5.2 Tag Switching over ATM

5.2 Tag Switching over ATM

In this section we describe how Tag Switching operates on ATM switches. We refer to such switches as ATM-TSRs. Because ATM and Tag Switching use precisely the same forwarding paradigm, label swapping, Tag Switching can use ATM forwarding (?ATM User Plane?) pretty much ?as is.? This means that Tag Switching can run on unmodified ATM switch hardware. Although it preserves the ATM User Plane, Tag Switching replaces the ATM Control Plane with the Tag Switching Control Component. Supporting Tag Switching on a ATM switch means that operations of the switch are controlled by the Tag Switching control component rather than by the protocols defined by either the ITU or ATM Forum. Thus an ATM-TSR controls its operations by running protocols such as OSPF, BGP, PIM, and RSVP, rather than protocols such as UNI and PNNI.

When Tag Switching is used with ATM switches, the forwarding performance of such a device is determined by the capabilities of the ATM switches, whereas its functionality is comparable to a router. This is because, from the forwarding point of view, it is totally irrelevant whether the ATM forwarding table is constructed using the Tag Switching control component or using UNI, PNNI, and so forth. And from the functionality point of view, the functionality is determined largely by the control component, rather than by specifics of how such a device forwards data.

We begin the discussion by describing how tag information can be carried when Tag Switching operates over ATM...

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Switching in IP Networks: IP Switching, Tag Switching, & Related Technologies

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5.2 Tag Switching over ATM

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