*
*        Local Port and Limited Server Enhancements
*
*        TPNS Version 3 Release 5 Service Level 9711
*       APARs PQ14597, PQ14602, PQ16617, PQ16840 recommended
*
*       Updated 6/12/98, to change offsets in ITPDSP to
*                        avoid overlaying areas used when
*                        running SNA simulations.
*
* This zap provides two enhancements to the TPNS TCP/IP
* simulation support.
*
* The first enhancement allows the specification of the
* local port number to be used by a Simple TCP (STCP) or
* Simple UDP (SUDP) device instead of having that port
* automatically assigned by TCP/IP.  After the socket
* has been obtained, TPNS will BIND that socket to the
* specified local port.
*
* The second enhancement builds on the first and provides
* a limited server simulation function. After BINDing
* to the specified local port, TPNS can accept a connection
* (STCP) or wait to receive data (SUDP).  For STCP, only
* one connection at a time can be processed, and TPNS closes
* the listen socket between connections. For SUDP, an exit
* (see below) is provided to glean the address associated
* with the sender of an incoming message and to set the
* address of the recipient for an outgoing message.
*
* To specify the local port to be used by a particular
* simulated client or server, code the following two operands
* on the DEV statement for that resource:
*
*           TRANS=YES    indicating that a specific
*                        Local Port is to be used;
*           BLKDLY=Fxxxxx where xxxxx is the decimal
*                         value of the local port to
*                         be used; the F must be
*                         included as shown.
*
* To specify that a particular DEV is to act as a limited
* server, code the following operand on the DEV statement
* for that resource:
*
*           RTR=YES      indicating that the DEV should
*                        wait for an incoming connection
*                        before generating any message.
*
* Note1: RTR=YES should not be coded unless TRANS=YES and
*        BLKDLY=Fn are also coded. This is not enforced but
*        unpredictable results will be obtained if the
*        restriction is not observed.
*
* Note2: All these operands MUST be coded ON THE DEV statement
*        to be effective.  They will not default from higher
*        levels, even though in other circumstances the same
*        operands would so default.
*
* Note3: Clearly these operands are not normally valid on a
*        DEV following a TCPIP statement. Ignore their normal
*        meanings when using them on such a DEV. If this
*        enhancement is later supplied in other than zap
*        form, new operands will very likely be introduced
*        in lieu of these.
*
* Note4: For a DEV with TYPE=STCP and RTR=YES, the SERVADDR
*        and PORT operands, while they must have valid values,
*        are not used. For a DEV with TYPE=UDP and RTR=YES,
*        the SERVADDR and PORT are used as the destination
*        of all datagrams transmitted by the server. They
*        can be modified dynamically by the script for
*        particular messages using the ITPGSIPA exit described
*        below.
*
*
*           Associated Available User Exits
*
* In addition to this zap, two TPNS User Exits are available
* that may be useful. These are available in separate files
* and should be installed in accordance with directions in
* the TPNS User Exits publication (SC31-6071).
*
* The ITPGSIPA exit can particularly helpful in a UDP server
* environment. When specified as an input exit (INEXIT=ITPGSIPA
* on the NTWRK statement) it will cause the full INET address
* (including IP and port addresses) of the sender of each
* message received by an STCP or SUDP device to be placed in
* network save area 13. This address can be saved using an STL
* ONIN scripting statement or an IF statement with WHEN=IN in
* the TPNS Scripting Language.
*
* The same exit can also be specified in an STL script as
* USEREXIT('ITPGSIPA') or in a TPNS Scripting Language script
* as EXIT NAME=ITPGSIPA to cause the contents of network save
* area 13 to be set as the address for the next message to be
* transmitted by the UDP device (or the next connection to be
* made by an STCP client).
*
* In addition, an information exit, ITPWR47X, is available to
* write ITP477I and ITP478I informational messages, which are
* the messaes logged when TCP/IP indicates any type of socket
* call error, to the operator as well as to the TPNS log.
* Use of this exit would be specified by coding
* INFOEXIT=ITPWR47X on the NTWRK statement.
*
* Further information about these exits is available in the
* separate jobs provided to install them.