---
title: "Delays in packet switched network"
subject: "Internet and Intranet"
chapter: 1
key: "semester_8/internet_and_intranet:packet-switched-delays"
source: https://www.bctengineer.com/q/semester_8/internet_and_intranet/packet-switched-delays
site: BCT Engineering
---

# Delays in packet switched network

Internet and Intranet · Chapter 1: Introduction

- Asked in: 2069 Bhadra (old course), 7 marks
- Video: [1.4 Performance](https://www.youtube.com/watch?v=hm1y4LsphQQ) — JimKurose
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_8/internet_and_intranet/packet-switched-delays
- Whole chapter: https://www.bctengineer.com/md/semester_8/internet_and_intranet/chapter-1

## Question

Explain the various types of delays in packet switched Network.

## Short answer

Nodal delay comprises processing (header check), queuing (buffer wait), transmission (L/R), and propagation (d/s). Queuing delay increases with traffic intensity; transmission delay depends on packet size and link rate; propagation depends on distance. Total end-to-end delay is the sum over all hops.

## Answer

In a packet-switched network a packet passes through many nodes (routers) from source to destination. At each node it suffers a **nodal delay**:

**d_nodal = d_proc + d_queue + d_trans + d_prop**

```text
 Host A ---[ Router ]------------- Host B
            ^   ^   ^       ^
         proc queue trans  prop
```

1. **Processing delay (d_proc):** the time the router takes to examine the packet header, check for bit errors and decide the output link (routing table lookup). It is usually microseconds or less.

2. **Queuing delay (d_queue):** time the packet waits in the output buffer before it can be sent because other packets are ahead. It depends on traffic intensity **La/R** (L = packet size in bits, a = average arrival rate in packets/s, R = link rate in bps). If La/R is near 1 the delay becomes very large; if La/R > 1, the buffer fills and packets are lost. It varies from packet to packet (jitter).

3. **Transmission delay (d_trans):** time to push all the bits of the packet onto the link.
   **d_trans = L / R**
   Example: L = 1500 bytes = 12,000 bits, R = 10 Mbps, so d_trans = 12,000 / 10^7 = 1.2 ms.

4. **Propagation delay (d_prop):** time for a bit to travel along the link from one end to the other.
   **d_prop = d / s**, where d is link length and s is propagation speed (about 2 x 10^8 m/s in fibre/copper).
   Example: 2,000 km link, so d_prop = 2 x 10^6 / 2 x 10^8 = 10 ms.

Note: transmission delay depends on packet size and link rate; propagation delay depends on distance and medium. They are different.

**End-to-end delay** for N links in a path with no queuing: roughly N(d_proc + d_trans + d_prop). In a store-and-forward router the whole packet must arrive before it is forwarded, so d_trans appears at each hop.

Ways to reduce delay: faster links (lower d_trans), fast hardware (lower d_proc), proper queue management and QoS (lower d_queue), shorter routes or CDNs (lower d_prop).

## Check yourself

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

1. What are the four components of nodal delay?
   A. Processing, queuing, transmission, propagation
   B. Processing, routing, switching, receiving
   C. Queuing, error, buffer, hop
   D. Transmission, DNS, ARP, propagation
   Answer: A. d_nodal = d_proc + d_queue + d_trans + d_prop. (Key point: Nodal delay components)

2. A 1500-byte packet is sent on a 10 Mbps link. What is the transmission delay?
   A. 12 ms
   B. 0.12 ms
   C. 1.2 ms
   D. 10 ms
   Answer: C. L = 12,000 bits, so d_trans = 12,000 / 10^7 = 1.2 ms. (Key point: Transmission delay calculation)

3. A 2,000 km link with propagation speed 2 x 10^8 m/s has what propagation delay?
   A. 1 ms
   B. 10 ms
   C. 100 ms
   D. 0.1 ms
   Answer: B. d_prop = d/s = 2 x 10^6 / 2 x 10^8 = 0.01 s = 10 ms; it depends on distance and medium, not packet size. (Key point: Propagation delay)

4. What happens to queuing delay as traffic intensity La/R approaches 1 and goes above 1?
   A. Delay stays constant
   B. Delay becomes very large near 1; above 1 the buffer fills and packets are lost
   C. Delay drops to zero
   D. Only propagation delay increases
   Answer: B. Near-saturated links give very large queuing delay, and La/R > 1 overflows the buffer causing loss. (Key point: Queuing delay and traffic intensity)

## Related in other subjects

- [Queuing theory in delay systems](https://www.bctengineer.com/question.md?key=semester_8%2Ftelecommunications%3Aqueuing-theory-delay-systems) — Telecommunications, chapter 6