Stream Control Transmission Protocol
Encyclopedia
In computer networking, the Stream Control Transmission Protocol (SCTP) is a Transport Layer
protocol
, serving in a similar role to the popular protocols Transmission Control Protocol
(TCP) and User Datagram Protocol
(UDP). It provides some of the same service features of both: it is message-oriented like UDP and ensures reliable, in-sequence transport of messages with congestion control like TCP.
The protocol was defined by the IETF Signaling Transport (SIGTRAN
) working group in 2000, and is maintained by the IETF Transport Area (TSVWG) working group. RFC 4960 defines the protocol. RFC 3286 provides an introduction.
In the absence of native SCTP support in operating systems it is possible to tunnel
SCTP over UDP, as well as mapping TCP API calls to SCTP ones.
, consists of a packet header, SCTP control chunks when necessary, followed by SCTP data chunks when available.
SCTP may be characterized as message-oriented, meaning it transports a sequence of messages (each being a group of bytes), rather than transporting an unbroken stream of bytes as does TCP. As in UDP, in SCTP a sender sends a message in one operation, and that exact message is passed to the receiving application process in one operation. In contrast, TCP is stream-oriented protocol, transporting streams of bytes
reliably and in order. However TCP does not allow the receiver to know how many times the sender application called on the TCP transport passing it groups of bytes to be sent out. At the sender TCP effectively simply appends more bytes to a queue of bytes waiting to go out over the network, rather than having to keep a queue of individual separate outbound messages which must be preserved as such.
The term multi-streaming refers to the capability of SCTP to transmit several independent streams of chunks in parallel, for example transmitting web page
images together with the web page text. In essence, it is the bundling of several connections into a single SCTP association, operating on messages (or chunks) rather than bytes.
TCP preserves byte order in the stream by assigning a sequence number to each packet. SCTP, on the other hand, assigns a sequence number to each message sent in a stream. This allows independent ordering of messages in different streams. However, message ordering is optional in SCTP; a receiving application may choose to process messages in the order they are received instead of the order they were sent.
The designers of SCTP originally intended it for the transport of telephony (Signaling System 7) over Internet Protocol, with the goal of duplicating some of the reliability attributes of the SS7 signaling network in IP. This IETF effort is known as SIGTRAN
. In the meantime, other uses have been proposed, for example, the Diameter protocol and Reliable server pooling
(RSerPool).
SCTP packets have a simpler basic structure than TCP packets. Each consists of two basic sections:
Each chunk has a type identifier that is one byte long yielding, at most, 255 different chunk types. RFC 4960 defines a list of chunk types and there are currently 15 types defined. The remainder of the chunk is a two byte length (maximum size of 65,535 bytes) and the data. If the chunk does not form a multiple of 4 bytes (i.e., the length is not a multiple of 4) then it is implicitly padded with zeros which are not included in the chunk length.
(compared to TCP 3-way handshake) to protect against SYN flood
ing attacks, and large "cookies" for association verification and authenticity.
Reliability was also a key aspect of the security design of SCTP. Multi-homing enables an association to stay open even when some routes and interfaces are down. This is of particular importance for SIGTRAN
as it carries SS7 over an IP network using SCTP, and requires strong resilience during link outages to maintain telecommunication service even when enduring network anomalies.
SCTP is sometimes a good fingerprinting candidate. Some operating systems ship with SCTP support enabled, and, as it is not as well known as TCP or UDP, it is sometimes overlooked in firewall and intrusion detection configurations, thus often permitting probing traffic.
s implement SCTP:
Userspace library:
Transport layer
In computer networking, the transport layer or layer 4 provides end-to-end communication services for applications within a layered architecture of network components and protocols...
protocol
Communications protocol
A communications protocol is a system of digital message formats and rules for exchanging those messages in or between computing systems and in telecommunications...
, serving in a similar role to the popular protocols Transmission Control Protocol
Transmission Control Protocol
The Transmission Control Protocol is one of the core protocols of the Internet Protocol Suite. TCP is one of the two original components of the suite, complementing the Internet Protocol , and therefore the entire suite is commonly referred to as TCP/IP...
