Incomputer networking, thePoint-to-Point Protocol overATM (PPPoA) is alayer 2 data-link protocol typically used to connect domestic broadbandmodems toISPs via phone lines. It is used mainly withDOCSIS andDSL carriers, byencapsulating Point-to-Point Protocol (PPP) frames in ATMAAL5. PPPoA is specified by theInternet Engineering Task Force (IETF) in RFC 2364.[1]
It offers standardPPP features such asauthentication,encryption, andcompression. It also supports the encapsulation types:VC-MUX andLLC — seeRFC 2364.
If it is used as the connection encapsulation method on an ATM based network, it can reduce overhead significantly compared withPPPoEoA — by between 0 and ~3.125% for long packets, depending on the packet length and also on the choices of header options in PPPoEoA — seePPPoEoA 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.[2][3][4]
It also avoids the issues that PPPoE suffers from, related to sometimes needing to use an IPMTU 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.
Configuration of a PPPoA requires PPP configuration and ATM configuration. These data are generally stored in acable modem orDSL modem, and may or may not be visible to—or configurable by—anend-user.
PPP configuration generally includes: user credentials, user name and password, and is unique to each user.
ATM configuration includes:
ATM configuration can either be performed manually, or it may be hard-coded (or pre-set) into thefirmware of a DSL modem provided by the user's ISP; it cannot be automatically negotiated.
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