PPPoA

PPPoA stands for PPP over ATM, a method for carrying PPP frames over ATM networks by encapsulating them in an ATM Adaptation Layer 5 (AAL5) payload. It is commonly used on DSL connections, particularly ADSL, where the customer premises equipment connects to an ISP's ATM-based backbone.

In PPPoA, the PPP session is terminated at the edge device and the PPP frames are mapped into the ATM network over a specific VPI/VCI. The PPP negotiation, including the Link Control Protocol (LCP) and network-layer IPCP, proceeds in the usual PPP manner, and an IP address (and other configuration) is assigned through PPP.

PPPoA provides a connection-oriented, end-to-end PPP session over the ATM transport, with the PPP frames segmented into ATM cells. This approach avoids some of the overhead associated with carrying PPP inside Ethernet, and is well-suited to ATM-based DSL infrastructure.

Compared with PPPoE (PPP over Ethernet), PPPoA generally offers lower protocol overhead on ATM networks, but requires ATM-capable customer equipment and ISP support. It is less common today in many regions, where ISPs increasingly deploy PPPoE over Ethernet or IPoA.

Limitations and considerations include device compatibility (not all consumer routers support PPPoA), the need for a DSL modem/ONT to handle ATM VPI/VCI and PPP negotiation, and the fact that some networks have migrated away from PPPoA to other encapsulations.