I'm uploading a large file.
The problem is: uploading speed jumps to 134 KiB/s (≈100% of my bandwidth) and then immediately back to 67 Kib/s (≈50% of my bW): every 3 seconds it tries to increase & falls back. My uplink is 1 Mibit/s, but I can't use it.
My connection is stable & working, the server is okay: same thing happens while uploading to other hosts, but not with downloading. Skype up-traffic is also stable: maybe, because it does not use the whole BW.
My schematic 'traceroute': [PC] → [Switch] → [ADSL Modem, NAT] → (The Internets)
What the hell could be happening?
UPD: Now MTU is 1492 all over my network & is equal to the ISP's MTU. The problem remains.
UPD2: With MTU <=600 speed is constantly at 50% BW, no spikes