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This appendix contains tables ( Table 1 through Table 8) that summarize the SNA control requests
and indicators sent and received by VTAM® application
programs. The tables summarize: - Normal-flow data-flow-control requests
- Expedited-flow data-flow-control requests
- Session-control requests
- Change-direction indicator
- Bracket indicators.
For normal-flow data-flow-control requests,
expedited-flow data-flow-control
requests, and session-control requests, the following information
for sending each request is provided: - The purpose of each request
- Who can send it
- The macroinstruction used by an application program to send it
- The RU type of the request
- The next action to be taken by the sender
The following information for receiving each request is also
provided: - Who can receive it
- How it is received by the application program
- Who sends the response to the request
- The next action to be taken by the receiver
For the change-direction and bracket indicators,
the information is summarized with the entry for each indicator providing
information on both sending and receiving the indicator.
The ability to send and receive the indicators
and control requests described in this appendix is determined by the
session parameter agreed on by the application program and the logical
unit (LU) when the session is established. For detailed information
on a session parameter, see Specifying a session parameter.
Table 1. Summary of sending
normal-flow data-flow-control requestsRequest sent |
Function |
Who can send |
Macroinstruction used by application
program to send |
RU type |
Next action by sender |
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Bid |
Asks receiver for permission to begin
a bracket. |
Primary or secondary logical unit |
SEND STYPE=REQ, CONTROL=BID |
DFSYN |
Expects response from receiver. Response
indicates whether the sender can begin a bracket. |
Bracket Initiation Stopped (BIS) |
Tells the receiver that the sender
will not begin any new brackets. |
Primary or secondary logical unit |
SEND STYPE=REQ, CONTROL=BIS |
DFSYN |
Expects response from receiver. Refrains
from beginning any new brackets. |
Cancel |
Tells receiver to purge request of
incomplete chain it is receiving. |
Primary or secondary logical unit |
SEND STYPE=REQ, CONTROL=BIS |
DFSYN |
Expects response from receiver. Positive
response indicates that chain requests have been purged. |
CHASE |
Tells receiver to send response to
any data request or normal-flow request it has not yet responded to. |
Primary or secondary logical unit |
SEND STYPE=REQ, CONTROL=CANCEL |
DFSYN |
Expects response from receiver. When
response to CHASE request is received, the sender of the request knows
that all normal-flow responses are accounted for. |
Logical Unit Status (LUSTAT) |
Informs receiver of a condition encountered
at the sender's end of the session. Codes indicating reason for sending
the request are placed in the SSENSEO, SSENSMO and USENSEO fields
of the RPL. |
Primary or secondary logical unit |
SEND STYPE=REQ, CONTROL=LUS |
DFSYN |
Expects response from receiver. Subsequent
action depends on the sense information sent in LUSTAT. |
Quiesce Complete (QC) |
Tells receiver that the sender has
quiesced itself (as the result of receipt of a Quiesce at End of Chain
request) and will not send any normal-flow requests until released. |
Primary or secondary logical unit |
SEND STYPE=REQ, CONTROL=QC |
DFSYN |
Expects response from receiver. Refrains
from sending any normal-flow requests until a Release Quiesce request
is received. |
Ready to Receive (RTR) |
Tells the receiver that the receiver
can now send a request to begin a bracket. |
Primary or secondary logical unit |
SEND STYPE=REQ, CONTROL=RTR |
DFSYN |
Expects response from receiver. After
receiving the response, an application program issues RECEIVE RTYPE=DFSYN
to receive a normal-flow request with the begin-bracket indicator
set on. |
Notes:
An application program
can receive the response in one of the following ways, depending on
how the program is coded: - By specifying POST=RESP in SEND (SEND is not completed until response
is received)
- By issuing RECEIVE RTYPE=RESP (a RESP response)
- In a RESP exit routine
- By issuing RECEIVE RTYPE=DFSYN (a DFSYN response).
(See How requests and responses are exchanged for further
details about controlling the handling of normal-flow requests.)
