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\documentclass[a4paper]{article}
%
\usepackage{longtable}
%
\title{Socket API for the SCTP User-land Implementation (usrsctp)}
\author{I.~R\"ungeler%
        \thanks{M\"unster University of Applied Sciences,
                Department of Electrical Engineering
                and Computer Science,
                Stegerwaldstr.~39,
                D-48565 Steinfurt,
                Germany,
                \texttt{i.ruengeler@fh-muenster.de}.}
        \and
        M.~T\"uxen%
        \thanks{M\"unster University of Applied Sciences,
                Department of Electrical Engineering
                and Computer Science,
                Stegerwaldstr.~39,
                D-48565 Steinfurt,
                Germany,
                \texttt{tuexen@fh-muenster.de}.}
}
%
\begin{document}
\setcounter{secnumdepth}{4}
\setcounter{tocdepth}{4}
\maketitle
\tableofcontents

\section{Introduction}
In this manual the socket API for the SCTP User-land implementation will be described. 
It is based on RFC 6458~\cite{socketAPI}. The main focus of this document is on pointing out
 the differences to the SCTP Sockets API. For all aspects of the sockets API that are not
 mentioned in this document, please refer to RFC~6458. Questions about SCTP can hopefully be
 answered by RFC~4960~\cite{SCTP}.
 
\section{Getting Started}
The User-land stack has been tested on FreeBSD 10.0, Ubuntu 11.10, Windows 7, Mac OS X 10.6, 
and MAC OS X 10.7.
The current version of the User-land stack is provided on \textit{http://sctp.fh-muenster.de/sctp-user-land-stack.html}.
Download the tarball and untar it in a folder of your choice. 
The tarball contains all the sources to build the libusrsctp, which has to be linked to the object file of an 
example program. In addition there are two applications in the folder \textit{programs} that can be built and run.
 
\subsection{Building the Library and the Applications}
\subsubsection{Unix-like Operating Systems}
In the folder \textit{usrsctp} type
\begin{verbatim}
./bootstrap
./configure
make
\end{verbatim}
Now, the library \textit{libusrsctp.la} has been built in the subdirectory \textit{usrsctplib}, and the example 
programs are ready to run from the subdirectory \textit{programs}.

If you have root privileges or are in the sudoer group, you can install the library in \textit{/usr/local/lib} 
and copy the header file to \textit{/usr/include} with the command
\begin{verbatim}
sudo make install
\end{verbatim}

\subsubsection{Windows}
On Windows you need a compiler like Microsoft Visual Studio. You can build the library and the
example programs with the command line tool of the compiler by typing
\begin{verbatim}
nmake -f Makefile.nmake
\end{verbatim}
in the directory \textit{usrsctp}.

\subsection{Running the Test Programs}
There are two test programs included, a discard server and a client. You can run both to send data from the
client to the server. The client reads data from stdin and sends them to the server, which prints the message
in the terminal and discards it. The sources of the server are also provided in Section~\ref{server} and those
of the client in Section~\ref{client}.

\subsubsection{Using UDP Encapsulation}
Both programs can either send data over SCTP directly or use UDP encapsulation, thus encapsulating the
SCTP packet in a UDP datagram. The first mode works on loopback or in a protected setup without any 
NAT boxes involved. In all other cases it is better to use UDP encapsulation.

The usage of the discard\_server is
\begin{verbatim}
discard_server [local_encaps_port remote_encaps_port]
\end{verbatim}
For UDP encapsulation the ports have to be specified. The local and remote encapsulation ports can be arbitrarily
set.
For example, you can call
\begin{verbatim}
./discard_server 11111 22222
\end{verbatim}
on a Unix-like OS and
\begin{verbatim}
discard_server.exe 11111 22222
\end{verbatim}
on Windows.

The client needs two additional parameters, the server's address and its port.
Its usage is
\begin{verbatim}
client remote_addr remote_port [local_port local_encaps_port remote_encaps_port]
\end{verbatim}
The remote address is the server's address. If client and server are started on the same machine,
the loopback address 127.0.0.1 can be used for Unix-like OSs and the local address on Windows.
The discard port is 9, thus 9 has to be taken as remote port. The encapsulation ports have to
match those of the server, i.e. the server's local\_encaps\_port is the client's
remote\_encaps\_port and vice versa. Thus, the client can be started with
\begin{verbatim}
./client 127.0.0.1 9 0 22222 11111
\end{verbatim}
on a Unix-like OS and
\begin{verbatim}
client.exe 192.168.0.1 9 0 22222 11111
\end{verbatim}
on Windows provided your local IP address is 192.168.0.1.

\subsubsection{Sending over SCTP}
To send data over SCTP directly you might need root privileges because raw sockets are used.
Thus instead of specifying the encapsulation ports you have to start the programs prepending 
\texttt{sudo} or in case of Windows start the program from an administrator console.

\subsubsection{Using the Callback API}
Instead of asking constantly for new data, a callback API can be used that is triggered by 
SCTP. A callback function has to be registered that will be called whenever data is ready to
be delivered to the application.

The discard\_server has a flag to switch between the two modi. If  use\_cb is set to 1, the
callback API will be used. To change the setting, just set the flag and compile the program again.


\section{Basic Operations}
All system calls start with the prefix \textit{usrsctp\_} to distinguish them from the kernel variants. 
Some of them are changed to account for the different demands in the userland environment. 

\subsection{Differences to RFC 6458}
\subsubsection{usrsctp\_init()}
Every application has to start with \textit{usrsctp\_init()}. This function calls \textit{sctp\_init()} and reserves
the memory necessary to administer the data transfer.
The function prototype is 
\begin{verbatim}
void
usrsctp_init(uint16_t udp_port)
\end{verbatim}
As it is not always possible to send data directly over SCTP because not all NAT boxes can
process SCTP packets, the data can be sent over UDP. To encapsulate SCTP into UDP
a UDP port has to be specified, to which the datagrams can be sent. This local UDP port  is set 
with the parameter \texttt{udp\_port}. The default value is 9899, the standard UDP encapsulation port.
If UDP encapsulation is not necessary, the UDP port has to be set to 0.

\subsubsection{usrsctp\_finish()}
At the end of the program \textit{usrsctp\_finish()} should be called to free all the memory that has been
allocated before.
The function prototype is 
\begin{verbatim}
int
usrsctp_finish(void).
\end{verbatim}
The return code is 0 on success and -1 in case of an error.

\subsubsection{usrsctp\_socket()}
A representation of an SCTP endpoint is a socket. Is it created with \textit{usrsctp\_socket()}.
The function prototype is:
\begin{verbatim}
struct socket *
usrsctp_socket(int domain, 
               int type, 
               int protocol,
               int (*receive_cb)(struct socket *sock, 
                                 union sctp_sockstore addr, 
                                 void *data,
                                 size_t datalen, 
                                 struct sctp_rcvinfo, 
                                 int flags,
                                 void *ulp_info),
               int (*send_cb)(struct socket *sock, 
                              uint32_t sb_free),
               uint32_t sb_threshold,
               void *ulp_info).
\end{verbatim}
The arguments taken from RFC~6458 are:
\begin{itemize}
\item domain: PF\_INET or PF\_INET6 can be used.
\item type: In case of a one-to-many style socket it is SOCK\_SEQPACKET, in case of a one-to-one style 
socket it is SOCK\_STREAM. For an explanation of the differences between the socket types please
refer to RFC~6458.
\item protocol: Set IPPROTO\_SCTP.
\end{itemize}

In usrsctp, a callback API can be used.
\begin{itemize}
\item The function pointers of the receive and send callbacks are new arguments to the socket call. If no callback API is used, these must be \textit{NULL}.
\item The \textit{sb\_threshold} specifies the amount of free space in the send socket buffer before the send function in the application is called. If a send callback function is specified and \textit{sb\_threshold} is 0, the function is called whenever there is room in the send socket buffer.
\item Additional data may be passed along within the \textit{ulp\_info} parameter. This value will be passed to the \textit{receive\_cb} when it is invoked.
\end{itemize}

On success \textit{usrsctp\_socket()} returns the pointer to the new socket in the \texttt{struct socket} data type. 
It will be needed in all other system calls. In case of a failure NULL is returned and
errno is set to the appropriate error code.

