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+$Id: INTERFACE,v 1.15.8.2 2001/03/13 16:17:07 kai Exp $
+
+Description of the Interface between Linklevel and Hardwarelevel
+  of isdn4linux:
+
+
+  The Communication between Linklevel (LL) and Hardwarelevel (HL)
+  is based on the struct isdn_if (defined in isdnif.h).
+
+  An HL-driver can register itself at LL by calling the function
+  register_isdn() with a pointer to that struct. Prior to that, it has
+  to preset some of the fields of isdn_if. The LL sets the rest of
+  the fields. All further communication is done via callbacks using
+  the function-pointers defined in isdn_if.
+
+  Changes/Version numbering:
+
+  During development of the ISDN subsystem, several changes have been
+  made to the interface. Before it went into kernel, the package
+  had a unique version number. The last version, distributed separately
+  was 0.7.4. When the subsystem went into kernel, every functional unit
+  got a separate version number. These numbers are shown at initialization,
+  separated by slashes:
+
+     c.c/t.t/n.n/p.p/a.a/v.v
+
+  where
+
+   c.c is the revision of the common code.
+   t.t is the revision of the tty related code.
+   n.n is the revision of the network related code.
+   p.p is the revision of the ppp related code.
+   a.a is the revision of the audio related code.
+   v.v is the revision of the V.110 related code.
+
+  Changes in this document are marked with '***CHANGEx' where x representing
+  the version number. If that number starts with 0, it refers to the old,
+  separately distributed package. If it starts with one of the letters
+  above, it refers to the revision of the corresponding module. 
+  ***CHANGEIx refers to the revision number of the isdnif.h  
+
+1. Description of the fields of isdn_if:
+
+  int channels;
+
+    This field has to be set by the HL-driver to the number of channels
+    supported prior to calling register_isdn(). Upon return of the call,
+    the LL puts an id there, which has to be used by the HL-driver when
+    invoking the other callbacks.
+
+  int maxbufsize;
+
+    ***CHANGE0.6: New since this version.
+
+    Also to be preset by the HL-driver. With this value the HL-driver
+    tells the LL the maximum size of a data-packet it will accept. 
+
+  unsigned long features;
+
+    To be preset by the HL-driver. Using this field, the HL-driver
+    announces the features supported. At the moment this is limited to
+    report the supported layer2 and layer3-protocols. For setting this
+    field the constants ISDN_FEATURE..., declared in isdnif.h have to be
+    used.
+
+    ***CHANGE0.7.1: The line type (1TR6, EDSS1) has to be set.
+
+  unsigned short hl_hdrlen;
+
+    ***CHANGE0.7.4: New field.
+
+    To be preset by the HL-driver, if it supports sk_buff's. The driver
+    should put here the amount of additional space needed in sk_buff's for
+    its internal purposes. Drivers not supporting sk_buff's should 
+    initialize this field to 0.
+
+  void (*rcvcallb_skb)(int, int, struct sk_buff *)
+
+    ***CHANGE0.7.4: New field.
+
+    This field will be set by LL. The HL-driver delivers received data-
+    packets by calling this function. Upon calling, the HL-driver must
+    already have its private data pulled off the head of the sk_buff.
+
+    Parameter:
+      int              driver-Id
+      int              Channel-number locally to the driver. (starting with 0)
+      struct sk_buff * Pointer to sk_buff, containing received data.
+
+  int (*statcallb)(isdn_ctrl*);
+
+    This field will be set by LL. This function has to be called by the
+    HL-driver for signaling status-changes or other events to the LL.
+
+    Parameter:
+      isdn_ctrl*
+
+      The struct isdn_ctrl also defined in isdn_if. The exact meanings of its
+      fields are described together with the descriptions of the possible
+      events. Here is only a short description of the fields:
+
+        driver  = driver Id.
+        command = event-type. (one of the constants ISDN_STAT_...)
+        arg     = depends on event-type.
+        num     = depends on event-type.
