SCTP Programmer's Guide

Glossary
Bundling An optional multiplexing operation, where more than one user message can be carried in the
same SCTP packet. Each user message occupies its own DATA chunk.
Chunk A unit of information within an SCTP packet, consisting of a chunk header and chunk-specific
content.
Congestion
Window
An SCTP variable that limits the data (in bytes) that a sender can send to a particular destination
transport address before receiving an acknowledgement.
Maximum
Transmission
Unit
The Maximum Transmission Unit (MTU) determines the maximum size of the packet that is
supported by a communications protocol.
Message Data submitted to SCTP by the Upper Layer Protocol (ULP).
Path The route taken by the SCTP packets sent by one SCTP endpoint to a specific destination transport
address of its peer SCTP endpoint
Receiver
Window
An SCTP variable that a sender uses to store the most recently calculated receiver window (in
bytes) of its peer. The value of rwnd indicates the space available in the receiver's inbound buffer.
SCTP
association
A protocol relationship between two SCTP endpoints. The association also contains the protocol
state information that includes verification tags and the currently active set of TSNs. An association
can be uniquely identified by the transport addresses used by the endpoints in the association.
SCTP
endpoint
The logical sender or receiver of SCTP packets. On a multi-homed host, an SCTP endpoint is
represented to its peers as a combination of a set of eligible destination transport addresses to
which SCTP packets can be sent and a set of eligible source transport addresses from which SCTP
packets can be received. All transport addresses used by an SCTP endpoint must use the same
port number but the endpoint can use multiple IP addresses. A transport address is unique to an
SCTP endpoint. Therefore, a transport address used by an SCTP endpoint must not be used by
another SCTP endpoint.
SCTP packet The unit of data delivery across the interface between SCTP and the connectionless packet network
(for example, IP). An SCTP packet contains the common SCTP header, possible SCTP control
chunks, and user data encapsulated within SCTP DATA chunks.
Slow Start
Threshold
An SCTP variable. This is the threshold (in bytes) that the endpoint uses to determine whether
to perform slow start or congestion avoidance on a particular destination transport address.
Stream A uni-directional logical channel established from one to another associated SCTP endpoint,
within which all user messages are delivered in sequence except for those submitted to the
unordered delivery service.
Stream
Sequence
Number
A 16-bit sequence number used by SCTP to assure sequenced delivery of the user messages within
a given stream. One stream sequence number is attached to each user message.
Transmission
Control Block
The transmission control block (TCB) is an internal data structure created by an SCTP endpoint
for each SCTP association. TCB contains the status and operational information for the endpoint
to maintain and manage the association.
Transmission
Sequence
Number
The transmission sequence number (TSN) is a 32-bit sequence number used by SCTP. One TSN
is attached to each chunk containing user data to permit the receiving SCTP endpoint to
acknowledge its receipt and detect duplicate deliveries.
Transport
address
A transport address is defined by the network layer address, the transport layer protocol, and
the transport layer port number. In the case of SCTP running over IP, a transport address is
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