\subsubsection{usrsctp\_close()}

The function prototype of \textit{usrsctp\_close()} is 
\begin{verbatim}   
void
usrsctp_close(struct socket *so).
 \end{verbatim}
Thus the only difference is the absence of a return code. 
 
\subsection{Same Functionality as RFC 6458}
The following functions have the same functionality as their kernel pendants. There prototypes
are described in the following subsections. For a detailed description please refer to RFC~6458.

\subsubsection{usrsctp\_bind()}
The function prototype of \textit{usrsctp\_bind()} is 
\begin{verbatim}
int
usrsctp_bind(struct socket *so,
             struct sockaddr *addr,
             socklen_t addrlen).
\end{verbatim}     
The arguments are
\begin{itemize}
\item so: Pointer to the socket as returned by \textit{usrsctp\_socket()}.
\item addr: The address structure (struct sockaddr\_in for an IPv4 address
      or struct sockaddr\_in6 for an IPv6 address).
\item addrlen: The size of the address structure.
\end{itemize}
\textit{usrsctp\_bind()} returns 0 on success and -1 in case of an error.

\subsubsection{usrsctp\_listen()}
The function prototype of \textit{usrsctp\_listen()} is 
\begin{verbatim}
int
usrsctp_listen(struct socket *so,
               int backlog).
 \end{verbatim}      
The arguments are
\begin{itemize}
\item so: Pointer to the socket as returned by \textit{usrsctp\_socket()}.
\item backlog: If backlog is non-zero, enable listening, else disable
      listening.
\end{itemize}
\textit{usrsctp\_listen()} returns 0 on success and -1 in case of an error.

\subsubsection{usrsctp\_accept()}
The function prototype of \textit{usrsctp\_accept()} is 
\begin{verbatim}                
struct socket *
usrsctp_accept(struct socket *so,
               struct sockaddr * addr,
               socklen_t * addrlen).
 \end{verbatim}
 The arguments are
\begin{itemize}
\item so: Pointer to the socket as returned by \textit{usrsctp\_socket()}.
\item addr: On return,  the primary address of the peer (struct sockaddr\_in for an IPv4 address or
      struct sockaddr\_in6 for an IPv6 address).
\item addrlen: Size of the returned address structure.
\end{itemize}
\textit{usrsctp\_accept()} returns the accepted socket on success and NULL in case of an error.

\subsubsection{usrsctp\_connect()}
The function prototype of \textit{usrsctp\_connect()} is 
\begin{verbatim}     
int
usrsctp_connect(struct socket *so,
                struct sockaddr *name,
                socklen_t addrlen)
 \end{verbatim}
The arguments are
\begin{itemize}
\item so: Pointer to the socket as returned by \textit{usrsctp\_socket()}.
 \item name: Address of the peer to connect to (struct sockaddr\_in for an IPv4 address or
      struct sockaddr\_in6 for an IPv6 address).
\item addrlen: Size of the peer's address.
\end{itemize}
\textit{usrsctp\_connect()} returns 0 on success and -1 in case of an error.

\subsubsection{usrsctp\_shutdown()} 
The function prototype of \textit{usrsctp\_shutdown()} is 
\begin{verbatim}   
int
usrsctp_shutdown(struct socket *so, int how).
\end{verbatim}
The arguments are
\begin{itemize}
\item so: Pointer to the socket of the association to be closed.
\item how: Specifies the type of shutdown.  The values are as follows:
\begin{itemize}
\item SHUT\_RD:  Disables further receive operations.  No SCTP protocol
         action is taken.
\item SHUT\_WR:  Disables further send operations, and initiates the SCTP
         shutdown sequence.
\item SHUT\_RDWR:  Disables further send and receive operations, and
         initiates the SCTP shutdown sequence.
\end{itemize}
\end{itemize}
\textit{usrsctp\_shutdown()} returns 0 on success and -1 in case of an error.

\section{Sending and Receiving Data}
Since the publication of RFC~6458 there is only one function for sending and one for receiving
that is not deprecated. Therefore, only these two are described here.

\subsection{usrsctp\_sendv()}
The function prototype is
\begin{verbatim}
ssize_t
usrsctp_sendv(struct socket *so,
              const void *data,
              size_t len,
              struct sockaddr *addrs,
              int addrcnt,
              void *info,
              socklen_t infolen,
              unsigned int infotype,
              int flags).
\end{verbatim}
The arguments are
\begin{itemize}
\item so: The socket to send data on.
\item data: As it is more convenient to send data in a buffer and not a \texttt{struct iovec} data structure, we
chose to pass the data as a void pointer.
\item len: Length of the data.
\item addrs: In this version of usrsctp at most one destination address is supported. In the case of a connected
socket, the parameter \texttt{addrs} can be set to NULL.
\item addrcnt: Number of addresses. As at most one address is supported, addrcnt is 0 if addrs is NULL and 
1 otherwise.
\item info: Additional information for a message is stored in \texttt{void *info}. The data types \texttt{struct~sctp\_sndinfo},
\texttt{struct~sctp\_prinfo}, and \texttt{struct} \linebreak \texttt{sctp\_sendv\_spa} are supported as defined in 
RFC~6458. Support for \texttt{structsctp\_authinfo} is not implemented yet, therefore, errno is set EINVAL
and -1 will be returned, if it is used.
\item infolen: Length of info in bytes.
\item infotype: Identifies the type of the information provided in info. Possible values are
SCTP\_SENDV\_NOINFO, SCTP\_SENDV\_SNDINFO, \linebreak SCTP\_SENDV\_PRINFO, SCTP\_SENDV\_SPA. 
For additional information please refer to RFC~6458.
\item flags: Flags as described in RFC~6458.
\end{itemize}

\textit{usrsctp\_sendv()} returns the number of bytes sent, or -1 if an error
occurred.  The variable errno is then set appropriately.

