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Stcn presentation

  1. 1. SCTP Presented by: Sutanu Paul CSI 13023 MTECH(IT) TEZPUR UNIVERSITY
  2. 2. CONTENTS • What is SCTP? • Why not TCP? • SCTP Services -Multiple Streams -Multihoming -Full-Duplex Communication -Connection-Oriented Service -Reliable Service • • • • • SCTP Features FOUR Way Hand Shake Graceful Shutdown Flow Control Mechanism in SCTP Congestion Control Mechanism in SCTP
  3. 3. SCTP Stream Control Transmission Protocol (SCTP) is a new reliable, message-oriented transport-layer protocol. It combines the best features of UDP and TCP. • Why TCP can’t be used as a common Protocol? TCP provides reliable data transfer and strict order-of-transmission delivery. _ The problem of this approach is that a loss at any point in the stream blocks the delivery of the rest of the data. – some applications(real time data such as audio or video ) need reliable transfer but not sequence maintenance. They suffer head-of-line (HOL) blocking. • TCP was never designed to be multi-homed – A multi-homed host is one that has several network cards, and can make use of a number of IP addresses at the same time. • TCP is relatively vulnerable to denial of service attacks. – This kind of attacks try to make unavailable one service, by exhausting the resources it uses. One of such well-known attacks is the so-called SYN attack.
  4. 4. SCTP SERVICES • • • • • Multiple Streams Multihoming Full-Duplex Communication Connection-Oriented Service Reliable Service
  5. 5. Multi-stream SCTP allows multistream service in each connection ,which is called association in SCTP terminology. If one of the streams is blocked, the other streams can still • SCTP is a message-oriented, deliver their data. The idea is similar to multiple lanes reliable lane can be used for a different type on a highway, eachprotocol that combines the of traffic. • best features of UDP and TCP.
  6. 6. Multihoming The following figure depicts a typical multi-homed host • A multi-homed host is one that has several network cards, and can make use of a number of IP addresses at the same time. App-3 App-2 App-1 OS NI-1 NI-2 NI-3
  7. 7. Multihoming (contd) • A TCP connection involves one source and one destination IP address i.e. even if the sender or receiver is a multihomed ,only one of these IP addresses per end can be utilized during the connection. • An SCTP association on the other hand support multihoming service. The sender and receiver can define multiple IP addresses in each end for an association • In this fault-tolerant approach ,when one path fails, another interface can be used for data delivery without interruption.
  8. 8. SCTP Endpoint : An SCTP endpoint can be represented as a list of SCTP transport addresses with the same port: endpoint = [, : 80] [ : 2223] Application-1 NI-1 NI-2 NI-3
  9. 9. SCTP Endpoint (contd) • Application-1 has bound one IP address of the host with the port 2223. • If a new application is started Application-2, it may legally bind [ : 2223] or [ : 2223] or even [, : 2223] • The new application will NOT be able to bind the existing SCTP Transport address that Application-1 has bound i.e.: [ : 2223]
  10. 10. • Client and server are connected to two networks with two IP addresses each .They can make an association ,using four different pairs of IP address. • However in current implementations only one pair of IP addresses can be chosen for normal communication ;the alternative is used if the main fails. i.e. At present, SCTP does not allow load sharing between different path. Currently, it is only for fault-tolerance. 10
  11. 11. SCTP SERVICES(contd) • Full-Duplex Communication: data can flow in both the directions. • Connection-Oriented Service: two SCTP’s establish an association between each other. • Reliable Service: uses acknowledgement mechanism to check the safe and sound arrival of data.
  12. 12. SCTP FEATURES • • • • Transmission Sequence Number (TSN) Stream Identifier (SI) Stream Sequence Number (SSN) Packets
  13. 13. The unit of data in SCTP is called data chunk. In SCTP, a data chunk is numbered using a TSN. • To distinguish between different streams, SCTP uses an SI. To distinguish between different data chunks belonging to the same stream, SCTP uses SSNs. • Data chunks are identified by three identifiers: TSN, SI, and SSN. • TSN is a cumulative number identifying the association
  14. 14. A scenario: Suppose that process A needs to send 11 messages to process B in three streams, the first four in first stream, the second three in second stream, and last four in third stream
  15. 15. PACKET FORMAT • An SCTP packet has a mandatory general header and a set of blocks called chunks. There are two types of chunks: control chunks and data chunks.
  16. 16. Chunks
  17. 17. FOUR- WAY HANDSHAKE • The client sends the first packet which contain an INIT chunk. • The server sends the second packet which contains an INIT ACK chunk. • The client sends the third packet which includes a COOKIE ECHO chunk, this is a simple chunk that echoes without any change to the cookie sent by the server. • The server sends the fourth packet, which includes the COOKIE ACK CHUNK that acknowledges the receipt of the COOKIE ECHO chunk. • It prevents Denial Of Service Attack .
  18. 18. An SCTP association: 4 way handshake
  19. 19. 3 way handshake inTCP A t=0 1RTT B
  20. 20. Problem in 3 way handshake :SYN Flooding Attack in TCP attackers victim SYN SYN SYN Flooded!! TCB TCB TCB TCB TCB Unavailable, reserved resources • There is no ACK in response to the SYN-ACK, hence connection remains half-open • Other genuine clients cannot open connections to the victim • The victim is unable to provide service
  21. 21. Graceful Shutdown App signals shutdown A B Shutdown pending Shutdown sent Shutdown received Shutdown-Ack sent Closed Closed
  22. 22. • Framing : preserve message boundaries • Flow Control – SCTP uses an end-to-end window based flow and congestion control mechanism similar to the one that is used in TCP • Flow Control for Multi-homed Endpoints – By default, all transmission is done to a previously selected address from the set of destination addresses, which is called the Primary Address. – Retransmissions should be done on different paths, so that if one path is overloaded, retransmissions do not affect this path. • Congestion Control – The congestion control mechanisms for SCTP have been derived from TCP Congestion Control), and been adapted for multi-homing. • Slow Start and Congestion Avoidance is used with different parameters for different paths.
  23. 23. References • Data Communication and Networking by Behrouz A. Forouzan (4th edition) • Wikipedia
  24. 24. THANK YOU