Transmission container (T-CONT)

T-CONT is short for Transmission Container. Entity used for upstream BW allocation.

In the upstream direction, data is contained in GEM frames (b/w ONT–OLT) . Why does the T-CONT need to be introduced?

It can be regarded as QoS control. In GPON, the T-CONT implements dynamic bandwidth assignment (DBA). An ONU applies for bandwidth using T-CONTs, and the OLT allocates bandwidth to T-CONT. In this way, the bandwidth is dynamically allocated in the upstream direction in the GPON system. 

Bandwidth authority is correlated with only one T-CONT.

The bandwidth information is sent to the ONU through the BWmap field of the downstream frame. After receiving the bandwidth information, the ONU allocates the bandwidth to the queues on the T-CONT.

T-CONT is the minimum scheduling unit for upstream bandwidth allocation. Each T-CONT is uniquely identified with an Alloc-ID that is globally allocated by the OLT , namely, each ONU of the OLT can only use a T-CONT with the unique Alloc-ID.