TECHNOLOGY
PON Versus Plus Active Ethernet
For years, FTTH deployers and vendors argued the merits of passive and active optical networks. The best answer: Use each technology where it makes the most sense.
By David Stallworth ■ OFS N
etwork builders often ask me, "Which fiber-to-the-home tech- nology should I deploy, passive
optical network (PON) or active Eth- ernet (AE)?" My answer often surprises the questioner because my answer is not PON or AE. Figure 1 shows the outside plant
(OSP) design for AE. Two choices are available: one
requires placing active
equipment in the field, and the other re- quires terminating a separate fiber in the central office (CO) for each unit served. Active equipment in the field re-
Figure 1: Active Ethernet Design Splitters may be placed in centralized
Network designers have a number of different design options for deploying fiber-to-the-home networks.
quires supporting structures (cabinets) as well as backup power. Using this design may make sense if the equip- ment is connected by a fiber ring built around the area served. A ring provides redundancy because it allows data to be rerouted if a fault occurs on the primary route to the CO. When fibers are terminated in the
CO, the costs of terminating bays, jumpers and CO square footage must be included in the analysis. Tis design is called "home run" because a fiber has to be run from the CO directly to each unit served.
Figure 2 shows two conventional
ways to deploy a PON design. A PON includes an optical splitter somewhere in the network between the optical line terminal (the OLT, which is usually in the CO) and the ONT at the unit served. Te typical split ratio is 1x32, although other ratios can be used.
About the Author
David Stallworth is the design and product manager at OFS, a manufacturer of optical fiber and connectivity solutions. You can reach him at 770-798-2423 or by email at dstallworth@ofsoptics.com.
24 | BROADBAND COMMUNITIES | www.broadbandcommunities.com | JULY 2012
cabinets that each serve several hundred homes. (Research suggests that the ideal cabinet size in most urban or suburban single-family neighborhoods
serves an
area of between 256 and 288 homes.) Another possibility is to distribute split- ters throughout a network, placing each splitter in the middle of the 32 units it serves. A third alternative, not shown, is to home run the fiber in a manner simi- lar to the AE home-run option.
COMPARING THE COSTS
To compare these options requires exam- ining the costs of both the OSP and the equipment. At the beginning of the cen-