NAME

SYNOPSIS

DESCRIPTION

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

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 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 */
};
    

CONTROL MESSAGES

NGM_SSCOP_SETPARAM (setparam)

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 (getparam)

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

NGM_SSCOP_ENABLE (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 (disable)

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

NGM_SSCOP_SETDEBUG (setdebug)

Set debugging flags. The argument is a uint32_t.

NGM_SSCOP_GETDEBUG (getdebug)

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

NGM_SSCOP_GETSTATE (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

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

SEE ALSO

AUTHORS