FTTH - Help me learn: SFP, LR/SR, XGS-PON, etc...

Hi all,

Apparently Community Fibre are coming to my area and offering fibre to the home. Generally I prefer to run my own equipment, so I like to bypass the ISP's stuff when I can. For example, right now I have Virgin Media (fastest I could get in my area, though asymetrical) and run their device in modem mode, plugged into my pfsense's WAN port. Since optical is the future and my plan will expire in a few months, I'm considering Community Fibre seriously and want to learn more about fibre connections and their technology.

So I've learned that there's now SFP/SFP+ ports on network equipment into which you plug in traceivers. Those can adapt the SFP port to traditional RJ45, or to some optical type. I've been reading about two major types: LR and SR (long or short reach). These use different types of light (one is multi-modal laser for fast speed at short distances, the other is longer range and uses single-mode laser). At this point, I wanted to understand what type of plug I'd need (if I want to run my own router) and I figured that if I have anything with an SFP+ port, then it's just a matter of having the appropriate tranceiver so that I may plug the Community Fibre cable into it.

As such, I set out to try and figure out what they use by looking at the equipment they offer. They have a tech query page where I found two types of equipment:

Case A: separate modem/router, the latter being a Linksys Velop. The modem is either an Adtran 621X or a Huwaei whose model is not mentioned.

Case B: They also offer two modem/router combo devices with one being the Huawei EchoLife HG8245Q2 and the other seems to be the Zyxel AX7501.

So, they don't mention LR/SR. Instead I've found the the Adtran 621X mentions "XGS-PON WAN port with SFP+ pluggable". The Zyxel also mentions "BBF.247 certified XGS-PON" as well as that sports an "SFP+ cage".

So now I'm getting the idea that the tansceiver is neirther LR, nor SR: it is "XGS-PON" which is some alternative type. What's more, I probably don't need to worry about the transceiver at all: the equipment they provide seems to rely on SFP+ ports! That indicates that they bring "some" cable, which plugs into "some" tranceiver that is inserted to an SFP+ port of their device. Therefore if I have my own device with SFP+, I just need to unplug the transceiver from the device they installed and plug it into the SFP+ port of my own (say a netgate 6100) device, right?

Am I waaaaay off here or am I on to something?

In a corporate, point-to-point, type connection you could do as you suggest and have the optical connection directly on your own equipment.

However in a consumer, FTTP, deployment, the Passive Optical Network design requires the Optical Network Terminal (ONT) from the network operator to be in your building. This connects to the fibre from the street and provides an RJ45 Ethernet socket you connect to your own equipment. The ONT is registered to the PON network and handles the fact the fibre network is shared with upto 32 other customers. (This is the unit you call 'modem', which is not actually a modem).

I think Community Fibre is one of the few to offer 1Gbps and 3Gbps speeds, maybe others. You probably want to buy your own hardware that can cope with at least 2.5Gbps on the WAN port, depending what sort of WAN speeds you are looking at.

Edited by jchamier (Fri 07-Oct-22 19:40:05)

What speed are you planning to get from Community Fibre?

In reply to a post by karypid:

Case A: separate modem/router, the latter being a Linksys Velop. The modem is either an Adtran 621X or a Huwaei whose model is not mentioned.

Case B: They also offer two modem/router combo devices with one being the Huawei EchoLife HG8245Q2 and the other seems to be the Zyxel AX7501.

Case A is what they install if you purchase 1Gb or below. In this case, I would use their Adtran 'modem' and use another router instead if you wish.

Case B is if you order their 3Gb service. Here, I would just see how you get on with the Zyxel etc and if you don't like it, then just use it in modem only mode as you currently do with Virgin.

You could in theory use your own kit instead of Community Fibre's OLT but would need to spoof their units details and I personally wouldn't recommend it/don't see the benefit.

Finally, if you know an existing Community Fibre customer, you can get a £100 in Amazon vouchers if referred by an existing customer. Let me know if you would be interested in this.

In reply to a post by karypid:

So now I'm getting the idea that the tansceiver is neirther LR, nor SR: it is "XGS-PON" which is some alternative type.

Right.

