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PON opens the bandwidth door to the home

By Armin Schulz
November 20, 2006

A look at the challenges to increased content delivery and the evolving role of PON, MoCA, and other technologies

Competition for delivering high-bandwidth "multi-play" services (video, voice, data, mobile, etc.) continues to intensify. Offering a fatter pipe to the end user through passive optical network (PON) technologies provides the foundation for such advanced service delivery.

However, deploying an all-optical infrastructure is quite expensive, and unfortunately does not guarantee increasing revenues in the long run. While the cost per megabit continues to decline, subscribers spend more money on entertainment like TV and gaming. Defining and providing new means for content delivery, in-home distribution, and storage for advanced residential applications will be the key to long-term success.

Television, streaming video with personalized ads, gaming, storage and backup for pictures and home video, along with sharing of personal content via homepages are just some examples of the applications that will drive future revenue for service providers. In some cases, subscribers will pay directly for the services and in other cases new revenue models could emerge, with carriers offering platforms for targeted advertising based on user demographics.

This article looks at the choices and challenges service providers face as they bring new entertainment and communication possibilities to their customers and how these trends influence system and semiconductor requirements alike.

The access network

A PON consists of an optical line termination (OLT) at the central office and a number of optical network terminals (ONTs) at the end user locations, along with all of the intervening fibers, splitters, etc., which collectively are called the optical distribution network (ODN).

In general, PONs offer a cost advantage over actively switched architectures. PON allows carriers to deploy distribution fibers deep into the neighborhood, where a passive optical splitter is then used to broadcast the signal via individual fiber strands to up to 64 homes. A key advantage of this technology is that the optical splitter does not require power, which lowers both deployment and operating costs.

Definitions of PON technologies were originally created by the Full Service Access Network (FSAN) working group and have since been adopted as ITU-T standards. Initially FSAN and ITU ratified APON, based on ATM technology, which was subsequently expanded to BPON (Broadband PON). In response to the need for higher bandwidth and an efficient transport of Ethernet, the FSAN working group and the ITU have now ratified GPON for operation at rates of 2.5 Gbits/sec downstream and 1.25 Gbits/sec upstream. GPON is not backwards compatible to APON or BPON, but instead has been designed for optimal efficiency in terms of revenue bandwidth; operations, administration, and maintenance (OAM); scalability; and support for multiple services.

In parallel, the IEEE has defined Ethernet PON (EPON) under IEEE 802.3ah, using a similar point-to-multipoint network topology and a Multi-Point Control Protocol (MPCP) to communicate between the OLT and optical network units (ONUs). While the FSAN-developed ITU standards have been mainly driven by carriers and invited system vendors, IEEE specifications usually have little to no carrier involvement. Therefore, the IEEE developed EPON specifications are not being ratified nor acknowledged by ITU-T.

GPON is the latest PON technology that is getting endorsed by carriers worldwide through ITU-T. It offers a higher split ratio, longer reach, and higher downstream bandwidth compared to EPON. GPON also offers an advantage over EPON as a result of its high-efficiency mapping of Ethernet packets using a Generic Framing Procedure (GFP) -like scheme. (For a comparison of BPON, EPON, and GPON, see Table 1.)

While there are still provisions to transport ATM, almost all carriers participating in FSAN have decided to deploy GPON in its Ethernet-only version, called GPON-lite. This is where GPON beats EPON on its home turf. EPON's underlying 8B/10B encoding structure imposes a significant overhead-to-payload penalty. In the downstream direction EPON efficiency is around 73 percent, which results in 875 Mbits/sec of billable bandwidth. In the upstream direction, the bandwidth efficiency is even worse and can be as low as 61 percent. In comparison, GPON bandwidth efficiency downstream is approximately 94 percent, thereby providing 2,250 Mbits/sec of billable bandwidth. Upstream efficiency is about 93 percent.

