
Configuring ATM Services
2-10 114056 Rev. A
• SVC service records
• Individual PVCs
NULL Encapsulation
RFC 1483 refers to this method as “VC-based multiplexing.” This method
performs higher-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
Originally developed for Frame Relay networks, 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 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).
Note: Assigning LLC/SNAP to an SVC service record automatically invokes
the technology defined in RFC 1577, Classical IP and ARP over ATM.
Note: Assigning NULL to an SVC service record automatically invokes the
technology defined in RFC 1577, Classical IP and ARP over ATM.
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