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Tune.Doc for NIC Bridge/Async Version 1.1i
Nov 12 1992
Copyright (c) Eighth Layer Systems 1990-1992.
All rights reserved.
Warning: The possibility of file corruption exists when using any software.
Please take whatever steps are required to protect vital files.
This documentation is formatted with 23 line pages. It contains
IBM PC type block graphics characters.
┌────────┐
│ TUNING │
└────────┘
─────────
General
─────────
Local Area Network protocols often require tuning in order to be used
over low speed links. This is due to the fact that they often incorporate
default timeout values which, while suitable for the high speeds of Ethernet
and Token Ring, are unsuitable for the low speeds of serial ports.
Testing with MS/IBM NetBEUI has shown that it can be tuned for used at
speeds as low as 300 baud. 3Com NBP has been tuned to be successfully used at
speeds as low as 2400 baud. MS TCP/IP has been used at speeds as low as 9600
baud with no Lanman.Ini or Protocol.Ini tuning.
The following sections detail tuning considerations for the MS/IBM
NetBEUI protocol and the 3Com NBP protocol.
─────────────────────────────────
NetBEUI - Lanman.Ini/IBMLan.Ini
─────────────────────────────────
The tuning option of NicSetup modifies the Lanman.Ini/IBMLan.Ini
Workstation/Requester parameters for slow links. These modifications have been
compiled from those recommended by Microsoft for slow links and used by MS LM
Remote Access Service.
Testing with MS NetBEUI over relatively error free links has shown
some of these modifications to be detrimental to performance when copying
large files. Using default Lanman.Ini parameters can increase the performance
of large file copies. Most other operations, however, will not benefit.
Lanman.Ini/IBMLan.Ini [workstation]/[requester] parameters as modified
by NicSetup for DOS enhanced workstations:
- WRKHEURISTICS: bit 8 = 0 for Opportunistic Locking off
bit 9 = 0 for Open-Read SMB off
bit 11 = 9 for 36 second beep window
bit 14 = 1 for Raw I/O off
Lanman.Ini/IBMLan.Ini [workstation]/[requester] parameters desirable
for DOS enhanced workstations:
- SIZWORKBUF: sizworkbuf = 4096 (or higher)
- WRKHEURISTICS: bit 8 = 0 for Opportunistic Locking off
bit 9 = 1 for Open-Read SMB on
bit 11 = 9 for 36 second beep window
bit 14 = 0 for Raw I/O on
Lanman.Ini/IBMLan.Ini [workstation]/[requester] parameters as modified
by NicSetup for OS/2 workstations:
- WRKHEURISTICS: bit 0 = 0 for Opportunistic Locking off
bit 6 = 0 for Open-Read SMBs off
bit 8 = 0 for NCB Chain Sends off
bit 9 = 0 for Buffer Small R/W Requests off
bit 11 = 0 for Raw R/W SMBs off
- SESSTIMEOUT: sesstimeout = 60000
Lanman.Ini/IBMLan.Ini [workstation]/[requester] parameters desirable
for OS/2 workstations:
- SIZWORKBUF: sizworkbuf = 4096 (or higher)
- WRKHEURISTICS: bit 0 = 0 for Opportunistic Locking off
bit 6 = 1 for Open-Read SMBs on
bit 8 = 1 for NCB Chain Sends on
bit 9 = 1 for Buffer Small R/W Requests on
bit 11 = 1 for Raw R/W SMBs on
- SESSTIMEOUT: sesstimeout = 60000
────────────────────────
NetBEUI - Protocol.Ini
────────────────────────
The tuning option of NicSetup modifies the NetBEUI Protocol.Ini
parameters for speeds as low as 2400 baud. Specifically, the following
parameters are set:
NETBIOSRETRIES = 2
NETBIOSTIMEOUT = 2000
ADAPTRATE = 0
MAXIN = 1
MAXOUT = 1
PIGGYBACKACKS = 0
T1 = 12000
TI = 60000
The T1 (T One) timeout value may be modified according to the minimum
expected baudrate for remote links. Recommended values are shown below.
