Hi Gang

We are seeing an issue with one of our BBCS-F customers which we can not quite explain. So I wonder if you also experience the same issue with 'some' of your customers.

* Swisscom Profile 1G/1G. * ZyXEL PM7300 Bridge (also swapped for Nokia Bridge or FritzBox) * PPPoE session terminated on Linux Notebook (also tested with Windows behind FritzBox). * Testing with iperf3

Result Upstream: ~900 Mbit/s as expected.

Result Downstream: 1 TCP Session: ~280 Mbit/s not OK 5 TCP Session: ~500 Mbit/s not OK 10 TCP Session: ~800 MBit/s acceptable

Iperf3 shows a slightly increased number of TCP retransmits. iperf3 UDP test with pushing 800Mbit/s shows about 0.2% packetloss. Well, this somehow explains why 1 TCP session does not get up to speed.

Customer is working with an applications downloading large data junks from the cloud - using one TCP session at the time - of course he is not happy.

Exact same set-up on another BBCS-F 1G/1G service, in a neighboring town reaches ~900Mbit/s in UP and DOWN with just one TCP session - less packetloss with UDP less retransmits.

Case opened with Swisscom FAN-port was switched. Case closed.

Issue got slightly better but still not acceptable. Case re-opened meeting with Swisscom/Cablex tech on customer site. He connects his test-device which shows 900Mbit/s Downstream. Our tech checks this test-device and finds out, it opens 100 concurrent TCP connections to a Swisscom Speed-Test servers - our tech asked to Swisscom tech to please re-test in a more realistic scenario, 1 to 2 TCP session. Swisscom tech does so, download speed drops to below 300 Mbit/s, upload speed is fine, confirming our measurements.

So we persuaded Swisscom the issue is real, they will continue to investigate and hopefully find and fix the cause right?

Case closed: Resolution: Test was performed by 'standard' Swisscom Speed-Test opening 100 concurrent TCP connections. Proof was provided that there is no speed issue with 'standard' customer behavior. Customer has to open multiple TCP connections to reach advertised speed which Swisscom considers to be the way Customers have to use their service.

I managed to re-open the case to more deeply investigate, why this is the issue with this one customer and not with our reference service about 3km away reaching 900Mbit/s down with just one TCP connection.

So out of curiosity: Do others also observe this 'one TCP connection slow because of slight packetloss' issue with some BBCS-F customers? Is there known cause and solution?

Mit freundlichen Grüssen

-Benoît Panizzon-