ZyXEL Communications P-3202HN-Ba User Manual page 242

Appendix A Passive Optical Networks
Ethernet PON (EPON), meanwhile, offers slightly slower data transmission rates
but shows a smaller overhead and is markedly better at transmitting over the
Ethernet layer using IP. Because Ethernet is so widespread and relies on a well-
established universal networking protocol, manufacturers can use existing
hardware to build EPON units, making it a very cost effective solution in
comparison to the other types of PON devices available. Moreover, Ethernet cables
(RJ-45) and infrastructure already exist in many office buildings, so making the
transition to EPON is even easier.
GEPON is the other name by which EPON is known and marketed. For all intents
and purposes, it is the same. Both fall under the purview of the IEEE802.3ah
specification.
Gigabit Ethernet PON (GPON) offers a speed boost over APON/BPON and EPON. It
retains ATM compatibility in addition to offering Time-Division Multiplexing (TDM).
It can utilize both the ATM and Ethernet transport layers, but only by emulating
them with the Generic Encapsulation Protocol (GEM).
The following table outlines the major differences between the three PON
protocols.
Table 79 PON Types Comparison
PARAMETERS
Standard
Standardization Date
Speed
Basic Protocol
Protocol Overhead for
IP
US MAC Scheme
Coding Line
BER
ODN Type
Max Reach
Standard Driver
PON Limitations
The most significant limitation of PON is something known as "attenuation." This is
the gradual decrease in signal strength as the light wave passes down the fiber
optical cable stemming from a combination of absorption and scattering.
242
EPON/GEPON APON/BPON
IEEE802.3ah ITU-T (FSAN)
2004.07 1998 ITU.T G.983
1 Gbps 155/622 Mbps
622/1244 Mbps
Ethernet ATM
Small Large
TDMA TDMA
8B/10B Scramble NRZ
-12
10 10
Type1, Type2 Class A, B
Type1 up to 10 km 20 km
Type2 up to 20 km
Vendors Service Provider
GPON
ITU-T SG15 (FSAN)
2003.11 ITU.T
G.984
1.25 Gbps
symmetric and
higher (up to 2.488
Gbps)
Ethernet/ATM/TDM
Middle
TDMA
Scramble NRZ
-10 -12
10
Class A, B, C
20 km (Max 60 km
for ranging
protocol)
Service Provider
IAD User's Guide