functions of transport layer

Question

which are not the functions of transport layers?

I. Transport layer breaks messages into segmentation.
II. Function of Error Control.
III. Function of flow control & congestion control.
IV. Function of multiplexing and demultiplexing sessions together.

Comments

iv seems false

Answer 1

1. yes it breaks data into segments.

2. yes it computes Checksum on TCP header and data.

3. yes it has flow and congestion control.

4. This seems incorrect. Multiplexing is a property of Transport layer, but multiplexing is done between connections at different ports. This means that an outgoing packet will be multiplexed to go through the common channel and an incoming packet will be demultiplexed so as to go to correct port/application. What is mentioned here is multiiplexing with sessions, and session management is not handled by Transport Layer.