The 852 protocol acts as the transport service to convey 709.1 messages over Internet Protocol (IP) networks, i.e. tunnel. As previously mentioned, in 852 parlance the tunneled protocol is a Component Network (CN) protocol. The 852 protocol is a generic tunneling protocol and is not limited to 709.1. However, a particular implementation of the 852 protocol may only support the tunneling of a single CN protocol. The tunneled CN messages have no information or awareness of the tunneling process. Although some of the figures in this document use CN or CN/IP to represent a component network or component network to internet protocol connection, the CN in this case is 709.1
852 not only provides the vehicle to transport 709.1 messages across IP, but it also provides management of these connections or routes. A logical grouping of 852 devices that exchange packets is called an 852 channel. One may think of an 852 channel as a kind of virtual LAN on an IP network. An 852 device may be a node, a router, a gateway, a bridge, a monitor, or some combination of one or more of these devices. The typical use of 852 is that the devices are 709.1 routers that tunnel over IP using 852. These are often called LON/IP or LON/IP-852 routers. Currently Adept SystemsTM, EchelonTM, and LoyTecTM manufacture LON/IP (709.1/852) routers. Additionally other types of devices such as (endpoint sensor, actuator, control) nodes and multi-protocol gateways are starting too appear. Indeed one could potentially build a complete 709.1 system using an IP-852 based channel such as Ethernet or WiFi as the only channel.
Network connection devices can operate at different layers of particular networks protocol stack. 709.1 is an OSI 7 Layer type protocol. Whereas the Internet Protocol has only 4 layers. (See below for a diagram of the different layers of the two protocols.)
Fig. 1.1: Network Layers
A network connector is a device that joins different parts of a network. Connectors have a specific name that is dependent on the layer at which the connector operates. For example a router operates at the network layer and a gateway at the application layer. Because higher layers of the protocol do not have access to some of the information stripped away by lower layers, network connectors operating at different layers have different capabilities. There is also some abuse of terminology so that the descriptions of network connectors from different manufacturers may be confusing. For example, a repeating router may be called a repeater for short. Although a repeating router acts similarly to a physical layer repeater, it operates at the network layer and is not equivalent. Getting the terminology right, requires knowing which layer a network connector operates.
Fig. 1.2: Network Connector Types and Associated Layers