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ng_sscop(4)

NAME

     ng_sscop -- netgraph SSCOP node type

SYNOPSIS

     #include <netnatm/saal/sscopdef.h>
     #include <netgraph/atm/ng_sscop.h>

DESCRIPTION

     The sscop netgraph node type implements the ITU-T standard Q.2110.  This
     standard describes the so called Service Specific Connection Oriented
     Protocol (SSCOP) that is used to carry signalling messages over the pri-
     vate and public UNIs and the public NNI.  This protocol is a transport
     protocol with selective acknowledgements, and can be tailored to the
     environment.  This implementation is a full implementation of that stan-
     dard.

     After creation of the node, the SSCOP instance must be created by sending
     an ``enable'' message to the node.  If the node is enabled, the SSCOP
     parameters can be retrieved and modified and the protocol can be started.

     The node is shut down either by a NGM_SHUTDOWN message, or when all hooks
     are disconnected.

HOOKS

     Each sscop node has three hooks with fixed names:

     lower   This hook must be connected to a node that ensures transport of
	     packets to and from the remote peer node.	Normally this is a
	     ng_atm(4) node with an AAL5 hook, but the sscop node is able to
	     work on any packet-transporting layer, like, for example, IP or
	     UDP.  The node handles flow control messages received on this
	     hook: if it receives a NGM_HIGH_WATER_PASSED message, it declares
	     the ``lower layer busy'' state.  If a NGM_LOW_WATER_PASSED mes-
	     sage is received, the busy state is cleared.  Note that the node
	     does not look at the message contents of these flow control mes-
	     sages.

     upper   This is the interface to the SSCOP user.  This interface uses the
	     following message format:

	     struct sscop_arg {
		     uint32_t sig;
		     uint32_t arg;   /* opt. sequence number or clear-buff */
		     u_char   data[];
	     };

	     The sig field is one of the signals defined in the standard:

	     enum sscop_aasig {
		 SSCOP_ESTABLISH_request,    /* <- UU, BR */
		 SSCOP_ESTABLISH_indication, /* -> UU */
		 SSCOP_ESTABLISH_response,   /* <- UU, BR */
		 SSCOP_ESTABLISH_confirm,    /* -> UU */

		 SSCOP_RELEASE_request,      /* <- UU */
		 SSCOP_RELEASE_indication,   /* -> UU, SRC */
		 SSCOP_RELEASE_confirm,      /* -> */
		 SSCOP_RECOVER_response,     /* <- */

		 SSCOP_RESYNC_request,	     /* <- UU */
		 SSCOP_RESYNC_indication,    /* -> UU */
		 SSCOP_RESYNC_response,      /* <- */
		 SSCOP_RESYNC_confirm,	     /* -> */

		 SSCOP_RETRIEVE_request,     /* <- RN */
		 SSCOP_RETRIEVE_indication,  /* -> MU */
		 SSCOP_RETRIEVE_COMPL_indication,/* -> */
	     };

	     The arrows in the comment show the direction of the signal,
	     whether it is a signal that comes out of the node (`->'), or is
	     sent by the node user to the node (`<-').	The arg field contains
	     the argument to some of the signals: it is either a PDU sequence
	     number, or the CLEAR-BUFFER flag.	There are a number of special
	     sequence numbers for some operations:

		   SSCOP_MAXSEQNO	   maximum legal sequence number
		   SSCOP_RETRIEVE_UNKNOWN  retrieve transmission queue
		   SSCOP_RETRIEVE_TOTAL    retrieve transmission buffer and
					   queue

	     For signals that carry user data (as, for example,
	     SSCOP_DATA_request) these two fields are followed by the variable
	     sized user data.

	     If the upper hook is disconnected and the SSCOP instance is not
	     in the idle state, and the lower hook is still connected, an
	     SSCOP_RELEASE_request is executed to release the SSCOP connec-
	     tion.

     manage  This is the management interface defined in the standard.	The
	     data structure used here is:

	     struct sscop_marg {
		     uint32_t sig;
		     u_char   data[];
	     };

	     Here sig is one of

	     enum sscop_maasig {
		 SSCOP_MDATA_request,	     /* <- MU */
		 SSCOP_MDATA_indication,     /* -> MU */
		 SSCOP_MERROR_indication,    /* -> CODE, CNT */
	     };

	     The SSCOP_MDATA signals are followed by the actual management
	     data, where the SSCOP_MERROR signal has the form:

	     struct sscop_merr {
		     uint32_t sig;
		     uint32_t err;   /* error code */
		     uint32_t cnt;   /* error count */
	     };

	     struct ng_sscop_setparam {
		     uint32_t		     mask;
		     struct sscop_param      param;
	     };

