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Topics to Consider

Reliability for Wireless Field Network

Sensor / field device applications

Emerson’s Smart Wireless field network solutions utilize self-organizing network technology to ensure that your measurement information will always be available. Self-organizing networks automatically optimize connectivity to achieve greater than 99% data reliability. Unlike many approaches to in-plant wireless which require direct line-of-sight between the instrument and the communications gateway, Emerson’s Smart Wireless approach ensures the greatest network integrity by allowing devices to communicate with each other. This means there is no single point of failure, every device serves as a network connector. The gateway automatically finds the best communication paths for each device. Then the gateway continuously monitors these paths for degradation and repairs the paths if required. In the event a temporary obstruction blocks a direct connection, the gateway automatically reroutes the signal to an adjacent device, ensuring network reliability and data integrity.

To achieve reliability higher than 99% Smart Wireless products employs five methods of diversity:

Time diversity is a technique in which data transmission is scheduled intelligently to minimize collisions and recover from losses. WirelessHART achieves time diversity by the use of Synchronized Time Division Multiplexing in which time slots are dynamically managed. The optimizing algorithm maximizes the packet success rate of any wireless link in the network by avoiding collisions.

The coding diversity technique allows effective use of the radio spectrum while enhancing reliability. With this method, a specific transmission can be easily separated from the noise of other communications going on at the same time. WirelessHART leverages this technology from the IEEE802.15.4 radio standard.

Frequency diversity is a technique where the wireless devices dynamically choose different channels of operation to avoid jamming and/or mitigate interference from other wireless systems. WirelessHART achieves frequency diversity by the use of channel hopping.

Path/Space diversity is enabled by the use of mesh networking. The objective is to provide redundant communication paths for the communication between two or more wireless devices. In addition, this technique allows the use of lower power transmissions (enough to be heard by a neighbor router) which minimizes coexistence issues due to power jamming.

Power diversity is performed by controlling the transmission power of radio links to the minimum level where destination devices can receive the signal, in order to limit the RF pollution against the other users of the spectrum.

Reliability for Wireless Plant Network

Business / operations applications

The Self-Configuring and Self-Healing Network

  • The Cisco Aironet 1500 Series access points can be installed anywhere power is available, without the need for a network connection. Intelligent wireless routing based on LWAPP allows a remote access point to dynamically optimize the best route to the connected network within the mesh, providing resiliency against interference and helping ensure high network capacity. LWAPP also performs a smoothing function to signal condition information, ensuring that the ephemeral nature of RF environments does not affect network stability.
  • Deployment and management costs for the access points are reduced through support of zerotouch configuration deployments and through the ability of the access points to bring themselves back to operational status (self-heal) in response to interference or outages.

Managed Mesh Network

  • Cisco Wireless Control System is a centralized platform for WLAN planning, configuration, and management.
  • Cisco WCS itself facilitates load balancing and traffic management, policy provisioning, network optimization, troubleshooting, user tracking, and monitoring for end-to-end security.

Robust Software

  • The Cisco mesh solution software provides robust, optimal parent selection and fast convergence to help nodes organize themselves quickly and support better mesh network management.
  • It includes mechanisms to guard against stranded access points, as well as a software-based recovery mechanism so that engineers or administrators do not have to dispatch a technician to the access points any time one goes down.
  • The network automatically recovers from mis-configurations, such as a wrong IP address, DHCP server errors, bridge group name typos, or mis-provisioning of the network.
  • Cisco’s “exclusion list” algorithm allows a child node to intelligently exclude a parent node in case of a routing problem, and only return to the relationship based on the parent node’s subsequent behavior.

802.11 QOS

  • Cisco QoS standard is based on 802.11e-2005, an approved amendment to the IEE 802.11 standard. This specification defines a set of QoS enhancement for WLAN applications through modifications of the MAC layer, allowing QoS to be configured with great precision. QoS-enabled access points have the ability to request specific transmission parameters (such as data rate or jitter) that allow more complex applications to work more effectively on the Wi-Fi network.
  • Based on this standard, the capabilities of the wireless network for providing a high-quality data stream are enhanced through a new coordination function, the Hybrid Coordination Function (HCF). This provides two methods of channel access, both of which define traffic classes to help differentiate high-priority and low-priority traffic.