FTTC Conformity Testing
Openreach carry out conformance testing on FTTC modems to ensure they meet BT's SIN498 standard. This is a long-winded test taking many weeks to complete.
A modem that has passed this testing is not a requirement, but Openreach may choose to withhold or limit the service if it has not.
Here is an extract from SIN498:
SIN 498 v6 says:
2.4... The CP provided modem and filtering devices must meet the requirements of this specification in order to provide reliable operation and to avoid harm to other VDSL2 lines sharing the same cable binder. Openreach reserves the right to withhold or limit service where potential violation of the Access Network Frequency Plan (ANFP) [9] or impact to another customers’ service is detected