On 19/02/13 11:29, Reuben Farrelly wrote:
On 19/02/2013 9:21 PM, Peter Rathlev wrote:
This is a classic example of when a Gig port in name is not a Gig port
in throughput, ie it may link up at that speed but you'd be lucky to get
the rated throughput in all but ideal circumstances.
Funny thing is that many lower end switches (i.e. cheaper) have better
buffer characteristics than a 2960 or similar. And even though the 2960
is cheap compared to other high end switches it isn't compared to
gigabit switches in general.
Notwithstanding that this is a Cisco list, is this limited buffer
problem something common to many other vendor's lower end switches too?
Do switches from vendor J, Mikrotik and HP also have a similar problem?
Many do, because many are built on the same hardware these days. A lot
of the 1U gig/10gig devices are all pretty much standard Broadcom designs.
The situation gets slightly more complex with some newer switches that
are cut-through, where the buffers are only eaten into if there's
contention or a port-speed mismatch between ingress and egress.
It's obviously used as a differentiator of high and low end switches for
Cisco, but I've often wondered if it's used as a deliberate "cripple" to
the kit, surely it can't be THAT hard and expensive to engineer
increased shared buffer space in a low end chassis from 12M to, say 60M?
Well, the RAM needs to be pretty fast, so it's not cheap, but the ASIC
also needs to be able to *address* that size of RAM; it might have e.g.
a 24-bit address space.
The buffer size thing is a pain, but equally over-buffering is also bad;
there's no easy solution AFAICT.
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