Data Communications Protocols
DigiPoints, Volume 1
Page 7.1
Student Workbook
DigiPoints Volume 1
Leader Guide
Module 7 – Data Communications Protocols
Summary
This module describes basic data communications protocols. Protocols are the established
rules that regulate data transmission between computers.
Module Objectives
Upon successful completion of the module, the student should be able to:
•
•
•
•
•
•
•
Define the purpose of a data communications protocol.
Describe the basic functions of a protocol.
Compare and contrast layered versus hierarchical protocols.
Describe the purpose of the OSI Model.
Identify the 7 Layers of the OSI Model.
Identify the basic components of the TCP/IP Protocol.
Relate the OSI Model to the TCP/IP Protocol.
Prerequisites
Read DigiPoints, Volume 1, Chapter 7.
SCTE
Data Communications Protocols
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PROTOCOL FUNCTIONS
• Segmentation & Re-assembly
• Encapsulation
• Connection Control
• Flow Control
• Error Control
• Synchronization
• Sequencing
• Addressing
• Multiplexing
• Transmission Services
There are 10 general functions of a protocol. What is the purpose of a protocol?
SCTE
Data Communications Protocols
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Page 7.3
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Segmentation & Re-Assembly
Network Data Blocks
User Data Blocks
T1
D1
H1
T2
T3
D2
D3
H2
H3
T
D
H
T
D
H
T
D
H
H = Header
D = User Data
T = Trailer
How are the blocks on the left side of the page different from those on the right?
Why is this important?
What is the significance of multiple paths in the network?
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Different Paths Use
Data Communications Protocols
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Encapsulation
T+
D
H+
Protocol Data Unit
What occurs during this step?
Why are the Trailer and the Header shown with “+” signs? What does this represent?
Describe a Protocol Data Unit (PDU).
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Data Communications Protocols
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Page 7.5
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Connection Control
Flow Control
Error Control
ACK
End
End
Terminal
Terminal
Network
What are the functions of “Connection Control”?
How does “Flow Control” maintain data integrity?
How is “Error Control” related to the other two “control” functions?
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Data Communications Protocols
DigiPoints, Volume 1
Page 7.6
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Synchronization
Sequencing
For example:
1st
2nd
3rd
- Establish the connection
- Acknowledge data receipt
- Terminate connection
Put the data back together
in the correct order.
What is the purpose of “Synchronization”?
How is it different from the synchronization discussed earlier as it pertained to
transmitting 1s and 0s?
Why is “Sequencing” important? Be specific and relate it back to “Segmentation and
Reassembly”.
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Data Communications Protocols
DigiPoints, Volume 1
Page 7.7
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Addressing
Where is THX123?
Locale A
A
Local
Network
Global
C
B
Local
Locale B
Local
NEW
Locale C
How are DNA and DNS used in addressing?
Why are “hierarchical” schemes preferred over “flat” addressing methods?
How many bits are used for an Internet address? How are these bits organized?
What are the four (4) classes of addresses?
Which is most limited? Why?
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Data Communications Protocols
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Page 7.8
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Multiplexing
Downward
ONE Upper level protocol uses MANY lower
level connections
• Route diversity
• Improved reliability
Upward
MANY Upper level protocols use ONE lower
level connections
• Only one lower level path available
• Maximizes usage of a lower level connection
How does “Downward” multiplexing provide increased reliability?
How does “Upward” multiplexing increase the chance for failure?
How is this form of multiplexing different from the multiplexing described earlier, e.g.,
TDM systems?
What is meant by “Transmission Services”? How is it measured?
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Data Communications Protocols
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Page 7.9
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The Layer Concept
(N+1)
Layer
(N+1)
Entity
(N) Service
Access Point
Interface
(N)
Layer
(N)
Protocol
Entity
(N-1) Service
Access Point
Interface
(N-1)
Layer
What is the standard reference model for layered protocols?
What are the two types of protocols?
Which one is predominately used? Why?
What is a primitive? Where does it fit in the protocol software?
Name the four basic interlayer communications primitives:
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P
r
i
m
a
t
i
v
e
s
Services
Data Communications Protocols
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The OSI Model
Set of Rules
7
Application
6
Presentation
5
Session
4
Transport
3
Network
2
Datalink
Physical
1
Header
User Info
What is the lowest layer of this model?
