FTTx Technology Choices

Transcription

1 Technical Brief FTTx Technology Choices When it comes to FTTx deployment, many carriers mistakenly assume that PON is the best or only game in town. This paper addresses some of the myths surrounding Active Ethernet and PON technologies and explains why Active Ethernet networks are becoming the preferred choice among many leading service providers. Two of the largest FTTP initiatives in North America have chosen active solutions, citing lower CapEx and OpEx as key drivers. So which is the better solution? That s what this white paper will cover. By now we ve all heard of the Super RFP issued by the RBOCs in 2003 for their plans to deploy fiber to the premises (FTTP). Their decision to deploy BPON, a Passive Optical Network architecture based on ATM standards, has thrust PON into the spotlight and has given some people the idea that PON is the only viable option for FTTP networks. Meanwhile, two of the largest FTTP initiatives in North America, SureWest Communications and UTOPIA, have both decided to deploy Active Ethernet fiber solutions citing the lower CapEx (capital expenditure) and OpEx (operating expenditure) of Active Ethernet as key decision drivers. So which is the better solution? The answer depends on many factors, including legacy infrastructure, bandwidth requirements, and the services to be offered. This paper will explore some of the myths about PON and Active networks and provide an in-depth look at why Active Ethernet is quietly becoming the preferred choice among leading service providers worldwide for their fiber deployments. Active vs. PON FTTx Technology Choices, 6/30/04, Rev A PAGE 1 of 10

2 PON uses powered equipment in the central office and customer premise. In the outside plant, it uses passive splitters and couplers to divide bandwidth among up to 32 users over a distance of 10-20km. A Passive Optical Network (PON) consists of an optical line terminator (OLT) located at the Central Office (CO) and a set of associated optical network terminals (ONT) to terminate the fiber usually located at the customer s premise. Both of these devices require power. PON gets its name because instead of using powered electronics in the outside plant, it instead uses passive splitters and couplers to divide up the bandwidth among the end users typically 32 over a maximum distance of 10-20km. Because this is a shared network, it is sometimes referred to as Point to Multipoint or P2MP. OLT Usually km ONT Optical splitter 1x16 (1x2, 1x8) 1x32 (1x4, 1x8) Figure 1: PON Architecture Similar to PON, Active networks use powered, hardened equipment in the field, enabling them to provide a dedicated pipe to each subscriber. Active networks can serve a virtually unlimited number of subscribers over an 80km distance. An Active network looks very similar to a PON, however, there are three main differences. First, instead of having passive, unmanageable splitters in the field, it uses environmentally hardened Ethernet electronics to provide fiber access aggregation. Second, instead of sharing bandwidth among multiple subscribers, each end user is provided a dedicated pipe that provides full bi-directional bandwidth. Because of its dedicated nature, this type of architecture is sometimes referred to as Point to Point (P2P). The third architectural difference between PON and Active is the distance limitation. In a PON network, the furthest subscriber must be within 10-20km from the CO, depending on the total number of splits (more splits = less distance). An Active network, on the other hand, has a distance limitation of 80km, regardless of the number of subscribers being served. The number of subscribers is limited only by the switches employed, and not by the infrastructure itself, as in the case of PON. Switch Up to 70 km Up to 10 km Single Fiber (EFM) CPE Powered Device (Ethernet Switch) Figure 2: Active Architecture Active vs. PON FTTx Technology Choices, 6/30/04, Rev A PAGE 2 of 10

