Hi everyone.
Continuing with the GPIN technology, this time we will discuss the GPON 'S Protocol
GPON PRINCIPLES
GPON Protocol Analysis
GPON Standards Protocols
GPON Service Mapping—Upstream Multiplexing
· Figure 1 shows the service multiplexing principle in the GPON system. Services are first mapped to different GEM ports on the ONT. Services carried by GEM ports are then mapped to different types of T-CONTs for upstream transmission. A T-CONT is the basic bearer unit in the upstream direction of the GPON line. The T-CONT demodulates the GEM port unit on the OLT side, sends the GEM port unit to the GPON MAC chip, demodulates the services in the GEM port payload, and sends the services to the related service processing unit for processing. Other processing steps are the same as those in switches or the access network.
· Figure 2 shows the mapping between services, GEM ports, and T-CONTs. A GEM port is the smallest service unit in the GPON system. A GEM port can carry one or more services. Services carried by a GEM port are mapped to the T-CONTs for upstream service scheduling. Each ONT supports multiple T-CONTs and can be configured with different service types. One T-CONT can carry one or multiple GEM ports, depending on the specific configuration of the user. After the data carried by the T-CONT is transmitted upstream to the OLT, the GEM port is demodulated, and then the service payload in the GEM port is demodulated for processing.
GPON Service Mapping—Downstream Multiplexing
· In the downstream direction, all services are encapsulated into the GEM port in the GPON service processing unit and broadcast to all the ONUs connected to the GPON port, an ONU filters the data according to the GEM port ID, retains only the GEM port belonging to the ONU, decapsulates the service, and then sends the service from the service interface of the ONU to the user equipment
· A shared GEM port is a multicast GEM port
GPON Frame Structure
· The OLT uses the Flag field in the Bwmap to indicate whether the PLSu, PLOAMu, or DBRu information is transmitted in each allocation. When setting the transmission period, the OLT scheduler also needs to consider the bandwidth and delay requirements of these auxiliary channels.
· The status information of the PLOu is included in the allocation arrangement. Each time an ONU takes over a PON medium from another ONU, a copy of the new PLOu data must be sent. When an ONU is allocated with two consecutive IDs (the StopTime of one ID is 1 less than the StartTime of the other), the ONU suppresses the sending of the PLOu data to the second Alloc_ID. When the OLT authorizes multiple consecutive Alloc_ID to the ONU, the suppression can occur multiple times. Note that the continuous OLT allocations to the same ONU must have intervals. The allocations must be strictly continuous or for 2 different ONUs.
· User payload data is followed by these overheads during transmission until the position indicated by the StopTime pointer is reached.
Mapping Mode of Ethernet Services in GPON
· The GPON system parses Ethernet frames and directly maps the data to the GEM Payload for transmission.
· A GEM frame automatically encapsulates the header information
· The mapping format is clear and easy to implement, and the compatibility is excellent
PLI: payload size, 12 bits. That is, the maximum payload length of each GEM frame is 4095 bytes.
PORT ID: 12-bit 4096 GEM PORT IDs.
PTI: 3-bit payload type. The last bit indicates whether the segment is the last segment.
HEC: 13 bits for header error control.
Mapping Mode of TDM Services in GPON
· TDM services are first imported into the buffer for queuing and then multiplexed into GEM frames for transmission in a fixed number of bytes.
· In this mode, the system is not aware of specific TDM services and only transparently transmits data.
· A GEM frame has a fixed length and is beneficial to the transmission TDM services.
Here we finish with the post. The following takes you to the part 1. Please, share, comment and click on
https://forum.huawei.com/enterprise/en/huaweis-access-network-gpon-principles/thread/603932-100181
