Point-to-Point Protocol over ATM

The Point-to-Point Protocol over ATM (PPPoA) is a network protocol for encapsulating PPP frames in AAL5. It is used mainly with DOCSIS and DSL carriers.

It offers standard PPP features such as authentication, encryption, and compression. If it is used as the connection encapsulation method on an ATM based network it can reduce overhead slightly (around 0.58%) in comparison to PPPoE. It also avoids the issues that PPPoE suffers from, related to having a MTU lower than that of standard Ethernet transmission protocols. It also supports (as does PPPoE) the encapsulation types: VC-MUX and LLC based.

Point-to-Point Protocol over Asynchronous Transfer Mode (PPPoA) is specified in RFC 2364.

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

Configuration

Configuration of a PPPoA requires PPP configuration and ATM configuration. These data are generally stored in a cable modem or DSL modem, and may or may not be visible to or configurable by a user.

PPP configuration is generally user credentials – user name and password – and is unique to each user.

ATM configuration includes:

• Virtual Channel Link (VCL) – Virtual Path Identifier & Virtual Circuit Identifier (VPI/VCI), such as 0/32, analogous to a phone number
• Modulation, such as G.DMT
• Encapsulation, such as VC-MUX

ATM configuration is generally manual (not automatically negotiated), and may be hard-coded (or pre-set) into a modem provided by the ISP.

See also

• PPPoE
• L2TP
• ATM
• DSL

External links

• A typical PPPoA architecture diagram (out of date and no longer maintained)

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