Detecting Cellular Middleboxes Using Passive Measurement Techniques

The Transmission Control Protocol (TCP) follows the endto-end principle – when a client establishes a connection with a server, the connection is only shared by two physical machines, the client and the server. In current cellular networks, a myriad of middleboxes disregard the end-to-end principle to enable network operators to deploy services such as content caching, compression, and protocol optimization to improve end-to-end network performance. If server operators remain unaware of such middleboxes, TCP connections may not be optimized specifically for middleboxes and instead are optimized for mobile devices. We argue that without costly active measurement, it remains challenging for server operators to reliably detect the presence of middleboxes that split TCP connections. In this paper, we present three techniques (based on latency, loss, and characteristics of TCP SYN packets) for server operators to passively identify Connection Terminating Proxies (CTPs) in cellular networks, with the goal to optimize TCP connections for faster content delivery. Using TCP and HTTP logs recorded by Content Delivery Network (CDN) servers, we demonstrate that our passive techniques are as reliable and accurate as active techniques in detecting CTPs deployed in cellular networks worldwide.