---
title: "Short note: IP switching"
subject: "Telecommunications"
chapter: 8
key: "semester_8/telecommunications:short-note-ip-switching"
source: https://www.bctengineer.com/q/semester_8/telecommunications/short-note-ip-switching
site: BCT Engineering
---

# Short note: IP switching

Telecommunications · Chapter 8: Data Communication

- Asked in: 2081 Baisakh, 4 marks; 2072 Kartik, 5 marks (asked 2 times)
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_8/telecommunications/short-note-ip-switching
- Whole chapter: https://www.bctengineer.com/md/semester_8/telecommunications/chapter-8

## Question

Write a short note on 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.

## Answer

**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.

```text
 +-------------------------------+
 | 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.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. What does IP switching combine?
   A. Static and flooding routing
   B. Layer-2 (ATM/label) switching speed with Layer-3 IP routing flexibility
   C. Layer-1 speed with layer-7 flexibility
   D. Circuit and message switching
   Answer: B. It routes the first packets of a flow, then switches the rest in hardware. (Key point: IP switching idea)

2. What happens to a long-lived flow in an IP switch?
   A. It is dropped
   B. It is broadcast
   C. It is moved onto a new label/VC and switched in hardware without IP lookup
   D. Every packet goes through IP lookup
   Answer: C. The controller detects the flow, uses IFMP to ask upstream for a new label and GSMP to set up the fabric. (Key point: Flow handling)

3. What is GSMP used for in IP switching?
   A. To set up connections in the switching fabric from the controller
   B. To ask the upstream node to use a new label
   C. To encrypt packets
   D. To flood link-state packets
   Answer: A. IFMP talks to the upstream node; GSMP controls the switching fabric. (Key point: IFMP and GSMP)

## Related in Telecommunications

- [NTA functions; IP switching structure](https://www.bctengineer.com/question.md?key=semester_8%2Ftelecommunications%3Anta-functions-ip-switching) — Telecommunications, chapter 7
- [IP and soft switching for PC-to-PSTN calls](https://www.bctengineer.com/question.md?key=semester_8%2Ftelecommunications%3Aip-soft-switching-skype-pstn) — Telecommunications, chapter 8