+
+    Returnvalue:
+      0 on success, else -1
+
+  int (*command)(isdn_ctrl*);
+
+    This field has to be preset by the HL-driver. It points to a function,
+    to be called by LL to perform functions like dialing, B-channel
+    setup, etc. The exact meaning of the parameters is described with the
+    descriptions of the possible commands.
+
+    Parameter:
+      isdn_ctrl*
+        driver  = driver-Id
+        command = command to perform. (one of the constants ISDN_CMD_...)
+        arg     = depends on command.
+        num     = depends on command.
+    
+    Returnvalue:
+      >=0 on success, else error-code (-ENODEV etc.)
+
+  int (*writebuf_skb)(int, int, int, struct sk_buff *)
+
+    ***CHANGE0.7.4: New field.
+    ***CHANGEI.1.21: New field.
+
+    This field has to be preset by the HL-driver. The given function will
+    be called by the LL for delivering data to be send via B-Channel.
+
+ 
+    Parameter:
+      int              driver-Id ***CHANGE0.7.4: New parameter.
+      int              channel-number locally to the HL-driver. (starts with 0)
+      int	       ack ***ChangeI1.21: New parameter
+		       If this is !0, the driver has to signal the delivery
+		       by sending an ISDN_STAT_BSENT. If this is 0, the driver
+		       MUST NOT send an ISDN_STAT_BSENT.
+      struct sk_buff * Pointer to sk_buff containing data to be send via
+                       B-channel.
+
+    Returnvalue:
+      Length of data accepted on success, else error-code (-EINVAL on
+      oversized packets etc.)
+
+  int (*writecmd)(u_char*, int, int, int, int);
+
+    This field has to be preset by the HL-driver. The given function will be
+    called to perform write-requests on /dev/isdnctrl (i.e. sending commands
+    to the card) The data-format is hardware-specific. This function is
+    intended for debugging only. It is not necessary for normal operation
+    and never will be called by the tty-emulation- or network-code. If
+    this function is not supported, the driver has to set NULL here.
+
+    Parameter:
+      u_char* pointer to data.
+      int     length of data.
+      int     flag: 0 = call from within kernel-space. (HL-driver must use
+                        memcpy, may NOT use schedule())
+                    1 = call from user-space. (HL-driver must use
+                        memcpy_fromfs, use of schedule() allowed)
+      int     driver-Id.
+      int     channel-number locally to the HL-driver. (starts with 0)
+
+***CHANGEI1.14: The driver-Id and channel-number are new since this revision.
+
+    Returnvalue:
+      Length of data accepted on success, else error-code (-EINVAL etc.)
+
+  int (*readstat)(u_char*, int, int, int, int);
+
+    This field has to be preset by the HL-driver. The given function will be
+    called to perform read-requests on /dev/isdnctrl (i.e. reading replies
+    from the card) The data-format is hardware-specific. This function is
+    intended for debugging only. It is not necessary for normal operation
+    and never will be called by the tty-emulation- or network-code. If
+    this function is not supported, the driver has to set NULL here.
+
+    Parameter:
+      u_char* pointer to data.
+      int     length of data.
+      int     flag: 0 = call from within kernel-space. (HL-driver must use
+                        memcpy, may NOT use schedule())
+                    1 = call from user-space. (HL-driver must use
+                        memcpy_fromfs, use of schedule() allowed)
+      int     driver-Id.
+      int     channel-number locally to the HL-driver. (starts with 0)
+
+***CHANGEI1.14: The driver-Id and channel-number are new since this revision.
+
+    Returnvalue:
+      Length of data on success, else error-code (-EINVAL etc.)
+
+  char id[20];
+       ***CHANGE0.7: New since this version.
+
+   This string has to be preset by the HL-driver. Its purpose is for
+   identification of the driver by the user. Eg.: it is shown in the
+   status-info of /dev/isdninfo. Furthermore it is used as Id for binding
+   net-interfaces to a specific channel. If a string of length zero is
+   given, upon return, isdn4linux will replace it by a generic name. (line0,
+   line1 etc.) It is recommended to make this string configurable during
+   module-load-time. (copy a global variable to this string.) For doing that,
+   modules 1.2.8 or newer are necessary.
