The main difference between EPON and APON lies in their data transmission protocols. EPON, based on the IEEE 802.3 standard, allows for variable packet lengths up to 1518 bytes, while APON, using ATM protocol, operates with fixed 53-byte packets. This difference significantly affects the efficiency of IP data transport, making APON less effective.
In EPON, data transmission from the OLT (Optical Line Terminal) to multiple ONUs (Optical Network Units) and vice versa employs distinct techniques. Upon activation, the OLT broadcasts information regarding access slots. ONUs, upon power-up, initiate registration requests based on this broadcast, receiving unique logical link identifiers (LLIDs) for authentication and access.
Downstream data is sent using Time Division Multiplexing (TDM), with each frame header containing the specific LLID for designated ONUs, enabling selective data reception. Conversely, upstream traffic utilizes Time Division Multiple Access (TDMA), with the OLT allocating bandwidth dynamically based on ONU status, ensuring synchronized and interference-free transmission.
For security, ONU communications are routed through the OLT, which can control access permissions. Downstream, EPON employs several measures to safeguard information, including authentication of ONUs, LLID checks for data frame reception, AES encryption for ONU-OLT communications, and VLAN isolation for user group segmentation. These strategies collectively enhance the security and efficiency of the EPON architecture.