Table of Contents:

Definition and Overview

1. History of Subscriber Carriers

2. Early Next-Generation Digital Loop Carriers

3. Next-Generation Digital Loop Carriers for Rural and Suburban Applications

4. NGDLC Applications

5. Future Directions

6. Economics

7. The Multiservice DLC

Self-Test

Glossary

PDF of this tutorial

The economics of local loop access equipment must be modular, and a common control must remain low—it is simply not economical to pay for ATM common control to deploy twenty-five lines of POTS. Although it must have the minimum subset of frame relay-type capabilities (just enough to get it in the box), these should not be paid for until services are about to be deployed. It must be possible to enlarge the system, starting with one shelf to keep the common control low. As more services become necessary, shelves and more common control can be added. If there is a reason to move to ATM, a lot more common control can be put in place.

As the subscription rate increases for some of the high-bandwidth services, the corporate user working at home will want a LAN extension. In this vein, most architectures will probably move to a three-stage architecture in which where there is a high-speed SONET bus capable of supporting four or five gigabits per second of traffic coming in and out: drop-and-insert type of traffic. At the same time, there will be a high-speed cell bus capable of some very basic functionality, just enough to fully utilize bandwidth between terminals. The cell bus provides a very low-cost muxing solution with the capability to add more administration as it is needed, again without paying for it up front in the initial deployment of the box. Finally, the traditional TDM bus will be kept for some of the low-speed services and transport.

There must be some common control that has the ability to bridge all three of those types of traffic and it should be upgradable. In one possible scenario, all of the channel slots are universal and can accommodate either transport, common control, or service cards. This keeps the common control low. There are a couple of dedicated slots to allow bare minimum common control capability. In this way, more common control can be added to the common slots or the multipurpose slots as the movement from the TDM world to the cell-bus world takes place and capabilities are added.