+
+2. Description of the commands, a HL-driver has to support:
+
+   All commands will be performed by calling the function command() described
+   above from within the LL. The field command of the struct-parameter will
+   contain the desired command, the field driver is always set to the
+   appropriate driver-Id.
+
+   Until now, the following commands are defined:
+
+***CHANGEI1.34: The parameter "num" has been replaced by a union "parm" containing
+                the old "num" and a new setup_type struct used for ISDN_CMD_DIAL
+                and ISDN_STAT_ICALL callback.
+
+   ISDN_CMD_IOCTL:
+
+     This command is intended for performing ioctl-calls for configuring
+     hardware or similar purposes (setting port-addresses, loading firmware
+     etc.) For this purpose, in the LL all ioctl-calls with an argument
+     >= IIOCDRVCTL (0x100) will be handed transparently to this
+     function after subtracting 0x100 and placing the result in arg.
+     Example:
+       If a userlevel-program calls ioctl(0x101,...) the function gets
+       called with the field command set to 1.
+
+     Parameter:
+       driver   = driver-Id.
+       command  = ISDN_CMD_IOCTL
+       arg      = Original ioctl-cmd - IIOCDRVCTL
+       parm.num = first bytes filled with (unsigned long)arg
+   
+     Returnvalue:
+       Depending on driver.
+
+  
+  ISDN_CMD_DIAL:
+
+    This command is used to tell the HL-driver it should dial a given
+    number.
+
+    Parameter:
+      driver      = driver-Id.
+      command     = ISDN_CMD_DIAL
+      arg         = channel-number locally to the driver. (starting with 0)
+      
+      parm.setup.phone  = An ASCII-String containing the number to dial.
+      parm.setup.eazmsn = An ASCII-Sting containing the own EAZ or MSN.
+      parm.setup.si1    = The Service-Indicator.
+      parm.setup.si2    = Additional Service-Indicator.
+
+                    If the Line has been designed as SPV (a special german
+                    feature, meaning semi-leased-line) the phone has to
+                    start with an "S".
+      ***CHANGE0.6: In previous versions the EAZ has been given in the
+                    highbyte of arg.
+    ***CHANGE0.7.1: New since this version: ServiceIndicator and AddInfo.
+
+  ISDN_CMD_ACCEPTD:
+
+    With this command, the HL-driver is told to accept a D-Channel-setup.
+    (Response to an incoming call)
+
+    Parameter:
+      driver      = driver-Id.
+      command     = ISDN_CMD_ACCEPTD
+      arg         = channel-number locally to the driver. (starting with 0)
+      parm        = unused.
+
+  ISDN_CMD_ACCEPTB:
+
+    With this command, the HL-driver is told to perform a B-Channel-setup.
+    (after establishing D-Channel-Connection)
+
+    Parameter:
+      driver      = driver-Id.
+      command     = ISDN_CMD_ACCEPTB
+      arg         = channel-number locally to the driver. (starting with 0)
+      parm        = unused.
+
+  ISDN_CMD_HANGUP:
+
+    With this command, the HL-driver is told to hangup (B-Channel if
+    established first, then D-Channel). This command is also used for
+    actively rejecting an incoming call.
+
+    Parameter:
+      driver      = driver-Id.
+      command     = ISDN_CMD_HANGUP
+      arg         = channel-number locally to the driver. (starting with 0)
+      parm        = unused.
+
+  ISDN_CMD_CLREAZ:
+
+    With this command, the HL-driver is told not to signal incoming
+    calls to the LL.
+
+    Parameter:
+      driver      = driver-Id.
+      command     = ISDN_CMD_CLREAZ
+      arg         = channel-number locally to the driver. (starting with 0)
+      parm        = unused.
+
+  ISDN_CMD_SETEAZ:
+
+    With this command, the HL-driver is told to signal incoming calls for
+    the given EAZs/MSNs to the LL.
+
+    Parameter:
+      driver      = driver-Id.
+      command     = ISDN_CMD_SETEAZ
+      arg         = channel-number locally to the driver. (starting with 0)
+      parm.num    = ASCII-String, containing the desired EAZ's/MSN's
+                    (comma-separated). If an empty String is given, the
+                    HL-driver should respond to ALL incoming calls,
+                    regardless of the destination-address.
