Documentation/isdn/INTERFACE

   1 $Id: INTERFACE,v 1.15.8.2 2001/03/13 16:17:07 kai Exp $
   2
   3 Description of the Interface between Linklevel and Hardwarelevel
   4   of isdn4linux:
   5
   6
   7   The Communication between Linklevel (LL) and Hardwarelevel (HL)
   8   is based on the struct isdn_if (defined in isdnif.h).
   9
  10   An HL-driver can register itself at LL by calling the function
  11   register_isdn() with a pointer to that struct. Prior to that, it has
  12   to preset some of the fields of isdn_if. The LL sets the rest of
  13   the fields. All further communication is done via callbacks using
  14   the function-pointers defined in isdn_if.
  15
  16   Changes/Version numbering:
  17
  18   During development of the ISDN subsystem, several changes have been
  19   made to the interface. Before it went into kernel, the package
  20   had a unique version number. The last version, distributed separately
  21   was 0.7.4. When the subsystem went into kernel, every functional unit
  22   got a separate version number. These numbers are shown at initialization,
  23   separated by slashes:
  24
  25      c.c/t.t/n.n/p.p/a.a/v.v
  26
  27   where
  28
  29    c.c is the revision of the common code.
  30    t.t is the revision of the tty related code.
  31    n.n is the revision of the network related code.
  32    p.p is the revision of the ppp related code.
  33    a.a is the revision of the audio related code.
  34    v.v is the revision of the V.110 related code.
  35
  36   Changes in this document are marked with '***CHANGEx' where x representing
  37   the version number. If that number starts with 0, it refers to the old,
  38   separately distributed package. If it starts with one of the letters
  39   above, it refers to the revision of the corresponding module.
  40   ***CHANGEIx refers to the revision number of the isdnif.h
  41
  42 1. Description of the fields of isdn_if:
  43
  44   int channels;
  45
  46     This field has to be set by the HL-driver to the number of channels
  47     supported prior to calling register_isdn(). Upon return of the call,
  48     the LL puts an id there, which has to be used by the HL-driver when
  49     invoking the other callbacks.
  50
  51   int maxbufsize;
  52
  53     ***CHANGE0.6: New since this version.
  54
  55     Also to be preset by the HL-driver. With this value the HL-driver
  56     tells the LL the maximum size of a data-packet it will accept.
  57
  58   unsigned long features;
  59
  60     To be preset by the HL-driver. Using this field, the HL-driver
  61     announces the features supported. At the moment this is limited to
  62     report the supported layer2 and layer3-protocols. For setting this
  63     field the constants ISDN_FEATURE..., declared in isdnif.h have to be
  64     used.
  65
  66     ***CHANGE0.7.1: The line type (1TR6, EDSS1) has to be set.
  67
  68   unsigned short hl_hdrlen;
  69
  70     ***CHANGE0.7.4: New field.
  71
  72     To be preset by the HL-driver, if it supports sk_buff's. The driver
  73     should put here the amount of additional space needed in sk_buff's for
  74     its internal purposes. Drivers not supporting sk_buff's should
  75     initialize this field to 0.
  76
  77   void (*rcvcallb_skb)(int, int, struct sk_buff *)
  78
  79     ***CHANGE0.7.4: New field.
  80
  81     This field will be set by LL. The HL-driver delivers received data-
  82     packets by calling this function. Upon calling, the HL-driver must
  83     already have its private data pulled off the head of the sk_buff.
  84
  85     Parameter:
  86       int              driver-Id
  87       int              Channel-number locally to the driver. (starting with 0)
  88       struct sk_buff * Pointer to sk_buff, containing received data.
  89
  90   int (*statcallb)(isdn_ctrl*);
  91
  92     This field will be set by LL. This function has to be called by the
  93     HL-driver for signaling status-changes or other events to the LL.
  94
  95     Parameter:
  96       isdn_ctrl*
  97
  98       The struct isdn_ctrl also defined in isdn_if. The exact meanings of its
  99       fields are described together with the descriptions of the possible
 100       events. Here is only a short description of the fields:
 101
 102         driver  = driver Id.
 103         command = event-type. (one of the constants ISDN_STAT_...)
 104         arg     = depends on event-type.
 105         num     = depends on event-type.
