Frame aggregation is a feature of the IEEE 802.11e, 802.11n and 802.11ac wireless LAN standards that increases throughput by sending two or more data frames in a single transmission.

Every frame transmitted by an 802.11 device has a significant amount of overhead, including radio level headers, media access control (MAC) frame fields, interframe spacing, and acknowledgment of transmitted frames. At the highest data rates, this overhead can consume more bandwidth than the payload data frame.To address this issue, the 802.11n standard defines frame aggregation to group several data frames into one large frame. Because management information needs to be specified only once per frame, the ratio of payload data to the total volume of data is higher, allowing higher throughput.

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 packets aggregated it results in a lesser number of ACKs. Hence, more data packets are transmitted per unit time leading to a higher application throughput. 


Frame aggregation is useful in situations where each transmission unit may have significant overhead (preambles, headers, cyclic redundancy check, etc.) or where the expected frame size is small compared to the maximum amount of information that can be transmitted


Follow the steps given below to understand frame aggregation using Netsim:


1. Create a scenario as shown below:

2. In Access point and wireless node properties, select standard as IEEE802.11n

3. Set channel characteristics to Pathloss_only, pathloss_model as Log distance, and pathloss_exponent as 3.

4. Create a CBR application with a Generation rate 100Mbps (packet size=100 bytes and IAT=116 microseconds).

5. In Physical layer properties of Wireless node and Access point, set No. of packets aggregated to 1.

6. In the wireless node, set Wireshark capture to offline.

7. Enable packet trace and run the simulation for 10s.

8. Repeat the above steps with  No. of packets aggregated=3,5,7,10 etc.


Results &Inference


1. Throughput obtained:


With an increase in the number of packets to be aggregated, there will be an increment in the throughput obtained.


2. 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 packets to be aggregated (if say number of packets aggregated is 5). If the Access Point buffer has more than 5 packets, it will aggregate 5 packets and then send. After sending 5 Packets it will receive one WLAN_Block_Ack.


Packet aggregation can be viewed in Packet trace and Wireshark by following steps:


a. Open Packet trace and filter Transmitter_ID to Access_Point and Wireless_Node. You can see that for packet       

    aggregation=1,a WLAN_BLOCK_ACK packet will be transmitted after the transmission of one successful data packet.


b.Open Packet capture for the wireless node from the results dashboard


 In Wireshark capture, you can see the data packets transmitted as follows:

After each data packet gets transmitted, a BLOCK_ACK packet is transmitted. This can be observed in Wireshark as follows:


c. Similarly, for No. of packets aggregated=3, you will get 3 successful data packets followed by a WLAN_BLOCK_ACK and WLAN_RTS-CTS packets.


d. In Wireshark, we can see the data packet followed by a Block_ACK and RTS-CTS packets:


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