User's Manual
Introduction
Trango Broadband Wireless — User Manual M2400S Rev. A
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The M2400S radios are powered using "Power over Ethernet" for ease and low-cost installation. A
single Cat-5 cable carries both Ethernet and DC power to the radio.
Both APs and SUs feature a handy "site survey" tool to check for interference as well as RSSI tools for
optimizing antenna positioning. The M2400S also feature variable receiver threshold, full power control,
dual polarized antennas, and various link diagnostic tools
SmartPolling™ & Bandwidth Throttling
One of the major advantages of the M2400S system is the ability of the AP to handle multiple SU
connections and share the 5 Mbps data throughput efficiently. Bandwidth allocation is managed
by the AP’s SMART Polling™ algorithm according to provisioning rules set up by the system
administrator. The AP polls each SU in a round robin format to determine if the SU has data to
transfer. The SU only transmits the data “upstream” to the AP when the AP gives authorization
via a “transmit grant”. The SU passes every “downstream” data packet from the AP and
identifies packets intended for it. In order for an SU to communicate with an AP, the system
administrator must first add the MAC address and ID number of the SU to the user database in
the AP. The SMART Polling™ algorithm will poll active SUs more often, thus making the most
efficient use of the 5 Mbps bandwidth. Several other parameters are considered in the Smart
Polling™ algorithm including upstream/downstream committed information rate (CIR),
upstream/downstream maximum information rate (MIR), and Priority Setting.
Each of the above parameters is set in the AP by the system administrator and cannot be
controlled at the SU. These parameters will be covered in greater detail later in this text.
When power is first applied to a properly installed SU, it will scan all available channels, listening
for a grant from an AP with matching Base ID and the SU’s MAC in the AP’s SU Database. The
SU will then stop on that channel and respond to the AP using maximum RF power. Before the
AP can add the SU to the polling list, it must authenticate the SU by verifying the MAC address,
and performing a ranging operation to the SU. Upon successfully locating and ranging the SU,
the AP will then add the SU to the normal polling list. Once the SU is regularly being polled by
the AP, the SU is said to be “associated” to the AP.
Once associated, the AP will send a command to the SU to adjust the SU’s RF transmit power based on
the Target RSSI parameter in the AP. This process is referred to as “power leveling”.
System operators may limit allowable bandwidth to specific customers utilizing the built-in CIR and MIR
settings (measured in kbps) for each SU.
Auto-retransmit Feature (ARQ)
The M2400S features ARQ or “Automatic Request for Re-transmission”, which is the ability to correct for
missing or errored packets of data by requesting the sending radio to re-transmit the data. Both the AP
and SU units implement a form of ARQ known as 'ARQ with Selected Repeat’. The use of ARQ is
especially important in areas of high interference. The ARQ feature can be turned on or off.