EPON is based on long-distance
optical fiber transmission
network Ethernet access technology. EPON uses multipoint architecture,
an optical fiber carrying data signals down the line, after 1: N optical
splitter signal into N Road, branch coverage of light multiple access
point or access users.
EPON network structure
EPON
and GEPON term in tradition, there is not a state error. Early EPON
equipment industry is based FE bus, bus-based EPON equipment GE
launched, in order to distinguish called GEPON, EPON equipment industry
at present is essentially based on GE bus. At present basically referred
to EPON.
A typical system consists of
EPON system is composed of OLT, ONU and ODN. EPON network structure shown in Figure 1.
OLT in the center machine room, it can be seen as a L2 switch or L3
routing switch. In the downstream direction, OLT to provide for passive
optical network (ODN) optical interface; In the upstream direction, OLT
will provide GE optical or electrical interface, the future of 10Gbit/s
Ethernet technology standards after setting, OLT will also support a
similar high-speed interface. In order to provide multi-service access,
OLT also supports E1 and OC3 interfaces, to achieve the traditional
voice access or circuit relay service.
In terms of EPON network
management, OLT is the main control center, the built-in OAMP Agent, can
manage the ONU in its terminal equipment, to achieve the five functions
of network management. EPON network management can be defined on the
OLT through the user bandwidth parameter to control the quality of user
services by writing an access control list to implement network security
control, by reading the MIB to obtain system status and user status
informatioin, but also provide a valid user isolation.
ODN is the
optical distribution network, composed of passive optical splitter and
fiber composition. The passive optical splitter is connected to the OLT
and the ONU passive device, its function is to distribute the downlink
data and uplink data centralized. The deployment of passive optical
splitter is quite flexible, because it is a pssive device, be adapted to
almost all environments. Generally passive optical splitter ratio has
1:2,1:4,1:8,1:16,1:32,1:64 so on. General recommended a splitting,
splitting up not more than two.
ONU is placed on the customer
premises side of the terminal device, EPON ONU in the Ethernet protocol,
the realization of the second layer of low-cost Ethernet switching. The
use of the Ethernet protocol, the process of the communication protocol
conversion is no longer necessary to achieve the ONU transparent
transmission of user data. Between the OLT to the ONU using encryption
protocol to ensure the security of user data.
Based on EPON FTTH's
advantage lie in its strong converage, as far as covering up to 20 km
(1:32 split ratio), starting from the end office, after OND connecting
the optical access point.
Traditional optical access network,
optical fiber extends the range to the network access point cutoff
general, to achieve fiber to the home, you need to configure a large
number of the access point port access layer switch expensive. With the
passive optical network technologies emerge and mature, especially now
that the EPON technology that can provide fiber tip directly to the
user's economically viable solution, FTTH become efficient access. In
FTTx solution based on EPON, the introduction of how to solve the
optical cable to the building, community, planning OLT, ODN, indoor user
terminal (OUN) optical fiber connection becomes key.
EPON uplink and downlink technology
Between
the OLT and ONU EPON using a single optical fiber to provide symmetric
1.25Gbps bandwidth limitations by physical interface, the actual
provision of 1Gbps bandwidth to transmit data, voice and video services.
EPON in a singel fiber using WDM technology, the upper and lower rows
of data streams are transmitted in different frequency bands. Among
them, the downstream 1490nm, upstream 1310nm, 1550nm optional for CATV.
Downlink
data stream using broadcast, OLT will be 802.3 Ethernet frame format
data flow through unicast replication pushed all the way at the ONU; ONU
Ethernet frame header by determining where the OLT assigned LLID
(Logical Link ID ) to determine whether the received data frame received
their own, their data will not discard the frame. Shown in Figure 2.
Upstream
data stream using time division multiple access (TDMA) technology, the
uplink time into a number of time slices, according to the allocated
bandwidth and service ONU priority to the ONU upstream data streams are
allocated different time slots, each time point the optical fiber
transmission is only one ONU upstream data streams. Negotiated between
the OLT and ONU, ONU upstream avoid conflicts between, will not cause
data loss. Shown in Figure 3.
