Sync is essentially the signal from the local exchange indicating the potential speeds your line can achieve depending on the distance and quality of your line. If sync isn’t present then you won’t be able to connect to our service.
The best way of confirming the presence of sync is to login to the router interface and look for confirmation of an upstream and downstream speed. All too often customers refer to the presence of lights on the front of the router. With there being so many makes and models its not always possible for support personnel to be able to confirm what each light means for each router.