 106
 107     Returnvalue:
 108       0 on success, else -1
 109
 110   int (*command)(isdn_ctrl*);
 111
 112     This field has to be preset by the HL-driver. It points to a function,
 113     to be called by LL to perform functions like dialing, B-channel
 114     setup, etc. The exact meaning of the parameters is described with the
 115     descriptions of the possible commands.
 116
 117     Parameter:
 118       isdn_ctrl*
 119         driver  = driver-Id
 120         command = command to perform. (one of the constants ISDN_CMD_...)
 121         arg     = depends on command.
 122         num     = depends on command.
 123
 124     Returnvalue:
 125       >=0 on success, else error-code (-ENODEV etc.)
 126
 127   int (*writebuf_skb)(int, int, int, struct sk_buff *)
 128
 129     ***CHANGE0.7.4: New field.
 130     ***CHANGEI.1.21: New field.
 131
 132     This field has to be preset by the HL-driver. The given function will
 133     be called by the LL for delivering data to be send via B-Channel.
 134
 135
 136     Parameter:
 137       int              driver-Id ***CHANGE0.7.4: New parameter.
 138       int              channel-number locally to the HL-driver. (starts with 0)
 139       int              ack ***ChangeI1.21: New parameter
 140                        If this is !0, the driver has to signal the delivery
 141                        by sending an ISDN_STAT_BSENT. If this is 0, the driver
 142                        MUST NOT send an ISDN_STAT_BSENT.
 143       struct sk_buff * Pointer to sk_buff containing data to be send via
 144                        B-channel.
 145
 146     Returnvalue:
 147       Length of data accepted on success, else error-code (-EINVAL on
 148       oversized packets etc.)
 149
 150   int (*writecmd)(u_char*, int, int, int, int);
 151
 152     This field has to be preset by the HL-driver. The given function will be
 153     called to perform write-requests on /dev/isdnctrl (i.e. sending commands
 154     to the card) The data-format is hardware-specific. This function is
 155     intended for debugging only. It is not necessary for normal operation
 156     and never will be called by the tty-emulation- or network-code. If
 157     this function is not supported, the driver has to set NULL here.
 158
 159     Parameter:
 160       u_char* pointer to data.
 161       int     length of data.
 162       int     flag: 0 = call from within kernel-space. (HL-driver must use
 163                         memcpy, may NOT use schedule())
 164                     1 = call from user-space. (HL-driver must use
 165                         memcpy_fromfs, use of schedule() allowed)
 166       int     driver-Id.
 167       int     channel-number locally to the HL-driver. (starts with 0)
 168
 169 ***CHANGEI1.14: The driver-Id and channel-number are new since this revision.
 170
 171     Returnvalue:
 172       Length of data accepted on success, else error-code (-EINVAL etc.)
 173
 174   int (*readstat)(u_char*, int, int, int, int);
 175
 176     This field has to be preset by the HL-driver. The given function will be
 177     called to perform read-requests on /dev/isdnctrl (i.e. reading replies
 178     from the card) The data-format is hardware-specific. This function is
 179     intended for debugging only. It is not necessary for normal operation
 180     and never will be called by the tty-emulation- or network-code. If
 181     this function is not supported, the driver has to set NULL here.
 182
 183     Parameter:
 184       u_char* pointer to data.
 185       int     length of data.
 186       int     flag: 0 = call from within kernel-space. (HL-driver must use
 187                         memcpy, may NOT use schedule())
 188                     1 = call from user-space. (HL-driver must use
 189                         memcpy_fromfs, use of schedule() allowed)
 190       int     driver-Id.
 191       int     channel-number locally to the HL-driver. (starts with 0)
 192
 193 ***CHANGEI1.14: The driver-Id and channel-number are new since this revision.
 194
 195     Returnvalue:
 196       Length of data on success, else error-code (-EINVAL etc.)
 197
 198   char id[20];
 199        ***CHANGE0.7: New since this version.
 200
 201    This string has to be preset by the HL-driver. Its purpose is for
 202    identification of the driver by the user. Eg.: it is shown in the
 203    status-info of /dev/isdninfo. Furthermore it is used as Id for binding
 204    net-interfaces to a specific channel. If a string of length zero is
 205    given, upon return, isdn4linux will replace it by a generic name. (line0,
 206    line1 etc.) It is recommended to make this string configurable during
 207    module-load-time. (copy a global variable to this string.) For doing that,
 208    modules 1.2.8 or newer are necessary.
