I read an article earlier this year about how Comcast is planning to upgrade broadband access speeds to as fast at 160 Mbps. From almost all perspectives, this is great. Faster broadband means a better user experience, interactive applications, and HDTV. But, what does this mean for VPN access to work? Well, first, it would seem great. Think of working remotely with the same performance as in the office. That would be great, especially for applications like VoIP, desktop video conferencing, and file transfers. But the real problem could be at the office. Today’s VPN connections are limited by the bandwidth at the access layer. But that goes away when cable modems go to 160 Mbps. Under the best of Internet and TCP conditions (which is possible in the US), you could see up to 13 Mbps per TCP stream. Under more normal conditions, each TCP session could use 6.5 Mbps. Both are nothing to sneeze at. Let’s just figure: 10 Mbps per TCP session 3 active TCP sessions per user 300 users connected to VPN device 9 Gbps. Ouch! Do you have those pipes to the Internet? Or how about the VPN devices to handle that speed. But, realistically, there won’t be 900 high-bandwidth, active TCP sessions flowing traffic at the same time. So, let’s just say it happens 10% of the time. That’s 900 Mbps. Ouch! Ok, ok, only 1% of the time…90 Mbps! That might be possible, but still is pretty beefy for all but some Fortune 500 companies, universities, and governments. And what about the other Internet bandwidth you need for the people actually at the office? Ouch! Many organizations will need to consider how they will provide VPN access with existing Internet circuits. Yes, TCP has the mechanism (flow control and congestion avoidance) to adjust to drops, but you can’t fill circuits and expect TCP to handle it. TCP can handle about 2% packet loss before it just stops working. Things will fail and users will get angry. This should be fun. I can wait till I get my 160 Mbps connection.
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