There are two protocalls that operate in the transport layer: TCP and UDP.
TCP
- Is reliable and connection oriented
- Breaks data into segments
- Numbers the segments through sequencing
- Assembles the segments at the destination
- Resends segments if lost
UDP
- Is connectionless and does not verify
- UDP just sends the data and hopes it gets there. It thinks the application will do the checking.
- Is used for voice and video
- Has a much smaller header that TCP
Because UDP doesn’t do any checking the rest of this section mostly deals with TCP.
Three Way Handshake
- ISN – Initial Sequence Number
- SYN – Synchronize
- ACK – Acknowledgement
Session Multiplexing
- Assigns unique numbers to different sessions of the same application so that they don’t get mixed up with each other
Segmentation
- Breaking up the data into smaller pieces so that it can be sent
- TCP – Makes sure that the data fits the size of the MTU
- UDP – Does no checking because it expects the segments to be the right size already
Flow Control
- The size of the window is set in the ACK header
- The size of the window is the number of bytes that the receiving end and receive at a time
- The window size can be made smaller if there is congestion on the network (sliding window)
Acknowledgment
- Forward Reference Acknowledgement – when the receiver tells the sender which bytes to send next.
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