subrate SFP?

Jamie Bowden jamie at
Fri Aug 30 11:42:04 UTC 2013

> From: Saku Ytti [mailto:saku at]

> I got quite a bit of replies from sellers selling me cuSFP, insisting they
> work.
> So I'd like to clear up on this. For 10/100 to work on SFP slot, the PHY in
> the host needs to be multirate. Exception is SGMII which supposedly
> supports magic mode where SFP can ask it to send same bit 10 times, then
> SFP can discard 9/10 bits, to remain very dumb yet deliver 100M client on
> 1GE host.
> RGMII does not support this trick and this trick does not bring you down to
> 10M. One box that we have right now, which can't do any of this is ME-4924.
> There is absolutely no reason that you couldn't deliver 'media converter'
> or '2 port switch' in a SFP casing, to get that 1 10/100 port in every
> 4500-X or EX4550 port you need to cater some legacy. If my desire is odd (2
> people have expressed off list they want same) this won't be built. But if
> this is somewhat common demand and missing product, we can certainly get
> such SFP built.
> Obviously this SFP would cost bit more than normal cuSFP, as it needs to do
> rudimentary buffering, packet dropping and it needs to have frame parser.

Considering that Dell and HP at least are shipping brand new hardware with IPMI/BMC/iLO/whatever management ports that can only speak 100mbit when every other Ethernet interface in the box at least gigabit, having a useful way to talk to that port without having to keep separate switching hardware around would be nice.  I'm not holding my breath, but you know, along with a pony, this would be nice.


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