ECM 1413 Transport Layer

Question 1

TCP (Transmission Control Protocol)

Answer 1

• Connection-oriented protocol, RFC 793^1
• Reliable delivery with higher overhead and latency
• Examples - HTTP, FTP, Telnet and SMTP

Question 2

UDP (User Datagram Protocol)

Answer 2

• Connectionless protocol, RFC 768^2
• Unreliable (best effort delivery), minimal overhead and latency
• DHCP, RIP, TFTP, Online games, Video Streaming and VoIP

Question 3

TCP and UDP Shared Functions

Answer 3

• Segmentation and Reassembly
• Conversation Multiplexing using port number
• Error detection

Question 4

Additional TCP Functions

Answer 4

• Connection Establishment (3-way handshake)
• Connection Management: Reliability (ack), Flow control and Error correction
• Connection Termination (4-way handshake)

Question 5

What does the transport layer do

Answer 5

The transport layer divides the data into pieces and adds a header delivery over the network

Question 6

UDP header provides for

Answer 6

Source and destination (ports)

Question 7

TCP header provides for

Answer 7

• Source and destination (ports)
• Sequencing for same-order delivery
• Acknowledgement of received segments
• Flow control and congestion management

Question 8

Types of networking ports (OSI L4)

Answer 8

• Well-known ports (0 to 1023) - reserved for well-known services
• Registered Ports (1024 to 49151) - assigned for user processes & others
• Dynamic or Private Ports (49152 to 65535) - Dynamically chosen by a client when initiating a connection to a server

Question 9

Well-known port examples

Answer 9

telnet(TCP/23)
SMTP(TCP/25)
HTTPS(TCP/443)
RIP(UDP/520)

Question 10

Registered Ports examples

Answer 10

MySQL(TCP/3306)
HTTP Alternate (8080)

Question 11

Netstat

Answer 11

examines the open connections on a host

Question 12

Segmentation of PDU allows session multiplexing. What is session multiplexing

Answer 12

multiple application can use the network at the same time

Question 13

Benefit of data segmentation

Answer 13

facilitates data carriage by the lower network layers

Question 14

Difference between TCP and UDP on out-of-order packets

Answer 14

(UDP) Out of order datagrams are not re-ordered. Lost datagrams aren’t resent

(TCP) Data is divided into segments. Having taken different routes to the destination, segments arrive out of order. TCP re-orders the segments to the original order

Question 15

TCP 3-way handshake

Answer 15

a process which is used in a TCP/IP network to make a connection between the server and client. It is a three-step process that requires both the client and server to exchange synchronization and acknowledgment packets before the real data communication process starts.

Question 16

TCP message types

Answer 16

Syn: Used to initiate and establish a connection. It also helps you to synchronize sequence numbers between devices. (Synchronization)

ACK: Helps to confirm to the other side that it has received the SYN. (acknowledgement number)

SEQ: Sequence number

SYN-ACK: SYN message from local device and ACK of the earlier packet.

FIN: Used to terminate a connection.

Question 17

TCP Connection Establishment Between two systems A and B

Answer 17

1) A sends SYN request to B
2) B sends ACK response and SYN request to A
3) A sends ACK response to B

Question 18

Connection Termination

Answer 18

1) A Sends FIN request B
2) B Sends ACK response to A
3) B Sends FIN response to A
4) A Sends ACK response to B