SCTP Concepts

SCTP is a connection-oriented transport protocol that overcomes some of the limitations of both TCP and UDP that prevent reliable transfer of data over IP-based networks (such as those used by telephony systems and carrier networks). The ‘Stream’ in SCTP refers to the sequence of user messages or packets that are considered at the same time to be individual objects and also treated as a whole by networked systems. SCTP is less vulnerable to congestion and flooding due to more advanced error handling and flood protection built into the protocol.

SCTP features as compared to TCP and UDP

Feature	SCTP	TCP	UDP
State required at each endpoint	yes	yes	no
Reliable data transfer	yes	yes	no
Congestion control and avoidance	yes	yes	no
Message boundary conservation	yes	no	yes
Path MTU discovery and message fragmentation	yes	yes	no
Message bundling	yes	yes	no
Multi-homed hosts support	yes	no	no
Multi-stream support	yes	no	no
Unordered data delivery	yes	no	yes
Security cookie against SYN flood attack	yes	no	no
Built-in heartbeat (reachability check)	yes	no	N/A

All of these features are built into the design of the Protocol, and the structure of SCTP packets and networks. The FortiGate unit interprets the traffic and provides the necessary support for maintenance and verification features, but the features are not FortiGate specific. These features are documented in greater detail below.