ZyXEL Communications P-870HN-51B - V1.0 Manual page 86

Chapter 5 WAN Setup
since the ZyXEL Device does that part of the task. Furthermore, with NAT, all of
the LANs' computers will have access.
PPPoA
PPPoA stands for Point to Point Protocol over ATM Adaptation Layer 5 (AAL5). A
PPPoA connection functions like a dial-up Internet connection. The ZyXEL Device
encapsulates the PPP session based on RFC1483 and sends it through an ATM PVC
(Permanent Virtual Circuit) to the Internet Service Provider's (ISP) DSLAM (digital
access multiplexer). Please refer to RFC 2364 for more information on PPPoA.
Refer to RFC 1661 for more information on PPP.
RFC 1483
RFC 1483 describes two methods for Multiprotocol Encapsulation over ATM
Adaptation Layer 5 (AAL5). The first method allows multiplexing of multiple
protocols over a single ATM virtual circuit (LLC-based multiplexing) and the second
method assumes that each protocol is carried over a separate ATM virtual circuit
(VC-based multiplexing). Please refer to RFC 1483 for more detailed information.
Multiplexing
There are two conventions to identify what protocols the virtual circuit (VC) is
carrying. Be sure to use the multiplexing method required by your ISP.
VC-based Multiplexing
In this case, by prior mutual agreement, each protocol is assigned to a specific
virtual circuit; for example, VC1 carries IP, etc. VC-based multiplexing may be
dominant in environments where dynamic creation of large numbers of ATM VCs is
fast and economical.
LLC-based Multiplexing
In this case one VC carries multiple protocols with protocol identifying information
being contained in each packet header. Despite the extra bandwidth and
processing overhead, this method may be advantageous if it is not practical to
have a separate VC for each carried protocol, for example, if charging heavily
depends on the number of simultaneous VCs.
Traffic Shaping
Traffic Shaping is an agreement between the carrier and the subscriber to regulate
the average rate and fluctuations of data transmission over an ATM network. This
agreement helps eliminate congestion, which is important for transmission of real
time data such as audio and video connections.
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P-870HN-51b User's Guide