Terminology - BCOM Buffers, Windows and records

Please consult Table 1 below for the syntax of the following parameters on each platform.

1. The BCOM buffer (MAXBLK). The BCOM buffer is the basic unit transmission between BCOM partners. Its length is specified in the configuration file (see the table, next page) and defaults to 2048 bytes or 4096 bytes, depending on the platform. BCOM always fills its buffer to achieve maximum performance and usage. Up to version C01, the range of accepted values was from 512 to 4096. Starting with version C02 (for MVS, NSK Guardian and Windows NT), the maximum has been raised to 32760 (mileage may vary according to the platform, please see below).

2. The BCOM windows. BCOM implements its own windowing protocol, somewhat akin to SNA’s pacing protocol. Its used is to regulate the flow of information between BCOM nodes, prevent receiving node overflow but still augment throughput by sending large amount of data before requesting acknowledgment. The windows count (number of BCOM buffers) is specified in the configuration file. BCOM implements its windows through SNA’s Chaining. For example, if the Window Count is specified at 5, block 1 will be first-in-chain, 2, 3 and 4 will be middle-if-chain and 5 will be last-in-chain.

3. The file record size. When a file is being transferred (send, receive, print, etc.) by BCOM, the file’s records are either broken down to fit the buffer size or grouped together for an optimal usage. This blocking and segmentation is totally transparent to the user and is totally independent from SNA Segmentation, Chaining and Pacing.

PLATFORM	BUFFER			WINDOW
	Parameter	Range	Default	Parameter	Range	Default
MVS	FS62LCL MAXBLK=	512:32760	4096	FS62LCL DEFWIND=	1:50	10
NSK Guardian	DEFINE LTRANSFER-PARAMETERS MAXBLK	512:32760	4096	DEFINE LTRANSFER-PARAMETERS WINDCNT	1:32768	3
Windows NT	local_location max_blk	512:32760	2048	local_location defwind	1:50	5
OS/2	local_location max_blk	256:4096	2048	local_location defwind	1:50	5
VAX	local_location max_blk	256:4096	2048	local_location defwind	1:50	5
AS/400	STRBFSCFG Maximum Size of Transfer Buffers	256:4096	2048	STRBFSCFG Windows Count	1:50	5

Table 1 - BCOM Configuration Parameters