Structure of Network

Question 1

What is protocol?

Answer 1

Set of rules for data transmission which are agreed upon by both sender and receiver (data format, type, size etc.)

Question 2

Reasons for layering

Answer 2

• Simplifies network model
• Provides design modularity
• Enables programmers to specialise in a particular layer of the model
• Allows for standardised interfaces to be produced by networking vendors

Question 3

TCP/IP Model Layers

Answer 3

1. Application
2. Transport
3. Network
4. Data Link
5. Physical
   - Each layer only communicates with adjacent layers
   - At each layer, as required by the protocol, headers with relevant information are added to the data unit in the sender’s process, while removed from the data unit in the receiver’s process

Question 4

Application Layer

Answer 4

• High-level functionality to end users

- Data unit: message

Question 5

Application Layer - Protocols

Answer 5

• File transfer: FTP, SSH
• Email: SMTP, POP3, IMAP4
• Webpage: HTTP, HTTPS

Question 6

Transport Layer

Answer 6

• Functionality to transmit messages between any two programs
• Data unit: segment

Question 7

Transport Layer - Port Number

Answer 7

• Number representing a process running on a network
• In every data segment, both source and destination port are embedded in the header
• Commonly used ports: port 80 - HTTP; port 143 - IMAP; port 53 - DNS

Question 8

Transport Layer - Socket

Answer 8

• Identifier for an application process on a network

- Combination of IP address and port number

Question 9

Transport Layer - Protocols

Answer 9

• Transmission Control Protocol (TCP)

- Universal Datagram Protocol (UDP)

Question 10

Transport Layer - TCP

Answer 10

• Uses three-way-handshake to establish a connection before data transmission
• Break up data into segments with sequential numbers for reassembly at the receiver
• This ensures security and validation of the data
• Data can be sent only after handshake completes
• Preferred over UDP as it establishes connection between applications of two hosts

Question 11

Transport Layer - Handshake (TCP)

Answer 11

1. A sends B a packet with the SYN bit set
2. B responds to A with its own SYN packet; ACK bit is now set
3. A responds to B’s SYN with its own ACK

Question 12

Transport Layer - Sequencing (TCP)

Answer 12

• Data is transmitted in many segments at this layer; they may not arrive in the same order they were sent
• TCP places a sequential number on each segment when they were sent for receiver to reorder

Question 13

Transport Layer - UDP

Answer 13

• No waiting time for connection (connectionless)
• Stability and reliability may be missing
• Applicable when performance is more important than the ability to receive all data
• Example: streaming media

Question 14

Network Layer

Answer 14

• Functionality to determine a route between any two devices

- Data unit: packet

Question 15

Network Layer - Switching

Answer 15

• Method used to transmit data over a network to destination network devices

Question 16

Network Layer - Circuit Switching

Answer 16

• Two nodes establish a dedicated communication channel before transmitting data

Question 17

Network Layer - Packet Switching

Answer 17

• Data is broken into small units (packets)
• Each packet takes the best route available and travels independently to reach destination device
• Preferred over circuit switching as it determines the best routes between two hosts

Question 18

Network Layer - Packet Switching Advantages

Answer 18

• Efficient as each packet finds the fasteset route

- More secured since it is harder to attack multiple routes

Question 19

Network Layer - Packet Switching Disadvantages

Answer 19

• Sequence of packets are altered and requires assembly at destination device