3 With the basics of these topologies understood, we can now explore the five most common myths surrounding PON vs. Active networks: Years ago, Active Ethernet required two fibers, and did not have options for outside plant, but new standards and products have removed those concerns. 1. PON Networks Make Better Use of Fiber 2. Active Electronics In the Field Are a Liability 3. PON Systems Don t Require Set Top Boxes for Video 4. PON Systems Provide Plenty of Bandwidth 5. PON Has Dominant Market Share Over Active.!"# $%& The root of this misperception is one based in reality. However, it is no longer valid because of two technological developments that have occurred in the past year. The first of these developments is the completion of the IEEE 802.3ah Ethernet in the First Mile (EFM) standard that defines, among other things, a method for delivering Ethernet over a single strand of fiber. Before this standard emerged, Active Ethernet solutions required two strands of fiber to every subscriber (one to send, the other to receive). Years ago, when fiber was very expensive, one can understand what a costly proposition this was. The second development has been the evolution of environmentally hardened Ethernet devices that can be placed in the outside plant. Prior to the availability of this type of gear, network operators would have to pull the fiber from every subscriber all the way back to their CO or else rely on Controlled Environment Vaults (CEVs) or other types of air conditioned/heated Remote Terminals (RTs). The two of these developments, along with the fact that fiber costs have dropped to a fraction of what they were just a few years ago, make the question of which network uses less fiber virtually a non-issue. '!()* To assess where it makes most sense to place powered devices, one should understand the different theories of outside plant design. These designs, along with their pros and cons, are described below. Traditional PON The promise of PON has been that you can push a single strand of fiber far out into the field and split it with a passive, unmanageable device close to the customer premises (Figure 3). Unfortunately, this approach has a number of drawbacks. One of the biggest disadvantages is that these splitters have no intelligence, and therefore cannot be managed. You cannot communicate with them remotely, and with hundreds or thousands of splitters scattered around in the field, driving to each one to check for problems when a service outage occurs becomes a very slow and a very expensive proposition. Figure 3: Traditional PON Another major disadvantage to PON is its inflexibility. If a 1x4 splitter is used to serve four homes, hooking up a fifth customer requires pulling a new strand of fiber all the way from the upstream splitter, or re-designing the network to accommodate a larger splitter near the customer premises without violating the 32 split maximum allowed. Unfortunately, changing any splitter in the network requires all downstream customers to come offline while the work is done. PAGE 3 of 10

4 Traditional PON s 32- split maximum can be mitigated by underutilizing capacity, but that can drive up persubscriber costs. A logical alternative to alleviate this problem is to under-utilize the capacity in the outside plant. In other words, instead of maxing out each PON port with 32 splits, only deploy 16 or 24 splits to allow room for growth. Important to remember, however, is that each PON port in the OLT carries a very high price tag since it is intended to be amortized across 32 customers. By not fully loading up that PON port, you increase the per-subscriber costs dramatically. The network operator, in this scenario, is forced to decide which is the lesser of two evils low flexibility or inflated per-subscriber costs. Finally, since PONs are shared networks, each subscriber becomes a homogonous member of the PON port they are connected to. Each subscriber gets the same bandwidth, each must receive software updates at the same time, and each must have the same ONT at the customer prem. This introduces significant challenges when businesses looking for higher bandwidth services are mixed in with these residential subscribers, when updating a new load of code, or when migrating to new technology in the future (eg. BPON to GPON). Figure 4: Passive Star Passive Star PON provides more centralized troubleshooting, but is still limited by PON s tree-based topologies. Active Star networks require power in the outside plant; however, those active electronics do bring intelligence and management to the access edge. Passive Star PON A Passive Star architecture is designed to alleviate some of the flexibility challenges of a traditional PON topology. Instead of pushing the splitters all the way out to the customer premises location, they are pulled back and aggregated in a more centralized location, typically housed in a cabinet. This design helps drive more efficiency and lightens the burden of troubleshooting since the splitters are now more centralized. But Passive Star is still subject to the inherent drawbacks of a PON network. One of these is the lack of diverse paths through the network. PONs, by their nature, subscribe to tree-based topologies. Even if the splitters are pulled back to an aggregation cabinet, there is still only one physical path upstream, and that introduces a dangerous dependency on that link. Because these splitters have no intelligence, there is no ability to provide emergency fail over to a diverse path in the event of a link failure. Another drawback is high first subscriber costs. As mentioned earlier, each PON port carries a high price because it is expected to be divided by 32 subscribers. Therefore, to activate that first subscriber, a significant CapEx investment must be made to provide them service. Active Star An Active Star architecture has one arguable drawback from a deployment perspective, and that s the requirement for power in the outside plant. However, Active electronics in the field are nothing new. Telcos have been deploying DLC networks for decades that have powered electronics in the field. As the types of services evolve to include advanced, bandwidth intensive content like video, having intelligent devices at the edge of a network actually becomes an extremely significant advantage for the following reasons. For video applications, intelligence at the edge of a network allows multicast streams to be replicated for downstream delivery using IGMP. This means regardless of how many people downstream of the switch are watching the PAGE 4 of 10

