You’ve probably heard things like:
- TCP is reliable, UDP isn’t
- TCP needs a connection, UDP doesn’t
UDP Lets You Broadcast, TCP Doesn’t
Broadcasting means sending one message to all devices on a network at the same time.
With UDP, a device can do exactly that.
TCP needs a separate connection for each device, so true broadcasting isn’t possible.
TCP Eats More Bandwidth, UDP Doesn’t
UDP has a fixed 8-byte header, keeping it light and fast.
TCP’s header starts at 20 bytes and can go up to 60 bytes with extra options.
Fun fact: For very tiny messages, TCP’s header can be bigger than the actual data, eating bandwidth.
TCP Recovers, UDP Moves On
TCP does this using retransmission — acknowledgments and sequence numbers.
- Retransmission resending lost data so nothing gets lost
- Sequence number each piece of data is numbered so the receiver knows the order
- Acknowledgment (ACK) receiver tells the sender, “I got this packet #3!”
Example
- You send packets #1, #2, #3, #4
- Packet #2 gets lost
- Receiver sends ACKs: Got #1, #2 missing, Got #3, Got #4
- Sender retransmits #2
- Receiver now has all packets in order
In UDP, if packet #2 is lost,
there’s no retransmission (means no built-in) it’s gone.