1.\"
2.\" Copyright (c) 2001-2003
3.\" Fraunhofer Institute for Open Communication Systems (FhG Fokus).
4.\" All rights reserved.
5.\"
6.\" Redistribution and use in source and binary forms, with or without
7.\" modification, are permitted provided that the following conditions
8.\" are met:
9.\" 1. Redistributions of source code must retain the above copyright
10.\" notice, this list of conditions and the following disclaimer.
11.\" 2. Redistributions in binary form must reproduce the above copyright
12.\" notice, this list of conditions and the following disclaimer in the
13.\" documentation and/or other materials provided with the distribution.
14.\"
15.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
16.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
17.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
18.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
19.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
20.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
21.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
22.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
23.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
24.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
25.\" SUCH DAMAGE.
26.\"
27.\" Author: Hartmut Brandt <harti@freebsd.org>
28.\"
| 1.\"
2.\" Copyright (c) 2001-2003
3.\" Fraunhofer Institute for Open Communication Systems (FhG Fokus).
4.\" All rights reserved.
5.\"
6.\" Redistribution and use in source and binary forms, with or without
7.\" modification, are permitted provided that the following conditions
8.\" are met:
9.\" 1. Redistributions of source code must retain the above copyright
10.\" notice, this list of conditions and the following disclaimer.
11.\" 2. Redistributions in binary form must reproduce the above copyright
12.\" notice, this list of conditions and the following disclaimer in the
13.\" documentation and/or other materials provided with the distribution.
14.\"
15.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
16.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
17.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
18.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
19.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
20.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
21.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
22.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
23.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
24.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
25.\" SUCH DAMAGE.
26.\"
27.\" Author: Hartmut Brandt <harti@freebsd.org>
28.\"
|
29.\" $FreeBSD: head/share/man/man4/ng_sscop.4 131472 2004-07-02 19:07:33Z ru $
| 29.\" $FreeBSD: head/share/man/man4/ng_sscop.4 131530 2004-07-03 18:29:24Z ru $
|
30.\"
31.\" ng_sscop(4) man page
32.\"
33.Dd October 24, 2003
34.Dt NG_SSCOP 4
35.Os FreeBSD
36.Sh NAME
37.Nm ng_sscop
38.Nd netgraph SSCOP node type
39.Sh SYNOPSIS
40.Fd #include <netnatm/saal/sscopdef.h>
41.Fd #include <netgraph/atm/ng_sscop.h>
42.Sh DESCIPTION
43The
44.Nm
| 30.\"
31.\" ng_sscop(4) man page
32.\"
33.Dd October 24, 2003
34.Dt NG_SSCOP 4
35.Os FreeBSD
36.Sh NAME
37.Nm ng_sscop
38.Nd netgraph SSCOP node type
39.Sh SYNOPSIS
40.Fd #include <netnatm/saal/sscopdef.h>
41.Fd #include <netgraph/atm/ng_sscop.h>
42.Sh DESCIPTION
43The
44.Nm
|
45netgraph node implements the ITU-T standard Q.2110. This standard describes
| 45netgraph node implements the ITU-T standard Q.2110.
46This standard describes
|
46the so called Service Specific Connection Oriented Protocol (SSCOP) that
47is used to carry signalling messages over the private and public UNIs and
48the public NNI.
49This protocol is a transport protocol with selective
50acknowledgements and can be tailored to the environment.
51This implementation is a full implementation of that standard.
52.Pp
53After creation of the node, the SSCOP instance must be created by sending
54an enable message to the node.
55If the node is enabled, the SSCOP parameters
56can be retrieved and modified and the protocol can be started.
57.Pp
58The node is shutdown either by a
59.Dv NGM_SHUTDOWN
60message or when all hooks are disconnected.
61.Sh HOOKS
62Each
63.Nm
64node has three hooks with fixed names:
65.Bl -tag -width manage
66.It Dv lower
67This hook is the hook that must be connected to a node that ensures
| 47the so called Service Specific Connection Oriented Protocol (SSCOP) that
48is used to carry signalling messages over the private and public UNIs and
49the public NNI.
50This protocol is a transport protocol with selective
51acknowledgements and can be tailored to the environment.
52This implementation is a full implementation of that standard.
53.Pp
54After creation of the node, the SSCOP instance must be created by sending
55an enable message to the node.
56If the node is enabled, the SSCOP parameters
57can be retrieved and modified and the protocol can be started.
