1.1 Why 852?

This entry is part 4 of 11 in the series Lon over IP (709.1/852)

As building automation networks continue to expand in size and complexity the ability to  employ building information technology (IT) internet protocol (IP) based infrastructure becomes an important part of a successful integration task. Whether the building automation system (BAS) leverages existing infrastructure or has a dedicated side-by-side system, IT components provide scalability, remote accessibility, and portals into building management systems. Several different terms are used to refer to non-IP based automation networks such as fieldbus. In this article we will use the term Component Network (CN) as a generic description for a network channel whose primary purpose is to connect sensor, actuator, and control endpoint devices. The first requirement for a CN to be able to leverage IP is a means for tunneling the CN over IP. The technique of using another protocol to transport a message over an alternate media is often referred to as tunneling.

Most of the popular CN protocols such as BacNet, LonTalk®, etc have a standard IP tunneling approach. Typically the tunneling approach is very basic, consisting of nothing more than direct unicast TCP or UDP socket connections between endpoint gateways. There is no provision for managing the CN specific requirements that may be deleteriously affected by or incompatible with IP networks. Nor is there any kind of routing capability for bandwidth partitioning. Thus the systems integrator is forced into haphazard or site specific setups that are not scalable or robust to changes in the IT infrastructure. Any traffic management must be done with dedicated LAN or VLAN which requires extensive work on the part of the IT staff. As a result the only viable approach is more costly side-by-side implementation.

In this respect, systems based on the ANSI/EIA 709.1 protocol (trademarked name LonTalk® ) uniquely benefit because 709.1 over IP tunneling is based on a tunneling standard called ANSI/EIA 852, that is designed specifically to overcome IP specific limitations with respect to CN network behavior.  In other words, 852 makes IP tunneling highly transparent to the attached CN protocol. ANSI/EIA 852 also includes support for a virtual CN channel that makes it easier to integrate into existing IT infrastructure.

A 709.1 network is also commonly referred to as a Local Operating Network or LON. This document will use 709.1 network and LON interchangeably. Both the ANSI/EIA 709.1 and ANSI/EIA 852 are defined by the Consumer Electronics Association Technology & Standards R7.1 HCS1 Subcommittee. For more details see http://ce.org/. The current revision of 852 is 852-B but for the sake of brevity, we will just use 852 for short. Also for the sake of brevity the remainder of the document will refer to the standards as 709.1 and 852. When we say LON/IP tunneling we mean tunneling 709.1 over IP using 852. Although 852 is most commonly used for 709.1, it is a generic protocol that could be adapted to other CN protocols besides 709.1.

The important features of 852 that support CN over IP tunneling are as follows:

  • Out of order packet detection and reordering
  • Duplicate packet detection and filtering
  • Packet aggregation
  • Stale packet detection and filtering
  • IP packet authentication
  • Virtual IP/CN channels
  • Multiple devices on a single virtual CN/IP channel
  • Selective forwarding for optimized unicast
  • Multicast CN/IP channels
  • Combined unicast and multicast virtual CN/IP channels
  • Packet segmentation for low latency UDP channel management packets
  • Sever based and manual mode configuration

The goal of this article is to explain some of the beneficial features of 852 for LON/IP tunneling and how it can be applied to BAS integration.

Series Navigation1.5 Configuration2. Applications of the CN/IP Routers
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