Transport Optional Upgrade Release (TOUR) 3.0 Release Notes

What Is New in This Version

Congestion Window Validation

The estimate of the available network capacity is reflected by the congestion validation

window. Previously, this estimation becomes less accurate over time. This happens when the

capacity that was previously used by a network-limited connection is used by other traffic.

Thus the most recent knowledge of the TCP connection, regarding the state of the network

path, is not reflected when the sender is application limited.

Congestion window validation supports RFC 2861. The capacity reflected by the congestion

window is more accurate due to the following modifications:

• TCP's congestion control algorithm decays the congestion window cwnd after transitioning

from a sufficiently long application-limited period while using the slow-start threshold

ssthresh to save the previous value of the congestion window.

• An application-limited TCP sender that has not fully used the current congestion window,

does not increase the congestion window.

Internal TCP and UDP Enhancements

TOUR 3.0 contains enhancements that modify some of the internal behavior of TCP and UDP.

This results in improved network scalability, especially for high end Non-Uniform Memory

Access (NUMA) systems and under heavy load conditions.

HP-UX STREAMS Enhancement

This section provides a summary of the HP-UX STREAMS enhancement included in TOUR

3.0.

NOSYNC Synchronization

In previous STREAMS releases, one execution of the put procedure of a given queue is

supported at a time. When there are multiple requests to the same queue, the STREAMS

framework synchronizes the requests depending on the synchronization level of a module.

Synchronization ensures that only one request will be executed at a time. With high speed

I/O, the synchronization limits imposed by STREAMS may lead to a performance bottleneck.

TOUR 3.0 lifts the restriction imposed by the previous STREAMS synchronization methods.

This is done by providing a new synchronization method referred to as NOSYNC. This feature

allows multiple instances of a put procedure for a given queue, as well as the service routine

for that queue, to run concurrently. Modules and drivers are responsible for synchronizing

access to their own private data structures accordingly.