Is Multi-Link Operation of 802.11be TCP Friendly? Analysis and Solution

IEEE 802.11be introduces MLO (Multi-Link Operation) where MLDs (Multi-Link Devices) can take advantage of the multiple available radios to concurrently transmit over frequency channels located in the 2.4, 5 and 6 GHz bands. As the flow is distributed across multiple links, there might be some interesting consequences of this on the performance, especially in the case of TCP traffic, as it involves the transmission of TCP ACKs in the reverse direction of TCP data packets. In this paper, we analyze the interaction of MLO with TCP using the latest 802.11be models supplied by network simulator NS-3 (version 3.40). As expected, throughput increases with multiple links; however, the latency suffers in many cases, specifically the tail latency. This is in contradiction to one of the key objectives of MLO, which is to improve latency. We then find out that the root cause is an increase in collisions with the number of links. We thus propose a solution where we map certain links to a specific traffic type. We observe that it reduces collisions and helps improve both throughput and latency.