Why are we fixated on Multimode fiber for high bandwidth communication?
I've been working with 40 gig for a few years. When I first ordered a switch, one of the first publicly available with full 40 gig, I was appalled that I was going to have to use 4 pair of multimode fiber for each of my connections. I had planned on using single mode because I can do that with 1 pair. Even today, we're still looking at MM fiber instead of SM, even with the horrendous limitations and cost issues of MM. For instance, if you need to go 301 meters or more, you've got to go OM4 which is very expensive. You have to lay 4 times the number of pairs as SM and when we move to 100G, it'll be even worse because they're still doing things in 6,12,etc... SM can do 100G easily, up to 1K with the lower grade fiber, so in the SM 100G world, you'd be installing 1/12 the strands as you would in multi mode. I just can't figure where this makes sense.... I am aware that single mode has more expensive optics, and I know how much they cost when I first looked at this, but if this were the standard, that price would drop enormously. Anyone know why the industry has their head stuck on MultiMode?
On Dec 31, 2013, at 2:00 PM, eric clark <cabenth@gmail.com> wrote:
Anyone know why the industry has their head stuck on MultiMode?
at 10G the optics costs are about 1/3 that of SMF (SR vs LR). We tend to keep things SMF, but within many older datacenters MMF is broadly available and does meet the needs at a lower cost. There seems to be a shifting trend as well in UPC vs APC connectors. I think much of this problem is clearly articulated here: http://xkcd.com/927/ Everyones needs are a bit different. - Jared
Basic economics. MM optics come with looser tolerances and are therefore easier to produce. The wider core of the fiber and higher dispersion allowances also mean that the fiber is easier to make. The fiber, though, is the small end of this equation. The optics are the big one. For those who are buying two or three optics a year, a $150 price difference is no big deal. For those who buy two or three hundred optics every other month, this really makes a difference and those are the ones driving the MM development. -Wayne On Tue, Dec 31, 2013 at 02:08:36PM -0500, Jared Mauch wrote:
On Dec 31, 2013, at 2:00 PM, eric clark <cabenth@gmail.com> wrote:
Anyone know why the industry has their head stuck on MultiMode?
at 10G the optics costs are about 1/3 that of SMF (SR vs LR).
We tend to keep things SMF, but within many older datacenters MMF is broadly available and does meet the needs at a lower cost.
There seems to be a shifting trend as well in UPC vs APC connectors.
I think much of this problem is clearly articulated here: http://xkcd.com/927/
Everyones needs are a bit different.
- Jared
--- Wayne Bouchard web@typo.org Network Dude http://www.typo.org/~web/
My guess would be it's due to existing cable plants. I've worked at a number of places that have tons of multimode fiber run everywhere. If you can re-terminate and re-use, even if inefficiently, it often beats the time and expense required to run new fiber, especially if it's a place that pulling cable may involve trade unions; that gets very expensive to pull what could be a not so expensive cable one or two hundred meters. -----Original Message----- From: eric clark [mailto:cabenth@gmail.com] Sent: Tuesday, December 31, 2013 2:01 PM To: NANOG list Subject: Why are we fixated on Multimode fiber for high bandwidth communication? I've been working with 40 gig for a few years. When I first ordered a switch, one of the first publicly available with full 40 gig, I was appalled that I was going to have to use 4 pair of multimode fiber for each of my connections. I had planned on using single mode because I can do that with 1 pair. Even today, we're still looking at MM fiber instead of SM, even with the horrendous limitations and cost issues of MM. For instance, if you need to go 301 meters or more, you've got to go OM4 which is very expensive. You have to lay 4 times the number of pairs as SM and when we move to 100G, it'll be even worse because they're still doing things in 6,12,etc... SM can do 100G easily, up to 1K with the lower grade fiber, so in the SM 100G world, you'd be installing 1/12 the strands as you would in multi mode. I just can't figure where this makes sense.... I am aware that single mode has more expensive optics, and I know how much they cost when I first looked at this, but if this were the standard, that price would drop enormously. Anyone know why the industry has their head stuck on MultiMode?
On Tue, 31 Dec 2013, David Hubbard wrote:
My guess would be it's due to existing cable plants. I've worked at a number of places that have tons of multimode fiber run everywhere. If you can re-terminate and re-use, even if inefficiently, it often beats the time and expense required to run new fiber, especially if it's a place that pulling cable may involve trade unions; that gets very expensive to pull what could be a not so expensive cable one or two hundred meters.
Playing devil's avocate here... Compared to the cost difference between, say 40G SR equivalent optics and 40G LR equivalent optics, the cost of pulling, terminating, and testing new SMF between two relatively close points is pretty small. I say that with the following qualifier: If you have usable path (conduit, innerduct, rackspace for new termination bays, etc) in place between points A and B. If it turns into a situation where you need to dig to lay in new conduit, that's a different matter altogether. The problem is markedly worse at 100G. DPO-24 is just evil, but the cost difference between 100G SR10, LR4, and ER4 optics is still ridiculous. jms
Money, really. The optics and fiber cost is cheaper than SM. The standards around SM optics are to reach relatively long distances, so the transmitters and receivers are more expensive and they use way more power. That being said, I see MM in modern datacenters being used in-rack or very short distances due to the reasoning you mentioned, having to run at least 4 pair for 40G or 12 pair in the case of 100GBase-SR10. I know there are structured cabling solutions for handling the bundles but it sure seems like a pain. QSFP28 will bring 100G back down to 4 pairs of fibers at least for those who want to use MM. There was significant push by Google and others to come up with a shorter-reach 100G SM standard (LR10) because people don't want to use 12-pair MTP cables around their datacenter and LR4 wasn't a good fit. We are pretty much all SM for anything 10G and above as a standard, but have looked at 100GBase-SR10 for short-reach 100G interconnects due to the significant reduction in cost and power compared to 100GBase-LR4. Phil On 12/31/13, 2:00 PM, "eric clark" <cabenth@gmail.com> wrote:
I've been working with 40 gig for a few years. When I first ordered a switch, one of the first publicly available with full 40 gig, I was appalled that I was going to have to use 4 pair of multimode fiber for each of my connections. I had planned on using single mode because I can do that with 1 pair.
Even today, we're still looking at MM fiber instead of SM, even with the horrendous limitations and cost issues of MM. For instance, if you need to go 301 meters or more, you've got to go OM4 which is very expensive. You have to lay 4 times the number of pairs as SM and when we move to 100G, it'll be even worse because they're still doing things in 6,12,etc... SM can do 100G easily, up to 1K with the lower grade fiber, so in the SM 100G world, you'd be installing 1/12 the strands as you would in multi mode. I just can't figure where this makes sense....
I am aware that single mode has more expensive optics, and I know how much they cost when I first looked at this, but if this were the standard, that price would drop enormously.
Anyone know why the industry has their head stuck on MultiMode?
participants (6)
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David Hubbard -
eric clark -
Jared Mauch -
Justin M. Streiner -
Phil Bedard -
Wayne E Bouchard