5 same channel, only one stream is pulled down from the head end. That multicast stream is then replicated in the Access switch and sent to the subscribers. This not only speeds up channel change times, but it also makes more efficient use of your network backbone. Figure 5: Active Star While PON systems do not require a settop box for analog signals and mono sound, today s digital applications do require a set-top box when run over both Active and PON infrastructure. Another benefit to having Active electronics in the field is resiliency. By ringing these nodes together and choosing a vendor that supports Ethernet Protection Switching Rings (EPSR), true carrier-class resiliency is introduced which provides sub-50ms failover in the event of a link failure. For a video customer, it means a split second of picture tiling in the worst case, and for a voice customer, it means the call is not dropped. Other advantages, of course, include full management and troubleshooting capabilities, high flexibility for deploying different services to residential and business customers, and low first subscriber costs. When striving for Five Nines reliability and maximum flexibility in a FTTP network, one can quickly see how venerable a PON network is to link failure, and how deploying Active electronics in the field actually becomes an asset instead of a liability. +!"#,-."/$0&1) PON systems are able to support a somewhat complex method for deploying video services that most closely resembles what MSO s (ie. cable TV providers) do today. This method utilizes EDFA s (Erbium-Doped Fiber Amplifiers) to send an RF signal over a separate wavelength on the fiber to deliver a signal to the customer prem. This is sometimes referred to as delivering video out of band since it is outside of the IP data stream. Figure 6: Video Deployment Options If this signal contains analog video when it reaches the customer premise, it can be delivered straight to the television without the need for a set top box just like the basic service many people receive from cable TV providers today. The experience is exactly the same the same video quality and the same mono sound. If the signal contains digital video when it reaches the customer premises, however, a digital set top box must be introduced again just as in a digital cable service offered today by the MSO s. This set top box descrambles the digital video signal and delivers it to the TV. Where it starts to get more complex is when advanced, interactive services are introduced like video on demand (VoD). Since an RF signal is a one-way PAGE 5 of 10

6 When providing ondemand services, PON systems must eventually use IP to communicate with the Head End and therefore require adapters to convert the RF signal. Active Ethernet systems use IP from end to end, using an IP set top box to convert the signals. Depending on the type of PON deployed, downstream bandwidth can range from 19Mbps to 38Mpbs. Underutilized splits offer more bandwidth, but speeds become steadily slower as more subscribers join the network. communication, the IP stream must be utilized to send commands up to the head end. In order to do this, an RF adaptor must be added at the customer premises to demodulate the upstream set top box communications and translate them into IP packets. Once converted to IP, they are sent up through the IP path (or in-band ) to the head end to make the specified request. The requested content is then sent back down over the RF path (out of band) using DWDM to that specific subscriber location. Obviously, this requires a good bit of effort to provide a service that many would consider to be the same as what cable TV operators are already doing today. As with any me too service, this approach leaves very little opportunity to differentiate based on anything other than price. The alternative, and what many consider to be the best way of delivering advanced video services, is using IP to deliver the content. This is sometimes called IP Video or Switched Digital Video. In this solution, instead of having a traditional digital set top box, an IP set top box is used to receive the IP packets, decode them, and provide audio and video output to the TV. The experience is a powerful, all-digital experience with full Dolby 5.1 sound, crisp, high quality video, and interactivity unmatched by any other service available today. Think of the interactive power of the Internet combined with high quality broadcast TV. The result is strong differentiation that allows service providers to compete on things other than just price. While IP Set Top Boxes carry a slightly higher price tag today than traditional digital set top boxes, when you add in the cost of the RF adaptor required at each customer premises, the CapEx costs for both solutions are quite comparable. From the network perspective, the most compelling advantage for deploying IP video is having a fully converged IP network to manage and maintain. IP has long been the protocol-of-choice for delivering data services, and in recent years we have seen the rapid emergence of Voice over IP (VoIP) as the preferred method for delivering voice services as well. Using IP for video as well allows a network operator to use the same infrastructure for all three services and realize significant CapEx and OpEx savings by standardizing on one network infrastructure instead of two as is required in an RF video deployment. 2!"# )&$) ) To determine how much bandwidth is enough, a service provider must evaluate what services they intend to offer over the life of the network. Since the capacity and longevity of a fiber infrastructure is virtually limitless, one must look out as far as possible to ensure the equipment that is deployed will handle the bandwidth needs for the foreseeable future. Mbps '3 3!" #!"! 6$ ( $!"!% 7 % Figure 7: Bandwidth Comparison by Technology PAGE 6 of 10

