How to verify transmission quality & cables on gigabit network?

[Debbie Deutsch]

Rob wrote:

[SNIP]

> Question 1:
> Should I worry about this reduced speed?

Do you need to be able to transmit at more than 500mbps?  Will it cause
you noticeable delays in accomplishing what you need to do?  If not, why
worry?

I'm not being sarcastic.  I'm just trying to imagine what would need all
that bandwidth on an ongoing basis.

> 
> Question 2:
> How to check the transmission quality?
> Should I inspect the output of "/sbin/ifconfig eth0"
> for errors/dropped/overruns/collisions etc. in the
> RX/TX lines?
> 
> 
> Lan card info:
>  master: Tigon3 10/100/1000BaseT Ethernet
>    tg3: eth0: Link is up at 1000 Mbps, full duplex.
>    tg3: eth0: Flow control is on for TX and on for RX.
>  nodes: Realtek RTL8169
>    eth0: Auto-negotiation Enabled.
>    eth0: 1000Mbps Full-duplex operation.
> 
> 
> Thanks for advice and help!
> Rob.
> 
> 

The other question I would ask is whether your systems are capable of
driving their gigE interfaces at full capacity (not just bursting, but a
sustained data stream).  It's been a number of years since I looked into
this, but for a long time it was the case that  the networking interface
was not the limiting factor in how fast a computer system could transmit
or receive information.  At the time this was true, I was the product
line manager for some large, enterprise-class gigabit routers/switches.
 So, I needed to understand how much switching our customers really needed.

Finally, if buffers are getting filled faster than they can be drained,
and flow control comes into play, that could reduce your effective
throughput.  It's a symptom of what I was talking about in the paragraph
before this one.  The computers themselves may not be capable of
sourcing or sinking gigabit-speed data flows.

Debbie