Motorola PTP 400 Series User Manual

Page 78

Link Mode Optimization:

By default, Link Mode Optimization of a point-to-point link is set to

‘IP Traffic’. In this configuration the wireless minimizes packet transmission errors by

automatically adapting the active modulation mode based on instantaneous vector error

measurements and the presence of codeword errors. This mode of operation is

recommended for connection oriented IP traffic protocols where packet loss is perceived by

the protocols as an indication of network congestion. It is recommended that when using this

mode of operation the ARQ state is set to ‘enabled’. The ‘TDM Traffic’ mode is recommended

for E1 / T1 applications and connectionless oriented protocols. In this mode the wireless link

is optimized for minimum transmission latency and preservation of data throughput by

allowing the link to maintain a higher modulation mode in the presence of a limited number of

codeword errors. It is recommended that when operating the link in TDM mode that the ARQ

state is set to disabled and that the Spectrum Management controls are used to fix the

wireless link to a single frequency. This can be achieved by using the installation wizard to

configure single frequency operation. In either case, a system reboot will be required.

Link Symmetry:

By default Link Symmetry of a point-to-point link is ‘Symmetrical Data Rate

(1:1)’ in this configuration the ratio of time the wireless link spends transmitting and receiving

is equal. When Link Symmetry is configured to Asymmetric Data Rate (2:1) the wireless link

Master will spend twice as long transmitting as receiving. It should be noted that the data rate

available to the end users might not follow these ratios exactly. The exact data rates will be

dependant on the prevailing modulation modes.

Throughput Optimization:

Throughput Optimization has two distinct modes:

• Data Throughput

configures the wireless link for maximum data throughput.

• Low Latency

configures the wireless link to minimize packet latency during transmission

over the wireless link. When Low Latency mode is selected, the Link Symmetry is

automatically reconfigured to a symmetric link. Link asymmetry is not supported in Low

Latency mode.

Note:

The “Throughput Optimization" option is not available on 4.9GHz variants.

ARQ State:

Automatic Repeat reQuest (ARQ) is a mechanism where packets lost due to

transmission errors over the wireless link are retransmitted rapidly. The retransmission helps

to prevent TCP congestion mechanisms from inadvertently interpreting intermittent packet

loss as network congestion. ARQ must be enabled on both ends of the point-to-point link for it

to function.