 209
 210 2. Description of the commands, a HL-driver has to support:
 211
 212    All commands will be performed by calling the function command() described
 213    above from within the LL. The field command of the struct-parameter will
 214    contain the desired command, the field driver is always set to the
 215    appropriate driver-Id.
 216
 217    Until now, the following commands are defined:
 218
 219 ***CHANGEI1.34: The parameter "num" has been replaced by a union "parm" containing
 220                 the old "num" and a new setup_type struct used for ISDN_CMD_DIAL
 221                 and ISDN_STAT_ICALL callback.
 222
 223    ISDN_CMD_IOCTL:
 224
 225      This command is intended for performing ioctl-calls for configuring
 226      hardware or similar purposes (setting port-addresses, loading firmware
 227      etc.) For this purpose, in the LL all ioctl-calls with an argument
 228      >= IIOCDRVCTL (0x100) will be handed transparently to this
 229      function after subtracting 0x100 and placing the result in arg.
 230      Example:
 231        If a userlevel-program calls ioctl(0x101,...) the function gets
 232        called with the field command set to 1.
 233
 234      Parameter:
 235        driver   = driver-Id.
 236        command  = ISDN_CMD_IOCTL
 237        arg      = Original ioctl-cmd - IIOCDRVCTL
 238        parm.num = first bytes filled with (unsigned long)arg
 239
 240      Returnvalue:
 241        Depending on driver.
 242
 243
 244   ISDN_CMD_DIAL:
 245
 246     This command is used to tell the HL-driver it should dial a given
 247     number.
 248
 249     Parameter:
 250       driver      = driver-Id.
 251       command     = ISDN_CMD_DIAL
 252       arg         = channel-number locally to the driver. (starting with 0)
 253
 254       parm.setup.phone  = An ASCII-String containing the number to dial.
 255       parm.setup.eazmsn = An ASCII-Sting containing the own EAZ or MSN.
 256       parm.setup.si1    = The Service-Indicator.
 257       parm.setup.si2    = Additional Service-Indicator.
 258
 259                     If the Line has been designed as SPV (a special german
 260                     feature, meaning semi-leased-line) the phone has to
 261                     start with an "S".
 262       ***CHANGE0.6: In previous versions the EAZ has been given in the
 263                     highbyte of arg.
 264     ***CHANGE0.7.1: New since this version: ServiceIndicator and AddInfo.
 265
 266   ISDN_CMD_ACCEPTD:
 267
 268     With this command, the HL-driver is told to accept a D-Channel-setup.
 269     (Response to an incoming call)
 270
 271     Parameter:
 272       driver      = driver-Id.
 273       command     = ISDN_CMD_ACCEPTD
 274       arg         = channel-number locally to the driver. (starting with 0)
 275       parm        = unused.
 276
 277   ISDN_CMD_ACCEPTB:
 278
 279     With this command, the HL-driver is told to perform a B-Channel-setup.
 280     (after establishing D-Channel-Connection)
 281
 282     Parameter:
 283       driver      = driver-Id.
 284       command     = ISDN_CMD_ACCEPTB
 285       arg         = channel-number locally to the driver. (starting with 0)
 286       parm        = unused.
 287
 288   ISDN_CMD_HANGUP:
 289
 290     With this command, the HL-driver is told to hangup (B-Channel if
 291     established first, then D-Channel). This command is also used for
 292     actively rejecting an incoming call.
 293
 294     Parameter:
 295       driver      = driver-Id.
 296       command     = ISDN_CMD_HANGUP
 297       arg         = channel-number locally to the driver. (starting with 0)
 298       parm        = unused.
 299
 300   ISDN_CMD_CLREAZ:
 301
 302     With this command, the HL-driver is told not to signal incoming
 303     calls to the LL.
 304
 305     Parameter:
 306       driver      = driver-Id.
 307       command     = ISDN_CMD_CLREAZ
 308       arg         = channel-number locally to the driver. (starting with 0)
 309       parm        = unused.
 310
 311   ISDN_CMD_SETEAZ:
 312
 313     With this command, the HL-driver is told to signal incoming calls for
 314     the given EAZs/MSNs to the LL.
 315
 316     Parameter:
 317       driver      = driver-Id.
