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Understanding the network.pdf - Back to Home

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circuit descrip<strong>to</strong>r, is <strong>the</strong> PVC ID used by <strong>the</strong> ATM switch and router <strong>to</strong> distinguish<br />

different PVCs. The [aal-encapsulation] command designates <strong>the</strong> ATM<br />

adaptation layer and encapsulation used with <strong>the</strong> PVC. The encapsulation choices<br />

are <strong>the</strong> same ones available with serial configuration. You should recall <strong>the</strong>re are<br />

three ATM adaptation layers: AAL1, AAL3/4, and AAL5, <strong>the</strong> last of which is <strong>the</strong> best<br />

choice for most LAN/WAN environments.<br />

Let's look at a basic PVC configuration:<br />

orion(config)#interface atm0/0<br />

orion(config-if)#172.16.56.2 255.255.255.252<br />

orion(config-if)#atm pvc 2 2 31 all5mux<br />

When <strong>the</strong> interface is configured, it is also necessary <strong>to</strong> create Layer 3 <strong>to</strong> VCI/VPI<br />

mappings. However, with ATM interface processors, instead of creating and<br />

applying individual map entries as we would if this were an ATM serial interface,<br />

Layer 3 <strong>to</strong> VCI/VPI map entries are made in<strong>to</strong> a map-list.<br />

Map-lists are created in <strong>the</strong> same fashion as ACLs: one entry per line. In <strong>the</strong><br />

following example, we will finish configuring <strong>the</strong> ATM interface on orion, by creating<br />

and applying <strong>the</strong> ATM map-group. A map-list is created in global configuration mode<br />

using . After <strong>the</strong> list is created, entries are added<br />

using <strong>the</strong> map-list subcommand :<br />

orion(config)#map-list jupter<br />

orion(config)(config-map-list)# ip 172.16.56.1 atm vc 2 broadcast<br />

orion(config)(config-map-list)#exit<br />

orion(config)#interface atm0/0<br />

orion(config-if)#map-group jupter<br />

orion(config-if)#exit<br />

orion(config)#<br />

After <strong>the</strong> map-list is created, it is applied <strong>to</strong> <strong>the</strong> interface—oddly enough, as a<br />

map-group—with <strong>the</strong> interface processor subcommand .<br />

Cisco supports ATM SVCs in fully meshed (point-<strong>to</strong>-point) and multipoint <strong>to</strong>pologies.<br />

The idea behind SVCs is <strong>to</strong> provide a "bandwidth on demand" service model. SVCs

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