Network

As the NCCS will be a distributed control system it will have to rely enormously on the network³.

The network must have the following characteristics :

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be an industry standard well supported by commercial vendors and software,

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have sufficient bandwidth to support quasi-realtime control i.e. it must support a sustained traffic between two nodes of a minimum of 10 Hz for small messages with 50 Hz being desirable for data capture from radiometers,

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transmission speeds must be predictable,

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it must be secure from the outside world,

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it must support the Internet protocol standard TCP/IP,

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because networks are evolving all the time the network chosen should be easily upgradeable to accommodate new standards.

Based on the above requirements the obvious choice for the network is Ethernet using TCP/IP as protocol. In order to make Ethernet predictable and secure the Ethernet control segment should be a dedicated segment separate from the rest of the observatory Ethernet segment(s). Sustained traffic load should not exceed a maximum of 30% to ensure predictability. Access to the control segment should only be allowed to the computers dedicated to control. One of the control computers should have two Ethernet cards so that it can act as (IP) router between the control network and the rest of the world. Ethernet can be upgraded to 100 MHz when necessary.