• Subject: Re: Errors on Token Ring line
  • From: dhandy@xxxxxxxxxxx (Douglas Handy)
  • Date: Tue, 11 Jan 2000 20:44:25 -0500

Larry,

>On a token-ring you can go as high as 16393.  If you have systems
>communicating on a local ring these huge packets can really boost throughput 
>for
>large file transfers (including spool files).  They won't affect things like
>Telent a whit.

Where can I find documentation on the interrelationships of the max
frame size of the LIND, the MTU of the interface, and all the rest of
the stuff related to datagram size etc?  I tried the OS/400 TCP/IP
Configuration and Reference manual, and it didn't have much to say, at
least in my V3R7 copy.  Haven't checked the V4 copies on the web.

Last weekend I was experimenting on trying to increase the throughput
of my local TR network (no routers) and had mixed success.  I was able
to boost transfers from my 400 to the PC to run at about 950K/sec, but
can only achieve half of that when transferring from my PC to the 400.

I surmise it is a problem with packet sizes, but can't figure out the
magic combinations.  Here's the best throughput I've got yet:

 AS/400:
 - 2619 adapter; 16M line speed; *HALF duplex
 - 16393 max frame size; early token release set to *YES
 - Interface set to *NORMAL type of service, MTU of *LIND
 - Interface shows a MTU of 16388 while active

 PC's:
 - IBM PCI Auto LanStreamer adapters
 - Max TX frame size set to 8156 (16393 didn't work!)
 - Receive buffer size set to 16388

 Connected via passive MSAU (a SMC Elite 4016RN)

Obviously the PC's max frame size of 8156 could explain why I get much
lower throughput on PC to 400 then 400 to PC.  But when I set the PC
to 16388 or 16393, I can't even ping the 400 let alone transfer
anything.  The PC driver lets me specify the TX frame size but not the
MTU, so I had figured 16393 would be the value to use.  The driver
lets me enter any arbitrary value I want (not just select from a list
of values).

When I couldn't get 16393 or 16388 to work, I went down to 8156
because it is the next lower value listed by the 400 help text for a
"suggested" TR frame size.

I also tried setting the 400 interface type of service to *MAXTHRPUT
instead of *NORMAL, but again couldn't ping between the systems until
I went back to *NORMAL.

Any ideas?  I'd like to get my upload speeds to match the 950K/sec I
can now get with downloads.  There are only 5 devices on my network:
two AS/400's, two PC's, and a HP JetDirect.

Doug
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