By Armin Schulz
AMCC
SOURCE: LIGHTWAVE
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 (www.amcc.com).
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