Technical data

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Different types of switches
Depending on the application and installation requirements there are a number of dif-
ferent switches. First we differentiate between the interfaces, where there are TX
(copper) and FX (fibre). Other variants are unmanaged/managed switches, this means
you either have or do not have the possibility of communicating with and monitoring
the switch using SNMP. Finally we differentiate between ring and time synchronised
switches which are used when you intend to build a ring network with redundancy or
a network where demands on time synchronisation are made.
FRNT and Spanning Tree
Complex networks with requirements on redundancy must be possible to reconfigure
should a network error occur.
Reconfiguration is handled by the switch, that is to say, the switch must identify that
a link error has occurred. This can be done in different ways, of which standardised
solutions are, IEEE Spanning Tree Protocol (STP) or Rapid Spanning Tree Protocol
(RSTP). The Spanning Tree Protocol creates a connection through the network at the
same time as it eliminates unwanted loops in the network. Redundancy is created by
the protocol keeping the tree structure in the network in order, where some connec-
tions are blocked (set in standby mode). When a segment can not be reached, the
network is reconfigured using the Spanning Tree algorithm, which results in connec-
tions set to standby becoming active. Reconfiguration of a STP network can take up to
30 seconds, as new conditions must be calculated and switches updated. This calcula-
tion is complex as the network does not have a determined topology. RSTP is a deve-
lopment of STP with faster reconfiguration, from the earlier 30 seconds a network can
be reconfigured in 5 seconds.
There are also specially developed solutions available, for example, Fast Recovery
Network Topology (FRNT), which is used in our ring switch R200 and time synchro-
nised switch T200. FRNT is a patented solution that reconfigures the network
extremely quickly, <30 ms. This is achieved through the switches knowing the network
configuration, which is also a ring topology. In addition, reconfiguration is event con-
trolled, ”idle traffic” is sent between each device in the ring to check whether the link
is up. When an error is detected, information is sent immediately to the ring’s focal
point (ringmaster) which reconfigures the network.
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