SCTP: State of the art in Research, Products, and Technical Challenges

1. SCTP: State of the art in Research, Products, and Technical Challenges Mohammed AtiquzzamanSchool of Computer ScienceUniversity of Oklahoma. Email: atiq@ieee.orgWeb: www.cs.ou.edu/~atiq Co-Author: Shaojian Fu

2. Introduction • Stream Control Transmission Protocol (SCTP) • proposed by IETF in October 2000 to accomplish SS7 signaling transport. • SCTP should be useful in a wider range of applications instead of just the signaling transport area. • SCTP has received much attention from the research community due to its attractive new features • multi-streaming • multi-homing. Objectives: Update readers with recent research activities related to SCTP, products, and open problems

3. Outline • Main features of SCTP • Comparison of SCTP and TCP • State-of-the-art in SCTP research activities • SCTP research tools • Commercial SCTP products • Open issues and research challenges

4. Stream Control Transmission Protocol

5. Stream Control Transmission Protocol • SCTP (RFC 2960) is being developed by IETF as the next generation transport protocol. • Reliable: retransmission of lost packets, ack of packets. • In-order delivery: re-sequencing at the destination. • Transport layer protocol which operates on top of an unreliable connectionless network layer such as IP. • Transparent to IPv4 or IPv6 • Key unique features: • Multistreaming: Support for multiple logical streams to improve data transmission throughput; • Multihoming: Support for multiple network interfaces to achieve high availability; .

6. Upper layer applications TCP, UDP, SCTP IP Link Layer Physical Layer SCTP in the Internet Protocol suite

7. Multi-streaming and Multihoming

8. Illustration of SCTP multihoming

9. SCTP Multi-streaming

10. Web page transfer with multi-streaming

11. Differences between TCP and SCTP

12. State-of-the-art in SCTP RESEARCH

13. Congestion Control • Can SCTP co-exist fairly with TCP in a shared network? • Study 1: SCTP and TCP share a WAN link [Jungmaier:2000] • SCTP and TCP shared the bandwidth fairly. • TCP faced no adverse effect due to the presence of SCTP. • Study 2: SCTP and TCP share Satellite link [Alamgir, et.al. 2002] • TCP and SCTP shared the satellite link fairly • TCP achieved slightly higher throughput because of its advanced retransmission policy Both studies demonstrated that SCTP can coexist with TCP

14. Multi-homing • Fast failure recovery for high-availability, seamless switchover at transport layer vs. switchover at user-layer [Jungmaier:2002]. • Transport layer switchover based on multi-homing • User layer switchover using two associations Transport layer switchover resulted in smoother transition by having a lower average segment delay.

15. Multi-streaming • Transport multimedia traffic over lossy network [Caro:2001,Atiquzzaman:2002] • Eliminate HOL effect by utilizing inter-stream independence. • Sensitivity of transport layer throughput to network loss decreased compared with TCP. • User satisfaction on the picture quality increased. • Reduced receiver buffer requirements.

16. Application in Wireless/Mobile Environment Make SCTP well suited for wireless channel characteristics and mobility issues arising from 3G and beyond wireless networks. • Delay spikes are common in wireless network. Like TCP, SCTP also suffers Spurious Timeout after the delay spike, but SACK can be used to make SCTP free of Spurious Fast Retransmissions [Fu:2002]. • SCTP in Mobile-IP networks (as a dumb transport protocol) can achieve a better performance than TCP-SACK by exploiting SCTP's support of large number of GapACK blocks in its SACK [Fu:2003]. • SCTP multi-homing can be used to reduce the network load caused by triangular routing after a Mobile handover [Noonan:2002]. • SCTP over ad-hoc networks, e.g. IEEE 802.11 network.

17. SCTP Products

18. Free Software • Reference Implementation: Kernel module for BSD/OS 4.3, FreeBSD 4.7, NetBSD 1.6, and OpenBSD 3.2 available. Work on Solaris discontinued. • SCTP patch for the ns-2 simulator: provides the core SCTP features (as specified in RFC 2960) including multi-streaming, multi-homing, congestion-control, chunk bundling, etc. • Linux Kernel SCTP (LKSCTP): An open source implementation under GNU GPL (General Public License) to provide an SCTP module in Linux kernel 2.6.0-test4.

19. Commercial Products • Geared towards providing a SS7 signaling transport solution. • Cisco ITP in IOS 12.2. • Adax APS-SCTP/T • Ulticom SignalWare • Dataconnection DC-SCTP

20. Future SCTP Research

21. Issues and Challenges • Meeting the Reliability Requirements of the SS7 Standard: • The time needed to switch to another link when link failure occurs should be less than 800ms • The availability of communication service between two signaling points should be at least 99.998%. • No more than one in 107 messages may be lost at Message Transfer Part (MTP) layer • Performance in wireless networks: • SCTP is designed with wire-line environments in mind; wireless mobile networks encounter higher Bit Error Rates (BER) and more frequent delay spikes which will cause SCTP’s poor performance • Dynamic Address Reconfiguration: • Useful in mission-critical applications or mobile environments by supporting service reconfiguration without interrupting on-going data transfers.

22. Acknowledgements • National Aeronautics and Space Administration (NASA) • William Ivancic, NASA. • Further Information Dr. Mohammed Atiquzzaman atiq@ou.edu, (405) 325 8077 • These slides are available at www.cs.ou.edu/~atiq Thank you