Cable Operators Getting Aggressive on Passive Optics

BTR_Feature_Art_GPON8-19-13 The basic idea behind passive optical networks (PONs) is simple: The fewer electronic devices that are used to transmit data, the less likely it is that there will be a problem. Bicycles, after all,  break down far less often than cars. PON signals also are cleaner and are delivered at a cost that is lower than active platforms.

PONs have made inroads among cable operators, but the progress does not appear to be overwhelming, observers say. Perhaps the biggest issue that is throwing a monkey wrench into the arc of development is that there are two incompatible approaches to the technology: Gigabit PONs and Ethernet PONs.

There are two important things to be said about EPON and GPON. One is obvious, and one a bit more hidden.

The obvious fact is that EPONs and GPONs offer different data rates. Brady Volpe, the founder and principal of the Volpe Firm, said GPONs offer speeds of 2 Gbps downstream and half that up. EPONs offer symmetrical 1 Gbps speeds. Bill Beesley, the principal solutions architect for Fujitsu Network Communications, said recent advances are pushing speeds higher in both directions for EPON and in the downstream for GPON.

The more subtle difference is that, despite their similar names, GPON and EPON are completely different approaches that are not interoperable. The main reason is that the provenance of each is different: GPON was were developed by the International Telecommunication Union and EPON by the  Institute of Electrical and Electronics Engineers in its 802.3 working group.

The fact that GPON and EPON are an either/or scenario may be causing operators to delay, with the exception of Bright House Networks, which is a firm proponent of EPON. Observers say the industry is being pushed in the EPON direction by development of a set of standards in 2010 from CableLabs called Data Provisioning over Ethernet (DPoE). DPoE does two very important things: It allows DOCSIS provisioning to be used in EPONs and creates interoperability between optical networking units (ONUs) and optical line terminals (OLTs) from different vendors.

Observers agree that the functionality added by DPoE is tipping the scales toward EPON. "We see it as more of a gradual shift rather than something that is happening overnight," said Shridhar Kulkami, Aurora Networks' product manager for access network solutions.

GPON is by no means dead, however. Johnny Hill, the chief operating officer of Clearfield (NASDAQ: CLFD) said the passive optical trials in which his company is involved use GPON. Beesley added that though the scales are tipping toward EPON, some operators don’t foresee DOCSIS as the best approach for managing commercial services and backhaul business initiatives; therefore, they may be more open to GPON, at least in the short term. Volpe concurs with the idea that GPON still has life. He says operators may be learning toward EPON now, but some are struggling to decide whether to strand the investment in GPON or move ahead with those projects.

It is apparent, though, that the powers that be are aiming squarely at EPON. In addition to marrying EPON and DOCSIS through DPoE, CableLabs is developing a standard designed to extend the  EPON tool chest through an approach called Ethernet Passive Optical Network Protocol over Coax (EPoC). As the name implies, the idea is to make EPON usable over coaxial cable. The upside, said Beesley, is that it makes the expensive job of replacing the existing drops with fiber unnecessary.

EPoC will become a big deal as time moves on. PONs now are aimed at commercial services and cellular backhaul. EPoC will become an important tool in the tool chest when residential customers - and the millions of drops they use - begin to be fed by EPON architectures. "EPoC is an opportunity for the cable companies to rely on [their] deep coax infrastructure to deliver Ethernet as opposed to having do to it over fiber," said Barry Zipp, the industry marketing director for Ciena (NASDAQ:  CIEN) . "That's an important development for the cable industry."

Clearly, PON is a potent tool for the industry. It is just as obvious that the schism between the two types of PON will force operators to make strategic decisions early in the process. "The cable companies are going after small and medium-size business services, trying to find ways to lower the cost," Beesley said. "Active fiber costs a few thousand bucks and PON a few 100 bucks. If the operator is trying to get a low cost to customers for a few phones and a few megabits of data, PON is ideal for them .... They want something that offers fiber performance at cable modem price, and PON gives them that."

Carl Weinschenk is the Senior Editor of Broadband Technology Report. Contact him at

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