TOUR Transition Release Notes (September 2004)(11i v1 and 11i v2)

Transport Optional Upgrade Release Transition Release Notes
Announcement
12
Forward-Retransmission Timeout (F-RTO) This feature was introduced in TOUR 3.0.
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.
The transition patches PHNE_35351 (for HP-UX 11i v1) and PHNE_35765 (for HP-UX 11i v2
September 2004) implement the F-RTO algorithm supported by RFC 4138 to detect spurious
timeouts.
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, the following new ndd tunable is provided:
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.
New Parameter for the route Command This feature was introduced in TOUR 3.0.
Previously, the route command had no routing ioctls to set the source IP address of an
interface. The kernel always determined a default interface for a route. Users could neither
change this specification, nor force the route to be associated with a specific interface.
The transition patches PHNE_35351 (for HP-UX 11i v1) and PHNE_35765 (for HP-UX 11i v2
September 2004) implement the enhanced route command that has the following syntax:
route [-f] [-n] [-p pmtu] add [net|host] destination [netmask mask] gateway
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