How do I improve the transfer speed of a RVS4000 VPN tunnel?

I have a VPN tunnel using 2 Linksys RVS4000 routers. I'm using the same ISP at both ends ( a cable provider with 512 Kbps upload speed and 7.5 Mbps download) . I have a Windows PCs at both ends. The transfer speeds are impossibly slow. When I transfer a 1 M file between 2 machines I get about 10 kbps transfer rates.

I need secure access to a 54M database and these speed make access impossible.

These are the settings of the tunnel

Keying Mode:        IKE with Preshared Key
Phase 1:                
Encryption:               3DES
Authentication:       MD5
Group:                       768-bit
Key Life Time:         86400 Sec.

Phase 2:
Encryption:                3DES
Authentication:        SHA-1
Perfect Forward Secrecy:       enable
Preshared Key:       
Group:                         768-bit
Key Life Time:          28800
Who is Participating?
MikeKaneConnect With a Mentor Commented:
Alot of this will depend on the the total traffic at both sites.   A 512 up at each end gets you about 62.5Kbps transfer rate if my math is correct.    To this add any other traffic that is leaving the site, how many users, any uploads happening?  How about other site to site transfers when the VPN is up? AD replication going on?  Other syncs?  

As you think about the above, also consider that the ISP oversold the speed.   Consider that 62.5 number will lose 10-15% in signalling and other errors.    Have you certified that both sites are actually getting that upload speed?  Try any of the speedtests online to verify.  

Lastly, what kind of file were you moving and how were you moving it?   Was it a large file over SMB?   FTP?   Different methods will have different overhead costs.    

jkepplerAuthor Commented:
At the time I tested this there would have been essentially no other upload traffic on either end.

I've tried moving both smaller files (images - <1MB) and larger files ( data files - 50 MB) with speed ranging from 2 - 17 kbps. These files were moved using using shared folders on Windows which I believe is SMB.

Using I got 2.57 MB/s download 0.46 Mb/s upload and 105 ms ping.
MikeKaneConnect With a Mentor Commented:
Then another item you can look at is possible fragmentation.    Check the MTU size on each router and adjust accordingly.  

I use a utility called MTUROUTE to check for the maximum mtu size.    If this is set to large, you get fragmentation and connection issues.    Doesn't really sound like what you have, but its worth a check anyway.
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