In reply to a post by karypid:

What's more, I probably don't need to worry about the transceiver at all: the equipment they provide seems to rely on SFP+ ports! That indicates that they bring "some" cable, which plugs into "some" tranceiver that is inserted to an SFP+ port of their device.

Right.

In reply to a post by karypid:

Therefore if I have my own device with SFP+, I just need to unplug the transceiver from the device they installed and plug it into the SFP+ port of my own (say a netgate 6100) device, right?

Wrong.

Most routers or switches which accept standard ethernet SFP+ modules take ethernet modules (1000base<XXX> or 10Gbase<XXX>) but will not work with PON modules.

The solution is to accept the ONT that they provide, and connect it to your router's WAN port. The ONT is the demarcation point to their network, in the same way as an Openreach ONT on OR FTTP, or the Virgin Media cable router/modem on the Virgin network.

The ONT itself could present on the customer side in different ways: it could be 1G, 2.5G or 10G copper, or it could be another SFP+ port which takes an *ethernet* SFP+.

In reply to a post by jchamier:

However in a consumer, FTTP, deployment, the Passive Optical Network design requires the Optical Network Terminal (ONT) from the network operator to be in your building. This connects to the fibre from the street and provides an RJ45 Ethernet socket you connect to your own equipment. The ONT is registered to the PON network and handles the fact the fibre network is shared with upto 32 other customers. (This is the unit you call 'modem', which is not actually a modem).

If the ONT is separate, does it provide a public IP address that is presented via DHCP on its Ethernet side (where you'd plug the WAN port of your router)?

Community Fibre 3Gbps SFP+

In reply to a post by candlerb:

Most routers or switches which accept standard ethernet SFP+ modules take ethernet modules (1000base<XXX> or 10Gbase<XXX>) but will not work with PON modules.

Ok this is very useful. My initial assumption is that SFP is a standard protocol/connector that is Ethernet-based no matter what. So this is more like the days of ATM where the PON is something else and you need something that will "adapt" between it and Ethernet (which is what the ONT does I guess).

In reply to a post by candlerb:

The solution is to accept the ONT that they provide, and connect it to your router's WAN port. The ONT is the demarcation point to their network, in the same way as an Openreach ONT on OR FTTP, or the Virgin Media cable router/modem on the Virgin network.

Ok I understand now, but would a simple ONT provide an Ethernet port that "bridges" the public IP network to the house (the same way my Virgin equipment provides a public Internet IP when running in modem mode), or are you fully restricted to a NATed service?

CF do a mixture of CGNAT or public IP (though not necessarily static) depending on the speed tier of the package you choose. 500 Mbps and above seems to be the point at which they flip from CGNAT.

Or you could use IPv6

In reply to a post by karypid:

Ok this is very useful. My initial assumption is that SFP is a standard protocol/connector that is Ethernet-based no matter what. So this is more like the days of ATM where the PON is something else and you need something that will "adapt" between it and Ethernet (which is what the ONT does I guess).

That is correct - the protocol that runs over the optical network is *not* native Ethernet it is XGS-PON (in the case of Community Fibre and other similar AltNets) and is a faster, newer symmetricated version of the original GPON circa early naughties. These protocols essentially encapsulate ethernet frames. The ONT then presents pure unadulatered Ethernet on its copper RJ45 interface. What is running in the layers above the physical layer of Ethernet (IP, PPP etc etc) is then in the remit of the operator.

SFP is a physical transceiver specification - you may associate it with Gigabit Ethernet (and beyond in latter incarnations and variations) but it can also be used for Fibre Channel, SONET, PON and other comms protocols.

Ok I understand now, but would a simple ONT provide an Ethernet port that "bridges" the public IP network to the house (the same way my Virgin equipment provides a public Internet IP when running in modem mode), or are you fully restricted to a NATed service?

As said, the ONT is basically a physical layer and protocol bridge. Well its a bit more than that - but for the purposes here that is its basic function.

IPv4, IPv6, PPP, NAT, CGNAT etc etc are constructs and concepts outside of this. They are in the layers that sit above.

Edited by Pheasant (Fri 07-Oct-22 23:37:11)

In reply to a post by dect:

Community Fibre 3Gbps SFP+

Ah, this is perfect. Thank you!