1946/5000 Structure and Key Techniques of GPON System 3-GPON Up and Down Frame Structure

- Jul 08, 2019-

Structure and Key Techniques of GPON System 3-GPON Up and Down Frame Structure
The GPON system uses a fixed 125us periodic downlink to ensure the timing relationship of the entire system. The downlink frame structure is shown in Figure 5[3].

imageOn the Structure and Key Techniques of GPON System
Figure 5 Structure diagram of the next line frame
The next line frame is composed of PCB D and load. PCB D is a downlink physical control block that provides OAM functions such as frame synchronization, timing, and dynamic bandwidth allocation.
The PCB D consists of the following fields:
The Physical Syncing field is a fixed 32-bit style. The ONU logic circuit uses this field to find the starting position of the next line frame for synchronization with the OLT.
The low 30 bits of the Ident field contain a super-frame counter, and the Irent of each frame will be 1 larger than the previous one. When this counter reaches its maximum value, the next frame counter will be reset to 0. It is mainly used in user data encryption systems and can also be used to provide synchronization reference signals at lower rates.
The PLOAMd field is used to transfer management information from the physical layer. BIP is an interbit parity 8-bit code used for error monitoring.
The Plend field specifies the length of the bandwidth mapping and ATM section. The field is sent twice to ensure the robustness of the error.
BWmap is a scalar array of 8-byte allocation structures. Each item of this array represents a special T-CONT bandwidth map. The item N in the mapping array has been given in the Plend field. It is mainly used for uplink bandwidth allocation.
As shown in Figure 6, the upstream frame of the GPON system consists of many burst pulses, and each uplink burst should contain at least PLOu. In addition to the load, it may also contain PLOAMu, PLSu, and DBRu fields. OLT indicates through the Flags field in BWmap whether ONU is allowed to send PLOAM, PLSu, and DBRu information in each allocation. The load of the upstream frame consists of ATM load, GEM load, and DBA load.
On the Structure and Key Techniques of GPON System

imageFigure 6 is the uplink frame structure of GTC
The uplink physical layer overhead(PLOu) contains the lead code and delimiter for system synchronization, which allows proper operation of the uplink burst link.
The PLOAMA field is used to hold information on the management of the uplink physical layer. PLSu is a power measurement sequence with a length of 120 bytes for adjusting optical power. DBRu is used to report the uplink bandwidth requirements of ONU to OLT, and OLT makes an appropriate uplink bandwidth allocation based on the report.
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