The burst sizes, as well as the physical layer overhead, are large in EPONs. As
an example, let??™s consider the maximum automatic gain control (AGC) interval, which
is set to 400 ns, thus providing enough time for the optical line terminal (OLT) to adjust
gain without the need for optical network units (ONUs) to perform power-leveling. This
simplicity enhances robustness and reduces cost. Additionally, because the laser on and
off times are capped at 512 ns, a value significantly greater than that of GPON (16-bit
times), lower quality, and thus much cheaper lasers, as well as receiver modules, can
be used in EPON systems.
Moreover, EPON interfaces seamlessly with an IP core network, due to its inherent
capability to carry variable sized datagrams, transparency for higher network layers,
simplicity and OAM robustness. Newly adopted quality-of-service (QoS) techniques, including
full-duplex transmission mode, prioritization (IEEE 802.1p), and virtual LAN
(VLAN) tagging (IEEE 802.1Q), make Ethernet networks capable of supporting voice,
data, and video. Not surprisingly, Ethernet is poised to become the architecture of
choice for next-generation subscriber access networks.
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