558
13 Fiber Optic Communication Networks
office to the user can be up to 20 km. Thus active devices exist only in the central
office and at the user end.
Several alternative PON implementation schemes have been used since the passive
network concept inception [61–65]. The main ones are as follows:
• Broadband PON (BPON) is based on the G.983.1 to G.983.5 series of ITU-T
Recommendations that specified the asynchronous transport mode (ATM) technique as the transport and signaling protocol. This legacy PON has been phased
out due to its relatively high cost compared to Ethernet and its incompatibility
with current IP over DWDM technology.
• Gigabit PON (GPON) was the next evolution of the BPON standard. GPON
provides downstream speeds of 2.5 Gb/s and upstream speeds of 1.25 Gb/s. It is
based on the G.984.1 to G.984.6 series of ITU-T Recommendations. Typically 32
users share the bandwidth. A drawback of GPON is that it uses an inefficient and
complicated data encapsulation method that is time-consuming and adds cost to
the terminal equipment in both the central office and at the user locations.
• Ethernet PON (EPON) or gigabit Ethernet PON (GE-PON) uses 1-Gb/s Ethernet
as the underlying protocol. The EPON operation is described in the IEEE 802.3
EPON standard (several versions of 802.3 have been ratified by IEEE during its
evolution depending on the latest data rate capabilities). Because Ethernet devices
are used universally from the home or business all the way through worldwide
backbone networks, EPON provides efficient connectivity for any type of IP-based
traffic. Thus EPON can be much more cost-effective compared to GPON.
• Moving beyond the capabilities of EPON are the 10-Gb/s PON technologies.
The two main versions are called XG-PON (or 10G-PON) and XGS-PON. The
XG-PON version specifies an upstream rate of 2.5 Gb/s and a downstream rate
of 10 Gb/s. XGS-PON is a symmetric version that transmits at 10 Gb/s in both
the upstream and downstream directions. These versions are based on the IEEE
802.3av EPON standard and on the ITU-T Recommendation G.987 series for
sending both upstream and downstream traffic at 10 Gb/s. The 10 Gigabit PON
wavelengths are 1577 nm for downstream and 1270 nm for upstream transmissions. These differ from the 1490-nm downstream/1310-nm upstream wavelengths of GPON and EPON, thereby allowing 10G-PON systems to coexist on
the same fiber with either of the earlier PON versions.
• A further extension of PON capabilities is the NG-PON2 (Next-Generation
PON2), which operates at 40 Gb/s in both the upstream and downstream directions (IEEE 802.3ca). To enable simultaneous implementation on the same fiber
as all earlier generation PONs, the NG-PON2 wavelengths are 1524 to 1540 nm
for upstream transmissions and 1596–1603 nm for downstream traffic.
• WDM PON uses a different wavelength for each user to greatly enhance network
capacity. In this architecture a wavelength multiplexer (usually an AWG) is used
in place of the power splitter shown in Fig. 13.40. Its flexible service offering is
a major advantage of a WDM PON compared to other PON types. Because each
user has a dedicated wavelength that is not shared with others, a customer with
very high bandwidth demands can easily be
13 Fiber Optic Communication Networks
office to the user can be up to 20 km. Thus active devices exist only in the central
office and at the user end.
Several alternative PON implementation schemes have been used since the passive
network concept inception [61–65]. The main ones are as follows:
• Broadband PON (BPON) is based on the G.983.1 to G.983.5 series of ITU-T
Recommendations that specified the asynchronous transport mode (ATM) technique as the transport and signaling protocol. This legacy PON has been phased
out due to its relatively high cost compared to Ethernet and its incompatibility
with current IP over DWDM technology.
• Gigabit PON (GPON) was the next evolution of the BPON standard. GPON
provides downstream speeds of 2.5 Gb/s and upstream speeds of 1.25 Gb/s. It is
based on the G.984.1 to G.984.6 series of ITU-T Recommendations. Typically 32
users share the bandwidth. A drawback of GPON is that it uses an inefficient and
complicated data encapsulation method that is time-consuming and adds cost to
the terminal equipment in both the central office and at the user locations.
• Ethernet PON (EPON) or gigabit Ethernet PON (GE-PON) uses 1-Gb/s Ethernet
as the underlying protocol. The EPON operation is described in the IEEE 802.3
EPON standard (several versions of 802.3 have been ratified by IEEE during its
evolution depending on the latest data rate capabilities). Because Ethernet devices
are used universally from the home or business all the way through worldwide
backbone networks, EPON provides efficient connectivity for any type of IP-based
traffic. Thus EPON can be much more cost-effective compared to GPON.
• Moving beyond the capabilities of EPON are the 10-Gb/s PON technologies.
The two main versions are called XG-PON (or 10G-PON) and XGS-PON. The
XG-PON version specifies an upstream rate of 2.5 Gb/s and a downstream rate
of 10 Gb/s. XGS-PON is a symmetric version that transmits at 10 Gb/s in both
the upstream and downstream directions. These versions are based on the IEEE
802.3av EPON standard and on the ITU-T Recommendation G.987 series for
sending both upstream and downstream traffic at 10 Gb/s. The 10 Gigabit PON
wavelengths are 1577 nm for downstream and 1270 nm for upstream transmissions. These differ from the 1490-nm downstream/1310-nm upstream wavelengths of GPON and EPON, thereby allowing 10G-PON systems to coexist on
the same fiber with either of the earlier PON versions.
• A further extension of PON capabilities is the NG-PON2 (Next-Generation
PON2), which operates at 40 Gb/s in both the upstream and downstream directions (IEEE 802.3ca). To enable simultaneous implementation on the same fiber
as all earlier generation PONs, the NG-PON2 wavelengths are 1524 to 1540 nm
for upstream transmissions and 1596–1603 nm for downstream traffic.
• WDM PON uses a different wavelength for each user to greatly enhance network
capacity. In this architecture a wavelength multiplexer (usually an AWG) is used
in place of the power splitter shown in Fig. 13.40. Its flexible service offering is
a major advantage of a WDM PON compared to other PON types. Because each
user has a dedicated wavelength that is not shared with others, a customer with
very high bandwidth demands can easily be