Using NS3000/iX Network Services (36920-90008)

46 Chapter 3

Remote File Access

RFA Compression

Remote File Access (RFA) allows for data compression. RFA data

compression can provide faster data transfer, especially over a slow link

and when the ﬁle being remotely accessed has large records with

repeated characters.To invoke data compression for the RFA service,

specify the keyword, COMP, in the DSLINE command. The COMP keyword

compresses both NFT and RFA data associated to the remote

environment speciﬁed in the DSLINE command. For example, issuing

the command DSLINE NODE1;COMP allows for compression of all RFA

and NFT data to the remote node called NODE1.

To terminate data compression to the speciﬁed environment, specify the

keyword NOCOMP in the on of any new remote ﬁles opened as well as

prevents data compression of any future NFT data to the environment

speciﬁed in the DSLINE command. Files opened remotely while

compression is in effect for the environment remain in compressed

mode even after the DSLINE;NOCOMP command is issued.

The same algorithm is used for both RFA and NFT data compression.

The same algorithm is also used with DS Services compression: each

sequence of up to 64 consecutive repeated characters is compressed to

two bytes, and repeated blanks are compressed to one byte.

Without RFA compression enabled, the RFA service can transfer up to

29,900 bytes of data at one time. However, due to overhead associated

with managing a compressed data transfer, the RFA service with

compression enabled can transfer up to a maximum of 29,000 bytes of

data at one time between MPE/iX-based HP 3000s. For transfers

between an MPE/iX-based system and an MPE-V based system the

maximum amount of compressed data that can be transferred at one

time is 14,500 bytes.

RFA compression only compresses data transmitted with the FREAD,

FREADDIR, FREADBACKWARD, FWRITE, FWRITEDIR and FUDPATE

intrinsics. Therefore, RFA compression is not supported with the

Remote DataBase Access (RDBA) service.

RFA compression is currently only available on HP 3000 Series 900

systems with version B.00.05 or later of the NS 3000/iX Network

Services. If you request RFA compression of a ﬁle residing on a system

that does not support RFA compression (such as systems running

NS 3000/V software released prior to version A.00.12), RFA completes

the request without compressing the RFA data. No error or warning

messages are issued in this situation.