Effective bandwidth reduction over WAN

To SSH mailing list:

 

 

I have a somewhat unusual question.  I do not know if this issue is truly a
bug or just a feature of the protocol.

 

I have two sites that are distantly connected to each other via a DS3 WAN.
When we tried to replace FTP with SCP or SFTP we ran into throughput
problems.  We then set up a test in our lab to see if we could isolate the
factor that was impacting throughput.  This test setup was composed of two
nodes hooked up through a WAN emulator.  They were connected using Gigabit
Ethernet, but the rate was throttled back to 45 mbps (DS3 rate).  All of the
testing used an MTU of 1500 and files sizes of 10 MB, 100Mb, 1 GB, and 5 GB.
We ran FTP tests with the same setup for a baseline.  For SCP and SFTP we
tried each of the three encryption algorithms (3-des, arcfour, & blowfish).
We then varied the WAN latency.  We are using the latest version of the
Portable SSP for Solaris.  The OS is Solaris 8.

 

The results were

 

0 latency      FTP - Ave. 39.5 mbps    SCP - Ave. 39.4 mbps      SFTP - Ave.
38.8 mbps

60 millisec    FTP - Ave. 37.7 mbps    SCP - Ave.  2.9 mbps       SFTP -
Ave.  2.9 mbps

100 millisec  FTP - Ave. 33.0 mbps    SCP - Ave.   2.0 mbps      SFTP - Ave.
1.8 mbps

 

Can anyone tell me why the throughput of SCP and SFTP drop so drastically
when we try to use SSP protocols over a WAN?

 

Eric Meijer