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Table 2. Summary of receiving
normal-flow data-flow-control requestsRequest received |
Who can receive |
How received by application program |
Who sends response if receiver
is a VTAM application program |
Next action by receiver |
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Bid |
Primary or secondary logical unit |
RECEIVE RTYPE=DFSYN CONTROL field
in RPL will contain BID. |
Application program |
Sends positive response to indicate
bidder can start a bracket. Sends a negative response to deny permission
to start a bracket. Application program sends response with SEND ....,STYPE=RESP,
CONTROL=BID, RESPOND=(response operands). |
Bracket Initiation Stopped (BIS) |
Primary or secondary logical unit |
RECEIVE RTYPE=DFSYN CONTROL field
in RPL will contain BIS. |
Application program |
Sends response to Bracket Initiation
chains that have been received. Then sends positive response. Application
SEND ...,STYPE=RESP, CONTROL=BIS, RESPOND=(response
operands). |
Cancel |
Primary or secondary logical unit |
RECEIVE RTYPE=DFSYN CONTROL field
in RPL will contain CANCEL. |
Application program |
Purges any requests of incomplete
chains that have been received. Then sends positive response. Application
program sends response with SEND ...,STYPE=RESP, CONTROL=CANCEL,
RESPOND=(response operands). |
Chase |
Primary or secondary logical unit |
RECEIVE RTYPE=DFSYN CONTROL field
in RPL will contain CHASE. |
Application program |
If any responses to previously received
data requests or normal-flow requests have not been sent, sends those
responses. Then sends response to Chase request. Application program
sends response to Chase request with SEND ...,STYPE=RESP, CONTROL=CHASE,
RESPOND=(response operands). |
Logical Unit Status (LUSTAT) |
Primary or secondary logical unit |
RECEIVE RTYPE=DFSYN CONTROL field
in RPL will contain LUS. Codes indicating reason for the request are
in the SSENSEI, SSENSMI, and USENSEI fields of the RPL. |
Application program |
Examines codes in SSENSEI, SSENSMI,
and USENSEI fields of RPL and takes action based on those codes. Then
sends response to LUSTAT request. Application program sends response
with SEND ...,STYPE=RESP, CONTROL=LUS, RESPOND=(response
operands). |
Quiesce Complete (QC) |
Primary or secondary logical unit |
RECEIVE RTYPE=DFSYN CONTROL field
in RPL will contain QC. |
Application program |
Sends response to Quiesce Complete
request. Application program sends response with SEND ...,STYPE=RESP,
CONTROL=LUS, RESPOND=(response operands). |
Ready to Receive (RTR) |
Primary or secondary logical unit |
RECEIVE RTYPE=DFSYN CONTROL field
in RPL will contain RTR. |
Application program |
Sends response to Ready to Receive
request by using SEND ....,STYPE=RESP, CONTROL=RTR, RESPOND=(response
operands). Then sends a request that includes BRACKET=BB. |
Note:
If
the application program sends a negative response, the SSENSEO, SSENSMO,
and USENSEO fields are used.
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Table 3. Summary of sending
expedited-flow-control requestsRequest sent |
Function |
Who can send |
Macroinstruction used by application
program |
RU type |
Next action by sender |
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Quiesce at End of Chain (QEC) |
Tells the receiver to quit sending
normal-flow requests now, or, if chaining, at the end of the chain
being sent. |
Primary or secondary logical unit |
SEND STYPE=REQ, CONTROL=QEC |
DFASY |
Expects response from receiver. After
receiving positive response, awaits Quiesce Complete. |
Release Quiesce |
Tells the receiver that it can now
resume sending normal-flow requests. |
Primary or secondary logical unit |
SEND STYPE=REQ, CONTROL=RELQ |
DFASY |
Expects response from receiver. After
receiving positive response, prepares to receive normal-flow input.
