Cambium Networks cnReach N500 Handleiding (253 Pagina's)

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cnReach N500 User Guide

Technical Reference

phn-4673_002v000 (March 2018)

3-16

Max Payload Bytes

The Max Payload Bytes (or ‘packet size’) configuration is the key parameter to establish the size of the

frame used in the air interface. The cnReach radio determines the duration of the uplink and downlink

portions of the frame by combining the # of bytes in the max payload and the data rate of the

maximum modulation. Essentially, the frame duration is the amount of time it takes the radio to send

the maximum size payload at the maximum modulation.

Keep in mind that this setting is only used in multipoint networks. In PTP networks, the frame duration

adjusts based on the modulation. In PMP networks, the frame must be fixed to enable communications

to all of the end points.

With this in mind, there are several reasons to modify the max payload bytes:

• By choosing different max payload bytes from the AP and EP direction you can adjust how much

time is spent in each direction. For example if most of the data is in the uplink direction you can

make the EP payload bytes larger than the AP payload bytes.

• Selecting a larger value for payload bytes reduces the percentage of time allocated to the fixed

overhead of each packet and in most cases increases overall capacity of the network. (the

exception is when the network is predominately sending small packets)

• The smaller the payload bytes the lower the latency but also a lower capacity (see number 2).

• A larger max payload bytes will also take longer to transmit especially at low modulations. This can

cause increased packet loss in a noisy environment as the noise floor can change in the middle of a

packet transfer.

• You MUST set the Max payload bytes to AT LEAST the value in the tables below for Minimum Max

Payload Bytes. The reason for this is that the radio must have enough duration in each direction to

send 64 bytes.

Max Payload Bytes for Access Point and End Point range from 64 to 1600 Bytes with a default setting of

256.

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