RACOM RipEX, Руководство пользователя

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• in report-by-exception networks the load of hops connecting the centre to major repeaters forms
the bottle-neck of total network capacity. Moving these hops to another channel, or, even better, to
a wire (fibre, microwave) links can multiply the throughput of the network. It saves not only the load
itself, it also significantly reduces the probability of collision. More on that in the following chapter
3.6..
3.6. Hybrid networks
If an extensive area needs to be covered and multiple retranslation would be uneconomical or unsuitable,
RipEX’s can be interconnected via any IP network (WLAN, Internet, 3G, etc.). This is quite simple be-
cause RipEX is a standard IP router with an Ethernet interface. Consequently interconnecting two or
more RipEX's over a nested IP network is a standard routing issue and the concrete solution depends
on that network.
3.7. Assorted practical comments
Let us mention few issues, whose influence on network reliability or performance is sometimes neglected
by less experienced planners:
• Both vegetation and construction can grow. Especially when planning a high data rate hop which
requires a near-LOS terrain profile, take into consideration the possible future growth of obstacles.
• When the signal passes a considerable amount of vegetation (e.g. a 100m strip of forest), think of
the season. Typically the path loss imposed by vegetation increases when the foliage gets dense
or wet (late spring, rainy season). Hence the fade margin should be increased if your field measure-
ments are done in a dry autumn month. The attenuation depends on the distance the signal must
penetrate through the forest, and it increases with frequency. According to a CCIR, the attenuation
is of the order of 0.05 dB/m at 200 MHz, 0.1 dB/m at 500 MHz, 0.2 dB/m at 1 GHz. At lower frequen-
cies, the attenuation is somewhat lower for horizontal polarization than for vertical, but the difference
disappears above about 1 GHz.
• Though being a rare problem, moving metallic objects may cause serious disruptions, especially
when they are close to one end of the radio hop. They may be cars on a highway, blades of a wind
turbine, planes taking off from a nearby airport runway etc.
• Even when the signal is very strong, be careful when considering various cheap whips or more
generally any antennas requiring a ground plane to function properly. A tempting scenario is to use
the body of the metallic box, where the radio modem and connected application equipment (often
a computer) is installed, as the ground plane, which leads to never-ending problems with locally
RipEX Radio modem & Router – © RACOM s.r.o. 40
Network planning