ng_sscop -- netgraph SSCOP node type
#include <netnatm/saal/sscopdef.h>
#include <netgraph/atm/ng_sscop.h>
The ng_sscop netgraph node 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 shutdown either by a NGM_SHUTDOWN message or when all hooks
are disconnected.
Each ng_sscop node has three hooks with fixed names:
lower This hook is the hook that 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
ng_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[];
};
sig 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 */
};
The ng_sscop node understands the generic messages plus the following:
NGM_SSCOP_SETPARAM
Set 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 the 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.
NGM_SSCOP_GETPARAM
This message returns the current operational parameters of the SSCOP
instance in a 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 not set and
all message 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 an uint32_t.
NGM_SSCOP_GETDEBUG
Retrieve the actual debugging flags. Needs no arguments and
responds with an uint32_t.
NGM_SSCOP_GETSTATE
Responds with the current state of the SSCOP instance in an
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 ng_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 receive still 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 too or higher than high_watermark than 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 <[email protected]>
FreeBSD October 24, 2003 FreeBSD
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