PPPoA (Point-to-Point Protocol over ATM)

In computer networking, the Point-to-Point Protocol over ATM (PPPoA) is a layer 2 data-link protocol typically used to connect domestic broadband modems to ISPs via phone lines. It is used mainly with DOCSIS and DSL carriers, by encapsulating PPP frames in ATM AAL5. Point-to-Point Protocol over Asynchronous Transfer Mode (PPPoA) is specified by The Internet Engineering Task Force (IETF) in RFC 2364.

It offers standard PPP features such as authentication, encryption, and compression. It also supports (as does PPPoE) the encapsulation types: VC-MUX and LLC – see RFC 2364.

If it is used as the connection encapsulation method on an ATM based network it can reduce overhead significantly compared with PPPoEoA – by between 0 and ~3.125% for long packets, depending on the packet length and also on the choices of header options in PPPoEoA – see PPPoEoA protocol overheads. This is because it uses headers that are short so imposes minimal overheads, 2 bytes for PPP and 8 bytes for PPPoA (with the RFC2364 VC-MUX option) = 10 bytes.

It also avoids the issues that PPPoEoE suffers from, related to sometimes needing to use an IP MTU of 1492 bytes or less, lower than the standard 1500 bytes.

The use of PPPoA over PPPoE is not geographically significant; rather, it varies by the provider’s preference.

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