IoT based smart city communication protocols consists of short ranges and long range technologies like Zigbee, Bluetooth, WI-FI, WiMAX, GPRS, LTE etc. These protocols are used based on the applications. For example, short range communication protocols can be used in smart metering, e-health, traffic management, parking etc. low cost, low power consumption, maximum quality of service, flexibility, security, reliability, scalability are the requirements of IoT based smart city solutions. Fiware, ocean, OM2M and open daylight IoT data management are the open IoT platforms. The authors identified busan green u-city, smart Santander, Chicago are case studies running for IoT smart city solutions. Security, privacy, trust, interoperability, big data are the challenges in IoT based smart city solutions.