Format of APPC/PC "Allocate" control block:
Offset	Size	Description	)
 00h 12 BYTEs	reserved
 0Ch	WORD	0100h (verb "Allocate" or "MC_Allocate")
 0Eh	BYTE	1 if MC_ (mapped conversation) form of verb
		0 if basic verb
 0Fh  5 BYTEs	reserved (0)
 14h	WORD	(big-endian) primary return code (see #03681)
 16h	DWORD	(big-endian) error code (see #03682)
 1Ah  8 BYTEs	(big-endian) TP_ID
 22h	DWORD	(big-endian) conversation ID
 26h	BYTE	(MC_Allocate only) conversation type
		0 basic conversation
		1 mapped conversation
 27h	BYTE	SYNC_LEVEL (00h none, 01h confirm)
 28h	WORD	0000h
 2Ah	BYTE	RETURN_CONTROL
		00h when session allocated
		01h immediate
		02h when session free
 2Bh  8 BYTEs	00h
 33h  8 BYTEs	(big-endian) partner logical unit name
 3Bh  8 BYTEs	(big-endian) mode name
 43h 65 BYTEs	(counted string) TP name
 84h	BYTE	security (00h none, 01h same, 02h pgm)
 85h 11 BYTEs	00h
 90h 11 BYTEs	(counted string) password
 9Bh 11 BYTEs	(counted string) user ID
 A6h	WORD	PIP_DATA length
 A8h	DWORD	pointer to PIP_DATA