58.Pp
59The node is shutdown either by a
60.Dv NGM_SHUTDOWN
61message or when all hooks are disconnected.
62.Sh HOOKS
63Each
64.Nm
65node has three hooks with fixed names:
66.Bl -tag -width manage
67.It Dv lower
68This hook is the hook that must be connected to a node that ensures
|
68transport of packets to and from the remote peer node. Normally this is a
| 69transport of packets to and from the remote peer node.
70Normally this is a
|
69.Xr ng_atm 4
70node with an AAL5 hook, but the
71.Nm
72node is able to work on any packet-transporting layer, like, for example,
73IP or UDP.
74The node handles flow control messages received on
75this hook: if it receives a
76.Dv NGM_HIGH_WATER_PASSED
77message it declares the
78.Ql lower layer busy
79state.
80If a
81.Dv NGM_LOW_WATER_PASSED
82message is received the busy state is cleared.
83Note, that the node does not
84look at the message contents of these flow control messages.
85.It Dv upper
86This is the interface to the SSCOP user.
87This interface uses the following message format:
88.Bd -literal
89struct sscop_arg {
90 uint32_t sig;
91 uint32_t arg; /* opt. sequence number or clear-buff */
92 u_char data[];
93};
94.Ed
95.Pp
96.Fa sig
97is one of the signals defined in the standard:
98.Bd -literal
99enum sscop_aasig {
100 SSCOP_ESTABLISH_request, /* <- UU, BR */
101 SSCOP_ESTABLISH_indication, /* -> UU */
102 SSCOP_ESTABLISH_response, /* <- UU, BR */
103 SSCOP_ESTABLISH_confirm, /* -> UU */
104
105 SSCOP_RELEASE_request, /* <- UU */
106 SSCOP_RELEASE_indication, /* -> UU, SRC */
107 SSCOP_RELEASE_confirm, /* -> */
108
109 SSCOP_DATA_request, /* <- MU */
110 SSCOP_DATA_indication, /* -> MU, SN */
111
112 SSCOP_UDATA_request, /* <- MU */
113 SSCOP_UDATA_indication, /* -> MU */
114
115 SSCOP_RECOVER_indication, /* -> */
116 SSCOP_RECOVER_response, /* <- */
117
118 SSCOP_RESYNC_request, /* <- UU */
119 SSCOP_RESYNC_indication, /* -> UU */
120 SSCOP_RESYNC_response, /* <- */
121 SSCOP_RESYNC_confirm, /* -> */
122
123 SSCOP_RETRIEVE_request, /* <- RN */
124 SSCOP_RETRIEVE_indication, /* -> MU */
125 SSCOP_RETRIEVE_COMPL_indication,/* -> */
126};
127.Ed
128.Pp
129The arrows in the comment show the direction of the signal whether it
130is a signal that comes out of the node
131.Ql ->
132or is sent by the node user to the node
133.Ql <- .
134The
135.Fa arg
136field contains the argument to some of the signals: it is either a PDU
137sequence number or the
138.Dv CLEAR-BUFFER
139flag.
140There are a number of special sequence numbers for some operations:
141.Bl -column SSCOP_RETRIEVE_UNKNOWN -offset indent
142.It Dv SSCOP_MAXSEQNO Ta maximum legal sequence number
143.It Dv SSCOP_RETRIEVE_UNKNOWN Ta retrieve transmission queue
144.It Dv SSCOP_RETRIEVE_TOTAL Ta retrieve transmission buffer and queue
145.El
146.Pp
147For signals that carry user data (as, for example,
148.Dv SSCOP_DATA_request )
149these two fields are followed by the variable sized user data.
150.Pp
151If the upper hook is disconnected and the SSCOP instance is not in the idle
152state and the lower hook is still connected, an
153.Dv SSCOP_RELEASE_request
154is executed to release the SSCOP connection.
155.It Dv manage
156This is the management interface defined in the standard.
