User's Manual

pulsAR radio Operator’s Manual
2-12
2.4.5 Synchronization with NetCrossing Gateways
The Afar NetCrossing Gateway devices convert between a synchronous serial data stream and
Ethernet packets. They can be paired with the PulsAR to establish wireless point to point serial
synchronous links. When you have multiple such links and need to co-locate radios, the gateways
can participate in the heartbeat negotiation and site synchronization. The gateways are equipped with
a SYNC port through which they propagate the synchronization information, without having to
connect the radio LANs together.
Figure 2.6 shows a network with mixed radios and gateways (NxG) and illustrates how the SPAN
synchronization is achieved.
In the gateways the tdd sync-mode can be set to three different values: off (which is the default),
auto, and master. The figure shows the appropriate setting of each gateway. All radios should have
the tdd sync-mode configured to the default auto setting.
Tx Rx Tx Rx Tx Rx
Rx Tx Rx Tx Rx Tx
Time
(A)
(B)
NxG 2
Sync
Radio
2 (A)
NxG 3
Sync
Radio
3 (A)
tdd sync=master
NxG 1
Sync
Radio
1 (A)
NxG 4
Sync
Radio
4 (B)
tdd sync=off
NxG 5
Sync
Radio
5 (B)
NxG 6
Sync
Radio
6 (B)
NxG 9
Sync
Radio
9 (A)
tdd sync=auto tdd sync=off
Radio
7 (B)
Radio
8 (B)
NxG 10
Sync
Radio
10 (A)
tdd sync=off
Figure 2.6– Synchronization with NetCrossing Gateways
The site on the left shows three gateways, each one connected to a respective radio. These radios are
co-located and therefore their TDD cycles need to be synchronized to avoid self-interference. Since
their LAN ports are not connected to each other the synchronization is achieved through the SYNC
ports of the gateways. You must connect all the SYNC ports together in a daisy-chain manner, and
configure the gateways tdd sync-mode to master. In master mode each gateway keeps a cycle timer
running, synchronized to the other gateways. This synchronization is shared, i.e. no single gateway
is the synchronization source. In fact any gateway can be added or dropped without affecting the
cycle timers of the remaining gateways.