Avaya Configuring ATM Services Manual do Utilizador Página 49

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Understanding ATM Concepts
114056 Rev. A 2-9
Data Encapsulation
Bay Networks ATM routers support multiprotocol encapsulation (as defined in
RFC 1483), enabling the router to multiplex (combine) and demultiplex (separate)
bridged or routed protocol data units (PDUs).
For transmission, the encapsulation process adds a header between two and eight
octets in length to the PDU to allow decoding. The decoding process determines
the proper service access point (SAP).
When receiving information, the encapsulation method evaluates the header to
determine whether the PDU is a valid routed or bridged cell. If it is valid, the
encapsulation method then strips the header from the cell and passes it to the
appropriate SAP for routing or bridging.
You can choose from four data encapsulation types: LANE, LLC/SNAP, NLPID,
and NULL. How you assign a data encapsulation type and which data
encapsulation type takes precedence depends on the virtual circuit type and, for
PVCs, the order in which you assign the encapsulation type.
Encapsulation Methods
Each ATM device must encapsulate PDUs before sending them to the SAR
sublayer.
LANE
LANE provides Ethernet (IEEE 802.3) encapsulation of ATM PDUs for
transmission over an emulated LAN. You can assign LANE to SVCs only.
LLC/SNAP Encapsulation
Logical Link Control / Subnetwork Access Protocol (LLC/SNAP; RFC 1294)
allows multiplexing of multiple protocols over a single ATM virtual circuit. In this
approach, an IEEE 802.2 Logical Link Control (LLC) header prefixes each PDU.
You can assign LLC/SNAP encapsulation to
PVC service records
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