157The data structure used here is:
158.Bd -literal
159struct sscop_marg {
160 uint32_t sig;
161 u_char data[];
162};
163.Ed
164.Pp
165Here
166.Dv sig
167is one of
168.Bd -literal
169enum sscop_maasig {
170 SSCOP_MDATA_request, /* <- MU */
171 SSCOP_MDATA_indication, /* -> MU */
172 SSCOP_MERROR_indication, /* -> CODE, CNT */
173};
174.Ed
175.Pp
176The
177.Dv SSCOP_MDATA
178signals are followed by the actual management data, where the
179.Dv SSCOP_MERROR
180signal has the form:
181.Bd -literal
182struct sscop_merr {
183 uint32_t sig;
184 uint32_t err; /* error code */
185 uint32_t cnt; /* error count */
186};
187.Ed
188.Sh CONTROL MESSAGES
189The
190.Nm
191node understands the generic messages plus the following:
192.Bl -tag -width xxx
193.It Dv NGM_SSCOP_SETPARAM
194Set operational parameters of the SSCOP instance and takes the
195following structure:
196.Bd -literal
197struct ng_sscop_setparam {
198 uint32_t mask;
199 struct sscop_param param;
200};
201.Ed
202.Pp
203The sub-structure
204.Dv param
205contains the parameters to set and the
206.Dv mask
207field contains a bit mask, telling which of the parameters to set and which
208to ignore.
209If a bit is set, the corresponding parameter is set.
210The parameters are:
211.Bd -literal
212struct sscop_param {
213 uint32_t timer_cc; /* timer_cc in msec */
214 uint32_t timer_poll; /* timer_poll im msec */
215 uint32_t timer_keep_alive;/* timer_keep_alive in msec */
216 uint32_t timer_no_response;/*timer_no_response in msec */
217 uint32_t timer_idle; /* timer_idle in msec */
218 uint32_t maxk; /* maximum user data in bytes */
219 uint32_t maxj; /* maximum u-u info in bytes */
220 uint32_t maxcc; /* max. retransmissions for control packets */
221 uint32_t maxpd; /* max. vt(pd) before sending poll */
222 uint32_t maxstat; /* max. number of elements in stat list */
223 uint32_t mr; /* initial window */
224 uint32_t flags; /* flags */
225};
226.Ed
227.Pp
228The
229.Dv flags
230field contains the following flags influencing SSCOP operation:
231.Bl -column SSCOP_POLLREX -offset indent
232.It Dv SSCOP_ROBUST Ta enable atmf/97-0216 robustness enhancement
233.It Dv SSCOP_POLLREX Ta send POLL after each retransmission
234.El
235.Pp
236The bitmap has the following bits:
237.Bl -column SSCOP_POLLREXx -offset indent
238.It Dv SSCOP_SET_TCC Ta set Dv timer_cc
239.It Dv SSCOP_SET_TPOLL Ta set Dv timer_poll
240.It Dv SSCOP_SET_TKA Ta set Dv timer_keep_alive
241.It Dv SSCOP_SET_TNR Ta set Dv timer_no_response
242.It Dv SSCOP_SET_TIDLE Ta set Dv timer_idle
243.It Dv SSCOP_SET_MAXK Ta set Dv maxk
244.It Dv SSCOP_SET_MAXJ Ta set Dv maxj
245.It Dv SSCOP_SET_MAXCC Ta set Dv maxcc
246.It Dv SSCOP_SET_MAXPD Ta set Dv maxpd
247.It Dv SSCOP_SET_MAXSTAT Ta set Dv maxstat
248.It Dv SSCOP_SET_MR Ta set the initial window
249.It Dv SSCOP_SET_ROBUST Ta set or clear Dv SSCOP_ROBUST
250.It Dv SSCOP_SET_POLLREX Ta set or clear Dv SSCOP_POLLREX
251.El
252.Pp
253The node responds to the
254.Dv NGM_SSCOP_SETPARAM
255message with the following response:
256.Bd -literal
257struct ng_sscop_setparam_resp {
258 uint32_t mask;
259 int32_t error;
260};
261.Ed
262.Pp
263Here
264.Dv mask
265contains the a bitmask of the parameters that the user requested to set,
266but that could not be set and
267.Dv error
268is an
269.Xr errno 3
270code describing why the parameter could not be set.
271.It Dv NGM_SSCOP_GETPARAM
272This message returns the current operational parameters of the SSCOP
273instance in a
274.Fa sscop_param
275structure.
276.It Dv NGM_SSCOP_ENABLE
277This message creates the actual SSCOP instance and initializes it.
278Until this is done, parameters may neither be retrieved not set and all
279message received on any hook are discarded.
280.It Dv NGM_SSCOP_DISABLE
| 71.Xr ng_atm 4
72node with an AAL5 hook, but the
73.Nm
74node is able to work on any packet-transporting layer, like, for example,
75IP or UDP.
