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Time synchronised networks

Up until now distributed real time systems have usually been based on fieldbuses, but

switched Ethernet is now an option. This is partly due to features such as: bandwidth,

possibility of prioritisation and industrial specification of network equipment. However,

also because Ethernet equipment prices have dropped.

Variable delay (latency) in a switched network means that data sent from nodes can

be affected by different delays. This is due, among others, to the current load on the

network. The accuracy of time synchronised transfer mainly depends on the following

factors:

1. Variable network delay depends on: network load, speed, packet size and the archi-

tecture used in switches

2. The preferred protocol is of minor significance bearing in mind the above condi-

tions, however we recommend SNTP/NTP as these are standards with few limita-

tions.

3. Time stamping of incoming and outgoing data packets is done as close to the hard-

ware as possible, i.e. on the lowest layers of the OSI-model.

Time client

Time delay

Time server

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