Data Link Layer

Question 1

Main idea

Answer 1

Provides means for exchanging data frames over a common media

Detect and possibly correct errors that may occur in physical layer (crc?)

Question 2

Main function 2

Answer 2

Controls how data is placed into medium via Mac and error detection techniques

Question 3

Network

Answer 3

Two or more devices connected by a common medium

Question 4

Sublayers

Answer 4

Upper sublayer = LLC (frames network layer packet, identifies network layer protocol)
Lower sublayer = MAC (addresses, marks beginning and end of frame)

Question 5

MAC depends on

Answer 5

Media sharing, topology

Question 6

MAC methods for share media

Answer 6

Controlled (deterministic; ex: token ring, fddi)

Contention (CSMA; transmit at any time)

Question 7

Full duplex

Answer 7

Receive, transmit simultaneously

Question 8

Half duplex

Answer 8

Receive, transmit one at a time

Question 9

Ethernet

Answer 9

CSMA/CD

Question 10

Wireless

Answer 10

CSMA/CA

Question 11

Physical topology

Answer 11

Actual arrangement of nodes an physical connections between them

Question 12

Logical topology

Answer 12

The way a network transfers frames from one nose to the next

Question 13

P2P

Answer 13

Two nodes directly connected; MAC method used by DLL determined by logical point to point; use of intermediate devices don’t affect local topology

Question 14

Characteristics of multi access topology

Answer 14

Data from a node can be placed at any one time
Only node for which it is for process contents of frame
Typically uses CSMA/CD OR CSMA/CA

Question 15

Token passing (ring topology)

Answer 15

Each node receives a frame until it reaches its destination

Usually only one frame at a time is usually carried by the media

Question 16

Fragile environment

Answer 16

More controls, larger header and trailer

Question 17

Protected

Answer 17

Less controls; smaller header and trailer

Question 18

Physical addressing

Answer 18

Aka MAC address

Used to transport frame across shared local media from DLL

ONLY USED FOR LOCAL DELIVERY

Question 19

Error detection techniques

Answer 19

Cyclic redundancy check matches initial and received

Frame check sequence: DLL because this is where data is transferred across the media

Question 20

Encapsulation

Answer 20

Encapsulates packet by a header and trailer

Question 21

Header includes…

Answer 21

Start frame 8 bytes
Addressing DLL source dest address 12 bytes
Type of pdu in frame (what kind of data is being sent or length of frame) 2 bytes
Control
Priority/Qos

Question 22

Preamble

Answer 22

Used for synchronization; contains delimiter to mark end of the timing information