Welcome to the third and final segment of our blog series on power-saving methods in modern Wi-Fi systems. In the first blog post, “Exploring Legacy Power Save Methods with Managed Clients“, we delved into Legacy Power Save mechanisms, examining the crucial roles of PS-Poll and Non-PS-Poll, particularly in managing power consumption, especially for older devices connected to Wi-Fi networks. These methods strike a balance between power efficiency and responsiveness.
The second blog, titled “WMM Power Save Test Using Managed Client,” explored technology designed to enhance data transmission efficiency in wireless networks. It introduced you to the concept of conserving power through data packet pauses and the intelligent data buffering of access points. We also discussed WMM/U-APSD, an innovative feature automating power-saving for unscheduled data. It’s a testament to the enduring presence of Wi-Fi, even in our fast-paced, ever-changing environment.
In this final segment, we will dive deeper into the concept of Target Wake Time (TWT) Power Save with a Managed Client. We’ll dive into two TWT modes: Individual TWT and TWT Announced and Unannounced Power Save Mechanisms, exploring how each can be leveraged to optimize your network’s performance.
Target Wake Time (TWT)
Target Wake Time (TWT) reduces power consumption and improves spectral efficiency by enabling devices to determine how often to wake in order to send/receive data. This technology enables 802.11ax deployments to consistently deliver a higher quality of service to many different devices with minimal contention or overlap.
TWT brings two advantages to Wi-Fi products:
- Reduce wireless resource competition among users and make the network more efficient.
- Allow Wi-Fi6 devices to increase sleep time to achieve more power saving.
Individual TWT
Clients will be assigned specific times to wake up and exchange frames. The schedule is determined and delivered by the AP. There is a different mode of TWT such as explicit TWT. A client doesn’t need to know about another client’s TWT values. Each individual device has its own wakeup time.
How to check if Individual TWT is enabled:
Under Action Frame in wireless management – Fixed parameter – Control Field – Negotiation type – Individual TWT.
TWT Announced
In TWT’s announced power save, the devices explicitly communicate with the access point (AP) to schedule their wake-up and sleep periods. This scheduling is coordinated and synchronized between the device and the AP.
TWT announced power save is well-suited for scenarios where the AP and the devices have prior knowledge of their communication needs.
Steps for TWT Announced Power Save Mechanism:
Assumptions:
- One client/station is connected to AP
- Client supports TWT capability from TWT Power Save Mechanism.
Steps:
- In Association Request under HE Capabilities check whether TWT is supported in the client.
2. After the Beacon, client sends one Null Data packet with power management bit 1 (i.e. STA will go to sleep)to AP. AP replies with ACK.
3. Enable the Announced TWT Power Save Mechanism in the client for the chosen time interval.
4. After Enabling TWT we can see the client Request TWT in the Action frame. We can confirm by verifying flow type as Announced.
5. After Enabling TWT request, now AP will respond with Accept TWT in Action Frame. As we see Announced TWT.
6. Run Ping traffic, when AP has buffer data, it indicates in the Beacon frame.
- Beacon frame has TIM [Traffic Indication Map] field. Under TIM there is Partial Virtual Bitmap to indicate for which AID, AP has buffer data.
7. Client checks the beacon frame and if the beacon has the AID of this client, then the client knows the AP has buffer data.
8. Client is ready to receive buffer data.
9. AP starts sending buffer data.
10. After the Data buffered client will send Block ACK to AP.
TWT Unannounced
TWT unannounced power save does not involve explicit scheduling of wake-up and sleep times between devices and the AP. Instead, devices enter a power-saving state autonomously.
This mode is more suitable for devices with unpredictable communication patterns. Devices decide when to wake up based on their immediate data transmission needs.
Steps for TWT Unannounced Power Save Mechanism:
Assumptions:
- One client/station is connected to AP
- Client supports TWT capability from TWT Power Save Mechanism.
Steps:
- In Association Request under the HE Capabilities check whether TWT is supported in the client.
2. After the Beacon, client sends one Null Data packet with power management bit 1 (i.e. STA will go to sleep) to AP. AP replies with ACK.
3. Enable Unannounced TWT Power Save Mechanism in the client for desired time interval.
4. After Enabling TWT we can see the client Request TWT in the Action frame. We can confirm by verifying flow type as unannounced.
5. After Enabling TWT request, now AP will respond with Accept TWT in Action Frame. As we see Unannounced TWT
6. Run Ping traffic, when AP has buffer data, it indicates in the Beacon frame.
- Beacon frame has TIM [Traffic Indication Map] field. Under TIM there is Partial Virtual Bitmap to indicate for which AID, AP has buffer data.
7. Client checks the beacon frame and if the beacon has the AID of this client, then the client knows the AP has buffer data.
8. Client is ready to receive buffer data.
9. AP starts sending buffer data.
10. After the Data buffered client will send Block ACK to AP.
In summary, Target Wake Time (TWT) is a game-changer in Wi-Fi technology, reducing power consumption and enhancing spectral efficiency. It empowers devices to wake up intelligently for data transmission, providing consistent service quality for numerous devices and reducing contention.
TWT Announced Power Save involves explicit communication for scheduled wake-up and sleep, ideal when communication needs are known. TWT Unannounced Power Save is for unpredictable patterns, with devices autonomously waking for data.
Overall, TWT optimizes power efficiency and network performance, meeting the demands of wireless connectivity.
Keep an eye out for more valuable insights and information on this subject. Should you require additional details or wish to discuss how Alethea Communication Technologies can assist in validating power-saving mechanisms for your Access Points, Routers, or Client Devices, please don’t hesitate to reach out to us at sales@aletheatech.com. We’re here to provide the support you need.
Reference
- Understanding WLAN Power Save Mode
- Legacy Power Save Mode
- U-APSD
- Legacy Power Save Test using Managed Client
- WMM Power Save Test using Managed Client
