SCTP Programmer's Guide

Table 1-1 Chunk Types (continued)
DefinitionChunk
Tests the connectivity of a specific destination
address in the association.
Heartbeat Request (
HEARTBEAT)
Acknowledges the receipt of the HEARTBEAT
chunk.
Heartbeat Acknowledgement (
HEARTBEAT ACK)
Informs the peer endpoint to close the
association. The ABORT chunk also informs the
receiver of the reason for aborting the
association.
Abort Association (ABORT)
Reports error conditions. The ERROR chunk
contains parameters that determine the type
of error.
Operation Error (ERROR)
Triggers a graceful shutdown of an association
with a peer endpoint.
Shutdown Association (
SHUTDOWN)
Acknowledges the receipt of the SHUTDOWN
chunk at the end of the shutdown process.
Shutdown Acknowledgement
(SHUTDOWN ACK)
Concludes the shutdown procedure.Shutdown Complete (
SHUTDOWN COMPLETE)
Chunk Flag
This field contains the flags, such as U (unordered bit), B (beginning
fragment bit), and E (ending fragment bit). Usage of this field
depends on the chunk type specified in the chunk type field. Unless
otherwise specified, SCTP sets this field to 0 while transmitting the
packet and ignores the chunk flag on receipt of the packet.
Chunk Length This field represents the size of the fields chunk type, chunk flag,
chunk length, and chunk value, in bytes.
Chunk Data This field contains the actual information to be transferred in the
chunk. The usage and format of this field depends on the chunk
type.
The number of chunks in an SCTP packet is determined by the MTU size of the
transmission path. Multiple chunks can be bundled into one SCTP packet except the
INIT, INIT ACK, and SHUTDOWN COMPLETE chunks. The SCTP packet size must not
be more than the MTU size.
The SCTP packet format supports bundling of multiple DATA and control chunks into
a single packet, to improve transport efficiency. An application can control bundling,
to avoid bundling during initial transmission. Bundling occurs on retransmission of
DATA chunks, to reduce the possibility of congestion. If the user data does not fit into
one packet, SCTP fragments data into multiple chunks.
For more information on the SCTP packet format, see RFC 2960 (Stream Control
Transmission Protocol).
SCTP Architecture 25