Echelon IP-852 Channel - Manual (Page 35)

IP-852 Channel User’s Guide 27
Set a channel timeout when using MD5 authentication. When using MD5
authentication, start with a minimum channel timeout of 100 ms and a channel delay of
200 ms. The following factors in affect the Channel Timeout property:
• Variations on each leg of a round trip. Factor the maximum delay into one leg of the
trip.
• Maximum difference between the times on the IP-852 devices. The IP-852 device
stamps its time on a packet when it is sent on the IP network and the target IP-852
device compares the stamp to its own time. If the time has expired, (time of device –
time stamp in packet is greater than channel timeout), the IP packet is discarded by
the target device as stale. You can estimate the maximum difference between the
times on the devices by comparing the offsets displayed in the IP-852 Configuration
Server log window log when you run the channel Time Check command.
Channel Delay
The channel delay specifies the value of the expected round trip time of a message (for
example, message and response). This allows expected traffic patterns to be input to the
system so that the timer calculations can be affected accordingly. You can set this
property using a network management tool such as the LonMaker tool. See you network
management tool documentation for more information on the Channel Delay property.
Packet Reorder Timer
You can use the packet reorder timer property to set the amount of time that an IP-852
device will wait for an out-of-order IP packet to arrive. This parameter is important for
wide area networks (WANs) 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 property defaults to 64 milliseconds.
Packets on a local area network do not get out-of-order; therefore, you can clear the
Reorder Packets check box 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 L ON W ORKS network.
Using SNTP When Creating IP-852 Channels
In small IP networks where there is no appreciable latency, it is not necessary to specify
an SNTP server for your IP-852 channel; however, when creating IP-852 channels that
span large IP networks where large network delays may be present, you must specify an
SNTP time server. This allows each participant in the channel to synchronize to a
common time base. Time synchronization is required to implement some of the
L ON W ORKS protocol’s messaging services. For example, the L ON W ORKS protocol’s stale
packet detection algorithm requires a common time base to function properly.
You can specify SNTP servers at three 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: