Transport Optional Upgrade Release (TOUR) 3.0 Release Notes

What Is New in This Version

requests simultaneously. This enhancement improves network throughput for high speed

network interfaces such as multi-port Gigabit cards in an Auto Port Aggregation (APA)

configuration or 10Gigabit cards.

To realize the performance gains of NOSYNC, all the STREAMS modules (i.e. IPFilter and

DLPI) between IP and the LAN driver must also be NOSYNC enabled. Refer to the NOSYNC

Software Dependencies under Installing TOUR 3.0 for more information on IPFilter and

DLPI NOSYNC-aware products.

Forward-Retransmission Timeout (F-RTO)

When a retransmission timeout occurs, the last window of data is retransmitted. Spurious

retransmission timeouts occur, especially due to mobile network devices switching between

access points. In such cases, the unnecessary retransmission of the last window of data

degrades TCP performance.

TOUR 3.0 uses the F-RTO algorithm supported by RFC 4138 to detect spurious timeouts.

F-RTO is a TCP sender-only algorithm that does not require any TCP options to operate.

The F-RTO algorithm also responds to a spurious timeout. When the Retransmission Timeout

(RTO) expires, F-RTO retransmits the first unacknowledged segment and monitors the

incoming acknowledgments to determine if the timeout was spurious. Then, F-RTO

determines whether to send new segments or retransmit the unacknowledged segments. The

algorithm effectively reduces additional unnecessary retransmissions. The impact of spurious

timeouts on TCP performance is reduced. Refer to the RFC at

http://www.ietf.org/rfc/rfc4138.txt?number=4138 for more details.

Alternatively, TCP Congestion Window Validation supported by RFC 2861 can be used to

respond to spurious timeouts detected by F-RTO. Refer to the RFC at

http://www.ietf.org/rfc/rfc2861.txt?number=2861 for details.

F-RTO is disabled by default. To enable F-RTO, TOUR 3.0 provides the following new ndd

tunable:

tcp_frto_enable

The values for tcp_frto_enable are:

0 The local system does not use F-RTO. This is the default value.

1 The local system uses the F-RTO algorithm for detecting and responding to

spurious timeouts.

2 The local system uses the F-RTO algorithm for detecting spurious timeouts.

The response algorithm is based on TCP Congestion Window Validation.