Layer 4 (Transport Layer)

Question 1

What is Flow Control?

Answer 1

Flow control is the process of adjusting the flow of data

from the sender. Ensures that the receiving host can handle it.

Question 2

What is Session Multiplexing?

Answer 2

Session Multiplexing is the process which a host can support multiple session and manage individual traffic.

Question 3

What are the two most commonly used protocols in the Layer 4?

Answer 3

TCP(Transmission Control Protocol)

UDP (User Datagram Protocol)

Question 4

What does the Layer 4 do?

Answer 4

• Provides transparent transfer of data between host.

- It is responsible for end to end recovery, and flow control.

Question 5

TCP is…

Answer 5

• Connection Oriented : Once a connection is established, data can be sent bi-directionally on that connection.
• Carries out sequencing: It ensures all segments get carried out in the correct order and none are missing.
• TCP IS RELIABLE

Question 6

What is the TCP Header?

Answer 6

1. Source Port (16 bits) / Destination Port (16 bits)
2. Sequencing Number (32 bits)
3. Acknowledgement Number (32 bits)
4. a) Header length(4-bits)
   b) Reserved (6-Bits)
   c) Code Bits (6-Bits)
   d) Window (16 bits)
5. Checksum (16 bits) / Urgent (16bits)
6. Options (0 or 32 if any)
7. Data (Varies)

Question 7

What does the UDP do?

Answer 7

• Sends traffic at best effort

- Best usage is for low latency devices that reliability is not an issue.

Question 8

UDP Is…

Answer 8

• Not connection oriented
• Does not carry out sequencing to ensure all segments are carried out in the correct order and if any are missing.
• Not Reliable

Question 9

What is the UDP Header?

Answer 9

1. Source Port / Destination Port
2. Length / UDP Checksum
3. Data

Question 10

What are five common TCP applications and their port numbers?

Answer 10

1. FTP (Port 21)
2. SSH -Secure Shell (Port 22)
3. Telnet (Port 23)
4. HTTP (Port 80)
5. HTTPS (Port 443)

Question 11

What are two common UDP applications and their port numbers?

Answer 11

1. TFTP (Port 69)

2. SNMP (Port 161)

Question 12

TCP and UDP Applications…

Answer 12

DNS (Port 53)

Question 13

What does TFTP stand for and What Port Number is it? Is it supported by TCP or UDP?

Answer 13

Trivial File Transfer Protocol
Port 69

It is supported by UDP.

Question 14

What does SNMP stand for? What port number is it?

Answer 14

Simple Network Management Protocol
Port 161

It is supported by UDP.