On the Buses: Last station still far off 2

Published:2011/8/9 21:39:00 Author:Amy From:SeekIC

David Daamen

Networking

Standards like RS-485, Ethernet, FireWire, HomePNA HomePlug, MoCA, USB and XI0 are primarily descrip­tions of ways to communicate over a physical medium. HomePNA, for instance, is a standard with widespread use in the USA, describing how connections with speeds up to 240 Mbit/s can be established within the home using the (existing) telephone wiring. The Multimedia over Coax Alliance has published a standard based on the same principle: making use of existing cabling — in this case, coax cabling already installed in many homes for the distribution of (analogue) radio and TV signals. According to the MoCA, the standard is future-proof and capable of speeds up to 1 Gbit/s.

The HomePlug standard now ’on the rise’ in Europe also employs existing cabling — the mains wiring installed in your home. Speeds up to 14 Mbit/s are said to be within reach.

Arguably, wireless standards like Bluetooth, ZigBee, DECT, WiFi and IrDA also belong to the network cate­gory. The ’Bus Systems’ inset provides links to more information on all these standards.

In the network layer, the focus is on physical interoper­ability (connectivity), hence most standards do not go beyond the first layers of the OSI model.

The upshot is that such standards are not terribly useful without agreements on how data is being transmitted and this is where the need for a networking protocol becomes apparent. Today, IP (Internet protocol) is the most fre­quently used.

Communication

The comms layer comprises standards like BACnet, Bat-iBUS, EIB, EIBA, LonWorks and KNX. The latter will be reverted to below. These are primarily communications systems. The standards describe the data packets trav­elling up and down the network between machines (terminals), without a connection having been set up beforehand.

In this context, inter-operability is crucial. One of the ways to achieve it is to agree on a transmission scheme that’s not dependent on the data being sent. This will fit in very well in an ’open’ system, the protocols being uni­versal and free for use by anyone. Incidentally, a system based on ’open’ specifications is eventually closed of its own accord when it is used in a certain application or configuration!

Application

Within the standards normally associated with this layer, the emphasis is on system and application management. Consequently, the main aim of the standard is to define a so-called network-independent API (Application Programming Interface). This category comprises standards like CEBUs, ModBus, PROFIBUS, HAVi, EHS, OSGi and UPnP.

Whereas CEBus is used predominantly in the US of A, initiatives like HAVi and UPnP refer to truly global devel­opments. You may already have heard of UPnP, the con­cept of plug-and-play being familiar from the Windows/PC environment where it is fully integrated in the hardware and software concepts.

For clarity’s sake we should mention that there is an amount of overlap in the categories mentioned. For example, certain standards from the network category are often complemented with solutions for management and control. The opposite also applies where a certain medium is sometimes chosen as the basis for an applica­tion group. This applies to, for example, HAVi, a system with Its roots firmly in Firewire (IEEE 1394) and intended as a connection standard for digital audio and video sig­nals (Figure 2).

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