By Edward Boyd, Tibit Communications, Kevin A. Noll, Time Warner Cable, Saifur Rahman & Nagesh Nandiraju, Comcast Cable, and Fernando Villarruel, Cisco Systems
Ethernet Passive Optical Network (EPON) systems have been successfully deployed worldwide for high-speed access networks and are enjoying a growing adoption by cable operators.
However, MSO access networks have challenges beyond the capabilities of traditional PON solutions. First, many operators have fewer trunk fibers to the node available for PON than required for a large number of subscribers. Second, Cable operators often find that their current access networks reach farther than the distances supported by traditional PON solutions. Greenfield deployments offer little relief because they are sometimes located far from the operator's existing head end or hub sites.
In an attempt to simplify maintenance, reduce operational costs, and improve reliability, many operators prefer a centralized network deployment model which reduces the number of head ends and hub sites and aggregates many customers over a large service area. Collapsing the head ends and hub sites in favor of a more centralized model naturally leads to longer distances between the network aggregation systems and the customers. This escalates the difficulties related to reaching those customers using traditional PON architectures.
Operators need a way to support a longer reach network that uses existing PON standards, technology, and systems. One approach to this problem can be gleaned from the network topology used in HFC architectures in use today. A remote NODE can provide an enclosure for an active PON device to extend the reach, minimize the fibers required to serve subscribers, and allow for large centralized systems.
This paper compares and contrasts several solutions for implementing a PON in a NODEbased architecture. The solutions examined here will include a simple PON extender, a remote optical line terminal (OLT), and a distributed PON MAC/PHY solution. Each solution is examined for its impact on trunk fiber efficiency, equipment cost, power, subscriber count, physical space, PON efficiency, physical layer performance, packet jitter, and packet delay. The operator requirements for the remote PON network are discussed to highlight the differences between these solutions and their impacts to the service opportunities.