(TCP) and User Datagram Protocol
User Datagram Protocol
The User Datagram Protocol is one of the core members of the Internet Protocol Suite, the set of network protocols used for the Internet. With UDP, computer applications can send messages, in this case referred to as datagrams, to other hosts on an Internet Protocol network without requiring...
(UDP). It provides some of the same service features of both: it is message-oriented like UDP and ensures reliable, in-sequence transport of messages with congestion control like TCP.
The protocol was defined by the IETF Signaling Transport (SIGTRAN
SIGTRAN
SIGTRAN is the name, derived from signaling transport, of the former Internet Engineering Task Force working group that produced specifications for a family of protocols that provide reliable datagram service and user layer adaptations for Signaling System 7 and ISDN communications protocols....
) working group in 2000, and is maintained by the IETF Transport Area (TSVWG) working group. RFC 4960 defines the protocol. RFC 3286 provides an introduction.
In the absence of native SCTP support in operating systems it is possible to tunnel
Tunneling protocol
Computer networks use a tunneling protocol when one network protocol encapsulates a different payload protocol...
SCTP over UDP, as well as mapping TCP API calls to SCTP ones.
Message-based multi-streaming
SCTP applications submit their data to be transmitted in messages (groups of bytes) to the SCTP transport layer. SCTP places messages and control information into separate chunks (data chunks and control chunks), each identified by a chunk header. A message can be fragmented over a number of data chunks, but each data chunk contains data from only one user message. SCTP chunks are bundled into SCTP packets. The SCTP packet, which is submitted to the Internet ProtocolInternet Protocol
The Internet Protocol is the principal communications protocol used for relaying datagrams across an internetwork using the Internet Protocol Suite...
, consists of a packet header, SCTP control chunks when necessary, followed by SCTP data chunks when available.
SCTP may be characterized as message-oriented, meaning it transports a sequence of messages (each being a group of bytes), rather than transporting an unbroken stream of bytes as does TCP. As in UDP, in SCTP a sender sends a message in one operation, and that exact message is passed to the receiving application process in one operation. In contrast, TCP is stream-oriented protocol, transporting streams of bytes
Byte stream
In computer science, a byte stream is a bit stream, in which data bits are grouped into units, called bytes.In computer networking the term octet stream is sometimes used to refer to the same thing; it emphasizes the use of bytes having the length of 8 bits, known as octets.Formally, a byte stream...
reliably and in order. However TCP does not allow the receiver to know how many times the sender application called on the TCP transport passing it groups of bytes to be sent out. At the sender TCP effectively simply appends more bytes to a queue of bytes waiting to go out over the network, rather than having to keep a queue of individual separate outbound messages which must be preserved as such.
The term multi-streaming refers to the capability of SCTP to transmit several independent streams of chunks in parallel, for example transmitting web page
Web page
A web page or webpage is a document or information resource that is suitable for the World Wide Web and can be accessed through a web browser and displayed on a monitor or mobile device. This information is usually in HTML or XHTML format, and may provide navigation to other web pages via hypertext...
images together with the web page text. In essence, it is the bundling of several connections into a single SCTP association, operating on messages (or chunks) rather than bytes.
TCP preserves byte order in the stream by assigning a sequence number to each packet. SCTP, on the other hand, assigns a sequence number to each message sent in a stream. This allows independent ordering of messages in different streams. However, message ordering is optional in SCTP; a receiving application may choose to process messages in the order they are received instead of the order they were sent.
Features
Features of SCTP include:- MultihomingMultihomingMultihoming is a technique used to increase the reliability of the Internet connection for an IP network. As an adjective, it is typically used to describe a customer, rather than an Internet service provider network...
support in which one or both endpoints of a connection can consist of more than one IP address, enabling transparent fail-over between redundant network paths. - Delivery of chunks within independent streams eliminate unnecessary head-of-line blockingHead-of-line blockingHead-of-line blocking is a performance-limiting phenomenon that occurs in buffered telecommunication network switches.-Description:...
, as opposed to TCP byte-stream delivery. - Path selection and monitoring select a primary data transmission path and test the connectivity of the transmission path.
- Validation and acknowledgment mechanisms protect against flooding attacks and provide notification of duplicated or missing data chunks.
- Improved error detection suitable for Ethernet jumbo framesJumbo FramesIn computer networking, jumbo frames are Ethernet frames with more than 1500 bytes of payload. Conventionally, jumbo frames can carry up to 9000 bytes of payload, but variations exist and some care must be taken when using the term. Many Gigabit Ethernet switches and Gigabit Ethernet network...
