Cirronet HopNet 10 Series, User Manual

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Network Communication
HopNet Family of Products 800281Rev. B 42
Each remote time slot will be:
10 ms – 2.3 ms – (9)·0.5 ms
10
From our RF data rate of 460.8kbps we see that it takes 17.36
µ
s to send a byte of
data, so each remote will be able to send up to
= 18 bytes of data per hop.
Note that the 18 bytes is the actual number of data bytes that can be sent. If the
HopNet is using a protocol mode, the packet overhead does not need to be
considered. So in this example, the total capacity per remote would be:
If we figure a minimum margin of safety for lost packets and retransmissions of
about 20%, we see that this would be more than sufficient to support 14.4 kbps of
continuous data per remote. It is also useful to remember that the asynchronous
data input to the HopNet is stripped of its start and stop bits during transmission
by the radio, yielding a "bonus" of 10/8 or 25% in additional capacity.
The above calculations are provided as a means of estimating the capacity of a
multipoint HopNet network. To determine the precise amount of capacity, you
can actually set up the radio system and then query the
maximum data length from
one of the remotes in control mode to discover its exact setting. Divide this
number by the hop duration as above to get the remote's exact capacity.
Full Duplex Communication
From an application perspective, the HopNet communicates in full duplex. That
is, both the user application and the remote terminal can be transmitting data
without waiting for the other to finish. At the radio level, the base station and
remotes do not actually transmit at the same time. If they did, the transmissions
would collide. As discussed earlier, the base station transmits a synchronization
signal at the beginning of each hop. After the base station transmission, the
remotes will transmit. Each base station and remote transmission may be just
part of a complete transmission from the user application or the remote terminal.
Thus, from an application perspective, the radios are communicating in full
duplex mode since the base station will receive data from a remote before
completing a transmission to the remote.
= 0.32 ms
0.32 ms
17.36
µ
s us
18 bytes
10 ms
= 18 kbps