This isn't particularly tied to the ISP I'm with, but more a question on to interpret symptoms and test results....
I have an FTTC connection from Eclipse (who buy from BT Wholesale). I'm a long way from the cab, and the wiring in the area is known to be in poor condition, but for most of the time the line runs at a solid, stable 21 Mbit/s down. That's rather better than BT's speed estimator gave (17 Mbit/s)
In this state, speed tests here, and real world usage, will give me the full 21 Mbit/s for any single stream, or I'll get an aggregate 21 Mbit/s for multiple streams. Ping latency shows consistently around 18 mSec.
But the line has moments - sometimes hours, sometimes days - when throughput is decidedly bad for *single* streams. It will run badly, then it'll get better all by itself.
Testing here will give me an aggregate 21 Mbit/s for the 6 x HTTP stream test; but the single-stream TBB test will show anywhere from 2 Mbit/s to around 10 Mbit/s, and the speed can vary right across the range within a single test.
However, ping latency is still reported as around 18 mSec.
If I use BT's speed tester at http://speedtest.btwholesale.com/,
I'll typically see 21 Mbit/s even when the line is running badly; but ping latency there can show 30 - 40 mSec. Only rarely will the BT speedtester show a poor performance, and the worst I've seen is 10 Mbit/s. Netstat indicates that the test is using multiple parallel streams anyway to 18.104.22.168, so wouldn't show the problem I have.
The BT speed tester isn't consistent with other testers: just now it reported 11 Mbit/s, but here gave me 19 Mbt/s and Speedtest.net gave 15.
Eclipse aren't particularly interested. When I was in this state for a few weeks they blamed it on "the Internet being slow with people downloading iOS 7". They suggested I run the detailed phase of BT's speed test, but I can't get that to work at all. Packet traces I've done of this show the PPP login works, but then no packets get a response. Eclipse have no idea what to do with the packet trace I sent them and won't help further.
The problem doesn't last long enough to get a handle on it - if I do get Eclipse to report it to BTW it'll likely be gone before they get to look, and that's £128 gone.
Does this sound to you as if there is throttling going on here (Eclipse claim they don't do any, so presumably it would be BT). Given that I can get 21 Mbit/s from multiple streams and ping latency does not get worse, am I being limited on the throughput to each individual port here?
Anyone got a helpful suggestion? What do the symptoms indicate to you?