\subsection{usrsctp\_recvv()}
The function prototype is
\begin{verbatim}
ssize_t
usrsctp_recvv(struct socket *so,
             void *dbuf,
             size_t len,
             struct sockaddr *from,
             socklen_t * fromlen,
             void *info,
             socklen_t *infolen,
             unsigned int *infotype,
             int *msg_flags).
\end{verbatim}
The arguments are
\begin{itemize}
\item so: The socket to receive data on.
\item dbuf: Analog to \textit{usrsctp\_sendv()} the data is returned in a buffer.
\item len: Length of the buffer in bytes.
\item from: A pointer to an address to be filled with the sender of the
      received message's address.
\item fromlen: An in/out parameter describing the from length.
\item info: A pointer to the buffer to hold the attributes of the received
      message.  The structure type of info is determined by the
      infotype parameter. The attributes returned in \texttt{info} have to be 
      handled in the same way as specified in RFC~6458.
\item infolen:  An in/out parameter describing the size of the info buffer.
\item infotype:  On return, *infotype is set to the type of the info
      buffer.  The current defined values are SCTP\_RECVV\_NOINFO, 
      SCTP\_RECVV\_RCVINFO, SCTP\_RECVV\_NXTINFO, and
      SCTP\_RECVV\_RN. A detailed description is given in RFC~6458.
\item flags: A pointer to an integer to be filled with any message flags
      (e.g., MSG\_NOTIFICATION).  Note that this field is an in/out
      parameter.  Options for the receive may also be passed into the
      value (e.g., MSG\_EOR).  Returning from the call, the flags' value
      will differ from its original value.
\end{itemize}

\textit{usrsctp\_recvv()} returns the number of bytes sent, or -1 if an error
occurred.  The variable errno is then set appropriately.

  
\section{Socket Options}
Socket options are used to change the default behavior of socket calls.
Their behavior is specified in RFC~6458. The functions to get or set them are

\begin{verbatim}
int
usrsctp_getsockopt(struct socket *so,
                     int level,
                     int optname,
                     void *optval,
                     socklen_t *optlen)
\end{verbatim}
and
\begin{verbatim}
int
usrsctp_setsockopt(struct socket *so,
                     int level,
                     int optname,
                     const void *optval,
                     socklen_t optlen).
\end{verbatim}

and the arguments are
\begin{itemize}
\item so:  The socket of type struct socket.
\item level:  Set to IPPROTO\_SCTP for all SCTP options.
\item optname:  The option name as specified in Table~\ref{options}.
\item optval: The buffer to store the value of the option as specified in the second column of Table~\ref{options}.
\item optlen:  The size of the buffer (or the length of the option
      returned in case of \textit{usrsctp\_getsockopt}).
\end{itemize}

These functions return 0 on success and -1 in case of an error.

\begin{longtable}{|l|l|c|} 
\hline
{\bfseries Option}&{\bfseries Datatype} &{\bfseries r/w}\tabularnewline 
\endhead
\hline
SCTP\_RTOINFO&struct sctp\_rtoinfo&r/w\tabularnewline \hline
SCTP\_ASSOCINFO&struct sctp\_assocparams&r/w\tabularnewline \hline
SCTP\_INITMSG&struct sctp\_initmsg&r/w\tabularnewline \hline
SCTP\_NODELAY&int&r/w\tabularnewline \hline
SCTP\_AUTOCLOSE&int&r/w\tabularnewline \hline
SCTP\_PRIMARY\_ADDR&struct sctp\_setprim&r/w\tabularnewline \hline
SCTP\_ADAPTATION\_LAYER&struct sctp\_setadaptation&r/w\tabularnewline \hline
SCTP\_DISABLE\_FRAGMENTS&int&r/w\tabularnewline \hline
SCTP\_PEER\_ADDR\_PARAMS&struct sctp\_paddrparams&r/w\tabularnewline \hline
SCTP\_I\_WANT\_MAPPED\_V4\_ADDR&int&r/w\tabularnewline \hline
SCTP\_MAXSEG&struct sctp\_assoc\_value&r/w\tabularnewline \hline
SCTP\_DELAYED\_SACK&struct sctp\_sack\_info&r/w\tabularnewline \hline
SCTP\_FRAGMENT\_INTERLEAVE&int&r/w\tabularnewline \hline
SCTP\_PARTIAL\_DELIVERY\_POINT&int&r/w\tabularnewline \hline
SCTP\_HMAC\_IDENT&struct sctp\_hmacalgo&r/w\tabularnewline \hline
SCTP\_AUTH\_ACTIVE\_KEY&struct sctp\_authkeyid&r/w\tabularnewline \hline
SCTP\_AUTO\_ASCONF&int&r/w\tabularnewline \hline
SCTP\_MAX\_BURST&struct sctp\_assoc\_value&r/w\tabularnewline \hline
SCTP\_CONTEXT&struct sctp\_assoc\_value&r/w\tabularnewline \hline
SCTP\_EXPLICIT\_EOR&int&r/w\tabularnewline \hline
SCTP\_REUSE\_PORT&int&r/w\tabularnewline \hline
SCTP\_EVENT&struct sctp\_event&r/w\tabularnewline \hline
SCTP\_RECVRCVINFO&int&r/w\tabularnewline \hline
SCTP\_RECVNXTINFO&int&r/w\tabularnewline \hline
SCTP\_DEFAULT\_SNDINFO&struct sctp\_sndinfo&r/w\tabularnewline \hline
SCTP\_DEFAULT\_PRINFO&struct sctp\_default\_prinfo&r/w\tabularnewline \hline
SCTP\_REMOTE\_UDP\_ENCAPS\_PORT&int&r/w\tabularnewline \hline
SCTP\_ENABLE\_STREAM\_RESET&struct sctp\_assoc\_value&r/w\tabularnewline \hline
SCTP\_STATUS&struct sctp\_status&r\tabularnewline \hline
SCTP\_GET\_PEER\_ADDR\_INFO&struct sctp\_paddrinfo&r\tabularnewline \hline
SCTP\_PEER\_AUTH\_CHUNKS&struct sctp\_authchunks&r\tabularnewline \hline
SCTP\_LOCAL\_AUTH\_CHUNKS&struct sctp\_authchunks&r\tabularnewline \hline
SCTP\_GET\_ASSOC\_NUMBER&uint32\_t&r\tabularnewline \hline
SCTP\_GET\_ASSOC\_ID\_LIST&struct sctp\_assoc\_ids&r\tabularnewline \hline
SCTP\_RESET\_STREAMS&struct sctp\_reset\_streams&w\tabularnewline \hline
SCTP\_RESET\_ASSOC&struct sctp\_assoc\_t&w\tabularnewline \hline
SCTP\_ADD\_STREAMS&struct sctp\_add\_streams&w\tabularnewline \hline
\caption{Socket Options supported by usrsctp}
\label{options}
\end{longtable}
An overview of the supported options is given in Table~\ref{options}. Their use is described in RFC~6458~\cite{socketAPI}, RFC~6525~\cite{streamReset}, and~\cite{udpencaps}.

\section{Sysctl variables}

In kernel implementations like for instance FreeBSD, it is possible to change parameters
in the operating system. These parameters are called sysctl variables.

In usrsctp applications can set or retrieve these variables with the functions
\begin{verbatim}
void
usrsctp_sysctl_set_ ## (uint32_t value)
\end{verbatim}
and
\begin{verbatim}
uint32_t
usrsctp_sysctl_get_ ## (void)
\end{verbatim}
respectively, where \#\# stands for the name of the variable.

In the following paragraphs a short description of the parameters will be given.

\subsection{Manipulate Memory}
\subsubsection{usrsctp\_sysctl\_set\_sctp\_sendspace()}
The space of the available send buffer can be changed from its default value of 262,144 bytes
to a value between 0 and $2^{32}-1$ bytes.

\subsubsection{usrsctp\_sysctl\_set\_sctp\_recvspace()}
The space of the available receive buffer can be changed from its default value of 262,144 bytes
to a value between 0 and $2^{32}-1$ bytes.

