This guide describes performance@ functional@ and communication needs of phasor data concentrators (PDCs) for power system protection@ control@ and monitoring applications. The guide covers synchrophasor system needs and testing procedures for PDCs. It includes functional requirements for associated interfaces with phasor measurement units (PMUs) to a PDC and PDC systems. In particular@ it includes requirements for synchronization@ synchrophasor data processing@ and real-time access. Purpose The purpose of this guide is to assist users to specify the performance and functional requirements of typical phasor data concentrators and define performance testing for PDC systems. It includes consideration of PDC latency@ input and output streams supported@ interface and data transport protocols@ the ability to configure output stream payload@ the communication media supported@ time alignment functions@ error handling@ etc.