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2 Enabling ADSL Mass Deployment By J. Eiblmeier Product Marketing Infineon 1. Introduction As with all technologies and the services enabled by them, the deployment of ADSL services is happening in phases. The first phase consisted of the definition of the standards and network topologies, and first field trials. In this phase, two factors were important for success. The first one was achieving agreement between the service providers, systems manufacturers, silicon vendors, and other important players in the industry as to the definition of standards that would allow for the inter-working of the various ADSL solutions between themselves and with preexisting services. The second important success factor was proving that ADSL service could, in fact, coexist with preexisting services, and that deployment would be technically and economically viable. This was determined by results from field trials. The second phase in ADSL deployment is the ramp-up. This is the phase that we are currently in and consists of ADSL lines being deployed at an exponentially increasing rate. In this phase, the most important factor for success is the availability of reliable, interoperable, and well performing solutions, both on the system side as well as on the chipset side. The third phase in the life cycle of ADSL services is that of mass deployment. By mass deployment we mean when a significant percentage of the subscriber base is connected to ADSL services. This is the next phase and is the most important one because it is the phase in which service providers, systems manufacturers, and chipset vendors alike obtain their return on investment and make profits. This phase is also the most important one for end users who now have access to the service at a lower price and the service is accessible to all layers of society. As well as being a benefit to consumers, this phase fulfils the goals of regulatory and government policy, and drives related industries such as the internet. The key question that we need to ask is what requirements need to be satisfied for full ADSL mass deployment, as defined above, to take place. This paper tries to answer this question from the system hardware standpoint, and identifies ways in which semiconductor manufacturers can help satisfy these requirements. 2. System Level Implications of ADSL Mass Deployment Let us take a look at the system level implications of ADSL deployment. Figure 1 below shows how ADSL is deployed today. ADSL service is superimposed on the subscriber line where base-band voice (POTS) service is already being offered. The Main Distribution Frame (MDF), to which the twisted pair wire coming from the subscriber is connected, is rewired and the subscriber line is rerouted to a POTS splitter, which splits the voice from the ADSL signal. The voice signal is then routed back to the MDF and on to the voice switch. The ADSL signal, on the other hand, is routed to a DSLAM that

3 contains ADSL linecards. This is a system that was designed to add DSL services to a network that was built for traditional voice service, and works quite well for a small number of DSL subscribers. However, it has many drawbacks. PSTN DSLAM Voice switch Splitter shelf Data Network Main Distribution Frame UTP Cable Bundle Voice+Data Figure 1. System architecture for today's ADSL deployment. There are essentially three areas of difficulty that this approach poses. These are represented in Figure 2 below. Main Distribution Frame DSLAM Data Network splitter Network Management &Maintenance System A Rewiring: high labor costs time consuming error probability System overhead: high extra cost significant space requirement difficulty to test line Confusion Network Management & Maintenance System B CO/DLC/AN PSTN Figure 2. Areas of difficulty associated with today's ADSL deployment approach.

4 The first area of difficulty is the rewiring of the Main Distribution Frame. Figure 3 below shows two views of a typical MDF. As can be seen, there are thousands of wires bundled up that run across long racks. Every time a subscriber asks for ADSL service, one of these wires must be identified, disconnected from the original piece of equipment, and connected to the POTS splitter. The wire carrying the voice signal from the splitter is then connected back to the MDF where it then must be reconnected to the ports where the subscriber line was originally connected. This operation is feasible if done for a limited number of subscribers but becomes unwieldy if done for a large percentage of the subscribers connected to the MDF. This level of complexity causes a very high probability of error. In addition, the rewiring operation is very time consuming and, hence, also very expensive. These are all factors that play against mass deployment. Figure 3. Views of a typical Main Distribution Frame. The second area of difficulty is in the system overhead that is required to offer both voice and data services to the same subscriber. Since voice service is offered by the voice switch and data service is offered by the DSLAM, both these types of equipment need to be present and co-located for the subscriber to obtain both services. This duplication of equipment poses three problems. The first one is cost: a DSLAM or a voice switch represents a step increase in equipment cost and also carries with it significant installation costs. The second problem is that co-location of equipment occupies a lot of space and, if the space available is limited, this will, in turn, limit the number of subscribers that can be served out of one building or cabinet. This, in turn, limits the market penetration of the service. The third problem is testing the line. Traditionally, subscriber lines have always been tested in order to assess whether the condition of the line is adequate for voice service to be provided and to diagnose problems on the line. These tests were and are performed by test units that reside with the voice switch equipment. With the advent of DSL services, similar tests need to be performed to determine whether DSL service can be provided on a particular line and to diagnose problems. The

