[Sephiroth]

OK - I've been into this a bity more and have, of course, found the reporting buttons that allow me to copy & paste. Bearing in mind that Speedtest.net reports 50/4.7, this NDT test now reports 22.5/3.5 after tweaking up my RWIN buffer. This compares with my previous NDT result of 9.2/3.5.

The reports produced by NDT are quite deep (that's good), but leaves me with unanswerable questions. Here are some salient points.

Upload speed 3.5 mb/s
Download speed 22 mb/s
Network latency: 1.9e+2 msec round trip time

Jitter: 1.8e+2 msec
Your system: Windows Vista version 6.0
Java version: 1.6.0_26 (x86)

TCP receive window: 4156416 current, 4597504 maximum
9.9522E-5 packets lost during test
Round trip time: 173 msec (minimum), 350 msec (maximum), 188.55 msec (average)
Jitter: 177 msec
0 seconds spend waiting following a timeout
TCP time-out counter: 394
1685 selective acknowledgement packets received

No duplex mismatch condition was detected.
The test did not detect a cable fault.
Network congestion may be limiting the connection.
No network addess translation appliance was detected.

0.9382% of the time was not spent in a receiver limited or sender limited state.
3.74% of the time the connection is limited by the client machine's receive buffer.
Optimal receive buffer: 412876800 bytes
Bottleneck link: 10 Mbps Ethernet
0 duplicate ACKs set

What 10 meg bottleneck is that? My topology, punting the 50 meg service, is:

Modem 1Gig --> Router 200 meg (through 1 Gig port) --> Homeplug 200 meg (161 meg effective) --> Netgear GS108 Switch 1 Gig port to --> 1 Gig ethernet port on PC.

So there's something about this test and how it probes what that needs explaining to me at least.

The "Advanced" tab reports (amongst other things):

The theoretical network limit is 5.92 Mbps
The NDT server has a 1833.0 KByte buffer which limits the throughput to 151.97 Mbps
Your PC/Workstation has a 4489.0 KByte buffer which limits the throughput to 186.03 Mbps
The network based flow control limits the throughput to 83.00 Mbps
Client Data reports link is 'Ethernet',
Client Acks report link is 'Ethernet'
Server Data reports link is 'OC-48',
Server Acks report link is 'null'

So, at this stage, it merits further investigation and perhaps a bit of playing around with TCP Optimizer.