 318       command     = ISDN_CMD_SETEAZ
 319       arg         = channel-number locally to the driver. (starting with 0)
 320       parm.num    = ASCII-String, containing the desired EAZ's/MSN's
 321                     (comma-separated). If an empty String is given, the
 322                     HL-driver should respond to ALL incoming calls,
 323                     regardless of the destination-address.
 324       ***CHANGE0.6: New since this version the "empty-string"-feature.
 325
 326   ISDN_CMD_GETEAZ: (currently unused)
 327
 328     With this command, the HL-driver is told to report the current setting
 329     given with ISDN_CMD_SETEAZ.
 330
 331     Parameter:
 332       driver      = driver-Id.
 333       command     = ISDN_CMD_GETEAZ
 334       arg         = channel-number locally to the driver. (starting with 0)
 335       parm.num    = ASCII-String, containing the current EAZ's/MSN's
 336
 337   ISDN_CMD_SETSIL: (currently unused)
 338
 339     With this command, the HL-driver is told to signal only incoming
 340     calls with the given Service-Indicators.
 341
 342     Parameter:
 343       driver      = driver-Id.
 344       command     = ISDN_CMD_SETSIL
 345       arg         = channel-number locally to the driver. (starting with 0)
 346       parm.num    = ASCII-String, containing the desired Service-Indicators.
 347
 348   ISDN_CMD_GETSIL: (currently unused)
 349
 350     With this command, the HL-driver is told to return the current
 351     Service-Indicators it will respond to.
 352
 353     Parameter:
 354       driver      = driver-Id.
 355       command     = ISDN_CMD_SETSIL
 356       arg         = channel-number locally to the driver. (starting with 0)
 357       parm.num    = ASCII-String, containing the current Service-Indicators.
 358
 359   ISDN_CMD_SETL2:
 360
 361     With this command, the HL-driver is told to select the given Layer-2-
 362     protocol. This command is issued by the LL prior to ISDN_CMD_DIAL or
 363     ISDN_CMD_ACCEPTD.
 364
 365
 366     Parameter:
 367       driver      = driver-Id.
 368       command     = ISDN_CMD_SETL2
 369       arg         = channel-number locally to the driver. (starting with 0)
 370                     logical or'ed with (protocol-Id << 8)
 371                     protocol-Id is one of the constants ISDN_PROTO_L2...
 372       parm        = unused.
 373
 374   ISDN_CMD_GETL2: (currently unused)
 375
 376     With this command, the HL-driver is told to return the current
 377     setting of the Layer-2-protocol.
 378
 379     Parameter:
 380       driver      = driver-Id.
 381       command     = ISDN_CMD_GETL2
 382       arg         = channel-number locally to the driver. (starting with 0)
 383       parm        = unused.
 384     Returnvalue:
 385       current protocol-Id (one of the constants ISDN_L2_PROTO)
 386
 387   ISDN_CMD_SETL3:
 388
 389     With this command, the HL-driver is told to select the given Layer-3-
 390     protocol. This command is issued by the LL prior to ISDN_CMD_DIAL or
 391     ISDN_CMD_ACCEPTD.
 392
 393
 394     Parameter:
 395       driver      = driver-Id.
 396       command     = ISDN_CMD_SETL3
 397       arg         = channel-number locally to the driver. (starting with 0)
 398                     logical or'ed with (protocol-Id << 8)
 399                     protocol-Id is one of the constants ISDN_PROTO_L3...
 400       parm.fax    = Pointer to T30_s fax struct. (fax usage only)
 401
 402   ISDN_CMD_GETL2: (currently unused)
 403
 404     With this command, the HL-driver is told to return the current
 405     setting of the Layer-3-protocol.
 406
 407     Parameter:
 408       driver      = driver-Id.
 409       command     = ISDN_CMD_GETL3
 410       arg         = channel-number locally to the driver. (starting with 0)
 411       parm        = unused.
 412     Returnvalue:
 413       current protocol-Id (one of the constants ISDN_L3_PROTO)
 414
 415   ISDN_CMD_PROCEED:
 416
 417     With this command, the HL-driver is told to proceed with a incoming call.
 418
 419     Parameter:
 420       driver      = driver-Id.
 421       command     = ISDN_CMD_PROCEED
 422       arg         = channel-number locally to the driver. (starting with 0)
 423       setup.eazmsn= empty string or string send as uus1 in DSS1 with
 424                     PROCEED message
 425
 426   ISDN_CMD_ALERT:
 427
 428     With this command, the HL-driver is told to alert a proceeding call.
 429
 430     Parameter:
 431       driver      = driver-Id.
