Low price - so it can be a layer really crowded and cheap to deploy.
Integrated communications: Radio Frequency, Infra-red, LPWAN, WIFI, serial, ethernet, etc.
Open hardware design
Integration with Layer 0 by I2C, 1Wire, SPI, etc
Small storage capacity for data caching and code download
Software and protocols
FreeRTOS/Mongoose, OpenWRT and similars. Even Linux
CoAP and MQTT
Autodiscovery and ZeroConf(mdns, dns-sd, ssdp, uPnp, etc)
AllJoyn has to be chequed
Functions
With Layer0
** Sensor reading and calibration
** Actuators control
** Very simple protocol bridging
Within Layer1
** Local data cache
** Neighbours discovery
** Communication proxy
** Path discovery
With Layer2
** Send/publish data, status and structures (CoAP/MQTT)
** Send/publish own resources and Layer0 capabilities (resources and services)
** Receive/subscribe to commands and logic/code updates
** Simple communications with Blockchain
** Service discovery / announcement
Management
Web GUI with:
** Monitoring (REST)
** Configuration
** Updates