Contiki was the first operating system for wireless sensor nodes that provided IP communication with the uIP TCP/IP stack. In 2008, the Contiki system incorporated uIPv6, the world’s smallest IPv6 stack. The footprints of the uIP and uIPv6 stacks are small: less than 5 kB for the uIP stack and approximately 11 kB for uIPv6. This makes them suitable for use in the constrained environment of a wireless sensor node.