ng_sscop

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 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 standard. 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 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:

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

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:

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:

Here sig is one of

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

CONTROL MESSAGES

The sscop node understands the generic control messages, plus the following:

NGM_SSCOP_SETPARAM (setparam)

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

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:

The flags field contains the following flags influencing SSCOP operation:

The bitmap has the following bits:

The node responds to the NGM_SSCOP_SETPARAM message with the following response:

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

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 window, 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 <[email protected]>