Overview of SCTP

SCTP provides a connection-oriented transport service between two endpoints.

SCTP provides reliable transmission, ensuring that data is delivered in order, without loss or duplication.

SCTP is full duplex.

SCTP employs a windowing mechanism to provide flow control.

SCTP provides multiple data streams between the two endpoints. Within each data stream, messages are delivered in order without loss or duplication. Independent data exchanges may be delivered over different streams—message loss in any one stream does not affect data delivery within other streams. TCP provides a single stream of data, where a message loss delays delivery of all subsequent messages. This is sometimes referred to as the head-of-line blocking problem. Minimizing the head-of-line blocking problem is the SCTP feature of greatest benefit to Diameter.

SCTP is message oriented; that is, SCTP maintains message boundaries and delivers complete messages, which SCTP calls chunks, between the upper layer protocols employing SCTP. TCP is byte-oriented; that is, TCP does not preserve data units within a transmitted byte stream, requiring the upper layer protocol to count and accumulate the bytes of each message.

SCTP understands, and makes use of, the notion of multi-homed hosts. A multi-homed host is one with more than one IP interface. At initialization time, SCTP peers exchange lists of their IP interface addresses. An SCTP message requiring retransmission can be sent to an alternate IP address, which increases the survivability of an SCTP session in the event of network failures. SCTP uses multi-homed hosts for redundancy, not for load-sharing. In contrast, a TCP session involves a single IP address at each endpoint, resulting in session failure should that single IP interface become unreachable.