CNOS general data stream (GDS) variable

The GDS is architected to provide a common understanding between transaction programs (TPs) using LU 6.2 protocols. GDS variables standardize the data format so that both sending and receiving TPs can process the data.

The CNOS GDS variable is a mapping of what VTAM® builds and sends on the CNOS conversation. The description of the CNOS GDS is shown in Table 1.

Table 1. CNOS (X'1210') GDS variable
Byte	Bit	Content
0—1		Length (17 or n—1), in binary, of CNOS GDS variable, including this Length field
	GDS ID: X'1210'
4		Service flag:
	0—3	Reserved
	4—7	Request/reply indicator: 0010 request 1000 reply, function completed abnormal 1010 reply, function accepted but not yet completed
5		Reply modifier (reserved if byte 4, bits 4—7 = 0010): X'00' normal—no negotiation performed X'01' abnormal—command race deleted X'02' abnormal—mode name not recognized X'03' reserved X'04' normal—negotiated reply X'05' abnormal—(LU-mode) session limit is 0
6		Action: X'00' set, (LU-mode) session limits X'01' reserved X'02' close
7		Drain immediacy:
	0—2	Reserved
	3	Source LU drain (reserved if byte 6 is not equal to 02): 0 no (send BIS at next opportunity) 1 yes
	4—6	Reserved
	7	Target LU drain (reserved if byte 6 is not equal to 02): 0 no (send BIS at next opportunity) 1 yes
8		Action flags:
	0—6	Reserved
	7	Session deactivation responsibility: 0 sender of CNOS request (source LU) 1 receiver of CNOS request (target LU)
9—10		(LU-mode) session limit:
	0	Reserved
	1—15	Maximum (LU-mode) session count, in binary
11—12		Source LU contention winners:
	0	Reserved
	1—15	Guaranteed minimum number of contention-winner sessions at source LU, in binary
13—14		Target LU contention winners:
	0	Reserved
	1—15	Guaranteed minimum number of contention-winner sessions at target LU, in binary
15		Mode name selection:
	0—6	Reserved
	7	Mode names affected by this command: 0 A single mode name is affected. 1 All mode names are affected (valid if byte 6 = 02).
16		Length (values 0 to 8 are valid; reserved if byte 15, bit 7 = 1), in binary, of mode name
	Mode name (omitted if byte 16 = X'00')
Note: Bytes 9—14 are reserved if byte 6 is not equal to 0.