Access control systems: Ethernet vs proprietary bus network cabling

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When designing a security system for a site, the question of how it should be interconnected is often one of the first you need to answer. Should you choose a system that has its own proprietary bus network, which might require twisted pair cabling, or perhaps one based on an ethernet backbone? Both types of network have their advantages and disadvantages as discussed below.

Some security systems are based on a number of modules, and each module is connected to its own ethernet connection. One big advantage of a system like this is that, in many cases, it can be much more convenient, allowing the installer to utilise existing network cabling and other infrastructure, rather than needing to install new cabling.

On the other hand, if a security system relies entirely on networking infrastructure controlled by others, typically the IT department, then the stability and reliability of the security system is dependent on that network being available when your system needs it.

Another potential disadvantage is that certain areas of the premises may not be equipped with a nearby network outlet, and if the network in question is not managed by you, it might be necessary to request the IT department add an outlet for you to use.

A system with its own proprietary bus network can also have advantages. Perhaps the first and most important difference is that, because the network cabling is installed specifically for the security system, the designer has the luxury of being able to decide exactly where the wiring should be placed and terminated. Another advantage is that the cabling would only be used by the security system, so the installation company can be sure the network will always be available, and there would be very little chance part of it could be accidentally unplugged.

Another potential advantage is that some systems are able to run bus cabling of distances well over 1,000 metres, whereas individual ethernet connections are typically limited to 100 metres or less. Another consideration, which applies particularly to intruder and holdup alarm systems, is that communications between elements of the security system should not be prevented by other factors, such as a power failure. Obviously, if a part of such a network is formed by ethernet infrastructure, such as network switches and/or media converters, then that infrastructure needs to be battery backed, and the power supply must be monitored. In some cases, the equipment must be able to withstand a power failure of 24 or even 60 hours.

Such long standby times are unusual in IT infrastructure when selecting a system. It is usually most helpful to have a flexible system that can support a number of different deployment options. This is especially true if the system in question can support a combination of different interconnection types. For example, a single system that can contain a variety of interconnections can then be deployed in a very wide variety of systems where existing infrastructure may be used to aid in the design and deployment:
Fibre connections – Many modern sites are pre-cabled with existing fibre connections which can be used to form a dedicated interconnection between system components which can be of the order of kilometres apart.
Ethernet connectivity – With the increasing ubiquity of networking within premises, some elements of a security system can be deployed using the existing infrastructure.
Repeater – For very large or densely packed systems, a device that can be used as a form of “repeater” can be extremely useful to permit very long interconnect cabling distances.

Some security systems can be set up to enable multiple discrete access control modules to be deployed, connected to an existing ethernet network, and treated as a single ‘system’ by the management software, while retaining full offline functionality in the event the network becomes unavailable. Further, some systems can be formed by utilising a fusion of all of the above connectivity methods.

In practice, of course some applications would suit a deployment that relied solely on ethernet connectivity. Some other applications, especially systems or parts of systems that are part of an intruder and/or holdup alarm system, would better suit a deployment using a dedicated proprietary bus network, and other systems would suit a combination of these communications options. Selecting a system that can be deployed in a variety of ways can be enormously helpful in providing the flexibility projects might demand.