.
The designers of SCTP originally intended it for the transport of telephony (Signaling System 7) over Internet Protocol, with the goal of duplicating some of the reliability attributes of the SS7 signaling network in IP. This IETF effort is known as SIGTRAN
SIGTRAN
SIGTRAN is the name, derived from signaling transport, of the former Internet Engineering Task Force working group that produced specifications for a family of protocols that provide reliable datagram service and user layer adaptations for Signaling System 7 and ISDN communications protocols....
. In the meantime, other uses have been proposed, for example, the Diameter protocol and Reliable server pooling
Reliable server pooling
Reliable server pooling is a computer protocol framework for management of and access to multiple, coordinated servers...
(RSerPool).
Motivations
TCP has provided the primary means to transfer data reliably across the Internet, however TCP has imposed limitations on several applications. From RFC 4960:Packet structure
EWLINE
|
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
SCTP packets have a simpler basic structure than TCP packets. Each consists of two basic sections:
- The common header, which occupies the first 12 bytes and is highlighted in blue, and
- The data chunks, which occupy the remaining portion of the packet. The first chunk is highlighted in green, and the last of N chunks (Chunk N) is highlighted in red.
Each chunk has a type identifier that is one byte long yielding, at most, 255 different chunk types. RFC 4960 defines a list of chunk types and there are currently 15 types defined. The remainder of the chunk is a two byte length (maximum size of 65,535 bytes) and the data. If the chunk does not form a multiple of 4 bytes (i.e., the length is not a multiple of 4) then it is implicitly padded with zeros which are not included in the chunk length.
Security
Although Encryption was not part of the original SCTP design, SCTP was designed with features for improved security, such as 4-way handshakeHandshaking
In information technology, telecommunications, and related fields, handshaking is an automated process of negotiation that dynamically sets parameters of a communications channel established between two entities before normal communication over the channel begins...
(compared to TCP 3-way handshake) to protect against SYN flood
SYN flood
A SYN flood is a form of denial-of-service attack in which an attacker sends a succession of SYN requests to a target's system in an attempt to consume enough server resources to make the system unresponsive to legitimate traffic.-Technical details:...
ing attacks, and large "cookies" for association verification and authenticity.
Reliability was also a key aspect of the security design of SCTP. Multi-homing enables an association to stay open even when some routes and interfaces are down. This is of particular importance for SIGTRAN
SIGTRAN
SIGTRAN is the name, derived from signaling transport, of the former Internet Engineering Task Force working group that produced specifications for a family of protocols that provide reliable datagram service and user layer adaptations for Signaling System 7 and ISDN communications protocols....
as it carries SS7 over an IP network using SCTP, and requires strong resilience during link outages to maintain telecommunication service even when enduring network anomalies.
SCTP is sometimes a good fingerprinting candidate. Some operating systems ship with SCTP support enabled, and, as it is not as well known as TCP or UDP, it is sometimes overlooked in firewall and intrusion detection configurations, thus often permitting probing traffic.
Implementations
The following operating systemOperating system
An operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer system...
s implement SCTP:
- AIXAIX operating systemAIX AIX AIX (Advanced Interactive eXecutive, pronounced "a i ex" is a series of proprietary Unix operating systems developed and sold by IBM for several of its computer platforms...
Version 5 - Generic BSD with external patch at KAME projectKAME projectThe KAME project was a joint effort of six organizations in Japan which aimed to provide a free IPv6 and IPsec protocol stack implementation for variants of the BSD Unix computer operating-system...
- Cisco IOSCisco IOSCisco IOS is the software used on the vast majority of Cisco Systems routers and current Cisco network switches...
12 - DragonFly BSDDragonFly BSDDragonFly BSD is a free Unix-like operating system created as a fork of FreeBSD 4.8. Matthew Dillon, an Amiga developer in the late 1980s and early 1990s and a FreeBSD developer between 1994 and 2003, began work on DragonFly BSD in June 2003 and announced it on the FreeBSD mailing lists on July...
since version 1.4 - FreeBSDFreeBSDFreeBSD is a free Unix-like operating system descended from AT&T UNIX via BSD UNIX. Although for legal reasons FreeBSD cannot be called “UNIX”, as the direct descendant of BSD UNIX , FreeBSD’s internals and system APIs are UNIX-compliant...