+      ***CHANGE0.6: New since this version the "empty-string"-feature.
+
+  ISDN_CMD_GETEAZ: (currently unused)
+
+    With this command, the HL-driver is told to report the current setting
+    given with ISDN_CMD_SETEAZ.
+
+    Parameter:
+      driver      = driver-Id.
+      command     = ISDN_CMD_GETEAZ
+      arg         = channel-number locally to the driver. (starting with 0)
+      parm.num    = ASCII-String, containing the current EAZ's/MSN's
+
+  ISDN_CMD_SETSIL: (currently unused)
+
+    With this command, the HL-driver is told to signal only incoming
+    calls with the given Service-Indicators.
+
+    Parameter:
+      driver      = driver-Id.
+      command     = ISDN_CMD_SETSIL
+      arg         = channel-number locally to the driver. (starting with 0)
+      parm.num    = ASCII-String, containing the desired Service-Indicators.
+
+  ISDN_CMD_GETSIL: (currently unused)
+
+    With this command, the HL-driver is told to return the current
+    Service-Indicators it will respond to.
+
+    Parameter:
+      driver      = driver-Id.
+      command     = ISDN_CMD_SETSIL
+      arg         = channel-number locally to the driver. (starting with 0)
+      parm.num    = ASCII-String, containing the current Service-Indicators.
+
+  ISDN_CMD_SETL2:
+
+    With this command, the HL-driver is told to select the given Layer-2-
+    protocol. This command is issued by the LL prior to ISDN_CMD_DIAL or
+    ISDN_CMD_ACCEPTD.
+
+
+    Parameter:
+      driver      = driver-Id.
+      command     = ISDN_CMD_SETL2
+      arg         = channel-number locally to the driver. (starting with 0)
+                    logical or'ed with (protocol-Id << 8)
+                    protocol-Id is one of the constants ISDN_PROTO_L2...
+      parm        = unused.
+
+  ISDN_CMD_GETL2: (currently unused)
+
+    With this command, the HL-driver is told to return the current
+    setting of the Layer-2-protocol.
+
+    Parameter:
+      driver      = driver-Id.
+      command     = ISDN_CMD_GETL2
+      arg         = channel-number locally to the driver. (starting with 0)
+      parm        = unused.
+    Returnvalue:
+      current protocol-Id (one of the constants ISDN_L2_PROTO)
+
+  ISDN_CMD_SETL3:
+
+    With this command, the HL-driver is told to select the given Layer-3-
+    protocol. This command is issued by the LL prior to ISDN_CMD_DIAL or
+    ISDN_CMD_ACCEPTD.
+
+
+    Parameter:
+      driver      = driver-Id.
+      command     = ISDN_CMD_SETL3
+      arg         = channel-number locally to the driver. (starting with 0)
+                    logical or'ed with (protocol-Id << 8)
+                    protocol-Id is one of the constants ISDN_PROTO_L3...
+      parm.fax    = Pointer to T30_s fax struct. (fax usage only)
+
+  ISDN_CMD_GETL2: (currently unused)
+
+    With this command, the HL-driver is told to return the current
+    setting of the Layer-3-protocol.
+
+    Parameter:
+      driver      = driver-Id.
+      command     = ISDN_CMD_GETL3
+      arg         = channel-number locally to the driver. (starting with 0)
+      parm        = unused.
+    Returnvalue:
+      current protocol-Id (one of the constants ISDN_L3_PROTO)
+
+  ISDN_CMD_PROCEED: 
+
+    With this command, the HL-driver is told to proceed with a incoming call.
+
+    Parameter:
+      driver      = driver-Id.
+      command     = ISDN_CMD_PROCEED
+      arg         = channel-number locally to the driver. (starting with 0)
+      setup.eazmsn= empty string or string send as uus1 in DSS1 with 
+                    PROCEED message
+
+  ISDN_CMD_ALERT: 
+
+    With this command, the HL-driver is told to alert a proceeding call.
