
Chapter 4: Feature Description
Innovative Techniques to Boost Capacity and Reduce
Latency
ACM Radio Scripts
An ACM radio script is constructed of a set of profiles. Each profile is defined by a modulation
order (QAM) and coding rate, and defines the profile’s capacity (bps). When an ACM script is
activated, the system automatically chooses which profile to use according to the channel fading
conditions.
The ACM TX profile can be different from the ACM RX profile.
The ACM TX profile is determined by remote RX MSE performance. The RX end is the one that
initiates an ACM profile upgrade or downgrade. When MSE improves above a predefined
threshold, RX generates a request to the remote TX to upgrade its profile. If MSE degrades below
a predefined threshold, RX generates a request to the remote TX to downgrade its profile.
ACM profiles are decreased or increased in an errorless operation, without affecting traffic.
ACM scripts can be activated in one of two modes:
•
Fixed Mode. In this mode, the user can select the specific profile from all available profiles in
the script. The selected profile is the only profile that will be valid, and the ACM engine will be
forced to be OFF. This mode can be chosen without an ACM license.
•
Adaptive Mode. In this mode, the ACM engine is running, which means that the radio adapts
its profile according to the channel fading conditions. Adaptive mode requires an ACM license.
The user can define a maximum profile. For example, if the user selects a maximum profile of 9,
the system will not climb above the profile 9, even if channel fading conditions allow it.
ACM Benefits
The advantages of PTP 820S’s dynamic ACM include:
•
Maximized spectrum usage
•
Increased capacity over a given bandwidth
•
11 modulation/coding work points (~3 dB system gain for each point change)
•
Hitless and errorless modulation/coding changes, based on signal quality
•
An integrated QoS mechanism that enables intelligent congestion management to ensure that
high priority traffic is not affected during link fading
ACM and Built-In QoS
PTP 820S’s ACM mechanism is designed to work with PTP 820S’s QoS mechanism to ensure that
high priority voice and data frames are never dropped, thus maintaining even the most stringent
SLAs. Since QoS provides priority support for different classes of service, according to a wide
range of criteria, you can configure PTP 820S to discard only low priority frames as conditions
deteriorate.
If you want to rely on an external switch’s QoS, ACM can work with the switch via the flow control
mechanism supported in the radio.
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