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What causes my overseas VPN connection to slow during the day?

Learn what slows connectivity for a VPN overseas during particular times of day, in this Q&A with VPN expert Sampath Ramaswami.

I am using a Nortel Connectivity VPN client and connecting to a remote site in France. When I am connecting in the morning the speed is ok, however, during the day the speed of the connection gradually gets slower and slower until a screen refresh can potentially take up to 1-2 minutes. Do you have any idea what could be causing this? The site is using broadband at about 400 Kbps upload and just under 3 Mbps download. We have a Windows 2003 SBS network with a domain, and a Vigor 2600 router/modem as a gateway. The version of the client is 4.01.

Since your performance appears to be related to the time of day, it is likely due to congestion points in the network. One possibility is that you may be suffering from congestion on the link over the Atlantic. Depending on your Internet provider's peers, the trans-Atlantic connections can be undersized for peak usage, particularly during US business hours. This can result in high latency and packet loss, and a corresponding drop in throughput. You could confirm this by testing your performance outside of the VPN during the slow times, from a server located in France.

Another issue could be the number of users on the host site concentrator. Congestion on this server could also result in slower user performance. You can confirm the concentrator load by examining its logs for the number of concurrent users during the slow performance period. Your VPN provider should be able to provide guidance on whether this number is within the specifications for the concentrator capacity.

This was last published in April 2007

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