76The node handles flow control messages received on
77this hook: if it receives a
78.Dv NGM_HIGH_WATER_PASSED
79message it declares the
80.Ql lower layer busy
81state.
82If a
83.Dv NGM_LOW_WATER_PASSED
84message is received the busy state is cleared.
85Note, that the node does not
86look at the message contents of these flow control messages.
87.It Dv upper
88This is the interface to the SSCOP user.
89This interface uses the following message format:
90.Bd -literal
91struct sscop_arg {
92 uint32_t sig;
93 uint32_t arg; /* opt. sequence number or clear-buff */
94 u_char data[];
95};
96.Ed
97.Pp
98.Fa sig
99is one of the signals defined in the standard:
100.Bd -literal
101enum sscop_aasig {
102 SSCOP_ESTABLISH_request, /* <- UU, BR */
103 SSCOP_ESTABLISH_indication, /* -> UU */
104 SSCOP_ESTABLISH_response, /* <- UU, BR */
105 SSCOP_ESTABLISH_confirm, /* -> UU */
106
107 SSCOP_RELEASE_request, /* <- UU */
108 SSCOP_RELEASE_indication, /* -> UU, SRC */
109 SSCOP_RELEASE_confirm, /* -> */
110
111 SSCOP_DATA_request, /* <- MU */
112 SSCOP_DATA_indication, /* -> MU, SN */
113
114 SSCOP_UDATA_request, /* <- MU */
115 SSCOP_UDATA_indication, /* -> MU */
116
117 SSCOP_RECOVER_indication, /* -> */
118 SSCOP_RECOVER_response, /* <- */
119
120 SSCOP_RESYNC_request, /* <- UU */
121 SSCOP_RESYNC_indication, /* -> UU */
122 SSCOP_RESYNC_response, /* <- */
123 SSCOP_RESYNC_confirm, /* -> */
124
125 SSCOP_RETRIEVE_request, /* <- RN */
126 SSCOP_RETRIEVE_indication, /* -> MU */
127 SSCOP_RETRIEVE_COMPL_indication,/* -> */
128};
129.Ed
130.Pp
131The arrows in the comment show the direction of the signal whether it
132is a signal that comes out of the node
133.Ql ->
134or is sent by the node user to the node
135.Ql <- .
136The
137.Fa arg
138field contains the argument to some of the signals: it is either a PDU
139sequence number or the
140.Dv CLEAR-BUFFER
141flag.
142There are a number of special sequence numbers for some operations:
143.Bl -column SSCOP_RETRIEVE_UNKNOWN -offset indent
144.It Dv SSCOP_MAXSEQNO Ta maximum legal sequence number
145.It Dv SSCOP_RETRIEVE_UNKNOWN Ta retrieve transmission queue
146.It Dv SSCOP_RETRIEVE_TOTAL Ta retrieve transmission buffer and queue
147.El
148.Pp
149For signals that carry user data (as, for example,
150.Dv SSCOP_DATA_request )
151these two fields are followed by the variable sized user data.
152.Pp
153If the upper hook is disconnected and the SSCOP instance is not in the idle
154state and the lower hook is still connected, an
155.Dv SSCOP_RELEASE_request
156is executed to release the SSCOP connection.
157.It Dv manage
158This is the management interface defined in the standard.
159The data structure used here is:
160.Bd -literal
161struct sscop_marg {
162 uint32_t sig;
163 u_char data[];
164};
165.Ed
166.Pp
167Here
168.Dv sig
169is one of
170.Bd -literal
171enum sscop_maasig {
172 SSCOP_MDATA_request, /* <- MU */
173 SSCOP_MDATA_indication, /* -> MU */
174 SSCOP_MERROR_indication, /* -> CODE, CNT */
175};
176.Ed
177.Pp
178The
179.Dv SSCOP_MDATA
180signals are followed by the actual management data, where the
181.Dv SSCOP_MERROR
182signal has the form:
183.Bd -literal
184struct sscop_merr {
185 uint32_t sig;
186 uint32_t err; /* error code */
187 uint32_t cnt; /* error count */
188};
189.Ed
190.Sh CONTROL MESSAGES
191The
192.Nm
193node understands the generic messages plus the following:
194.Bl -tag -width xxx
195.It Dv NGM_SSCOP_SETPARAM
196Set operational parameters of the SSCOP instance and takes the
197following structure:
198.Bd -literal
199struct ng_sscop_setparam {
200 uint32_t mask;
201 struct sscop_param param;
202};
203.Ed
204.Pp
205The sub-structure
206.Dv param
207contains the parameters to set and the
208.Dv mask
209field contains a bit mask, telling which of the parameters to set and which
210to ignore.