 432       command     = ISDN_CMD_ALERT
 433       arg         = channel-number locally to the driver. (starting with 0)
 434       setup.eazmsn= empty string or string send as uus1 in DSS1 with
 435                     ALERT message
 436
 437   ISDN_CMD_REDIR:
 438
 439     With this command, the HL-driver is told to redirect a call in proceeding
 440     or alerting state.
 441
 442     Parameter:
 443       driver      = driver-Id.
 444       command     = ISDN_CMD_REDIR
 445       arg         = channel-number locally to the driver. (starting with 0)
 446       setup.eazmsn= empty string or string send as uus1 in DSS1 protocol
 447       setup.screen= screening indicator
 448       setup.phone = redirected to party number
 449
 450   ISDN_CMD_PROT_IO:
 451
 452     With this call, the LL-driver invokes protocol specific features through
 453     the LL.
 454     The call is not implicitely bound to a connection.
 455
 456     Parameter:
 457       driver      = driver-Id
 458       command     = ISDN_CMD_PROT_IO
 459       arg         = The lower 8 Bits define the addressed protocol as defined
 460                     in ISDN_PTYPE..., the upper bits are used to differentiate
 461                     the protocol specific CMD.
 462
 463       para        = protocol and function specific. See isdnif.h for detail.
 464
 465
 466   ISDN_CMD_FAXCMD:
 467
 468     With this command the HL-driver receives a fax sub-command.
 469     For details refer to INTERFACE.fax
 470
 471     Parameter:
 472       driver      = driver-Id.
 473       command     = ISDN_CMD_FAXCMD
 474       arg         = channel-number locally to the driver. (starting with 0)
 475       parm        = unused.
 476
 477
 478 3. Description of the events to be signaled by the HL-driver to the LL.
 479
 480   All status-changes are signaled via calling the previously described
 481   function statcallb(). The field command of the struct isdn_cmd has
 482   to be set by the HL-driver with the appropriate Status-Id (event-number).
 483   The field arg has to be set to the channel-number (locally to the driver,
 484   starting with 0) to which this event applies. (Exception: STAVAIL-event)
 485
 486   Until now, the following Status-Ids are defined:
 487
 488   ISDN_STAT_AVAIL:
 489
 490     With this call, the HL-driver signals the availability of new data
 491     for readstat(). Used only for debugging-purposes, see description
 492     of readstat().
 493
 494     Parameter:
 495       driver      = driver-Id
 496       command     = ISDN_STAT_STAVAIL
 497       arg         = length of available data.
 498       parm        = unused.
 499
 500   ISDN_STAT_ICALL:
 501   ISDN_STAT_ICALLW:
 502
 503     With this call, the HL-driver signals an incoming call to the LL.
 504     If ICALLW is signalled the incoming call is a waiting call without
 505     a available B-chan.
 506
 507     Parameter:
 508       driver            = driver-Id
 509       command           = ISDN_STAT_ICALL
 510       arg               = channel-number, locally to the driver. (starting with 0)
 511       para.setup.phone  = Callernumber.
 512       para.setup.eazmsn = CalledNumber.
 513       para.setup.si1    = Service Indicator.
 514       para.setup.si2    = Additional Service Indicator.
 515       para.setup.plan   = octet 3 from Calling party number Information Element.
 516       para.setup.screen = octet 3a from Calling party number Information Element.
 517
 518     Return:
 519       0           = No device matching this call.
 520       1           = At least one device matching this call (RING on ttyI).
 521                     HL-driver may send ALERTING on the D-channel in this case.
 522       2           = Call will be rejected.
 523       3           = Incoming called party number is currently incomplete.
 524                     Additional digits are required.
 525                     Used for signalling with PtP connections.
 526       4           = Call will be held in a proceeding state
 527                     (HL driver sends PROCEEDING)
 528                     Used when a user space prog needs time to interpret a call
 529                     para.setup.eazmsn may be filled with an uus1 message of
 530                     30 octets maximum. Empty string if no uus.
 531       5           = Call will be actively deflected to another party
 532                     Only available in DSS1/EURO protocol
 533                     para.setup.phone must be set to destination party number
 534                     para.setup.eazmsn may be filled with an uus1 message of
 535                     30 octets maximum. Empty string if no uus.
