User's Manual

Exalt Installation and Management Guide
ExtendAir
®
(TDD) Series Direct Mount
14 000000-001
2011-08-26
Figure 7 Synchronization for radios in a chain
Offset Timing
For GPS implementations, manual control of offset timing is also allowed. This provides a means to
delay the synchronization signal using a user-defined offset. This is helpful when Exalt radios are near
other devices operating in the same frequency band that also use a timing source, such as GPS. The
timing source to the Exalt radios can be adjusted to match the other radio system timing source
mechanism.
Offset timing can also optimize timing intervals for repeaters and backbones. As the distance of each
link results in a unique factor for speed-of-light transmission of the radio signal, a subsequent radio can
be delayed in timing so that the overall synchronization of radios is precisely maintained.
Offset timing can be adjusted in 1-ms intervals, from zero to the radio’s frame length setting. For
example, if using a 2-ms frame length, the offset timing can be set from zero up to 1999 ms.
When Sync is Lost
If the primary sync source (for example, the GPS source) signal is lost due to equipment failure, a
disconnected sync cable, loss of satellite link, or other condition, the radio is said to be flywheeling.
When flywheeling, the radio’s clock is free-running off internal clocking and is no longer
synchronized to any source. If the original sync source is restored to the flywheeling radio’s
configuration, it attempts to synchronize to this signal without causing transmission interruption.
When the flywheeling radio runs independently for long periods of time, the synchronization signal
may be too far outside the capture range of the synchronization loop, and portions of transmission
frames can be lost during this re-synchronization process. This condition is temporary and all
interconnected radios will re-synchronize to the sync source, as necessary.
If the flywheeling period is exceeded, the radio will stop transmitting. There is a setting for infinite
flywheeling; however, long periods of flywheeling can cause interference with collocated radios.
Virtual Local Area Network (VLAN)
VLAN segments information in a single connection and creates multiple separate connections to
secure information of one type or for one set of users from other information types or for other sets of
users. Exalt’s VLAN communications implementation adheres to the IEEE standard 802.1q.
In most cases, an Exalt radio acting as a Layer 2 bridge between two locations is only required to pass
traffic with VLAN tagging. Without additional configuration, all Exalt radios support frame sizes in
excess of 1900 bytes, which currently supports all defined VLAN packet sizes.