Guest editorial

Passive optical network (PON)-based access technology represents a profound departure from the ??traditional,?? point-to-point twisted-pair-based network architecture that telecommunications operators have used for more than 100 years. First, it is an optical network that employs different components, relies on different design principles, and requires different deployment, troubleshooting, and maintenance procedures. Second, a timedivision multiple access (TDMA)-PON, which includes IEEE Ethernet PON (EPON) and International Telecommunication Union Telecommunication Standardization Sector (ITU-T) Gigabit PON (GPON), can be viewed as a form of distributed switch that spans the entire access area. All of the intelligence of this distributed switch is concentrated in the edge devices, while the switching fabric is just a passive point-to-multipoint medium. To ensure seamless delivery of the various services, quality of service (QoS) enforcement, various network monitoring features, and various power-saving modes, the optical line terminals (OLTs) and optical network units (ONUs) must fully interoperate at all protocol layers. At the same time, the OLT and ONUs are separate physical devices, which typically are supplied by different vendors.