ODN Alternatives for MSOs: RFoG, EPON/GPON, DPON, Hybrid RF PON

Here s another tidbit that is non-intuitive at first, but makes sense when you think about it: as you give people more speed, the utilization of your network does not go up proportionally. That is, if you suddenly give each subscriber on a PON twice the bandwidth, your data load on the network will not go up. That s because each subscriber transfers the same number of bits he would have had he had the lower speed. Over time, of course, applications will be written to take advantage of higher speed, but until they get deployed, more bandwidth per subscriber results in the same utilization of the network. In FTTH we have developed the bad habit of not taking statistics into account in thinking about PON data capacity. On the other hand, there are unknowns in how data will be used in the future, as we put on more IPTV and as we deal with more over-the-top video plus new applications I m not smart enough to think of. We can get a pretty good idea of what IPTV will do to bandwidth it is and will be the data hog, though not quite to the extent some people say but what else is going to happen? The lesson is to monitor capacity utilization, and make sure you have enough, without spending money on unneeded capacity. So now, hopefully you are not in too much of a fog about RFoG, and maybe you have a bit more perspective on the difference between DOCSIS and EPON/GPON. And maybe I kind of justified the time I spent developing the over-simplified model to illustrate the advantage of statistics in data loading. ODN Alternatives for MSOs: RFoG, EPON/GPON, DPON, Hybrid RF PON Tom Anderson, Director of Product Marketing, Alloptic Bob Remillard, Technical Publications Manager, Alloptic MSOs are considering an array of options for network evolution as they compete for a dominant position in both residential and business services. Terms like RFoG, PON, and DPON are tossed about as the ultimate solution. It is no surprise that each of these technologies has advantages and shortcomings. What follows is an overview and comparison of four approaches to giving MSOs an optical distribution network (ODN) that offers a competitive edge. Among the alternatives being evaluated are RFoG, EPON/GPON, DPON, Hybrid RF PON, and point-to-point (P2P) architectures. This article focuses on the first four options because of their similarities. The PON vs. P2P debate is deserving of separate exploration. (Ed. Note: A topic we have covered extensively and will continue to pursue.) One commonality among the ODN options being evaluated is that they are all built on a passive optical network (PON) architecture. Let s look at each in turn. 7

RF over Glass (RFoG) RFoG is a technology receiving considerable interest among HFC network operators and equipment suppliers. Indeed, a number of vendors have announced either products or development efforts in this area, SCTE is working on a standard for RFoG, and deployments are underway. But what is RFoG? Simply put, RF over Glass is a first order move from today s HFC network to a fiber ODN. The coax portion of the HFC network is replaced with fiber in an architecture that resembles a passive optical network as shown in Figures 1 and 2. Figure1: HFC Topology Figure2: RfoG Topology With RFoG, the optical fiber carries the RF signal between the headend or hub and the RFoG transceiver. The transceiver provides the conversion from optical fiber to a coax network at the subscriber location. In the RFoG network, DOCSIS provides the management and control of the cable modem just as it does for HFC networks. Set top box and MTA control is unchanged, as well. The RFoG transceiver simply acts as a media converter between the network fiber and the subscriber s coax wiring. There are many aspects of this solution that HFC network operators find attractive. Here are three advantages. 8

First, RFoG leverages the current network investment. Subscribers' cable modems, set-top boxes, and MTAs are unchanged and remain in place, as does the coaxial wiring in subscribers home or business. The same headend equipment (e.g. laser transmitters, optical amplifiers, return path receivers and transmitters, CMTS, and set top box control) continues to be used, as well. And perhaps even more important is that the RFoG network is transparent to operations and billings support systems. OSS and BSS are unaffected by RFoG. It should be noted that most RFoG equipment operates to 1 GHz, and some to 1.1 GHz. To take advantage of the additional spectrum, headend, hub, and CPE must also support the wider spectrum. Second, RFoG is compatible with HFC. The two technologies work alongside one another so that RFoG can be installed without a wholesale changeout of the distribution network. That means it is not just for new greenfield networks. RFoG can be used cost-effectively in situations that require node-splitting, as well as for plant rebuild or rehab projects. 9