+
+    Parameter:
+      driver      = driver-Id.
+      command     = ISDN_CMD_ALERT
+      arg         = channel-number locally to the driver. (starting with 0)
+      setup.eazmsn= empty string or string send as uus1 in DSS1 with 
+                    ALERT message
+
+  ISDN_CMD_REDIR: 
+
+    With this command, the HL-driver is told to redirect a call in proceeding
+    or alerting state.  
+
+    Parameter:
+      driver      = driver-Id.
+      command     = ISDN_CMD_REDIR
+      arg         = channel-number locally to the driver. (starting with 0)
+      setup.eazmsn= empty string or string send as uus1 in DSS1 protocol
+      setup.screen= screening indicator
+      setup.phone = redirected to party number
+
+  ISDN_CMD_PROT_IO:
+
+    With this call, the LL-driver invokes protocol specific features through
+    the LL.
+    The call is not implicitely bound to a connection.
+
+    Parameter:
+      driver      = driver-Id
+      command     = ISDN_CMD_PROT_IO
+      arg         = The lower 8 Bits define the addressed protocol as defined
+                    in ISDN_PTYPE..., the upper bits are used to differentiate
+                    the protocol specific CMD.  
+      
+      para        = protocol and function specific. See isdnif.h for detail.
+
+
+  ISDN_CMD_FAXCMD:
+
+    With this command the HL-driver receives a fax sub-command.
+    For details refer to INTERFACE.fax
+
+    Parameter:
+      driver      = driver-Id.
+      command     = ISDN_CMD_FAXCMD
+      arg         = channel-number locally to the driver. (starting with 0)
+      parm        = unused.
+
+
+3. Description of the events to be signaled by the HL-driver to the LL.
+
+  All status-changes are signaled via calling the previously described
+  function statcallb(). The field command of the struct isdn_cmd has
+  to be set by the HL-driver with the appropriate Status-Id (event-number).
+  The field arg has to be set to the channel-number (locally to the driver,
+  starting with 0) to which this event applies. (Exception: STAVAIL-event)
+
+  Until now, the following Status-Ids are defined:
+
+  ISDN_STAT_AVAIL:
+
+    With this call, the HL-driver signals the availability of new data
+    for readstat(). Used only for debugging-purposes, see description
+    of readstat().
+
+    Parameter:
+      driver      = driver-Id
+      command     = ISDN_STAT_STAVAIL
+      arg         = length of available data.
+      parm        = unused.
+
+  ISDN_STAT_ICALL:
+  ISDN_STAT_ICALLW:
+
+    With this call, the HL-driver signals an incoming call to the LL.
+    If ICALLW is signalled the incoming call is a waiting call without
+    a available B-chan.
+
+    Parameter:
+      driver            = driver-Id
+      command           = ISDN_STAT_ICALL
+      arg               = channel-number, locally to the driver. (starting with 0)
+      para.setup.phone  = Callernumber.
+      para.setup.eazmsn = CalledNumber.
+      para.setup.si1    = Service Indicator.
+      para.setup.si2    = Additional Service Indicator.
+      para.setup.plan   = octet 3 from Calling party number Information Element.
+      para.setup.screen = octet 3a from Calling party number Information Element.
+
+    Return:
+      0           = No device matching this call.
+      1           = At least one device matching this call (RING on ttyI).
+                    HL-driver may send ALERTING on the D-channel in this case.
+      2           = Call will be rejected.
+      3           = Incoming called party number is currently incomplete.
+                    Additional digits are required. 
+                    Used for signalling with PtP connections.
+      4	          = Call will be held in a proceeding state 
+                    (HL driver sends PROCEEDING)
+                    Used when a user space prog needs time to interpret a call
+		    para.setup.eazmsn may be filled with an uus1 message of
+		    30 octets maximum. Empty string if no uus. 
+      5           = Call will be actively deflected to another party
+                    Only available in DSS1/EURO protocol
+		    para.setup.phone must be set to destination party number
+		    para.setup.eazmsn may be filled with an uus1 message of
+		    30 octets maximum. Empty string if no uus. 
