I. EPON technical standards and comparison between EPON and GPON
With the rapid development of broadband services, IPTV and other new broadband services are gradually valued and expected by everyone, and the large-scale application of these broadband services is undoubtedly inseparable from the support of broadband access network technology. As a broadband optical access technology to FTTH, PON has attracted great attention from the market since it was put forward.
Standardization of 1. 1 EPON technology
EPON technology was first proposed and standardized by IEEE802.3ah project team, namely EFM (the first mile of Ethernet). The main goal of EFM is to promote the application of Ethernet technology in user access network. This standard is a supplement to the IEEE 802.3 standard, and follows the original MAC sublayer, MAC control sublayer and related physical sublayer of IEEE 802.3 as much as possible. In addition, the standard also includes the content of network operation management and maintenance (OAM) mechanism, which is convenient for network operation and fault handling.
EFM defines two EPON interfaces, namely 1000BASE-PX 10 and 1000BASE-PX20. 1000BASE-PX20-D can interoperate with 1000BASE-PX 10-U, and support the upgrade of10km2mp network to 20km network.
EFM also gives the point-to-multipoint (P2MP) topology supported by EPON, which can be realized in three ways: single splitter topology, tree topology and mixed media topology. Among them, the mixed media topology combines point-to-point (P2P), P2MP optical connection and copper link.
The communication industry standard of EPON in China is mainly drafted by the Access Network Working Group of CCSA TC6 (Transmission Network and Access Network Technical Committee). The technical requirements of EPON were formulated in March 2003, and are currently in the stage of soliciting opinions. The testing method of EPON was established in June 2005 at 5438+0, and the standardization work is expected to be completed in early 2006.
China's draft EPON standard mainly refers to the requirements of IEEEStd802.3ah-2004 for PMD sublayer, rs sublayer, OAM sublayer and MPCP protocol of EPON system, and modifies the relevant contents in combination with China's actual application requirements, and at the same time, it also increases the specifications of EPON system in terms of business capabilities, business interface types, system functions and network management.
Characteristics of 1.2 EPON
1, there are only optical passive devices such as optical fiber and optical splitter between the local office (OLT) and the user (ONU), so there is no need to rent a computer room, equip with power supply and maintain active equipment, which can effectively save construction and operation costs;
2.EPON adopts Ethernet transmission format, which is also the mainstream technology of local area network/resident network. The natural integration of the two technologies eliminates the cost factor caused by complex transmission protocol conversion;
3. Using single fiber wavelength division multiplexing technology (downlink 1490nm, uplink 13 10nm), there is only one backbone fiber and one OLT, and the transmission distance can reach 20 kilometers. On ONU side, it is distributed to up to 32 users through optical splitter, so the cost pressure of OLT and backbone optical fiber can be greatly reduced;
4. Uplink and downlink are gigabit rates. Downlink uses encrypted broadcast transmission for different users to enjoy the bandwidth, and uplink uses time division multiplexing (TDMA) to enjoy the bandwidth. High-speed broadband fully meets the bandwidth requirements of access network customers, and can dynamically allocate bandwidth conveniently and flexibly according to the changes of user needs;
5. Point-to-multipoint structure, the system can be easily expanded and upgraded only by increasing the number of ONU and a small number of optical fibers at the user end, which fully protects the investment of operators;
6.EPON has the ability to transmit TDM, IP data and video broadcasting at the same time, in which TDM and IP data are transmitted in IEEE 802.3 Ethernet format, supplemented by carrier-level network management system, which is enough to ensure the transmission quality. By extending the third wavelength (usually 1550nm), the broadcast transmission of video service can be realized.
As can be seen from the above, EPON optical access system has the advantages of fast and flexible network deployment, multi-service, high-performance access and high cost performance.
Comparison between 1.3 GPON and EPON technology
According to the different characteristics of GPON and EPON technologies, we can analyze these two technologies as follows.
1.GPON supports multiple rate levels, and can support asymmetric uplink and downlink rates. Uplink may not necessarily support rates above 1 Gbit. Therefore, compared with EPON, which can only support symmetric 1 Gbit single rate, GPON has greater redundancy in the selection of optical devices, thus reducing the cost.
2.EPON only supports ODN grades of Class A and Class B,
GPON can support Class A, Class B and Class C, so GPON can support split ratio as high as 128 and transmission distance as long as 20km.
3. In terms of protocol, EPON standard is based on 802.3 architecture, so compared with GPON standard, its protocol layering is simpler and the system implementation is easier. In view of the maturity of Ethernet chip, its system cost is low.
4.ITU has followed many concepts of APON standard G.983 in the process of formulating GPON standard, which is more perfect than EPON standard formulated by EFM. However, due to the increase of TC sublayer, it also increases some overhead, which runs counter to the hope that Ethernet technology can be simple and economical to some extent.
The characteristics of this original intention. Therefore, defining an efficient TC layer mechanism will become the key for ITU to formulate GPON standards.
5.GPON standard stipulates that TC sublayer can be encapsulated by ATM and GFP, among which GFP encapsulation is suitable for carrying IP/PPP and other packet-based high-level protocols. However, it remains to be discussed whether the ATM encapsulation defined to support ATM services is suitable for GPON system based on Ethernet.
6. The technology of carrying TDM services on Ethernet is not mature, and it is difficult to meet the QoS requirements of operators. Therefore, EPON must design a new MAC mechanism and add new software and hardware to carry TDM services and voice services. GPON can easily support TDM services and voice services due to its designed TC sublayer structure and ATM encapsulation mode, and adopts the frame length and timing mechanism of 125us.
Second, the advantages of using GEPON system for FTTH multi-service integrated access
Multi-service integrated access network structure of 1 and GEPON system
Deploy OLT: optical line terminal (OLT) equipment MSC in the operator's marginal computer room or community center computer room, and connect broadband Internet through GE interface to provide broadband services for users; Connect operator's PSTN network through E 1 V5 interface to provide users with traditional voice telephone services. GEPON system of our company does not provide E 1 V5 interface for the time being.
Downward, the passive optical splitter is connected to the single-core optical fiber through the PON interface of MSC equipment, and finally connected to the optical network unit (ONU) equipment MSTB placed in the corridor unit or the ONU equipment MSTH located in the user's home, providing users with access to broadband, telephone, E 1 transparent transmission services and other services.
2, FTTH broadband and telephone integrated access advantages 2. 1 open network system 2.2 multi-service support, high bandwidth.
GEPON network system can provide transmission backbone bandwidth as high as 1.25G, and can support the longest transmission distance of 20KM at the split ratio of 1: 32, with passive network in the middle, with an average bandwidth of 30M per household, but the maximum user bandwidth can reach 1000M.
The system can support the access of voice, broadband and other services.
2.3 Simplify the district wiring system
FTTH network adopts optical fiber to the home directly, which avoids complex integrated lines in the community, between buildings and inside buildings.
The above is the difference between EPON and GPON.