Campbell-scientific CR3000 Micrologger Manual de usuario descargar pdf (Pagina 359)

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101

Section 8. Operation

359

• hello-request

• CVI

• beacon

To form a network, nodes must establish links with neighbors (neighbors are

adjacent nodes). Links are established through a process called discovery.

Discovery occurs when nodes exchange hellos. A hello-exchange occurs during a

hello-message between two nodes.

8.5.3.1 Hello-message (two-way exchange)

A hello-message is an interchange between two nodes that negotiates a neighbor

link. A hello-message is sent out in response to one or both of either a beacon or a

hello-request.

8.5.3.2 Beacon (one-way broadcast)

A beacon is a broadcast sent by a node at a specified interval telling all nodes

within hearing that a hello-message can be sent. If a node wishes to establish itself

as a neighbor to the beaconing node, it will then send a hello-message to the

beaconing node. Nodes already established as neighbors will not respond to a

beacon.

8.5.3.3 Hello-request (one-way broadcast)

All nodes hearing a hello-request broadcast (existing and potential neighbors) will

issue a hello-message to negotiate or re-negotiate a neighbor relationship with the

broadcasting node.

8.5.3.4 Neighbor Lists

PakBus® devices in a network can be configured with a neighbor list. The

CR3000 sends out a hello-message to each node in the list whose CVI has expired

at a random interval

. If a node responds, a hello-message is exchanged and the

node becomes a neighbor.

Neighbor filters dictate which nodes are neighbors and force packets to take

routes specified by the network administrator. LoggerNet, which is a PakBus

node, derives its neighbor filter from link information in the LoggerNet Setup

device map.

Interval is a random number of seconds between the interval and two times the interval, where the

interval is the CVI (if non-zero) or 300 seconds if the CVI setting is set to zero.

8.5.3.5 Adjusting Links

PakBusGraph, a client of LoggerNet, is particularly useful when testing and

adjusting PakBus

routes. Paths established by way of beaconing may be

redundant and vary in reliability. Redundant paths can provide backup links in the

event the primary path fails. Redundant and unreliable paths can be eliminated by

activating neighbor-filters in the various nodes and by disabling some beacons.

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