MPCP is used in EPON for traffic regulation downstream and upstream.
- ONT registration
- bandwidth polling
- bandwidth assignment
64-byte control messages are used for these functions:
- GATE and REPORT messages (used for assigning and requesting bandwidth)
- REGISTER_REQUEST, REGISTER, REGISTER_ACK messages (used for implementing the ONT auto-discovery, ONT registration and ranging processes)
One of the main features of EPON is the ability of recognition of an ONT and registering it (assigning LLID, allocating bandwidth, compensating time delays). Every time ONT is turned on or reset it is waiting for the discovery GATE message from the OLT, containing LLID. OLT is broadcasting this kind of message periodically to all ONTs. Messages used for registration of an ONT (GATE, REGISTER_REQUEST, REGISTER, REGISTER_ACK) and show ONT as belonging to the EPON. They are having unique LLID and all the necessary bandwidth slots. The whole process takes less than a second.
Traffic sent by users usually is sent in bursts, which should be handled by PON, because in wide area network and metro area network, traffic is relatively smooth. That’s why upstream traffic is divided in time-slot units. ONT’s are requesting the units and OLT is controlling and assigning those, based on request. Basically, slots can be reserved or be assigned dynamically. DBA is used for reassigning reserved slots that are not used by the OLT to other ONTs that may need it.
REPORT and GATE control messages
MPCP is using 64-byte control messages (REPORT and GATE) for assigning and requesting bandwidth. REPORT message is sent by ONT for indicating the requirements of bandwidth. It can indicate the status of up to eight queues, while having multiple thresholds in each queue. If ONT has only one queue, it can report up to 13 tresholds, while when there are eight queues, there might be up to two tresholds per queue. OLT is recieving the REPORT, it sends it to DBA algoritm, which calculates the timetable of all ONTs. After completing scheduling, OLT is sending multiple GATE message to all ONTs. One GATE message can support up to four transmission grants.