SCTP Release Notes HP-UX 11i v2, HP-UX 11i v3 (5900-1238, October 2010)

that must not be transmitted or retransmitted by
the sender.
Support for ECN-Nonces in SCTP
SCTP supports the Explicit Congestion Notification (ECN)-nonce congestion control
method to detect congestion in a network. The ECN-nonce is a modification of the ECN
signaling mechanism, which uses packet marking to indicate congestion instead of
dropping the packets. Similar to ECN, ECN-nonce uses the ECN-Capable Transport
ECT(0) and ECT(1) code points, the IP header flag, the cwr, and the ECNE bits to
handle and report congestion.
The drawback in ECN is that a poorly implemented receiver or an intermediate network
element, such as router, firewall, intrusion detection system, can erase the ECN-Echo
(ECNE) flag that provides congestion signal to the sender. This is because ECN does
not contain mechanisms to avoid network elements from clearing the ECNE flag.
ECN-nonce overcomes this problem by using a nonce sum (NS). The sender randomly
generates a single bit nonce and encodes it in the ECT codepoints, ECT(0) or ECT(1).
To indicate congestion in the network, routers overwrite the ECT codepoints with the
CE bit. The nonce sum (NS) is a cumulative one bit addition of the nonces received
from the receiver. The receiver calculates the nonce sum and returns it in the NS flag
of the SACK chunk. The sender verifies the value of the NS flag in the SACK chunk. An
incorrect nonce sum implies that one or more nonces are missing at the receiver, because
all the nonces are required to calculate the correct nonce sum. If an incorrect nonce
sum is received by the sender without ECNE signals, the sender can infer that the
receiver is concealing congestion notifications.
The ECN-nonce support in SCTP includes the following:
• A single nonce-supported parameter in the INIT or INIT-ACK chunk that is
exchanged during the association establishment, to indicate to the peer whether
ECN-nonce is supported at both endpoints.
• A single bit flag in the SACK chunk called the Nonce Sum (NS).
For more information about ECN-nonce in SCTP, see the SCTP Programmer's Guide
available at:
HP-UX 11i v2 Networking Software
HP-UX 11i v3 Networking Software
Installing SCTP
This section describes how to install SCTP. It also lists the prerequisites for installing
SCTP.
This section addresses the following topics:
• “Prerequisites” (page 11)
• “Installation Instructions” (page 11)
10 SCTP Release Notes