---
title: "Datagram vs virtual circuit switching"
subject: "Data Communication"
chapter: 7
key: "semester_5/data_communication:datagram-vs-virtual-circuit"
source: https://www.bctengineer.com/q/semester_5/data_communication/datagram-vs-virtual-circuit
site: BCT Engineering
---

# Datagram vs virtual circuit switching

Data Communication · Chapter 7: Switching

- Asked in: 2073 Shrawan, 2+6 marks; 2072 Kartik, 5 marks; 2069 Chaitra, 2+3 marks (asked 3 times)
- Video: [Lec-19: Datagram Switching Vs Virtual Circuit Switching in Packet Switching | Computer Networks](https://www.youtube.com/watch?v=-S-NThI_79o) — Gate Smashers
- Answer checked by Claude Sonnet 5.5 on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/data_communication/datagram-vs-virtual-circuit
- Whole chapter: https://www.bctengineer.com/md/semester_5/data_communication/chapter-7

## Question

What is data switching? Clarify the differences between datagram switching and virtual circuit packet switching.

## Short answer

Packet switching includes datagram and virtual circuit. Datagram is connectionless: each packet carries full destination address, routed independently, may arrive out of order. Virtual circuit uses a pre-established path, carries a short VC identifier, delivers packets in order, and provides easier QoS.

## Answer

#### Data switching
**Switching** is the process of transferring data from a source to a destination through a series of intermediate nodes, so that every pair of devices need not be directly connected. The main types are circuit, message and packet switching.

Packet switching has two forms: **datagram** and **virtual circuit**.

- **Datagram:** each packet (datagram) is treated independently and carries the full destination address; routers choose the route for each packet. No call setup.
- **Virtual circuit:** a logical path is set up first by a call-request, all packets then carry a short VC number and follow that path in order, and the path is cleared at the end.

```text
 Datagram: P1 -> R1 -> R2 -> B
           P2 -> R1 -> R3 -> B   (different paths)
 VC      : setup A..R1..R2..B ; all packets use this path
```

| Point | Datagram | Virtual circuit |
|---|---|---|
| Connection | Connectionless | Connection-oriented |
| Setup phase | None | Required (call setup and clear) |
| Header | Full destination address | Short VC identifier |
| Routing | Decision for every packet | Once, at setup |
| Order of delivery | May be out of order | In order |
| Reliability | Reordering and error control by end hosts | Can be provided by the network (e.g. X.25) |
| Failure of a node | Packets re-routed, little loss | All circuits through it fail |
| Resource reservation | None | Possible, QoS easier |
| Congestion | Handled per packet, harder to control | Easier to control |
| Examples | IP (Internet) | X.25, frame relay, ATM |

## Check yourself

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

1. Which needs a call setup phase?
   A. Datagram
   B. Virtual circuit
   C. Both
   D. Neither
   Answer: B. Virtual circuit sets up with a call request; datagram is connectionless. (Key point: Setup)

2. What does each packet carry?
   A. Datagram: short VC number; VC: full address
   B. Both full addresses
   C. Datagram: full destination address; VC: short VC identifier
   D. Neither has an address
   Answer: C. Datagram packets carry the full destination; VC packets carry a short VC number. (Key point: Header)

3. Which delivers packets in order?
   A. Datagram
   B. Virtual circuit
   C. Neither
   D. Both
   Answer: B. Packets follow one path in a VC so they arrive in order. (Key point: Order)

4. What happens when a node fails?
   A. Datagram re-routes with little loss; all VCs through it fail
   B. Both fail
   C. VCs re-route
   D. Datagram circuits all fail
   Answer: A. Datagram packets re-route; virtual circuits through the node fail. (Key point: Node failure)

## Related in Data Communication

- [Circuit vs packet switching](https://www.bctengineer.com/question.md?key=semester_5%2Fdata_communication%3Acircuit-vs-packet-switching) — Data Communication, chapter 7, asked 4×
- [Switching, circuit vs packet, X.25 layers](https://www.bctengineer.com/question.md?key=semester_5%2Fdata_communication%3Aswitching-define-compare-x25-layers) — Data Communication, chapter 7
- [Packet vs message switching](https://www.bctengineer.com/question.md?key=semester_5%2Fdata_communication%3Apacket-vs-message-switching) — Data Communication, chapter 7
- [Packet switching](https://www.bctengineer.com/question.md?key=semester_5%2Fdata_communication%3Apacket-switching-explain) — Data Communication, chapter 7, asked 3×

## Related in other subjects

- [Datagram vs virtual circuit switching](https://www.bctengineer.com/question.md?key=semester_8%2Ftelecommunications%3Adatagram-vs-virtual-circuit) — Telecommunications, chapter 8
- [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×
- [Virtual circuit switching](https://www.bctengineer.com/question.md?key=semester_7%2Fcomputer_networks_and_security%3Avirtual-circuit-switching) — Computer Networks and Security, chapter 2
- [Circuit switch vs packet switch](https://www.bctengineer.com/question.md?key=semester_8%2Ftelecommunications%3Acircuit-vs-packet-switch) — Telecommunications, chapter 8