sctp
SCTP(7) Linux Programmer's Manual SCTP(7)
NAME
sctp - SCTP protocol.
SYNOPSIS
#include <sys/socket.h>
#include <netinet/in.h>
#include <netinet/sctp.h>
sctp_socket = socket(PF_INET, SOCK_STREAM, IPPROTO_SCTP);
sctp_socket = socket(PF_INET, SOCK_SEQPACKET, IPPROTO_SCTP);
DESCRIPTION
This is an implementation of the SCTP protocol as defined in RFC2960
and RFC3309. It is a message oriented, reliable transport protocol with
direct support for multihoming that runs on top of ip(7), and supports
both v4 and v6 versions.
Like TCP, SCTP provides reliable, connection oriented data delivery
with congestion control. Unlike TCP, SCTP also provides message bound-
ary preservation, ordered and unordered message delivery, multi-stream-
ing and multi-homing. Detection of data corruption, loss of data and
duplication of data is achieved by using checksums and sequence num-
bers. A selective retransmission mechanism is applied to correct loss
or corruption of data.
This implementation supports a mapping of SCTP into sockets API as de-
fined in the draft-ietf-tsvwg-sctpsocket-10.txt(Sockets API extensions
for SCTP). Two styles of interfaces are supported.
A one-to-many style interface with 1 to MANY relationship between
socket and associations where the outbound association setup is im-
plicit. The syntax of a one-to-many style socket() call is
sd = socket(PF_INET, SOCK_SEQPACKET, IPPROTO_SCTP);
A typical server in this style uses the following socket calls in se-
quence to prepare an endpoint for servicing requests.
1. socket()
2. bind()
3. listen()
4. recvmsg()
5. sendmsg()
6. close()
A typical client uses the following calls in sequence to setup an asso-
ciation with a server to request services.
1. socket()
2. sendmsg()
3. recvmsg()
4. close()
A one-to-one style interface with a 1 to 1 relationship between socket
and association which enables existing TCP applications to be ported to
SCTP with very little effort. The syntax of a one-to-one style socket()
call is
sd = socket(PF_INET, SOCK_STREAM, IPPROTO_SCTP);
A typical server in one-to-one style uses the following system call se-
quence to prepare an SCTP endpoint for servicing requests:
1. socket()
2. bind()
3. listen()
4. accept()
The accept() call blocks until a new association is set up. It returns
with a new socket descriptor. The server then uses the new socket de-
scriptor to communicate with the client, using recv() and send() calls
to get requests and send back responses. Then it calls
5. close()
to terminate the association. A typical client uses the following sys-
tem call sequence to setup an association with a server to request ser-
vices:
1. socket()
2. connect()
After returning from connect(), the client uses send() and recv() calls
to send out requests and receive responses from the server. The client
calls
3. close()
to terminate this association when done.
ADDRESS FORMATS
SCTP is built on top of IP (see ip(7)). The address formats defined by
ip(7) apply to SCTP. SCTP only supports point-to-point communication;
broadcasting and multicasting are not supported.
SYSCTLS
These variables can be accessed by the /proc/sys/net/sctp/* files or
with the sysctl(2) interface. In addition, most IP sysctls also apply
to SCTP. See ip(7).
Please check kernel documentation for this, at Documentation/network-
ing/ip-sysctl.txt.
STATISTICS
These variables can be accessed by the /proc/net/sctp/* files.
assocs Displays the following information about the active associa-
tions. assoc ptr, sock ptr, socket style, sock state, associa-
tion state, hash bucket, association id, bytes in transmit
queue, bytes in receive queue, user id, inode, local port, re-
mote port, local addresses and remote addresses.
eps Displays the following information about the active endpoints.
endpoint ptr, sock ptr, socket style, sock state, hash bucket,
local port, user id, inode and local addresses.
snmp Displays the following statistics related to SCTP states, pack-
ets and chunks.
SctpCurrEstab
The number of associations for which the current state is either
ESTABLISHED, SHUTDOWN-RECEIVED or SHUTDOWN-PENDING.
SctpActiveEstabs
The number of times that associations have made a direct transi-
tion to the ESTABLISHED state from the COOKIE-ECHOED state. The
upper layer initiated the association attempt.
