308 lines
14 KiB
Plaintext
308 lines
14 KiB
Plaintext
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Short technical overview of isdn4bsd
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====================================
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Copyright (c) 1998 Hellmuth Michaelis. All rights reserved.
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$FreeBSD$
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Last edit-date: [Tue Oct 27 11:26:03 1998]
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-hm starting an overview ...
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Contents:
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---------
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Functional block diagram
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Layer 1
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Layer 2
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Layer 3
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Debugging control
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Layer 4
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ISDN protocol trace
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Functional block diagram
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========================
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isdndebug isdnd isdntrace
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+-------+ +----------------------------------------------------+ +--------+
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+-------+ +----------------------------------------------------+ +--------+
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| /dev/i4bctl Userland | /dev/i4b /dev/i4btrc<n> |
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===============================================================================
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| Kernel | |
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+-------+ +----------------------------------------------------+ +--------+
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|i4bctl | | i4b | | i4btrc |
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| (6) | | (7) | | (8) |
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| debug | | Layer 4 - common call control interface | | ISDN |
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|control| | | | trace |
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+:-:-:--+ +----------------------------------------------------+ +--------+
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: : : ^ ^ ^
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: : : Call | various ptr arrays | Call %
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. . . Control | in i4b_l3l4.h | Control %
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V V %
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+----------------------+ +----------------------+ %
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| | | | %
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| i4bq931 | ISDN | active card | %
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| (5) | ##### | %
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| Layer 3 (Q.931) | # | driver | %
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| | # | | %
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+----------------------+ # +----------------------+ %
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^ # B + %
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| i4b_l2l3_func function # | + +------------+ %
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| ptr array in i4b_l2l3.h # C +++++ isp |----> %
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V # h + +------------+ IP %
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+----------------------+ # a + Subsys %
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| | # n + +------------+ %
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| i4bq921 | # n +++++ ipr |----> %
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| (4) | # e + +------------+ IP %
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| Layer 2 (Q.921) | # l + Subsys %
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| | # + +------------+ %
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+----------------------+ # D +++++ tel/rbch |----> %
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^ # a + +------------+ to %
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| i4b_l1l2_func function # t + /dev/i4btel<n> %
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| ptr array in i4b_l1l2.h # a + or /dev/i4brbch<n>%
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V # + %
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+----------------------+ # +---------------------+ %
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| | # | | %
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| isic (ISAC part) | D-ch trace # | isic (HSCX part) |B-ch%
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| (2) |%%%%%%%%%%%% # | (3) |%%%%%
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| Layer 1 (I.430) | % # | non-HDLC / HDLC |trc %
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| | % # | | %
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+----------------------+ % # +---------------------+ %
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^ % # ^ %
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D-channel | % # B-channels | %
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+-----------------------------------------------+ %
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| function ptr in % # %
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| in isic_softc in %%%%%%%%#%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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V i4b_l1.h #
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+----------------------+ #
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| | #
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| isic | #
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| (1) | #
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| Card hardware driver | #
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| for Teles, AVM, USR | #
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| | #
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+----------#-----------+ #
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# #
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# #
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# #
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# #
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|=========#===============================#============================|
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ISDN S0 bus
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Layer 1
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=======
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(1) A driver for a special card hardware consists of a
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- probe routine
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- attach routine
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- FIFO read
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- FIFO write
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- register read
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- register write
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routines. These routines handle the card/manufacturer specific stuff
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required to talk to a particular card.
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The addresses of the read/write routines are put into an array found
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in struct isic_softc and they are later called by the macros:
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ISAC_READ(r), ISAC_WRITE(r,v), ISAC_RDFIFO(b,s), ISAC_WRFIFO(b,s),
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HSCX_READ(n,r), HSCX_WRITE(n,r,v), HSCX_RDFIFO(n,b,s), HSCX_WRFIFO(n,b,s)
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(see file layer1/i4b_l1.h)
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Files currently used for this purpose are
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- i4b_avm_a1.c AVM A1 and AVM Fritz!Card drivers
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- i4b_ctx_s0P.c Creatix S0 PnP (experimental!)
