PON refers to passive optical fiber networks.In other words, there are no electronic devices or electronic power sources in the optical distribution network, and ODN is composed of passive devices such as optical splitters, without the need for valuable active electronic equipment.A passive optical network consists of an optical line terminal (OLT) installed at a central control station and a number of ancillary optical network units (ONUs) installed at the user site.The optical distribution network (ODN) between OLT and ONU consists of an optical fiber and a passive spectrometer or coupler.At present, passive optical network PON is considered as the future development direction of access network.On the one hand, because the bandwidth it provides can meet the needs of all kinds of broadband services now and in the future, it is generally favored to solve the problem of broadband access.On the other hand, the cost is relatively low in both equipment cost and operation and maintenance management.Comprehensive economic and technical analysis shows that PON is the main technology to realize FTTB/FTTH.
EPON means Ethernet Passive Optical Network. As the name implies, it is a PON technology based on Ethernet.It adopts point-to-multi-point structure, passive optical fiber transmission and provides multiple services over Ethernet.The EPON system is mainly composed of optical line terminal (OLT), optical distribution network (ODN) and optical network unit (ONU).In the EPON system, OLT is both a switch or router and a multi-service provider platform that provides fiber interfaces for passive fiber networks.
As an emerging broadband access technology, EPON achieves integrated data, voice and video service access through a single fiber optic access system with good economy.It is widely believed in the industry that FTTH is the ultimate solution for broadband access and EPON will become a mainstream broadband access technology.Due to the characteristics of EPON network structure, the special advantages of broadband access, and the organic combination with computer network, experts all over the world agree that passive optical network is the best transmission medium to realize the integration of ''three networks'' and solve the ''last kilometer'' of information superhighway.
In the EPON system, the downlink data flow adopts time division multiplexing (TDM) technology and the uplink data flow adopts time division multiple access (TDMA) technology. In this way, when the ONU receives the data packet, each ONU extracts the data packet according to the specific address information and there is no interference between ONU, which can avoid transmission conflicts.EPON technology combines low-cost and high-bandwidth Ethernet equipment with low-cost fiber network technology, which has the advantages of good compatibility, low construction and maintenance cost and high access reliability.However, it has the disadvantages of poor scalability and low cost advantage.
GPON refers to gigabit-passive Optical Networks.GPON technology is the latest generation of broadband passive optical integrated access standard based on ITU.TG.984.x standard. It is regarded by most operators as an ideal technology to realize broadband and integrated transformation of access network services.GPON technology adopts the same network topology as EPON, which is mainly divided into ONU, ODN and OLT.OLT provides the interface between the network side and the core network, and connects with each ONU through ODN.As the core functional equipment of the PON system, OLT has the functions of centralized bandwidth allocation, control of ONU, real-time monitoring, operation, maintenance and management of the PON system.ONU provides user-side interface for access network, and provides access to voice, data, video and other multi-service streams and ODN, which is controlled centrally by OLT.The branch ratio supported by the system is 1:16/32/64. With the development and evolution of the optical transceiver module, the branch ratio supported will reach 1:128.
The transmission mechanism of GPON is completely the same as that of EPON. Single fiber bidirectional transmission mechanism is adopted. WDM technology is used to transmit upstream and downstream data with different wavelengths on the same optical fiber.On the same optical fiber, GPON can realize two-way signal transmission using WDM technology.Based on the traditional tree topology, the PON protection structure can be used to improve the network survivability.GPON has three major advantages, namely, longer transmission distance, higher bandwidth and strong spectral characteristics.But the technology is relatively complex and the equipment cost is high.
The main difference between GPON and EPON is the use of completely different standards.On application,GPON has a bigger bandwidth than EPON, its business carrying more efficient, spectral ability stronger, can transmit more bandwidth business, achieve more users access, pay more attention to business and QoS guarantee, but more complex, so cost is responsible for its relative EPON is higher, but with the large-scale deployment of GPON technology, EPON and GPON is diminishing cost differences.EPON aims to be compatible with the current Ethernet technology. It is the continuation of 802.3 protocol in optical access network, fully inheriting the advantages of Ethernet, such as low price, flexible protocol, mature technology, etc., it has a wide market and good compatibility.GPON, on the other hand, is positioned as the telecommunications industry’s demand for multi-service, QoS guaranteed all-service access, and strives to seek an optimal solution that supports all services and has the highest efficiency, and proposes to “completely and completely reconsider the openness of all protocols”.EPON and GPON have different technical characteristics, which are as follows:
Ethernet is the best carrier for IP service
Easy to maintain, easy to extend and easy to upgrade
EPON equipment is mature and available. Millions of lines of EPON have been laid in Asia. The third-generation commercial chip has been launched
The EPON protocol is simple and has low implementation cost and low equipment cost. The most appropriate technology, rather than the best technology, is needed for urban access network
More suitable for domestic, metropolitan area network without ATM or BPON equipment burden
More suitable for the future, IP hosts all services, Ethernet hosts IP services
Access network for telecom operation
High bandwidth: line speed, 2.488GB /s downstream, 1.244GB /s upstream
High transmission efficiency: 94% down (actual bandwidth up to 2.4g) 93% up (actual bandwidth up to 1.1g)
Full service support: The G.984.x standard strictly defines the full service (voice, data, and video) that supports the telecommunications level
Strong management ability: rich functions, sufficient OAM domain is reserved in frame structure, and OMCI standard is established
High quality of service: a variety of QoS levels, can strictly guarantee the bandwidth and delay requirements of the service
Low comprehensive cost: long transmission distance, high spectral ratio, effective allocation of OLT cost, reduce user access cost
Due to different technical characteristics, EPON and GPON technology are actually two different market applications. EPON technology is more suitable for Internet access application type, while GPON technology is more suitable for full business operation and three-network integration application type.From the perspective of business, these are actually two market segments, but from the perspective of end users, both EPON and GPON are actually invisible to users, especially in the FTTB construction mode. Users’ terminal devices in their homes only see Ethernet interfaces and telephone interfaces, so there is no need to think about GPON and EPON.
GPON and EPON have their own features, with different application scopes and overlapping application scenarios, such as FTTB for residential users.Looking to the future of the broadband access market may not be who replaces who, should be complementary coexistence.For customers with high bandwidth, multi-service, QoS and security requirements and ATM technology as backbone network, GPON will be more suitable.For cost-sensitive, QoS and security requirements are not high customer base, EPON became the dominant.