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DNT90 Integration Guide - 05/10/12
3. In each router, load a unique base-mode network ID into the
BaseModeNetID
parameter in Bank
0, and into the base if a router is set to 0x00.
4. To configure a specific system topology, set the parent network ID parameter,
ParentNwkID,
and
optionally the alternate parent network ID parameter,
AltParentNwkID
, in all routers and
remotes. Note that a store-and-forward system topology can be formed either automatically or
manually, based on the settings of the
ParentNetworkID
and optionally the
AltParentNwkID
parameters:
- Setting the
ParentNwkID
parameter to 0xFF in all routers and remotes allows each
router and remote to automatically link to a parent, causing the system to form
automatically (child routers picking each other as a parent cannot occur). In this case, the
AltParent-NwkID
parameter should be set to 0xFF, which disables it.
- Setting the
ParentNwkID
and optionally the
AltParentNwkID
parameters
to specific val-
ues in each router and remote allows full manual control of the network topology.
The benefit of automatic system formation is self-healing. If a parent router fails, its child nodes
can re-link to any other parent router they can receive. However, automatic topology formation
can result in an unnecessary number of hops between routers or remotes and the base.
The benefit of manual system topology formation is to avoid unnecessary extra hops in the sys-
tem, and to balance the number of children supported by each parent router. If a parent router
fails and an active alternate parent network ID has not been assigned, all children downstream
from the failure will be off the system until the failed router is repaired or replaced.
4.6 Slot Buffer Sizes, Number of Slots, Messages per Hop and Hop Duration
The
base slot size
(BSS) sets the maximum number of payload bytes the base can transmit during a sin-
gle hop when the base is sending
one
message per hop.
The maximum BSS is 105 bytes when a DNT90
system is configured for
one
slot.
Adding additional slots reduces the maximum BSS by three bytes per
slot
.
The BSS
buffer
is set nine bytes larger than the BSS, to a maximum of 114 bytes
.
The base can po-
tentially send more than one message per beacon, up to the limit set by its
MsgsPerHop
parameter value.
Each message in the BSS buffer occupies nine header bytes plus the payload.
For example, the base can send three messages per hop when the BSS is 90 bytes, provided the total
payload bytes in the three messages is 72 bytes or less:
slot size
= 90
buffer
= 90 + 9 = 99
3 headers
= 3*9 = 27
net for payload = 99 - 27 = 72
The BSS must be large enough to accommodate any protocol-formatted message that may be sent over
the wireless link, as each protocol-formatted message
must
be sent in a single transmission.
The
remote slot size
(RSS) is the maximum number of payload bytes a child can transmit during a single
hop when it is sending
one
message per hop. The RSS is the same for all slots. The maximum RSS is
109 bytes. The RSS
buffer
is set nine bytes larger than the RSS, to a maximum of 118 bytes
.
A child can
potentially send more than one message in a slot, up to the limit set by its
MsgsPerHop
parameter value.
Each message in the transmit buffer occupies nine header bytes plus the payload. For example, a child