7 Active Ethernet provides dedicated bandwidth to each subscriber, regardless of network population. Speeds are most commonly 100Mbps to 1Gbps. As illustrated in Figure 7, different technologies will offer different levels of bandwidth in the upstream and downstream directions. APON and BPON, for example, deliver 622Mbps in the downstream direction, so assuming it is split among 32 subscribers, it provides 19Mbps to each customer. In the upstream direction, it provides 155Mbps split 32 ways, resulting in under 5Mbps. EPON is a technology that provides 1Gbps in both the downstream and upstream directions, providing 30Mbps of bi-directional bandwidth to each subscriber. Finally, GPON, the newest standard for PON technology, provides 1.2Gbps in the downstream direction resulting in 38Mbps per subscriber assuming 32 splits, and 622Mbps in the upstream direction allowing 19Mbps per subscriber. Active Ethernet, in comparison, provides dedicated bandwidth to each subscriber, which means there is no sharing of network traffic. Speeds most commonly found in the marketplace today are 100Mbps bi-directional to residential customers and even 1Gbps to business customers. When you consider that Active Ethernet solutions, on average, cost less to deploy and maintain than comparable PON systems, the opportunity to secure more bandwidth for less investment is certainly a compelling proposition. But how much bandwidth is enough? All of these speeds are compelling by today s DSL and Cable broadband standards, but deploying advanced IP video and other next generation services takes things to a completely new level. Consider what s being offered today at SureWest Communications in Sacramento, CA. Over their Active Ethernet FTTP network, they offer residential customers a service bundle of 200 digital channels with interactive TV services such as video on demand, voice service with a full package of features such as call waiting and various messaging options, and 10Mbps of high-speed internet for one low monthly price. To deliver these types of services, a network would require at least 22Mbps of bandwidth assuming 3 TV s per house at 4Mbps per video stream plus the 10Mbps for high speed Internet. Based on the bandwidth capabilities of PON-based architectures, it is clear this network would already be beyond the capabilities of BPON and pushing up against the capabilities of even the newest PON standard, GPON. Broadcast TV (IP): 4Mbps per stream x 3 TV s: 12Mbps HDTV (IP): 20Mbps per stream x 3 TV s: 60Mbps High Speed Internet: 10Mbps High Speed Internet: 10Mbps Figure 8: FTTP Residential Services Today vs. Tomorrow PAGE 7 of 10

