My friends,
Please allow me to join.
Nu'man, with telecommunication and internet service providers, you are purchasing a communication service, and in order to use it, you have to connect your equipment to that service somehow. For the service provider, it is very important to properly define where and how you connect your network to their network, for a few reasons.
The first reason is that this definition clearly describes, in technical details, the interface between your and their network. Nowadays it may appear simple - Ethernet almost everywhere, either fiber optics or copper. Even there, though, there may be variants: Single mode fiber? Multimode fiber? Or copper? And at what speed? In the past, there were far more WAN access technologies - V.24 (RS-232) interfaces, X.21 interfaces, V.35 interfaces, DSL with all their variants, and more, and then the data link framing on top of it - HDLC, PPP, X.25, Frame Relay, perhaps even ATM. For ISDN, there was the U-type interface in US and S/T-type interface over here in Europe. You had to match the interface type offered by the service provider perfectly in order to be able to connect to it.
The second reason is that it defines clearly what is the boundary of the responsibility for your and the service provider's network. This is extremely important: If the service stops working, and the investigation shows that the communication from your part of the network up to and including the service termination point is okay, it's the responsibility of the service provider to fix it - and you as a customer may be eligible for compensation if the outage lasts for too long. And conversely, if the fault is found on your part of the network, before the service termination point, the service provider will wash their hands and say - "your problem". Also, the service provider is not allowed to tamper with your part of the network and your are not allowed to tamper with their part of the network - and what is "your" and "their" is delineated exactly by this service termination point.
All in all, with service providers, it is always about interconnecting two networks with different ownership - yours and theirs. This interconnection must have a clear boundary to define the mutual domains of responsibility, and must have clear and well defined technical parameters so that you know how to connect to it and what to expect, even what rules to abide.
This all is why the service termination point is an important concept.
Best regards,
Peter
