# Transmission control in TCP

There are two main components of transmission control. These tackle two distinct problems that a connection may have:

• Flow control in TCP : Allows the receiver to control how much data gets sent to it in one go, and
• Congestion control in TCP : Allows probing of the network to guarantee maximum network utilisation without disruption to service.

These both ultimately effect the number of unacknowledged messages allowed to be sent in ARQ . This will be the minimum of the two window sizes provided by the above controls.

UDP lets the Application layer hand transmission control. Whereas TCP sees this a a widely shared feature that it can abstract away.