 536       -1          = An error happened. (Invalid parameters for example.)
 537   The keypad support now is included in the dial command.
 538
 539
 540   ISDN_STAT_RUN:
 541
 542     With this call, the HL-driver signals availability of the ISDN-card.
 543     (after initializing, loading firmware)
 544
 545     Parameter:
 546       driver      = driver-Id
 547       command     = ISDN_STAT_RUN
 548       arg         = unused.
 549       parm        = unused.
 550
 551   ISDN_STAT_STOP:
 552
 553     With this call, the HL-driver signals unavailability of the ISDN-card.
 554     (before unloading, while resetting/reconfiguring the card)
 555
 556     Parameter:
 557       driver      = driver-Id
 558       command     = ISDN_STAT_STOP
 559       arg         = unused.
 560       parm        = unused.
 561
 562   ISDN_STAT_DCONN:
 563
 564    With this call, the HL-driver signals the successful establishment of
 565    a D-Channel-connection. (Response to ISDN_CMD_ACCEPTD or ISDN_CMD_DIAL)
 566
 567     Parameter:
 568       driver      = driver-Id
 569       command     = ISDN_STAT_DCONN
 570       arg         = channel-number, locally to the driver. (starting with 0)
 571       parm        = unused.
 572
 573   ISDN_STAT_BCONN:
 574
 575    With this call, the HL-driver signals the successful establishment of
 576    a B-Channel-connection. (Response to ISDN_CMD_ACCEPTB or because the
 577    remote-station has initiated establishment)
 578
 579    The HL driver should call this when the logical l2/l3 protocol
 580    connection on top of the physical B-channel is established.
 581
 582     Parameter:
 583       driver      = driver-Id
 584       command     = ISDN_STAT_BCONN
 585       arg         = channel-number, locally to the driver. (starting with 0)
 586       parm.num    = ASCII-String, containing type of connection (for analog
 587                     modem only). This will be appended to the CONNECT message
 588                     e.g. 14400/V.32bis
 589
 590   ISDN_STAT_DHUP:
 591
 592    With this call, the HL-driver signals the shutdown of a
 593    D-Channel-connection. This could be a response to a prior ISDN_CMD_HANGUP,
 594    or caused by a remote-hangup or if the remote-station has actively
 595    rejected a call.
 596
 597     Parameter:
 598       driver      = driver-Id
 599       command     = ISDN_STAT_DHUP
 600       arg         = channel-number, locally to the driver. (starting with 0)
 601       parm        = unused.
 602
 603   ISDN_STAT_BHUP:
 604
 605    With this call, the HL-driver signals the shutdown of a
 606    B-Channel-connection. This could be a response to a prior ISDN_CMD_HANGUP,
 607    or caused by a remote-hangup.
 608
 609    The HL driver should call this as soon as the logical l2/l3 protocol
 610    connection on top of the physical B-channel is released.
 611
 612     Parameter:
 613       driver      = driver-Id
 614       command     = ISDN_STAT_BHUP
 615       arg         = channel-number, locally to the driver. (starting with 0)
 616       parm        = unused.
 617
 618   ISDN_STAT_CINF:
 619
 620    With this call, the HL-driver delivers charge-unit information to the
 621    LL.
 622
 623     Parameter:
 624       driver      = driver-Id
 625       command     = ISDN_STAT_CINF
 626       arg         = channel-number, locally to the driver. (starting with 0)
 627       parm.num    = ASCII string containing charge-units (digits only).
 628
 629   ISDN_STAT_LOAD: (currently unused)
 630
 631   ISDN_STAT_UNLOAD:
 632
 633    With this call, the HL-driver signals that it will be unloaded now. This
 634    tells the LL to release all corresponding data-structures.
 635
 636     Parameter:
 637       driver      = driver-Id
 638       command     = ISDN_STAT_UNLOAD
 639       arg         = unused.
 640       parm        = unused.
 641
 642   ISDN_STAT_BSENT:
 643
 644     With this call the HL-driver signals the delivery of a data-packet.
 645     This callback is used by the network-interfaces only, tty-Emulation
 646     does not need this call.
 647
 648     Parameter:
 649       driver      = driver-Id
 650       command     = ISDN_STAT_BSENT
 651       arg         = channel-number, locally to the driver. (starting with 0)
 652       parm.length = ***CHANGEI.1.21: New field.
