CCNA Wan services

Have a question or want to start a discussion? Post it! No Registration Necessary.  Now with pictures!

Threaded View
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.


Re: CCNA Wan services
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 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.

Quoted text here. Click to load it

Re: CCNA Wan services
Quoted text here. Click to load it

The simple answer...

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.

Hope that helps.


Re: CCNA Wan services
Quoted text here. Click to load it


If the telco lends you a CSU/DSU the demarc is is shifted to this device.
This is common in some countries where the ILEC gives you the NT1+ for you
to connect your consumer ISDN CPE equipment.


Site Timeline