\subsubsection{usrsctp\_sysctl\_set\_sctp\_hashtblsize()}
The TCB (Thread Control Block) hash table sizes, i.e. the size of one TCB in the hash table, can be tuned between 
1 and $2^{32}-1$ bytes. The default value is 1,024 bytes. A TCB contains for instance pointers to the socket, the
endpoint, information about the association and some statistic data.

\subsubsection{usrsctp\_sysctl\_set\_sctp\_pcbtblsize()}
The PCB (Protocol Control Block) hash table sizes, i.e. the size of one PCB in the hash table, can be tuned between 
1 and $2^{32}-1$ bytes. The default value is 256 bytes. The PCB contains all variables that characterize an endpoint.

\subsubsection{usrsctp\_sysctl\_set\_sctp\_system\_free\_resc\_limit()}
This parameters tunes the maximum number of cached resources in the system. It can be set between 
0 and $2^{32}-1$. The default value is 1000.

\subsubsection{usrsctp\_sysctl\_set\_sctp\_asoc\_free\_resc\_limit()}
This parameters tunes the maximum number of cached resources in an association. It can be set between 
0 and $2^{32}-1$. The default value is 10.

\subsubsection{usrsctp\_sysctl\_set\_sctp\_mbuf\_threshold\_count()}
Data is stored in mbufs. Several mbufs can be chained together. The maximum number of small mbufs in a chain
can be set with this parameter, before an mbuf cluset is used. The default is 5.

\subsubsection{usrsctp\_sysctl\_set\_sctp\_add\_more\_threshold()}
TBD
This parameter configures the threshold below which more space should be added to a socket send buffer.
The default value is 1452 bytes.


\subsection{Configure RTO}
The retransmission timeout (RTO), i.e. the time that controls the retransmission of messages, has
several parameters, that can be changed, for example to shorten the time, before a message is
retransmitted. The range of these parameters is between 0 and $2^{32}-1$~ms. 

\subsubsection{usrsctp\_sysctl\_set\_sctp\_rto\_max\_default()}
The default value for the maximum retransmission timeout in ms is 60,000 (60~secs). 

\subsubsection{usrsctp\_sysctl\_set\_sctp\_rto\_min\_default()}
The default value for the minimum retransmission timeout in ms is 1,000 (1~sec). 

\subsubsection{usrsctp\_sysctl\_set\_sctp\_rto\_initial\_default()}
The default value for the initial retransmission timeout in ms is 3,000 (3~sec). This value is only
needed before the first calculation of a round trip time took place.

\subsubsection{usrsctp\_sysctl\_set\_sctp\_init\_rto\_max\_default()}
The default value for the maximum retransmission timeout for an INIT chunk in ms is 60,000 (60~secs). 


\subsection{Set Timers}
\subsubsection{usrsctp\_sysctl\_set\_sctp\_valid\_cookie\_life\_default()}
A cookie has a specified life time. If it expires the cookie is not valid any more and an ABORT is sent.
The default value in ms is 60,000 (60~secs).

\subsubsection{usrsctp\_sysctl\_set\_sctp\_heartbeat\_interval\_default()}
Set the default time between two heartbeats. The default is 30,000~ms.

\subsubsection{usrsctp\_sysctl\_set\_sctp\_shutdown\_guard\_time\_default()}
If a SHUTDOWN is not answered with a SHUTDOWN-ACK while the shutdown guard timer is still
running, the association will be aborted after the default of 180~secs.

\subsubsection{usrsctp\_sysctl\_set\_sctp\_pmtu\_raise\_time\_default()}
TBD
To set the size of the packets to the highest value possible, the maximum transfer unit (MTU)
of the complete path has to be known. The default time interval for the path mtu discovery
is 600~secs.

\subsubsection{usrsctp\_sysctl\_set\_sctp\_secret\_lifetime\_default()}
TBD
The default secret lifetime of a server is 3600~secs.

\subsubsection{usrsctp\_sysctl\_set\_sctp\_vtag\_time\_wait()}
TBD
Vtag time wait time, 0 disables it. Default: 60~secs


\subsection{Set Failure Limits}
Transmissions and retransmissions of messages might fail. To protect the system against too many
retransmissions, limits have to be defined.

\subsubsection{usrsctp\_sysctl\_set\_sctp\_init\_rtx\_max\_default()}
The default maximum number of retransmissions of an INIT chunks is 8, before an ABORT is sent.

\subsubsection{usrsctp\_sysctl\_set\_sctp\_assoc\_rtx\_max\_default()}
This parameter sets the maximum number of failed retransmissions before the association is aborted.
The default value is 10.

\subsubsection{usrsctp\_sysctl\_set\_sctp\_path\_rtx\_max\_default()}
This parameter sets the maximum number of path failures before the association is aborted.
The default value is 5. Notice that the number of paths multiplied by this value should be 
equal to sctp\_assoc\_rtx\_max\_default. That means that the default configuration is good for two 
paths.

\subsubsection{usrsctp\_sysctl\_set\_sctp\_max\_retran\_chunk()}
The parameter configures how many times an unlucky chunk can be retransmitted before the 
association aborts. The default is set to 30.
				
\subsubsection{usrsctp\_sysctl\_set\_sctp\_path\_pf\_threshold()}
TBD
Default potentially failed threshold. Default: 65535		

\subsubsection{usrsctp\_sysctl\_set\_sctp\_abort\_if\_one\_2\_one\_hits\_limit()}
TBD
When one-2-one hits qlimit abort. Default: 0

		
\subsection{Control the Sending of SACKs}
\subsubsection{usrsctp\_sysctl\_set\_sctp\_sack\_freq\_default()}
The SACK frequency defines the number of packets that are awaited, before a SACK is sent. 
The default value is 2.

\subsubsection{usrsctp\_sysctl\_set\_sctp\_delayed\_sack\_time\_default()}
As a SACK (Selective Acknowlegment) is sent after every other packet, a timer is set to send a
SACK in case another packet does not arrive in due time. The default value for this timer is
200~ms.

\subsubsection{usrsctp\_sysctl\_set\_sctp\_strict\_sacks()}
TBD
This is a flag to turn the controlling of the coherence of SACKs on or off. The default value is
1 (on).

\subsubsection{usrsctp\_sysctl\_set\_sctp\_nr\_sack\_on\_off()}
If a slow hosts receives data on a lossy link it is possible that its receiver window is full and new 
data can only be accepted if one chunk with a higher TSN (Transmission Sequence Number) that has 
previously been acknowledged is dropped. As a consequence the sender has to store data, even if
they have been acknowledged in case they have to be retransmitted. If this behavior is not necessary,
non-renegable SACKs can be turned on. 
By default the use of non-renegable SACKs is turned off.

\subsubsection{usrsctp\_sysctl\_set\_sctp\_enable\_sack\_immediately()}
In some cases it is not desirable to wait for the SACK timer to expire before a SACK is sent. In these
cases a bit called SACK-IMMEDIATELY~\cite{sack-imm} can be set to provoke the instant sending of a SACK. 
The default is to turn it off. 

\subsubsection{usrsctp\_sysctl\_set\_sctp\_L2\_abc\_variable()}
TBD
SCTP ABC max increase per SACK (L). Default: 1

\subsection{Change Max Burst}
Max burst defines the maximum number of packets that may be sent in one flight.

