Echelon i.LON 1000, User Manual, Page: 55 / 126

i .LON 1000 Internet Server User’s Guide 8-3
2.
The maximum difference between the times on the L
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/IP devices. The
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/IP device stamps its time on a packet when it is sent on the IP network and
the receiving L
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/IP device compares the stamp to its own time. If the time has
expired, (i.e., (time of device – time stamp in packet) > channel timeout)), the IP packet is
discarded by the receiving device as stale. You can estimate the maximum difference
between the times on the devices by comparing the offsets displayed in the Configuration
Server Log window log when the channel Time Check command is issued.
Packet Reorder Timer
Packet Reorder Timer is a L
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/IP channel property that allows you to set the amount
of time that the device will wait for an out-of-order IP packet to arrive. This parameter is
important for wide area networks where IP packets can traverse multiple routers from
source to destination causing packets to appear on the receiver in a different order than
transmitted. If selected, the value defaults to 64 milliseconds.
Packets on a local area network do not get out-of-order, so you should not set the reorder
packets parameter in this case. Using the packet reordering feature or an overly long
reordering timer value can cause unnecessary delays in packet processing if a packet is lost
or corrupted. Whether enabled or disabled, out-of-order packets are never sent onto the
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network.
Channel Delay
Channel Delay is an LNS property that specifies the value of the expected round trip time of
a message (i.e. message and response). This allows expected traffic patterns to be input to
the system so that the timer calculations can be affected accordingly. This property can be
set using an LNS based tool such as LonMaker. See the LNS and LonMaker documentation
for more information on the Channel Delay property.
Using SNTP When Creating L
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/IP Channels
In small IP networks where there is no appreciable latency, it is not necessary to specify a
SNTP server for your L
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/IP channel.
However, when creating L
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/IP channels that span large IP networks, like the
Internet, where large network delays may be present, you must specify a SNTP time server
for the L
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/IP channel. Specifying a time server allows each participant in the
channel to synchronize to a common time base. Time synchronization is required to
implement some of the L
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protocol’s messaging services. For example, the
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protocol’s stale packet detection algorithm requires a common time base to
function properly.
You can specify SNTP servers at 3 levels: system, channel, and device. Each device and
channel may be configured to synchronize to its own SNTP servers, or default to the next
level up. For example, a device can default to its channel SNTP servers, and a channel can
default to its system SNTP servers.
Specifying System SNTP Servers
To specify the system SNTP servers, follow these steps: