---
title: "Channel allocation problem"
subject: "Computer Networks and Security"
chapter: 3
key: "semester_7/computer_networks_and_security:channel-allocation-problem"
source: https://www.bctengineer.com/q/semester_7/computer_networks_and_security/channel-allocation-problem
site: BCT Engineering
---

# Channel allocation problem

Computer Networks and Security · Chapter 3: Data Link Layer

- Asked in: 2072 Kartik, 5 marks
- Video: [Channel Allocation in Computer Network | Static channel allocation v/s Dynamic channel allocation](https://www.youtube.com/watch?v=i_-2xdlkksU) — STUDY4SUB
- 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/channel-allocation-problem
- Whole chapter: https://www.bctengineer.com/md/semester_7/computer_networks_and_security/chapter-3

## Question

Explain the channel allocation problem with example.

## Short answer

The channel allocation problem is dividing a shared broadcast channel among competing users fairly with minimal collisions. Static assignment (FDM/TDM) wastes capacity when traffic is bursty; dynamic allocation (e.g., CSMA/CD) gives channel on demand.

## Answer

The **channel allocation problem** is how to divide a single broadcast channel among competing users so that each gets a fair share with the least collisions and highest efficiency. It is solved in the MAC sublayer.

#### Static allocation
The channel is divided into fixed portions by **FDM** or **TDM** and each of N users gets 1/N of the capacity.
**Example:** a 100 Mbps channel is divided among 10 users, each gets 10 Mbps. If only 2 users have data, the other 8 portions are idle, but the 2 active users still get only 10 Mbps each. Delay also becomes N times larger: T_FDM = N·T. So static allocation wastes bandwidth with bursty traffic.

#### Dynamic allocation
The channel is given on demand, based on these assumptions:
1. **Station model:** N independent stations, each generates frames, then waits until sent.
2. **Single channel:** all stations use one shared channel.
3. **Collision:** if two frames overlap in time, they are destroyed and must be resent.
4. **Time:** continuous (frames start at any time) or slotted (only at slot boundaries).
5. **Carrier sense:** stations can (CSMA) or cannot (ALOHA) sense whether the channel is busy before sending.

**Examples of dynamic protocols:** ALOHA, CSMA, CSMA/CD, token passing and reservation.

For instance, in 10 offices sharing one Ethernet cable, CSMA/CD lets any office use the full bandwidth whenever it is free instead of a fixed 1/10 share.

## Check yourself

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

1. What is the channel allocation problem?
   A. Choosing the best route for packets
   B. Dividing one broadcast channel among competing users fairly with few collisions
   C. Assigning IP addresses to hosts
   D. Encrypting a shared channel
   Answer: B. It is how to share a single broadcast channel among users efficiently; it is solved in the MAC sublayer. (Key point: Channel allocation problem)

2. A 100 Mbps channel is statically divided among 10 users and only 2 have data. What happens?
   A. Each active user gets 50 Mbps
   B. Each active user still gets only 10 Mbps and 8 shares are idle
   C. Each active user gets 100 Mbps
   D. The channel is shut down
   Answer: B. Static FDM/TDM gives fixed 1/N shares, so unused shares are wasted and active users cannot borrow them. (Key point: Static allocation waste)

3. How does static division among N users affect delay?
   A. Delay is reduced N times
   B. Delay is unchanged
   C. Delay becomes N times larger (T_FDM = N.T)
   D. Delay becomes N^2 times larger
   Answer: C. Each user gets only 1/N of the capacity, so delay is N times that with the whole channel. (Key point: Delay in static allocation)

4. Which assumption distinguishes CSMA from ALOHA in the dynamic allocation model?
   A. Time is slotted
   B. Stations can sense whether the channel is busy before sending
   C. Collisions are not destroyed
   D. Only one station exists
   Answer: B. Carrier sense lets stations in CSMA check the channel; ALOHA stations cannot. (Key point: Dynamic allocation assumption)

## Related in other subjects

- [Non-linear effect in FDMA; channels numerical](https://www.bctengineer.com/question.md?key=semester_7%2Fwireless_communication%3Afdma-nonlinear-channels) — Wireless Communication, chapter 7