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Configuring ATM and MPLS Services
1-14
117374-C Rev 00
NULL Encapsulation
RFC 1483 refers to NULL encapsulation as “VC-based multiplexing.” This
method performs upper-layer protocol multiplexing implicitly using ATM virtual
circuits. You can assign NULL encapsulation to:
PVC service records
SVC service records
Individual PVCs that are also members of an LLC/SNAP service record
NLPID Encapsulation
You can use Network Layer Protocol ID (NLPID; RFC 1490) in an ATM
environment for frame relay/ATM internetworking. You can assign NLPID
encapsulation to PVC service records.
Selecting a Data Encapsulation Method
Generally speaking, the designers of these data encapsulation methods envisioned
that NULL encapsulation would dominate in environments where the 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 billing 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.
Note:
Assigning NULL to an SVC service record automatically uses the
technology defined in RFC 1577, Classical IP and ARP over ATM. For
information about RFC 1577, see “Classical IP over ATM Concepts
” on
page 1-28
.
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