Serial data port variable parameters
Two key serial port parameters will be adjusted during optimization. The following initial values have been
determined as a suitable for the SEL 2505 device which is the fastest device 4RF has lab tested. It is a
suitable start point to carry out optimization for other devices.
Inter-Frame Gap – initially set to 0.2
• IFG is dependent on serial line baud rate only
• The Mirrored Bits® protocol is essentially timed to a base clock, the slower the baud rate the longer
the period to transmit a packet resulting in less time between packets
• A low baud rate is ideal as it increase the time period before a ROK error will occur as this is
dependent on serial packet transmission time
• The minimum baud rate currently proven to provide reliable communications is 9600 bit, with this
rate an IFG of 0.2 is required to be used
• With the 2505 device the IFG increases with increases in serial baud rate, while easier to detect
gaps the ROK error period is reduced
MTU – initially set to 32 bytes
• Dependent on serial line baud rate, channel size, modulation, security settings, intended traffic mix
and all other settings that influence OTA speed and capacity available for external traffic
• MTU affects latency, if a large MTU then the radio will ‘wait’ for the number of bytes before sending
the packet OTA
• Ideally a low MTU will be used – the minimum needs to support the various settings above and
intended mix of traffic
• MTU can be changed in steps of +/- 8 when trying different configurations
• Refer table in section 5 for start point of MTU based on channel size, modulation and serial baud
rate, this assumes the general radio settings as above
• Increase by 8 for new devices or in attempt to support some Ethernet or other services
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