BT Openreach Modem Conformance Test (MCT)

What is MCT What tests are performed during MCT testing? What is BT SIN 498 MCT Is it mandatory to use an MCT modem? History behind SIN 498 MCT Why did Openreach introduce MCT? Do we need MCT compliance? List of MCT approved modems

 ~ What is MCT?

Modem Conformance Testing (MCT) is a series of tests carried out by BT to ensure that modem/routers are compatible with BT Openreach's FTTC cabinets and conform to VDSL2 mandatory requirements for transceivers as specified in ITU G.993.2.

 ~ What checks are performed during MCT?

The modem will undergo rigorous testing to ensure that it can connect reliably with Openreach's DSLAMs It should also able to perform other standards such as G.INP retransmission, vectoring, SRA as well as being responsive to any changes made by the DLM or line testing & diagnostics for faults.

 ~ What is BT SIN 498 MCT?

BT SIN 498 gives very specific requirements of the tests performed and what the modems should be capable of to be able to pass MCT.

~ Is it mandatory to use a modem which has passed MCT?

Yes.  BT state the following:

"It is prohibited to connect a device to a VDSL2 phone socket which has not passed BT's MCT (Modem Conformance Testing for SIN498).  BT will be using OAM loopback to perform diagnostics on FTTC service and identify the CPE connected. Detection of unauthorised CPE may result in the following:

• Request for removal of unauthorised CPE 
• Limitation or disconnection of Service 
• Lack of support when troubleshooting faults 
• Abortive visit charges or SFI Customer Misoperation charges when engineers find unauthorised equipment on site.

In addition, the usage of equipment which does not comply with the SIN 498 ANFP or interferes with other subscriber's service may result in the service being terminated."    

It is unlikely that using a non compliant modem will result in termination of service, but it is possible that you could end up being responsible for charges in respect of a line fault as a result of using a non compliant modem. 

Most ISP's will refuse to investigate a line fault unless they detect you are using an MCT approved modem - They are able to check remotely and can recognise if an approved modem is attached to your line.

 ~ History behind SIN 498 MCT

When FTTC was first introduced all new 'fibre' connections were installed by either an Openreach engineer or an official contractor such MJQuinn/KellyComms acting on behalf of Openreach.  These engineers installed a SSFP to the master socket and all customers were given an Openreach approved modem to which the EU attached either an ISP supplied router or one of their own.
	In 2012, there was very little choice for combined VDSL modem routers and practically everyone had to use a separate modem and router.  Combined units were very expensive and the cheapest started in excess of £200. Circa 2014 router manufactureres started supplying consumer grade VDSL modem/routers at an affordable price and the market for all in one units started to grow as demand for an all in one solution increased.
At about the same time BT retail started supplying the all-in-one HomeHub5 as did Sky with their SkyHub2 (SR102).  These units negated the need for a separate modem which was previously included in the installation costs.
Now ISP's were requesting Openreach for cheaper installation costs and from 2015 Openreach started offering wires only (self install) VDSL where the onus for supplying the modem and or router fell to the ISP or the end user.

~ Why did Openreach introduce SIN 498 MCT compliance?

When Openreach installed FTTC and provided EU's with modems, they had been tested so that the ECI modems worked with the ECI cabinets and the Huawei modems worked with the Huawei cabinets.  Openreach no longer had control over the equipment connecting to their DSLAMs.  

Unexpected behavior can occur if the modem is not capable of certain functions.  Some modems don't have OAM loopback; without which Openreach are unable to carry out remote line tests for fault diagnostics.  Other modems may allow the line to be configured incorrectly and attempt to connect to incorrect bandplans or have settings allowing the user to over-ride the DLM or cause cross-talk for other lines.  If BT ever do decide to enable vectoring, then all lines on that DSLAM need to also have a modem capable of vectoring to ensure all lines benefit from cross-talk cancellation.

~ Do we need some form of MCT compliance?

Yes!  On the whole most modem/routers conform with ITU G.993.2 standards & Openreach equipment, but not all do. 

There have been some minor niggles to EU's such as when Openreach introduced G.INP/retransmission on their Huawei cabs in 2015 whereby some modems did not work quite as expected costing 10Mbps of sync speed and increased latency. Interestingly one of the affected modems was Openreach's own ECI modem which they did not realise had been issued for users on Huawei cabinets. TP-Link also had an affected modem/router, but TP-Link very quickly worked to roll out new firmware.

At the time of writing, rollout of G.INP retransmission on ECI cabs has been reversed.  Openreach are remaining silent on the exact cause but it is suspected that some modems are not behaving as expected which has resulted in an increase in faults being reported. Particular problems have been seen with some of the older Draytek routers.

More serious issues have been spotted on our forums, such as certain ASUS routers being able to ignore Power Cutback and adjusting GAIN. Also Fritz!boxes attempting to connect to band plans which are not used in the UK and ITU specs. All of these could cause noise and cross-talk or other problems for neighbouring lines.* 

 ~ List of approved MCT modems

Modems listed below do not include some ISP specific devices such as the BT HomeHub or Sky Hub which will have been submitted by the ISPs themselves.

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