Minimum-Pairs Protocol
The minimum-pairs (or MP) is an active measurement protocol to estimate in real-time the smaller of the forward and reverse one-way network delays (OWDs). It is designed to work in hostile environments, where a set of three network nodes can estimate an upper-bound OWD between themselves and a fourth untrusted node. All four nodes must cooperate, though honest cooperation from the fourth node is not required. The objective is to conduct such estimates without involving the untrusted nodes in clock synchronization, and in a manner more accurate than simply half the round-trip time (RTT). The MP protocol can be used in delay-sensitive applications (such as placing content delivery network replicas) or for secure Internet geolocation. Methodology The MP protocol requires the three trusted network nodes to synchronize their clocks, and securely have access to their public keys, which could be achieved through a closed public key infrastructure (PKI) system. The untrusted node need not follow suit because it is not assumed to cooperate honestly. To estimate an upper bound to the smaller of the forward and reverse OWD between node A and the untrusted node X (see figure for notation), X first establishes an application-layer connection to all three nodes.