When I was researching my story about Allied Telesis being the first to put XFP slots into edge switches, I have to admit I was sceptical. Surely all those claims of 10Gig support from others must mean something?

But it turned out to be true - most switch vendors do indeed expect you to pay extra for slots to add XFP optics. Talking to some of them, I discovered this was typically £800 to £1000 per XFP slot, and yes, as Allied says, that could almost double the price of a switch.

One way around the cost of 10Gig fibre is to use copper instead - a few vendors build CX4 sockets in as standard, but copper is low range compared to fibre, so these are intended much more for stacking than uplinking.

But as Allied's Melvyn Wray says, if you want to get 10Gig to market now - as an uplink technology - XFP is really the only game in town. Sure, there is X2, and others are on the way such as the more compact SFP+, but XFP is what's most likely to be in use already.

(As an aside, there's also issues of XFP compatibility. While many suppliers lock their switches so they'll work only with their XFPs, smaller and more open vendors, such as Allied and Force10, will let you use any XFP. The downside is that even a supposedly-open supplier may make its warranty conditional on your using an 'approved' XFP. Suppliers warn too that XFPs are not completely standard, so a different vendor's XFP may not return the same diagnostic info as their own.)

The challenge is what happens once we do start wanting to use SFP+, for example. Suppliers that take the modular approach can develop a new 10Gig module to use with existing switches, but Allied will need a new switch.

Melvyn Wray says he's not too worried by that - there will be a product refresh at some point anyway, and in any case he reckons it's not clear yet what will succeed XFP.