Motorola MOTOWI 4 User Manual page 87

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Target MAC Address:It is the MAC Address of the peer unit that will be at the other end of
the wireless link. This is used by the system to ensure the unit establishes a wireless link to the
correct peer.
The MAC Address can be found embedded within the serial number of the unit. The last six
characters of the serial number are the last three bytes of the unit's MAC address. (Note: A PTP
500 Series system is shipped as a pair of units with pre-loaded correct MAC addresses. Target
MAC addresses will only need to be entered if an existing unit has to be replaced in the field or
the units configuration has been erased).
Master Slave Mode:At this point it is necessary to decide which end will designate a Master.
The Master unit is the controlling unit with respect to the point-to-point link and its maintenance.
The master transmits until the link is made, while the Slave listens for its peer and only transmits
when the peer has been identified.
Link Mode Optimization:Optimizes the link behavior according to the type of traffic that will
be bridged. There are two modes to choose from: IP and TDM.
In IP Mode, the PTP 500 product runs an Adaptive TDD scheme. Basically an unloaded link
runs 10:10 mode (10 OFDM bursts alternately in each direction). A sustained traffic load in one
direction for example may cause a threshold to be reached where the TDD mode automatically
adapts to say 20:10. If the load continues to increase, then the TDD structure may adapt even
further through 30:10 to 40:10. This is a state of maximum link asymmetry (40 OFDM bursts
in one direction compared with 10 in the other). If the load increases in BOTH directions, then
the TDD structure can adapt from 10:10, through 20:20, 30:30 and finally 40:40. This is a state
of maximum aggregate throughput. So if three out of these combinations are considered; 10:10,
40:10 and 40:40 they would give the following characteristics:
10:10: equal performance in each direction, lowest aggregate throughput and lowest Latency.
40:10: achieves maximum one way throughput performance, to the detriment of both latency and
throughput in the opposite direction.
40:40: Maximum link aggregate rate, balanced performance in each direction, higher latency.
Note that there is an engineering trade-off between the flexibility of ATDD and Latency as follows:
When the TDD structure changes, there will be a short term impact on Latency for a few Frames.
This would not affect the steady state long term average latency, but could be recorded as a
Maximum latency. This affect may be amplified for short Latency tests or if the traffic loading
is oscillating either side of a boundary condition. As the TDD burst length increases, Traffic in
each direction will have to wait longer before a Transmit window is available, but more data can
be sent during the burst. There is an impact on latency but it varies depending upon installation
range, Frame size and modulation mode.
In TDM mode, two major differences in link behaviour occur compared with IP mode. First the
TDD structure is fixed symmetrically. Either 10:10, 20:20, 30:30 or 40:40 based upon the installed
range.
Secondly, the point at which a modulation mode changes for given RF conditions is more conser-
vative. In practice, this means that the link will typically stay in a lower modulation mode, but
with increased tolerance to RF variability.
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