211If a bit is set, the corresponding parameter is set.
212The parameters are:
213.Bd -literal
214struct sscop_param {
215 uint32_t timer_cc; /* timer_cc in msec */
216 uint32_t timer_poll; /* timer_poll im msec */
217 uint32_t timer_keep_alive;/* timer_keep_alive in msec */
218 uint32_t timer_no_response;/*timer_no_response in msec */
219 uint32_t timer_idle; /* timer_idle in msec */
220 uint32_t maxk; /* maximum user data in bytes */
221 uint32_t maxj; /* maximum u-u info in bytes */
222 uint32_t maxcc; /* max. retransmissions for control packets */
223 uint32_t maxpd; /* max. vt(pd) before sending poll */
224 uint32_t maxstat; /* max. number of elements in stat list */
225 uint32_t mr; /* initial window */
226 uint32_t flags; /* flags */
227};
228.Ed
229.Pp
230The
231.Dv flags
232field contains the following flags influencing SSCOP operation:
233.Bl -column SSCOP_POLLREX -offset indent
234.It Dv SSCOP_ROBUST Ta enable atmf/97-0216 robustness enhancement
235.It Dv SSCOP_POLLREX Ta send POLL after each retransmission
236.El
237.Pp
238The bitmap has the following bits:
239.Bl -column SSCOP_POLLREXx -offset indent
240.It Dv SSCOP_SET_TCC Ta set Dv timer_cc
241.It Dv SSCOP_SET_TPOLL Ta set Dv timer_poll
242.It Dv SSCOP_SET_TKA Ta set Dv timer_keep_alive
243.It Dv SSCOP_SET_TNR Ta set Dv timer_no_response
244.It Dv SSCOP_SET_TIDLE Ta set Dv timer_idle
245.It Dv SSCOP_SET_MAXK Ta set Dv maxk
246.It Dv SSCOP_SET_MAXJ Ta set Dv maxj
247.It Dv SSCOP_SET_MAXCC Ta set Dv maxcc
248.It Dv SSCOP_SET_MAXPD Ta set Dv maxpd
249.It Dv SSCOP_SET_MAXSTAT Ta set Dv maxstat
250.It Dv SSCOP_SET_MR Ta set the initial window
251.It Dv SSCOP_SET_ROBUST Ta set or clear Dv SSCOP_ROBUST
252.It Dv SSCOP_SET_POLLREX Ta set or clear Dv SSCOP_POLLREX
253.El
254.Pp
255The node responds to the
256.Dv NGM_SSCOP_SETPARAM
257message with the following response:
258.Bd -literal
259struct ng_sscop_setparam_resp {
260 uint32_t mask;
261 int32_t error;
262};
263.Ed
264.Pp
265Here
266.Dv mask
267contains the a bitmask of the parameters that the user requested to set,
268but that could not be set and
269.Dv error
270is an
271.Xr errno 3
272code describing why the parameter could not be set.
273.It Dv NGM_SSCOP_GETPARAM
274This message returns the current operational parameters of the SSCOP
275instance in a
276.Fa sscop_param
277structure.
278.It Dv NGM_SSCOP_ENABLE
279This message creates the actual SSCOP instance and initializes it.
280Until this is done, parameters may neither be retrieved not set and all
281message received on any hook are discarded.
282.It Dv NGM_SSCOP_DISABLE
|
281Destroy the SSCOP instance. After this all messages on any hooks are
| 283Destroy the SSCOP instance.
284After this all messages on any hooks are
|
282discarded.
283.It Dv NGM_SSCOP_SETDEBUG
| 285discarded.
286.It Dv NGM_SSCOP_SETDEBUG
|
284Set debugging flags. The argument is an
| 287Set debugging flags.
288The argument is an
|
285.Vt uint32_t .
286.It Dv NGM_SSCOP_GETDEBUG
287Retrieve the actual debugging flags.
288Needs no arguments and responds with an
289.Vt uint32_t .
290.It Dv NGM_SSCOP_GETSTATE
291Responds with the current state of the SSCOP instance in an
292.Vt uint32_t .
293If the node is not enabled the retrieved state is 0.
294.El
295.Sh FLOW CONTROL
| 289.Vt uint32_t .
