Hi everyone I'm studying for the CCNA exams and there is one thing that I'm not sure of. In the CCNA intro book they talk about demarcation or demarc and local loop or last mile. Can I compare demarcation with the point where for example your DSL router/modem is conected to in your house or is it the DSLAM where the subscribers meet? As a result of the above I'm not sure what the actual local loop is. I'm just getting into this internetworking concept so any help will be appreciated.
Typically, the point of demarcation with the provider is the data closet. In residential service, the demarcation point defines where the responsibiliy of the carrier starts and stops. You can also have an extended demarc.
Extended Demarc Example: Your office is on the 5th floor of a building. The bandwidth provider has a demarcation room on the first floor. They are responsible for getting the service into the room and that room only. Now if you have requested and paid for an extended demarc, your building IT support will extend the services to a demarc on the 5th floor.
In your house, the typically the telephone network interface is considered the demarc. Telco is responsible for everything between your demarc and the Central Office. You are typically responsible for everything between the demarc and your telephone.
Let's say you have ordered a DS1 from Sprintco, and you want it to link two offices to each other in a point to point arrangement. One office is in Chicago, the other office is in Indianapolis. Sprintco will provide a DS1 between the two LEC's (Local Exchange Carriers). The LEC on each end will connect and configure the "local loop". The local loop is the circuit between your office and the switch containing one end of the Sprintco circuit. you will have two local loops in this case...one with Chicago LEC and one with Indianapolis LEC.
The local loop carriers have you by the short hairs, and sometimes you will pay MORE for the 5 mile local loop than you do for the 600 mile DS1 circuit. They can charge pretty much whatever they want if they are the only LEC. When I was configuring WAN connections for a company in Cincinnati, I was at the mercy of Cincinnati Bell, and they sucked in every possible way.
DSLAM is equipment in the telco central office. Demarc is in your building and is the point where the telco hands off responsibility to you. The local loop is the connection from the central office to your dmarc.