| TCP option 8, Time Stamp |
Description:
RFC 1323, pg. 1:
The timestamps are used for two distinct mechanisms: RTTM (Round Trip Time Measurement) and PAWS (Protect Against Wrapped Sequences).
| MAC header | IP header | TCP header | TCP option | Data |
TCP Option 8:
| 00 | 01 | 02 | 03 | 04 | 05 | 06 | 07 | 08 | 09 | 10 | 11 | 12 | 13 | 14 | 15 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Kind | Length | ||||||||||||||
| Timestamp Value
::: |
|||||||||||||||
| Timestamp Echo Reply
::: |
|||||||||||||||
Kind. 8 bits. Set to 8.
Length. 8 bits. Set to 10.
Timestamp Value (TSval). 32 bits.
This field contains the current value of the timestamp
clock of the TCP sending the option.
Timestamp Echo Reply (TSecr). 32 bits.
This field is only valid if the ACK bit is set in
the TCP header; if it is valid, it echos a timestamp value that was sent by the
remote TCP in the TSval field of a Timestamps option. When TSecr is not valid,
its value must be zero. The TSecr value will generally be from the most recent
Timestamp option that was received; however, there are exceptions that are
explained below. A TCP may send the Timestamps option (TSopt) in an initial SYN
segment (i.e., segment containing a SYN bit and no ACK bit), and may send a
TSopt in other segments only if it received a TSopt in the initial SYN
segment for the connection.
Glossary:
RFCs:
[RFC 1323] TCP Extensions for High Performance.
Obsolete RFCs:
[RFC 1072] TCP Extensions for Long-Delay Paths.
[RFC 1185] TCP Extension for High-Speed Paths.