Upgrading to BT's Fibre Service

[tim-pelican]

Ahh a BT worker LOL, The router is normally BT's own .. so unless you train folk to use there own router  , then there always will be that " black " area  that has to be addressed.

Nope, but I *do* work in the industry, and might have caused confusion for people who aren't aware of how it all works by glossing over the fact that there are three different BT companies (and they *are* separate companies) involved.

BT Openreach are responsible for the infrastructure.  They provide the fibre to the cabinet, the VDSL DSLAM in the cabinet, the copper to the premise, and the VDSL modem attached to the copper, which presents an Ethernet port onwards.  They supply the guy who turns up to do the install, but they don't have any contractual relationship with end-users.

BT Retail (sorry, I wrote Residential earlier) sell Internet service over this infrastructure.  They buy, from BT Openreach, a service connected to the DSLAM.  They connect their router to the Ethernet port on the BT Openreach modem, and they pick up the corresponding PPP session in the exchange.  Other ISPs are allowed to buy the same service from BT Openreach in the same way and at the same price, as long as they pay to install equipment in the exchanges to pick up the PPP sessions and provide their own Internet connectivity from there on.

BT Wholesale also buy the connectivity service from BT Openreach, but rather than put their own routers behind the modem, they resell the circuit to other ISPs.  The difference is that BT Wholesale aggregate connections from the exchanges and backhaul them all to one or more interconnect points, so the ISP only has to have their own equipment in a few locations, rather than in every exchange where they want to provide service.  The ISP is free to attach whatever router they want to the customer side of the connection, or even to provide a "wires-only" service and let the customer use their own router.

Both the BT Openreach and BT Wholesale parts of the service support the mini-jumbo frames, full size IP packets, and have no issues whatsoever with VPNs.  It's down to the ISP, their equipment and their config riding on top of the connectivity service as to whether the end customer sees any problems or not.

I have no idea if BT Retail are supplying a router which can't handle mini-jumbos and hence has VPN problems (and potentially problems with other sites that don't handle path MTU discovery correctly).  Other ISPs are definitely supplying a router / config that doesn't have these issues, without the customer needing to do anything with their own router.  I have two running to my house right now.

None of the branding / marketing exercises help clarify this, especially since most residential customers don't know how BT was split up, and assume that the BT Retail product must somehow be better or the "real" product, when really they're just another customer of BT Openreach.

"FTTC" or (incorrectly) "fibre broadband" is the BT Openreach and / or Wholesale connectivity, can be sold by any ISP.
"Infinity" is BT Retail's Internet product built on top of BT Openreach's FTTC.

Virgin have their own infrastructure outside all of this, but aren't obliged to open it up in the same way Openreach are.

Sorry for the long post, hopefully it's of at least some interest or information.

[Malc]

Just a quick question Tim, why does VPN use require mini jumbo frames? I've out of touch with WAN, but the only time I've come across mini-jumbo is with Fibre Channel over ethernet (2500 bytes).

[tim-pelican]

It's the PPPoE overhead, Malc.  If something on your LAN sends a 1500-byte IP packet (1514-byte Ethernet frame), by the time the router's put PPPoE headers on it, it's a 1508-byte packet which translates to a 1522-byte Ethernet frame.  This won't go out of a "regular" Ethernet interface, so either gets fragmented, or returns a "too big" ICMP error so the sender can work out to send smaller packets.

In theory, path MTU discovery (PMTUD) sorts all this out and both ends agree on the largest packet size that works, but over-zealous firewall admins frequently break it.

It gets worse for VPN specifically, because there's *another* layer of encapsulation (IPSec, GRE, SSL shim, or whatever), the effective MTU gets even smaller, and there's another set of devices or programs which can fail to do PMTUD correctly.  A lot of the time, the VPN part will assume a 1500-byte MTU and account for its own overhead against that, but not deal very well with a 1492-byte MTU (8 bytes lost for PPPoE).

By making just the Ethernet segment from the router outwards (so no changes on the customer's LAN) deal with 1508-byte packets / 1522-byte Ethernet frames, the LAN side can ignore all of this and carry on running at 1500-bytes IP / 1514-bytes Ethernet.

Similar issue to FCoE, in that you've got something bigger than 1500 bytes that you *really* don't want to fragment...

[Malc]

Thanks for the info Tim, now I know. It doesn't affect me as I am a Virgin Cable user and I don't use VPN.

Regards
Malc

[GlenP]

My FTC connection went in this morning as promised. It was a relatively painless process! It turned out that I did have an internal master socket - fortunately it was the one in the "play room" where I wanted the router anyway.

It took about an hour and a half to get everything installed, connected and for PlusNet to activate.

Running Speedtest on the upstairs laptop (the one connected by Gb Ethernet to the router) shows the full 70Mb+ download speed and 15Mb or so up - a massive improvement on 2.5Mb down! Web pages tend to just appear now.

I've tried the VPN connection to work as well and no apparent problems there (I have an alternative connection via an SSL portal anyway if it had proved to be an issue).

Glen

[buckle247]

Has anyone upgraded to this new BT Fibre, Whats peoples opinions on it. Is it worth it. I would prefer to get it through SKY than BT, but BT has a better offer.

Depends what you use the connection for? Just web browsing and the odd video, 6mb is more than adequate.

If you have a couple of people in your house trying to browse, stream HD or game simultaneously then it would be well worth the upgrade. Or if you regularly download big files.

I am around 500m from my cab and get 38mb. Cables less than 350-400m tend to not lose much speed, after that it starts to drop off quicker.

As for FTTP, its available. BT charge £35 a month for it, for 160mb. Only a handful of exchanges offer it at the moment. Not sure what the initial install charge is.

[GlenP]

I will say I probably wouldn't have bothered if I was getting a decent speed before, however living at the end of a long bit of string from the exchange meant the signal was always iffy!

Glen