Broadband Access: Wireline and Wireless - Alternatives for Internet Services

3IEEE Passive Optical Networks

3.1 Introduction

IEEE 802.3 has developed two PON (point-to-multi-point) protocols based on their point-to-point protocols of the same rate. These include the Ethernet PON (EPON) protocol based on 1 Gigabit/s Ethernet and the 10G EPON protocol based on 10 Gbit/s Ethernet. EPON has seen extensive use, especially in Asia, with Japan taking the lead role in deploying it. Its re-use of Ethernet technology has given it some significant benefits, and 10G EPON is expected similarly to benefit from 10 Gbit/s Ethernet technology.

EPON uses 1 Gbit/s rates in both the upstream and downstream directions, and 10G EPON uses a 10 Gbit/s downstream rate with both 1 and 10 Gbit/s supported in the upstream direction. The downstream directions of both protocols are essentially the same as for point-to-point Ethernet streams of those rates, with some changes to the Ethernet frame overhead and additional management frames defined in order to support the point-to-multipoint operation. The upstream direction uses a TDMA protocol in which the ONU upstream transmissions are bursts compromised of Ethernet frames. No frame fragmentation is allowed.

In order to maximize backward compatibility and to allow co-existence on the same PON, 10G EPON is largely an extension of the EPON protocol (which is described in detail in the first section of this chapter). The second section describes 10G EPON protocol primarily in terms of how it differs from EPON. The differences between ...