Overlap - What is it? - Network graphs/reporting

[TidalWave]

Hi All,

I'm having a hard time understanding what the overlap graph means. I understand the Rx and the Tx fields, but Overlap.... I'm at a lost. Could someone please help me understand what overlap means? See attached image.

 

[TidalWave]

anyone?

 

[MikeyG]

It looks like overlap is used to express minimum or common bandwidth used in both directions during a time period. So if you are sending 1mbps, and receiving 2mbps, then at least 1mbps is being sent in both directions, making the overlap 1mbps. I'm not sure why this would ever be useful information though.

 

[Gcon]

The above description is correct. The most important use is for gauging utilisation of PCIe lanes. From a bit of searching I see that PCIe 2.x is 5 gigatransfers/sec and when overheads are taken into account (8b/10b encoding), this works out to 4Gbps usable per lane. The Intel X540 has 2x 10Gig NICs so at full throughput in both directions that's theoretically 40Gbps looking at all flows in all directions - but the card is only PCI 2.0 sporting 8 lanes so you are limited to 32Gbps on the PCIe backplane (a "blocking" architecture) thus end up being 8Gbps short! Thus overlap can matter greatly if you are saturating multiple ports in both directions at the same time.

It is also useful on half-duplex links, but those are extremely rare these days.