- tcpsegmentsize (the maximum size of a single TCP segment)
- tcpwindowsize (the amount of data a receiving TCP stack can buffer)
- nbsessions (the maximum number of NetBIOS sessions available)
- tcpconnections (the maximum number of TCP connections available)
Also for optimum performance, tcpwindowsize should typically be as large as possible, in increments of tcpsegmentsize. Increasing tcpwindowsize, however, requires more memory, which can be a problem under MS-DOS. The TCP driver must load into a single 64K segment of memory. The driver must be able to buffer "tcpwindowsize" bytes of data on EACH tcpconnection, so the tcpwindowsize and tcpconnections values must be balanced against each other to achieve the best overall performance and connectivity.
So, tuning can be reduced to a simple process:
- Determine the number of TCP connections needed on your workstation.
- Set nbsessions and TCPUTILS.INI parameters as appropriate.
- Use the table below to choose the largest possible tcpwindowsize.
ExampleA "net use" command on the client shows:
Notice there are sessions to three servers, using three nbsessions, and three tcpconnections. In addition, assume you have the Microsoft TCP/IP Utilities for LAN Manager installed, and you use one telnet session and three sockets. By default, the value of nbsessions is 6, which allows some headroom for sessions to more LAN Manager servers.
Status Local name Remote name
OK D: \\server1\shareD
OK E: \\server1\shareE
OK F: \\server2\shareF
OK G: \\server2\shareG
OK H: \\server3\shareH
OK I: \\server3\shareI
OK LPT1 \\server1\laser
OK LPT2 \\server1\lineprint
The formula used internally for tcpconnections is:
Nsessions and numsockets exist only if the utilities are installed, and examining the TCPUTILS.INI file reveals their default values to be 2 and 8, respectively. (In LAN Manager 2.2, the value for numsockets is scheduled to change to 4).
tcpconnections = nbsessions + 1 + [nsessions + numsockets]
So, if you are using LAN Manager version 2.1a or earlier, the default tcpconnections are 6 + 1 + 2 + 8 = 17. You only need one telnet connection and three sockets, so you should first reduce those parameters in TCPUTILS.INI. After the reduction, you are left with 6 + 1 + 1 + 3 = 11 tcpconnections. The table below shows that you can support a tcpwindowsize of no more than 2900 bytes on an MS-DOS client.
You can add these parameters to the PROTOCOL.INI file in the [TCPIP_XIF] section. You should also modify the MS OS/2 server for versions 2.1 and 2.1a. In PROTOCOL.INI, set:
tcpconnections tcpwindowsize tcpsegmentsize
6 or less 5800 1450
7 - 8 4350 1450
9 - 11 2900 1450 <-- Optimum configuration
12 - 22 1450 1450 for 11 tcpconnections
Microsoft no longer recommends setting the tcpconnections value in PROTOCOL.INI, and may remove the parameter in a future version. For the best results, adjust the parameters that are used to calculate tcpconnections and allow it to adjust internally.
tcpsegmentsize=1450 (the same as for the clients)
tcpwindowsize=4350 (MS OS/2 normally has plenty of memory for this)
Note that if you don't have the utilities installed and aren't using sockets or telnet, tcpconnections calculates to 6 + 1 = 7, so you would select a tcpwindowsize of 4350 from the above table.
NOTE: If your network adapter card is incapable of handling a tcpwindowsize burst of frames, it may drop one or more of them. If this occurs, performance will degrade seriously. Some older cards may be able to buffer only one incoming frame at a time.
The tcpwindowsize should be as large as possible within the memory constraints of the systems involved. On MS OS/2, tcpwindowsize should work at 4350 in all cases, and this will be the new default in LAN Manager 2.2. Performance gains will be most significant on high-delay networks such as those found in many WAN environments.
Article ID: 93444 - Last Review: May 26, 2014 - Revision: 1