Mobile phone with Multipath-TCP: How many subflows?

Question

Only one subflow over LTE and one subflow over WiFi, or a number of subflows over LTE and WiFi?

Thank you.

Answer 1

@Lena I'm afraid your answer is not %100 correct. MPTCP as well as TCP use "pairs" of IP's and ports. So, the limitation of subflows is mainly in the port quantity. Thus, it is possible to create more than one subflow between two IP.

And what for? It is mainly to give more robustness to the connection. You can transmit the same thing from two subflows, and then compare it in the destination.

But it can be used to obtain a higher throughput too. Where? Imagine you have a mobile phone with two IP addresses and a server with two network interfaces. You can create four independent subflows pairing IP1-IP3, IP1-IP4, IP2-IP3, IP2-IP4.

Mobile phone: IP1 (LTE) --- IP2 (WiFi)

Server: IP3 ---- IP4

In conclusion, you can use different configurations for different purpouses. But yes, it is possible to have more than 2 subflows with 2 network interfaces.

Answer 2

The subflow is still a TCP connection, so it needs an IP address. Usually, when the mobile is connected to WiFi, it has an IP. The same is for LTE. So the mobile device has two IP addresses available. That's why when MPTCP connection is established, it's one subflow over LTE and one over WiFi. If multiple IP addresses can be established over LTE or Wifi, then for sure multiple subflows can be created over one channel.