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Data type


Default value


0 | 1 | 2 | 3



Determines whether TCP uses the timestamping and window scaling features described in RFC 1323, TCP Extensions for High Performance.

Window scaling permits TCP to negotiate a scaling factor for the TCP receive window size, allowing for a very large TCP receive window of up to 1 GB. The TCP receive window is the amount of data the sending host can send at one time on a connection.

Timestamps help TCP measure round trip time (RTT) accurately in order to adjust retransmission timeouts. The Timestamps option provides two timestamp fields of 4 bytes each in the TCP header, one to record the time the initial transmission is sent and one to record the time on the remote host.

This entry is a 2-bit bitmask. The lower bit determines whether scaling is enabled; the higher bit determines whether timestamps are enabled. To enable a feature, set the bit representing the feature to 1. To disable a feature, set its bit to 0.



0 (00)

Timestamps and window scaling are disabled.

1 (01)

Window scaling is enabled.

2 (10)

Timestamps are enabled.

3 (11)

Timestamps and window scaling are enabled.

Note Image Note

Windows 2000 does not add this entry to the registry. You can add it by editing the registry or by using a program that edits the registry.

Tip Image Tip

For more information about RFC 1323, see the Request for Comments (RFC) link on the Web Resources page.

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