Microwave Data Systems EL805, Руководство по установке и эксплуатации

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46 MDS TransNET 900 I&O Guide MDS 05-2708A01, Rev. B
9.0 OPERATING PRINCIPLES AND CONFIGURATION
9.1 Synchronization—Basic Network
Remotes acquire synchronization and configuration information via SYNC
messages.They can synchronize to the Master (the
MODE M
unit) or to any
valid Extension (a
MODE X
unit).
The Master will always transmit
SYNC
messages. An Extension will only
start sending
SYNC
messages after synchronization is achieved with its
Master.
The ability to synchronize to a given radio is further qualified by the sender’s
Extended Address (
XADDR
) and by receiver’s Synchronization Qualifiers
(
XMAP
,
XPRI
, and
XRSSI
).
When a primary is specified (
XPRI
is 0...31), a radio will always attempt to
find the primary first. If 30 seconds elapses and the primary is not found, then
the radio will attempt to synchronize with any non-primary radio in the
XMAP
list.
Once every 30 minutes, if a primary is defined, the radio will check its
synchronization source. If the radio is synchronized to a unit other than the
primary, then the current
RSSI
value is compared to the
XRSSI
value. If
RSSI
is less than
XRSSI
(or if
XRSSI
is
NONE
) the radio will force a
loss-of-synchronization, and hunt for the primary again (as described in the
previous paragraph).
By default, Extensions (and the Master) begin with
XADDR
0 .
Synchronization qualifiers are set to
XMAP 0
,
XPRI 0
, and
XRSSI NONE
,
respectively. This default configuration allows any radio to hear the Master.
When an Extension is added, the extended address of the Extension must be
set to a unique value. All remotes that need to hear that extension can specify
this either by designating the extension as the primary (
XPRI
), or by including
it in their list of valid synchronization sources (
XMAP
).
9.2 Extension Operation with SAF
The Store-and-Forward (SAF) capability operates by dividing a network into
a vertical hierarchy of two or more sub-networks. (See
Figure 6 on Page 5 .)
Adjacent sub-networks are connected via Extension radios operating in
“
MODE X ” which move data from one sub-network to the next one.
The Store-and-Forward implementation adheres to the general polling
principles used in most multiple-address systems (MAS). Polls originate from
the Master station, broadcast to all radios within the network, and travel
hierarchically downward. All Remotes will hear the same message, but only
one Remote will respond. Messages within a hierarchy only travel in one
direction at a time.
Using SAF will cut the overall data throughput in half, however, multiple
networks can be inter-connected with no additional loss in network
throughput.