Network Layers

Question 1

What are the layers in ascending order in the OSI model ?

Answer 1

Physical Layer, Link Layer, Network Layer, Transport Layer, Session Layer, Presentation Layer, Application Layer

Question 2

What services does the link layer provide and how are they provided ?

Answer 2

Framing, fragmentation, Link access, reliable delivery

Framing, this is the encapsulation of the frames sent from the datagrams with a header and a trailer

Fragmentation, if a frame is too large it will be broken down into smaller frames and sent off

Link access, MAC protocol is used at this stage

Reliable delivery, MAC protocol used to ensure this

Question 3

What error handling methods are there in the link layer ?

Answer 3

This is the MAC protocol, this is done through handshaking, flow control by using the take in turn, random access protocol, or channel partitioning

Question 4

What protocols are there in the link layer ?

Answer 4

MAC protocol

Question 5

What services does the network layer provide ?

Answer 5

Fragmentation, encapsulation, logical addressing, error handling

Question 6

What error handling methods are there in the link layer ?

Answer 6

MAC protocol once a collision has occurred there will be a time where they will back off and have a random time where they will refire their packets

Question 7

What does ICMP stand for ?

Answer 7

Internet control message protocol

Question 8

What is a PDU and what does it stand for ?

Answer 8

Protocol data unit

Question 9

What protocols are there in the transport layer ?

Answer 9

TCP/IP UDP, windowing

Question 10

What is TCP/IP ?

Answer 10

TCP is an extension of the IP protocol that uses acknowledgments, flow control, congestion control and windowing to ensure the reliable delivery of segments as well as multiplexing

Question 11

What is multiplexing ?

Answer 11

Combining multiple signals into one complex signal

Question 12

Where is multiplexing used ?

Answer 12

In the transport layer

Question 13

What is ICMP?

Answer 13

This is a error handling protocol in the link layer, that provides feedback to the user in case of the errors

Question 14

What is packet loss ?

Answer 14

Where a packet is either dropped during transmission because it has surpassed the time to live, or has been dropped because the router buffer is full

Question 15

What is a subnet ?

Answer 15

A subnet is a network within a larger network

Question 16

What are the benefits of using a subnet ?

Answer 16

Manageable, more secure, extension of space, more IP addresses and more space for people

Question 17

What are the issues with IPv4 ?

Answer 17

There is a limit to the amount of IP addresses to use

Question 18

What are the error checking methods used in the link layer ?

Answer 18

Checksum, Cyclic redundancy check, parity checking

Question 19

What is the checksum check within the link layer /

Answer 19

The entire frame will be placed into a 16 bit sequence, this is then sent once recieved it will be checked against the sent form.

Question 20

What is CRC and how does it work ?

Answer 20

The bits of data will be added to to with a bit string pattern, the entire frame will then be divided by 2, if it can be then there is no error else then there is an error

Question 21

What is partiy checking ?

Answer 21

They will store the amount of 1’s there are, once recieved if this has changed then there has been an issue

Question 22

What is the address resolution protocol and which layer is it used in ?

Answer 22

This is used within the network layer, because IP delivery isnt reliable the delivery of packets is used with the devices MAC address.

Question 23

What is CSMA/CD and what does it stand for ?

Answer 23

This is a collision detection system that will detect colliisons within the network, Carrier sense multiple access with collision detection