An application program issues RECEIVE RTYPE=DFSYN. |
Request Shutdown (RSHUTD) |
Asks the primary logical unit to
terminate this session with the secondary logical unit. |
Secondary logical unit only |
SEND STYPE=REQ, CONTROL=RSHUTD |
DFASY |
Expects response from receiver. Response
indicates that request has been properly received. Prepares for session
termination. |
Shutdown Complete (SHUTC) |
Tells the primary logical unit that
shutdown operations (requested previously in a Shutdown request from
the primary logical unit) have been completed. |
Secondary logical unit only |
SEND STYPE=REQ, CONTROL=SHUTC |
DFASY |
Expects response from receiver. Response
indicates that request has been properly received. |
Shutdown (SHUTD) |
Tells the secondary logical unit
to quiesce itself and to perform all preparations for Shutdown. |
Primary logical unit only |
SEND STYPE=REQ, CONTROL=SHUTD |
DFASY |
Expects response from receiver. Response
indicates that request has been properly received. Then, expects to
receive Shutdown Complete request from the secondary logical unit. |
Signal |
Passes 4 bytes of Signal information
with an agreed-upon meaning. Signal information is placed in the SIGDATA
field of the RPL. |
Primary or secondary logical unit |
SEND STYPE=REQ, CONTROL=SIGNAL |
DFASY |
Expects response from receiver. Response
indicates that request has been properly received. |
Stop Bracket Initiation (SBI) |
Tells receiver not to begin any new
brackets. |
Primary or secondary logical unit |
SEND STYPE=REQ, CONTROL=SBI |
DFASY |
Expects response from receiver. Response
indicates that request has been properly received. |
Note:
An
application program receives the response in SEND (SEND is not completed
unit response is received).
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Table 4. Summary of receiving
expedited-flow data-flow-control requestsRequest received |
Who can receive |
How received by application program |
Who sends response if receiver
is a VTAM application program |
Next action by receiver |
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Quiesce at End of Chain (QEC) |
Primary or secondary logical unit |
Either RECEIVE RTYPE=DFASY or in
DFASY exit routine. CONTROL field in RPL will contain QEC. |
Either VTAM or
the program sends the response. |
Halts sending of normal-flow requests
immediately or at end of chain. Then sends Quiesce Complete (QC) request
to sender of QEC request. |
Release Quiesce (RELQ) |
Primary or secondary logical unit |
Either RECEIVE RTYPE=DFASY or in
DFASY exit routine. CONTROL field in RPL contains RELQ. |
Either VTAM or
the program sends the response. |
Sends a normal-flow request to sender
of RELQ request, if desired. |
Request Shutdown (RSHUTD) |
Primary logical unit only |
Either RECEIVE RTYPE=DFASY or in
DFASY exit routine. CONTROL field in RPL contains RSHUTD. |
Either VTAM or
the program sends the response. |
Terminates the session with the secondary
logical unit. |
Shutdown Complete (SHUTC) |
Primary logical unit only |
Either RECEIVE RTYPE=DFASY or in
DFASY exit routine. CONTROL field in RPL will contain SHUTC. |
Either VTAM or
the program sends the response. |
Issues a Chase request (if permitted
by FM profile) to ensure that all responses have been received. Then
ends the session with the secondary logical unit. |
Shutdown (SHUTD) |
Secondary logical unit only |
Either RECEIVE RTYPE=DFASY or in
DFASY exit routine. CONTROL field in RPL will contain SHUTD. |
Either VTAM or
the program sends the response. |
If necessary, stops normal-flow transmission
to the primary logical unit. Performs all preparations for shutdown.
Then sends the Shutdown Complete request to the primary logical unit. |
Signal |
Primary or secondary logical unit |
Either RECEIVE RTYPE=DFASY or in
DFASY exit routine. CONTROL field in RPL contains SIGNAL. Four byes
of information are in the SIGDATA field of the RPL. |
Either VTAM or
the program sends the response. |
Depends on the contents of the Signal
information. |
Stop Bracket Initiation (SBI) |
Primary or secondary logical unit |
Either RECEIVE RTYPE=DFASY or in
DFASY exit routine. CONTROL field in RPL will contain SBI. |
Either VTAM or
the program sends the response. |
Sends a Bracket Initiation Stopped
(BIS) request to SBI sender and then refrains from initiating any
new brackets. |
Notes:
The responder to expedited-flow
data-flow-control request is determined by the setting of a PROC option
in the NIB when the session is established: - If PROC=APPLRESP was specified in the NIB, the application program
sends the response using SEND...,STYPE=RESP,CONTROL=request
code or received request,
RESPOND=(response operands). If a negative
response is sent the SSENSEO, SSENSMO, and USENSEO fields are used.
