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PON moves forward

Feb 18, 20036 mins

The Passive Optical Networking industry has made some key steps forward since our last column on the subject two months ago. Most significantly, the ITU-T has approved the first two components of the Gigabit PON standard – G.984.1 and G.984.2 – and reached an “almost frozen” draft stage on a third, G.984.3.

The Passive Optical Networking industry has made some key steps forward since our last column on the subject two months ago. Most significantly, the ITU-T has approved the first two components of the Gigabit PON standard – G.984.1 and G.984.2 – and reached an “almost frozen” draft stage on a third, G.984.3.

This is an official “Really Big Deal” because the .1 and .2 standards have defined both the Gigabit Service Requirement (GSR) for service providers and the Gigabit Physical Media (GPM) standards. The physical media standards, among other things, define the optical characteristics of the network, and the speeds and feeds required in the upstream and downstream directions. The third piece of the standards puzzle, the protocol layer, hasn’t been ratified yet but a nearly complete draft is in place and expected to be ratified at the next meeting in October.

What this really means is that vendors in the GPON space can begin to develop products in earnest (if they haven’t already). One vendor, FlexLight Networks, has already announced general availability of a G.984.1- and .2- compliant system, and is releasing its 984.3 system ahead of the final spec with plans to make modifications per the final standard. Other Full Service Access Network (FSAN) member vendors can be expected to do so this year.

In the IEEE, work continues on standards development for EPON systems. One of the next big decisions for Ethernet PON (EPON)/Ethernet-in-the-First Mile (EFM) committee members concerns PON timing parameters. In particular, a decision is pending regarding whether the finalized EPON/EFM standard will support tight or loose timing.

Because PON Optical Network Terminals transmit data in synchronized bursts and not continuously, each transmission is proceeded by a guard time – the delay between transmissions by adjacent ONTs – as well as an initial overhead time, which allows the ONT to synchronize and adjust power levels. Tight and loose timing refers to the actual elapsed time for this guard time and initial overhead. Systems with tight timing have shorter overhead periods than loose timing systems.

The regional Bell operating companies, in their FSAN requirements, have been supporters of tight timing. We spoke about this with Brian Ford, manager of Exploratory Services in BellSouth’s Science and Technology division: “BellSouth will support tight timing (which closely matches GPON specifications) because it gives us more confidence on delivering the services we need to deliver.”

Some vendors in the EPON community feel that loose timing is best for the EFM specification, and we’ve not yet seen a clear indication regarding which way the EFM committee will go.

Ford and others in the PON industry also tell us that the adoption of these tight timing standards by the EPON/EFM folks will increase the chances of allowing common optics to be shared by both EPON and GPON vendors. This will create higher volumes and pricing advantages that can be shared by both camps. So it’s an important development to watch.

For telcos, particularly incumbent local exchange carriers (ILEC) in North America, development of standards are, of course, crucial prerequisites for any deployment. For this reason, most deployments to date have used older (and older is a very relative term in the new world of PON) Broadband PON (BPON) technology.

In our last column on the subject, we talked a bit about SBC’s trial BPON deployments. BellSouth is also moving forward with some early PON deployments using this BPON standard. While they haven’t shared exact details (like the names of the cities where they’ll be deploying), they did share with us some interesting information:

•  BellSouth is examining user demographics in their top 10 cities to identify areas for PON deployments. In particular, BellSouth is looking at greenfield deployments in areas with high growth. The service will initially be focused on business services, not residential. BellSouth is already pursuing a Fiber-to-the-Curb deployment architecture for residential customers (bringing fiber to within 500 ft. of many residential customers), and will probably continue to offer asymmetric DSL data services and coax-based video services to those customers in the near term.



Completely gelled standards and successful trial deployments are, of course, key factors in moving ILECs ahead with PON deployments. Equally important in our mind are forthcoming Federal Communications Commission decisions about competition in the local loop. We don’t have a crystal ball telling us exactly what is coming in the Triennial Review, but we’re reasonably sure that it will be good news from the ILEC perspective.

The deployments of PON in the U.S. ILEC territories will be in the tens this year, hundreds next and thousands in the year after that, ramping towards mass market penetration in the latter part of 2005, we believe. The solidifying of the GPON standards – backed by most service providers – combined with the consistent progress on the EPON front have significantly moved PON forward. We expect the announcement soon of several completed trials and their results, all of which anecdotally we have heard have been going quite well in hashing out Fiber-to-the-Home and -Business network and service processes and procedures – a critical step for the ILECs before serious service launches. We are watching for further developments in the lasers, as the ability to use common lasers regardless of EPON or GPON approaches will be what drives down the price significantly towards mass-market levels.

“We are letting both groups know very clearly that that is something we’d like to see and see soon so that we can get the costs down to the point where this is something we do widely,” Ford said.

For more information on GPON, FSAN, EPON, and PON in general, we recommend taking a look at the FSAN’s new Web site:, the site, and the EFM Alliance site at