SCTP (Stream Control Transmission Protocol) is a transport-layer protocol, similar to TCP and UDP, but designed to overcome some of the limitations of both. Originally developed to transport telephony signaling messages over IP networks, SCTP provides some distinct features:
- Multistreaming: One of the standout features of SCTP is its ability to support multiple streams within a single connection. This means that if one stream is blocked due to some reason, others can still proceed, avoiding head-of-line blocking which is a problem in TCP.
- Multi-homing: A single SCTP association (or connection) can span across multiple IP addresses from each endpoint. This provides redundancy; if one path fails, the protocol can switch to another available path.
- Reliable Data Transfer: Like TCP, SCTP offers reliable data transfer, ensuring that data is delivered to the other end without errors and in the correct order.
- Ordered and Unordered Delivery: While SCTP provides ordered delivery by default, it also supports unordered delivery upon request. This feature is particularly useful for applications that prioritize timely delivery over the sequence.
- Chunk Bundling and Fragmentation: SCTP packets consist of chunks, which can be bundled together into a single SCTP packet or fragmented as needed.
- Four-way Handshake: Unlike the three-way handshake in TCP, SCTP employs a four-way handshake mechanism to establish a connection, adding an extra layer of security to protect against certain types of attack (like SYN flood attacks).
- Built-in Heartbeat Mechanism: SCTP constantly checks the viability of the end-to-end path with a built-in heartbeat mechanism, ensuring that the path is still alive and usable.
- Protection Against Blind Attacks: SCTP incorporates a number of security features to guard against blind mass attacks.
- Flexible on Errors: In situations where a message encounters an error in transmission, SCTP allows applications to decide whether to continue or abort the message, providing more control over error management.
- Applications and Use Cases: Given its features, SCTP is widely used in telecom networks, particularly in the signaling path for Voice over IP (VoIP) and in carrying SS7 over IP (using a protocol called SIGTRAN). Its multistreaming capability also makes it suitable for web transport and file sharing protocols.
In summary, SCTP is a robust and versatile transport protocol that combines the best features of TCP and UDP while introducing several enhancements. It’s particularly relevant in contexts that require reliable, yet flexible communication, such as telecommunication systems.