Third, RFoG delivers economic advantages. The initial installed costs (CapEx) of RFoG networks are comparable to those of HFC. Depending primarily upon subscriber density variations, RFoG CapEx will be in the range of 15 percent more or less than HFC. The financial benefits are much more significant for operating expenses (OpEx); optical distribution networks are less costly to operate and maintain. These savings come from several sources including: Reduction and possible elimination of active elements in the ODN Reduction and possible elimination of regulatory (CLI and sweep) tests Less power consumption Less battery and emergency power requirements Increased reliability / fewer maintenance dispatches Operators deploying RFoG have reported reductions in OpEx of as much as 68 percent and maintenance rate improvements of over 90 percent i. A final economic advantage is the possibility of revenue enhancement from the spectrum extension to 1 GHz. This opens the possibility of added services for network operators in the band beyond 870 MHz. One consideration in deploying RFoG technology is that it perpetuates DOCSIS. Those network operators wanting to deliver services beyond DOCSIS capabilities need a different technology. For example, network operators actively pursuing medium and large business subscribers or those with near-term plans for IP video services are looking for other solutions that support their business objectives. Many have already established networks separate from their HFC or RFoG plants to deal with these needs. The next three architectures EPON/GPON, Hybrid RF PON, and DPON all address services beyond DOCSIS. EPON and GPON Systems To address the limitations of DOCSIS, network operators have turned to EPON and GPON technology. As shown in Figure 3, these systems use the same optical network architecture as RFoG. Figure3: EPON / GPON Topology 10

Instead of the RF headend/stb and CMTS/cable modem systems used by HFC and RFoG, they operate with an OLT (optical line terminal) in the headend or hub communicating with an ONT (optical network terminal) at the subscriber s home or business. Groups of up to 32 ONTs share the single fiber connection to the OLT, and they share bandwidth of 1 Gbps or 2.4 Gbps, depending upon technology. The ability to allocate this bandwidth as needed per ONTs is fundamental to PON system operation. Whether business or residential, subscribers get the bandwidth needed for VoIP, data services, and even IPTV. Like RFoG, there are advantages in using EPON/GPON technology. The most obvious is the bandwidth available for IP-based services as described above. With bandwidth optimization methods such as DBA (dynamic bandwidth allocation) and IGMP implementation, today s needs are more than adequately served. Additionally, both EPON and GPON are actively adopting 10 Gbps capabilities, ensuring that even the most aggressive projections for future bandwidth needs can be met with EPON and GPON technologies. EPON/GPON systems deliver the rich Ethernet features needed for successful business services, for instance, tagged and untagged VLAN data, E-line and E-LAN services, Q-in-Q, and other business-class Ethernet capabilities. Another key advantage is that it uses the same PON architecture described for RFoG. The benefits of FTTH topologies are immediately realized. Active devices are located only in the headend and at the subscribers location, lowering maintenance, reducing OpEx, and simplifying the network. One concern with EPON/GPON is that IPTV is not yet widely deployed; RF continues to be the predominant video delivery mechanism and many EPON and GPON systems support downstream RF video. This is done by using a second downstream wavelength, which is dedicated to RF services. However, with the widespread use of 2-way RF (enabling STB control and cable modem services), EPON/GPON systems typically cannot fully support RF. To make use of EPON and GPON systems for residential services, bi-directional RF services must be accommodated. For MSOs, one concern with EPON/GPON systems is the management interface. Management depends upon the PON systems internal control mechanisms interfacing with OSS/BSS systems. This is typically done via SNMP, command line, or similar protocols, but it is not DOCSIS. Thus, the EPON/GPON system cannot be managed by the existing DOCSIS-based OSS. This issue is addressed by the next technology, DPON. 11

