1. Stream Control Transmission Protocol (SCTP)
Group 2: HARRISON cLIFFORD, fRANK kIMANI & nAWAL aHMED

2. What is SCTP? Stream Control Transmission Protocol
Transport layer protocol
Message-oriented
Reliable
Relatively new

3. RFC 4960 Describes SCTP
Acknowledged error-free non-duplicated transfer of user data;
Data fragmentation to conform to discovered path MTU size;
Sequenced delivery of user messages within multiple streams, with option for order-of-arrival delivery of individual user messages;
Optional bundling of multiple user messages into single SCTP packet;
Network-level fault tolerance by supporting multi-homing at either or both ends of an association.

4. Basic SCTP terminology
Chunk – A unit of data within an SCTP packet, similar to UDP Datagram
Path – A connection between two IPs
Association – The set of paths between two endpoints on a network
Transmission Sequence Number (TSN) – A number assigned to each data chunk to keep track of it

5. Multihoming
Sending and receiving hosts can have multiple IP addresses.
TCP connection can only handle one IP per end.
An SCTP association can handle multiple IP addresses at each end.
Fault-tolerant

6. Creating an SCTP Association
SCTP requires a four-way step process also called a handshake:
1. INIT – Request sent by client to server
2. INIT ACK – Response to INIT, provides a Verification Tag and a Cookie which defines the current server state
3. COOKIE ECHO – Client echoes the Cookie
4. COOKIE ACK – Final acknowledgement of the connection
Difficult to perform a DoS attack

7. SCTP Packet Structure
Multiple chunks can be held together in the same packet.
Control information is carried in chunks
Verification Tag – Unique identifier for the current Association

8. SCTP Chunk Structure
Type field – Data, Association requests, Acknowledgements, etc.
Flag field – Defines what flags a chunk may need
Length – Total size of the chunk in bytes

9. Multistream Delivery
SCTP can support multiple different streams for data transfer
Each stream is assigned a Stream Identifier (SI)
Each stream can have either ordered or unordered delivery
Ordered delivery – Data chunks are assigned Stream Sequence Numbers (SSNs)
Unordered delivery – Data can be sent in any order, so long as all chunks are eventually received

10. Error Control
Whenever a data chunk is received, an acknowledgement is returned to the transmitter.
If the transmitter does not receive an acknowledgement within a certain time frame (RTO), the chunk is retransmitted.
If a receiver notices missing data chunks, it sends a selective acknowledgement to the transmitter.

11. TCP and UDP compared to SCTP
Attribute
TCP
UDP
SCTP
Reliability
Reliable
Unreliable
Connection Management
Connection Oriented
Connectionless
Transmission
Byte Oriented
Message Oriented
Flow Control
Yes No
Congestion Control
Fault Tolerance
Data Delivery
Strictly Ordered
Unordered
Partially Ordered
Security
Improved

12. Popularity Issues TCP/IP is very widespread and integrated.
Lacks native support with Windows and Mac OS.
Does not cross NAT very well. Less than 1% of home or enterprise routers do NAT on SCTP.
SCTP fills peculiar needs that are not needed by many applications like multistream and ordered reliable datagrams.

13. References
Forouzan, Behrouz A. TCP/IP Protocol Suite. 4th ed., McGraw-Hill,
training.co.uk/signallingtransportsigtranusingsctp_41.php