summaryrefslogtreecommitdiffstats
path: root/share/examples/isdn/Overview
blob: 2f2fc181a81dc75eed39a56f666881dd9a1d59b0 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307

        Short technical overview of isdn4bsd
        ====================================

	Copyright (c) 1998 Hellmuth Michaelis. All rights reserved.

	$Id: Overview,v 1.3 1998/10/27 10:28:54 hm Exp $

	Last edit-date: [Tue Oct 27 11:26:03 1998]

	-hm	starting an overview ...


Contents:
---------
	Functional block diagram
	Layer 1
	Layer 2
	Layer 3
	Debugging control
	Layer 4    
	ISDN protocol trace


Functional block diagram
========================

 isdndebug                         isdnd                             isdntrace
 +-------+  +----------------------------------------------------+   +--------+
 |       |  |                                                    |   |        |
 |       |  |                                                    |   |        |
 +-------+  +----------------------------------------------------+   +--------+
     |                               |                                    |
     |                               |                                    |
     | /dev/i4bctl    Userland       | /dev/i4b            /dev/i4btrc<n> |
===============================================================================
     |                Kernel         |                                    |
     |                               |                                    |
 +-------+  +----------------------------------------------------+   +--------+
 |       |  |                                                    |   |        |
 |i4bctl |  |                       i4b                          |   | i4btrc |
 |  (6)  |  |                       (7)                          |   |   (8)  |
 | debug |  |     Layer 4 - common call control interface        |   |  ISDN  |
 |control|  |                                                    |   | trace  |
 +:-:-:--+  +----------------------------------------------------+   +--------+
  : : :          ^                                          ^              ^ 
  : : :     Call |           various ptr arrays             | Call         %
  . . .  Control |             in i4b_l3l4.h                | Control      %
                 V                                          V              %
 +----------------------+                       +----------------------+   %
 |                      |                       |                      |   %
 |       i4bq931        |                  ISDN |     active card      |   %
 |         (5)          |                   #####                      |   %
 |    Layer 3 (Q.931)   |                   #   |       driver         |   %
 |                      |                   #   |                      |   %
 +----------------------+                   #   +----------------------+   %
            ^                               #   B +                        %
            |  i4b_l2l3_func function       #   | +   +------------+       %
            |  ptr array in i4b_l2l3.h      #   C +++++    isp     |---->  %
            V                               #   h +   +------------+ IP    %
 +----------------------+                   #   a +                Subsys  %
 |                      |                   #   n +   +------------+       %
 |       i4bq921        |                   #   n +++++    ipr     |---->  %
 |         (4)          |                   #   e +   +------------+ IP    %
 |    Layer 2 (Q.921)   |                   #   l +                Subsys  %
 |                      |                   #     +   +------------+       %
 +----------------------+                   #   D +++++  tel/rbch  |---->  %
            ^                               #   a +   +------------+ to    %
            |  i4b_l1l2_func function       #   t +         /dev/i4btel<n> %
            |  ptr array in i4b_l1l2.h      #   a +      or /dev/i4brbch<n>%
            V                               #     +                        %
 +----------------------+                   #   +---------------------+    %
 |                      |                   #   |                     |    %
 |    isic (ISAC part)  |  D-ch trace       #   |   isic (HSCX part)  |B-ch%
 |         (2)          |%%%%%%%%%%%%       #   |        (3)          |%%%%%
 |    Layer 1 (I.430)   |           %       #   |   non-HDLC / HDLC   |trc %
 |                      |           %       #   |                     |    %
 +----------------------+           %       #   +---------------------+    %
            ^                       %       #               ^              %
 D-channel  |                       %       #    B-channels |              %
            +-----------------------------------------------+              %
            |  function ptr in      %       #                              %
            |  in isic_softc in     %%%%%%%%#%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
            V  i4b_l1.h                     #
 +----------------------+                   #
 |                      |                   #
 |         isic         |                   #
 |         (1)          |                   #
 | Card hardware driver |                   #
 | for Teles, AVM, USR  |                   #
 |                      |                   #
 +----------#-----------+                   #
            #                               #
            #                               #
            #                               #
            #                               #
  |=========#===============================#============================|
        ISDN S0 bus


Layer 1
=======

(1) A driver for a special card hardware consists of a
	- probe routine
	- attach routine
	- FIFO read
	- FIFO write
	- register read
	- register write
   routines. These routines handle the card/manufacturer specific stuff
   required to talk to a particular card.

