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Status-Acknowledge(Ack)

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The Status-Acknowledge(Ack) message flows from the node to the application and from the application to the node, and is used with both system services control point (SSCP) and primary logical unit (PLU) connections.

The following structure shows the message format for all SSCP messages and for PLU messages flowing from the node to the application.

Syntax

struct Status-Acknowledge(Ack) {  
    PTRBFHDR  nxtqptr;  
    PTRBFELT  hdreptr;  
    CHAR      numelts;  
    CHAR      msgtype;  
    CHAR      srcl;  
    CHAR      srcp;  
    INTEGER   srci;  
    CHAR      destl;  
    CHAR      destp;  
    INTEGER   desti;  
    CHAR      sfhdr.stackhdr.akstat;  
    CHAR      sfhdr.stackhdr.akqual;  
    INTEGER   sfhdr.stackhdr.akmsgkey;  
    CHAR      sfhdr.stackhdr.akflags1;  
    CHAR      sfhdr.stackhdr.akflags2;  
    INTEGER   sfhdr.stackhdr.aknumb1;  
    INTEGER   sfhdr.stackhdr.aknumb2;  
    INTEGER   sfhdr.stackhdr.akseqno;  
};   
struct Status-Acknowledge(Ack) {  
    PTRBFELT   hdreptr->elteptr;  
    INTEGER    hdreptr->startd;  
    INTEGER    hdreptr->endd;  
    CHAR       hdreptr->trpad;  
    CHAR[268]  hdreptr->dataru;  
};

Members

nxtqptr
Pointer to next buffer header.

hdreptr
Pointer to buffer element (NIL if not using LUA).

numelts
Number of buffer elements (0x00 if not using LUA).

msgtype
Message type STATFMI (0x21).

srcl
Source locality.

srcp
Source partner.

srci
Source index.

destl
Destination locality.

destp
Destination partner.

desti
Destination index.

sfhdr.stackhdr.akstat
Status type ACK (0x01).

sfhdr.stackhdr.akqual
Acknowledgment type ACKPOS (0x02).

sfhdr.stackhdr.akmsgkey
Message key.

sfhdr.stackhdr.akflags1
Application flag 1.

sfhdr.stackhdr.akflags2
Application flag 2.

sfhdr.stackhdr.aknumb1
Undefined.

sfhdr.stackhdr.aknumb2
Reserved.

sfhdr.stackhdr.akseqno
SNA sequence number.

LUA only (see Remarks):
Element

hdreptr–>elteptr
Pointer to buffer element (NIL).

hdreptr–>startd
Start of data in this buffer element.

13 or 10 for second and subsequent segments of outbound segmented request/response units (RUs)

hdreptr–>endd
End of data in this buffer element.

hdreptr–>trpad
Reserved.

hdreptr–>dataru
Data RU.

The message format for PLU messages flowing from the application to the node is identical to the preceding format, except that the application flag 1 and application flag 2 fields are not used. They are replaced by the following INTEGER field:

sfhdr.stackhdr.akmsgtim
Last host response time.

  • (0xFFFF) No response time measured.
  • (0xnnnn) Last response time measured, in units of 0.1 second.

Remarks

  • The message key and application flags reflect the message key and application flags of the data message to which this is an acknowledgment. (For more information, see the note about LUA that follows.)

  • For outbound Status-Acknowledge(Ack) messages from the local node to the application, the SNA sequence number gives the sequence number of the inbound data message to which this is an acknowledgment. (For more information, see the note about LUA that follows.) It is normally used only by Transmission Service profile (TS profile) 4 applications.

  • For inbound Status-Acknowledge(Ack) messages from the application to the local node, the SNA sequence number reflects the sequence number of the outbound data message to which this is an acknowledgment.

  • If the host specified that response time statistics are to be maintained, the application is responsible for measuring and reporting response times to the local node, using the akmsgtim field of this message. (For details, see RTM Parameters and Response Time Monitor Data.)

  • If the application is using the LUA variant of the function management interface (FMI), the transmission header (TH) and (if appropriate) response header (RH) are included in the data, and the startd field points to the TH. The akmsgkey, akflags1, and akflags2 fields are undefined and should not be used. The corresponding data from the element should be used instead. The akseqno field is similarly undefined on messages from the local node to the application. It must be set on messages from the application to the local node. The akseqno field is used to hold the sequence number of the request being acknowledged. (For more information about FMI, see FMI Concepts.)

  • If the application is not using the LUA variant of the FMI, the message consists of a buffer header only. There is no buffer element.