---
title: "Virtual circuit switching"
subject: "Computer Networks and Security"
chapter: 2
key: "semester_7/computer_networks_and_security:virtual-circuit-switching"
source: https://www.bctengineer.com/q/semester_7/computer_networks_and_security/virtual-circuit-switching
site: BCT Engineering
---

# Virtual circuit switching

Computer Networks and Security · Chapter 2: Physical Layer

- Asked in: 2070 Asar, 4 marks
- Video: [Virtual Circuit Networks](https://www.youtube.com/watch?v=naN6LNPBHAs) — TutorialsPoint
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_7/computer_networks_and_security/virtual-circuit-switching
- Whole chapter: https://www.bctengineer.com/md/semester_7/computer_networks_and_security/chapter-2

## Question

Explain virtual circuit switching.

## Short answer

Virtual circuit switching sets up a logical path before data transfer, with packets following the same path using a VCI. It combines circuit and packet switching, gives in-order delivery and small headers, but has setup delay and fails if a switch fails. Examples: X.25, Frame Relay, ATM.

## Answer

**Virtual circuit (VC) switching** is a packet-switching technique that combines features of circuit and packet switching. A logical path (virtual circuit) is set up between source and destination before data is sent, and all packets of the session follow this same path in order. The resources are not reserved exclusively, so bandwidth is still shared.

#### Phases
1. **Connection setup:** a request packet travels to the destination; each switch chooses an outgoing link and records a **VCI** (virtual circuit identifier) in its table.
2. **Data transfer:** every packet carries only a short VCI, not the full destination address. Switches use the VCI to forward and may change it on each link.
3. **Teardown:** the connection is closed and table entries are removed.

```text
 A --VCI 5--> [S1] --VCI 9--> [S2] --VCI 3--> B
```

#### Features
- Packets arrive in order; no reordering.
- Smaller header, fast forwarding after setup.
- Drawbacks: there is a setup delay, and the circuit fails if a switch on the path fails.
- Examples: X.25, Frame Relay, ATM.

It differs from datagram switching, where each packet is routed independently by full address.

## Check yourself

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

1. What happens during VC connection setup?
   A. Packets carry full destination address
   B. Switches choose an outgoing link and record a VCI in their table
   C. Resources are exclusively reserved
   D. Packets are routed independently
   Answer: B. Each switch records a VCI in its table during setup. (Key point: Setup)

2. What do packets carry during data transfer?
   A. Only a short VCI rather than the full destination address
   B. The full destination address
   C. No header
   D. Only a MAC trailer
   Answer: A. A short VCI is enough for switches to forward packets. (Key point: Header)

3. How do VC packets arrive?
   A. In order, along the same path
   B. Out of order by different paths
   C. Never arrive
   D. Randomly rerouted
   Answer: A. All packets follow the same logical path, so no reordering. (Key point: Order of packets)

4. How does VC differ from datagram switching?
   A. In VC each packet is routed independently by full address
   B. In datagram each packet is routed independently by full address; VC uses a pre-set path
   C. They are identical
   D. Datagram needs setup
   Answer: B. Datagram routes each packet separately by full address, while VC sets up a path first. (Key point: Datagram difference)

## Related in Computer Networks and Security

- [Circuit vs packet switching](https://www.bctengineer.com/question.md?key=semester_7%2Fcomputer_networks_and_security%3Acircuit-vs-packet-switching) — Computer Networks and Security, chapter 2, asked 3×

## Related in other subjects

- [Datagram vs virtual circuit switching](https://www.bctengineer.com/question.md?key=semester_5%2Fdata_communication%3Adatagram-vs-virtual-circuit) — Data Communication, chapter 7, asked 3×
- [Datagram vs virtual circuit switching](https://www.bctengineer.com/question.md?key=semester_8%2Ftelecommunications%3Adatagram-vs-virtual-circuit) — Telecommunications, chapter 8
- [Short note: Virtual-circuit network](https://www.bctengineer.com/question.md?key=semester_8%2Ftelecommunications%3Ashort-note-virtual-circuit) — Telecommunications, chapter 8, asked 2×
- [Virtual short circuit and inverting integrator](https://www.bctengineer.com/question.md?key=semester_2%2Fbasic_electronics_engineering%3Avirtual-short-integrator) — Basic Electronics Engineering, chapter 4