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Short note: IP switching

Short answer

IP switching combines hardware switching with IP routing by routing only initial packets of a flow. The controller identifies long-lived flows, assigns a label/VC, and sets up a fast path in the switching fabric, so subsequent packets are switched directly. This yields high throughput and QoS, and evolved into MPLS.

Write a short note on IP switching.

IP switching is a technique that combines the speed of Layer-2 (ATM/label) switching with the flexibility of Layer-3 IP routing. Normal routers examine the full IP header of every packet and look up a large routing table, which is slow. An IP switch routes only the first packets of a flow; then it sets up a fast hardware path for the rest.

 +-------------------------------+
 | IP switch controller          |
 | (routing, flow classifier)    |
 +---------------+---------------+
                 | GSMP
 +---------------+---------------+
 | ATM / label switching fabric  |
 +-------------------------------+

Operation

  1. Packets first go on a default path to the controller, which routes them normally.
  2. The controller identifies long-lived flows (same source, destination, ports).
  3. Using IFMP (Ipsilon Flow Management Protocol) it asks the upstream node to send that flow on a new label/VC.
  4. Through GSMP it sets up a connection in the switching fabric.
  5. Later packets of the flow are switched in hardware without IP lookup; short flows stay routed.

Advantages

  • High throughput and low delay.
  • QoS for selected flows.
  • Uses low-cost switching hardware.

This idea led to tag switching and MPLS, used in today's ISP backbones.

✓ Answer checked by Claude Opus 5.5 (high effort)

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