I was asked today what the difference between SFP and SFP+ is. I did really know, so I looked it up and it seems that the SFP spec provides capabilities for data rates up to 4.25Gb/s, whereas SFP+ supports up to 10Gb/s. Naturally, this made me wonder whether or not an optic that supported 10GbE always conformed to the SFP+ standard inherently, or if there are cases where a 10GbE optic might only support the SFP standard, thus having a 4.25Gb/s bottleneck.
Jason - there are no SFP-10G parts based off of the original SFP; they
all are based on the SFP+ standard, so there will be no issues with the
optic not being able to work at the full 10Gbps it's rated for.
Sam Chesluk
Network Hardware Resale
I'm curious also. Could you use a SFP in a ten gig port if you only need 4gb of throughput?
Depends on the switch. Some, like the 2960S and 4948E, have 1G/10G
ports. They will, however, not operate at 4Gbps (that particular speed
was chosen to allow the core components to work for gigabit Ethernet,
OC48, 2G FC, and 4G FC).
Sam Chesluk
Network Hardware Resale
4G SFPs are relatively rare, and only for fibre channel. Multi-rate SFPs
that do up to 2.5G (for OC48) are a lot more common, but they cost more
than just a simple 1GE SFP. Since all you can do with Ethernet is 1G or
10G anyways, "most" SFPs you'll encounter in the field will be the
cheaper non-multirate kind.
For more information about SFP+, as well as some comparisons between
different 10G optic types, take a look at:
http://www.nanog.org/meetings/nanog42/presentations/pluggables.pdf
As an update (since this presentation is from Feb 2008), SFP+ is just
now finally starting to get into 40km/ER reach territory. Supplies are
limited, as they just very recently started shipping, but they do exist.
Of course since they moved the electronic dispersion compensation (EDC)
off the optic and onto the host board, the exact distances you'll be
able to achieve are still based on the quality of the device you're
plugging them into. SFP+ is still mostly an enterprise box or high
density / short reach offering, and XFP is still required for full
functionality.
Are there are any optics that plug into 10G ports but have a copper or
optical 1G interface? There's some equipment that I'm specing where it is
$10K for a multi-port 1G card, even while I really may only *occasionally*
need a single 1G port and there's a free 10G port for me to use.
Frank
It doesn't work that way. The closest you can get is that the device can
support either 1G or 10G in the same port (since SFP and SFP+ are
physically and electrically the same), but it requires support from the
device (since both PHYs have to be implemented).
You can plug SFP module (copper or fiber) into any SFP+ port.
So, on 10G port you can run either 1GE or 10GE.
Peter Nowak
Not true. Some devices support this, since SFP and SFP+ are physically
and electrically compatible, but not all. The device must be
specifically designed to support both PHYs, which is NOT a given.
A well known counterexample of this is the Cisco Nexus5k, where only some of the SFP+ ports are 1G capable (first 8 on the 20 port box, and the first 16 on the 40 port box).
Nick
Are there are any optics that plug into 10G ports but have a copper or
optical 1G interface? There's some equipment that I'm specing where it is
$10K for a multi-port 1G card, even while I really may only *occasionally*
need a single 1G port and there's a free 10G port for me to use.
Some of the cisco stuff supports a twingig converter module, One tengig
to 2 one gig (and from there a copper or optical SFP)
http://www.cisco.com/en/US/prod/collateral/switches/ps5718/ps7077/product_data_sheet0900aecd805bbee3.html
Vince
Are there are any optics that plug into 10G ports but have a copper or
optical 1G interface? There's some equipment that I'm specing where it is
$10K for a multi-port 1G card, even while I really may only *occasionally*
need a single 1G port and there's a free 10G port for me to use.
Some of the cisco stuff supports a twingig converter module, One tengig
to 2 one gig (and from there a copper or optical SFP)
http://www.cisco.com/en/US/prod/collateral/switches/ps5718/ps7077/product_data_sheet0900aecd805bbee3.html
Vince