Echelon 14315R, User Manual

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LonWorks Router User’s Guide 15
must be increased, and the count of nonpriority buffers decreased. See Chapter 8
of the Neuron C Programmer’s Guide to understand how the network buffer sizes
are calculated. See Chapter 7, Network Management Messages , on page 71, for a
description of how to change the size and count of buffers. You can also use the
NodeUtil Node Utility, which you can download from the Echelon Web site.
However you allocate the buffer sizes and counts, the total memory required by
the three buffer queues must not exceed 1254 bytes.
The default buffer configuration places the bulk of the buffers on the output
queues of the router. For example, the standard configuration places two
network buffers on the input queue and 17 buffers on the output queue (2 priority
and 15 non-priority) of each router side. The reasoning behind this configuration
is to keep buffered packets on the output queues, after they have been processed
for forwarding. This processing includes checking for priority packets. Priority
packets are sensed and forwarded through the router’s priority output buffers, so
that priority packets are processed as quickly as possible, rather than allowing
them to be delayed behind non-priority packages in a large input queue.
There are applications, however, where the network traffic can be “bursty”,
where many packets appear on the network almost at the same time. In these
cases, the traffic bursts could cause the input queue to become full and lose
excess packets.
In this case, it might be preferable to move more of the packet buffering from the
output queue to the input queue by increasing the size of the input queue and
decreasing the size of the output queue. A router with a larger input queue can
handle larger bursts of traffic, at the risk of priority messages’ being queued
behind a number of non-priority messages.
Router 5000 Message Buffers
Each router side has maximum 26 623 bytes of buffer space available. Because
the Router 5000 has sufficient RAM available for any router configuration, you
can allocate this space with any combination of buffers, for example, seven input
buffers, two priority output buffers, and seven non-priority buffers. You can
specify any valid buffer size (see Chapter 8 of the Neuron C Programmer’s Guide
for information about valid buffer sizes), but, in general, there is no reason not to
specify the maximum size of 255 bytes. Table 3 shows a general buffer
configuration.
Table 3 . General Router 5000 Buffer Configuration
Queue Count
Size
(Bytes) Total Bytes
Input Buffer Queue 7 255 1785
Priority Output Buffer Queue 2 255 510
Non-Priority Output Buffer Queue 7 255 1785
Total 4080
The buffer size of 255 bytes allows the router to handle packets with maximum
address overhead and data size for any network variable message or explicit