Smart Factories and the Challenges of the Proximity Network
Networking the Edge Device- The decision to use wired Ethernet over Wi-Fi or 802.15.4 dictates much of the downstream considerations such as distributed intelligence, deployment and longterm maintenance.
Integrating with IT- If IT requires integration with the IIoT network there are really two choices. Either the edge devices use the existing IP network to communicate with the gateway or the integration occurs at the gateway and the edge devices operate in a separate network. 802.15.4 and Wi-Fi can both operate in the 2.4 GHz frequency space. There are mechanisms, such as using specific channels, to keep them from interfering, but this must be considered at design time. Additionally, there are 802.15.4 solutions that run over a 900 MHz carrier frequency that will not interfere.
Data Bandwidth – Two key characteristics of a communication technology is the maximum bandwidth and maximum transmission unit( MTU). 2.4 GHz 802.15.4 typically runs at a line rate of 250 kbps and uses packet sizes of 128 bytes. Wired Ethernet and Wi-Fi support much higher data rates and typical Ethernet MTU sizes.
Data Reliability- Applications typically use the well-proven mechanism of TCP / IP over wired Ethernet or Wi-Fi for data reliability. Although Transmission Control Protocol( TCP) can be run over 802.15.4 it is very undesirable for low-power applications. It requires precious RF time to create a connection and then utilizes a significant portion of each 128-byte packet just for transport. In this case, reliability is typically implemented with a different mechanism much more like reliable UDP. Some robust implementations contain a powered set of 802.15.4 repeaters that store information sent by battery-operated devices for reliable gathering. 802.15.4 provides the ability to mesh so that the communication network can more easily work around obstacles and heal when a particular link is interrupted.
3.3 Backhaul Network
The backhaul network is considered in this paper as it dictates a large portion of the gateway functions, in turn affecting the proximity network. The backhaul network typically runs IP over wired Ethernet, Wi-Fi or cellular.
Integrating with IT- If IT integration is desired then wired Ethernet or Wi-Fi is typically used. The gateway is given an IP address on the internal network and may not even send data outside of the local IT network. For those cases where IT integration is not desired, cellular is used. This is sometimes problematic and cellular coverage can be unreliable in certain locations.
Data Bandwidth- The bandwidth needed in the backhaul network is directly related to the amount of data sent / received to / from the edge devices plus any additional management traffic.
Data Reliability- TCP is used ubiquitously in the backhaul network for data reliability.
- 72- January 2017