FTTC Modem: Difference between revisions

[[Category:Routers]]

=No longer supplied=

Note, these Openreach modems are no longer supplied, but they can still be purchased from some 'auction' web sites.

With FTTC, BT OpenReach used to supply and install a VDSL modem (the Active NTE in BT speak), You will then need a PPPoE device (router or software) to use the service.

*PPPoE username = as supplied, e.g. x@a.1

*Auth Protocol = CHAP

If the sync light flashes, then there is no sync, and will probably need to be reported as a fault.

==Types==

The Openreach modem will either be:

*ECI Telecom - B-Focus

*Huawei EchoLife HG612

Openreach tend to install the FTTC modem to match the DSLAM in the Cabinet. However, later they were installing ECI modems whether the DSLAM is an ECI or not.

[[File:FTTCModems.png|600px]]

How to tell the difference?

The 2 modems both look very similar! There are a few differences though:

*The ECI is larger

*The ECI has 'circular' LEDs, the Huawei has 'square' LEDs

*The ECI has a yellow LAN1 socket, The Huawei has a metallic LAN1 socket

[[File:FTTCModem-LEDs.png|600px]]

The FTTC modem supplied by Openreach is described in detail on [http://www.btplc.com/sinet/SINs/pdf/498v7p1.pdf BT SIN 498]

= Huawei HG612 PPP/UDP/VPN Bug=

In 2013 we discovered a bug with the HG612 which affects VPNs when the PPP drops. The shot version of the bug is that UDP session, such as a VPN, has problems re-establishing when PPP drops. This is due to the modem blacklisting the packets. More information can be found on these pages:

*https://www.revk.uk/2013/11/bt-huawei-fttc-modem-bug-breaking-vpns.html

*https://aastatus.net/1854

*https://www.revk.uk/2013/11/bt-huawei-working-with-us.html

{| class="wikitable" align="center" style="text-align:center;"

!Router

!Sync Speed

!Throughput

!Notes

|style="color:red"|~18Mbit/s

|It should be able to handle around 350Mbit/s!

The Firebrick 2700 is a great router for FTTC, and even bonding FTTC. See the [[:Category:FireBrick|Firebrick]] pages for more info

When using a router with an external modem, one has to use PPPoE on the router as the connection method. This normally means that the MTU on the PPPoE link

can be no higher than 1492 octets (PPPoE has an 8 octet overhead, and the whole packets has to fit in a 1500 octet Ethernet frame). However, there is a

technique to use ''baby jumbo frames'' to extend the Ethernet frame size to 1508 octets and allow the full 1500 octets on the PPPoE link.

In order to use baby jumbo frames on FTTC, the customer's router must support RFC 4638. It is not enough that the router supports baby jumbo frames via

configuration, the router must be able to do the negotiation described in RFC 4638.

Some pointers for RFC 4638 on Linux-based routers.

#The wan interface needs to be set to an MTU of 1508 on the assumption that there needs to be room for the 1500 MTU PPPoE packet on the way to the modem (1500 may work - untested though).

#Using ppp's debug option will allow you to see the rp-pppoe plugin negotiating a PPP-Max-Payload option in the PADI/PADR packets with the BRAS. If this isn't seen, then your MTU is forced back to 1492.