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- i4b_tel_s016.c Teles S0/16 and clones
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- i4b_tel_s0163.c Teles S0/16.3
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- i4b_tel_s08.c Teles S0/8 and clones
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- i4b_tel_s0P.c Teles S0/16 PnP (experimental!)
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- i4b_usr_sti.c 3Com USRobotics Sportster
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(2) The files i4b_isac.c and i4b_isac.h contain the code to control the
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ISAC chip by using the above mentioned macros.
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Files i4b_l1.c and i4b_l1.h handle stuff used to access layer 1
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functions from layer 2.
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Layer 1 and layer 2 access functionality of each other by using
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a well known function pointer array, which contains addresses of
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"primitives" functions which are defined in I.430 and Q.921. The
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function pointer array for layer 1/2 communication is defined in
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file include/i4b_l1l2.h and is initialized i4b_l1.c at the very
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beginning.
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File i4b_isic.c contains the main code for the "isic" device driver.
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i4b_l1fsm.c is the heart of layer 1 containing the state machine which
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implements the protocol described in I.430 and the ISAC data book.
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(3) All above code is used for handling of the D channel, the files
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i4b_bchan.c, i4b_hscx.c and i4b_hscx.h contain the code for handling
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the B-channel, the HSCX is used to interface the userland drivers
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isp, ipr, tel and rbch to one of the B-channels and i4b_hscx.c and
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i4b_hscx.h contain the code to handle it (also by using the above
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mentioned macros). i4b_bchan.c contains various maintenance code for
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interfacing to the upper layers.
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Layer 2
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=======
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(4) Layer 2 implements the LAPD protocol described in Q.920/Q.921. Layer 2
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interfaces to layer 1 by the above described function pointer array,
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where layer 1 calls layer 2 functions to provide input to layer 2 and
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layer 2 calls layer 1 functions to feed data to layer 1.
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The same mechanism is used for layer 2 / layer 3 communication, the
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pointer array interface is defined in include/i4b_l2l3.h ad the array
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is initialized at the very beginning of i4b_l2.c which also contains
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some layer 1 and some layer 3 interface routines. As with l1/l2, the
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l2/l3 array also contains addresses for "primitives" functions which
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are specified in Q.920/Q.921 and Q.931.
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i4b_l2.h contains the definition of l2_softc_t, which describes the
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complete state of a layer 2 link between the exchange and the local
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terminal equipment.
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i4b_l2.c contains the entrance of data from layer 1 into the system,
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which is split up in i4b_ph_data_ind() into the 3 classes of layer 2
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frames called S-frame, I-frame and U-frame. They are handled in files
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i4b_sframe.c, i4b_iframe.c and i4b_uframe.c together with the respective
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routines to send data with each ones frame type.
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i4b_l2timer.c implements the timers required by Q.921.
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i4b_tei.c contains the TEI handling routines.
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i4b_lme.c implements a rudimentary layer management entity.
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i4b_util.c implements the many utility functions specified
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in Q.921 together wit some misc routines required for overall
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functionality.
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i4b_mbuf.c handles all (!) requests for mbufs and frees all mbufs used
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by the whole isdn4bsd kernel part. It should probably be moved else-
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where.
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i4b_l2fsm.c and i4b_l2fsm.h contain the heart of layer 2, the state-
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machine implementing the protocol as specified in Q.921.
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Layer 3
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=======
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(5) i4b_l2if.c and i4b_l4if.c contain the interface routines to communicate
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to layer 2 and layer 4 respectively.
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i4b_l3timer.c implements the timers required by layer 3.
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i4b_q931.c and i4b_q931.h implement the message and information element
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decoding of the Q.931 protocol.
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i4b_q932fac.c and i4b_q932fac.h implement a partial decoding of facility
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messages and/or information elements; the only decoding done here is
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the decoding of AOCD and AOCE, advice of charge during and at end of
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call.
