*COMDECK NHIMS
#* * * * * * * * * * ----------  NHEADER ----------* * * * * * * * * * #
*IF DEF,IMS 
 #
*1DC  NHEADER 
* 
*     NHEADER CONTAINS THE TEMPLATE FOR THE BLOCK HEADER OF BLOCKS IN 
*     NIP-S INBOUND AND OUTBOUND BUFFERS. WE SHALL REFER TO THIS TYPE 
*     OF BLOCK HEADER AS THE NETWORK HEADER. FOR DOWNLINE BLOCKS, THE 
*     NETWORK HEADER IS FORMATTED BY NIP WHILE FOR UPLINE BLOCKS, IT IS 
*     FORMATTED BY CCP AND PIP. 
* 
*     THE NETWORK HEADER HAS THE FOLLOWING FORMAT : 
* 
*     0    8    16   24      25      28   32      40      44  48   59 
*     I----I----I----I-------I-------I----I-------I-------I---I----I
*     I DN I SN I CN I NHPRI I NHBSN I BT I NHDBC I NHACT I B I CC I
*     I----I----I----I-------I-------I----I-------I-------I---I----I
* 
*     WHERE : 
* 
*        DN      = DESTINATION NODE NUMBER
*        SN      = SOURCE NODE NUMBER 
*        CN      = CONNECTION NUMBER
*        NHPRI   = PRIORITY BIT. SET TO 1 FOR HIGH PRIORITY DATA AND 0
*                  FOR LOW PRIORITY DATA, ALL BLOCKS ON THE SAME
*                  CONNECTION ARE ASSIGNED THE SAME PRIORITY. PRIORITY
*                  OF A PCB/QCB IS SET AT CREATION TIME AND IS USED TO
*                  DETERMINE PRIORITY FOR LOGICAL LINK REGULATION.
*        NHBSN   = BLOCK SEQUENCE NUMBER (1-7). THE BSN SUPPLIED IN A 
*                  DOWNLINE BLOCK OF TYPE -MSG-, -BLK- OR -CMD- MUST
*                  BE RETURNED IN THE BSN FIELD OF THE UPLINE -BACK-
*                  WHICH ACKNOWLEDGES THAT SPECIFIC BLOCK. WHEN A -BRK- 
*                  OR -STP- IS SENT, THE BSN RETURNED MUST BE THE SAME
*                  BSN OF LAST -BACK- SENT FOR THE CONNECTION. THE BSN
*                  WILL ALWAYS BE ZERO ON OTHER UPLINE OR DOWNLINE
*                  BLOCKS. THIS FIELD ALSO CONTAIN THE ISN - INIT 
*                  SEQUENCE NUMBER WHICH IS SET UP BY NIP FOR DOWNLINE
*                  -INIT- AND BY CCP FOR UPLINE -INIT-. 
*        BT      = BLOCK TYPE. SEE CCP IMS FOR DETAILS. 
*        NHDBC   = DATA BLOCK CLARIFIER. IT EXISTS ONLY FOR BLOCK TYPES 
*                  -MSG- AND -BLK-, SEE CCP IMS FOR DETAILS.
*        NHACT   = APPLICATION CHARACTER TYPE. ONLY CHARACTER TYPE 2
*                  (ASCII-8), 3(ASCII-12) AND 4(DISPLAY CODE) ARE VALID 
*                  FOR DOWNLINE BLOCKS. UPLINE DATA IS ALWAYS IN ASCII-8
*                  FORMAT AND THIS FIELD IS ZEROED FOR UPLINE BLOCKS. 
*        B       = BLOCK TYPE FOR BAD UPLINE BLOCK. WHEN PIP DETECTS
*                  AN UPLINE DATA TRANSMISSION ERROR, THE BT FIELD IS 
*                  CLEARED SO THAT NIP MAY DAYFILE THE BAD UPLINE BLOCK.
*        CC      = TEXT LENGTH IN CHARACTERS. THIS IS SET BY NIP FOR
*                  DOWNLINE BLOCKS AND BY PIP FOR UPLINE BLOCKS.
* 
 #
*ENDIF
