Chapter 1

Question 1

What is the idea behind layering in the OSI model

Answer 1

That each layer is responsible for providing a service to the layer above by using the services of the layer below

Question 2

What is the communication between layer *n *and layer *n - 1 *known as?

Answer 2

interface

Question 3

What is the 1st Layer in the OSI Model

Answer 3

Physical

Question 4

What is the second layer in the OSI Model

Answer 4

Data Link

Question 5

What is the third layer in the OSI model?

Answer 5

Network

Question 6

What is the 4th layer in the OSI model

Answer 6

Transport

Question 7

What is the 5th layer in the OSI model

Answer 7

Session

Question 8

What is the 6th layer in the OSI model

Answer 8

Presentation

Question 9

What is the 7th Layer in the OSI model

Answer 9

Application

Question 10

What is the goal of the Presentation Layer

Answer 10

To agree on representations for data.

Question 11

What method of presentation does the Presentation Layer standardize on?

Answer 11

ASN.1 (Abstract Syntax Notation 1)

Question 12

What is bit stuffing and how does it work

Answer 12

Bit stuffing is a technique used to mark the start and end of a frame. In bit stuffing 6 1’s are used to denote the start and end of a frame. If 6 1’s are included in the data portion of a frame, after 5 1’s are transmitted the transmitting node knows to add a 0 into the data. The receiving node knows that once 5 1’s are received, followed by a 0 and another 1, it should remove the 0 and parse the date portion as if 6 1’s were being transmitted.

Question 13

What are two methods used to denote the beginning and end of a packet?

Answer 13

1) bit stuffing
2) using different physical signals for data bits, than for markers

Question 14

As it pertaines to layering, what is an envelope and when is it applied

Answer 14

An envelope is information glued onto the beginning/end of a packet for interpretation by a certain layer of the OSI model. These are known as the header and footer

Question 15

Each layer communicates with its peer layer through a ____

Answer 15

Protocol Data Unit (PDU)

Question 16

What kind of PDU’s does the data link layer use to communicate?

Answer 16

LPDU

Question 17

What kind of PDU is used to communicate with at the Network Layer?

Answer 17

NPDU

Question 18

Which kind of PDU is used to communicate with at the Transport Layer?

Answer 18

TPDU

Question 19

When layer N+1 gives information to layer n for transmission, what is the information known as?

Answer 19

An SDU, or Service Data Unit. The layer term is prepended to elminiate ambiguity (e.g. PSDU, SSDU, TSDU, NSDU…etc)

Question 20

Does an NSDU have a Network Layer envelope?

Answer 20

No, an NSDU defines the TPDU after it has been handed to the Network Layer. A packet that already has the Network Layer envelope added to it would be known as an NPDU if it resides at the network layer, or an LSDU if it resides at the Data Link Layer.

Question 21

What two functions does a connectionless service offer layer n?

Answer 21

1) it accepts packets for transmission from layer n
2) it delivers pacets to layer n

Question 22

In a connection-oriented service, what three phases does communication consist of?

Answer 22

1) Connection Setup
2) Data Transfer
3) Connection Release

Question 23

Does a service that is purely datagram make a guarantee about delivery?

Answer 23

No, datagram, aka best-effort, accepts data but makes no guarantee about it’s delivery.

Question 24

What does a reliable service guarantee

Answer 24

That data will be delivered in the order transmitted, without corruption, duplication, or loss.

Question 25

What are the two forms of service tramsission

Answer 25

1) reliable
2) datagram (aka best-effort)

Question 26

In a connectionless network layer, does it make sense to utilize a reliable service?

Answer 26

No, only datagram service makes sense in this instance because by definition nothing is keeping track of what gets delivered.

Question 27

Are IP, IPX, DECnet, CLNP, and AppleTalk examples of connection oriented or connectionless network layers?

Answer 27

connectionless