   This addresses of the read/write routines are put into a arrays found
   in struct isic_softc and they are later called by the macros:

   ISAC_READ(r), ISAC_WRITE(r,v), ISAC_RDFIFO(b,s), ISAC_WRFIFO(b,s),
   HSCX_READ(n,r), HSCX_WRITE(n,r,v), HSCX_RDFIFO(n,b,s), HSCX_WRFIFO(n,b,s)

   (see file layer1/i4b_l1.h)
   
   Files currently used for this purpose are
   	- i4b_avm_a1.c    AVM A1 and AVM Fritz!Card drivers
   	- i4b_ctx_s0P.c   Creatix S0 PnP (experimental!)
   	- i4b_tel_s016.c  Teles S0/16 and clones
   	- i4b_tel_s0163.c Teles S0/16.3
   	- i4b_tel_s08.c   Teles S0/8 and clones
   	- i4b_tel_s0P.c   Teles S0/16 PnP (experimental!)
   	- i4b_usr_sti.c   3Com USRobotics Sportster


(2) The files i4b_isac.c and i4b_isac.h contain the code to control the
    ISAC chip by using the above mentioned macros.

    Files i4b_l1.c and i4b_l1.h handle stuff used to access layer 1
    functions from layer 2.

    Layer 1 and layer 2 access functionality of each other by using
    a well known function pointer array, which contains addresses of
    "primitives" functions which are defined in I.430 and Q.921. The
    function pointer array for layer 1/2 communication is defined in
    file include/i4b_l1l2.h and is initialized i4b_l1.c at the very
    beginning.

    File i4b_isic.c contains the main code for the "isic" device driver.

    i4b_l1fsm.c is the heart of layer 1 containing the state machine which
    implements the protocol described in I.430 and the ISAC data book.


(3) All above code is used for handling of the D channel, the files
    i4b_bchan.c, i4b_hscx.c and i4b_hscx.h contain the code for handling
    the B-channel, the HSCX is used to interface the userland drivers
    isp, ipr, tel and rbch to one of the B-channels and i4b_hscx.c and
    i4b_hscx.h contain the code to handle it (also by using the above
    mentioned macros). i4b_bchan.c contains various maintenance code for
    interfacing to the upper layers.


Layer 2
=======

(4) Layer 2 implements the LAPD protocol described in Q.920/Q.921. Layer 2
    interfaces to layer 1 by the above described function pointer array,
    where layer 1 calls layer 2 functions to provide input to layer 2 and
    layer 2 calls layer 1 functions to feed data to layer 1.

    The same mechanism is used for layer 2 / layer 3 communication, the
    pointer array interface is defined in include/i4b_l2l3.h ad the array
    is initialized at the very beginning of i4b_l2.c which also contains
    some layer 1 and some layer 3 interface routines. As with l1/l2, the
    l2/l3 array also contains addresses for "primitives" functions which
    are specified in Q.920/Q.921 and Q.931.

    i4b_l2.h contains the definition of l2_softc_t, which describes the
    complete state of a layer 2 link between the exchange and the local
    terminal equipment.

    i4b_l2.c contains the entrance of data from layer 1 into the system,
    which is split up in i4b_ph_data_ind() into the 3 classes of layer 2
    frames called S-frame, I-frame and U-frame. They are handled in files
    i4b_sframe.c, i4b_iframe.c and i4b_uframe.c together with the respective
    routines to send data with each ones frame type.

    i4b_l2timer.c implements the timers required by Q.921.

    i4b_tei.c contains the TEI handling routines.

    i4b_lme.c implements a rudimentary layer management entity.

    i4b_util.c implements the many utility functions specified
    in Q.921 together wit some misc routines required for overall
    functionality.

    i4b_mbuf.c handles all (!) requests for mbufs and frees all mbufs used
    by the whole isdn4bsd kernel part. It should probably be moved else-
    where.

    i4b_l2fsm.c and i4b_l2fsm.h contain the heart of layer 2, the state-
    machine implementing the protocol as specified in Q.921.

