Week 10 - Packet switching & Network layer addressing

Question 1

What is packet switching and why is it used?

Answer 1

Packet switching in the context of datagram networks means that each packet is independent and travels the fastest route it can (ex: UDP).

It is used to connect multiple devices in a network to facilitate efficient point-to-point communication.

Question 2

What are the 5 services of the network layer?

Answer 2

Packetizing
Routing
Error control
Flow control
Congestion control

Question 3

How is network layer routing performed?

Answer 3

With the use of routing tables and network layer devices (routers).

MAC addresses are modified along the way.

If the dest MAC of datagram does not match, it is dropped.

Question 4

How is error control performed in the network layer?

Answer 4

Using the checksum field in the header of the datagram.

Checks only the header.

Only detects errors and drops packets, does not retransmit.

Question 5

What are the four facets of network layer delay?

Answer 5

1. Transmission time (n + 1) - Time to push all bits of packet onto a link (corresponds to # links)
2. Propagation time - Time required for a bit to travel from source to dest (based on distance and propagation speed)
3. Processing delay (n + 1) - time to process packet at router and destination
4. Queuing delays (n) - time packet held at each router

Question 6

What is throughput?

Answer 6

How fast we can actually send data through a network.
(Realistic: Throughput, Theoretical: Bandwidth)
Depends on link with min transmission rate.

Question 7

What is jitter?

Answer 7

Variations in delay (think of CounterStrike)

Question 8

What are the 3 metrics to measure network layer performance?

Answer 8

delay
throughput
packet loss

Question 9

What is IP forwarding AND
What 4 pieces of information are needed for IP forwarding?

Answer 9

IP forwarding is forwarding packets from one network to another based on the destination IP

mask
network address
interface number
IP address of next rouer

Question 10

What is address aggregation?

Answer 10

Combining rows in a forwarding table to represent a block of CIDR addresses for more efficient routing.

Question 11

Is the internet a packet-switched network?

Answer 11

Yes

Question 12

What is DHCP?

Answer 12

Dynamic Host Configuration Protocol (application layer)

Automatically assigns assignable addresses for each host or router.

Question 13

What is NAT?

Answer 13

Network Address Translation

In a small network, allows hosts to share the same public IP when accessing the internet.

Question 14

255.255.255.223 is a valid subnet mask.

Answer 14

F because a subnet mask must have contiguous 0s.

Question 15

In NAT translation table, every (source IP address, port #) is mapped
to (—, —) translation pair.

Answer 15

NAT IP address, new port #