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 */
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 connection.
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 */
};
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 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 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.
NGM_SSCOP_GETPARAM
This message returns the current operational parameters of the SSCOP instance in a .Vt sscop_param structure.
NGM_SSCOP_ENABLE
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.
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 .Vt uint32_t .
NGM_SSCOP_GETDEBUG
Retrieve the actual debugging flags. Needs no arguments and responds with a .Vt uint32_t .
NGM_SSCOP_GETSTATE
Responds with the current state of the SSCOP instance in a .Vt uint32_t . If the node is not enabled, the retrieved state is 0.
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 .Vt 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 window, the current window is opened up to this value. Automatic window updates are enabled if they were disabled.
