# Q1(a) · Mission-critical switching choice

Subject: Computer Networks

Exam: TEE

Reader: https://deep-learning-study-room.vercel.app/cn/#tee/papers/paper-2024-ai-final/q1a

Canonical: https://deep-learning-study-room.vercel.app/read/cn/tee/papers/paper-2024-ai-final--q1a/

Exact historical variant. Current-syllabus questions solved; excluded topics and source limitations stated.

### Q1(a). A rocket-launch mission needs real-time communication with minimal delay and absolute certainty of delivery. Which switching technique would you select and why? [5 marks]

### Answer

**Definition.** Switching selects how data passes through intermediate network nodes from a source to a destination.

**Simple meaning.** Raasta reserve karna, poora message ruk-ruk ke bhejna, ya chhote packets bhejna—yeh teen ideas hain.

Swipe across the diagram to read its labels ↔

![Three switching techniques: what is forwarded?](https://deep-learning-study-room.vercel.app/cn/fig/switching.2b51f856d9.svg)

Diagram: Three switching techniques: what is forwarded?. Labels: Three switching techniques: what is forwarded? | Three switching techniques: what is forwarded? | 1. Circuit: reserve a path, then stream data | Setup → reserved capacity → data transfer → release. | 2. Message: store the entire message at each node | Large forwarding unit; no packet-level pipeline. | 3. Packet: divide, then forward packet by packet | Shared links can simultaneously carry different packets.

Circuit, message and packet switching

## Understand it step by step

1. **Circuit switching:** establish a circuit, reserve resources, transfer data, then release the circuit. Capacity is dedicated even during a silent period.
2. **Message switching:** each intermediate node receives the entire message before forwarding it. Large messages require large buffers and can delay later messages.
3. **Packet switching:** divide data into smaller packets. Nodes forward packets individually; different links can carry successive packets at the same time.
4. The Internet uses packet switching. A traditional circuit-switched telephone call illustrates the circuit concept. Many current calls use packet-based networks, so do not label every phone call circuit-switched.

| Aspect | Circuit switching | Message switching | Packet switching |
| --- | --- | --- | --- |
| Unit handled | Continuous stream on established circuit | Whole message | Small packets |
| Resource use | Capacity reserved along a circuit | Shared; message stored at each intermediate node | Shared; each packet stored/forwarded in this model |
| Setup | Required before data transfer | No circuit setup required | Datagram: no connection setup; virtual circuit: setup |
| Delay | Setup delay, then relatively predictable service | Large store-and-forward delay for long messages | Variable delay; packet pipeline can reduce completion time |
| Main limitation | Reserved capacity can be idle | Large buffers; unsuitable for tight delay needs | Headers, possible queueing/loss; datagrams may reorder |

#### Practical example

A campus transferring web pages and files has bursty traffic. Packet switching allows multiple users to share link capacity instead of reserving a circuit that remains idle between bursts.

For ordinary bursty office data, packet switching is generally appropriate because resources are shared among active transfers. The design must still account for queueing, loss and the required service quality.

**Yaad rakho:** Circuit reserves; message waits whole; packets pipeline.

**Choice:** circuit switching reserves a path and capacity before communication, giving predictable service and avoiding packet-queue contention after setup. A dedicated voice circuit is a standard example. It sacrifices statistical sharing and may waste reserved capacity when silent.

For the rocket case, reservation fits the stated timing need. However, no switching technique alone guarantees absolute delivery: link failures, bit errors and equipment faults still require redundancy, error control and fault-tolerant system design. State the reservation advantage without promising impossible certainty.