GPON (Gigabit Passive Optical Network) technology is based on the latest generation of broadband passive optical integrated access standards based on the ITU-TG.984.x standard. It has many advantages such as high bandwidth, high efficiency, large coverage and rich user interface. Most operators regard the access network as a broadband technology, an integrated transformation of the ideal technology. GPON was originally proposed by the FSAN in September 2002. On this basis, ITU-T completed the formulation of ITU-T G.984.1 and G.984.2 in March 2003 and completed G in February and June 2004. 984.3 standardization. Which eventually formed a GPON standard family.
GPON technology originated in the gradual formation of ATM-PON technical standards in 1995, PON is “passive optical network” abbreviation. The Gigabit Passive Optical Network (GPON) was originally proposed by the FSAN in September 2002. On this basis, ITU-T completed the formulation of ITU-T G.984.1 and G.984.2 in March 2003, and in 2004 The standardization of G.984.3 was completed in February and June. Which eventually formed a GPON standard family. The basic structure of a device based on the GPON technology is similar to the existing PON. The OLT (Optical Line Terminal) at the central office and the ONT / ONU (Optical Network Terminal) at the user end are also connected. The first two devices are connected by a single mode optical fiber (SM fiber) and passive splitter that consisting of ODN (optical distribution network) and network management system.
The technical feature of GPON is that it draws on GFP (Generic Framing Procedure) defined by ITU-T on the second floor and extends the encapsulation format of General Encapsulation Methods (GEM) to recombine services of any type and any rate PON transmission, and GFM header contains the frame length indicator byte can be used for variable length packet delivery, improve the transmission efficiency, it can be more simple, common and efficient to support full-service. details as follows:
(1) Unprecedented high bandwidth. With a GPON rate of up to 2.5 Gbps, it provides enough bandwidth to meet the growing demand for high bandwidth in future networks, while asymmetric features are better suited to the broadband data services market.
(2) QoS guaranteed full-service access. GPON can carry ATM cell and/or GEM frame at the same time, have good service levels, support QoS guarantee and full-service access capability. At present, the technology of ATM carrying voice, PDH, Ethernet and other multi-services has been very mature. The technology of using GEM to bear various subscriber services has also been unanimously approved by everyone and has been widely applied and developed. GPON can be any type and any rate of the original business after the package format transmission PON transmission. Then how to achieve GPON data encapsulation? The GPON ONU receives the uplink ETH, TDM or SDH data from the UNI (User Network Interface) port, and the ONU encapsulates the uplink data into a GEM frame and sends the uplink data to the GPON OLT. The OLT decapsulates GEM frames into ETH, TDM or SDH data and sends them out through the uplink port. Downstream for similar treatment.
(3) TDM is well supported. TDM services are mapped to GEM frames. Since the GPON TC frame length is 125 μs, it can directly support TDM services. TDM services can also be mapped into ATM cells, but also provide a real-time transmission with QoS guarantees.
(4) Simple and efficient packet. GEM for multi-service flow to achieve a simple and efficient packet. In APON, all multi-service flow (voice, data traffic) must be converted into an ATM cell for transmission. As we all know, a 5-byte ATM header relative to 48 bytes of data, it will bring more than 10% of the bandwidth loss, especially for long packets of data packets, the packaging process is complex, the efficiency is very low. In EPON, although Ethernet frames are directly carried and the implementation process is simple, only 20% of the bandwidth is lost when considering the 8B / 10B line coding. In addition to the encapsulation and overhead of Ethernet frames, the EPON bandwidth utilization ratio GPON low about 30%. At the same time, when transmitting TDM services, it needs to be mapped into an Ethernet frame through protocol conversion. Currently, there is no unified standard for this technology. GPON’s GEM provides a flexible frame structure encapsulation to support the encapsulation of fixed-length and variable-length frames. It implements common mapping for multiple services and does not require protocol conversion. The process is simple, the overhead is low, and the protocol encapsulation efficiency is up to 94%, to achieve the full use of bandwidth resources.
(5) Powerful OAM capabilities. In view of the lack of network management and performance monitoring in 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 assume different OAM tasks, forming C / M Plane (control/management plane), the different information in the plane to manage their OAM functions. GPON also inherits the OAM requirements specified in G.9983, with rich business management and carrier-class network monitoring capabilities.
(6) GPON technology is relatively complex and with higher equipment costs. The advantages of GPON, such as multi-services with QoS guarantees and strong OAM capabilities, are largely at the expense of the complexity of the technology and equipment, resulting in higher equipment costs. However, with the development of GPON technology and large-scale application, the cost of GPON equipment may be correspondingly decreased.
GPON System Structure
Like all PON systems, GPON consists of ONUs, OLTs and passive optical distribution networks. The OLT provides the interface between the network side and the core network for the access network and connects with the ONUs through the ODN. As a core functional device of the PON system, the OLT has functions of centralized bandwidth allocation, control of ONUs, real-time monitoring, operation, maintenance and management of the PON system. The ONU provides a user-side interface for the access network to provide multiple services flows such as voice, data, and video to access the ODN, which is centrally controlled by the OLT. The branching ratio supported by the system is 1:16/32/64. With the development of optical transceivers, the branching ratio supported will reach 1:128. GPON transmission mechanism and EPON exactly the same, are using single-fiber bi-directional transmission mechanism on the same fiber, the use of WDM technology, using different wavelengths to transmit uplink and downlink data. On the same fiber, GPON can use Wavelength Division Multiplexing (WDM) technology to enable bi-directional signal transmission. According to actual needs, you can also use the corresponding PON protection structure to improve the survivability of the network based on the traditional tree topology.
GPON Technical Standard
Compared with other PON standards, GPON standard provides an unprecedented high bandwidth, downlink rate of up to 2.5Gbit / s, the asymmetric nature of the broadband data services to better adapt to the market. Provide full-service guarantee of QoS, carry ATM cell and/or GEM frame at the same time, have good service levels, support QoS guarantee and full-service access capability. When carrying GEM frames, TDM services can be mapped into GEM frames and TDM services can be directly supported using standard 8 kHz (125 μs) frames. As a carrier-class technology standard, GPON also provides protection mechanisms and complete OAM functions at the access network level.
The GPON standard specifies the types of services that need to be supported including data services (Ethernet services including IP services and MPEG video streaming), PSTN services (POTS and ISDN services), private lines (T1, E1, DS3, E3 and ATM services ) And video services (digital video). The multi-service in GPON maps to ATM cell or GEM frame for transmission, which can provide corresponding QoS guarantee for various service types.