Windows PowerShell command on Get-command SCTP

Manual Pages for UNIX Operating System command usage for man SCTP

Protocols sctp(7P)

NAME

sctp, SCTP - Stream Control Transmission Protocol

SYNOPSIS

#include

s = socket(AF_INET, SOCK_STREAM, IPPROTO_SCTP);

s = socket(AF_INET, SOCK_SEQPACKET, IPPROTO_SCTP);

s = socket(AF_INET6, SOCK_STREAM, IPPROTO_SCTP);

s = socket(AF_INET6, SOCK_SEQPACKET, IPPROTO_SCTP);

DESCRIPTION

SCTP is a transport protocol layered above the Internet Pro-

tocol (IP), or the Internet Protocol Version 6 (IPv6). SCTP

provides a reliable, session oriented, flow-controlled,

two-way transmission of data. It is a message- oriented pro-

tocol and supports framing of individual messages boun-

daries. An SCTP association is created between two endpoints

for data transfer which is maintained during the lifetime of

the transfer. An SCTP association is setup between two end-

points using a four-way handshake mechanism with the use of

a cookie to guard against some types of denial of service

(DoS) attacks. These endpoints may be represented by multi-

ple IP addresses.

An SCTP message includes a common SCTP header followed by

one or more chunks. Included in the common header is a 32-

bit field which contains the checksum (computed using CRC-

32c polynomial) of the entire SCTP packet.

SCTP transfers data payloads in the form of DATA chunks.

Each DATA chunk contains a Transmission Sequence Number

(TSN), which governs the transmission of messages and detec-

tion of loss. DATA chunk exchanges follow the Transmission Control Protocol's (TCP) Selective ACK (SACK) mechanism. The receiver acknowledges data by sending SACK chunks, which not only indicate the cumulative TSN range received, but also

non-cumulative TSNs received, implying gaps in the received

TSN sequence. SACKs are sent using the delayed acknowledg-

ment method similar to TCP, that is, one SCTP per every

other received packet with an upper bound on the delay (when there are gaps detected the frequency is increased to one

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Protocols sctp(7P) every received packet). Flow and congestion control follow TCP algorithms: Slow Start, Congestion Avoidance, Fast

Recovery and Fast retransmit. But unlike TCP, SCTP does not

support half-close connection and "urgent" data.

SCTP is designed to support a number of functions that are

critical for telephony signalling transport, including

multi-streaming. SCTP allows data to be partitioned into

multiple streams that have the property of independent sequenced delivery so that message loss in any one stream

only affects delivery within that stream. In many applica-

tions (particularly telephony signalling), it is only neces-

sary to maintain sequencing of messages that affect some resource. Other messages may be delivered without having to

maintain overall sequence integrity. A DATA chunk on an SCTP

association contains the Stream Id/Stream Sequence Number pair, in addition to the TSN, which is used for sequenced delivery within a stream.

SCTP uses IP's host level addressing and adds its own per-

host collection of port addresses. The endpoints of an SCTP

association are identified by the combination of IP

address(es) and an SCTP port number. By providing the abil-

ity for an endpoint to have multiple IP addresses, SCTP sup-

ports multi-homing, which makes an SCTP association more

resilient in the presence of network failures (assuming the network is constructed to provided redundancy). For a

multi-homed SCTP association, a single address is used as

the primary address, which is used as the destination address for normal DATA chunk transfers. Retransmitted DATA chunks are sent over alternate address(es) to increase the probability of reaching the remote endpoint. Continued failure to send DATA chunks over the primary address results in selecting an alternate address as the primary address.

Additionally, SCTP monitors the accessibility of all alter-

nate addresses by sending periodic "heartbeats" chunks. An

SCTP association supports multi-homing by exchanging the

available list of addresses during association setup (as

part of its four-way handshake mechanism). An SCTP endpoint

is associated with a local address using the bind(3SOCKET) call. Subsequently, the endpoint can be associated with

additional addresses using sctp_bindx(3SOCKET). By using a

special value of INADDR_ANY with IP or the unspecified

address (all zeros) with IPv6 in the bind() or sctp_bindx()

calls, an endpoint can be bound to all available IP or IPv6 addresses on the system.

SCTP uses a three-way mechanism to allow graceful shutdown,

where each endpoint has confirmation of the DATA chunks

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Protocols sctp(7P) received by the remote endpoint prior to completion of the shutdown. An Abort is provided for error cases when an immediate shutdown is needed.

Applications can access SCTP using the socket interface as a

SOCK_STREAM (one-to-one style) or SOCK_SEQPACKET (one-to-

many style) socket type.

