1. SCTP
Presented by:
Sutanu Paul
CSI 13023
MTECH(IT)
TEZPUR UNIVERSITY

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. 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. SCTP SERVICES
•
•
•
•
•
Multiple Streams
Multihoming
Full-Duplex Communication
Connection-Oriented Service
Reliable Service

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. 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
160.15.82.20
NI-3
10.1.61.11
161.10.8.221

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. SCTP Endpoint : An SCTP endpoint can be represented as a
list of SCTP transport addresses with the same port:
endpoint = [10.1.4.2, 10.1.5.3 : 80]
[161.10.8.221 : 2223]
Application-1
NI-1
NI-2
NI-3
10.1.61.11
160.15.82.20
161.10.8.221

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 [160.15.82.20 : 2223] or [10.1.61.11 :
2223] or even [160.15.82.20, 10.1.61.11 : 2223]
• The new application will NOT be able to bind the
existing SCTP Transport address that Application-1
has bound i.e.: [161.10.8.221 : 2223]

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. 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. SCTP FEATURES
•
•
•
•
Transmission Sequence Number (TSN)
Stream Identifier (SI)
Stream Sequence Number (SSN)
Packets

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. 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. 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. Chunks

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. An SCTP association: 4 way handshake

19. 3 way handshake inTCP
A
t=0
1RTT
B

20. Problem in 3 way handshake :SYN
Flooding Attack in TCP
attackers
128.3.4.5
192.10.2.8
130.2.4.15
victim
SYN
228.3.14.5
SYN
190.13.4.1
221.3.5.10
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. Graceful Shutdown
App signals
shutdown
A
B
Shutdown
pending
Shutdown
sent
Shutdown
received
Shutdown-Ack
sent
Closed
Closed

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. References
• Data Communication and Networking by
Behrouz A. Forouzan (4th edition)
• Wikipedia

24. THANK YOU