GPON equipment offerings are still at an early stage compared to BPON or EPON offerings and there is still a cost penalty due to the infancy of the market. In addition to that, Verizon, as the carrier with the most ambitious PON deployment plans in the U.S., is deploying its ONTs on the outside of homes, which requires the optical and electrical components to work over an extended temperature range and also requires additional hardening of the system. This adds cost to BPON and GPON ONTs. NTT, on the other hand, which is deploying EPON at a large scale in Japan, is taking a different approach by installing the ONTs inside of buildings. This strategy reduces the equipment cost, since environmental hardening and extended temperature components are not required.

Both the IEEE and ITU are looking ahead to 10-Gbit/sec and WDM-based PON. WDM is looking quite attractive, since it provides a relatively straightforward route for merging and scaling of existing EPON, BPON and GPON networks.

Bandwidth within the home

While PON presents an efficient way to provide high bandwidth to the home and helps solve one problem, another key challenge carriers face is the distribution of increasing bandwidth within the residential environment. In the U.S. most homes are wired with coax cabling in addition to telephone and power lines. The in-home coax wiring tree can carry more bandwidth than either power lines or telephone lines, but a coax outlet may not be available in all rooms. Cable service providers (and satellite companies) already use the coax infrastructure to offer TV and Internet services via set-top boxes and cable modems.

Table 2 provides an overview of home networking technologies that are being developed to run on the existing in-home wiring infrastructure and the performance levels that can be achieved.

The simplest way to remove the in-home bandwidth bottleneck would be to pull new CAT6 cable within every house, but unfortunately this is also the most labor-intensive approach and carriers will try to avoid this expensive scenario as much as possible. Thus far, Multimedia over Coax Alliance (MoCA), Home Phone Networking Alliance (HPNA), and HomePlug (using power line) are the technologies that have gained traction for in-home content distribution. MoCA is getting deployed by Verizon, HPNA by AT&T, and HomePlug is being looked at by European carriers. Although wireless technology holds future potential and is quite attractive for best-effort-type services, it will probably take another few years for it to meet all requirements with regards to reliability, reach, and quality of service in order to become a viable technology for video distribution.

Application platform inside the home

At least in the near term, there will be more than one box for controlling the different applications that are being run in the home, such as phones, PCs, gaming consoles, and set-top boxes (STBs). All these boxes provide the required interfaces and are designed for their specific target applications. Signing up for new entertainment services usually means more boxes in the house. For example, a user that signs up for video-on-demand service via PON would get an ONT outside the house and a router and one or more STBs inside.

The challenge carriers face here is to re-define the functional integration of these devices and to provide the right platform for launching vertically integrated applications that can and will be adopted by the end user. The idea is not new, and there are examples of various attempts by companies to widen their application space and claim a larger stake inside the home already. Perfect examples are Nintendo's new gaming/photo/Internet/messaging/shopping console Wii and Apple's iTV STB that will let you watch movies on your wireless video iPOD by simply downloading the latest DVD from the iTunes store.

With the deployment of PON, carriers have taken a disruptive step towards opening a huge bandwidth door to every home. But defining the right platform and providing more revenue-generating applications beyond traditional voice, video, and Internet services is the challenge that remains.

Technology enablers

A key factor in the successful deployment of new services and platforms inside the home is the underlying technology that enables small-form-factor, low-power, and user-friendly systems.

On the GPON front, new system-on-chip (SoC) offerings are being introduced that integrate all of the key elements needed for cost-effective deployment. The SoC implementation must combine a variety of technologies such as forward error correction (FEC), encryption, traffic management, switching, routing, VoIP, and embedded processing for control-plane functions.

In-home networking technologies like MoCA are less integrated and usually require two or more devices. A MoCA chip set, much like a DSL chip set, has a digital component and an analog front end, which has to be complemented with external RF filters and switches. Lower-scale semiconductor technologies with sufficient isolation may enable higher integration in the near-term future.

Combining these technologies with those from existing applications platforms like PCs and STBs and defining the right level of integration are the challenges system and semiconductor vendors face now. The right decisions will allow carriers to take the next step inside the home.

Armin Schulz is senior product marketing manager at AMCC (

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