протокол SCTP (SCTP protocol.)
Имя (Name)
sctp - SCTP protocol.
Синопсис (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);
Описание (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 boundary preservation, ordered and unordered message
delivery, multi-streaming and multi-homing. Detection of data
corruption, loss of data and duplication of data is achieved by
using checksums and sequence numbers. A selective retransmission
mechanism is applied to correct loss or corruption of data.
This implementation supports a mapping of SCTP into sockets API
as defined 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
implicit. 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
sequence 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
association 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 sequence 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 descriptor 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
system call sequence to setup an association with a server to
request services:
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/networking/ip-sysctl.txt.
Статистика (Statistics)
These variables can be accessed by the /proc/net/sctp/* files.
assocs Displays the following information about the active
associations. assoc ptr, sock ptr, socket style, sock
state, association state, hash bucket, association id,
bytes in transmit queue, bytes in receive queue, user id,
inode, local port, remote 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,
packets 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
transition 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
transition 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
transition 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
transition to the CLOSED state from either the SHUTDOWN-
SENT state or the SHUTDOWN-ACK-SENT state. Graceful
termination of the association.
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, including the proper checksum, but for
which the receiver was unable 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
setsockopt(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 timeout(RTO).
The structure 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 structure
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
unconnected socket (for one-to-many style sockets only
future associations are effected by the change). With one-
to-one style sockets, 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. Expects 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
association primary. The enclosed address must be one of
the association'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 defined 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_sndrcvinfo structure. The application
that wishes to use this socket option simply passes in to
this call the sctp_sndrcvinfo structure defined in
/usr/include/netinet/sctp.h. The input parameters 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 representation. 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 outgoing 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 address of an association, including its reachability
state, congestion window, and retransmission timer values.
This information is read-only. The structure
sctp_paddrinfo defined in /usr/include/netinet/sctp.h is
used to access this information.
SCTP_GET_ASSOC_STATS
Applications can retrieve current statistics about an
association, including SACKs sent and received, SCTP
packets sent and received. The complete list can be found
in /usr/include/netinet/sctp.h in struct sctp_assoc_stats.
