three primary ways that circuit access can
:
contention,polling,and token passing .
When any
that has traffic looks to see if the circuit is free, and if it is, begins sending its traffic the line control technique is called contention . www.gxmu.edu.cn
Chapter 7 Data Link Control Protocol Contention systems work best _____.
a. on circuits that have only two DTEs b. when the speed of the circuit is relatively fast c. on circuits that have
7.7.2
When a
asks each station on the circuit or network if it has traffic to send it is using a line control technique called polling . www.gxmu.edu.cn
Chapter 7 Data Link Control Protocol 7.7.2
Roll call polling Roll call polling is the most common implementation of a polling system.
In order to know what stations to poll and in what sequence, the master station uses a
.
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Chapter 7 Data Link Control Protocol 7.7.2
Fast select polling speeds up the polling
process because a slave station
that doesn’t have traffic isn’t required to return a character to the
.
P128
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Chapter 7 Data Link Control Protocol
Data messages normally consist of three
parts: the header, text, and trailer
. The header of a message contains and conveys information about the message, such as
the destination node’s address , a sequence number , and perhaps a date and time.
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Chapter 7 Data Link Control Protocol Figure 7-1 Message format showing examples of the kinds of control characters the protocol might employ.
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Chapter 7 Data Link Control Protocol
Techniques to ensure that a fast transmitting node does not send data faster than the receiving node can receive and process it are called flow control .
7.9.1 Stop-and-wait Flow Control
Stop-and-wait Flow Control is the simplest form control.
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Chapter 7 Data Link Control Protocol Figure 7-2 The data flow of stop-and-wait flow control.
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Chapter 7 Data Link Control Protocol
7.9.2
Sliding Window Flow Control
The flow control technique that allows
multiple frames to be in transit on the line at
one time is called sliding window .
There are two common implementations
of
sliding window flow control: go-back-n and selective repeat .
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Chapter 7 Data Link Control Protocol Figure 7-3 The data flow in a simple sliding window flow control.
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Chapter 7 Data Link Control Protocol
7.10.1 Point-to-Point Protocol(PPP)
A protocol that is primarily used by PC workstations to
send IP over dial-up lines , typically when dialing in to an ISP
for connection to the Internet, is called PPP.
PPP has largely replaced the
protocol because it
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Chapter 7 Data Link Control Protocol Figure 7-4 PPP’s frame format.
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Chapter 7 Data Link Control Protocol
The XMODEM protocol was developed for use between PCs, especially for transfers of data files between them.
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Chapter 7 Data Link Control Protocol
7.11
SYNCHRONOUS DATA LINK PROTOCOLS
Synchronous data link protocols typically deal with blocks of data,not individual characters.
character-oriented protocol
byte-count-oriented protocol
bit-oriented protocols
.
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Chapter 7 Data Link Control Protocol 7.11.1 Character-Oriented Protocols A character-oriented protocol uses special
the beginnings and ends of messages.
The best known character-oriented protocol
is the Binary Synchronous Communications Protocol(BSC) ,also known as BISYNC.
BISYNC is defined to only support the 6-bit transcode (SBT) , EBCDIC, and ASCII .
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Chapter 7 Data Link Control Protocol 7.11.2 Byte-Count-Oriented Protocols Byte-count-oriented protocols have a special characters to mark the beginning of the
header,followed by a count field that
indicate
how many characters are in the
data portion of the messages
The best known byte-count-oriented
Digital Data Communications Message Protocol(DDCMP)
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Chapter 7 Data Link Control Protocol 7.11.3 Bit-Oriented Protocols A bit-oriented protocol uses only one special
character,called the flag character
,which marks the beginning and end of parts of the message. The best known bit-oriented protocols are the
ISO’s High-Level Data Link Control (HDLC)
protocol. SDLC is a subset of HDLC. 7.12 OTHER DATA LINK PROTOCOLS P143 www.gxmu.edu.cn
Chapter 7 Data Link Control Protocol
7.13
PROTOCOL CONVERSION
A protocol converter changes one protocol to another, when, for example, a message is sent between two networks that use different protocols. www.gxmu.edu.cn
Chapter 7 Data Link Control Protocol
1.When an HDLC node receives a flag character, it knows that （
C
） .
× A 、 an error has occurred × B 、 it should signal the sender to stop sending traffic
√
C 、 a frame is beginning or ending × D 、 it should switch to transparent mode Redo Next Answer
Chapter 7 Data Link Control Protocol
2.When two stations on a circuit transmit at the same time, a(n) （
D
） occurs.
× A 、 division × B 、 polling × C 、 bit stuffing
√
D 、 collision Redo Next Answer
Chapter 7 Data Link Control Protocol
3.In order to know what stations to poll and in what sequence, the master station uses a （
B
） .
× A 、 message header
√
B 、 polling list × C 、 start of header character × D 、 cyclic redundancy check Redo Next Answer
Chapter 7 Data Link Control Protocol
4. Go-back-n and selective repeat are two common implementations of （
D
） .
× A 、 bit oriented protocols × B 、 byte protocols × C 、 byte-count oriented protocols
√
D 、 sliding window flow control Redo Next Answer
Chapter 7 Data Link Control Protocol √
5. When a receiver must acknowledge every block of data before the next block is sent, the （
A
） type of flow control is being used.
A 、 stop-and-wait × B 、 stop-and-check × C 、 sliding frame × D 、 sliding window Redo Next Answer
Chapter 7 Data Link Control Protocol
Answer 7.BISYNC is defined to only support the 6-bit transcode (SBT), Answer 8.A set of rules that define the exact format of messages exchanged between computers or between computers and Answer
Chapter 7 Data Link Control Protocol
9. A technique used to ensure that a fast transmitting node does not send data faster than a receiving node can receive and Answer 10.A protocol that is primarily used by PC workstations to send IP over dial-up lines, typically when dialing in to an ISP for Answer
Chapter 7 Data Link Control Protocol www.gxmu.edu.cn