[Paper Review] A Simple Multipath OpenFlow Controller using topology-based algorithm for Multipath TCP

Chawanat Nakasan, Kohei Ichikawa+2 more|arXiv (Cornell University)|Sep 28, 2015

Network Traffic and Congestion Control3 citations

TL;DR

This paper proposes smoc, a simple OpenFlow controller that uses network topology to route Multipath TCP (MPTCP) subflows across multiple paths, avoiding congestion by minimizing shared links. It outperforms traditional routing in both LAN and WAN SDN testbeds by improving bandwidth utilization without modifying applications or hosts.

ABSTRACT

Multipath TCP, or MPTCP, is a widely-researched mechanism that allows a single application-level connection to be split to more than one TCP stream, and consequently more than one network interface, as opposed to the traditional TCP/IP model. Being a transport layer protocol, MPTCP can easily interact between the application using it and the network supporting it. However, MPTCP does not have control of its own route. Default IP routing behavior generally takes all traffic through the shortest or best-metric path. However, this behavior may actually cause paths to collide with each other, creating contention for bandwidth in a number of edges. This can result in a bottleneck which limits the throughput of the network. Therefore, a multipath routing mechanism is necessary to ensure smooth operation of MPTCP. We created smoc, a Simple Multipath OpenFlow Controller, that uses only topology information of the network to avoid collision where possible. Evaluation of smoc in a virtual local-area and a physical wide-area SDNs showed favorable results as smoc provided better performance than simple or spanning-tree routing mechanisms.

Motivation & Objective

• To address the bottleneck and underutilization issues in MPTCP when using default IP routing.
• To design a lightweight, backward-compatible OpenFlow controller that leverages network topology for multipath routing.
• To improve MPTCP performance in multi-homed, multi-site SDN environments, especially in bandwidth-constrained WANs.
• To evaluate the controller's effectiveness in both virtual LAN and real-world WAN testbeds.
• To explore scalable and efficient multipath routing strategies for MPTCP using only topology information.

Proposed method

• The controller uses a topology-based algorithm that selects paths based on minimizing shared edges and hops.
• It computes path sets for MPTCP subflows using only static network topology, without requiring real-time monitoring or active probing.
• The controller is integrated with POX and OpenFlow to install flow rules on switches for subflow distribution.
• It maintains backward compatibility by not modifying applications or host stacks, only adjusting virtual machine kernel settings.
• Path installation is reactive, with a 2–3 second delay observed in experiments.
• The approach avoids complex mechanisms like bandwidth monitoring or active probing, focusing on simplicity and low overhead.

Experimental results

Research questions

• RQ1 Can a topology-only approach effectively distribute MPTCP subflows across multiple paths to avoid congestion?
• RQ2 How does the performance of a topology-based controller compare to traditional routing (e.g., STP) and simple routing in SDN environments?
• RQ3 What impact does path installation delay have on short-lived MPTCP flows, and how can it be mitigated?
• RQ4 How scalable is the controller in large networks with many switches and flows?
• RQ5 To what extent can a simple, reactive controller achieve high bandwidth utilization in WANs?

Key findings

• smoc outperformed POX S-T and simple routing in both LAN and WAN testbeds, achieving higher throughput.
• In the PRAGMA-ENT WAN testbed, smoc’s TCP flows reached approximately 160 Mbps after ~160 seconds due to slow window growth from high RTT.
• The controller achieved better bandwidth utilization than STP and simple routing by avoiding path collisions and underutilization.
• The 2–3 second path installation delay was observed to impact short flows and scalability, especially in high-volume environments.
• The use of only topology information proved effective despite the lack of real-time bandwidth data, suggesting that topology-based routing is viable for MPTCP.
• Proactive path preinstallation and caching of frequently used path sets were identified as promising strategies to reduce latency and improve scalability.