Network Speed Differences

by Johannes Helmig [Published on 8 Aug. 1999 / Last Updated on 8 Aug. 1999]

You think, that the network cabling for your Thin Ethernet (10base2), Twisted Pair Ethernet (10baseT/UTP) or Twisted Pair Ethernet (100baseTX/100BaseT4) is in good condition, but instead of the expected network throughput in both directions:

test 1 and 3:
1 file of 34 Mbyte

test 2 and 4:
2100 files of 18.5 Mbyte


you get different speeds, depending of the direction of transfering the data:

test 1 and 3:
1 file of 34 Mbyte

test 2 and 4:
2100 files of 18.5 Mbyte

In this example, reading the data from the network give only approx. 60 % of the throughput than writing the data, some people have reported slowdowns to 30% and even slower.

A possible reason could be re-transmittions, caused by network cable problems, which can depend on the location of a system on the network.

But for TCP/IP networks, there is another possibility:
some Browsers for Internet access (like: Neoplanet) allow to optimize access speed to the Internet by modifying some TCP/IP parameters by defining smaller TCP/IP packets, but these modified values slow down a Local TCP/IP Ethernet network (for details on the Windows TCP/IP Registry Entries, see the Knowledge base article Q158474): To restore the Network speed, reset the values to the Windows default.


MTU / MaxMTU :

Look under the key:
HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\Class\NetTrans ,
the sub-keys "0000", "0001", "0002", "0003" represent all the Bindings(defined in the Network-applet of the Control-Panel) of a protocol to a network adapter or Modem).
Locate the one defining under "DriverDesc": TCP/IP. You may have multiples TCP/IP- bindings, and since the example above does NOT define the IPaddress, this is the TCP/IP-Binding to the modem for Internet access.
The optimum value for Internet access is : 576, the Windows default value (optimal for LAN) is 1500.


RWIN / DefaultRcvWindow :

Look under the key:
HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\VxD\MSTCP,
for the value "DefaultRcvWindow".
The optimum value for Internet access is : 2144, the Windows default value (optimal for LAN) is 8192.
NOTE: There is some difference in the Data-type of this key betweeen Windows95 and Windows98: the KB article defines for Windows95 a Data-Type: DWORD and for Windows98 a Data-Type: String-Value.

See Also


The Author — Johannes Helmig

Dr.Johannes Helmig is working as Director, Technical Knowledge Management in the Belgium office of Gerber Technology where he is involved in Customer Service and internal training, with special interest in Networking.

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