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TCP Options (Cont.)
Single-byte options
- 0: End of options list, not necessary?
- 1: No-op, used for padding
Multiple-byte options
- 2: Maximum segment size (MSS)
- 4 bytes, used for path MTU discovery
- 3: Window scale
- 3 bytes, used to increase TCP’s sliding window beyond 16 bits
- 4,5: SACK
- Length varies, used for Selective Acknowledgements
- 8: Timestamp
- 10 bytes, used for round trip time (RTT) estimation and to detect wrapped sequence numbers
- RTT is hard to measure accurately due to packet loss