+      -1          = An error happened. (Invalid parameters for example.)
+  The keypad support now is included in the dial command.	        
+
+
+  ISDN_STAT_RUN:
+
+    With this call, the HL-driver signals availability of the ISDN-card.
+    (after initializing, loading firmware)
+
+    Parameter:
+      driver      = driver-Id
+      command     = ISDN_STAT_RUN
+      arg         = unused.
+      parm        = unused.
+
+  ISDN_STAT_STOP:
+
+    With this call, the HL-driver signals unavailability of the ISDN-card.
+    (before unloading, while resetting/reconfiguring the card)
+
+    Parameter:
+      driver      = driver-Id
+      command     = ISDN_STAT_STOP
+      arg         = unused.
+      parm        = unused.
+
+  ISDN_STAT_DCONN:
+
+   With this call, the HL-driver signals the successful establishment of
+   a D-Channel-connection. (Response to ISDN_CMD_ACCEPTD or ISDN_CMD_DIAL)
+
+    Parameter:
+      driver      = driver-Id
+      command     = ISDN_STAT_DCONN
+      arg         = channel-number, locally to the driver. (starting with 0)
+      parm        = unused.
+
+  ISDN_STAT_BCONN:
+
+   With this call, the HL-driver signals the successful establishment of
+   a B-Channel-connection. (Response to ISDN_CMD_ACCEPTB or because the
+   remote-station has initiated establishment)
+
+   The HL driver should call this when the logical l2/l3 protocol 
+   connection on top of the physical B-channel is established.
+
+    Parameter:
+      driver      = driver-Id
+      command     = ISDN_STAT_BCONN
+      arg         = channel-number, locally to the driver. (starting with 0)
+      parm.num    = ASCII-String, containing type of connection (for analog
+		    modem only). This will be appended to the CONNECT message
+		    e.g. 14400/V.32bis
+
+  ISDN_STAT_DHUP:
+
+   With this call, the HL-driver signals the shutdown of a
+   D-Channel-connection. This could be a response to a prior ISDN_CMD_HANGUP,
+   or caused by a remote-hangup or if the remote-station has actively
+   rejected a call.
+
+    Parameter:
+      driver      = driver-Id
+      command     = ISDN_STAT_DHUP
+      arg         = channel-number, locally to the driver. (starting with 0)
+      parm        = unused.
+
+  ISDN_STAT_BHUP:
+
+   With this call, the HL-driver signals the shutdown of a
+   B-Channel-connection. This could be a response to a prior ISDN_CMD_HANGUP,
+   or caused by a remote-hangup.
+
+   The HL driver should call this as soon as the logical l2/l3 protocol 
+   connection on top of the physical B-channel is released.
+
+    Parameter:
+      driver      = driver-Id
+      command     = ISDN_STAT_BHUP
+      arg         = channel-number, locally to the driver. (starting with 0)
+      parm        = unused.
+
+  ISDN_STAT_CINF:
+
+   With this call, the HL-driver delivers charge-unit information to the
+   LL.
+
+    Parameter:
+      driver      = driver-Id
+      command     = ISDN_STAT_CINF
+      arg         = channel-number, locally to the driver. (starting with 0)
+      parm.num    = ASCII string containing charge-units (digits only).
+
+  ISDN_STAT_LOAD: (currently unused)
+
+  ISDN_STAT_UNLOAD:
+
+   With this call, the HL-driver signals that it will be unloaded now. This
+   tells the LL to release all corresponding data-structures.
+
+    Parameter:
+      driver      = driver-Id
+      command     = ISDN_STAT_UNLOAD
+      arg         = unused.
+      parm        = unused.
+
+  ISDN_STAT_BSENT:
+
+    With this call the HL-driver signals the delivery of a data-packet.
+    This callback is used by the network-interfaces only, tty-Emulation
+    does not need this call.
+
+    Parameter:
+      driver      = driver-Id
+      command     = ISDN_STAT_BSENT
+      arg         = channel-number, locally to the driver. (starting with 0)
+      parm.length = ***CHANGEI.1.21: New field.