Layer 3
=======

(5) i4b_l2if.c and i4b_l4if.c contain the interface routines to communicate
    to layer 2 and layer 4 respectively.

    i4b_l3timer.c implements the timers required by layer 3.

    i4b_q931.c and i4b_q931.h implement the message and information element
    decoding of the Q.931 protocol.

    i4b_q932fac.c and i4b_q932fac.h implement a partial decoding of facility
    messages and/or information elements; the only decoding done here is
    the decoding of AOCD and AOCE, advice of charge during and at end of
    call.

    As usual, i4b_l3fsm.c and i4b_l3fsm.h contain the state machine required
    to handle the protocol as specified in Q.931.

    Layer 3 uses a structure defined in include/i4b_l3l4.h to store and
    request information about one particular isdncontroller, it is called
    ctrl_desc_t (controller descriptor). It contains information on the
    state of a controller (controller ready/down and which B channels are
    used or idle) as well as a pointer array used for communication of
    layer 4 with layer 3: layer 3 "knows" the routines to call within
    layer 4 by name, but in case layer 4 has to call layer 3, several
    possibilities exist (i.e. active / passive cards) so it has to call
    the routines which the ISDN controller had put into the the function
    pointer array (N_CONNECT_REQUEST, N_CONNECT_RESPONSE etc) at init time.

    Layer 3 shares a structure called call_desc_t (call descriptor) with
    layer 4. This structure is used to describe the state of one call. The
    reference to layer 3 is the Q.931 call reference value, the reference to
    layer 4 (and the isdn daemon, isdnd) is the cdid, an unique integer
    value uniquely describing one call, the call descriptor id.
              This structure is used to build an array of this structures
    (call_desc[N_CALL_DESC]), which must be large enough to hold as many
    calls as there are B channels in the system PLUS a reserve to be able
    to handle incoming SETUP messages although all channels are in use.

    More, this structure contains the so called "link table pointers"
    (isdn_link_t *ilt and drvr_link_t *dlt) which contain function pointers
    to "link" a B-channel (better the addresses of functions each participant
    needs to access each others functionality) after a successful call setup
    to a userland driver (such as isp, ipr, rbch or tel) to exchange user
    data in the desired protocol and format.

Debugging control
=================

(6) the device driver for /dev/i4bctl in conjunction with the userland
    program isdndebug(8) is used to set the debug level for each of the
    layers and several other parts of the system, information how to use
    this is contained in machine/i4b_debug.h and all parts of the kernel
    sources. It is only usable for passive cards.


Layer 4    
=======

(7) Layer 4 is "just" an abstraction layer used to shield the differences
    of the various possible Layer 3 interfaces (passive cards based on
    Siemens chip-sets, passive cards based on other chip-sets, active cards
    from different manufacturers using manufacturer-specific interfaces)
    and to provide a uniform interface to the isdnd userland daemon, which
    is used to handle all the required actions to setup and close calls
    and to the necessary retry handling and management functionality.

    Layer 4 communicates with the userland by using a well defined protocol
    consisting of "messages" sent to userland and which are read(2) by the
    isdnd. The isdnd in turn sends "messages" to the kernel by using the
    ioctl(2) call. This protocol and the required messages for both
    directions are documented in the machine/i4b_ioctl.h file and are
    implemented in files i4b_i4bdrv.c and i4b_l4.c, the latter also
    containing much of the Layer 4 interface to the lower layers.

    i4b_l4mgmt.c contains all the required routines to manage the above
    mentioned call descriptor id (cdid) in conjunction with the call
    descriptor (array) and the call reference seen from layer 3.

    i4b_l4timer.c implements a timeout timer for Layer 4.


ISDN protocol trace
===================

(8) ISDN D-channel protocol trace for layers 2 and 3 is possible by using
    hooks in the ISAC handling routines.

    In case D-channel trace is enabled, every frame is prepended with a
    header containing further data such as a time stamp and sent via the
    i4btrc driver found in driver/i4b_trace.c to one of the /dev/i4btrc<n>
    devices, where <n> corresponds to a passive controller unit number.

    If desired, B-channel data can be made available using the same
    mechanism - hooks in the HSCX handler send data up to the i4btrc
    device.

    The raw data is then read by the isdntrace userland program which
    decodes the layer 2 and/or layer 3 protocol and formats it to be
    easily readable by the user.

    B-channel data is not interpreted but dumped as a hex-dump.


/* EOF */
OpenPOWER on IntegriCloud