Huawei Yale University Samsung Huawei Nokia Bell Labs Telefonica Cost metric is a basic concept in Application-Layer Traffic Optimization (ALTO), and different applications may use different cost metrics. Since the ALTO base protocol (RFC 7285) defines only a single cost metric (i.e., the generic "routingcost" metric), if an application wants to issue a cost map or an endpoint cost request to determine the resource provider that offers better delay performance, the base protocol does not define the cost metric to be used. This document addresses the issue by introducing network performance metrics, including network delay, jitter, packet loss rate, hop count, and bandwidth. There are multiple sources (e.g., estimation based on measurements or service-level agreement) to derive a performance metric. This document introduces an additional "cost-context" field to the ALTO "cost-type" field to convey the source of a performance metric.