SctpPassiveEstabs
The number of times that associations have made a direct transi-
tion to the ESTABLISHED state from the CLOSED state. The remote
endpoint initiated the association attempt.
SctpAborteds
The number of times that associations have made a direct transi-
tion to the CLOSED state from any state using the primitive
'ABORT'. Ungraceful termination of the association.
SctpShutdowns
The number of times that associations have made a direct transi-
tion to the CLOSED state from either the SHUTDOWN-SENT state or
the SHUTDOWN-ACK-SENT state. Graceful termination of the associ-
ation.
SctpOutOfBlues
The number of out of the blue packets received by the host. An
out of the blue packet is an SCTP packet correctly formed, in-
cluding the proper checksum, but for which the receiver was un-
able to identify an appropriate association.
SctpChecksumErrors
The number of SCTP packets received with an invalid checksum.
SctpOutCtrlChunks
The number of SCTP control chunks sent (retransmissions are not
included). Control chunks are those chunks different from DATA.
SctpOutOrderChunks
The number of SCTP ordered data chunks sent (retransmissions are
not included).
SctpOutUnorderChunks
The number of SCTP unordered chunks(data chunks in which the U
bit is set to 1) sent (retransmissions are not included).
SctpInCtrlChunks
The number of SCTP control chunks received (no duplicate chunks
included).
SctpInOrderChunks
The number of SCTP ordered data chunks received (no duplicate
chunks included).
SctpInUnorderChunks
The number of SCTP unordered chunks(data chunks in which the U
bit is set to 1) received (no duplicate chunks included).
SctpFragUsrMsgs
The number of user messages that have to be fragmented because
of the MTU.
SctpReasmUsrMsgs
The number of user messages reassembled, after conversion into
DATA chunks.
SctpOutSCTPPacks
The number of SCTP packets sent. Retransmitted DATA chunks are
included.
SctpInSCTPPacks
The number of SCTP packets received. Duplicates are included.
SOCKET OPTIONS
To set or get a SCTP socket option, call getsockopt(2) to read or set-
sockopt(2) to write the option with the option level argument set to
SOL_SCTP.
SCTP_RTOINFO.
This option is used to get or set the protocol parameters used
to initialize and bound retransmission timout(RTO). The struc-
ture sctp_rtoinfo defined in /usr/include/netinet/sctp.h is used
to access and modify these parameters.
SCTP_ASSOCINFO
This option is used to both examine and set various association
and endpoint parameters. The sturcture sctp_assocparams defined
in /usr/include/netinet/sctp.h is used to access and modify
these parameters.
SCTP_INITMSG
This option is used to get or set the protocol parameters for
the default association initialization. The structure
sctp_initmsg defined in /usr/include/netinet/sctp.h is used to
access and modify these parameters.
Setting initialization parameters is effective only on an uncon-
nected socket (for one-to-many style sockets only future associ-
ations are effected by the change). With one-to-one style sock-
ets, this option is inherited by sockets derived from a listener
socket.
SCTP_NODELAY
Turn on/off any Nagle-like algorithm. This means that packets
are generally sent as soon as possible and no unnecessary delays
are introduced, at the cost of more packets in the network. Ex-
pects an integer boolean flag.
SCTP_AUTOCLOSE
This socket option is applicable to the one-to-many style socket
only. When set it will cause associations that are idle for more
than the specified number of seconds to automatically close. An
association being idle is defined an association that has NOT
sent or received user data. The special value of 0 indicates
that no automatic close of any associations should be performed.
The option expects an integer defining the number of seconds of
idle time before an association is closed.
SCTP_SET_PEER_PRIMARY_ADDR
Requests that the peer mark the enclosed address as the associa-
tion primary. The enclosed address must be one of the associa-
tion's locally bound addresses. The structure sctp_setpeerprim
defined in /usr/include/netinet/sctp.h is used to make a set
peer primary request.
SCTP_PRIMARY_ADDR
Requests that the local SCTP stack use the enclosed peer address
as the association primary. The enclosed address must be one of
the association peer's addresses. The structure sctp_prim de-
fined in /usr/include/netinet/sctp.h is used to make a get/set
primary request.
