PDF of this tutorialLine Sharing
With new Federal Communications Commission (FCC) regulations requiring ILECs to unbundle frequencies or share their existing lines with other service providers, an old issue resurfaces: plain old telephone service (POTS) splitters. These devices were initially viewed as a problem but did not really have an effect in early deployments because most service providers were using a dedicated second loop to provide DSL services.
Now, with line sharing, splitters are back in the thick of things. The problem with splitters is their placement. If they are installed on or near the ILEC’s MDF, they are effectively sitting between any test equipment and the local loop. For many tests, this situation is a big problem, regardless of the test vendor. Many tests cannot be accurately run through a splitter, as the signal will have its high or low frequencies filtered out, depending on whether the tests are conducted from the voice switch or the digital subscriber line access multiplexer (DSLAM).
A common solution being implemented today has the splitter sitting in the front of the DSLAM. This allows for accurate testing through a test access device (either a test access switch or a cross-connect) positioned in front of the splitters. There are, however, two problems remaining. First, any attempt to change the DSL service for a different service type or service provider cannot be managed from a distribution frame without affecting the POTS service. Second, in a collocation application, the ILEC’s POTS service must run through the CLEC’s collocation cage to access the splitter.
An ideal solution is to separate the splitters into two independent parts—a low-pass filter (LPF) and a high-pass filter (HPF) (see Figure 3)—and to install them on the ADF of the LMS. This means that one could switch lines through both filters independently and at will and still be able to connect test equipment to the line side of the splitter, eliminating the splitter from the tests.
Figures 4, 5, and 6 illustrate three examples of network configurations that address the issues completely.
Figure 3. Switchable Splitter
Figure 4. Line-Sharing Configuration #1
Figure 5. Line-Sharing Configuration #2
Figure 6. Line-Sharing Configuration #3
Lifeline for Voice over DSL (VoDSL)
As more and more customers get access to broadband services through DSL, the current practice of having multiple voice lines and separate data lines may be replaced by VoDSL service. Significant cost savings can be achieved by aggregating these multiple services into one packetized line.
Although current data services are quite reliable and improving, they are not yet quite as reliable as dedicated traditional voice services. A voice service is required to be available at all times. In the event of power failure, the telephone equipment is required to function normally in order to allow emergency responses. VoDSL also requires this lifeline feature.
For residential applications, where an asymmetric digital subscriber line (ADSL) service is installed, the issue is not so significant because the baseband is reserved for the POTS line. For business applications, however, a symmetrical DSL (SDSL) service having no baseband POTS is more popular. In this case, an LMS will prove invaluable to guarantee lifeline by offering access to a standby POTS service. This is a more elegant solution than having batteries as a power-failure backup in the customer premises equipment (CPE), as batteries are labor-intensive and require maintenance.
As shown in Figure 7, when the DSLAM detects that the CPE side is not responsive, it will report an alarm to a software monitor that will send the proper command to the LMS to switch over the equipment to a POTS service.
Figure 7. Lifeline Application for VoDSL
Wholesale Application
With the unbundling of the local loop, a new class of service provider will emerge. The ILEC (or a new subsidiary company specializing in managing the local loop) or a big CLEC sitting between the ILEC and the other service providers can serve as a wholesale provider of the local loop.
The local loop will become again a valuable resource that can be leased and generate revenue. An LMS will become a key tool in managing this resource. Many customers will change hands—perhaps more than once—to multiple service providers. These include non–facilities-based service providers with reseller status who are electronically bonded to the facilities-based carriers. The current practice is labor-intensive and therefore time-consuming and error-prone. With an LMS, positioned as in Figure 8, loops are just mouse clicks away from being passed to someone else—once all the loops are integrated and documented. It is an operation that takes minutes rather than hours or days.
This ease of process triggers notions of being able to provision services à la carte, whereby, for example, a user could self-provision a service via the Web on a pay-per-use basis with both variable bandwidth and service-provider choices.
Figure 8. Wholesale Application
Loop Qualification and Testing
The bulk of existing copper loops was meant to support POTS services and was never designed to support high-bandwidth applications. Thus, the lines were conditioned to optimize the zero to 4-kHz bandwidth range in which POTS runs. Many of the traditional techniques used to condition these lines can interfere with higher bandwidth protocols such as integrated service digital network (ISDN) and DSL.
Loop testing and qualification currently requires on-site intervention by an ILEC technician. Unfortunately, service providers presently have no cost-effective means of accurately prequalifying a line before deployment. Additionally, many current deployments rely solely on checking the loop records to verify if there are load coils or other conditions present that could interfere with the deployment of the service. Suffice it to say that these records are not always accurate. The service is then deployed with no further testing or qualification. This methodology leads to situations where the service is deployed to the subscriber and then disconnected as a result of excessive problems. The subscriber is then informed, after the fact, that the service is not available. In addition to the time, energy, and money needlessly expended, this situation leads to a poor customer perception of the service provider. With an LMS, loop testing and qualification can be validated by the service provider before a service is declared available for a customer. This function can be achieved without the need to send out a technician, and it can be performed much quicker. Additionally, loop qualification records are stored automatically so that the state of the loop at any given time can be compared to a base point.
