OSI Layer 4 - Transport Layer

Question 1

Layer 4 Overview

Answer 1

Provides transparent transfer of data between hosts

Responsible for end-to-end error recovery & flow control

Flow control

Question 2

Flow Control

Answer 2

The process of adjusting the flow of data from the sender to ensure the receiving host can handle all of it

Question 3

Session Multiplexing

Answer 3

The process by which a host is able to support multiple sessions simultaneously & manage the individual traffic streams over a single link

Question 4

Layer 4 Port Numbers

Answer 4

Layer 4 destination port number is used to identify the upper layer protocol

Sender also adds a source port to the Layer 4 header

Combination of source/destination port numbers can be used to track sessions

Question 5

TCP (Transport Control Protocol)

Answer 5

Connection oriented

Once established, data can be sent bidirectionally

Carries out sequencing to ensure segments are processed in the correct order & none are missing

Reliable - receiving host sends acknowledgements back to the sender

Performs flow control

Question 6

UDP (User Datagram Protocol)

Answer 6

Sends traffic best effort

Not connection oriented (no handshake)

Does not carry out sequencing

Not reliable; No flow control

If error detection/recovery is required, it is up to the upper layers