, version 7 and above - HP-UXHP-UXHP-UX is Hewlett-Packard's proprietary implementation of the Unix operating system, based on UNIX System V and first released in 1984...
, 11i v2 and above - LinuxLinuxLinux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. The defining component of any Linux system is the Linux kernel, an operating system kernel first released October 5, 1991 by Linus Torvalds...
kernel-based 2.4 and newer - Microsoft WindowsMicrosoft WindowsMicrosoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...
:- The SctpDrv kernel driver is a port of the BSD SCTP stack to Windows
- SCTP .NET
- QNXQNXQNX is a commercial Unix-like real-time operating system, aimed primarily at the embedded systems market. The product was originally developed by Canadian company, QNX Software Systems, which was later acquired by Canadian BlackBerry-producer Research In Motion.-Description:As a microkernel-based...
Neutrino Realtime OS, 6.3.0 and above - Sun Solaris 10 and above
- FreeBSDFreeBSDFreeBSD is a free Unix-like operating system descended from AT&T UNIX via BSD UNIX. Although for legal reasons FreeBSD cannot be called “UNIX”, as the direct descendant of BSD UNIX , FreeBSD’s internals and system APIs are UNIX-compliant...
contains the SCTP reference implementation.
Userspace library:
- The SCTP library
- Windows XPWindows XPWindows XP is an operating system produced by Microsoft for use on personal computers, including home and business desktops, laptops and media centers. First released to computer manufacturers on August 24, 2001, it is the second most popular version of Windows, based on installed user base...
port
- Windows XP
- Oracle Java SE 7
RFC history
- RFC 6096 Stream Control Transmission Protocol (SCTP) Chunk Flags Registration (updates RFC 4960)
- RFC 5062 Security Attacks Found Against the Stream Control Transmission Protocol (SCTP) and Current Countermeasures
- RFC 5061 Stream Control Transmission Protocol (SCTP) Dynamic Address Reconfiguration
- RFC 5043 Stream Control Transmission Protocol (SCTP) Direct Data Placement (DDP) Adaptation
- RFC 4960 Stream Control Transmission Protocol
- RFC 4895 Authenticated Chunks for the Stream Control Transmission Protocol (SCTP)
- RFC 4820 Padding Chunk and Parameter for the Stream Control Transmission Protocol (SCTP)
- RFC 4460 Stream Control Transmission Protocol (SCTP) Specification Errata and Issues
- RFC 3873 Stream Control Transmission Protocol (SCTP) Management Information BaseManagement information baseA management information base is a virtual database used for managing the entities in a communications network. Most often associated with the Simple Network Management Protocol , the term is also used more generically in contexts such as in OSI/ISO Network management model...
(MIB) - RFC 3758 Stream Control Transmission Protocol (SCTP) Partial Reliability Extension
- RFC 3554 On the Use of Stream Control Transmission Protocol (SCTP) with IPsecIPsecInternet Protocol Security is a protocol suite for securing Internet Protocol communications by authenticating and encrypting each IP packet of a communication session...
- RFC 3436 Transport Layer Security over Stream Control Transmission Protocol
- RFC 3309 Stream Control Transmission Protocol (SCTP) Checksum Change (obsoleted by RFC 4960)
- RFC 3286 An Introduction to the Stream Control Transmission Protocol
- RFC 3257 Stream Control Transmission Protocol Applicability Statement
- RFC 2960 Stream Control Transmission Protocol (updated by RFC 3309 and obsoleted by RFC 4960)
See also
- Transport protocol comparison table
- Session initiation protocolSession Initiation ProtocolThe Session Initiation Protocol is an IETF-defined signaling protocol widely used for controlling communication sessions such as voice and video calls over Internet Protocol . The protocol can be used for creating, modifying and terminating two-party or multiparty sessions...
(SIP), which may initiate multiple streams over SCTP, TCP or UDP
External links
- http://www.sigtran.org
- http://www.ietf.org/html.charters/sigtran-charter.html
- http://www.ietf.org/html.charters/tsvwg-charter.html
- http://www.openss7.org