It is a introduction of SCTP for software developer.

1. SCTP introduction
Richard Xiong
2013/2/8

2. Motivations
• Provide reliable transfer without sequence
maintenance.
• The stream-oriented nature of TCP is
often an inconvenience. SCTP provides
message based transfer.
• TCP is relatively vulnerable to denial-of-
service attacks, such as SYN attacks.
• …

3. History
• First implementation on 1991
• submitted to IETF on 1998. RFC 4960 defines
the protocol. RFC 3286 provides an introduction.
(RFC2960 and RFC3309 are obsoleted).
• Designed for telecom signaling transfer at first,
and used on other applications
• supported by Cisco, Linux, HP, Solaris, Alcatel-
Lucent,…
» refrence

4. Network layers
Upper layer applications
TCP UDP SCTP
IP
Link Layer
Physical Layer

5. Features
• Message-based
• Multi-homing
• Multi-stream
• Reliable transfer
• Robust and safety ( four way
handshake ,heartbeat, three way
shutdown )

6. Multi-homing
SW HUB
1 1
10.0.0.1
Alternate Path 10.0.0.3
End-point
A End-point
Z
10.0.0.65
10.0.0.68
SW HUB
2 2
Primary path

7. Multi-stream
Strm1 Strm2 Strm3
End-point SSN 1 SSN 1 SSN 1 End-point
A Z
Strm1 Strm2 Strm3
SSN 2 SSN 2 SSN 2
Strm1 Strm2 Strm3
SSN 3 SSN 3 SSN 3
SSN: Stream Sequence Number

8. Multi-stream
End-point End-point
A Z
Strm2 Strm3
Strm1 Strm2 Strm3
SSN 2 SSN 2
SSN 1 SSN 1 SSN 1
Strm1
SSN 2
Strm1 Strm2 Strm3
SSN 3 SSN 3 SSN 3

9. Multi-stream
End-point End-point
A Z
Strm2 Strm3
SSN 2 SSN 2
Strm1 Strm2 Strm3
Strm1
SSN 1 SSN 1 SSN 1
SSN 2
Strm1 Strm2 Strm3
SSN 3 SSN 3 SSN 3

10. Multi-stream
End-point End-point
A Z
Strm2 Strm3
Strm2 Strm1
SSN 2 SSN 2
SSN 3 SSN 2
Strm1 Strm2 Strm3
SSN 1 SSN 1 SSN 1
Strm1 Strm3
SSN 3 SSN 3

11. Multi-stream
End-point End-point
A Z
Strm2 Strm3
SSN 2 SSN 2
Strm2 Strm1
Strm1 Strm2 Strm3
SSN 3 SSN 2
SSN 1 SSN 1 SSN 1
Strm1 Strm3
SSN 3 SSN 3

12. Multi-stream
End-point End-point
A Z
Strm2 Strm1
Strm1 Strm2 Strm3
SSN 3 SSN 2
SSN 1 SSN 1 SSN 1
Strm2 Strm3
Strm1 Strm3
SSN 2 SSN 2
SSN 3 SSN 3

13. Multi-stream
End-point End-point
A Z
Strm3 Strm1
SSN 3 SSN 3
Strm2 Strm1
Strm1 Strm2 Strm3
SSN 3 SSN 2
SSN 1 SSN 1 SSN 1
Strm2 Strm3
SSN 2 SSN 2

14. Multi-stream
End-point End-point
A Z
Strm2 Strm1
Strm1 Strm2 Strm3
SSN 3 SSN 2
SSN 1 SSN 1 SSN 1
Strm2 Strm3
SSN 2 SSN 2
Strm1
Strm3
SSN 3
SSN 3

15. Multi-stream
End-point End-point
A Z
Strm1 Strm2 Strm3
Strm2 Strm1 SSN 1 SSN 1 SSN 1
SSN 3 SSN 2
Strm2 Strm3
SSN 2 SSN 2
Strm1
Strm3
SSN 3
SSN 3

16. Multi-stream
Strm2 Strm1
End-point SSN 3 SSN 2 End-point
A Z
Strm1 Strm2 Strm3
SSN 1 SSN 1 SSN 1
Strm2 Strm3
SSN 2 SSN 2
Strm1
Strm3
SSN 3
SSN 3

17. Multi-stream
End-point End-point
A Z
Strm1 Strm2 Strm3
SSN 1 SSN 1 SSN 1
Strm1 Strm2 Strm3
SSN 2 SSN 2 SSN 2
Strm1
Strm2 Strm3
SSN 3
SSN 3 SSN 3

18. Status of Association
CLOSED COOKIE_WAIT
COOKIE_ECHOED
SHUTDOWN-
ACK-SENT
SHUTDOWN-
RECIEVED
ESTABLISHED
SHUTDOWN-
SENT
SHUTDOWN-
PENDING

19. SCTP messages
• Data -- SACK
• INIT -- INIT ACK -- COOKIE ECHO --
COOKIE ACK
• Heartbeat -- Heartbeat ACK
• Shutdown – Shutdown ACK --
SHUTDOWN COMPLETE
• Abort

20. Setting Up
Endpoint A Endpoint Z
CLOSED CLOSED
INIT
1
COOKIE-WAIT
INIT-ACK
COOKIE-ECHO *
COOKIE-ECHOED 2
* COOKIE-ACK
ESTABLISHED ESTABLISHED
* -- User data can be attached

21. Transfer data

22. Close
Endpoint A Endpoint Z
Shutdown from application
SHUTDOWN-PENDING
Transfer remaining data
SHUTDOWN
SHUTDOWN-SENT SHUTDOWN-RECEIVED
SHUTDOWN ACK
SHUTDOWN-ACK-SENT
SHUTDOWN COMPLETE
CLOSED CLOSED

23. Packet Structure
Refer to wikipedia

24. Chunk structure--DATA chunk

25. Chunk structure--SACK chunk

26. Fault management
• Primary/alternate Path detection
• Resend mechanism
• Congestion control (RFC2581)

27. Installation on Linux (lksctp)
• Check if SCTP is installed
– grep SCTP /proc/net/protocols
– checksctp
• Download code from
http://lksctp.sourceforge.net/

28. SCTP socket API
• One-to-many style and one-to-one style are supported.
• Please read the API standard before programming, there
are lots of different features comparing to TCP socket.
• One-to-many server
– socket(PF_INET, SOCK_SEQPACKET, IPPROTO_SCTP)
– bind(sock, (struct sockaddr*)&addr, sizeof(struct sockaddr))
– setsockopt(m_fds[i].fd, SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on));
– listen(sock, 2);
– sctp_recvmsg(sock, buffer, BUFFER_SIZE, NULL, 0, NULL, &flags)
– close(sock)
• One-to-many client
– socket(PF_INET, SOCK_SEQPACKET, IPPROTO_SCTP))
– connect(sock, (struct sockaddr*)&addr, sizeof(struct sockaddr)
– send(sock, buffer, MSG_SIZE, 0)
– close(sock)
» Refer SCTP API

29. Others
• shortages
– http://datatag.web.cern.ch/datatag/WP3/sctp/tests.
• New research
– Concurrent multipath transfer

30. Reference
• http://en.wikipedia.org/wiki/Stream_Control_Transmission_Pro
• RFC4960
• RFC 2581
• http://www.youtube.com/watch?v=dIPwN-z6lVA
• http://www.sctp.org/
• http://www.sourceforge.net/projects/lksctp
• http://linux.die.net/man/7/sctp
• http://www.ibm.com/developerworks/library/l-sctp/
• http://www.linuxjournal.com/article/9784

31. Q&A