[c-nsp] Effect of simultaneous TCP sessions on bandwidth

[Youssef Bengelloun-Zahr]

Hello community,

Need your help and hands on experience to shed some light on some problem
I'm facing.

We have contracted a Layer 2 ethernet connection hand-off between our DC
(Frankfurt) and a customer site (Hamburg) with a carrier.

Carrier provides us with an ethernet MPLS pipe up to a DC in hamburg and
relies on a third party local loop provider to extend it up to customer
site. Nothing new under the sun here.

We have been testing this connection because we think we are facing
bandwidth issues. Let me summarize our results :

   - Carrier claims E2E Ethernet RFC2544 passed : we have been to check the
results and they seem OK,

   - UDP traffic reaches up to 95 Mbits/s for one way streams (both ways)
and simaltaneous bi-directionnal streams,

   - TCP traffic reaches up to 90 Mbits/s for one way streams (both ways),

   - TCP traffic hits some kind of limit and isn't able to achieve more
than 40-60 Mbits/s in average      <=== That's the problem we are facing.

One bit of information I think is relevant :

    - FRA Handoff between our provider and our PE is using a GigE port,

    - HBG Handoff between our provider and local-loop provider is using a
Fast ethernet ports between their facing equipments,

    - CE in Hamburg is a Fast Ethernet port and is forced with 100 Full
duplex,


We have carried tests with multiple devices directly connected behind our
PE in FRA and carrier's CE in HBG, results are always the same.

In the end, we connected servers directly in order to suppress any uneeded
equipments on the path, tests we're carried using iPerf and some other
tools.

We have been debugging this, no improvement. We have tried everything,
disabling all policiers, etc.... nothing nails it !

Our provider claims this is normal behavior for TCP. Does this sound normal
to you ?

Thanks for your help.

Best regards.