Chapter 2: The Open Systems Interconnection Specifications

Question 1

What are the seven layers of the OSI Reference Model?

Answer 1

• Application (Layer 7)
• Presentation (Layer 6)
• Session (Layer 5)
• Transport (Layer 4)
• Network (Layer 3)
• Data Link (Layer 2)
• Physical (Layer 1)

Question 2

Summarizing the functions, what occurs at the Application Layer of the OSI Model?

Answer 2

• File, print, message, database, and application services

Question 3

Summarizing the functions, what occurs at the Presentation Layer of the OSI Model?

Answer 3

• Data encryption, compression, and translation services

Question 4

Summarizing the functions, what occurs at the Session Layer of the OSI Model?

Answer 4

• Dialog control

Question 5

Summarizing the functions, what occurs at the Transport Layer of the OSI Model?

Answer 5

• End-to-end connection

Question 6

Summarizing the functions, what occurs at the Network Layer of the OSI Model?

Answer 6

• Routing

Question 7

Summarizing the functions, what occurs at the Data Link Layer of the OSI Model?

Answer 7

• Framing

Question 8

Summarizing the functions, what occurs at the Physical Layer of the OSI Model?

Answer 8

• Physical topology

Question 9

The OSI’s seven layers are divided into two groups. The top three layers define the rules of how the applications working within host machines communicate with each other as well as with end users. What are the three upper layers and their functions?

Answer 9

1. Application * Provides a user interface
2. Presentation * Presents data
   * Handles processing such as
   encryption
3. Session * Keeps different applications’ data
   separate

Question 10

The OSI’s seven layers are divided into two groups. The bottom four layers define how the actual data is transmitted from end to end. What are the four lower layers and their functions?

Answer 10

1. Transport *Provides reliable or unreliable delivery
   *Performs error correction before
   retransmit
2. Network *Provides logical addressing, which
   routers use for path determination
3. Data Link *Combines packets into bytes and
   bytes onto frames
   *Provides access to media using MAC
   address
   *Performs error detection, not
   correction
4. Physical *Moves bits between devices
   *Specifies voltage, wire speed, and pin-
   out of cables

Question 11

The Data Link layer has two sublayers, what are they

Answer 11

LLC and MAC

Question 12

What is the function of the LLC sublayer?

Answer 12

The LLC sublayer is responsible primarily for the multiplexing of Network layer protocols.

Question 13

What is the function of the MAC sublayer?

Answer 13

The MAC sublayer is responsible for physical addressing and determining the appropriate time to place data on the network.