Introduction
While studying for CompTIA Network+, I couldn't imagine how TPC worked. I could memorize that TPC stands for Transmit Power Control, but I couldn't comprehend why it was needed or how it actually worked.
Once I grasped TCP, everything fell into place. So, I decided to write it down.
What is TPC
TPC stands for Transmit Power Control
In a nutshell, it is a mechanism that automatically adjusts transmission power for Wi-Fi.
Why TPC is needed
If transmission power is too strong：
→ Radio waves spread further than necessary
→ Interfere with adjacent access point
→ Increase power consumption in vain
→ Radio wave end up reaching to outside of building (Security Risk)
If transmission power is too weak：
→ Radio wave cannot reach to an expected range
→ Connection is unstable
Solution
Automatic adjust depends on the situation is needed
→Deliver radio waves only where needed
→ Decrease interference
→ Save power consumption
Familiar example
Volume control for microphone in meeting
When you talk to person close to you
→Small volume is enough（ Decrease electric power）
When you talk to person far from you
→Big volume is required（ Increase electric power）
TPC automatically adjusts the volume for you
How TPC control
TPC is not for detecting devices but for adjusting electric power after measuring the strength of radio wave and feeding back it.
1. Devices connect to an access point
↓
2. Devices measure the strength of the radio waves they receive
↓
3. Devices report the strength to the access point
↓
4. The access point adjust transmission power depends on the information
↓
5. The access point transmits at only power level required
Pros for TPC
1. Reduce interference
→ Do not spread radio wave more than it is needed
→ Decrease interference with an adjacent access point
2. Save power consumption
→ Use only electric power is needed
→ Extend battery life
3. Enhance security
→ Ensure range radio wave reach
→ Prevent radio wave leaking outside a building
4. Improve overall network efficiency
→ Multiple access points work with adequate electric power
→ Improve performance
Relationship with IEEE 802.11h
What is IEEE 802.11h
IEEE 802.11h is a Wi-Fi standard that formally defines TPC and DFS as standard specifications
Why 802.11h is created
Background：
5GHz band has been originally used in military, weather radar, satellite communication
Problem：
Once Wi-Fi began using the same frequency band, interference with existing radar systems became a concern.
Solution：
Standardize TPC and DFS with 802.11h
→ Don’t output radio wave more than needed ( TPC )
→ Avoid frequency interfering with radar ( DFS )
The role of TPC and DFS
TPC（ Transmit Power Control）
→ Adjust transmission power
→ Decrease interference and save power consuming
DFS（ Dynamic Frequency Selection）
→ Automatically switch to other frequency when it detects radar
→ Avoid interference with radar systems
The relationship between TPC and 802.11h
TPC = Mechanism (concept) for automatically adjusting transmission power
802.11h = Defining TPC and DFS as standard
Although TPC existed as a concept before 802.11h, it was formally defined as an official standard by 802.11h
The region 802.11h is needed
It is a duty in mainly Europe
EU regulation：
Wi-Fi devices that use the 5GHz band are required to comply with 802.11h（TPC・DFS）
In fact, it is also common in Japan and North America
The relationship with OSI reference model
Layer 7 Application │
Layer 6 Presentation │
Layer 5 Session │ The layers TPC is not applicable
Layer 4 Transport │
Layer 3 Network │
Layer 2 Data Link │
─────────────────────────────
Layer 1 Physical ← The layer TPC works
─────────────────────────────
TCP operates at Layer 1 to control the physical strength of radio waves
Summary
TPC ：The method to automatically adjust transmission power of Wi-Fi
How it works： Devices measure the strength of received raido waves and report back to the access points
→ Access Point automatically adjust transmission power
Pros：
・Reduce interference
・Save power consumption
・Improve security
・Improve efficiency in whole network
Relationship with 802.11h：
TPC = Concept for automatic adjusting transmission power
802.11h = Define TPC and DFS as standard
→ It is created for prevent interference from radar in 5GHz band
OSI Layer： Physical Layer（ Layer 1）
Conclusion
I used to struggle with even memorizing the term itself, but everything clicked once I understood the relationship between TPC and 802.11h.
TPC = The method to automatically adjust the strength of radio wave depending on the situation 802.11h = The definition of TPC as standard
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