DSL Versus PON DSL and PON are different in many ways. DSL takes advantage of the copper telephone wiring that is already installed at most residences and businesses. PON requires installing new optical fiber, which can be particularly expensive in suburban and rural areas. Fiber offers far more bandwidth than copper wires, particularly at longer ranges. New VDSL2 chips offer up to 100Mbps per user both upstream and downstream, but only within a range of 500 meters. At 1,500 meters, VDSL2 offers up to 30Mbps, still enough for one or two channels of HDTV video. Current BPON chips deliver 622Mbps downstream, rising to 1Gbps for EPON and 2.5Gbps in the new GPON chips; this bandwidth does not decrease even at 20 kilometers. Unlike DSL, a PON must share its bandwidth among the active users (up to 32 in most installations); even so, GPON will usually deliver more bandwidth per user than VDSL2. To supplement its data bandwidth, PON allows an analog video “overlay” using a separate wavelength on the fiber. Without using any data bandwidth, this overlay can support 80 analog TV channels and 300MHz of digital TV. PON also supports an IPTV model in which video is sent to the subscriber using data packets. VDSL can deliver video only as IPTV. Because PON is a shared medium, any user can look at packets intended for other users on the same fiber. To ensure privacy, PON chip sets encrypt all packets; they can be decrypted only by the intended subscriber. Encryption is not required for DSL. PON chip sets are more expensive than DSL chip sets. The greater bandwidth of PON requires more complex signal processing (DSP) and packet processing. PON optics are more expensive than a simple copper connection, and DSL benefits from its greater unit volume. The average cost of a VDSL chip set was about $25 in 2005, $10 less than for a PON chip set. Although prices for both types of chips will drop by more than 50% by 2010, PON will remain the more expensive option. Most service providers prefer standards-based devices, so they can use equipment from multiple vendors as needed. VDSL deployment has been slow because of the lack of standards. Many chip vendors, however, are supporting the recently completed VDSL2 standard, which should help it gain in popularity. The PON market is moving to either EPON, an IEEE standard, or GPON, an ITU standard. Only a few vendors are supporting EPON, but we expect several vendors to deliver GPON chip sets by the end of 2006. Working Together One option for service providers is fiber to the home (FTTH), which connects a subscriber directly to the PON. This method provides the most bandwidth to the subscriber, but the cost of running fiber to each apartment and house can be high, and each home requires an expensive PON modem. A more popular option, particularly in Japan and Korea, has been fiber to the building (FTTB). In this hybrid scheme, a fiber connects to an optical network unit (ONU) in the basement of a building that contains several apartments or offices. Tapping into the existing phone wiring, the ONU uses VDSL to deliver high bandwidth to each subscriber in the building. The phone wiring in most buildings is less than 500 meters long, allowing VDSL to operate at its maximum speed. A similar scheme, called fiber to the node (FTTN), is used in suburban neighborhoods, placing an ONU within 1,500 meters of the subscriber. FTTB and FTTN take advantage of the long range of PON but cost less than FTTH. Although FTTH delivers greater bandwidth, we believe FTTB and FTTN will be adequate for most HDTV users. As service providers build new “triple play” networks to deliver video, voice, and data, demand for both PON and VDSL will grow rapidly. The Linley Group forecasts PON port shipments will reach 20 million in 2010. With the success of FTTB and FTTN, however, VDSL shipments will grow to more than 50 million ports in that year. This growth will help makers of VDSL and PON chip sets, equipment, and modems.
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