EPON and ADSL comparison
ADSL
After several years of vigorous development, has become China's most
popular fixed-line operators in broadband access means. ADSL using
traditional copper broadband data transmission resources, make full use
of the fixed-line operator's copper resources, China Telecom and China
Netcom such operators, the early development of broadband access is one
of the best choices.
ADSL/ADSL2 + Business is an asymmetrical
transmission of broadband access technologies, the uplink bandwidth is
limited, less than 1M, downstream bandwidth up to 26Mbps, the actual
business of covering no more than 3km distance, generally offer 512Kbps
to 2Mbps downstream bandwidth, the main application the public Internet.
However,
with a variety of new businesses, especially the rise of video
services, the user's bandwidth requirements are increasing. With the
long, online games, instant messaging, broadband telephony, video
telephony, personal photo album sharing applications such as the rapid
growth of users of the upstream bandwidth demand is also growing.
China
Telecom and China Netcom broadband network in the planning of their
future bi-directional bandwidth of individual users will reach 10M-20M.
ADSL bandwidth strictly limited by the transmissioin distance, the
higher the bandwidth achieved only over short distances, even after the
"Light of Copper" reform, reducing the coverage of ADSL, which is only
in a certain period of time, to a certain extent bandwidth requirements.
Based
on fiber access networks, the bandwidth is theoretically unlimited
extension. So with the EPON technology matures, its high bandwidth, long
distance coverage, making EPON technology replacing ADSL technology
will become the inevitable choice.
Relative ADSL, EPON at
relatively high initial construction expenditures, including pre-laying
equipment costs and fiber costs. However, due to network using passive
optical network technology, fiber-based PON technology in the operation
and maintenance of the costs to be much lower than ADSL and copper wire.
By
the late operation and maintenance cost is reduced, provide higher
bandwidth and more long-distance business coverage, and the resulting
ability to provide more new business, bring more revenue, can be
relatively offset on the cost of equipment and wiring. The fiber cost is
already very low, FTTx has entered a golden period of development, the
cost of equipment will also continue to reduce in the building. Thus,
through the deployment of EPON carriers can be enhanced, including
broadband access, including a comprehensive business competitiveness,
thereby stabilizing the user resources, and even brought the loss of the
user's back, it will be for operators to bring more revenue, enabling
operators to long-term benefit.
EPON technical advantages
With
EPON technology matures, the industry mainstream operators have started
large-scale deployment of EPON system, expand FTTx applications, and on
this basis to achieve Triple Play (triple play, to deliver voice, data
and video services), build triple play access platform.
Since
2004, the most developed in FTTH in Japan, Korea, Taiwan and the United
States, Europe and other countries and regions, EPON technology has been
large-scale applications, and further stimulate the IPTV business
prosperity. In the Chinese market, the current EPON products have been
held in all provinces of the pilot and commerical.
EPON technology
uses wavelength division multiplexing (WDM) technology in a single
fiber to achieve symmetrical 1Gbps bandwidth and client segments and can
be implemented in close spectroscopic down, save a lot of backbone
fiber resources. Currently the maximum achievable split ratio is 1:64.
EPON system is another advantage lie in its strong coverage in the 1:32
split ratio furthest covering up 20km, at 1:64 next, as far as coverage
bandwidth of each ONU user up to 30M or more, so that the video business
has been enough bandwidth guarantees.
The use of passive
optical splitter, save a lot of maintenance resources, saving room, power matching and other resources, reducing the overall cost of
FTTx network
construction and maintenance costs. In recent years, the cost of fiber
optic drop cable for the FTTx provide supporting cost reduction.
At
present the operators to provide broadband access services are mainly
two kinds of ADSL and LAN access, in addition, with the increasing
demand for bandwidth, VDSL is becoming an option. Other access methods,
such as Cable Modem, power line access, etc. As the market share of
small and are subject to industry resource constraints.
