What are the physical rate, theoretical rate, and actual rate in the 802.11 standard

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1. The WLAN physical rate is the physical layer rate of a radio interface, that is, the physical layer rate at which a radio interface keeps sending data. For example, the 802.11b physical rate is 11 Mbit/s and the 802.11g physical rate is 54 Mbit/s.

2. What is the relationship between the user theoretical rate and physical rate? The physical rate indicates only the performance of a radio interface, but users only care about how much bandwidth and rate they can use. The following uses the 802.11b standard as an example and assumes that a user packet is 1500 bytes. After a 32-byte header is prepended to the packet, the packet is longer than an Ethernet data frame. The checksum bits in 802.11b and Ethernet are both 4 bytes. The longest data frames (1536 bytes) are transmitted at the rate of 11 Mbit/s. The transmission time is [1536 (bytes) x 8 (bit)]/11 Mbit/s = 1117 microseconds.

On the WLAN, a link code and PLCP header (exclusively used by WLAN) are prepended to a data frame. The transmission time of the link code and PLCP header is 192 microseconds. In addition to the interframe gap, a random period (delay offset) is required during the transmission of data frames on WLANs. In 802.11b, the average delay offset is 360 microseconds.

On the WLAN, an ACK frame is received from the remote end each time a data frame is sent to confirm successful communication. The next data frame is sent only after the ACK frame is received. The total transmission time is 213 microseconds.

The transmission time of a 1500-byte data frame includes the waiting time and ACK transmission time, equaling 1882 microseconds.

1117 + 192 + 360 + 213 = 1882

In this case, the theoretical maximum UDP throughput for 1500-byte data frames is 7.1 Mbit/s.

3. The preceding calculation result is based on the UDP model and 1500-byte frames. The actual usage scenarios are much complex than the preceding scenario. Additionally, the number of STAs also greatly affects AP performance. Therefore, the actual user rate is usually tested. In most cases, the actual rate of 802.11b can reach about 4.7 Mbit/s.

Other related questions:
Is the WLAN rate the upstream or downstream rate
WLAN rate refers to the wireless rate of data transmissions between APs and STAs or between bridges and downstream nodes. Devices on both ends work in half-duplex mode, that is, they can only receive or send data at a time. The WLAN rate is the sum of upstream and downstream rates. Common users mainly use Internet access services to browse web pages, most of which is downstream traffic. In this case, the WLAN rate refers to the downstream rate.

Why is the rate limit for ICMP packets configured on an interface card inconsistent with the actual rate limit
An AR router implements rate limit to Layer 3 unicast packets by converting the number of packets into the number of bytes. ICMP packets are converted based on 84 bytes per packet. For example, if the rate limit configured for ICMP packets is 10, then the actual rate limit is calculated as 84 x 10 = 840 byte/s. If the actual packet length is not equal to 84 bytes, the actual rate limit will deviate from the configured value.

How to configure rate limiting on a physical interface
WAN-side physical interfaces support rate limiting. You can limit the rate of outgoing packets on a WAN-side physical interface by configuring the percentage of the rate of packets against the interface bandwidth. Perform the following configuration: 1. Run the system-view command to enter the system view. 2. (Optional) Run the qos overhead layer { link | physics } command to configure the mode to calculate the packet length during traffic policing or traffic shaping. By default, the system counts the physical-layer and link-layer compensation information in the packet length during traffic policing or traffic shaping. 3. Run the interface interface-type interface-number command to enter the interface view. Run the qos lr pct pct-value [ cbs cbs-value ] command to configure the percentage of traffic rate against the interface bandwidth. By default, the percentage of traffic rate against the interface bandwidth is 100.

What are the relationships between the conference rate and participant rate
The conference rate is the actual rate for a site to join a conference. The participant rate is the rate adapted by the multipoint control unit (MCU) and is the minimum value of conference rates. For example, terminal A and terminal B joins a conference at conference rates of 2 Mbit/s and 4 Mbit/s respectively. To ensure smooth video display in the two sites, the MCU adapts the rate to 2 Mbit/s, which is the participant rate of the conference.

Why is the actual rate limit different from the ICMP packet rate limit configured on the interface board
AR series routers convert the number of packets to a number of bytes when limiting the rate of Layer 3 unicast packets on the interface board. Each Internet Control Message Protocol (ICMP) packet is converted to 84 bytes. For example, if the ICMP packet rate limit is configured as 10 packets per second, the actual rate limit is 840 (84 x 10) bytes per second. If the actual length of ICMP packets is not 84 bytes, the actual rate limit is different from the configured value. -If the actual length of ICMP packets is greater than 84 bytes, the actual rate limit is less than the configured rate limit. For example, if the ICMP packet rate limit is configured to be 10 packets per second, and the actual packet length is 320 bytes, the actual rate limit is 840/320 (rounded down) packets per second, that is, 2 packets per second. -If the actual length of ICMP packets is less than 84 bytes, the actual rate limit is greater than the configured rate limit. For example, if the ICMP packet rate limit is configured to be 10 packets per second, and the actual packet length is 64 bytes, the actual rate limit is 840/64 (rounded down) packets per second, that is, 13 packets per second.

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