Cirronet HopNet 10 Series, User Manual

Page: 53 / 106

Multipoint Networks
800281 Rev. B HopNet Family of Products 45
Multipoint Networks
Introduction
Most multipoint networks require a base station with Omni-directional coverage,
such as the HN-1010 (outdoor applications) or the HN-1510 (indoor applications).
The wireless base station modem is typically combined with one of the following:
•
2 dB dipole antenna
•
9 dB omni-directional high-gain antenna
•
9 dB directional corner reflector
•
14 dB directional corner reflector
•
15 dB Yagi antenna
•
18 dB parabolic dish antenna
•
24 dB parabolic dish antenna
•
5 dB mobile antenna
You can use any of the HopNet wireless modems on the remote nodes of the
network. Using the HN-210 or the HN-3010 wireless modems with the integrated
antennas on the remote nodes can minimize cost and effort.
Packet Format
If the base station is to be responsible for directing data to a specific remote in point-
to-multipoint mode, the data sent to the base station by the user application must
adhere to a packet format. This allows transmissions from the base station to be
directed to a specific remote. Data received by a base station from a remote is
similarly formatted to identify to the user application the remote that sent the
transmission. The remotes may still use transparent mode without formatting to
send data to the base, if desired. HopNet supports 9 protocol formats that are
described in detail below. The protocol format is selected through the
Set Protocol
Mode
command.
Base and remote radios can use protocol modes to insure that a packet is transmitted
to the base without being broken up over multiple hops. The
data length
value in the
data packet becomes the effective minimum packet length and maximum packet length
for that packet. Note that if the remote
data length
is set to a number of bytes that is
longer than the number of bytes that can be transmitted by a remote on a single hop,
the packet will be discarded. For the base, this value is set by the
Set Base Slot Size
command. For remotes this value is dynamically available through the
Get Maximum
Data Length
command or may be calculated based on the maximum number of
remotes that can ever be registered at one time. See Sections 5.3 and 2.2.3
respectively. Also note that using protocol modes effectively disables
Data Transmit
Delay
. This means that a packet will not be transmitted until the entire packet has
been sent to the radio, regardless of the amount of time it takes.