+		    the driver has to set this to the original length
+		    of the skb at the time of receiving it from the linklevel.
+
+  ISDN_STAT_NODCH:
+
+    With this call, the driver has to respond to a prior ISDN_CMD_DIAL, if
+    no D-Channel is available.
+
+    Parameter:
+      driver      = driver-Id
+      command     = ISDN_STAT_NODCH
+      arg         = channel-number, locally to the driver. (starting with 0)
+      parm        = unused.
+
+  ISDN_STAT_ADDCH: 
+
+    This call is for HL-drivers, which are unable to check card-type
+    or numbers of supported channels before they have loaded any firmware
+    using ioctl. Those HL-driver simply set the channel-parameter to a
+    minimum channel-number when registering, and later if they know
+    the real amount, perform this call, allocating additional channels.
+
+    Parameter:
+      driver      = driver-Id
+      command     = ISDN_STAT_ADDCH
+      arg         = number of channels to be added.
+      parm        = unused.
+
+  ISDN_STAT_CAUSE:
+
+    With this call, the HL-driver delivers CAUSE-messages to the LL.
+    Currently the LL does not use this messages. Their contents is simply
+    logged via kernel-messages. Therefore, currently the format of the
+    messages is completely free. However they should be printable.
+
+    Parameter:
+      driver      = driver-Id
+      command     = ISDN_STAT_NODCH
+      arg         = channel-number, locally to the driver. (starting with 0)
+      parm.num    = ASCII string containing CAUSE-message.
+
+  ISDN_STAT_DISPLAY:
+
+    With this call, the HL-driver delivers DISPLAY-messages to the LL.
+    Currently the LL does not use this messages. 
+
+    Parameter:
+      driver      = driver-Id
+      command     = ISDN_STAT_DISPLAY
+      arg         = channel-number, locally to the driver. (starting with 0)
+      para.display= string containing DISPLAY-message.
+
+  ISDN_STAT_PROT:
+
+    With this call, the HL-driver delivers protocol specific infos to the LL.
+    The call is not implicitely bound to a connection.
+
+    Parameter:
+      driver      = driver-Id
+      command     = ISDN_STAT_PROT
+      arg         = The lower 8 Bits define the addressed protocol as defined
+                    in ISDN_PTYPE..., the upper bits are used to differentiate
+                    the protocol specific STAT.  
+      
+      para        = protocol and function specific. See isdnif.h for detail.
+
+  ISDN_STAT_DISCH:
+
+    With this call, the HL-driver signals the LL to disable or enable the
+    use of supplied channel and driver.
+    The call may be used to reduce the available number of B-channels after
+    loading the driver. The LL has to ignore a disabled channel when searching
+    for free channels. The HL driver itself never delivers STAT callbacks for
+    disabled channels. 	    
+    The LL returns a nonzero code if the operation was not successful or the
+    selected channel is actually regarded as busy.
+
+    Parameter:
+      driver      = driver-Id
+      command     = ISDN_STAT_DISCH
+      arg         = channel-number, locally to the driver. (starting with 0)
+      parm.num[0] = 0 if channel shall be disabled, else enabled.
+
+  ISDN_STAT_L1ERR:
+
+    ***CHANGEI1.21 new status message.
+    A signal can be sent to the linklevel if an Layer1-error results in
+    packet-loss on receive or send. The field errcode of the cmd.parm
+    union describes the error more precisely.
+
+    Parameter:
+      driver      = driver-Id
+      command     = ISDN_STAT_L1ERR
+      arg         = channel-number, locally to the driver. (starting with 0)
+      parm.errcode= ISDN_STAT_L1ERR_SEND:     Packet lost while sending.
+		    ISDN_STAT_L1ERR_RECV:     Packet lost while receiving.
+  ISDN_STAT_FAXIND:
+
+    With this call the HL-driver signals a fax sub-command to the LL.
+    For details refer to INTERFACE.fax
+
+    Parameter:
+      driver      = driver-Id.
+      command     = ISDN_STAT_FAXIND
+      arg         = channel-number, locally to the driver. (starting with 0)
+      parm        = unused.
+