3: Internet Protocols

Question 1

Why is the Internet vulnerable ?

Answer 1

• Services are ‘best-effort’
• No guarantee of quality (unlike telecom networks)
• Packets may be lost, corrupted, delayed, arrive out of sequence
• Problems may be overcome by a careful design of protocols

Question 2

What are the pieces of Internet ?

Answer 2

• Hosts (comp connected to a network)
• Routers (connecting a network to the Internet)
• Applications (various electronic devices)
• Protocols (rules for computer to talk)
• Hardware (Machines)
• Software (Programs)

The relationship between these pieces will be organised into layers.

Question 3

Reasons for a layered architecture ?

Answer 3

• Modularisation eases maintenance, updates

- Changes in the implementation of layer’s service are transparent to the rest of system

Question 4

What are the 5 layers of IP stack ?

Answer 4

Application layer
Transport layer
Network layer
Link layer
Physical layer

(ATNLP)

Question 5

• What are the 2 extra layers in ISO-OSI ?

Answer 5

• Presentation layer

- Session layer

Question 6

Application layer ?

Answer 6

• SMTP: Simple Mail Transfer Protocol
• HTTP: Hypertext Transfer Protocol
• Telnet: allows users on a computer to access and log into another computer
• FTP: File Transfer Protocol for transferring files between a client and server computers

Question 7

What is a client ?

Answer 7

A computer requests some service from another computer called a server providing this service to the client, eg sending emails.

Question 8

Transport layer ?

Answer 8

• TCP: Transfer Control Protocol

- UDP: User Datagram Protocol for transmission/reception packet-by-packet.

Question 9

Network layer ?

Answer 9

A set of protocols to transport packets from one host to another specified by an IP address.

• IP
• ICMP

Question 10

Data link layer ?

Answer 10

PPP: Point-to-point Protocol to establish a connection between 2 nodes in a network.

Ethernet protocols split a data stream into shorter pieces (frames) containing source and destination addresses, error-checking data.

Question 11

Physical layer ?

Answer 11

Defines how to transmit raw bits, not logical packets, over a physical link.

Question 12

Link:

Processes, Hosts, Transport protocol, Network-layer protocol, Link layer, Physical layer.

To:

• Hosts: two houses
• Connections between towns
• Trains or postal trucks
• Two sets of parents
• Two kids
• Royal Mail

Answer 12

• Processes: two kids
• Hosts: two houses
• Transport protocol: two sets of parents
• Network-layer protocol: Royal Mail
• Link layer: connections between towns
• Physical layer: trains or postal trucks