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GPON technology originated from the ATMPON technology standard that began to form in 1995. PON is the abbreviation of English "passive optical network". GPON (Gigabit-Capable PON) was first proposed by the FSAN organization in September 2002. On this basis, ITU-T completed the development of ITU-T G.984.1 and G.984.2 in March 2003, February 2004. And the standardization of G.984.3 was completed in June. Thus, the standard family of GPON is finally formed. The basic structure of the device based on GPON technology is similar to that of the existing PON. It is also the OLT (optical line terminal) of the central office, the ONT/ONU of the user end (the optical network terminal or optical network unit), and the first two devices are connected by the single mode. The optical fiber (SM fiber) and the passive splitter (Splitter) are composed of an ODN (Optical Distribution Network) and a network management system.
(1) Unprecedented high bandwidth. GPON rates of up to 2.5 Gbps provide enough bandwidth to meet the growing demand for high bandwidth in the future, while asymmetric features are better suited to the broadband data services market.
(2) Full service access with QoS guarantee. GPON can carry ATM cells and/or GEM frames at the same time, and has a good service level, QoS guarantee and full service access. At present, ATM technology for carrying multiple services such as voice, PDH, and Ethernet is very mature. The technology that uses GEM to carry various user services has also been widely recognized and has been widely applied and developed.
(3) Good support for TDM services. The TDM service is mapped into the GEM frame. Since the GPON TC frame length is 125 μs, it can directly support the TDM service. TDM services can also be mapped into ATM cells and provide real-time transport with QoS guarantees.
(4) Simple and efficient adapter package. GEM is used to implement simple and efficient adaptive encapsulation for multi-service flows. In APON, all multi-service flows (voice, data traffic) must be converted into protocols and mapped into ATM cells for transmission. As we all know, a 5-byte ATM header brings about 10% bandwidth loss compared to 48-byte data, especially for long-packet packets, which is complex and inefficient. In EPON, although the Ethernet frame is directly carried, the implementation process is simple, but only 20% of the bandwidth is wasted considering the line coding of 8B/10B, plus the encapsulation and overhead of the Ethernet frame, the EPON bandwidth utilization ratio GPON is about 30% lower. At the same time, when transmitting TDM services, they need to be mapped into Ethernet frames through protocol conversion. Currently, there is no uniform standard for this technology. GPON GEM provides a flexible frame structure encapsulation, supports encapsulation of fixed length and indefinite long frames, implements common mapping for multiple services, does not require protocol conversion, and has a simple implementation process, low overhead, and high protocol encapsulation efficiency. 94%, to achieve the full use of bandwidth resources.
(5) Powerful OAM capabilities. In response to the lack of network management and performance monitoring for Ethernet systems, GPON provides three OAM channels from the perspective of consumer demand and operator operation and maintenance management: embedded OAM channels, PLOAM and OMCI. They undertake different OAM tasks, forming a C/M Plane (control/management plane), and different information in the plane manages their respective OAM functions. GPON also inherits the OAM requirements specified in G.983, with rich service management and carrier-grade network monitoring capabilities.
(6) The technology is relatively complicated and the equipment cost is high. The advantages of GPON carrying multi-service with QoS guarantee and powerful OAM capability are largely at the expense of the complexity of technology and equipment, which makes the related equipment costly. However, with the development of GPON technology and large-scale application, the cost of GPON equipment may decrease accordingly.
For other PON standards, the GPON standard provides unprecedented high bandwidth, with a downlink rate of up to 2.5 Gbit/s, and its asymmetric characteristics are more suitable for the broadband data service market. It provides full service guarantee of QoS, and carries ATM cells and/or GEM frames. It has good service level, QoS guarantee and full service access. When carrying a GEM frame, the TDM service can be mapped into a GEM frame, and the standard 8 kHz (125 μs) frame can directly support the TDM service. As a carrier-class technical standard, GPON also specifies protection mechanisms and complete OAM functions at the access network level.
In the GPON standard, the types of services that need to be supported are clearly defined: data services (Ethernet services, including IP services and MPEG video streams), PSTN services (POTS, ISDN services), and dedicated lines (T1, E1, DS3, E3, and ATM services). ) and video services (digital video). Multi-services in GPON are mapped to ATM cells or GEM frames for transmission, providing corresponding QoS guarantees for various service types.