1. Stream Control Transmission Protocol 網路前瞻技術實驗室 陳旻槿

2. Outline Introduction SCTP Association SCTP Feature Format of SCTP Message User Data Transfer Summary

3. Introduction What is SCTP ? 1.Originally designed to support PSTN signaling messages over IP Networks 2.Similar to TCP and UDP, the Stream Control Transmission Protocol is another general-purpose transport protocol for IP network data communications. 3.Standard-RFC2960

4. Introduction The primary purpose of SCTP is to provide a reliable end-to-end message transportation service over IP-based network. –TCP data transportation services is byte- oriented. Like TCP and UDP,SCTP belong to transport layer in the IP architecture.

5. Introduction Motivation –Many applications need reliable message delivery – they do so by delineating a TCP stream –TCP provides both strict-ordering and reliability – many applications may not need both SCTP provides both ordered and unordered services, rather than the strictly ordered service in TCP or unordered service in UDP.

6. Introduction Although SCTP was originally designed to carry telephony signaling over IP networks, in recent years it has evolved to become a general purpose transport protocol like TCP and UDP. In the future, SCTP may further evolve to replace TCP and UDP.

7. SCTP Association SCTP is a connection-oriented transport protocol. –This means that before any application data can be transported from one SCTP endpoint to another, the two SCTP endpoints must go through a setup procedure to establish a communication relationship by exchanging state information. –This communication relationship is called an SCTP association.

8. SCTP Association It uses a four-way handshake to set up an SCTP association.

9. Circumvent DOS attack

10. SCTP Feature SCTP Multi-homing Unlink TCP communication endpoint, which can only have a single IP address. –SCTP endpoint can effectively control and aggregate multiple IP address on the multi-homed machine for sending and receiving data. The multi-home SCTP endpoint can be represented list of SCTP transport address on the machine that share a signal SCTP port.

11. SCTP Feature SCTP supports multi-homing, which allows more than one IP addresses to be assigned to a host. –One of the IP addresses is set to be the primary address. –When there is a connection failure between the primary addresses, the traffic is sent to another (secondary) address that is available.

13. SCTP Feature SCTP Multiple Stream The streams within an SCTP association allow the endpoints to transfer multiple sequences of messages at the same time, without introducing interdependencies among different message sequences.

14. SCTP Feature SCTP avoids the Head-Of-Line (HOL) queue blocking problem among different streams. –Within an SCTP association, the messages transferred in one stream would not be blocked by the losses or delays of the messages in other streams.

16. SCTP Feature Acknowledgment chunk SCTP detects packet losses by checking the blocking gaps in its Selective Acknowledgment (SACK) chunks. Compared to TCP, SCTP allows a larger number of SACK blocks to be reported in each SACK.

17. SCTP Feature SCTP makes more use of Selective Acknowledgements (SACK’s) –These contain more information about the packets that were received successfully –Generally, this improves performance SCTP can transmit on a lost packet using a different IP address –It reduces congestion

18. Format of SCTP Message

19. SCTP common header 1.Source Port Number This field contains the sender endpoint’s SCTP port number. 2.Destination Port Number This field contains the SCTP port number of the destination endpoint (that is, the intended receiver of SCTP packet).

20. Format of SCTP Message Verification tag –It provides a discrimination method that prevent an SCTP packet from a previous incarnation of an association (between the same pair of endpoint) from being mistaken for an SCTP packet belonging to current association. –It provides a protection against a blind attacker injecting data into an existing association. Checksum –This value provides a data integrity check on the transport level to ensure the correct transportation of SCTP packet.

21. Format of SCTP Message SCTP DATA Chunk The DATA Chunk is the container for all the user data transferred in SCTP.

22. Format of SCTP Message Chunk type –Type=0x00 ， This chunk carries a user data payload. Chunk flags –The lower three bits of chunk flags are In the DATA chunk, while upper five bits are reserved and are required to be set to zero. –Lower three bits are named the U,B and E. U set=0 unordered data chunk U set=1 ordered data chunk Chunk length –This field is variable because it is dependent on the length of the user data.

23. Format of SCTP Message

24. TSN –This field contains the transmission sequence number. Stream Identifier –This field indication for while stream sequence number the user data is destined. Stream sequence number –This field indicates what stream sequence number this user data contains. Payload protocol identifier –This field is a user-supplied value that is passed in every DATA chunk. User Data –This is the payload data.

25. User Data Transfer The size threshold used to determine whether a user message is too big, and thus should be fragmented, is normally the current Path Maximum Transmission Unit (PMTU). –When the user message is small enough, the conversion is simply to add a DATD chunk header to the message, froming a signal DATA chunk. –When user message is bigger than a certain threshold, the message will be first broken into several small parts, and then each of them will be converted into separate DATA chunk.

27. User Data Transfer

29. Summary Important features of SCTP –Message-Oriented Multi-homing –Multi-stream –Partial ordering –Security Mechanism (Cookie)