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

identifies gaps in the TSN sequence, it resends the missing DATA chunks to the
other endpoint. SCTP uses the “delayed ack” method to send the SACK chunks.
In this method, SACK is sent for every second packet, but with an upper limit on
the delay between SACKs. The frequency of sending SACKs increases to one per
received packet if gaps are detected in the TSN sequence.
• SCTP contains various congestion control algorithms, such as slow start, congestion
avoidance, fast recovery, and fast retransmit, to control the flow and retransmission
of data. In these algorithms, the receiver advertises the receive window and a
sender advertises a per-path congestion window to handle congestion. The receiver
window indicates buffer occupancy of the receiver. The per-path congestion
window manages the packets in flight. The congestion control algorithms in SCTP
are similar to that of TCP, except that the endpoints in an SCTP connection manages
the conversion between bytes sent and received and TSNs sent and received. This
is because a TSN is attached only to a chunk.
• An HP-UX application can specify a lifetime for the data to be transmitted. If the
lifetime of the data has expired and the data has not been transmitted, the data,
such as time-sensitive signalling messages, can be discarded. If the lifetime of the
data has expired and the data has been transmitted, data must be delivered to
avoid a hole in the TSN sequence
Support for Dynamic Address Reconfiguration
SCTP enables an endpoint to reconfigure the IP address information dynamically for
an existing association. When the endpoints exchange information during association
startup, the usability of SCTP also improves without modifying the SCTP protocol.
This feature is useful in computational and networking applications that add or remove
physical interface cards dynamically and need the IP address of the interface to be
changed dynamically. This feature also enables an endpoint to set the primary
destination address of a remote peer so that when the primary address of an endpoint
is deleted, the remote peer is informed of the address to which the data must be sent.
To enable SCTP to reconfigure IP addresses dynamically, an SCTP packet contains the
following chunk types:
Address Configuration Change
Chunk (ASCONF)
The ASCONF chunk communicates the
configuration change requests that must be
acknowledged, to the remote endpoint.
Address Configuration
Acknowledgment (ASCONF-ACK)
The ASCONF-ACK chunk is used by the receiver
of an ASCONF chunk to acknowledge the
reception of the ASCONF chunk.
Reporting Packet Drops to an Endpoint
When a packet drop occurs because of an error other than congestion, an endpoint can
mistakenly interpret the packet drop as an indication of congestion in the network. The
8 SCTP Release Notes