The PON network is sharing bandwidth between multiple users and it require each client to allocate time slot on the network. Due one transmitter it is relatively easy to allocate time for downstream signal. However, upstream direction is facing a problem of access with multiple upstream transmitters working at the same time. In PON architecture, this problem is solved using grants sent from OLT to each ONT. Grants are communicating in downstream messages and then inform clients ONT’s of their time slots.
Dynamic Bandwidth Assignment (DBA) helps utilizing and improving of the upstream signal. This concept was introduced first time in ITU-T Recommendation G.983.4. The DBA helps OLT monitoring bandwidth requirements of ONT’s and adjusts grants distribution.
The Transmission CONTainers (T-CONTs) were introduced in Recommendation G.983.4. T-CONT can combine one or several physical queues into a logical buffer. Implementation of DBA is resulting in association of grants with individual T-CONTs. Assignment process is using T-CONTs bandwidth-related parameters in grant assignment. DBA is defining four categories of bandwidth, listed from highest priority in terms of granting, to lowest:

• fixed
• assured
• nonassured
• best-effort

Up to five different T-CONT types are possible depending on combinations of these categories. Each ONT is capable of using one or more T-CONTs. The single T-CONT or a combination of T-CONTs is adapted to meet requirements of QoS of the traffic flows. Most flexible type of T-CONT is type 5: it uses all four bandwidth categories which allows to accommodate multiple traffic flows with a variety of QoS.
The DBA method is having two main features – idle cell monitoring and status reporting. As it is seen from the name, idle cell is monitoring amount of idle cells being sent from each T-CONT. On the other hand, status reporting is sending queue status and length reports of T-CONTs from ONTs to OLT. Using this information OLT allocates and adjusts the grants. Status reporting is having some advantages over idle cell monitoring, in scenarios where heavy usage of the PON is found.