Net. 1: Ch 4 Network Access (TCPIP Layer)

Question 1

node

Answer 1

Layer 2 notation for a network device connected to a common media.

Question 2

2 Basic Services of Data Link Layer

Answer 2

1. Accept Layer 3 data packets and packs them into frames.

2. Controls media access control and performs error detection.

Question 3

2 Sublayers of Data Link Layer

Answer 3

1. Logical Link Control

2. Media Access Control

Question 4

Logical Link Control

Answer 4

LLC: defines the software processes that provide services to the network protocols- identifies which network layer protocol is being used in the frame.

Question 5

Media Access Control

Answer 5

MAC: defines the media access processes performed by the hardware - provides data link layer addressing and delimiting of data.

Question 6

Actions of Router Along Path

Answer 6

1. Accepts frame from a medium.
2. De-encapsulates the frame.
3. Re-encapsulates the packet into a new frame.
4. Forwards new frame appropriate to the medium of that segment of the physical network.

Question 7

3 Parts of a Frame

Answer 7

1. Header
2. Data
3. Trailer

Question 8

Header

Answer 8

Part of a frame that contains control information , addressing, ahead of the PDU

Question 9

Data

Answer 9

contains IP header, transport layer header, and application data.

Question 10

Trailer

Answer 10

contains control information for error detection; after PDU

Question 11

Parts of Header

Answer 11

1. Start Flag: marks start of frame : used by MAC sublayer.
2. Addressing: used by MAC sublayer to identify source and destination nodes.
3. Type: used by LLC to identify the layer 3 protocol.
4. Control: id’s flow control/other control services.

Question 12

Parts of Trailer

Answer 12

1. Error Detection: CRC check for errors

2. Stop Flag: marks end of frame.

Question 13

Definers of Open L2 standards

Answer 13

1. Institute of Electrical and Electronics Engineers.
2. xx
3. International Telecommunications Union (ITU)
   ADSL, ISDN
4. International Organization for Standardization
   (ISO) High Level Data Link Control
5. American National Standards Institute (ANSI)
   Fiber Distributed Data Interface

Question 14

WAN Physical Topologies

Answer 14

1. Point to Point
2. Hub and Spoke: WAN star.
3. Mesh

Question 15

virtual circuit

Answer 15

logical connection between two network devices within a network

Question 16

half-duplex

Answer 16

communication mode where you can send or receive at the same time.

Question 17

full-duplex

Answer 17

communication mode where you can send and receive at the same time.

Question 18

Physical Lan Topologies

Answer 18

1. Bus
2. Star
3. Ring
4. Extended Star/Hybrid

Question 19

2 MAC Methods for Shared Media

Answer 19

1. Contention Based Access

2. Controlled Based Access

Question 20

Contention Based Access

Answer 20

All nodes compete for medium use but have plan if collisions occur.

Question 21

Controlled Based Access

Answer 21

Each node has how time to use the medium.

Question 22

Carrier Sense Multiple Access

Answer 22

CSMA: Method used in contention based networks to detect if another node is transmitting data.

Question 23

CSMA/CD

Answer 23

Carrier Sense Multiple Access/Collision Detection

Data is sent when medium is free, if collisions are detected all nodes stop Tx and resend later.

Question 24

CSMA/CA

Answer 24

Carrier Sense Multiple Access/Collision Avoidance
Checks for signal on medium; if free sends an intent to Tx signal over network; waits for confirmation to send then sends data.

Question 25

multi-access topology

Answer 25

One node at a time sends , but sends to all other nodes; only recipient node uses data.

Question 26

Controlled Access Topology

Answer 26

- network devices take turns to send data - uses token; only token holder can Tx - aka "scheduled access" or "deterministic"

Question 27

Possible Control Fields in Header/Control

Answer 27

1. Priority/Quality of Service 2. Logical connection control. 3. Physical Link Control: used to establish media link. 4. Flow Control Field 5. Congestion Control Field: indicates congestion

Question 28

Data Link Addressing

Answer 28

- referred to as physical address (MAC) - contained in frame header - device specific

Question 29

Frame Check Sequence

Answer 29

FCS: part of trailer used in cyclic redundancy check(CRC): carries value that is used to check to see if any errors in data has occured.

Question 30

3 Common Data Link LAN Protocols

Answer 30

1. Ethernet 802.2/802.3: CSMA/CD 2. Point to Point Protocol 3. 802.11 Wireless.

Question 31

Ethernet Frame Composition.

Answer 31

1. Preamble - used for synchronization 2. Destination Address: 48 bit MAC 3. Source Address: 48 bit MAC 4. Type: indicates which upper level protocol receives frame after Ethernet processes. 5. DataL Data PDU 6. Frame Check Sequence

Question 32

Point to Point Frame Composition

Answer 32

1. Flag: signals begin or end of frame: 01111110 2. Addresses: PPP broadcast station. 3. Control: calls for transmission of data in unsequenced frame: 00000011 4. Protocol: identifies protocol encapsulated in data field. 5. Data contains datagram 6. Frame Check Sequence: 16 or 32 bits.

Question 33

Wireless LAN Frame

Answer 33

1. Frame Control: includes many sublayers 2. Duration /ID: time in microseconds to transmit frame or Association ID (AID) of transmitting station. 3. Destination Address (AD): MAC 4. Source Address (SD): MAC 5. Receiver Address (RA): MAC of wireless device that is immediate recipient of frame. 6. Sequence Control 7. Tramsitter Address(TA): MAC of wireless device that transmitted the frame. 8. Frame Body 9. Frame Check Sequence: 32 bit crc value.