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What is the difference between PPPoE and PPPoA?

Posted on 2006-07-08
Medium Priority
Last Modified: 2013-11-29
Hi Everyone:

       The other day, I had to get a new DSL modem from Bellsouth.  Before I could use it, I had to configure it for a wireless router connection.  During the configuration process, I had to set the change PPPoE to Bridge Mode in order to disable DHCP within the DSL Modem, thereby, leaving the DHCP things handled by the router.  It is my understanding from a previous post that two network devices, like a DSL modem and router should not have DHCP enabled because of possible conflicts. Withing the router, I left it at PPPoE as the internet connection type.  

         Following the configuration of the DSL Modem and router, I was able to get online just fine through the router.  While within the configuration, I dd see some things which was somewhat confusing to me.  For instance, I saw an option called PPPoA as an internet connection type.  How is PPPoA different from PPPoE?  I believe PPPoE means point-to-point over ethernet, but, I do not know what PPPoA is all about.  Additionally, I believe PPPoE is used whenever there is a direction connection between two devices using an ethernet cable as well.

         In any case, I appreciated any additional feedback and/or corrections on any assumptions I may have here.  

         Thanks in advance for any attention given to this post.

Question by:GMartin
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LVL 32

Assisted Solution

rsivanandan earned 400 total points
ID: 17065524
PPPoA means PPP over ATM, it is another encapsulation technique which is a little different than PPPoE.

The overload is less over ATM networks and they are faster than traditional ethernet.


Author Comment

ID: 17065530

      What exactly are ATM networks?

LVL 32

Assisted Solution

rsivanandan earned 400 total points
ID: 17065542
Again take a look at the link below;

That should give you a fair amount of idea on what ATM is.

Like if you know there are a lot of encapsulation techniques for packet transfer. ATM (Asynchronous transfer mode) is one of them. Unlike others, the packet transfer is always 53 bytes, they are called cells. If I remember correct, the payload is 48 and 5 adds to the headers.

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Assisted Solution

ahm_khattab earned 200 total points
ID: 17066199
find below the difference between PPPoE and PPPoA

As customers deploy ADSL they must support PPP-style authentication and authorization over a large installed base of legacy bridging customer premises equipment (CPE). PPPoE provides the ability to connect a network of hosts over a simple bridging access device to a remote access concentrator or aggregation concentrator. With this model, each host uses its own PPP stack, thus presenting the user with a familiar user interface. Access control, billing, and type of service can be done on a per user, rather than a per site, basis.

As specified in RFC 2516, PPPoE has two distinct stages: a discovery stage and a PPP session stage. When a host initiates a PPPoE session, it must first perform discovery to identify which server can meet the client's request, then identify the Ethernet MAC address of the peer and establish a PPPoE session id. While PPP defines a peer-to-peer relationship, discovery is inherently a client-server relationship.

Primarily implemented as part of ADSL. It relies on RFC1483, operating in either Logical Link Control-Subnetwork Access Protocol (LLC-SNAP) or VC-Mux mode. A customer premises equipment (CPE) device encapsulates the PPP session based on this RFC for transport across the ADSL loop and the digital subscriber line access multiplexer (DSLAM).
LVL 44

Assisted Solution

scrathcyboy earned 400 total points
ID: 17066498
PPPoe and PPPoA are just two DIFFERENT ways that Telco companies connect yours and other modems to their DSL headend.  Some telcos, like Qwest, like PPPoA, and others like PPPoE.  YOu have little choice in the matter, if you have to use Qwest for DSL, then you MUST configure your modem to use PPPoA, and with other telco providers, you have no choice but to configure PPPoE.  It is THEIR choosing.

This is the NON-windows part of the modem setup.  It is the transport protocol that the modem uses to communicate with the DSL head-end (like a huge splitter) in the telco office.  It is the "hardware" part of the configuration.  It is not unlike the way your computer bus communicates with you network card in the computer -- this hardware-level communication is much lower level than TCP/IP, IPX, or any other transport layer.  It is not changeable by choice by the customer, usually, but it is configurable to tell the telco office that it is George Martin logging in to the telco headend with the correct login and password, so YES, he gets to use our DSL service.

Accepted Solution

dognamedmoses earned 1000 total points
ID: 17084267
To truly understand this difference you first must understand what PPP means.  point to point protocol describes the event of one client (you) connecting to another host (your isp) via two points.  The significance of ppp is that it allows communication, and in some cases, authentication.

Once you've got that part down, then you take a look at the E and the A (the wiki article are useful here).

E is ethernet.  In this situation, the PPP communication processes are established over the ethernet network.  This means that your Dsl modem/router gets itself an ip address and communicates with your isp over the same (basic) type of network that your home office is communicating on.  All of this is occuring on layer 3 of the osi model, the network layer.

  note:  you can learn about the osi model here: 
  this is the very most important basic step in understanding the way that computers communicate  on neworks.  If you don't want to learn about osi, then you probably don't want to really learn the difference between pppoe and pppoa.

now, the A:  A is for ATM as mentioned earlier.  This is communication via "frames" Frames are data packets that are encapsulated with less information than packets traveling on ip networks.  They communicate and rout via MAC addresses and through switches.  Frames travel more quickly and more efficiently than ip packets but they do not route, thus, you need a more "direct" connection between points.  In this situation, your dsl "modem" establishes the ppp connection below the Ip layer, and you have more of what's called a "bridge" from your isp to your own router.  the ip layer is re-established here so you can communicate with the rest of the internet.

All that to say what has already been said, it's really not a huge difference for the end user.  The ISP establishes the protocol and layer and then the user just needs to have the correct equipment.

Good luck with the articles.

Author Comment

ID: 17116479
Hi Everyone:

        Thanks so much for the great feedback and resourceful links.  I learned much from each reply.

         Thanks again.


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