DPON, or DOCSIS PON To address the added cost of network management that a GPON or EPON system can impose on an operator, which can be substantial, the concept of a DOCSIS PON or DPON has emerged. While the DPON uses the same OLT and ONTs of a traditional PON network, management of the network occurs over the existing DOCSIS management plane. To make this work, PON vendors place an abstraction layer of software on the OLT and ONT that allows the operator s current DOCSIS management to control the PON elements. In effect, the EPON/GPON ONT appears to the OSS as a cable modem. Figure 4: DPON Topology In comparing the EPON/GPON topology of Figure 3 with the DPON topology of Figure 4, the only difference is the interface between the OLT and OSS. With DPON, MSOs realize all the benefits of EPON/GPON, while continuing to use embedded OSS controls. The advantages of DPON are that it allows operators to: Offer rich Ethernet services to even the most demanding business accounts Leverage their existing OSS network management capabilties Enjoy the low OpEx of FTTH architectures DPON holds significant promise for the future, but it is not yet generally available. Equipment vendors are developing the interface capabilities. However, there are no standards for the DOCSIS control plane interface and those will be important for broad deployment. 12

Hybrid RF PON The concept of a hybrid RF PON has emerged to address the shortcomings in the other architectures, namely: Lack of an RF return path on EPON/GPON systems Lack of standards (and products) around DPON Bandwidth limitation of RFoG The Hybrid RFoG PON topology allows both RFoG and EPON/GPON to operate simultaneously on the same fiber distribution network. This is accomplished by using a fourth wavelength for the RF return path. In a Hybrid RF PON architecture, the wave plan is typically 1310nm and 1490nm are used for the EPON/GPON communications 1550nm is used for broadcast RF service 1590nm is used for return path RF service In this design shown in Figure 5, the RF services looks just like an RFoG network, while the voice and data looks just like a PON network. The RF portion is managed with the MSO s existing OSS, and the EPON/GPON system is managed separately. Figure 5: Hybrid RF PON Topology The Hybrid RF PON network offers the network operator the best of both RF and EPON/GPON technologies, while controlling costs. The investment in RF technology is leveraged while enhanced business services are enabled and the foundation for IPTV is established. And, not to be forgotten, low OpEx of a FTTH or FTTB architecture is established as a competitive advantage. For example, a residential subscriber might opt for a residential package that consists of VoIP, 20 Mbps data, and video service. For this customer, a mini or micro node would allow the operator to provide service at a fraction of the cost of placing a PON ONT. On the other hand, the neighbor in this example may be a telecommuter who requires 100 Mbps service to the house. For this customer, an ONT would be appropriate and the cost would be offset by higher service revenues generated from it. The beauty of the hybrid solution is that both of the neighbors in this example are served over the same fiber plant. 13

Ideally, the Hybrid RFoG PON network would support a DOCSIS management plane for the EPON/GPON equipment. It is reasonable to expect that once DPON becomes available, the EPON/GPON system can be managed via DOCSIS as well. Conclusion To compete with fiber-to-the-home and fiber-to-thebusiness networks being deployed, MSOs are considering, and in some cases deploying, their own fiber networks. Equipment vendors are rising to the challenge and are providing MSOs an array of network migration options. The one advantage MSOs have over their telco brethren is that their options are all based on a common network topology, a passive optical network that leverages their current network investment while delivering OpEx savings. All-Fiber Access Architectures for MSOs Mark Conner, Market Development Manager, Corning Cable Systems Introduction The market for telecommunications services has been completely transformed in the last two decades. Telephone companies (telcos) and multiple system operators (MSOs) once separately commanded the voice and video markets. Today, there exists a competitive matrix of telecom providers and services from which residential consumers can select the voice, video, high speed data and wireless services they need. The interplay among the competitive matrix, subscribers lifestyles and net dependency is constantly resetting what is required for providers to be competitive in the marketplace. MSOs have effectively leveraged a strategy of evolution in which new and improved technologies are regularly assimilated into their infrastructure and business model. While their original and core business basic video subscription has remained flat for the past ten years, their evolutionary strategy has allowed them to offer digital video, high speed data and voice, thus growing revenues and per subscriber value. Deploying all-fiber access networks (AFANs) is a logical progression in the MSOs strategy. As a testament to the longevity of cabling infrastructure, cable installed twenty years ago is still functioning in many networks today. Therefore, it is crucial that the cabling infrastructure deployed in new builds be able to support ever-increasing channel and bandwidth capacity requirements. Optical fiber is the one medium that is up to that 14