\subsubsection{usrsctp\_sysctl\_set\_sctp\_max\_burst\_default()}
The default value for max burst is 0, which means that the number of packets sent as a flight
is not limited by this parameter, but may be by another one, see the next paragraph.

\subsubsection{usrsctp\_sysctl\_set\_sctp\_use\_cwnd\_based\_maxburst()}
The use of max burst is based on the size of the congestion window (cwnd). 
This parameter is set by default.

\subsubsection{usrsctp\_sysctl\_set\_sctp\_hb\_maxburst()}
Heartbeats are mostly used to verify a path. Their number can be limited. The default is 4.

\subsubsection{usrsctp\_sysctl\_set\_sctp\_fr\_max\_burst\_default()}
In the state of fast retransmission the number of packet bursts can be limited. The default
value is 4.


\subsection{Handle Chunks}
\subsubsection{usrsctp\_sysctl\_set\_sctp\_peer\_chunk\_oh()}
In order to keep track of the peer's advertised receiver window, the sender calculates the window by
subtracting the amount of data sent. Yet, some OSs reduce the receiver window by the real space needed
to store the data. This parameter sets the additional amount to debit the peer's receiver window per
chunk sent. The default value is 256, which is the value needed by FreeBSD.

\subsubsection{usrsctp\_sysctl\_set\_sctp\_max\_chunks\_on\_queue()}
This parameter sets the maximum number of chunks that can be queued per association. The default 
value is 512.

\subsubsection{usrsctp\_sysctl\_set\_sctp\_min\_split\_point()}
TBD
The minimum size when splitting a chunk is 2904 bytes by default.

\subsubsection{usrsctp\_sysctl\_set\_sctp\_chunkscale()}
TBD
This parameter can be tuned for scaling of number of chunks and messages. The default is10.		
				
\subsubsection{usrsctp\_sysctl\_set\_sctp\_min\_residual()}
TBD
This parameter configures the minimum size of the residual data chunk in the second
part of the split. The default is 1452.


\subsection{Calculate RTT}
The calculation of the round trip time (RTT) depends on several parameters.

\subsubsection{usrsctp\_sysctl\_set\_sctp\_rttvar\_bw()}
TBD
Shift amount for bw smoothing on rtt calc. Default: 4

\subsubsection{usrsctp\_sysctl\_set\_sctp\_rttvar\_rtt()}
TBD
Shift amount for rtt smoothing on rtt calc. Default: 5

\subsubsection{usrsctp\_sysctl\_set\_sctp\_rttvar\_eqret()}
TBD
What to return when rtt and bw are unchanged. Default: 0


\subsection{Influence the Congestion Control}
The congestion control should protect the network against fast senders. 

\subsubsection{usrsctp\_sysctl\_set\_sctp\_ecn\_enable}
Explicit congestion notifications are turned on by default.

\subsubsection{usrsctp\_sysctl\_set\_sctp\_default\_cc\_module()}
This parameter sets the default algorithm for the congestion control.
Default is 0, i.e. the one specified in RFC~4960.

\subsubsection{usrsctp\_sysctl\_set\_sctp\_initial\_cwnd()}
Set the initial congestion window in MTUs. The default is 3.

\subsubsection{usrsctp\_sysctl\_set\_sctp\_use\_dccc\_ecn()}
TBD
Enable for RTCC CC datacenter ECN. Default: 1

\subsubsection{usrsctp\_sysctl\_set\_sctp\_steady\_step()}
TBD
How many the sames it takes to try step down of cwnd. Default: 20


\subsection{Configure AUTH and ADD-IP}
An important extension of SCTP is the dynamic address reconfiguration~\cite{addip}, also known as
ADD-IP, which allows the changing of addresses during the lifetime of an association.
For this feature the AUTH extension~\cite{auth} is necessary.

\subsubsection{usrsctp\_sysctl\_set\_sctp\_auto\_asconf()}
If SCTP Auto-ASCONF is enabled, the peer is informed automatically when a new address
is added or removed. This feature is enabled by default.

\subsubsection{usrsctp\_sysctl\_set\_sctp\_multiple\_asconfs()}
By default the sending of multiple ASCONFs is disabled.

\subsubsection{usrsctp\_sysctl\_set\_sctp\_auth\_disable()}
The use of AUTH, which is normally turned on, can be disabled by setting this parameter to 1.

\subsubsection{usrsctp\_sysctl\_set\_sctp\_asconf\_auth\_nochk()}
It is also possible to disable the requirement to use AUTH in conjunction with ADD-IP by setting this parameter
to 1.


\subsection{Concurrent Multipath Transfer (CMT)}
A prominent feature of SCTP is the possibility to use several addresses for the same association.
One is the primary path, and the others are needed in case of a path failure. Using CMT the data is sent 
on several paths to enhance the throughput.

\subsubsection{usrsctp\_sysctl\_set\_sctp\_cmt\_on\_off()}
To turn CMT on, this parameter has to be set to 1.

\subsubsection{usrsctp\_sysctl\_set\_sctp\_cmt\_use\_dac()}
To use delayed acknowledgments with CMT this parameter has to be set to 1.

\subsubsection{usrsctp\_sysctl\_set\_sctp\_buffer\_splitting()}
For CMT it makes sense to split the send and receive buffer to have shares for each path. 
By default buffer splitting is turned off.


\subsection{Network Address Translation (NAT)}
To be able to pass NAT boxes, the boxes have to handle SCTP packets in a specific way.

\subsubsection{usrsctp\_sysctl\_set\_sctp\_nat\_friendly()}
SCTP NAT friendly operation. Default:1

\subsubsection{usrsctp\_sysctl\_set\_sctp\_inits\_include\_nat\_friendly()}
Enable sending of the nat-friendly SCTP option on INITs. Default: 0

\subsubsection{usrsctp\_sysctl\_set\_sctp\_udp\_tunneling\_port()}
Set the SCTP/UDP tunneling port. Default: 9899

\subsection{SCTP Mobility}
\subsubsection{usrsctp\_sysctl\_set\_sctp\_mobility\_base()}
TBD
Enable SCTP base mobility. Default: 0


\subsubsection{usrsctp\_sysctl\_set\_sctp\_mobility\_fasthandoff()}
TBD
Enable SCTP fast handoff. default: 0


\subsection{Miscellaneous}
\subsubsection{usrsctp\_sysctl\_set\_sctp\_no\_csum\_on\_loopback()}
Calculating the checksum for packets sent on loopback is turned off by default.
To turn it on, set this parameter to 0.

\subsubsection{usrsctp\_sysctl\_set\_sctp\_nr\_outgoing\_streams\_default()}
The peer is notified about the number of outgoing streams in the INIT or INIT-ACK chunk.
The default is 10. 

\subsubsection{usrsctp\_sysctl\_set\_sctp\_do\_drain()}
Determines whether SCTP should respond to the drain calls. Default: 1		

\subsubsection{usrsctp\_sysctl\_set\_sctp\_strict\_data\_order()}
TBD
Enforce strict data ordering, abort if control inside data. Default: 0

\subsubsection{usrsctp\_sysctl\_set\_sctp\_default\_ss\_module()}
Set the default stream scheduling module. Implemented modules are:
SCTP\_SS\_DEFAULT, SCTP\_SS\_ROUND\_ROBIN, SCTP\_SS\_ROUND\_ROBIN\_PACKET,
SCTP\_SS\_PRIORITY, SCTP\_SS\_FAIR\_BANDWITH, and SCTP\_SS\_FIRST\_COME.

