The return of the Elephant

Over Christmas, I was out of my home base and needed access to a 1+ GByte file I left there. Only connection available to me at my place at that time was a 3G/4G one, serving around 4 MBit/sec in both directions max.

My home base unfortunately is equipped only with a 25/2.5 Mbit/sec connection, so uploading into the cloud that is the Internet was limited to about 2 MBit/sec. But even that slow speed wasn’t achieved by using scp: it maxed out around 1,5 Mbit/sec, then dropping, then slowly climbing to 2 Mbit/sec again, dropping — over all speed was more around the 150 kByte/sec mark.

As I was kind of urgently needing the file, I hit the big G and, of course, was told about Bandwith-by-Delay product, stuff I deemed long lost and gone since no-one actually DOES use satellite links anymore, right? (Timewarp: Back then, around 1996, my employer at that time used a satellite link from Europe to the US for bulk data, and that was when I first had to tune computer’s networking stacks for these “long, fat pipes”).

Looks like the “long, fat pipes” are a) much faster these days, b) much more common, and c) are called LFNs now. “Long fat networks”, pronounced, possibly, as “elephants” — I really like the English people for their abbreviations ;)

The linked Wikipedia article actually does mention HSPA as an example, although in my case the limiting factor was the sender’s VDSL upstream speed of 2,5 MBit/sec … And even with establishing an IPSec VPN between both sites, the best RTT I could get was around 140 ms:

traceroute to (, 30 hops max, 60 byte packets
 1  1.990 ms  2.600 ms  6.774 ms
 2  98.634 ms  109.375 ms  109.471 ms
 3  118.530 ms  129.010 ms  129.045 ms
 4  138.670 ms  169.734 ms  169.825 ms

Which basically gives: 2.5 * 1000 * 1000 Bit/sec * 0.140 sec = 350000 Bit (or ~44 kBytes) in transit.

Anyhow, the solution to my problem this holiday season was … bbcp. With that, even only using two streams, I was able to squeeze more out of that thin upstream:

1 file copied at effectively 205.8 KB/s

Still not blazingly fast, but if you are busy-waiting for that data, it might make a difference.