Minimum BaudRate: 300 1200 2400 9600 57600 115200
T1 Value to use: 65535 24000 12000 3000 500 500
NicSetup sets the NetBEUI MAXOUT parameter to 1. This is the number
of packets NetBEUI will send before waiting for an ACK or acknowledgement
packet. During this waiting time, no useful data is being transferred on the
link. This decreases performance, particularly through bridges and/or at
higher link speeds.
Setting MAXOUT to 4-8 provides much better performance. One problem
with this however is timeouts. For an example, if NetBEUI sends MAXOUT = 4
packets before waiting for an ACK packet, it must wait for the 4 packets to
be transmitted over the serial link, received and acknowledged. This could
take 4 times longer than waiting for 1 packet. Thus the recommended T1 (T One)
values shown below must be multiplied by the MAXOUT value.
T1 (T One) timeout value recommended if MAXOUT = 1:
Minimum BaudRate: 300 1200 2400 9600 57600 115200
T1 Value to use: 65535 24000 12000 3000 500 500
If MAXOUT = 4, the following values for T1 may be used:
Minimum BaudRate: 300 1200 2400 9600 57600 115200
T1 Value to use: ----- ----- 48000 12000 2000 2000
One potential problem with raising T1 concerns error prone links.
When an error occurs on the link, retransmission of the data will not take
place until the T1 timer has expired for the packet in error. During the
time that T1 is expiring, there is generally no data transmission occuring.
Thus, if MAXOUT = 1 at 2400 baud and T1 = 12000, a single transmission error
can cause the link to remain idle for 12 seconds. If MAXOUT = 4 and T1 = 48000
this idle time increases to 48 seconds.
Thus, raising T1 indiscriminately so as to raise MAXOUT is not a good
idea on error prone links. An error correcting modem and use of 16550 buffered
serial ports at higher speeds will both help to greatly reduce this problem.
Also note that the T1 value on a server will affect local users as well as
remote users.
One last potential problem with raising MAXOUT above 1 regards remote
bridge buffering. When NetBEUI on a server transmits MAXOUT packets and then
waits, those 4 packets will be received by the bridge in quick succession at
local network speeds. A remote bridge must buffer those packets for
transmission over the slow link. When all of the bridges' buffers are in use,
any further packets received will be dropped. This will cause timeouts and
lower the efficiency of the link.
By default the NBridge driver can buffer 16 packets. Theoretically,
this should allow up to 4 workstations to transfer files through the bridge
from a server set with MAXOUT = 4. Practically, some bridge buffers should
always be reserved for broadcasts.
If NAsync is installed on a server and bound directly to NetBEUI
a "trick" may be used to limit the T1 multiplier to 2. This requires setting
the following NetBEUI parameters in Protocol.Ini:
mintransmits = 1
maxtransmits = 2
This causes packets to be queued internally in NetBEUI rather than
in NAsync and postpones the start of the T1 timeout. The MAXOUT parameter
may then be raised as high as 8 or 16, while only doubling the T1 parameter
from its' MAXOUT = 1 value.
──────────────────
NBP - Lanman.Ini
──────────────────
Lanman.Ini [workstation] parameters required for DOS enhanced NBP
workstations:
- SIZWORKBUF: sizworkbuf = 1024
- WRKHEURISTICS: bit 8 = 0 for Opportunistic Locking off
bit 9 = 0 for Open-Read SMB off
bit 11 = 9 for 36 second beep window
bit 14 = 1 for Raw I/O off
Lanman.Ini [workstation] parameters required for OS/2 NBP
workstations:
- SIZWORKBUF: sizworkbuf = 1024
- WRKHEURISTICS: bit 0 = 0 for Opportunistic Locking off
bit 6 = 0 for Open-Read SMBs off
bit 8 = 0 for NCB Chain Sends off
bit 9 = 0 for Buffer Small R/W Requests off
bit 11 = 0 for Raw R/W SMBs off
- SESSTIMEOUT: sesstimeout = 60000
Lanman.Ini [server] parameters required for OS/2 NBP servers:
- SIZREQBUF: sizreqbuf = 1024
- NUMBIGBUF: numbigbuf = 0
- SRVHEURISTICS: bit 15 = 9 for Opportunistic Locking off
────────────────────
NBP - Protocol.Ini
────────────────────
The following Protocol.Ini NBP parameters should be set for low speed
links:
PROBETIMEOUT = 1000
MAXPROBETIMEOUT = 8000
The latest and possibly last version of 3Com NBP, version 2.0D, also
provides a RESCALE parameter. When present in Protocol.Ini it allows NBP to
more easily adapt to timeouts and may thus be useful on low speed links.
