Taicom Data Systems Co Ltd AWL1000G User Manual
Appendix B. Encapsulation Mode
Bridged mode（RFC-1483）
RFC-1483 provides the simplest method of connecting end station over an ATM network. User data
in the form of Ethernet frames is encapsulated into AAL5-PDU for transport over ATM. RFC-1483
provides no authentication and configuration such as would be provided by PPP. RFC-1483
implementation supports VC multiplexing and LLC/SNAP encapsulation in both routed and
bridged configurations.
Classical IP over ATM-IPOA（RFC1577）
User data in the form of IP packets is encapsulated into AAL-5 PDUs for transport over ATM. The
fact that the user data is routed at an IP layer instead of bridged MAC layer allows the source and
destination to be on different subnets. A notable drawback of IPoA is the lack of authentication and
configuration such as would be provided by PPP.
PPP over ATM-PPPoA（RFC-2364）
The use of PPPoA is similar to IPoA. However, a PPP session is established to the remote access
server (RAS). The PPP packets are encapsulated according to RFC-2364 for transmission over an
ATM link. On the receive side, the de-encapsulation is performed. The PPP session is terminated
and the IP packets can be delivered to the end user over Ethernet or other medium.
PPP over Ethernet-PPPoE（RFC-2516）
The PPP over Ethernet（PPPoE）encapsulation is used to transport PPP traffic from a PC to a DSL
device over Ethernet and then over the DSL link using RFC-1483 encapsulation. There may be
multiple PPP sessions, each terminated in a PC or in the CPE device and in a PPP aggregator on the
CO side.
RFC-1483 provides the simplest method of connecting end station over an ATM network. User data
in the form of Ethernet frames is encapsulated into AAL5-PDU for transport over ATM. RFC-1483
provides no authentication and configuration such as would be provided by PPP. RFC-1483
implementation supports VC multiplexing and LLC/SNAP encapsulation in both routed and
bridged configurations.
Classical IP over ATM-IPOA（RFC1577）
User data in the form of IP packets is encapsulated into AAL-5 PDUs for transport over ATM. The
fact that the user data is routed at an IP layer instead of bridged MAC layer allows the source and
destination to be on different subnets. A notable drawback of IPoA is the lack of authentication and
configuration such as would be provided by PPP.
PPP over ATM-PPPoA（RFC-2364）
The use of PPPoA is similar to IPoA. However, a PPP session is established to the remote access
server (RAS). The PPP packets are encapsulated according to RFC-2364 for transmission over an
ATM link. On the receive side, the de-encapsulation is performed. The PPP session is terminated
and the IP packets can be delivered to the end user over Ethernet or other medium.
PPP over Ethernet-PPPoE（RFC-2516）
The PPP over Ethernet（PPPoE）encapsulation is used to transport PPP traffic from a PC to a DSL
device over Ethernet and then over the DSL link using RFC-1483 encapsulation. There may be
multiple PPP sessions, each terminated in a PC or in the CPE device and in a PPP aggregator on the
CO side.
The PPPoE Client terminates PPPoE session within the CPE device, this configuration enables
PPPoE session without a need for additional software.
The PPP traffic for a Relay Agent is not terminated in the DSL device, rather it is relayed over
the DSL link to a PPP aggregator in the CO PPPoE relay agent determines on which session
locally originated PPPoE traffic belongs. The relay agent forwards that traffic, without any
unnecessary processing to the correct destination only. Similarly, received data is immediately
relayed only to the appropriate client PC. Not only does this approach enhance performance by
eliminating additional process, it also provides a critical security feature, so it prevents for
example corporate bound data from being exposed to the Internet.
locally originated PPPoE traffic belongs. The relay agent forwards that traffic, without any
unnecessary processing to the correct destination only. Similarly, received data is immediately
relayed only to the appropriate client PC. Not only does this approach enhance performance by
eliminating additional process, it also provides a critical security feature, so it prevents for
example corporate bound data from being exposed to the Internet.
51