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     ng_sscop — netgraph SSCOP node type


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


     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
     private 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

     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.


     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 message
             is received, the busy state is cleared.  Note that the node does
             not look at the message contents of these flow control messages.

     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_DATA_request,         /* <- MU */
                 SSCOP_DATA_indication,      /* -> MU, SN */

                 SSCOP_UDATA_request,        /* <- MU */
                 SSCOP_UDATA_indication,     /* -> MU */

                 SSCOP_RECOVER_indication,   /* -> */
                 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

             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

     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 */


     The sscop node understands the generic control messages, plus the

             Sets operational parameters of the SSCOP instance and takes the
             following structure:

             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

                   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
             following 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(2) code describing why the parameter could not be set.

             This message returns the current operational parameters of the
             SSCOP instance in a sscop_param structure.

             This message creates the actual SSCOP instance and initializes
             it.  Until this is done, parameters may neither be retrieved nor
             set, and all messages received on any hook are discarded.

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

             Set debugging flags.  The argument is a uint32_t.

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

             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 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:

             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.

             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.

             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
             window, the current window is opened up to this value.  Automatic
             window updates are enabled if they were disabled.


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


     Harti Brandt ⟨