It has been suggested that test access and even testing equipment be integrated directly into DSLAMs. While this could prove useful for some bit-error-rate testing (BERT) and possibly even higher-level protocol testing, testing and characterization of the loop should be left separate from the DSLAM for the following reasons:
- Adding loop testing equipment capability to DSLAMs will raise the cost of the overall test equipment investment. Every time a new DSLAM is purchased, additional test equipment is acquired unnecessarily. This recurring cost for the test equipment portion that is integrated in the DSLAM would be eliminated if the loop testing equipment were a part of the network infrastructure and revolve around a centralized, vendor-independent LMS.
- The loop must be connected to a particular port on the DSLAM before the testing can occur. If the loop fails to qualify and cannot be conditioned, it must be disconnected and another connected in its place. This results in a more labor-intensive process.
- As mentioned previously, many tests (e.g., load coil detection) cannot be accurately run through a splitter. Thus, if line-sharing mode is used, the test equipment cannot be placed at the DSLAM. It must be in front of the splitters, as would be the case with an LMS.
Remote Management
Unbundling the local loop for use by CLECs introduces the situation whereby the delivery of a service to a customer now involves two companies bound together by legislation and service-level agreements (SLAs). While the ILEC is solely responsible for managing the physical loop, both service providers hold final accountability for the condition and quality of the service they are delivering to their customers. They must, therefore, be well-equipped to handle maintenance-related issues.
For a CLEC, a collocation arrangement in the CO is somewhat like a large remote terminal. When they are put in place across the country, staff must be hired to manage them. Generally, though, these sites are not large enough to justify a full-time technician or, if so, certainly not on three shifts. Access to the premises, especially on off-hours, is often a problem. This issue is a large impediment to offering guaranteed service levels.
For both the ILEC and the CLEC, the newly competitive environment coupled with the delivery of high-speed Internet access for business users will require the offering of guaranteed service levels. The old methods of dispatching technicians to investigate problems and lengthy reporting mechanisms just will not suffice. More sophisticated on-line tools must be made available to the network management crew.
With an LMS, service providers are equipped to isolate problems quickly as well as assign responsibility for their correction, whether it is internal or external (i.e., ILEC– or CLEC–related), without having to dispatch a technician. In many cases, such as for an equipment failure, the service can be restored on the fly by provisioning a new equipment port directly from the network operations center (NOC). With an open architecture that would allow an LMS to integrate seamlessly into network management systems, this feature could be automated to enable a self-healing access network.
Flow-Through Provisioning and Future Requirements
Several companies have begun initiatives aimed at automating the provisioning cycle. Given the level of automation and manageability present in today’s line and network equipment, it is possible to automate many of the tasks in the provisioning cycle. There is, however, still one barrier to the completely automated provisioning system: the physical loop. If the loop can be integrated into the community of managed devices and procedures that make up an automated flow-through provisioning system, the last barrier will be removed.
An LMS is the catalyst that can facilitate this process. With a fully automated provisioning system, service providers can offer true service-on-demand and modify a subscriber’s service type as requested. This service can be offered through various means, such as customer representatives, Web sites, fax, or even automated 800 services.
Adding the intelligence and automation of an LMS to the physical layer breaks down the barriers to even more forward-looking applications and functionality. One can now imagine the complete automation of many tasks and facets of network provisioning and management.
- automated physical network discovery
- automated network inventory
- policy-based management with automated network configuration based on policies
- self-healing networks
System Application
Ideally, as mentioned earlier, the LMS hardware would replace a distribution frame and would in effect become an ADF. Additionally, with an integrated isolation displacement connector (IDC) punch-down connector interface, the ADF can act as the demarcation point, or point of termination (POT) between the ILEC and the CLEC.
This gives the service provider the ability to control the demarcation point remotely. From the NOC, it is able to test and monitor looking outward onto the loop or looking inward toward its own network using a loopback function.
For added flexibility, an LMS’s architecture should allow different faceplate modules carrying the connectors of choice (IDC punch-down, telco, wire-wrap, etc.). With this system in place, service providers could then assign, reassign, and troubleshoot residential and business subscriber circuits at will. An LMS in a CO environment will allow them to do so without ever dispatching a technician to provision a circuit or remedy the fault.
With an LMS in place, service providers will be able to provision any service (ISDN, POTS, DSL, and any future services such as asynchronous transfer mode [ATM]) in minutes, following a customer request (see Figures 9 and 10).
Figure 9. Today ’s Configuration
Figure 10. Vision Configuration
