Long-haul 100Mbps EPL circuit throughput issue

Fri Nov 6 02:17:01 UTC 2015

With default window size of 64KB, and a delay of 75 msec, you should only
get around 7Mbps of throughput with TCP.

You would need a window size of about 1MB in order to fill up the 100 Mbps
link.

1/0.75 = 13.333 (how many RTTs in a second)
13.333 * 65535 * 8 = 6,990,225.24 (about 7Mbps)

You would need to increase the window to 1,048,560 KB, in order to get
around 100Mbps.

13.333 * 1,048,560 * 8 = 111,843,603.84 (about 100 Mbps)

*Pablo Lucena*

*Cooper General Global Services*

*Network Administrator*

*Office: 305-418-4440 ext. 130*

*plucena at coopergeneral.com <plucena at coopergeneral.com>*

On Thu, Nov 5, 2015 at 6:31 PM, Bob Evans <bob at fiberinternetcenter.com>
wrote:

> Eric,
>
> I have seen that happen.
>
> 1st double check that the gear is truly full duplex....seems like it may
> claim it is and you just discovered it is not. That's always been an issue
> with manufactures claiming they are full duplex and on short distances
> it's not so noticeable.
>
> Try to perf in both directions at the same time and it become obvious.
>
> Thank You
> Bob Evans
> CTO
>
>
>
>
> > Hello NANOG,
> >
> > We've been dealing with an interesting throughput issue with one of our
> > carrier. Specs and topology:
> >
> > 100Mbps EPL, fiber from a national carrier. We do MPLS to the CPE
> > providing
> > a VRF circuit to our customer back to our data center through our MPLS
> > network. Circuit has 75 ms of latency since it's around 5000km.
> >
> > Linux test machine in customer's VRF <-> SRX100 <-> Carrier CPE (Cisco
> > 2960G) <-> Carrier's MPLS network <-> NNI - MX80 <-> Our MPLS network <->
> > Terminating edge - MX80 <-> Distribution switch - EX3300 <-> Linux test
> > machine in customer's VRF
> >
> > We can full the link in UDP traffic with iperf but with TCP, we can reach
> > 80-90% and then the traffic drops to 50% and slowly increase up to 90%.
> >
> > Any one have dealt with this kind of problem in the past? We've tested by
> > forcing ports to 100-FD at both ends, policing the circuit on our side,
> > called the carrier and escalated to L2/L3 support. They tried to also
> > police the circuit but as far as I know, they didn't modify anything
> else.
> > I've told our support to make them look for underrun errors on their
> Cisco
> > switch and they can see some. They're pretty much in the same boat as us
> > and they're not sure where to look at.
> >
> > Thanks
> > Eric
> >
>
>
>