One-to-one style socket interface supports similar semantics

as sockets for connection oriented protocols, such as TCP. Thus, a passive socket is created by calling the listen(3SOCKET) function after binding the socket using bind(). Associations to this passive socket can be received using accept(3SOCKET) function. Active sockets use the

connect(3SOCKET) function after binding to initiate an asso-

ciation. If an active socket is not explicitly bound, an implicit binding is performed. If an application wants to exchange data during the association setup phase, it should not call connect(), but use sendto(3SOCKET)/sendmsg(3SOCKET) to implicitly initiate an association. Once an association has been established, read(2) and write(2) can used to exchange data. Additionally, send(3SOCKET), recv(3SOCKET), sendto(), recvfrom(3SOCKET), sendmsg(), and recvmsg(3SOCKET) can be used.

One-to-many socket interface supports similar semantics as

sockets for connection less protocols, such as UDP (however,

unlike UDP, it does not support broadcast or multicast com-

munications). A passive socket is created using the listen() function after binding the socket using bind(). An accept() call is not needed to receive associations to this

passive socket (in fact, an accept() on a one-to-many socket

will fail). Associations are accepted automatically and notifications of new associations are delivered in recvmsg() provided notifications are enabled. Active sockets after binding (implicitly or explicitly) need not call connect() to establish an association, implicit associations can be created using sendmsg()/recvmsg() or sendto()/recvfrom() calls. Such implicit associations cannot be created using

send() and recv() calls. On an SCTP socket (one-to-one or

one-to-many), an association may be established using

sendmsg(). However, if an association already exists for the

destination address specified in the msg_name member of the

msg parameter, sendmsg() must include the association id in

msg_iov member of the msg parameter (using sctp_sndrcvinfo

structure) for a one-to-many SCTP socket. If the association

id is not provided, sendmsg() fails with EADDRINUSE. On a

one-to-one socket the destination information in the msg

parameter is ignored for an established association.

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Protocols sctp(7P)

A one-to-one style association can be created from a one-

to-many association by branching it off using the

sctp_peeloff(3SOCKET) call; send() and recv() can be used on

such peeled off associations. Calling close(2) on a one-to-

many socket will gracefully shutdown all the associations

represented by that one-to-many socket.

The sctp_sendmsg(3SOCKET) and sctp_recvmsg(3SOCKET) func-

tions can be used to access advanced features provided by

SCTP.

SCTP provides the following socket options which are set

using setsockopt(3SOCKET) and read using getsockopt(3SOCKET). The option level is the protocol number

for SCTP, available from getprotobyname(3SOCKET).

SCTP_NODELAY

Turn on/off any Nagle-like algorithm (similar to

TCP_NODELAY).

SO_RCVBUF

Set the receive buffer.

SO_SNDBUF

Set the send buffer.

SCTP_AUTOCLOSE

For one-to-many style socket, automatically close any

association that has been idle for more than the speci-

fied number of seconds. A value of '0' indicates that no associations should be closed automatically.

SCTP_EVENTS

Specify various notifications and ancillary data the user wants to receive.

SCTP_STATUS

Retrieve current status information about an SCTP asso-

ciation.

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Protocols sctp(7P)

In addition SCTP provides the following option to handle

gathering of a limited set of per endpoint association

statistics from a one-to-one socket.

SCTP_GET_ASSOC_STATS Gather and reset per endpoint asso-

ciation statistics. Example Usage:

#include

struct sctp_assoc_stats stat;

int rc;

int32_t len = sizeof (stat);

/* * Per endpoint stats use the socket descriptor for sctp association. */ /* Gather per endpoint association statistics */

rc = getsockopt(sd, IPPROTO_SCTP, SCTP_GET_ASSOC_STATS, &stat, &len);

-----

sctp.h /*

* SCTP socket option used to read per endpoint association statistics.

#define SCTP_GET_ASSOC_STATS 24

/* * A socket user request reads local per endpoint association stats.

* All stats are counts except sas_maxrto, which is the max value

* since the last user request for stats on this endpoint. */

typedef struct sctp_assoc_stats {

uint64_t sas_rtxchunks; /* Retransmitted Chunks */

uint64_t sas_gapcnt; /* Gap Acknowledgements Received */

uint64_t sas_maxrto; /* Maximum Observed RTO this period */

uint64_t sas_outseqtsns; /* TSN received > next expected */

uint64_t sas_osacks; /* SACKs sent */

uint64_t sas_isacks; /* SACKs received */

uint64_t sas_octrlchunks; /* Control chunks sent - no dups */

uint64_t sas_ictrlchunks; /* Control chunks received - no dups */

uint64_t sas_oodchunks; /* Ordered data chunks sent */

uint64_t sas_iodchunks; /* Ordered data chunks received */

uint64_t sas_ouodchunks; /* Unordered data chunks sent */

uint64_t sas_iuodchunks; /* Unordered data chunks received */

uint64_t sas_idupchunks; /* Dups received (ordered+unordered) */

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Protocols sctp(7P)

} sctp_assoc_stats_t;

MULTIHOMING

The ability of SCTP to use multiple addresses in an associa-

tion can create issues with some network utilities. This requires a system administrator to be careful in setting up the system.