 653                     the driver has to set this to the original length
 654                     of the skb at the time of receiving it from the linklevel.
 655
 656   ISDN_STAT_NODCH:
 657
 658     With this call, the driver has to respond to a prior ISDN_CMD_DIAL, if
 659     no D-Channel is available.
 660
 661     Parameter:
 662       driver      = driver-Id
 663       command     = ISDN_STAT_NODCH
 664       arg         = channel-number, locally to the driver. (starting with 0)
 665       parm        = unused.
 666
 667   ISDN_STAT_ADDCH:
 668
 669     This call is for HL-drivers, which are unable to check card-type
 670     or numbers of supported channels before they have loaded any firmware
 671     using ioctl. Those HL-driver simply set the channel-parameter to a
 672     minimum channel-number when registering, and later if they know
 673     the real amount, perform this call, allocating additional channels.
 674
 675     Parameter:
 676       driver      = driver-Id
 677       command     = ISDN_STAT_ADDCH
 678       arg         = number of channels to be added.
 679       parm        = unused.
 680
 681   ISDN_STAT_CAUSE:
 682
 683     With this call, the HL-driver delivers CAUSE-messages to the LL.
 684     Currently the LL does not use this messages. Their contents is simply
 685     logged via kernel-messages. Therefore, currently the format of the
 686     messages is completely free. However they should be printable.
 687
 688     Parameter:
 689       driver      = driver-Id
 690       command     = ISDN_STAT_NODCH
 691       arg         = channel-number, locally to the driver. (starting with 0)
 692       parm.num    = ASCII string containing CAUSE-message.
 693
 694   ISDN_STAT_DISPLAY:
 695
 696     With this call, the HL-driver delivers DISPLAY-messages to the LL.
 697     Currently the LL does not use this messages.
 698
 699     Parameter:
 700       driver      = driver-Id
 701       command     = ISDN_STAT_DISPLAY
 702       arg         = channel-number, locally to the driver. (starting with 0)
 703       para.display= string containing DISPLAY-message.
 704
 705   ISDN_STAT_PROT:
 706
 707     With this call, the HL-driver delivers protocol specific infos to the LL.
 708     The call is not implicitely bound to a connection.
 709
 710     Parameter:
 711       driver      = driver-Id
 712       command     = ISDN_STAT_PROT
 713       arg         = The lower 8 Bits define the addressed protocol as defined
 714                     in ISDN_PTYPE..., the upper bits are used to differentiate
 715                     the protocol specific STAT.
 716
 717       para        = protocol and function specific. See isdnif.h for detail.
 718
 719   ISDN_STAT_DISCH:
 720
 721     With this call, the HL-driver signals the LL to disable or enable the
 722     use of supplied channel and driver.
 723     The call may be used to reduce the available number of B-channels after
 724     loading the driver. The LL has to ignore a disabled channel when searching
 725     for free channels. The HL driver itself never delivers STAT callbacks for
 726     disabled channels.
 727     The LL returns a nonzero code if the operation was not successful or the
 728     selected channel is actually regarded as busy.
 729
 730     Parameter:
 731       driver      = driver-Id
 732       command     = ISDN_STAT_DISCH
 733       arg         = channel-number, locally to the driver. (starting with 0)
 734       parm.num[0] = 0 if channel shall be disabled, else enabled.
 735
 736   ISDN_STAT_L1ERR:
 737
 738     ***CHANGEI1.21 new status message.
 739     A signal can be sent to the linklevel if an Layer1-error results in
 740     packet-loss on receive or send. The field errcode of the cmd.parm
 741     union describes the error more precisely.
 742
 743     Parameter:
 744       driver      = driver-Id
 745       command     = ISDN_STAT_L1ERR
 746       arg         = channel-number, locally to the driver. (starting with 0)
 747       parm.errcode= ISDN_STAT_L1ERR_SEND:     Packet lost while sending.
 748                     ISDN_STAT_L1ERR_RECV:     Packet lost while receiving.
 749   ISDN_STAT_FAXIND:
 750
 751     With this call the HL-driver signals a fax sub-command to the LL.
 752     For details refer to INTERFACE.fax
 753
 754     Parameter:
 755       driver      = driver-Id.
 756       command     = ISDN_STAT_FAXIND
 757       arg         = channel-number, locally to the driver. (starting with 0)
 758       parm        = unused.
 759