How much bandwidth do you get when running a PPTP VPN?

SImple question.  How much bandwidth do you get when running a PPTP VPN?  Connecting a Windows XP computer to a Windows 2003 server.  No tweating of settings so far, so how much bandwidth will the person get? I suppose I may say, how much equivalent bandwidth do they get inf there's a chance everything's slowed down by encryption.  (Asking mainly because our VPNs seems very slow when people are downloaidng files.)
wibber1Asked:
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MikeKaneCommented:
More or less.   the MSS size of each possible packet is smaller so the tcp stream may need additional packets to complete.      The bandwidth is close, however the bottleneck might be the endpoint devices that have to do the encryption/decryption.....  

But to answer your question....   "about" 2.5-3% of each packet is lost to the vpn config.   Then you need to allow for the other traffic that will flow .    Plus there's always the latency between endpoints.   So when speaking about pure packet overhead, 3% is a safe guess,  but overall bandwidth is different and the speed will be affected by latency and the encrypt/decrypt process....
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MikeKaneCommented:
IIRC, PPTP has 32 bits of overhead on any packet.  

So a 1500 MTU packet, lets say you are on PPPoE DSL makes it 1500-8=1492, then a PPTP makes it 1492-36 = 1456.

So basically you would lose about 2.5% of bandwidth to PPTP overhead.  



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wibber1Author Commented:
So does that mean that the VPN should have as much bandwidth as the connection minus 2.5%?
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