[GPON Technical Posts 08] Resource Sharing: Multiplexing Principles

Hello, everyone!

GPON encapsulation mode (GEM) ports and transmission containers (T-CONTs) divide a PON network into virtual connections for service multiplexing.

Each GEM port can carry one or more types of service stream. After carrying service streams, a GEM port must be mapped to a T-CONT before upstream service scheduling. Each ONU supports multiple T-CONTs. Services provided by an ONU can be mapped to different T-CONTs based on service priorities.
A T-CONT can carry one or more GEM ports, depending on customers' data plan.

Service Mapping Relationships

Upstream direction

An ONU sends Ethernet frames to GEM ports based on configured mapping rules between service ports and GEM ports. Then, the GEM ports encapsulate the Ethernet frames into GEM frames and add these GEM frames to T-CONT queues based on mapping rules between GEM ports and T-CONT queues. Then, the T-CONT queues use timeslots for upstream transmission to send GEM frames to the OLT.
The OLT receives the GEM frames and obtains Ethernet frames from them. Then, the OLT sends Ethernet frames from a specified uplink port based on mapping rules between service ports and uplink ports.

The principle of service multiplexing in the upstream direction is described by using an example of sending goods by a logistics company. First, let's look at the metaphor of concepts:

Let's see the composition of an express delivery branch.

An express delivery branch has one receive compartment and one dispatch compartment. The receive compartment receive the user's goods and puts them into the package. Packages are transmitted between the receive compartment and dispatch compartment over the conveyor belt on the workbench.
One receive compartment houses one workbench or multiple workbenches. Usually, packages sent to different areas are transmitted on different workbenches. That's to say, different service types are carried on different T-CONTs.
A workbench can be installed with one conveyor belt or multiple conveyor belts. Packages sent to different cities in an area over different conveyor belts. This is the binding relationship between GEM ports and T-CONTs.

According to the preceding mapping relationship, after the goods in the receiving warehouse are packed into a packing case, the conveyor belt and the corresponding workbench are selected according to the destination city to send the goods to the delivery warehouse.

Downstream direction

As described previously, data is sent to the ONU in broadcast mode. The ONU filters the received data according to the GEM port ID contained in the GEM frame header and retains the data only belonging to the GEM ports of this ONU. Then, the ONU decapsulates the data to Ethernet frames and sends them to end-users using service ports.

Now, do not hesitate to read through the post and give us your correct answers. If you have any difficulty understanding the content or want to learn more about the GPON technology, please leave a message and reply to the post. We are looking forward to your comments.

Answers for the previous session:
BD

Questions for this session:
(Multiple choice with more than one correct answer) Which of the following statements about the service Multiplexing are incorrect?