Small estate on edge of a village, van and 3 chaps stringing a cable along the telegraph poles. Cable was about 6mm dia., black with a yellow stripe along it. Any idea what it is? I'm assuming frome the diameter and low flxibility (there were a couple of loose coils taking up a lot of the footway and the bit being handled wasn't floppy like flex) that it's possibly FTTP. The van didn't have any markings on it.
Thats the container for fibre, which is already inside it.
Yellow stripe usually indicates fibre. (and the cable "recyclers" have been educated that any time they see yellow stripes or cable flags there is no scrap value for it!)
Here is a termination point near us before any customers were hooked up to it - you can see the yellow stripe cable:
Probably a sub contractor for openreach.
Is it run to a DP and then to the properties, same as copper is? Certainly save digging.
hooked up
That's a joint bullet where one cable is split to two others (in this case).
After the split the cables will run to a fibre DP at the top of a pole or maybe another split. The fibre DPs are black with quite chunky downward pointing prongs. These are individual fibre ports fitted with a blanking plug. To connect a customer the blanking plug is removed and the cable plugged in, the blanking plug then mated with the cables cap to keep things clean. Fibre cable run to premises and a fibre connector fitted to plug into the ONT.
Round here its all on poles, so no digging required, just a drop cable from the pole direct to the house.
Thanks for the explanation. I'll see if it has made any progress next time I'm passing. FTTP might not be very good here. We get a steady 37Mbps down 9Mbps up and that's it on FTTC. The cabinet is about 3km from the exchange; I don't know if that is a factor with fibre.
58 km limit I believe.
The length of the copper between you and the cabinet is the important factor.
For single-mode fibre, IIRC.
FTTP is one of those things that generally works or doesn't - there is no practical variability in performance with distance.
Is that on a 80/20 or 40/10 service? Assuming the latter, it would indicate you are relatively close to the cabinet (under 1km)
That is not the metric that matters - the connection from cabinet to exchange will be fibre, and not particularly distance sensitive. What matters is the length of the copper wiring that has to run VDSL from the cabinet to the end user. So within a few hundred meters it will run flat out. Over than and it degrades with distance. Once you are over a few km, then performance will be down in the low single Mbit range, and probably no better than with ADSL.
Fibre does have distance limits - but those are "per segment" so you can extend by adding another repeater and another segment. So its much better suited to long runs out into the middle of nowhere.
For FTTC it's the length and condition of the copper from the cabinet to you that is important. With 37 Mbps down that equates to about 700 m.
That's certainly within the range of a single mode fibre point to point link but I think Openreach are installing GPON (Gigabit Passive Optical Network). This takes the fibre from the head end "line card" and optically splits it 32 (or even 64) ways. This reduces the range but it's still in the order of 10 km or more providing up to 1 Gbps symetrical (if they wanted to).
And almost certainly not the same exchange that the POTS copper pair goes to. When they installed FTTC here they also installed a new fibre cable for them all the way from Hexham 40 km away. Yes, they did have trouble with light levels on a couple of them.
Openreach won't market FTTC lines as such unless they are pretty sure that they will support "superfast" broadband, ie > 24 Mbps down. Our line is one such, it goes through "VDSL cabinet" but at the exchange about 4 km away so we are stuck with ADSL2+, which is currently doing very well. 7611 kbps down sync with a 6.1 dB S/N ratio.
Even the the longest runs from the exchange out here at 7 miles (11 km) are probably within the range of FTTP with the optical split at the head end (it doesn't have to be...).
If you use expensive optical kit, you can use 96 different wavelengths on a SM fibre with, IIRC, 100GHz separation. That allows 10Gbps per channel, although they probably do 40Gbps these days. That's for backbone networks, and was what we were doing when I retired. Dunno what they can do these days.
VERY dependeent on a lot of factors. But I agree 'tens of kilometers' is in the ball park for cooking grade monomode.
yes, and no. You have described what the Open Reach engineer said happened (optical splitting), but he said the fibre went 10 + miles to a big exchange, and could do more than that. It is really probably about the amount of *power* that can be sent down it - the splitter is a different sort of loss from a long fibre, in that its probably a flat loss across the band, not a load of frequency dependent phase shifts.
The limit of multimode is reached when all the different paths combine to give a mess of incoherent phases, not because the signal is too low. For example.
This may be of interest:
"As we all know, multimode fiber is usually divided into OM1, OM2, OM3, OM4 and OM5 fiber types. When it comes to single mode fiber types, it can be categorized into OS1 and OS2 fiber, which are SMF fiber specifications. OS1 and OS2 are standard single mode optical cables respectively used with wavelengths of 1310nm and 1550nm with a maximum attenuation of 1 dB/km and 0.4 dB/km. OS1 fiber is a tight buffered cable designed for use in indoor applications (such as campuses or data centers) where the maximum distance is 10 km. OS2 fiber is a loose tube cable designed for use in outdoor cases (like street, underground and burial) where the maximum distance is *up to 200 km*. Both OS1 and OS2 fiber optic cable support Gigabit and 10G Ethernet links. "
Certainly undersea repeaters are over 100km apart if possible.
And thinking about the splitter, that represents only really a 20 db loss for 100 way split...and provided the power is there that's no big loss.
It probably represents no more than a third of the usable length being lost.
Maybe DWDM (Dense Wavelength Division Multiplexing) seems that can support 192 channels at 100 Gbps/channel giving 19.2 Tbps over a single fibre pair. Openreach used 96 core cable to feed the FTTC boxes around here. Zayo have recently installed a 144 core cable between Penrith and Hexham.
144/2 * 91.2 = 1382.4 Tbps
Pre or post the optical split? The unsplit headend feed is quite "pokey" and can do considerable distances without amplification, 40 km from here to Hexham for example.
Are Openreach using multimode? Singlemode has a far greater range and doesn't mess up the signal(s). I don't think DWDM would work over multimode. I think GPON only uses two "carriers", (up/down), within a single fibre and uses TDM to share those two carriers between customers. That might work over multimode but for how far I don't know.
As you say the range of singlemode is really down to how bright (ie power) you can make the source laser. Powers are such that caution needs to be applied to protect your eyes when working on such sytems. You can't see the IR laser light.
I think it probably makes no difference. If my thinking is about right, the splitter simply represents - say - a
20dB loss in the path no matter where it is, in fact.If, let's say, we have 60dB of headroom, and the attenuation is 1 db per km, with no splitter that's 60km, with one splitter its 40km and with two its 20km.
And so on.
No, they (Openrach) are not, I cited that as a counter example, where high dispersion limits practical length to 'not very far'. I think monomode is limited by optical attenuation, not dispersion.
They are IR? I know there are standard wavelengths - dont know what they are, though..
Again, from 12 year ago: we only used MM for fibre patches within a PoP, to connect equipment where the signal was already de-muxed. Once it went off-site, everything was SM, including what the carriers provided us, whether dark or lit fibre.
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