Editing Point-to-Point Protocol over ATM

{{Short description|Computer network protocol}}
In [[computer networking]], the '''[[Point-to-Point Protocol]] over [[Asynchronous Transfer Mode|ATM]]''' ('''PPPoA''') is a [[OSI model|layer 2]] data-link protocol typically used to connect domestic broadband modems to ISPs via phone lines. It is used mainly with [[DOCSIS]] and [[Digital subscriber line|DSL]] carriers, by [[Encapsulation (networking)|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.<ref name=RFC2364>{{cite journal|title=RFC 2364, PPP over AAL5|year=1998|url=http://tools.ietf.org/html/rfc2364|accessdate=2013-04-15|publisher=IETF|ref=rfc:2364 |last1=Malis |first1=Anew G. |last2=Lin |first2=Arthur Y. |last3=Stephens |first3=John |last4=Gross |first4=George |last5=Kaycee |first5=Manu }}</ref>

It offers standard [[Point-to-point protocol|PPP]] features such as [[authentication]], [[encryption]], and [[Data compression|compression]]. It also supports the encapsulation types: [[VC-MUX]] and [[Logical Link Control|LLC]] - see [https://tools.ietf.org/html/rfc2364 RFC 2364].

If it is used as the connection encapsulation method on an ATM based network it can reduce overhead significantly compared with [[Point-to-Point Protocol over Ethernet|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 [[Point-to-Point Protocol over Ethernet#Use with DSL – PPPoE over ATM (PPPoEoA)|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'''.<ref>Dirk Van Aken, Sascha Peckelbeen [http://wand.cs.waikato.ac.nz/~513/2006/readings/adsl-2.pdf Encapsulation Overhead(s) in ADSL Access Networks], June 2003</ref><ref>[https://tools.ietf.org/html/rfc2364 RFC 2364]</ref><ref>[https://tools.ietf.org/html/rfc2684 RFC 2684]</ref>

It also avoids the issues that PPPoE suffers from, related to sometimes needing to use an IP [[MTU (networking)|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.

== 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—an [[User_(computing)#End_user|end-user]].

PPP configuration generally includes: user credentials, user name and password, and is unique to each user.

ATM configuration includes:

* [[Virtual channel link]] (VCL) – [[virtual path identifier]] and [[virtual channel identifier]] (VPI/VCI), such as 0/32 (analogous to a phone number)
* Modulation (Type): such as [[G.dmt]]
* Multiplexing (Method): such as [[VC-MUX]] or [[Logical Link Control|LLC]]

ATM configuration can either be performed manually, or it may be hard-coded (or pre-set) into the [[firmware]] of a [[DSL modem]] provided by the user's ISP; it cannot be automatically negotiated.

==See also==
*[[PPPoE]]
*[[PPPoX]]
*[[L2TP]]
*[[Asynchronous Transfer Mode|ATM]]
*[[DSL]]

== Notes ==
{{Reflist}}

== External links ==
*[http://www.dslreports.com/information/kb/DSL-1/pictures A typical PPPoA architecture diagram] (out of date and no longer maintained)

[[Category:Telecommunication protocols]]
[[Category:Tunneling protocols]]