Frame aggregation in 802.11n

Open NetSim and Select Examples > Internetworks > Wi-Fi > 802.11n Frame Aggregation then click on the tile in the middle panel to load the example as shown in below Figure.

Figure4-13

The following network topology is shown in NetSim UI as shown below Figure.

Figure4-14

Network Settings

  1. In the Environment Settings, Grid length is set to 50m * 50m
  2. Distance between Access Point and the Wireless Node is 20m
  3. Set DCF as the medium access layer protocol under datalink layer properties of Access point and wireless node.
  4. Packet Trace option is enabled
  5. Click on the Application icon present in the top ribbon/toolbar
    a. CBR Application with 100 Mbps Generation Rate (Packet Size: 1460, Inter Arrival Time: 116µs)
    b. Set Transport Protocol to UDP
  6. WLAN Standard is set to 802.11n and No. of Frames to Aggregate is set to 1 in both access point and wireless node (Right-Click Access Point or Wireless Node > Properties > Interface Wireless > No. of Frames to Aggregate)
  7. Channel Characteristics: Path Loss Only, Path Loss Model: Log Distance, and Path Loss Exponent: 3. (Wireless Link Properties)
  8. Simulate for 10s and check the throughput in the results window
  9. Go back to the scenario and increase the No. of Frames to Aggregate to 5 and 10 respectively and check the throughput in the results window.

Results and discussion#

No of Frames Aggregated Application Throughput
1 23.97 Mbps
5 44.78 Mbps
10 54.24 Mbps
  • Frame aggregation is responsible for joining multiple MSDUs into a single MPDU that can be delivered to the physical layer as a single unit for transmission. As we increase the number of frames aggregated it results in lesser number of ack’s. Hence, more data frames are transmitted per unit time leading to a higher application throughput.
  • For No. of frames to Aggregate is set to 5, we get five successive frames followed by a WLAN_Block_Ack (which is used to acknowledge that five frames are received successfully). Users can observe this in Packet Trace by filtering Tx_ID as Access Point and Wireless Node.
  • Note that in the early stages of the simulation the AP would transmit whatever the number of frames/packets in its buffer. It will not wait for 5 frames to be aggregated, if say number of frames to be aggregated is set as 5. If Access Point buffer has more than 5 frames, it will aggregate 5 frames and then send. After sending 5 frames it will receive one WLAN_Block_Ack.