Echelon LonWorks Router - Manual (Page 28)

In this case, reduce the number of lost messages by moving 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 and FT Router 5000 Message Buffers
Each router side has maximum 26 623 bytes of buffer space available. Because
both the Router 5000 and FT Router 5000 have 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 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 5 shows a
general buffer configuration.
Table 5. General Series 5000 Router 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
message. See Configuring a Series 5000 Half-Router for a description of how to
change the size and count of buffers. However you allocate the buffer sizes and
counts, the total memory required by the three buffer queues must not exceed 25
K bytes.
The general buffer configuration shown in Table 5 balances the buffers between
the input and output queues of the router. For systems with large bursts of
traffic, you could specify additional non-priority output buffers. 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.
Router Performance
A major criterion of router performance is network throughput. An optimal
router would be able to forward traffic at the wire-rate, with zero packet loss and
minimal delay. Thus, an optimal router would forward traffic from 9.8 kbps to
1.25 Mbps, depending on the router’s transceiver type.
A real router typically does not perform at the wire-rate because of latency within
the router, including the time to receive and buffer the incoming packet at the
near side, the time to forward the packet between the halves, and the time to
buffer and transmit the packet at the far side. You should measure your router
device’s latency to determine if its design meets your system’s needs.
18 Introduction to LONWORKS Routers