5 question that arises when two different pieces of equipment interface to the line is who is responsible for what tests. The presence of the POTS splitter that separates the two pieces of equipment makes it even more difficult to perform some tests. Currently testing is performed according to the configuration shown in Figure 4, where an expensive test machine isolates the subscriber during testing. This type of configuration is used in the linequalification phase and to diagnose the causes of a failure. However, it does not work well to proactively and periodically test the line to gather data and be able to predict failures. The latter type of testing is much more effective and increases the reliability of the network. Tester A DSLAM Test Matrix POTS splitter CO Tester B Figure 4. Today's line testing configuration The other major component of system overhead is represented by the analog POTS splitter. Analog POTS splitters are bulky, expensive pieces of equipment that are subject to aging. They usually come in the form of a card, similar in size to a regular linecard, and serve a certain number of subscribers. An example is shown in Figure 5. These cards need to be housed on a shelf along with regular linecards. This component effectively isolates the DSLAM from the line and, as mentioned above, creates some difficulties in line testing. Figure 5. The analog POTS splitter.

6 The third area of difficulty is that of the Network Management and Maintenance System. All Central Offices and/or DLCs of a service provider are connected together in a regional or national network so that all the nodes in the network can be controlled and monitored by means of a Network Management System. This also applies to DSLAMs that have to be connected in a similar way and monitored by such a system. However, even if the same service provider owns both voice and DSLAM equipment networks, these do not communicate between themselves. In many cases, a new Network Management System has to be created from scratch when, for example, a regional network of DSLAMs is installed. This makes managing the network much more difficult, causes confusion, and is an obstacle to integrated billing. All of the above difficulties can be overcome if the number of DSL subscribers is low but become an impediment if this number increases to mass deployment levels. The goal of this paper is to propose a solution to all these problems, and show a way that makes mass deployment possible. The solution is shown in Figure 6; that is, to integrate base-band voice and ADSL functionality onto the same linecard. This allows the two services to be offered from the same piece of equipment, be it a DLC, CO, DSLAM, or Access Network equipment. ADSL integration implemented by simply replacing the linecard Network Management and Maintenance System Main Distribution Frame IVD Linecard ❶ No or minor change only ❶ Min. equipment cost ❶ Min. installation cost Class 5 Switch/DLC/ AN/DSLAM ❶ One uniform Network Management and Maintenance System Figure 6. The solution to ADSL mass deployment. This represents a huge advantage for providers offering voice service that wish to add DSL service because all that needs to be done is for the POTS linecard to be removed and a broadband, integrated voice-data card to be put in its place. No rewiring of the MDF is necessary, thereby avoiding all the wiring errors and costs associated with personnel having to spend a lot of time tampering with the MDF.

