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.
PPPoA is specified in RFC 2364.
Virtual Circuit Multiplexing or VC-MUX is a form of network traffic control. It is used in situations where multiplexing is preferable to switching. Multiplexing is used when there's a need to transport multiple data streams over a single data link. VC-MUX is commonly used in conjunction with PPPoE and PPPoA. Which are used in various xDSL implementations.
According to the IEEE 802 family of standards (Ethernet, WiFi, etc), in VC Multiplexing (VC-MUX), each ATM Virtual Circut (VC) carries PDUs of exactly one protocol type. When multiple protocols need to be transported, there is a separate VC for each.
* VC multiplexing tends to reduce fragmentation overhead (e.g., an IPV4 datagram containing a TCP control packet with neither IP nor TCP options exactly fits into a single cell).
According to the IEEE 802 family of standards, Logical Link Control (LLC) is the upper sublayer of the OSI data link layer. The LLC is the same for the various physical media (such as Ethernet, token ring, and WLAN).
The LLC sublayer is primarily concerned with:
* Multiplexing protocols transmitted over the MAC layer (when transmitting) and demultiplexing them (when receiving).
* Optionally providing flow control and detection and retransmission of dropped packets, if requested.
The protocol used in IEEE 802 networks and in some non-IEEE 802 networks such as FDDI for LLC is specified by the IEEE 802.2 standard.
Some non-IEEE 802 protocols can be thought of as being split into MAC and LLC layers. For example, while HDLC specifies both MAC functions (framing of packets) and LLC functions (protocol multiplexing, flow control, and detection and retransmission of dropped packets), some protocols such as Cisco HDLC can use HDLC-like packet framing and their own LLC protocol.
PPPoE, Point-to-Point Protocol over Ethernet, is a network protocol for encapsulating PPP frames in Ethernet frames. It is used mainly with ADSL services. It offers standard PPP features such as authentication, encryption, and compression. Unfortunately it has an MTU lower than that of standard Ethernet which can sometimes cause problems with badly configured firewalls.
PPPoE is a tunneling protocol which allows layering IP, or other protocols that run over PPP, over a connection between two Ethernet ports, but with the software features of a PPP link, so it is used to virtually "dial" to another Ethernet machine and make a point to point connection with it, which is then used to transport IP packets, based on the features of PPP.
It allows the use of traditional PPP-based software to handle a connection which does not use a serial line, but a packet-oriented network like Ethernet, to provide a classical connection with login and password for Internet connection accounting. Also, the IP address on the other side of the link is only assigned when the PPPoE connection is open, allowing the dynamic reuse of IP addresses.
PPPoE was developed by UUNET, Redback Networks, and RouterWare. The protocol is specified in RFC 2516.
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