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Protocols For Packet Transfer
Connectionless
- Packets of arbitrary size are dispatched as soon as application provides data.
- Nobody knows if they arrived or not.
- Example: User Datagram Protocol
Connection-Oriented
- A connection is first established between source and destination.
- Checks to make sure that everything is transferred properly (sequence numbers, retransmission, timeouts)
- Example: Transmission Control Protocol
Notes:
Connectionless protocols (like UDP) are very fast, inexpensive (in terms of processing needed) and easy to deploy.
Connection-oriented protocols (like TCP) provide for reliability, flow and error control, so they have to perform lots of checks:
Checksums, to make sure that the packets reached the other side unharmed
Sequence number counting, to make sure that packets reached the destination in the right order, and that all of them reached it.
Dynamic retransmission timing, which decides how long to wait to re-send a packet that seems to have been lost during transit (not acknowledged by destination)
These protocols are extremely hard to design and implement properly, and known attacks and problems exist with the current TCP/IP implementation.