7 A provider offering DSL services through a DSLAM can add such IVD (Integrated Voice Data) linecards to their shelves, or use them as replacements for their existing pure data linecards, and now offer life-line voice service as well. The voice can now be transferred across the data network, for example using ATM, or, by means of a voice gateway, transferred to the PSTN. Changes only need to happen at the MDF level if the provider acquires new subscribers. These changes simply entail disconnecting the subscribers from one provider and connecting them to another. This is still easy compared to rerouting them through a POTS splitter and back to the MDF and then on to a voice switch. The other major advantage of this solution is that all the system overhead caused by the additional equipment is eliminated. Now there is only one type of equipment for voice and data services. This saves the cost of the extra DSLAM or voice switch, and its installation costs. It also saves a significant amount of space. This is particularly important when the service is offered out of a remote unit or on the curb side where availability of space is very limited. All the problems associated with having two separate Network Management and Maintenance systems now disappear. The provider can monitor and manage its network by means of one single Management system and does not have to create one from scratch if they are a voice service provider who wants to add DSL services or a DSL service provider who wants to add voice services. Sophisticated billing schemes can be supported resulting in unified billing for voice and DSL services, and existing features and services can be maintained. 3. The Semiconductor Aspect However, the above system of integration of voice and data is not possible without the collaboration of semiconductor manufacturers who have traditionally been the driving force behind system integration, packing more and more functionality into silicon and occupying less and less space. An IVD linecard is not easy to realize because it needs to perform the functions previously performed by three cards: the POTS linecard, the data linecard, and the POTS splitter boards. It would be very difficult, if not impossible, to realize such a linecard with the channel density required for ADSL mass deployment without the availability of a chipset that performed all three functions in an integrated fashion. With the help of the latest breakthroughs in semiconductor technology, such a chipset is available from Infineon Technologies and is illustrated in Figure 7. On the left side we can see the traditional approach of having separate POTS and data linecards, the former typically in the voice switch and the latter typically in the DSLAM. The POTS linecard contains the SLIC, voice codec, and voice DSP. The data linecard contains the line driver, analog front-end, and ADSL data pump. The POTS splitter is external and is on yet another card. On the right we see the fully integrated chipset. The voice and the data

8 go through a broad-band SLIC device that performs all the functions performed by a traditional voice SLIC and those performed by an ADSL line driver, all in one. However, a transformer is not needed to interface to the line. Traditional Analog POTS Linecard POTs Splitter SLIC A/D D/A DSP Voice Integrated Voice/ADSL Linecard PSTN ADSL Linecard LD A/D D/A 8-32 lines ADSL Datapump Broadband SLIC 8-16 lines A/D-D/A+ Digital POTS Splitter Voice DSP ADSL DSP 4-8 lines Data Network Figure 7. A chipset that can perform the functions of a pure ADSL chipset, a POTS chipset, and a POTS splitter, all in one. The voice and the data signals are passed to a special codec that converts the signals to digital ones and splits the voice from the data in the digital domain. The voice is then passed on to a voice DSP that performs all the voice functions and the data is passed on to a regular ADSL data pump. The voice is then presented to the PSTN world directly from the chipset on a PCM interface and the data directly to the data network on a Utopia interface. This totally eliminates the external, analog POTS splitter with all its nuisances. Not only, but, since the POTS splitting function is done digitally inside the chip, the characteristics of the POTS splitter can now be programmed and its out-ofband behavior improved due to the steeper digital filter. In contrast, with an external analog splitter, the various country requirements have to be met by means of different splitter designs. The elimination of the external splitter thus represents a huge cost savings, both in terms of equipment cost and less design effort, and permits much higher levels of subscriber density to be achieved at the linecard level. The latter is then reflected in higher subscriber density at the system level. All this propels mass deployment of ADSL services.

9 4. Conclusion In this paper, we have looked at how ADSL service is deployed today and identified a number of difficulties with this deployment method that could become an impediment to real mass deployment. Each one of these areas of difficulty was analyzed in detail. A solution to all these difficulties was proposed and all of its benefits explained. Such a solution consists of integrating voice and data services into the same piece of equipment. However, this is not possible without the availability of a sophisticated semiconductor solution that integrates voice, data, and POTS splitting functionality into the same chipset. The characteristics of such a chipset were explained. From the analysis in this paper, we can conclude that the integrated voicedata approach offers all the following benefits: Much lower costs, both at the equipment and the linecards levels; Only one piece of equipment is needed to offer both voice and data services; Single Network Management and Maintenance System; Much less space required to offer both services; No rewiring of the MDF with less error probability and lower deployment cost in the form of less man-hours needed to work on the MDF; Easier loop testing. All these benefits make the IVD approach the best solution to full ADSL mass deployment because it removes the technical obstacles that are currently making it difficult for this to happen. For more information on the IVD chipset, please contact Infineon Technologies. Infineon Technologies contact: Oliver Lyncker Marketing Manager ADSL Phone: oliver.lyncker@infineon.com