290.It Dv NGM_SSCOP_GETDEBUG
291Retrieve the actual debugging flags.
292Needs no arguments and responds with an
293.Vt uint32_t .
294.It Dv NGM_SSCOP_GETSTATE
295Responds with the current state of the SSCOP instance in an
296.Vt uint32_t .
297If the node is not enabled the retrieved state is 0.
298.El
299.Sh FLOW CONTROL
|
296Flow control works on the upper and on the lower layer interface. At the lower
| 300Flow control works on the upper and on the lower layer interface.
301At the lower
|
297layer interface the two messages
298.Dv NGM_HIGH_WATER_PASSED
299and
300.Dv NGM_LOW_WATER_PASSED
301are used to declare or clear the
302.Ql lower layer busy
303state of the protocol.
304.Pp
305At the upper layer interface the
306.Nm
307node handles three types of flow control messages:
308.Bl -tag -width xxx
309.It Dv NGM_HIGH_WATER_PASSED
310If this message is received the SSCOP stops moving the receive window.
311Each time a data message is handed over to the upper layer the receive
312window is moved by one message.
313Stopping these updates
314means that the window will start to close and if the peer has sent
315all messages allowed by the current window, it stops transmission.
316This means, that the upper layer must be able to receive still a full window
317amount of messages.
318.It Dv NGM_LOW_WATER_PASSED
319This will re-enable the automatic window updates and if the space indicated
320in the message is larger than the current window, the window will be opened
321by that amount.
322The space is computed as the difference of the
323.Fa max_queuelen_packets
324and
325.Fa current
326members of the
327.Fa ngm_queue_state
328structure.
329.It Dv NGM_SYNC_QUEUE_STATE
330If the upper layer buffer filling state as indicated by
331.Fa current
332is equal too or higher than
333.Fa high_watermark
334than the message is ignored.
335If this is not the case the amount
336of receiver space is computed as the difference of
337.Fa max_queuelen_packets
338and
339.Fa current ,
340if automatic window updates are currently allowed and as the difference of
341.Fa high_water_mark
342and
343.Fa current ,
344if window updates are disabled.
345If the resulting value is larger than the current window, the current window
346is opened up to this value.
347Automatic window updates are enabled, if they
348were disabled.
349.Sh SEE ALSO
350.Xr netgraph 4 ,
351.Xr ng_atm 4 ,
352.Xr ng_sscfu 4 ,
353.Xr ngctl 8
354.Sh AUTHORS
355.An Harti Brandt Aq harti@freebsd.org
| 302layer interface the two messages
303.Dv NGM_HIGH_WATER_PASSED
304and
305.Dv NGM_LOW_WATER_PASSED
306are used to declare or clear the
307.Ql lower layer busy
308state of the protocol.
309.Pp
310At the upper layer interface the
311.Nm
312node handles three types of flow control messages:
313.Bl -tag -width xxx
314.It Dv NGM_HIGH_WATER_PASSED
315If this message is received the SSCOP stops moving the receive window.
316Each time a data message is handed over to the upper layer the receive
317window is moved by one message.
318Stopping these updates
319means that the window will start to close and if the peer has sent
320all messages allowed by the current window, it stops transmission.
321This means, that the upper layer must be able to receive still a full window
322amount of messages.
323.It Dv NGM_LOW_WATER_PASSED
324This will re-enable the automatic window updates and if the space indicated
325in the message is larger than the current window, the window will be opened
326by that amount.
327The space is computed as the difference of the
328.Fa max_queuelen_packets
329and
330.Fa current
331members of the
332.Fa ngm_queue_state
333structure.
334.It Dv NGM_SYNC_QUEUE_STATE
335If the upper layer buffer filling state as indicated by
336.Fa current
337is equal too or higher than
338.Fa high_watermark
339than the message is ignored.
340If this is not the case the amount
341of receiver space is computed as the difference of
342.Fa max_queuelen_packets
343and
344.Fa current ,
345if automatic window updates are currently allowed and as the difference of
346.Fa high_water_mark
347and
348.Fa current ,
349if window updates are disabled.
350If the resulting value is larger than the current window, the current window
351is opened up to this value.
352Automatic window updates are enabled, if they
353were disabled.
354.Sh SEE ALSO
355.Xr netgraph 4 ,
356.Xr ng_atm 4 ,
357.Xr ng_sscfu 4 ,
358.Xr ngctl 8
359.Sh AUTHORS
360.An Harti Brandt Aq harti@freebsd.org
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