Q1(c) · SCTP services

Stream Control Transmission Protocol (SCTP) is a reliable message-oriented transport. A relationship between endpoints is an association. Its packets contain a common header followed by chunks, which carry data or control information.

Swipe across the diagram to read its labels ↔

Diagram: SCTP association setup. Labels: SCTP association setup | SCTP association setup | Endpoint A | Endpoint B | INIT | INIT ACK + state cookie | COOKIE ECHO | COOKIE ACK | Stream 0 ordered messages; stream 1 separately ordered messages. | Multihoming supplies alternate paths, not automatic rate addition.

1. INIT → INIT ACK → COOKIE ECHO → COOKIE ACK is the normal setup. The state cookie helps avoid committing full association resources solely on an initial request.
2. Data is organized into messages on streams. Transmission Sequence Numbers track reliable chunk delivery across the association; ordering information identifies order within an ordered stream.
3. Multiple streams allow a missing message in one stream to avoid forcing every other stream to wait for that stream’s ordering. They still share association/network resources, so this does not guarantee total independence.
4. Multihoming lets endpoints advertise multiple addresses, supporting alternate paths and failover. Standard multihoming does not automatically mean all paths’ bandwidth is aggregated.
5. SCTP supplies retransmission, selective acknowledgements, receiver flow control and congestion control. Its common header is 12 bytes; chunks add their own headers and data.