How are Layers 1 - 3 different from Layers 4 - 7?
Is this an architecture or a framework? How would these two items differ?
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Page 7.11
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Datalink Layer
7
6
5
4
3
2
Application
Presentation
Session
Transport
Network
Datalink
Physical
• Governs flow of data
• Provides
–High Throughput
–Fast Response
–Data Integrity
•Functionality
–Synchronization
–Flow Control
–Error Detection
–Identification of entities
–Identification of information
What is the purpose of this layer?
What functions are to be found in this layer?
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1
Header
User Info
Data Communications Protocols
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Page 7.12
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Network Layer
7
6
5
4
3
2
Application
Presentation
Session
Transport
Network
Datalink
Physical
• Governs communications of a group of networks
• Provides resolution for issues involving:
–PDUs of different sizes/formats
–Different timers/timeouts
–Various quality of services
–Different addressing techniques
–Different performance levels
–Different routing methods
–Different user interfaces
–Different security levels
–Different troubleshooting, diagnostic, and maintenance
methods
–Cost and billing determination
This layer governs the communications of a group of networks.
What is the purpose of this layer, i.e., what is managed in this layer?
How does this layer address segmentation and addressing?
Name two Layer 3 protocols.
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1
Header
User Info
Data Communications Protocols
DigiPoints, Volume 1
Page 7.13
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Transport Layer & Session Layer
7
6
5
4
3
2
Application
Presentation
Session
Transport
Network
Datalink
Physical
1
Header
UserInfo
Transport Layer
•End to end data integrity
•Manages interface between upper & lower layers
•Connection and termination of session
•Detection of lost, duplicate, or out of sequence data
•Control data flow
Session Layer
•Coordinates data exchange between applications
•Synchronization checkpoints
•Structures user application interactions
•Provides rules for users exchanging data
•Prevents lost data by closing dialogs properly
What functions does the Transport Layer manage? Relate this back to the 10 basic
protocol functions.
What functions does the Session Layer manage? Relate this back to the 10 basic protocol
functions.
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Data Communications Protocols
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Presentation Layer & Application Layer
7
6
5
4
3
2
Application
Presentation
Session
Transport
Network
Datalink
Physical
1
Header
User Info
Presentation Layer
•Allows end users to operate with different syntax
•Translates User 1’s syntax so User 2 can read
Application Layer
•Direct interface with the end user applications
•Application Service Elements key
–ASCE - Regulates user requests
–RTSE - Notifies sender of successes/failures
–ROSE - Allows interactive communications
–CCR - Manages database interactions
Why is it important that different users be allowed to use different syntax? What is
syntax?
What does the Application Layer do that is key to all end users?
What is an ASE and what does it permit/allow?
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Data Communications Protocols
DigiPoints, Volume 1
Page 7.15
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TCP/IP Protocol
OSI
Model
DOD
Standards
7
Application
FTP; SMTP
6
Presentation
TELNET
5
Session
4
Transport
3
Network
2
Data Link
1
Physical
TCP
IP
DOD
Model
Process/
Application
Host to Host
Internet
Network
Access
What type of architecture is TCP/IP?
What is the difference between the OSI Model and TCP/IP?
What is different about the layers in a Hierarchical Architecture and a Layered
Architecture?
Relate the terms agent, host, process, and network.
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Data Communications Protocols
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Page 7.16
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Study Questions
1. Why do protocols exist?
2. What are the two types of protocol architectures that have been discussed in this
module? How do they differ? How are they similar?
3. What is the function of a primitive, and what are the four basic types of primitive?
4. Explain the relationship of protocols, architectures, reference models, and primitives.
5. List the 10 general functions of any protocol.
6. List the seve n layers of the OSI model. Which pertain to channel or network services,
and which pertain to end-to-end communications?
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7. Why was TCP/IP developed? Where was it first used, and where is it used today?
8. _____________________ is the concept that a protocol data unit only has a given
time to go from one end of a network to the other.
9. List at least five issues that are resolved by Layer 3 (Network Layer) protocols.
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