- If PROC=SYSRESP was specified in the NIB, VTAM automatically sends the response before
presenting the request to the application program.
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The session-control
requests, described in the following table, control session-related
functions and are sent separately from normal- and expedited-flow-control
requests and their responses.
Table 5. Summary of sending
session-control requestsRequest sent |
Function |
Who can send |
Macroinstruction used by application program to send |
Next action by sender |
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Bind Session (BIND) |
Informs the receiver that the sender wants to go into session
with the receiver. A session parameter is sent as part of the Bind
Session request. |
Primary logical unit |
Indirectly, by issuing the OPNDST macroinstruction |
VTAM handles response
and does not complete the OPNDST until response is received. Positive
response causes VTAM to complete
setting up the session. Negative response negates the session. After
positive response, either VTAM or
the PLU application program sends the Start Data Traffic request (if
required by TS profile). |
Clear |
For certain TS profiles, tells VTAM and
the receiver to stop sending data and data-flow-control requests and
responses. Causes VTAM to discard
any requests and responses still in the network and not yet delivered.
Resets outbound and inbound sequence numbers at both ends of the session
to 0. |
Primary logical unit |
SESSIONC STYPE=REQ, CONTROL=CLEAR |
Response reflected in RPL on completion of SESSIONC macroinstruction. VTAM handles response. |
Request Recovery (RQR) |
Informs primary logical unit that recovery action is needed. |
Secondary logical unit |
SESSIONC STYPE=REQ, CONTROL=RQR |
In an SLU application program, response reflected in RPL on
completion of SESSIONC macroinstruction. After receiving positive
response, awaits next request from the primary logical unit (usually
the Clear request). |
Set and Test Sequence Numbers (STSN) |
Exchanges information with secondary logical unit to allow
sequence numbers to be determined or set or both. |
Primary logical unit |
SESSIONC STYPE=REQ, CONTROL=STSN and settings in IBSQAC,
OBSQAC, IBSQVAL, and OBSQVAL fields |
Response reflected in RPL on completion of SESSIONC macroinstruction.
Tests IBSQAC, OBSQAC, IBSQVAL, and OBSQVAL fields to determine answers
to action codes and values sent in the request. |
Start Data Traffic (SDT) |
Informs secondary logical unit that session setup or recovery
is complete and flow of data and data-flow-control requests and responses
can begin. |
Primary logical unit |
SESSIONC STYPE=REQ, CONTROL=SDT. VTAM sends command at beginning of session if
SDT=SYSTEM was set in NIB when the session was established. |
Depending on the session parameter, you may send first requested
or wait for secondary logical unit to send a request. |
Unbind Session (UNBIND) |
Informs VTAM and the
receiver that the session is being terminated. |
Primary logical unit, secondary logical unit, or other network
component |
PLU application program can send indirectly by issuing CLSDST
or TERMSESS. |
Continues communications on sessions with other logical units,
or closes program. |
Table 6. Summary of receiving
session-control requestsRequest
received |
Who can receive |
How received by application program |
Who sends response if receiver
is a VTAM application program |
Next action by receiver |
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Bind Session (BIND) |
Secondary logical unit |
In SCIP exit |
Application program ¹ |
Examines a session parameter in BIND
request and determines whether the complete set of parameters is acceptable.
If acceptable, sends positive response. (For SLU application program,
positive response results from issuance of the OPNSEC macroinstruction.)
