25-Gigabit PON

The industry has barely broken ground on 10-gigabit PON technology in terms of market deployments, and the vendors in the industry have already moved on to 25-gigabit PON technology. I know a few ISPS that are exclusively deploying 10-gigabit XGS-PON, but most ISPs are still deploying the fifteen-year-old GPON technology.

As a short primer, PON (passive optical network) technology is a last-mile technology that uses one laser in a core location to communicate with multiple customers. In the U.S., most ISPs don’t deploy GPON to more than 32 customers. The passive name in the technology is due to the fact that there are no electronics in the network between the core laser and the customer lasers. GPON technology delivers 2.4 Gbps of bandwidth to a PON (a group of customers connected to the same core laser). The upgrade to XGS-PON brings something close to 10 Gbps to PON, while the 25-GS-PON will bring 25 Gbps.

The PON technology is being championed by the 25-GS-PON MSA (multisource agreement) Group that has come together to create a standard specification for the 25-gigabit technology. It’s worth a glance at their website because it’s a virtual who’s-who of large ISPs, chip manufacturers, and electronics vendors.

I’m not hearing a lot of complaints yet about ISPs who are seeing GPON technology being overwhelmed in residential neighborhoods. I’ve asked recently, and most of the small ISPs I queried told me that individual neighborhood PONs average about 40% utilization, meaning that 40% of the bandwidth to customers is being used at the same time. ISPs start to get worried when utilization starts routinely crossing 80%, and ideally, ISPs never want to hit 100% utilization, which is when customers start getting blocked.

The cellular carriers were the first champions of 10-gigabit PON technology. This is the most affordable way to bring multi-gigabit speeds to small cell sites. The network owner can deploy a 10-gigabit core and communicate with multiple small cell sites without needing the extra field electronics used in a Metro Ethernet network. The 25-gigabit technology is aimed at cell sites and other large bandwidth users.

The technology is smartly being designed as an overlay onto existing GPON and XGS-PON deployments. In an overlay network, a GPON owner can continue to operate GPON for residential networks, can operate XGS-PON for a PON of businesses with larger bandwidth requirements. The 25GS-PON would be used for the real heavy hitters or perhaps to create a private network between locations in a market.

I’ve been thinking about the benefits of 25GS-PON over the other current GPON technologies.

  • This is a cheaper technology than the alternatives. The MSA group has designed this to be a natural progression beyond GPON and XGS-PON. That means most of the components of the technology benefit from the huge manufacturing economy of scale for PON technology. If 25G-PON costs are low enough, this could spell the eventual end of Metro Ethernet as a technology.
  • It’s a great way to bring big bandwidth to multiple customers in the same part of a network. This technology can supply bandwidth to small cell sites that wasn’t imaginable just a few years ago.
  • The technology is easy to add to an existing network by sliding a new card into a compatible PON chassis. That means no new racks in data centers or new shelves in huts.

Electronics manufacturers have been frustrated by how long the GPON technology has remained viable – and in many applications might be good for years to come. Telecom manufacturers thrived in the past when there was a full replacement and upgrade of electronics needed every seven years. Designing 25-gigabit PON as an overlay is an acknowledgment that upgrades in the future are going to be incremental, and upgrades that don’t overlay onto existing technologies will likely be shunned. ISPs are not interested in rip and replace technologies.

The 25GS-PON technology might become commercially available as early as the end of 2022. There have already been field trials of the technology. After that, the vendors will move on to the next PON upgrade. There’s already talk of whether the next generation should be 40-gigabit or 100-gigabit.