DSL as an Incremental Upgrade

DSL as an Incremental Upgrade To Existing Digital Loop Carrier Equipment. The bursting of the optical networking bubble in 2000 has basically proved one thing: the economic rules of the game haven’t changed. The name of the game is still to get the most out of your installed base of equipment while at the same time making incremental upgrades to bring on new revenue enhancing services.

One such service is DSL (Digital Subscriber Line) for high speed internet access. For customers within 18,000 feet of the central office the DSL equipment can be mounted in the CO and interfaced from the main frame. Space in the CO is always at a premium and first generation DSLAMs (DSL Access Multiplexer) did not support high port densities. As the market expands this problem only gets worse as first generation products offered low port densities and were neither scaleable or upgradeable. More often than not the entire system would have to be replaced when upgrading.

These first generation products were typically built to enterprise standards and did not provide the reliability, repairability, or operability that is required of a telephone company. Telcos require fully redundant solutions with no single point of failure. Things to look for are:

1. Control module redundancy, 1:1
2. Trunk port redundancy, 1:1
3. Subscriber port redundancy, 1:n

However for customers outside the CO serving area the situation becomes quite different. These customers receive dial tone over Digital Loop Carrier (DLC) equipment using fiber optic transmission back to the CO. Legacy DLC systems were mounted outdoors in “80 series” type cabinets and offered only voice service. These systems were manufactured and installed before the internet when just providing dial tone was a major accomplishment.

The problem and solution are depicted in the figure above. The AT&T, now Alcatel-Lucent SLC (subscriber line carrier) family of DLC equipment is probably the most widely deployed type of DLC in the U.S. So the question becomes how to offer DSL without ripping out the installed base.

But most importantly this upgrade of a legacy system to offer DSL should not box you into a corner. The equipment must also be compatible with the latest start of the art equipment that would be used in a new build out.

Operationally, service provisioning can become an issue. It often takes too long to test and qualify copper pairs, there are problems with loop reach, loading coils and bridged taps. The provisioning of virtual circuits and configuring the customer premises equipment (CPE), i.e. DSL modem, have been cumbersome and slow. The offered solution should provide some form of integrated loop access for testing that can be controlled from a centralized facility or NOC (Network Operations Center). End to end flow through provisioning should be available as an option as well as CPE devices that are “plug and play”, thus minimizing truck rolls.