Lancom Systems 821 - Manual (Page 72)

LANCOM 821 ADSL/ISDN – LANCOM 1621 ADSL/ISDN – LANCOM 1711 VPN
̈ Chapter 9: Troubleshooting
72
EN
Numerous other factors involving the Internet itself can also influence the
transfer rate.
Increasing the TCP/IP window size under Windows
If the actual transfer rate of a DSL connection is significantly below the fastest
rate listed by the provider, there are only a few possible causes (apart from the
above-mentioned external factors) which may involve one's own equipment.
One common problem occurs when large amounts of data are sent and
received simultaneously with a Windows PC using an asynchronous connec-
tion. This can cause a severe decrease in download speed. The cause of this
problem is what is known as the TCP/IP receive window size of the Windows
operating system that is set to a value too small for asynchronous connec-
tions.
Instructions on how to increase the Windows size can be found in the Knowl-
edge Base of the support section of the LANCOM web site (
www.lancom.de ).
9.3 Unwanted connections under Windows XP
Windows XP computers attempt to compare their clocks with a timeserver on
the Internet at start-up. This is why when a Windows XP in the WLAN is
started, a connection to the Internet is established by the LANCOM.
To resolve this issue, you can turn off the automatic time synchronization on
the Windows XP computers under Right mouse click on the time of day
̈
Properties
̈
Internet time.
9.4 Cable testing
LANCOM 1711 VPN
only A cabling defect might have occurred, if no data is transmitted over LAN or
WAN connection, although the configuration of the devices does not show
any discernible errors.
You can test the cabling with the built-in cable tester of your LANCOM.
Change under WEBconfig to menu item Expert configuration
̈ Status ̈
LAN statistics ̈ Cable test. Enter here the name of the interface to be