8 PON networks will be severely challenged by emerging highbandwidth applications such as HDTV. PON and Active Ethernet technologies currently split the FTTP market nearly equally Now if we look at what is just over the horizon HDTV we can quickly see how a PON network will not scale to meet the requirements. This is before we even begin to consider how other applications will take off such as distance learning, video conferencing, smart home services, personal video recorders (eg. TiVo), etc. Each of these will carry their own bandwidth requirements that must be planned for. 89: # " According to Render, Vanderslice & Associates, a noted research firm focused exclusively on the FTTP market, the number of actual deployments of FTTP networks shows a nearly equal split between PON and Active technologies at 48% and 46% respectively (Figure 9). When the RBOCs proclaimed they would deploy BPON in the Super RFP, many believed that PON would become the dominant technology choice for all FTTP deployments. When you stop to consider that their legacy infrastructure is ATM-based and that video is not a priority for them, however, it becomes clear that while it makes perfect sense for their needs, it most definitely will not be the best choice for all deployments. For network operators interested in offering video as a key differentiator and are not locked into a legacy ATM infrastructure, on the other hand, most are realizing the value of deploying a fully converged IP network that is based on the most ubiquitous technology in the world Ethernet. Homes Connected as of October 2003 APON/ BPON 48% Active 46% Hybrid Active/ PON 3% EPON 3% Source: Render, Vanderslice & Associates. Figure 9: Deployments by Technology PAGE 8 of 10

9 "## ; In the end, each network operator will make their decision of which technology to deploy based on their own unique circumstances. The purpose of this paper is not to suggest that one technology is the best for every situation. On the contrary, the intention of this paper is simply to make network operators aware that there is an attractive alternative to PON-based FTTP architectures that leverages the benefits of IP and Ethernet to deliver services that will provide compelling differentiation based on the unique experience it delivers to customers and not just on price. To learn more about Active Ethernet FTTP solutions and how Allied Telesyn is helping some of the world s largest FTTP network operators realize the benefits of carrier grade IP/Ethernet, visit or call ) # Active vs. PON FTTx Technology Choices, 6/30/04, Rev A PAGE 9 of 10

10 ;# )/9<, =/ A global company with nearly two decades of continuous profitability Our tagline: It s Our Network, Too, is a testament to our investment in our customers bottom line success Allied Telesyn focuses entirely on end-toend, purpose-built Ethernet applications A world-class engineering and support organization spanning five continents and more than 30 countries The ideal choice for cost- conscious IT professionals who are looking for highquality, feature-rich network solutions at a lower price. Founded in 1987 with the goal of producing feature-rich, reliable, standardsbased networking products, Allied Telesyn has a proven track record in bridging the gap left by other Ethernet networking manufacturers, whose solutions are often limited in scope or cost-prohibitive. By taking cues directly from our customers and leveraging our global manufacturing competencies, we ve evolved a market-focused approach to system development that is geared entirely to applications, rather than individual components. And by concentrating on battle-tested, end-to-end solutions for vertical market applications we avoid the scattershot, companyfocused approach common in the industry. Our tagline: It s Our Network, Too is a testament to our high-level of accountability and to our investment in our customers bottom line success. Allied Telesyn focuses entirely on end-to-end, purpose-built Ethernet and IP applications; with a complete line of networking products that includes Layer 2 switches, Layer 3 switches, carrier class fiber/copper Multiservice Access Platforms, and residential gateways. No other networking vendor can match Allied Telesyn s breadth and depth of Ethernet products we are the leading manufacturer of media converters, unmanaged Fast Ethernet switches and hubs, fiber optic network adapters and other feature-rich interconnectivity products, worldwide. Additionally, Allied Telesyn has developed a world class systems engineering and support organization that ensures networks are designed and implemented to handle the stress of providing voice, video and data services. With engineering, manufacturing, sales, and distribution divisions strategically located throughout the Americas, Europe, Asia and Japan, Allied Telesyn is able to deploy solutions anywhere in the world, quickly and efficiently. And by rigorously testing products in design and support centers and leveraging our design and manufacturing competencies, Allied Telesyn is able to offer reliable solutions for the access edge. This ideal combination helps our customers keep costs low, speed network deployment and maximize network uptime. Our customer-driven approach combined with a pragmatic, value-based pricing scheme and a superlative service organization has made Allied Telesyn a global networking leader, with more than 17 years of continuous profitability and products deployed in more than 50,000 companies in 30 countries and five continents. Allied Telesyn: the ideal choice for costconscious IT professionals who are looking for high-quality, feature-rich network solutions at a lower price. ) # Active vs. PON FTTx Technology Choices, 6/30/04, Rev A PAGE 10 of 10