Ch. sixthteen
a closer look at osi model
Summary
■ The OSI model is an abstract representation of data communications
developed by the ISO.
■ Network systems do not necessarily exactly match all layers of the OSI
model.
■ The application layer is where the user interfaces with the network system using
network programs such as a Web browser, FTP, Telnet, and an e-mail client.
■ The presentation layer is concerned with bit sequence and with using an
acceptable data format such as ASCII, EBCDIC, and CODEC.
■ The session layer is concerned with establishing, maintaining, and
terminating a connection between two nodes.
■ The transport layer is concerned with providing reliable, accurate data in the
most efficient manner.
■ The network layer is where IP addressing is inserted into a packet and where
decisions based on IP addresses are made.
■ The data link layer is where frames are converted into a serial stream of data
and decisions based on MAC addresses are made.
■ The physical layer provides the path for digital signals and represents the
media, connectors, and passive components.
■ While the OSI model tends to make encapsulation appear simple and direct,
actual communication is complex and generates hundreds or even thousands
of frames while carrying out the simplest of networking tasks.
■ Novell NetWare IPX is a connectionless protocol, and SPX is a connection-
oriented protocol.
■ AppleTalk Datagram Delivery Protocol (DDP) is a connectionless protocol
used to route packets across a network.
■ AppleTalk Datagram Delivery Protocol (DDP) relies on upper-level protocols
to form connection-oriented communication.
■ The Apple LocalTalk protocol is used to access network media in an Apple
network environment.
■ AppleShare IP is a protocol suite based on AppleShare and TCP/IP.
Review Questions
Answer the following questions on a separate sheet of paper. Please do not write in this book.
1. How does the ISO OSI model compare with the DoD model?
2. Why is the DoD model so simple when compared to the OSI model?
3. What is the major difference between the ISO version of the OSI model and
the IEEE 802 version of the OSI model?
4. The IEEE divided the data link layer into two sublayers. What are the two
sublayers called?
5. Briefly describe the function of each IEEE data link sublayer.
6. At which layer of the OSI model does a network interface card operate?
7. At which layer of the OSI model does a hub operate?
8. At which layers of the OSI model does a gateway operate?
9. At which later of the OSI model does a router operate?
10. Match the following terms to their definitions.
1. ApplicationA. Cabling and connectors.
B. Converts frames codes to a serial stream of data.
C. Responsible for connecting across WAN systems.
D. Repackages long messages into smaller units.
E. Establishes rules for communication between
two computers.
F. Translates data into a common compatible
format.
G. File transfer service, e-mail, and Web browser
programs.
1.Application A. Cabling and connectors.
2. Presentation B. Converts frames codes to a serial stream of data.
3. Session C. Responsible for connecting across WAN systems.
4. Transport D. Repackages long messages into smaller units.
5. Network E. Establishes rules for communication between two computers.
6. Data link F. Translates data into a common compatible format.
7. Physical G. File transfer service, e-mail, and Web browser programs.
11. At which layer does windowing take place?
12. At which layer is the MAC address inserted into the frame?
13. To which two layers of the OSI model do the IEEE 802.3 standards relate?
14. To which two layers of the OSI model do the Token Ring standards relate?
15. Briefly describe the encapsulation process.
16. Which Novell protocols align with the upper layers of the OSI model?
17. Which Novell protocol is similar in function to IP?
18. Which Novell protocol is similar in function to TCP?
19. Which Apple protocol is similar in function to IP?
20. What Apple protocol is used to access the network media?
21. Which Apple protocol aligns with the upper two layers of the OSI model?
22. How does the Apple protocol suite ensure delivery of data if the Datagram
Delivery Protocol (DDP) is a connectionless protocol?
23. What does the acronym RFC mean?
24. Who may write an RFC proposal?
■ The OSI model is an abstract representation of data communications
developed by the ISO.
■ Network systems do not necessarily exactly match all layers of the OSI
model.
■ The application layer is where the user interfaces with the network system using
network programs such as a Web browser, FTP, Telnet, and an e-mail client.
■ The presentation layer is concerned with bit sequence and with using an
acceptable data format such as ASCII, EBCDIC, and CODEC.
■ The session layer is concerned with establishing, maintaining, and
terminating a connection between two nodes.
■ The transport layer is concerned with providing reliable, accurate data in the
most efficient manner.
■ The network layer is where IP addressing is inserted into a packet and where
decisions based on IP addresses are made.
■ The data link layer is where frames are converted into a serial stream of data
and decisions based on MAC addresses are made.
■ The physical layer provides the path for digital signals and represents the
media, connectors, and passive components.
■ While the OSI model tends to make encapsulation appear simple and direct,
actual communication is complex and generates hundreds or even thousands
of frames while carrying out the simplest of networking tasks.
■ Novell NetWare IPX is a connectionless protocol, and SPX is a connection-
oriented protocol.
■ AppleTalk Datagram Delivery Protocol (DDP) is a connectionless protocol
used to route packets across a network.
■ AppleTalk Datagram Delivery Protocol (DDP) relies on upper-level protocols
to form connection-oriented communication.
■ The Apple LocalTalk protocol is used to access network media in an Apple
network environment.
■ AppleShare IP is a protocol suite based on AppleShare and TCP/IP.
Review Questions
Answer the following questions on a separate sheet of paper. Please do not write in this book.
1. How does the ISO OSI model compare with the DoD model?
2. Why is the DoD model so simple when compared to the OSI model?
3. What is the major difference between the ISO version of the OSI model and
the IEEE 802 version of the OSI model?
4. The IEEE divided the data link layer into two sublayers. What are the two
sublayers called?
5. Briefly describe the function of each IEEE data link sublayer.
6. At which layer of the OSI model does a network interface card operate?
7. At which layer of the OSI model does a hub operate?
8. At which layers of the OSI model does a gateway operate?
9. At which later of the OSI model does a router operate?
10. Match the following terms to their definitions.
1. ApplicationA. Cabling and connectors.
B. Converts frames codes to a serial stream of data.
C. Responsible for connecting across WAN systems.
D. Repackages long messages into smaller units.
E. Establishes rules for communication between
two computers.
F. Translates data into a common compatible
format.
G. File transfer service, e-mail, and Web browser
programs.
1.Application A. Cabling and connectors.
2. Presentation B. Converts frames codes to a serial stream of data.
3. Session C. Responsible for connecting across WAN systems.
4. Transport D. Repackages long messages into smaller units.
5. Network E. Establishes rules for communication between two computers.
6. Data link F. Translates data into a common compatible format.
7. Physical G. File transfer service, e-mail, and Web browser programs.
11. At which layer does windowing take place?
12. At which layer is the MAC address inserted into the frame?
13. To which two layers of the OSI model do the IEEE 802.3 standards relate?
14. To which two layers of the OSI model do the Token Ring standards relate?
15. Briefly describe the encapsulation process.
16. Which Novell protocols align with the upper layers of the OSI model?
17. Which Novell protocol is similar in function to IP?
18. Which Novell protocol is similar in function to TCP?
19. Which Apple protocol is similar in function to IP?
20. What Apple protocol is used to access the network media?
21. Which Apple protocol aligns with the upper two layers of the OSI model?
22. How does the Apple protocol suite ensure delivery of data if the Datagram
Delivery Protocol (DDP) is a connectionless protocol?
23. What does the acronym RFC mean?
24. Who may write an RFC proposal?