\subsubsection{usrsctp\_sysctl\_set\_sctp\_default\_frag\_interleave()}
TBD
Default fragment interleave level. Default: 1

\subsubsection{usrsctp\_sysctl\_set\_sctp\_blackhole()}
TBD
Enable SCTP blackholing. Default: 0

\subsubsection{usrsctp\_sysctl\_set\_sctp\_logging\_level()}
Set the logging level. The default is 0.


\subsubsection{usrsctp\_sysctl\_set\_sctp\_debug\_on()}
Turn debug output on or off. It is disabled by default. To obtain debug output,
SCTP\_DEBUG has to be set as a compile flag.

						
%The following variables are supported:
%\begin{longtable}{|l|l|c|} 
%\hline
%{\bfseries Parameter}&{\bfseries Meaning}&{\bfseries Default Value} \tabularnewline 
%\endhead
%\hline
%sctp\_sendspace&Send buffer space&1864135\tabularnewline \hline
%sctp\_recvspace&Receive buffer space&1864135 \tabularnewline \hline
%sctp\_hashtblsize&Tunable for TCB hash table sizes&1024 \tabularnewline \hline
%sctp\_pcbtblsize&Tunable for PCB hash table sizes&256 \tabularnewline \hline
%sctp\_system\_free\_resc\_limit&Cached resources in the system&1000 \tabularnewline \hline
%sctp\_asoc\_free\_resc\_limit&Cashed resources in an association&10 \tabularnewline \hline
%sctp\_rto\_max\_default&Default value for RTO\_max&60000~ms \tabularnewline \hline
%sctp\_rto\_min\_default&Default value for RTO\_min&1000~ms \tabularnewline \hline
%sctp\_rto\_initial\_default&Default value for RTO\_initial&3000~ms \tabularnewline \hline
%sctp\_init\_rto\_max\_default&Default value for the maximum RTO&60000~ms \tabularnewline
 %                                                  &for sending an INIT& \tabularnewline \hline
%sctp\_valid\_cookie\_life\_default&Valid cookie life time&60000~ms \tabularnewline \hline
%sctp\_init\_rtx\_max\_default&Maximum number of INIT retransmissions&8 \tabularnewline \hline
%sctp\_assoc\_rtx\_max\_default&Maximum number of failed retransmissions&10\tabularnewline
%						& before the association is aborted&\tabularnewline \hline
%sctp\_path\_rtx\_max\_default&Maximum number of failed retransmissions&5\tabularnewline
%						&before a path fails&\tabularnewline \hline
%sctp\_ecn\_enable&Enabling explicit congestion notifications&1\tabularnewline \hline
%sctp\_strict\_sacks&Control the coherence of SACKs&1 \tabularnewline \hline
%sctp\_delayed\_sack\_time\_default&Default delayed SACK timer&200~ms\tabularnewline \hline
%sctp\_sack\_freq\_default&Default SACK frequency&2 \tabularnewline \hline
%sctp\_nr\_sack\_on\_off&Turn non-renegable SACKs on or off&0 \tabularnewline \hline
%sctp\_enable\_sack\_immediately&Enable sending of the SACK-&0 \tabularnewline 						&IMMEDIATELY bit.&\tabularnewline \hline
%sctp\_no\_csum\_on\_loopback&Enable the compilation of the checksum on&1 \tabularnewline
%						&packets sent on loopback&\tabularnewline \hline
%sctp\_peer\_chunk\_oh&Amount to debit peers rwnd per chunk sent&256 \tabularnewline \hline
%sctp\_max\_burst\_default&Default max burst for SCTP endpoints&0 \tabularnewline \hline
%sctp\_use\_cwnd\_based\_maxburst&Use max burst based on the size of &1\tabularnewline				%							&the congestion window&\tabularnewline \hline
%sctp\_hb\_maxburst&Confirmation Heartbeat max burst&4 \tabularnewline \hline
%sctp\_max\_chunks\_on\_queue&Default max chunks on queue per asoc&512 \tabularnewline \hline
%sctp\_min\_split\_point&Minimum size when splitting a chunk&2904 \tabularnewline \hline
%sctp\_chunkscale&Tunable for Scaling of number of chunks and&10\tabularnewline 
%						&messages&\tabularnewline \hline
%sctp\_mbuf\_threshold\_count&Maximum number of small mbufs in a chain&5\tabularnewline \hline
%sctp\_heartbeat\_interval\_default&Deafult time between two Heartbeats&30000~ms\tabularnewline \hline
%sctp\_pmtu\_raise\_time\_default&Default PMTU raise timer&600~secs\tabularnewline \hline
%sctp\_shutdown\_guard\_time\_default&Default shutdown guard timer&180~secs\tabularnewline \hline
%sctp\_secret\_lifetime\_default&Default secret lifetime&3600~secs \tabularnewline \hline
%sctp\_add\_more\_threshold&Threshold when more space should &1452\tabularnewline 
%						&be added to a socket send buffer&\tabularnewline \hline
%sctp\_nr\_outgoing\_streams\_default&Default number of outgoing streams&10\tabularnewline \hline
%sctp\_cmt\_on\_off&Turn CMT on or off.&0\tabularnewline \hline
%sctp\_cmt\_use\_dac&Use delayed acknowledgment for CMT&0\tabularnewline \hline
%sctp\_fr\_max\_burst\_default&Default max burst for SCTP endpoints when &4\tabularnewline
%						&fast retransmitting&\tabularnewline \hline
%sctp\_auto\_asconf&Enable SCTP Auto-ASCONF&1\tabularnewline \hline
%sctp\_multiple\_asconfs&Enable SCTP Muliple-ASCONFs&0 \tabularnewline \hline
%sctp\_asconf\_auth\_nochk&Disable SCTP ASCONF AUTH requirement&0\tabularnewline \hline
%sctp\_auth\_disable&Disable SCTP AUTH function&0\tabularnewline \hline
%sctp\_nat\_friendly&SCTP NAT friendly operation&1\tabularnewline \hline
%sctp\_inits\_include\_nat\_friendly&Enable sending of the nat-friendly &0\tabularnewline
%					&SCTP option on INITs.&\tabularnewline \hline
%sctp\_udp\_tunneling\_port&Set the SCTP/UDP tunneling port&9899\tabularnewline \hline
%sctp\_do\_drain&Determines whether SCTP should respond&1\tabularnewline
%					&to the drain calls&\tabularnewline \hline
%sctp\_abort\_if\_one\_2\_one\_hits\_limit&When one-2-one hits qlimit abort&0 \tabularnewline \hline
%sctp\_strict\_data\_order&Enforce strict data ordering, abort if control&0\tabularnewline
%					&inside data&\tabularnewline \hline
%sctp\_min\_residual&Minimum residual data chunk in second&1452\tabularnewline
%					&part of split&\tabularnewline \hline
%sctp\_max\_retran\_chunk&Maximum times an unlucky chunk can be&30\tabularnewline
%				& retransmitted before the association aborts&\tabularnewline \hline
%sctp\_default\_cc\_module&Default congestion control module&0\tabularnewline \hline
%sctp\_default\_ss\_module&Default stream scheduling module&0 \tabularnewline \hline
%sctp\_default\_frag\_interleave&Default fragment interleave level&1\tabularnewline \hline
%sctp\_mobility\_base&Enable SCTP base mobility&0\tabularnewline \hline
%sctp\_mobility\_fasthandoff&Enable SCTP fast handoff&0\tabularnewline \hline
%sctp\_L2\_abc\_variable&SCTP ABC max increase per SACK (L)&1\tabularnewline \hline
%sctp\_vtag\_time\_wait&Vtag time wait time, 0 disables it.&60~secs\tabularnewline \hline
%sctp\_blackhole&Enable SCTP blackholing&0\tabularnewline \hline
%sctp\_path\_pf\_threshold&Default potentially failed threshold&65535\tabularnewline \hline
%sctp\_rttvar\_bw&Shift amount for bw smoothing on rtt calc&4 \tabularnewline \hline
%sctp\_rttvar\_rtt&Shift amount for rtt smoothing on rtt calc&5 \tabularnewline \hline
%sctp\_rttvar\_eqret &What to return when rtt and bw are&0\tabularnewline
%					&unchanged&\tabularnewline \hline
%sctp\_steady\_step&How many the sames it takes to try step&20\tabularnewline
%					&down of cwnd&\tabularnewline \hline
%sctp\_use\_dccc\_ecn&Enable for RTCC CC datacenter ECN&1 \tabularnewline \hline
%sctp\_buffer\_splitting&Enable send/receive buffer splitting&0 \tabularnewline \hline
%sctp\_initial\_cwnd&Initial congestion window in MTUs&3\tabularnewline \hline
%sctp\_logging\_level&Logging level&0 \tabularnewline \hline
%sctp\_debug\_on&Turns debug output on or off.&0 \tabularnewline \hline