SCTP_DISABLE_FRAGMENTS
This option is a on/off flag and is passed an integer where a
non-zero is on and a zero is off. If enabled no SCTP message
fragmentation will be performed. Instead if a message being
sent exceeds the current PMTU size, the message will NOT be sent
and an error will be indicated to the user.
SCTP_PEER_ADDR_PARAMS
Using this option, applications can enable or disable heartbeats
for any peer address of an association, modify an address's
heartbeat interval, force a heartbeat to be sent immediately,
and adjust the address's maximum number of retransmissions sent
before an address is considered unreachable. The structure
sctp_paddrparams defined in /usr/include/netinet/sctp.h is used
to access and modify an address's parameters.
SCTP_DEFAULT_SEND_PARAM
Applications that wish to use the sendto() system call may wish
to specify a default set of parameters that would normally be
supplied through the inclusion of ancillary data. This socket
option allows such an application to set the default sctp_sndr-
cvinfo structure. The application that wishes to use this socket
option simply passes in to this call the sctp_sndrcvinfo struc-
ture defined in /usr/include/netinet/sctp.h. The input parame-
ters accepted by this call include sinfo_stream, sinfo_flags,
sinfo_ppid, sinfo_context, sinfo_timetolive. The user must set
the sinfo_assoc_id field to identify the
association to affect if the caller is using the one-to-many
style.
SCTP_EVENTS
This socket option is used to specify various notifications and
ancillary data the user wishes to receive. The structure
sctp_event_subscribe defined in /usr/include/netinet/sctp.h is
used to access or modify the events of interest to the user.
SCTP_I_WANT_MAPPED_V4_ADDR
This socket option is a boolean flag which turns on or off
mapped V4 addresses. If this option is turned on and the socket
is type PF_INET6, then IPv4 addresses will be mapped to V6 rep-
resentation. If this option is turned off, then no mapping will
be done of V4 addresses and a user will receive both PF_INET6
and PF_INET type addresses on the socket.
By default this option is turned on and expects an integer to be
passed where non-zero turns on the option and zero turns off the
option.
SCTP_MAXSEG
This socket option specifies the maximum size to put in any out-
going SCTP DATA chunk. If a message is larger than this size it
will be fragmented by SCTP into the specified size. Note that
the underlying SCTP implementation may fragment into smaller
sized chunks when the PMTU of the underlying association is
smaller than the value set by the user. The option expects an
integer.
The default value for this option is 0 which indicates the user
is NOT limiting fragmentation and only the PMTU will effect
SCTP's choice of DATA chunk size.
SCTP_STATUS
Applications can retrieve current status information about an
association, including association state, peer receiver window
size, number of unacked data chunks, and number of data chunks
pending receipt. This information is read-only. The structure
sctp_status defined in /usr/include/netinet/sctp.h is used to
access this information.
SCTP_GET_PEER_ADDR_INFO
Applications can retrieve information about a specific peer ad-
dress of an association, including its reachability state, con-
gestion window, and retransmission timer values. This informa-
tion is read-only. The structure sctp_paddr_info defined in
/usr/include/netinet/sctp.h is used to access this information.
SCTP_GET_ASSOC_STATS
Applications can retrieve current statistics about an associa-
tion, including SACKs sent and received, SCTP packets sent and
received. The complete list can be found in /usr/in-
clude/netinet/sctp.h in struct sctp_assoc_stats.
AUTHORS
Sridhar Samudrala <sri@us.ibm.com>
SEE ALSO
socket(7), socket(2), ip(7), bind(2), listen(2), accept(2), connect(2),
sendmsg(2), recvmsg(2), sysctl(2), getsockopt(2), sctp_bindx(3),
sctp_connectx(3), sctp_sendmsg(3), sctp_sendv(3), sctp_send(3),
sctp_recvmsg(3), sctp_recvv(3), sctp_peeloff(3), sctp_getladdrs(3),
sctp_getpaddrs(3), sctp_opt_info(3).
RFC2960, RFC3309 for the SCTP specification.
Linux Man Page 2005-10-25 SCTP(7)
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