2023 Class Test 1

Question 1

Two reasons for using layering abstraction in communication networks

Answer 1

• Simplifies dealing with complex telecommunication networks
• Eases maintanance and updating of system.
  -explicit structure

Question 2

what is the responsibility of the application layer

Answer 2

network access to user applications

Question 3

what is the responsibility of the transport layer

Answer 3

Order delivery of packets, congestion control, flow control

Question 4

what is the responsibility of the network layer

Answer 4

datagram fowarding and routing

Question 5

what is the responsibility of the data link layer

Answer 5

Framing, reliable delivery, error control (detection and correction)

Question 6

what is the responsibility of the physical layer

Answer 6

Transmission of raw bit, modulation, demodulation, coding, equalization, synchronisation

Question 7

main difference between application layer and transport layer

Answer 7

Application layer specifies shared communication protocols and interface methods used by hosts in a communications network

Transport layer provides logical communication between process running on different hosts

Question 8

advantages of packet switching over circuit switching?

Answer 8

-simple to implement
- supports more users
- scalable
- no connection set up

Question 9

What is the importance of DNS

Answer 9

Maps between IP addresses and host names. Translates a host name to an IP address. Internet cannot function without it.

Question 10

3 classes of DNS?

Answer 10

Root DNS- provide IP addresses of Top level domain DNS servers.

Top level domain servers (TLD) - responsible for registry organisations of global domains and country code domains

Authoritative DNS server - Houses the DNS records of the names and respective IP addresses of hosts for an organisation. Publically accessible. Organisations can choose to make their own, or pay to have one from service provider.

Question 11

What is the minimum distribution time for client-server

Answer 11

Dc-s > max{NF/us,F/dmin}

Question 12

What is the minimum distribution time for peer-peer

Answer 12

Dp2p > max{F/us,F/dmin,NF/(us+sum(ui))}

Question 13

How does a receiver use a checksum to detect errors?

Answer 13

• receiver adds all TCP segments and checksum.
• if sum contains a zero, receiver knows theres an error in the received message