Transport Optional Upgrade Release (TOUR) 1.0 Release Notes

What Is in This Version

TOUR 1.0 includes the following components:

• Base HP-UX Transport with IPv4 enhancements and IPv6

• Point-to-Point Protocol (PPP) enhancements (PPPv6 and PPPoE)

• Router Advertisement Daemon

Features Overview

The features of the components bundled within TOUR 1.0 are as follows:

• IPv4 Features: TOUR 1.0 supports the following IPv4 feature (above base HP-UX 11i

v1):

— Limited Transmit: This is a TCP loss recovery enhancement. The enhancement is

transparent to users. Under certain circumstances, users will experience performance

improvement. For more information, see RFC 3042, “Enhancing TCP’s Loss Recovery

Using Limited Transmit.”

This RFC speciﬁes a new Transmission Control Protocol (TCP) mechanism that can

be used to more effectively recover lost segments when the congestion window of a

connection is small, or when a large number of segments are lost in a single

transmission window.

The Limited Transmit algorithm calls for sending a new data segment in response to

each of the ﬁrst two duplicate acknowledgments that the sender receives.

Transmitting these segments increases the probability that TCP can recover from a

single lost segment using the fast retransmit algorithm, instead of using a costly

retransmission timeout. Limited Transmit can be used both in conjunction with, and

in the absence of, the TCP selective acknowledgment (SACK) mechanism.

• IPv6 Features: Starting with TOUR 1.0,the following additional IPv6 transport features

are available:

— Multicast Listener Discovery (MLD): MLD is speciﬁed in RFC 2710. It is a protocol,

which is used by IPv6 routers to discover the presence of multicast listeners (that is,

nodes wishing to receive multicast packets) on its directly attached links. In addition,

it is used to discover the speciﬁc multicast addresses that are of interest to the

neighboring nodes. For more information, see RFC 2710, "Multicast Listener

Discovery (MLD) for IPv6".