From: Richard.E.Brown@dartmouth.edu (Richard E. Brown)
Newsgroups: comp.protocols.appletalk
Subject: ForceDDPChecksums
Summary: An INIT to force Macs to send checksums for data reliability.
Keywords: DDP checksum reliability
Date: 28 Sep 92 12:51:54 GMT
Organization: Dartmouth College, Hanover, NH
X-Posted-From: InterNews1.0a5@newshost.dartmouth.edu

As a couple people have pointed out, LaserWriter NTR's don't work if
your Mac/spooler uses DDP checksums. In addition, there was a bug in
Apple's .ATP code which failed when checksums were turned on. (This bug
was fixed by AppleTalk version 57.0.4) 

To guard against future incompatibilities with checksums, you can use a
small extension (INIT) I found on the net. This INIT patches the
DDPWrite call so the checksumFlag is always set true. If your software
doesn't work with this INIT installed, something is broken. 

[Climbing on soapbox] 

Checksums were included in the AppleTalk protocol to bolster end-to-end
reliability.  Although there are CRC's on every kind of link
imaginable, if an intermediate router has a bad memory bit, it *will*
corrupt the packet as it's relayed through.  If there aren't any
checksums in the packet, the recipient will be unaware of the packet
damage, and will do the right thing with the wrong data. Do you ever
haven un-repeatable errors with network services? This could be the
problem.

Developers: Please check your software with this INIT. Or just turn on
checksums in your product!

[End of soapbox]

Since it's so small, I've binhexed the INIT and appended it to the
message.

Rich Brown                    E-Mail: richard.e.brown@dartmouth.edu
Manager of Special Projects   AppleLink address:  A0183
Dartmouth College             Telephone: 603/646-3648
Kiewit Computer Center        Fax: 603/646-2810
Hanover, NH 03755-3523 USA         

----- ForceDDPChecksums INIT -----
(This file must be converted with BinHex 4.0)

:%%C[FQ0P4%433fKPBfY6G@d!58j*9%4298FJ!*!($0U,8J#3"!%!N!-,PJ!!#TB

!!!&%)(*PFh"[EQ3JG'mJ8Q9KC#"MB@aX!%4bDACPFL"MB@i34QpbBf9%4&"$D'9

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PBR9RCf9b)'PZFh4KE'aPC#"dEb"SB@jNE'8JC'9LG@F!!!%Q6PEri%MR"aK#Tbm

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bCA0[GA*MC3e3BA4MD%4%8%0VFh9Y"%eKD@j2"J:
Newsgroups: comp.protocols.appletalk