Stream Control Transmission Protocol (SCTP) is a Transport Layer protocol, serving in a similar role as the popular protocols Transmission Control Protocol (TCP) and User Datagram Protocol (UDP). Indeed, it provides some of the same service features of both, ensuring reliable, in-sequence transport of messages with congestion control.
Pujala Venkateswara Rao
Stream Control Transmission Protocol(SCTP)
– is a reliable transport protocol operating on top of a potentially unreliable connectionless packet service such as IP.
– offers acknowledged error-free non-duplicated(orginal) transfer of datagrams.
– a selective retransmission mechanism is applied to correct loss or corruption of data.
A BRIEF HISTORY
• RFCs of SCTP
• RFCs related to SCTP
• RFC 2960 : Steam Control Transmission Protocol
• RFC 3257 : Stream Control Transmission Protocol Applicability Statement
• RFC 3286 : An Introduction to the Stream Control Transmission Protocol (SCTP)
• RFC 3309 : Stream Control Transmission Protocol (SCTP) Checksum Change.
• RFC 3436 : Transport Layer Security over Stream Control Transmission Protocol.
• RFC 3554 : On the Use of Stream Control Transmission Protocol (SCTP) with IPsec.
• RFC 3758 : Stream Control Transmission Protocol (SCTP) Partial Reliability Extension.
MOTIVATIONS for developing SCTP
• Problems for TCP
– Byte-Stream Oriented
– Provide strict ordering of information, which causes Head of Line (HOL) Blocking problem
– Vulnerable(weak) for SYN flooding attacks (a kind of DoS attack using TCP three-way handshake
• Problems for UDP
– Unreliable data transfer
– No congestion/flow control (applications must handle it by themselves)
• Reliable Transmission
• congestion controlled
• 4-way handshake(Initiation)
• conserve(preserve) message boundaries
• SCTP is rate adaptive(make suitable) similar to TCP
• Support multiple streams
• Support multi-homed hosts
• SCTP Multi-Homing
• Multiple dest ip addresses
• Use of different physical paths not guaranteed
• Peer reachability and path status are monitored (heartbeat)
• One selectable default destination
• Parameters per path (cwnd, RTO, RTT)
• Association establishment and shutdown. SCTP uses a cookie mechanism in a four-way handshake to establish an association.
• The shutdown process is a three-way handshake.
• The "cookie" mechanism guards specifically against a blind attacker generating INIT chunks
• The server instead creates a Cookie parameter with the TCB information, together with a valid lifetime and a signature for authentication, and sends this back in the INIT ACK.
• The INIT ACK always goes back to the source address of the INIT, the blind attacker will not get the Cookie.
• By using cookie mechanism we reduce blind attackers.
SCTP Massage Packet
• Common Header
– Source/destination port : same as TCP
– Verification Tag : 32 bit
– Checksum : 32 bit (TCP : 16bit)
– Type : distinguish control and data chunks
– Flag : ordered/unordered bit
– Length : length is variable
SCTP Data Transmission
• Flow Control
• Congestion Control / Slow-start
• Selective Acknowledgement
• Ordered and Unordered Delivery
• Fragmentation and Reassembly
• TCP data transfer without loss
• TCP data transfer with loss
• TCP data transfer with single path failure
• SCTP data transfer without loss
• SCTP data transfer with loss
• SCTP data transfer with single path failure
• 4 SACK rule is used
• Path Failure
• No.of retransmissions,Heartbeat chunks
• A count is maintained across all destination addresses
• In addition to the verification tag and cookie mechanisms, SCTP specifies the use of IPSec if strong security and integrity protection is required.
• work is in progress on the use of Transport Layer Security (TLS) over SCTP.
• SCTP Extensions
• Partial Reliability-SCTP(PR-SCTP) is defined in RFC 3758.
• Mobile SCTP (mSCTP)
• Concurrent Multipath Transfer (CMT)
Difference between TCP,SCTP &CMT PROTOCOLS
• Features comparison
• SCTP Applications
– Reliable transmission (authentication, authorization system, etc.)
– Mobile IP
– Real-time internet multimedia (http, etc.)
– Security (SCTP based TLS)
– Transport layer protocol for future wireless all-IP networks
• SCTP à all-IP network
– Sun Microsystems : SCTP for 4G IP wireless communication
– SoftNetworks : SCTP for Voice over Mobile IP (VoMo)
• Improving Multimedia performance over lossy networks
• Robust SCTP
• Multi-homing for hand-off processing
• SCTP Characteristics
– 4 way handshaking association
– Monitoring data transmission path and idle path
– Ordered and Unordered Data Transmission
– Chunk Bundling
– Congestion Control
– Fragmentation and Reassembly
• Other Issues
– Congestion control
– PR-SCTP (Partial Reliable SCTP)
– MSCTP (Mobile SCTP)
Future & Vision
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