%\caption{Sysctl variables supported by usrsctp}
%\end{longtable}

\section{Examples}
\subsection{Discard Server}\label{server}
\begin{verbatim}
/*
 * Copyright (C) 2011-2012 Michael Tuexen
 *
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the project nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE PROJECT AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.	IN NO EVENT SHALL THE PROJECT OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

/*
 * Usage: discard_server [local_encaps_port] [remote_encaps_port]
 */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#if !defined(__Userspace_os_Windows)
#include <unistd.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#endif
#include <usrsctp.h>

#define BUFFER_SIZE 10240

const int use_cb = 0;

static int
receive_cb(struct socket *sock, union sctp_sockstore addr, void *data,
           size_t datalen, struct sctp_rcvinfo rcv, int flags)
{
    char name[INET6_ADDRSTRLEN];

    if (data) {
        if (flags & MSG_NOTIFICATION) {
            printf("Notification of length %d received.\n", (int)datalen);
        } else {
            printf("Msg of length %d received from %s:%u on stream %d with "
                   "SSN %u and TSN %u, PPID %d, context %u.\n",
                   (int)datalen,
                   addr.sa.sa_family == AF_INET ?
                       inet_ntop(AF_INET, &addr.sin.sin_addr, name, 
                                 INET6_ADDRSTRLEN):
                       inet_ntop(AF_INET6, &addr.sin6.sin6_addr, name, 
                                 INET6_ADDRSTRLEN),
                   ntohs(addr.sin.sin_port),
                   rcv.rcv_sid,
                   rcv.rcv_ssn,
                   rcv.rcv_tsn,
                   ntohl(rcv.rcv_ppid),
                   rcv.rcv_context);
        }
        free(data);
    }
    return 1;
}

int
main(int argc, char *argv[])
{
    struct socket *sock;
    struct sockaddr_in6 addr;
    struct sctp_udpencaps encaps;
    struct sctp_event event;
    uint16_t event_types[] = {SCTP_ASSOC_CHANGE,
	                              SCTP_PEER_ADDR_CHANGE,
	                              SCTP_REMOTE_ERROR,
	                              SCTP_SHUTDOWN_EVENT,
	                              SCTP_ADAPTATION_INDICATION,
	                              SCTP_PARTIAL_DELIVERY_EVENT};
    unsigned int i;
    struct sctp_assoc_value av;
    const int on = 1;
    int n, flags;
    socklen_t from_len;
    char buffer[BUFFER_SIZE];
    char name[INET6_ADDRSTRLEN];
    struct sctp_recvv_rn rn;
    socklen_t infolen = sizeof(struct sctp_recvv_rn);
    struct sctp_rcvinfo rcv;
    struct sctp_nxtinfo nxt;
    unsigned int infotype = 0;

    if (argc > 1) {
        usrsctp_init(atoi(argv[1]));
    } else {
        usrsctp_init(9899);
    }
    usrsctp_sysctl_set_sctp_debug_on(0);
    usrsctp_sysctl_set_sctp_blackhole(2);

    if ((sock = usrsctp_socket(AF_INET6, SOCK_SEQPACKET, IPPROTO_SCTP, 
    	                          use_cb?receive_cb:NULL, NULL, 0)) == NULL) {
        perror("userspace_socket");
    }
    if (usrsctp_setsockopt(sock, IPPROTO_SCTP, SCTP_I_WANT_MAPPED_V4_ADDR, 
                           (const void*)&on, (socklen_t)sizeof(int)) < 0) {
        perror("setsockopt");
    }
    memset(&av, 0, sizeof(struct sctp_assoc_value));
    av.assoc_id = SCTP_ALL_ASSOC;
    av.assoc_value = 47;

    if (usrsctp_setsockopt(sock, IPPROTO_SCTP, SCTP_CONTEXT, (const void*)&av, 
                           (socklen_t)sizeof(struct sctp_assoc_value)) < 0) {
        perror("setsockopt");
    }
    if (argc > 2) {
        memset(&encaps, 0, sizeof(struct sctp_udpencaps));
        encaps.sue_address.ss_family = AF_INET6;
        encaps.sue_port = htons(atoi(argv[2]));
        if (usrsctp_setsockopt(sock, IPPROTO_SCTP, SCTP_REMOTE_UDP_ENCAPS_PORT, 
                               (const void*)&encaps, 
                               (socklen_t)sizeof(struct sctp_udpencaps)) < 0) {
            perror("setsockopt");
        }
    }
    memset(&event, 0, sizeof(event));
    event.se_assoc_id = SCTP_FUTURE_ASSOC;
    event.se_on = 1;
    for (i = 0; i < (unsigned int)(sizeof(event_types)/sizeof(uint16_t)); i++) {
        event.se_type = event_types[i];
        if (usrsctp_setsockopt(sock, IPPROTO_SCTP, SCTP_EVENT, &event, 
                               sizeof(struct sctp_event)) < 0) {
            perror("userspace_setsockopt");
        }
    }
    memset((void *)&addr, 0, sizeof(struct sockaddr_in6));
#ifdef HAVE_SIN_LEN
    addr.sin6_len = sizeof(struct sockaddr_in6);
#endif
    addr.sin6_family = AF_INET6;
    addr.sin6_port = htons(9);
    addr.sin6_addr = in6addr_any;
    if (usrsctp_bind(sock, (struct sockaddr *)&addr, 
                     sizeof(struct sockaddr_in6)) < 0) {
        perror("userspace_bind");
    }
    if (usrsctp_listen(sock, 1) < 0) {
        perror("userspace_listen");
    }
    while (1) {
        if (use_cb) {
#if defined (__Userspace_os_Windows)
            Sleep(1*1000);
#else
            sleep(1);
#endif
        } else {
            from_len = (socklen_t)sizeof(struct sockaddr_in6);
            flags = 0;
            rn.recvv_rcvinfo = rcv;
            rn.recvv_nxtinfo = nxt;
            n = usrsctp_recvv(sock, (void*)buffer, BUFFER_SIZE, 
                              (struct sockaddr *) &addr, &from_len, (void *)&rn,
	                     &infolen, &infotype, &flags);
            if (n > 0) {
                if (flags & MSG_NOTIFICATION) {
                    printf("Notification of length %d received.\n", n);
                } else {
                    printf("Msg of length %d received from %s:%u on stream "
                           "%d with SSN %u and TSN %u, PPID %d, context %u, "
                           "complete %d.\n",
                           n,
                           inet_ntop(AF_INET6, &addr.sin6_addr, name, 
                                     INET6_ADDRSTRLEN), ntohs(addr.sin6_port),
                           rn.recvv_rcvinfo.rcv_sid,
                           rn.recvv_rcvinfo.rcv_ssn,
                           rn.recvv_rcvinfo.rcv_tsn,
                           ntohl(rn.recvv_rcvinfo.rcv_ppid),
                           rn.recvv_rcvinfo.rcv_context,
                           (flags & MSG_EOR) ? 1 : 0);
                }
            }
        }
    }
    usrsctp_close(sock);
    while (usrsctp_finish() != 0) {
#if defined (__Userspace_os_Windows)
        Sleep(1000);
#else
        sleep(1);
#endif
    }
    return (0);
}

