Specifications

was transmitting at the same time, then it will resend the multicast packet. This results in more
multicast packets making it through, but again at a throughput penalty.
The same criteria given for NV Parameter #16 apply to this one as well. You can try setting this
parameter to True, and see if it helps your application. If not, set it back to False.
ID 18 – Collision Avoidance
This lets you control use of “random jitter” to try and reduce collisions. This setting defaults to True.
The SNAP protocol uses a “random jitter” technique to reduce the number of collisions.
Before transmitting a packet, SNAP does a small random delay. This random delay reduces the
number of collisions, but increases packet latency
If you set this parameter to False, then this initial delay will not be used. This reduces latency (some
extremely time critical applications need this option) but increases the chances of an over-the-air
collision.
You should only change this parameter from its default setting of True if there is something else about
your application that reduces the chances of collision. For example, some applications operate in a
“command/response” fashion, where only one node at a time will be trying to respond anyway.
ID 19 – Radio Unicast Retries
This lets you control the number of unicast transmit attempts. This parameter defaults to 8.
This parameter refers to the total number of attempts that will be made to get an acknowledgement
back on a unicast transmission to another node.
In some applications, there are time constraints on the “useful lifetime” of a packet. In other words, if
the packet has not been successfully transferred by a certain point in time, it is no longer useful. In
these situations, the extra retries are not helpful – the application will have already “given up” by the
time the packet finally gets through.
By lowering this value from its default value of 8, you can tell SNAP to “give up” sooner. A value of 0
is treated the same as a value of 1 – a packet gets at least one chance to be delivered no matter what.
If your connection link quality is low and it is important that every packet get through, a higher value
here may help. However it may be appropriate to reevaluate your network setup to determine if it
would be better to change the number of nodes in your network to either add more nodes to the mesh
to forward requests, or reduce the number of nodes broadcasting to cut down on packet collisions.
ID 20 – Mesh Routing Maximum Timeout
This indicates the maximum time (in milliseconds) a route can “live.” This defaults to 0xEA60, or one
minute.
Page 98 of 202 SNAP Reference Manual Document Number 600-0007K