Afar AR24027, Operator'S Manual

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AR24027 Operator’s Manual
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2.3.3 PULSAR Network synchronization
The AR24027 can be operated in a fixed TDD mode, where the complete cycle is divided into fixed
length outbound and inbound phases. You can specify this cycle split to be 50/50 or asymmetric.
When you co-locate multiple devices you must choose a fixed split and it must be the same for all the
co-located radios. The radios will then synchronize their cycle periods so that all co-located radios
transmit at the same time and then receive at the same time. This avoids the situation depicted in
Figure 2.1 altogether. With a synchronized site you can then deploy upwards of 24 radios at the same
location.
The key to the synchronized PULSAR network is the generation and distribution of the
synchronization information or
heartbeat. All the different software builds implement the same
synchronization protocol, so you can build networks that mix different topologies (PtP, PmP and
Linear Networks) and yet keep all radios synchronized. At any site where there is more than one
device co-located the devices detect each other, and automatically negotiate which should become the
source of the heartbeat. If that device later is turned off or fails, another device will take its place
without user intervention.
Figure 2.2 shows an example of a mixed network with multiple topologies. When the whole network
is synchronized each radio runs its TDD in one of two timings, A or B, as shown in the figure. All
radios at a single site run on the same cycle.
The following are guidelines you need to follow to achieve a successful synchronization in a complex
network:
1. At any site with multiple radios ensure that all radios are connected to the same LAN. The LAN
connection between radios must be FULL DUPLEX. Use the
“>ether ” command to check that
the radio Ethernet port is in full duplex (see also section 2.3.5 for synchronizing a site where the
radios are paired with NetCrossing Gateways).
2. In the Linear Network the TDD split is always 50/50. Therefore if the total network includes a
section with one or more linear networks you must specify a 50/50 split in all networks.
3. The most typical situation where you would use an asymmetric split is when you have mutliple
hubs in a point to multipoint application with asymmetric traffic. You must configure all the
hubs with the same TDD split. All the remotes automatically set their TDD split to the
complement of the hubs (if the hubs were set to transmit 70%, the remotes will automatically be
set to transmit 30%). If you then co-locate a radio with any of those remotes, it needs to have its
TDD split set to transmit 30%. This restriction makes the 50/50 split the most natural when the
network starts growing in complexity.
4. A remote radio synchronizes its cycle to the hub. Therefore if it is co-located with another radio
it must be the source of the heartbeat. Any other radio co-located with the remote can only be a
hub or a leftmost node of a linear network.
5. The same applies to all radios in a linear network other than the leftmost radio. All those radios
synchronize their cycles to the respective left radio. Therefore they must be the heartbeat source
for that site.