Nevertheless, if more length is needed, it can be increased by the use of repeaters. Up to 128 devices can be installed on a single network in the physical layer using RS485 with a max physical length of 4000 feet, and speeds up to 115k baud. This method of BACnet the most common use to connect field devices to controllers and routers, to control applications. The MS stands for Master – Slave although in practice there are not many slaves out there and the TP stands for Token Passing. Routing between BACnet/IP and non-BACnet/IP networks is specified, including the case where IP and non-IP BACnet devices reside on the same LAN. This includes such things as encryption/decryption and compression/decompression that can be performed outside of the process of generating BACnet APDU/NPDUs, i.e., without altering the existing standard. Secondly, the concept of defining an extensible mechanism for peer-to-peer management of BACnet messages means that other manipulations. First it is extensible to other, future transport mechanisms such as IPv6, ATM, Sonet among others. There are many advantages to this approach. BACnet/IP communication is implemented by defining a new protocol layer called the “BACnet Virtual Link Layer” or BVLL. The BACnet/IP allows users to transfer data to and from devices over Ethernet using BACnet/IP Protocol. There are two distinct BACnet protocols being BACnet IP and BACnet MSTP. With ease of use in mind, BACnet is a certifiable standard, though certification is not required. Unlike connected protocols where devices have ongoing data transfers, communication in BACnet is unscheduled without any time critical operations. BACnet is an unconnected, peer network where any device can send service requests to any other device. These objects are defined by the BACnet specification and have both required and optional data. For example, the Control and Information Protocol (CIP) used in industrial application, BACnet uses objects to represent data on a network. Today, the majority of users prefer to use Ethernet. This leads to cost savings over proprietary systems, but also tremendous savings in resources, installation costs, maintenance costs, and energy savings. To further simplify things, with BACnet, devices from various manufacturers work in conjunction with each other with little or no additional integration. In these applications, motion detectors can be used to more efficiently measure human presence and activity and with a timer to make sure lights are off after hours. In a typical HVAC application BACnet would handle lighting, heating/cooling with a programmable thermostat, smoke detection and some form of security/safety applications. As a result, the BACnet protocol uses mobile and cloud-hosted devices, head-end computers, general-purpose direct digital controllers, and application-specific or unitary controllers with equal effect. Secondly, BACnet provides the ability to control and monitor any building automation process, to meet the needs of users, integrators, and equipment vendors. As a result, this approach standardizes the representation of processes and data. Its benefits include reusability, refactoring, extensibility, maintenance and efficiency). The BACnet protocol uses an Object-oriented approach (Object-oriented programming allows for simplified programming. Therefore, BACnet became an alternative to the proprietary and closed protocols offered by large vendors that were in existence at that time. Furthermore, in June of 1995, ASHRAE (The American Society of Heating, Refrigerating and Air-Conditioning Engineers) also adopted this same standard. In June of 1987, a group of HVAC and Building Automation professionals met in Nashville to develop this standard, open protocol specifically for the building automation industry. For example, by sharing sensors and data, BACnet gives our applications similar abilities to sight, hearing, taste, smell and touch to help us make better decisions. The protocol displays how data is represented and moved between BACnet nodes on the network and the services used to move it. BACnet (Building Automation and Control Network), is the communications protocol that defines communication services used between building control systems and building automation end-devices.
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