For the past 15+ years the majority of PON (Passive Optical Network) equipment sold worldwide has been based on the GPON (Gigabit-capable PON) standard.  This is the story of how GPON was created and why it became universally adopted.  Even though this is nearly 20 years old, this story is relevant today because it offers a lesson on the importance of industry standards and the importance of the specific standards bodies that create them.

In the Fall of 2003, the FSAN group completed the GPON standard.  It was formally submitted to the International Telecommunications Union (ITU-T) and subsequently ratified in February 2004.  Those of us who worked on it were pleased with what we created and had great hopes for it.  But the rest of the world expected GPON to go nowhere.  When the ITU announced its ratification, the only thing we heard was the sound of crickets! 

That’s because in 2004 the Internet world was abuzz with anticipation of the upcoming Ethernet PON (EPON) standard.  They were convinced it was going to be the global leader because EPON was an Ethernet standard, and Ethernet had an impressive record of beating out competing standards.

EPON, with symmetric downstream/upstream speeds of 1 Gbps/1 Gbps, was the IEEE’s first foray into a PON standard.  It was part of their Ethernet in the First Mile (or EFM) project.  Prior to this, Ethernet was essentially a peer-to-peer protocol.  In other words, each node on an Ethernet network operated autonomously.  It obeyed the same set of rules as every other node.  But the unique characteristics of a PON or any P2MP network cannot accommodate a peer-to-peer framework; an ONU cannot operate under the same rules as the OLT.  The IEEE was faced with a choice: it could have created a new standard like they did with Wi-Fi, 802.11, which also is a P2MP network.  But, for whatever reason, they decided to make EPON part of Ethernet standard, 802.3, despite the incompatibility.  Consequently, the EPON working group faced a monumental task of melding controller/client capabilities into the peer-to-peer structure of 802.3.  Essentially, they were asked to fit a square peg in a round hole.  What they accomplished was very clever.  For example, they effectively perform encapsulation by repurposing several bytes from the Preamble for the requisite header.  Ultimately, the EPON specification was released as part of 802.3ah in September of 2004.

When EPON equipment first became available in 2005, it entered a market where GPON had been selling for nearly a year.  The company I worked for, Optical Solutions, actually started shipping product in late 2003. In those early years our equipment used the lower bit rate option of 1.2 Gbps/622 Mbps.  So when EPON became available it had a 2x advantage over GPON in terms of upstream speed.  But EPON never took off, at least not in the US market that I’m familiar with.  In fact, I don’t recall EPON ever being a significant threat.  Our GPON sales did well initially and kept growing at a healthy rate.  By about 2007, all of us GPON vendors had switched to the 2.4 Gbps/1.2 Gbps option and we never hear about EPON again.

In 2009 the IEEE published a 10-Gbps version of EPON.  In keeping with their rule of only using powers of 10, the new version used 10 Gbps downstream and 1 Gbps upstream.  This new standard may have found some applications in Asia.  In the US there was only modest interest; mostly from Cable operators moving away from coax to all-fiber networks.  But it too never made much of a splash in the U.S. market.

GPON, on the other hand, went on to become the most successful PON standard in history.  I attribute this success to a couple of things.  First, at the risk of being self-congratulatory, GPON was written by folks from companies who had years of experience engineering PON equipment.  Second, and most importantly, the FSAN group had the structure that put operators in charge.  And the operators had the wisdom to accept two options for D/S and U/S bit rates and they had the courage to let us codify the new and untested encapsulation method we now know as GEM.

Of course, GPON soon will be surpassed by a new, higher speed standard.  But for a technology that was expected to go nowhere, GPON has definitely had a pretty good run!