For example, the tcpd allows an administrator to use a sim-

ple form of address/hostname access control. While tcpd can

work with SCTP, the access control part can have some prob-

lems. The tcpd access control is only based on one of the addresses at association setup time. Once as association is

allowed, no more checking is performed. This means that dur-

ing the life time of the association, SCTP packets from dif-

ferent addresses of the peer host can be received in the system. This may not be what the system administrator wants as some of the peer's addresses are supposed to be blocked. Another example is the use of IP Filter, which provides several functions such as IP packet filtering (ipf(1M)) and NAT ipnat(1M)). For packet filtering, one issue is that a filter policy can block packets from some of the addresses of an association while allowing packets from other

addresses to go through. This can degrade SCTP's performance

when failure occurs. There is a more serious issue with IP

address rewrite by NAT. At association setup time, SCTP end-

points exchange IP addresses. But IP Filter is not aware of this. So when NAT is done on a packet, it may change the

address to an unacceptable one. Thus the SCTP association

setup may succeed but packets cannot go through afterwards when a different IP address is used for the association.

trol Transmission Protocol (SCTP), May 2002.

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Protocols sctp(7P) RFC 4960, Stream Control Transmission Protocol, 2007. DIAGNOSTICS A socket operation may fail if:

EPROTONOSUPPORT The socket type is other than SOCK_STREAM

and SOCK_SEQPACKET.

ETIMEDOUT An association was dropped due to exces-

sive retransmissions. ECONNREFUSED The remote peer refused establishing an association. EADDRINUSE A bind() operation was attempted on a socket with a network address/port pair that has already been bound to another socket. EINVAL A bind() operation was attempted on a socket with an invalid network address. EPERM A bind() operation was attempted on a socket with a "reserved" port number and the effective user ID of the process was not the privileged user.

SunOS 5.11 Last change: 26 Aug 2010 7

Manual Pages for UNIX Operating System command usage for man SCTP

NAME

sctp, SCTP - Stream Control Transmission Protocol

SYNOPSIS

s = socket(AF_INET, SOCK_STREAM, IPPROTO_SCTP);

s = socket(AF_INET, SOCK_SEQPACKET, IPPROTO_SCTP);

s = socket(AF_INET6, SOCK_STREAM, IPPROTO_SCTP);

s = socket(AF_INET6, SOCK_SEQPACKET, IPPROTO_SCTP);

DESCRIPTION

SCTP is a transport protocol layered above the Internet Pro-

tocol (IP), or the Internet Protocol Version 6 (IPv6). SCTP

daries. An SCTP association is created between two endpoints

the transfer. An SCTP association is setup between two end-

An SCTP message includes a common SCTP header followed by

32c polynomial) of the entire SCTP packet.

SCTP transfers data payloads in the form of DATA chunks.

ment method similar to TCP, that is, one SCTP per every

Recovery and Fast retransmit. But unlike TCP, SCTP does not

SCTP is designed to support a number of functions that are

multi-streaming. SCTP allows data to be partitioned into

maintain overall sequence integrity. A DATA chunk on an SCTP

SCTP uses IP's host level addressing and adds its own per-

host collection of port addresses. The endpoints of an SCTP

address(es) and an SCTP port number. By providing the abil-

ity for an endpoint to have multiple IP addresses, SCTP sup-

ports multi-homing, which makes an SCTP association more

multi-homed SCTP association, a single address is used as

Additionally, SCTP monitors the accessibility of all alter-

SCTP association supports multi-homing by exchanging the

part of its four-way handshake mechanism). An SCTP endpoint

SCTP uses a three-way mechanism to allow graceful shutdown,

Applications can access SCTP using the socket interface as a

send() and recv() calls. On an SCTP socket (one-to-one or

structure) for a one-to-many SCTP socket. If the association

SCTP.

SCTP provides the following socket options which are set

for SCTP, available from getprotobyname(3SOCKET).

SCTP_NODELAY

SCTP_AUTOCLOSE

SCTP_EVENTS

SCTP_STATUS

Retrieve current status information about an SCTP asso-

In addition SCTP provides the following option to handle

SCTP_GET_ASSOC_STATS Gather and reset per endpoint asso-

rc = getsockopt(sd, IPPROTO_SCTP, SCTP_GET_ASSOC_STATS, &stat, &len);

* SCTP socket option used to read per endpoint association statistics.

#define SCTP_GET_ASSOC_STATS 24

The ability of SCTP to use multiple addresses in an associa-

work with SCTP, the access control part can have some prob-

ing the life time of the association, SCTP packets from dif-

addresses to go through. This can degrade SCTP's performance

address rewrite by NAT. At association setup time, SCTP end-

address to an unacceptable one. Thus the SCTP association

SEE ALSO

trol Transmission Protocol (SCTP), May 2002.