Wi-Fi MAC Protocols
Wi-Fi HT20/40
ESP32-C2 supports Wi-Fi bandwidth HT20 and does not support Wi-Fi bandwidth HT40 or HT20/40 coexist.
Wi-Fi QoS
ESP32-C2 supports all the mandatory features required in WFA Wi-Fi QoS Certification.
Four ACs (Access Category) are defined in Wi-Fi specification, and each AC has its own priority to access the Wi-Fi channel. Moreover, a map rule is defined to map the QoS priority of other protocol, e.g., 802.11D or TCP/IP precedence is mapped to Wi-Fi AC.
The table below describes how the IP Precedences are mapped to Wi-Fi ACs in ESP32-C2. It also indicates whether the AMPDU is supported for this AC. The table is sorted from high to low priority. That is to say, the AC_VO has the highest priority.
IP Precedence |
Wi-Fi AC |
Support AMPDU? |
|---|---|---|
6, 7 |
AC_VO (Voice) |
No |
4, 5 |
AC_VI (Video) |
Yes |
3, 0 |
AC_BE (Best Effort) |
Yes |
1, 2 |
AC_BK (Background) |
Yes |
The application can make use of the QoS feature by configuring the IP precedence via socket option IP_TOS. Here is an example to make the socket to use VI queue:
const int ip_precedence_vi = 4;
const int ip_precedence_offset = 5;
int priority = (ip_precedence_vi << ip_precedence_offset);
setsockopt(socket_id, IPPROTO_IP, IP_TOS, &priority, sizeof(priority));
Theoretically, the higher priority AC has better performance than the lower priority AC. However, it is not always true. Here are some suggestions about how to use the Wi-Fi QoS:
Some really important application traffic can be put into the AC_VO queue. But avoid using the AC_VO queue for heavy traffic, as it may impact the management frames which also use this queue. Eventually, it is worth noting that the AC_VO queue does not support AMPDU, and its performance with heavy traffic is no better than other queues.
Avoid using more than two precedences supported by different AMPDUs, e.g., when socket A uses precedence 0, socket B uses precedence 1, and socket C uses precedence 2. This can be a bad design because it may need much more memory. To be specific, the Wi-Fi driver may generate a Block Ack session for each precedence and it needs more memory if the Block Ack session is set up.
Wi-Fi Aggregate MAC Protocol Data Unit (AMPDU)
ESP32-C2 supports both receiving and transmitting AMPDU, and the AMPDU can greatly improve the Wi-Fi throughput.
Generally, the AMPDU should be enabled. Disabling AMPDU is usually for debugging purposes.
Wi-Fi AMSDU
ESP32-C2 supports receiving AMSDU.
Wi-Fi Fragment
ESP32-C2 supports Wi-Fi receiving and transmitting fragment.