Avaya Configuring ATM Services Bedienungsanleitung Seite 139

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ATM Editing Basics
7-19
LANE 802.3
LANE 802.3 provides Ethernet encapsulation of ATM PDUs for transmission over
an emulated Ethernet LAN. You can assign LANE 802.3 to SVCs only.
Selecting a Data Encapsulation Method
Generally speaking, the designers of these data encapsulation methods envisioned
that NULL encapsulation would dominate in environments where dynamic
creation of large numbers of ATM VCs is fast and economical. These conditions
usually exist in private ATM networks.
LLC/SNAP encapsulation is an alternative for environments in which it is not
practical to have a separate VC for each carried protocol (for example, if the ATM
network supports only PVCs, or if charging depends heavily on the number of
simultaneous virtual circuits).
The choice of multiplexing methods that two ATM stations use to exchange
connectionless network traffic depends on the type of virtual circuit involved:
For PVCs, you select the multiplexing method when you manually configure
the connection.
For SVCs, the stations themselves negotiate the multiplexing method by
sending B-ISDN signaling messages. These messages include “low-layer
compatibility” information that allows negotiation of AAL5 and the carried
(encapsulation) protocol.
LLC/SNAP Encapsulation
When the same virtual circuit carries several protocols, select LLC/SNAP
encapsulation. LLC/SNAP encapsulation attaches an LLC/SNAP header before
the PDU. This header includes information that the receiver needs to properly
process the incoming PDU. For bridged PDUs, this header also includes the type
of the bridged media.
Note: Routed and bridged PDUs are always encapsulated within the payload
field of the AAL5 CPCS PDU, regardless of the selected multiplexing method.
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