It should be noted that the use of the MAXPROBETIMOUT and RESCALE
parameters for NBP is not supported by 3Com.
──────────────
NAsync Driver
──────────────
In cases where a protocol cannot be tuned sufficiently for low speed
operation the NAsync Protocol.Ini parameter MAC_MAXFRAME may be useful. This
parameter sets the maximum framesize that NAsync reports it is capable of to
protocols. By default, MAC_MAXFRAME = 1514, the maximum framesize for an
Ethernet adapter. It may be set as low as 128 by adding to the [NASYNC_NIF]
section of Protocol.Ini the line "MAC_MAXFRAME = 128".
By setting the maximum framesize to 128 the maximum effective timeout
of a protocol may be increased more than 6 times, relative to the default.
Performance, however, will be adversely affected. If this parameter is
added, it should be added at both the client and host side.
The compression and encryption features of NAsync can both consume
considerable amounts of CPU power. In some situations however, the overhead
of compression may be able to provide an increase in throughput for remote
users and this may be more important than CPU consumption.
The NAsync Protocol.Ini parameter CHARS_FILTERBC can be set to "YES"
on servers to prevent the transmission of broadcast packets. This should only
be used on servers without NIC Bridge as the NBridge driver has its' own
parameter to filter broadcasts.
Due to the broadcast of an ARP request by a server running MS TCP/IP
during session setup, broadcast filtering cannot be used with MS TCP/IP. As
the most common server broadcast is the server announce broadcast (which
allows active servers to be determined with NET VIEW) it may be better to
to increase the interval of this broadcast. This can be done by increasing
the Lanman.Ini/IBMLan.Ini [server] SRVANNOUNCE parameter.
The retransmission of network packets caused by serial overrun errors
has a disastrous effect on performance. It has been observed that the MS/IBM
NetBEUI protocol driver can contribute to the likelihood of these errors,
particularly when not tuned for low speed use. This is one more reason to
ensure that NetBEUI is properly tuned for low speed use.
The use of serial ports with the 16550A UART can greatly reduce the
likelihood of serial overrun errors. When this UART is used NAsync will detect
it and enable support for it's special features. Some of these features
include the ability to dramatically reduce the CPU load required to support
the serial port.
The Protocol.Ini COMM_RXTRIGGER parameter is provided specifically for
the 16550A. This sets the number of characters, in a buffer of 16 characters,
which will normally be received before an interrupt is triggered. It can be
set to 0, 1, 4, 8 or 14. The value 0 will set the trigger level to a value
appropriate for the baudrate and is the default for OS/2. The value 1 provides
the greatest protection from serial overrun errors and is the default for DOS.
The value 14 provides the least protection but also provides the lowest
consumption of CPU power for a given baudrate. The tradeoff between these
factors is best determined by the given configuration.
─────────────────────────
NBridge & SRTok Drivers
─────────────────────────
The Nbridge driver allows filtering broadcasts with the Protocol.Ini
FILTERBC_MAC parameter. This can greatly decrease overhead on slow links
experiencing significant broadcast traffic. As noted in the NAsync Driver
section however, this does not allow the proper operation of MS TCP/IP. In
addition, broadcast filtering tends to be more useful for remote access,
rather than for remote bridging where it can block needed broadcasts.
In some situations the custom filtering available via the Protocol.Ini
CUSTOMFILTER parameter may be more appropriate. This can, for example, be used
to block broadcasts from certain network source addresses.
The SRTok driver provides a Protocol.Ini SRBC parameter which, when
set to "NO" will block single route broadcasts from being received on the
Token Ring adapter. This can be very effective for eliminating broadcasts
to remote PCs on a Token Ring network.
┌──────────────────┐
│ ACKNOWLEDGEMENTS │
└──────────────────┘
All trademarks are the property of their owners.
This includes, but is not limited to, the trademarks
of 3Com, IBM, Microsoft, and Hayes.
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