Configuration

Reserved Logical Data Area Definition

An area in the logical terminal table extension (LTT) area must be reserved for the zx25d driver for the X.25 link terminal ZLUs. This reserved area must start from byte zero in this LTT extension area. This reserved area will contain the X.25 configuration, statistical data, and state information for each X.25 link. The size of the area required by zx25d can be found by running zx25d_init (with or without the ZCOM system). The zx25d driver displays its revision code and the table area required in the ZCOM log file.

The definition for the required reserved area is as follows:

logical-data     10  X25CNT  0  X25CNT_LDSIZE

"10" is the application number for the X.25 link terminals.

If it is necessary to configure call user data for any outgoing calls from X.25 switched virtual circuits, then it will also be necessary to define another logical data area for the application number of these terminals. A definition for the X25UDT Logical-Data area is required if the Udata subparameter is specified for any virtual circuit terminal definition statement. Note that this definition is not needed if the call user data will always be supplied as a parameter in the zx25...() routines or if no call user data is being sent.

This definition, if required, is as follows:

logical-data     app  X25UDT  0  20

The app number is the application number parameter from the virtual circuit terminal definition statement. If multiple terminals with different application numbers require call user data, then the X25UDT should be allocated globally by specifying application zero (0).

The storage could be allocated at any valid offset within the logical terminal table extension area. In the example it is allocated at the first available byte (0). The minimum size of 20 bytes should be used (16 bytes for a fixed-size call user data buffer, plus two bytes in the front of the buffer for a count of the actual number of bytes used in the call user data buffer, plus two bytes at the end for data structure alignment purposes). If more than 16 bytes of call user data is needed, you must supply it as a parameter in the zx25...() routines. You could also define X25UDT to be bigger than 20 bytes. That would allow you to store Ldata entries after the Udata in this same X25UDT Logical-Data area.

Interface Definitions

A Mux definition line appears in the TTGEN configuration file for each multiplexer that will have X.25-connected terminals configured on it.

The firmware file that is used for ACC cards using X.25 is different from the firmware files that are used for other protocols. It is possible, however, to use other protocols with X.25 on a single ACC card, provided the firmware file has been customized to include those other protocols. Refer to the ACC Installation and Configuration Guide for more information on creating firmware files for multiple protocols.

Several sample interface definitions are as follows:

Z7200A   0   0:4    /opt/acc/z7200a/x25.zabs   /* 8-port card */
Z7350A   0   2:16   /opt/acc/z7350a/x25.zabs   /* 2-port card */
Z7300A   2   0:8    /opt/acc/z7300a/x25.zabs   /* 4-port E1/T1 */

The ".zabs" firmware file must have at least the X.25 and LAP-B protocol modules loaded into it, and it may contain other protocol modules. Refer to the TTGEN section of the ACC Utilities Reference Guide for more information on specifying the Mux number, bus, and slot parameters.

Port Definitions

On 2-port or 8-port cards, the ports used for X.25 must be defined as operating in SDLC mode. They will normally be defined with an external (modem supplied) clock; however, especially for a DCE link terminal, an internal (card supplied) clock may be used. With an external (modem supplied) clock, the speed is for documentation purposes only, and will not be used by the ZCOM subsystem.

The clock multiplier should be x1, and the encoding mode will normally be NRZ.

A sample z7200a port definition for X.25 is as follows:

       Port  01:4  RS232  9600   Ext    SDLC  x1     NRZ

A sample z7300a port definition for X.25 is as follows:

       Port  00:2  E1RJ45  Ext  CRCMF  HDB3

Refer to the TTGEN section of the ACC Utilities Reference Guide for more information on specifying the port parameters.

X.25 Link Term Definitions

Each port or E1/T1 subchannel to be used for X.25 must have one (and only one) X.25 link terminal defined. The link terminal defines the parameters for the HDLC/LAP-B protocol (level 2 of X.25), as well as defining some parameters related to the X.25 subscription, and global default parameters for all virtual circuits on this port.

The X.25 link terminal is defined by a TERM definition entry. Physically, the TERM definition for the link terminal must precede the virtual circuit definitions for each port. A sample X.25 link terminal definition line is as follows:

 Term   0100  01:4  X25.LAPB  X25_LINK_DTE_400    ~
        10 0 0 0 0      CALL:226633004  "X25 DTE POS 226633004"  
 *      no_autostart
        option 02h
        last_pvc      3
        first_insvc   4
        last_insvc    6
        first_svc     9
        last_svc     12
        first_outsvc 14
        last_outsvc  15
        def_inpacket  7
        def_outpacket 7
        def_inwindow  2
        def_outwindow 2
        T1_timer      res_100ms 4
        T2_timer      res_10ms  20
        T3_T4_timer   res_10s   4

Note that the "no_autostart" parameter is commented out which means that when the zx25d_init program is used to initialize the X.25 subsystem, the X.25 link will automatically be enabled. The application program would otherwise be responsible for establishing the X.25 link (by enabling the link ZLU).

This terminal definition defines an X.25 link terminal with ZLU 100 on ACC interface 1 port 4. It is configured as an X.25 DTE with T1 value of 400 milliseconds. The local subscription address is 226633004. In this example, the Logical Channel Number ranges are:

Logical Channels 7, 8, 13, and 16 to 4095 are unassigned. Note that these ranges are from the DTE's point-of-view. For more information, refer to the X.25 standard.

SVCs on this link have the inbound and outbound packet size set to 7 (128 bytes) and the inbound and outbound window size set to 2. These are the default parameters for the SVCs on this link, and they can be altered for an individual SVC at call setup through facilities negotiation. The equivalent parameters for PVCs are individually specified in the PVC's poll/select configuration bytes.

The T1, T2 and T4 timers have all been preconfigured for this link. They have been set to:

	NOTE: In this case the "T3_T4_time" parameter sets the T4 timer because this link is a DTE.

The Terminal-Definition takes the following general format:

Term  zlu  mux:port:subc device poll select 
	              appl_no inst_no brch_no wkst_no hunt_no name <option>
	            <Link keyword>        <value>

More specific information on the parameters in the link terminal definition follows.

	NOTE: The following X.25 link keywords are case sensitive and, if used, must be specified exactly as indicated, one per line.

	NOTE: The ITU-T specification states that T1 should be greater than T2, and that T3/T4 should be much greater than T1 or T2 (e.g. 10 times T1 or T2). If these rules are not observed, the HDLC/LAP-B (X.25 Level 2) may not operate correctly. T1 should have a value at least twice the time it takes to transmit the largest possible X.25 packet. This is dependent on the baud rate configured and the largest potential X.25 level 3 packet size configured.

  X25_LINK_DTE_400   800Ah   146Ah
  X25_LINK_DCE_400   000Ah   146Ah
  
  X25_LINK_DTE_1600  800Ah   486Ah
  X25_LINK_DCE_1600  000Ah   486Ah

X.25 Link Device Option Word Definition

The option word for the X.25 link (LAP-B) terminal defines:

The format of the option word for an X.25 link (LAP-B) terminal ZLU is as follows.

	WARNING! The "Hold Acknowledgments" option may cause the remote device to time-out if it has the T25 timer running.

The default Option Word for X25.LAPB is defined in /opt/acc/cfg/zcomdevice.txt to be 2. Refer to the ACC Utilities Reference Guide, chapter on ZDGEN, for more information on changing this default value.