If not acceptable, sends negative response. (SLU application program
sends negative response with SESSIONC ...,STYPE=RESP, CONTROL=BIND,
RESPOND=(response operands).) |
Clear |
Secondary logical unit |
In SCIP exit |
VTAM |
Stops sending requests and responses,
and awaits next request from the primary logical unit. |
Request Recovery (RQR) |
Primary logical unit |
In SCIP exit |
VTAM |
Initiates recovery action, usually
by sending the Clear request followed by a Set and Test Sequence Numbers
request and then a Start Data Traffic request. |
Set and Test Sequence Numbers (STSN) |
Secondary logical unit |
In SCIP exit |
Application program ¹ |
Examines action codes and sequence
number values provided with the request. Prepares answering action
codes and values and puts them in IBSQAC, OBSQAC, IBSQVAL, and OBSQVAL
fields. Then, sends response with SESSIONC ...,STYPE=RESP, CONTROL=STSN. |
Start Data Traffic (SDT) |
Secondary logical unit |
In SCIP exit |
Depending on the SDT field in the
NIB used during OPNSEC processing, either the secondary application
program ¹ or VTAM may respond
² |
After response is sent, depending
on session parameter, you may send first request or wait for primary
logical unit to send request. |
Unbind Session (UNBIND) |
Primary logical unit or secondary
logical unit |
In SCIP exit ³ |
VTAM |
Continues communication on sessions
with other logical units, or closes program. |
Notes: - If the application program sends a negative response,
the SSENSEO, SSENSMO, and USENSEO fields are used.
- If the secondary application program specified SDT=APPL
for the NIB used in OPNSEC processing, the secondary application program
responds. Otherwise (SDT=SYSTEM), VTAM responds.
- Alternatively, for a PLU application program, the
NSEXIT or LOSTERM exit routines may be invoked. See Session outage notification (SON) codes on UNBIND.
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- Change-direction indicator
- The change-direction indicator can be set on (designated CD) in
a normal-flow data request or in a Cancel, Chase, Quiesce Complete,
or LU Status request. The request containing the CD must be a single-request
chain (CHAIN=ONLY) or the last request in a chain.
Table 7. Summary of change-direction
indicatorIndicator |
Function |
PLU or SLU application program can send/receive |
Macroinstruction used or RPL field set |
RU type |
Next action expected |
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Change Direction (CD) |
Tells the receiver that it may
now send. |
Send |
SEND CHNGDIR=CMD |
DFSYN |
Start receiving from the opposite end of the
session. |
Receive |
CHNGDIR field in RPL contains CMD |
DFSYN |
Start sending from the opposite end of the session. |
- Bracket indicators
- The normal-flow control requests Bid and Ready to Receive are
used by the VTAM application
program to determine whether it can send a request with the begin-bracket
indicator set on (designated BB).
BB and CEB can be sent in a
data request or an LU Status request. The end-bracket indicator can
be set on (designated EB) in a data request or in a Cancel, Chase,
Quiesce Complete, or LU Status request. The request containing the
BB or EB must be a single-request chain (CHAIN=ONLY) or the first
request of a chain. The request containing the CEB must be a single-request
chain or the last request in a chain.
Table 8. Summary of bracket
indicatorsIndicator |
Function |
PLU or SLU application program can send/receive |
Macroinstruction used or RPL field set |
RU type |
Next action expected |
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Begin Bracket (BB) |
Indicates first chain in a bracket. |
Send |
SEND Bracket=BB |
DFSYN |
Continues to send or waits to receive, according
to user conventions. |
Receive |
BRACKET field in RPL contains BB |
DFSYN |
Accept or reject the request to start a bracket. |
End Bracket (EB) |
Indicates last chain in a bracket. |
Send |
SEND BRACKET=EB |
DFSYN |
Attempts to start a new bracket, or waits for
other LU to start a bracket, according to user conventions. |
Receive |
BRACKET field in RPL contains EB |
DFSYN |
Attempts to start a new bracket, or waits for other LU to start
a bracket, according to user conventions. |
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Conditional End Bracket (CEB) |
Indicates last chain in a bracket. |
Send |
SEND BRACKET=CEB |
DFSYN |
Attempts to start a new bracket, or waits for
other LU to start a bracket, according to user conventions. |
Receive |
BRACKET field in RPL contains CEB |
DFSYN |
Attempts to start a new bracket, or waits for other LU to start
a bracket, according to user conventions. |
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