	     The sub-structure param contains the parameters to set, and the
	     mask field contains a bit mask, telling which of the parameters
	     to set, and which to ignore.  If a bit is set, the corresponding
	     parameter is set.	The parameters are:

	     struct sscop_param {
		     uint32_t timer_cc;      /* timer_cc in msec */
		     uint32_t timer_poll;    /* timer_poll im msec */
		     uint32_t timer_keep_alive;/* timer_keep_alive in msec */
		     uint32_t timer_no_response;/*timer_no_response in msec */
		     uint32_t timer_idle;    /* timer_idle in msec */
		     uint32_t maxk;	     /* maximum user data in bytes */
		     uint32_t maxj;	     /* maximum u-u info in bytes */
		     uint32_t maxcc;	     /* max. retransmissions for control packets */
		     uint32_t maxpd;	     /* max. vt(pd) before sending poll */
		     uint32_t maxstat;	     /* max. number of elements in stat list */
		     uint32_t mr;	     /* initial window */
		     uint32_t flags;	     /* flags */
	     };

	     The flags field contains the following flags influencing SSCOP
	     operation:

		   SSCOP_ROBUST   enable atmf/97-0216 robustness enhancement
		   SSCOP_POLLREX  send POLL after each retransmission

	     The bitmap has the following bits:

		   SSCOP_SET_TCC      set timer_cc
		   SSCOP_SET_TPOLL    set timer_poll
		   SSCOP_SET_TKA      set timer_keep_alive
		   SSCOP_SET_TNR      set timer_no_response
		   SSCOP_SET_TIDLE    set timer_idle
		   SSCOP_SET_MAXK     set maxk
		   SSCOP_SET_MAXJ     set maxj
		   SSCOP_SET_MAXCC    set maxcc
		   SSCOP_SET_MAXPD    set maxpd
		   SSCOP_SET_MAXSTAT  set maxstat
		   SSCOP_SET_MR       set the initial window
		   SSCOP_SET_ROBUST   set or clear SSCOP_ROBUST
		   SSCOP_SET_POLLREX  set or clear SSCOP_POLLREX

	     The node responds to the NGM_SSCOP_SETPARAM message with the fol-
	     lowing response:

	     struct ng_sscop_setparam_resp {
		     uint32_t mask;
		     int32_t  error;
	     };

	     Here mask contains a bitmask of the parameters that the user
	     requested to set, but that could not be set and error is an
	     errno(3) code describing why the parameter could not be set.
	     set, and all messages received on any hook are discarded.

     NGM_SSCOP_DISABLE
	     Destroy the SSCOP instance.  After this, all messages on any
	     hooks are discarded.

     NGM_SSCOP_SETDEBUG
	     Set debugging flags.  The argument is a uint32_t.

     NGM_SSCOP_GETDEBUG
	     Retrieve the actual debugging flags.  Needs no arguments and
	     responds with a uint32_t.

     NGM_SSCOP_GETSTATE
	     Responds with the current state of the SSCOP instance in a
	     uint32_t.	If the node is not enabled, the retrieved state is 0.

FLOW CONTROL

     Flow control works on the upper and on the lower layer interface.	At the
     lower layer interface, the two messages, NGM_HIGH_WATER_PASSED and
     NGM_LOW_WATER_PASSED, are used to declare or clear the ``lower layer
     busy'' state of the protocol.

     At the upper layer interface, the sscop node handles three types of flow
     control messages:

     NGM_HIGH_WATER_PASSED
	     If this message is received, the SSCOP stops moving the receive
	     window.  Each time a data message is handed over to the upper
	     layer, the receive window is moved by one message.  Stopping
	     these updates means that the window will start to close and if
	     the peer has sent all messages allowed by the current window, it
	     stops transmission.  This means that the upper layer must be able
	     to still receive a full window amount of messages.

     NGM_LOW_WATER_PASSED
	     This will re-enable the automatic window updates, and if the
	     space indicated in the message is larger than the current window,
	     the window will be opened by that amount.	The space is computed
	     as the difference of the max_queuelen_packets and current members
	     of the ngm_queue_state structure.

     NGM_SYNC_QUEUE_STATE
	     If the upper layer buffer filling state, as indicated by current,
	     is equal to or greater than high_watermark then the message is
	     ignored.  If this is not the case, the amount of receiver space
	     is computed as the difference of max_queuelen_packets and current
	     if automatic window updates are currently allowed, and as the
	     difference of high_water_mark and current if window updates are
	     disabled.	If the resulting value is larger than the current win-
	     dow, the current window is opened up to this value.  Automatic
	     window updates are enabled if they were disabled.

SEE ALSO

     netgraph(4), ng_atm(4), ng_sscfu(4), ngctl(8)

AUTHORS

     Harti Brandt <harti@FreeBSD.org>

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