How do multiple ISPs serve their DSL customers using the same telco DSLAM?
Posted on 2004-11-23
let's make the following assumptions..
1. i have a phone line from Verizon at home,
2. My DSL Internet provider is Earthlink.
3. My neighbor also has a Verizon phone line and has DSL Internet access provided by AOL.
4. Earthlink and AOL don't have DSLAMs at the Verizon central office which serves me/my neighbor.
5. Both AOL and Earthlink have ATM WAN interfaces to Verizon's ATM backbone network, and the Verizon CO DSLAM also has interfaces connecting it to the same ATM backbone
How does Verizon configure the connection for the two customers here - me and my neighbor, who have different ISPs? I can think of the following options...
1. (Bridged?) VLAN
my phone loop lands on a particular DSLAM port A. This port is part of a VLAN which is specific to my ISP, and the VLAN spans multiple locations (other central offices) and includes the ISP WAN interface port (at the boundary Verizon ATM switch that connects to the ISP).
This would be a (bridged?) VLAN over an ATM WAN.
Similarly, my neighbor's port on the DSLAM would be part of a different VLAN.
2. ATM PVC
my port on the DSLAM maps to an ATM PVC between the DSLAM and the ISP's ATM equipment. The one reason i can see this happening is for giving me a static IP address. I dont think option 1 can give me a static address, though i can't explain how.
1. any wrong assumptions made in the statements above?
2. how is a VLAN over multiple locations mapped to ATM transport? I mean, how can the simultaneous use of a WAN ATM link be controlled?
3. How does the ISP router(which has an ATM interface with Verizon) see the multiple customers connected to the same DSLAM distinctly, so that they can each be assigned an IP address?