\end{verbatim}

\subsection{Client}\label{client}
\begin{verbatim}
/*
 * Copyright (C) 2011-2012 Michael Tuexen
 *
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the project nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE PROJECT AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.	IN NO EVENT SHALL THE PROJECT OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

/*
 * Usage: client remote_addr remote_port [local_encaps_port remote_encaps_port]
 */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#if !defined(__Userspace_os_Windows)
#include <unistd.h>
#endif
#include <sys/types.h>
#if !defined(__Userspace_os_Windows)
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#endif
#include <usrsctp.h>

int done = 0;

static int
receive_cb(struct socket *sock, union sctp_sockstore addr, void *data,
           size_t datalen, struct sctp_rcvinfo rcv, int flags)
{
    if (data == NULL) {
        done = 1;
        usrsctp_close(sock);
    } else {
        write(fileno(stdout), data, datalen);
        free(data);
    }
    return 1;
}

int
main(int argc, char *argv[])
{
    struct socket *sock;
    struct sockaddr_in addr4;
    struct sockaddr_in6 addr6;
    struct sctp_udpencaps encaps;
    char buffer[80];

    if (argc > 3) {
        usrsctp_init(atoi(argv[3]));
    } else {
        usrsctp_init(9899);
    }
    usrsctp_sysctl_set_sctp_debug_on(0);
    usrsctp_sysctl_set_sctp_blackhole(2);
    if ((sock = usrsctp_socket(AF_INET, SOCK_STREAM, IPPROTO_SCTP, 
                               receive_cb, NULL, 0)) == NULL) {
        perror("userspace_socket ipv6");
    }
    if (argc > 4) {
        memset(&encaps, 0, sizeof(struct sctp_udpencaps));
        encaps.sue_address.ss_family = AF_INET6;
        encaps.sue_port = htons(atoi(argv[4]));
        if (usrsctp_setsockopt(sock, IPPROTO_SCTP, SCTP_REMOTE_UDP_ENCAPS_PORT, 
                               (const void*)&encaps, 
                               (socklen_t)sizeof(struct sctp_udpencaps)) < 0) {
            perror("setsockopt");
        }
    }
    memset((void *)&addr4, 0, sizeof(struct sockaddr_in));
    memset((void *)&addr6, 0, sizeof(struct sockaddr_in6));
#if !defined(__Userspace_os_Linux) && !defined(__Userspace_os_Windows)
    addr4.sin_len = sizeof(struct sockaddr_in);
    addr6.sin6_len = sizeof(struct sockaddr_in6);
#endif
    addr4.sin_family = AF_INET;
    addr6.sin6_family = AF_INET6;
    addr4.sin_port = htons(atoi(argv[2]));
    addr6.sin6_port = htons(atoi(argv[2]));
    if (inet_pton(AF_INET6, argv[1], &addr6.sin6_addr) == 1) {
        if (usrsctp_connect(sock, (struct sockaddr *)&addr6, 
                            sizeof(struct sockaddr_in6)) < 0) {
            perror("userspace_connect");
        }
    } else if (inet_pton(AF_INET, argv[1], &addr4.sin_addr) == 1) {
        if (usrsctp_connect(sock, (struct sockaddr *)&addr4, 
                            sizeof(struct sockaddr_in)) < 0) {
            perror("userspace_connect");
        }
    } else {
        printf("Illegal destination address.\n");
    }
    while ((fgets(buffer, sizeof(buffer), stdin) != NULL) && !done) {
        usrsctp_sendv(sock, buffer, strlen(buffer), NULL, 0,
				                  NULL, 0, SCTP_SENDV_NOINFO, 0);
    }
    if (!done) {
        usrsctp_shutdown(sock, SHUT_WR);
    }
    while (!done) {
#if defined (__Userspace_os_Windows)
        Sleep(1*1000);
#else
        sleep(1);
#endif
    }
    while (usrsctp_finish() != 0) {
#if defined (__Userspace_os_Windows)
        Sleep(1000);
#else
        sleep(1);
#endif
    }
    return(0);
}

\end{verbatim}
\bibliographystyle{plain}
%
\begin{thebibliography}{99}

\bibitem{socketAPI}
R.~Stewart, M.~T\"uxen, K.~Poon, and V.~Yasevich:
\textit{Sockets API Extensions for the Stream Control Transmission Protocol (SCTP)}.
RFC~6458, Dezember~2011.

\bibitem{SCTP}
R.~Stewart:
\textit{Stream Control Transmission Protocol}.
RFC~4960, September~2007.


\bibitem{auth}
M.~T\"uxen, R.~Stewart, P.~Lei, and E.~Rescorla:
\textit{Authenticated Chunks for the Stream Control Transmission Protocol (SCTP)}.
RFC~4895, August~2007.

\bibitem{streamReset}
R.~Stewart, M.~T\"uxen, and P.~Lei:
\textit{Stream Control Transmission Protocol (SCTP) Stream Reconfiguration}.
RFC~6525, February~2012.


\bibitem{addip}
R.~Stewart,  Q.~Xie, M.~T\"uxen, S.~Maruyama, and M.~Kozuka:
\textit{Stream Control Transmission Protocol (SCTP) Dynamic Address Reconfiguration}.
RFC~5061, September~2007.

\bibitem{sack-imm}
M.~T\"uxen, I.~R\"ungeler, and R.~Stewart:
\textit{SACK-IMMEDIATELY Extension for the Stream Control Transmission Protocol}.
draft-tuexen-tsvwg-sctp-sack-immediately-09 (work in progress), April~2012.

\bibitem{udpencaps}
M.~T\"uxen and R.~Stewart
\textit{UDP Encapsulation of SCTP Packetsl}.
draft-ietf-tsvwg-sctp-udp-encaps-03 (work in progress), March~2012.

\end{thebibliography}
\end{document}