Direct Fibre (DFAS) - what SFPs to use?

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MMNZ1234

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Wannabe Geek

#291914 13-Dec-2021 11:42

I'm looking at ordering a DFAS link between two sites in the same small city, instead of our previous Carrier Ethernet links.

Has anyone else got experience of what SFPs to use to drive a DFAS at 1Gbps? The two sites are only 8km apart, but looking at the location of the sites, and even assuming "as the crow flies" routes to the central exchange building, the circuit paths will be just over 10km. (I did consider running the link at 10Gbps, but the new switch at one end only supports 1Gbps SFPs, I don't want to upgrade it yet, and current traffic on the link is a max 150Mbps)

I'm assuming the service needs something like a singlemode SFPs like a Cisco GLC-EX-SMD or equivalent? This SFP is rated up to 40km

Is this a detail that we'll be told when we actually order the DFAS from one of the possible suppliers?

Any advice would be greatly appreciated.

nztim

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TEAMnetwork

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#2831321 13-Dec-2021 11:59

Remember you need two DFAS circuits to each site (assuming they are both on the same exchange)

FS.com and CDL have great “compatible” SFPs at half the price so even if you hold spares you are still better off

Any views expressed on these forums are my own and don't necessarily reflect those of my employer.

wired

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#2831400 13-Dec-2021 12:55

You can buy bi-directional SFPs (BIDI) which means that you only need one fibre. They work by using one frequency for RX and another for TX. You need to make sure that you get a matched pair so that the frequencies line up between them. They can have up and down written on them to help you match them.

MMNZ1234

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Wannabe Geek

#2831497 13-Dec-2021 14:58

I'm glad you told me that - I hadn't worked it out for myself and could have been an embarrassing situation when I ended up with a Unidirectional Link! 😂

nztim

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#2831514 13-Dec-2021 15:41

wired:
You can buy bi-directional SFPs (BIDI) which means that you only need one fibre. They work by using one frequency for RX and another for TX. You need to make sure that you get a matched pair so that the frequencies line up between them. They can have up and down written on them to help you match them.

I should have clarified two single strand fibres one to each site using different wavelengths for tx/rx

Any views expressed on these forums are my own and don't necessarily reflect those of my employer.

BarTender

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#2831784 13-Dec-2021 21:43

nztim:
wired:
You can buy bi-directional SFPs (BIDI) which means that you only need one fibre. They work by using one frequency for RX and another for TX. You need to make sure that you get a matched pair so that the frequencies line up between them. They can have up and down written on them to help you match them.

I should have clarified two single strand fibres one to each site using different wavelengths for tx/rx

But instead of a pair you can order a single which works out cheaper in the long run as all you need is a single fibre and BIDI SFP which will give you a 1GBit or faster symmetrical connection depending on how much you want to spend on the BIDIs. It uses two different wavelengths for TX and RX so you need to buy them as a pair. As the TX is matched to the RX on the other end. And vice versa.

cyril7

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#2831817 14-Dec-2021 06:14

Hi, as others have said you need a BiDi pair assuming you are purchasing a single fibre core, not a duplex, which is the normal for DFAS (well all the ones I have ordered were spec'd that way, check with the supplier), this will do the job.

Cyril

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#2831827 14-Dec-2021 07:21

And I just saw there are 10G BIDIs that aren’t horrendously overpriced. https://www.gowifi.co.nz/fibre-optic-products/fibre-modules/uf-sm-10g-s.html
Order a standard pair and with a LAG you now have a 20GBit connection.

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cyril7

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#2832348 14-Dec-2021 19:27

Must admit any DFAS I have is 10G, you have to have that level of capacity to make it worth it. If all you want is 1G, then surely a p2p VPN or vlan WAN via a dedicated UFB circuit is way better value.

Cyril