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As usual, i4b_l3fsm.c and i4b_l3fsm.h contain the state machine required
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to handle the protocol as specified in Q.931.
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Layer 3 uses a structure defined in include/i4b_l3l4.h to store and
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request information about one particular isdncontroller, it is called
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ctrl_desc_t (controller descriptor). It contains information on the
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state of a controller (controller ready/down and which B channels are
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used or idle) as well as a pointer array used for communication of
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layer 4 with layer 3: layer 3 "knows" the routines to call within
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layer 4 by name, but in case layer 4 has to call layer 3, several
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possibilities exist (i.e. active / passive cards) so it has to call
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the routines which the ISDN controller had put into the the function
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pointer array (N_CONNECT_REQUEST, N_CONNECT_RESPONSE etc) at init time.
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Layer 3 shares a structure called call_desc_t (call descriptor) with
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layer 4. This structure is used to describe the state of one call. The
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reference to layer 3 is the Q.931 call reference value, the reference to
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layer 4 (and the isdn daemon, isdnd) is the cdid, an unique integer
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value uniquely describing one call, the call descriptor id.
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This structure is used to build an array of this structures
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(call_desc[N_CALL_DESC]), which must be large enough to hold as many
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calls as there are B channels in the system PLUS a reserve to be able
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to handle incoming SETUP messages although all channels are in use.
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More, this structure contains the so called "link table pointers"
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(isdn_link_t *ilt and drvr_link_t *dlt) which contain function pointers
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to "link" a B-channel (better the addresses of functions each participant
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needs to access each others functionality) after a successful call setup
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to a userland driver (such as isp, ipr, rbch or tel) to exchange user
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data in the desired protocol and format.
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Debugging control
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=================
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(6) the device driver for /dev/i4bctl in conjunction with the userland
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program isdndebug(8) is used to set the debug level for each of the
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layers and several other parts of the system, information how to use
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this is contained in machine/i4b_debug.h and all parts of the kernel
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sources. It is only usable for passive cards.
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Layer 4
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=======
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(7) Layer 4 is "just" an abstraction layer used to shield the differences
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of the various possible Layer 3 interfaces (passive cards based on
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Siemens chip-sets, passive cards based on other chip-sets, active cards
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from different manufacturers using manufacturer-specific interfaces)
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and to provide a uniform interface to the isdnd userland daemon, which
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is used to handle all the required actions to setup and close calls
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and to the necessary retry handling and management functionality.
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Layer 4 communicates with the userland by using a well defined protocol
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consisting of "messages" sent to userland and which are read(2) by the
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isdnd. The isdnd in turn sends "messages" to the kernel by using the
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ioctl(2) call. This protocol and the required messages for both
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directions are documented in the machine/i4b_ioctl.h file and are
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implemented in files i4b_i4bdrv.c and i4b_l4.c, the latter also
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containing much of the Layer 4 interface to the lower layers.
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i4b_l4mgmt.c contains all the required routines to manage the above
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mentioned call descriptor id (cdid) in conjunction with the call
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descriptor (array) and the call reference seen from layer 3.
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i4b_l4timer.c implements a timeout timer for Layer 4.
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ISDN protocol trace
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===================
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(8) ISDN D-channel protocol trace for layers 2 and 3 is possible by using
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hooks in the ISAC handling routines.
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In case D-channel trace is enabled, every frame is prepended with a
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header containing further data such as a time stamp and sent via the
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i4btrc driver found in driver/i4b_trace.c to one of the /dev/i4btrc<n>
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devices, where <n> corresponds to a passive controller unit number.
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If desired, B-channel data can be made available using the same
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mechanism - hooks in the HSCX handler send data up to the i4btrc
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device.
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The raw data is then read by the isdntrace userland program which
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decodes the layer 2 and/or layer 3 protocol and formats it to be
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easily readable by the user.
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B-channel data is not interpreted but dumped as a hex-dump.
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/* EOF */
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