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14 Introduction to LonWorks Routers
forwarded to the transmitting side of the router, priority messages have their
own outgoing buffer queue. Thus, priority processing of these outgoing messages
is assured because the transmitting side will send messages from the priority
output buffer queue before sending messages from the non-priority output buffer
queue. Figure 8 shows the message flow through the input and output buffer
queues. This message flow is duplicated for messages moving in the opposite
direction, that is, another set of input and output buffer queues exist for
messages flowing in the opposite direction.
Figure 8 . Buffering Scheme for a LonWorks Router
The size and count of the message buffers is limited by the amount of RAM on
the router.
RTR-10 Message Buffers
Each router side has 1254 bytes of buffer space available. By default, this space
is allocated as two input buffers, two priority output buffers, and 15 non-priority
buffers. The default buffers are all 66 bytes in size. Table 2 shows the default
buffer configuration.
Table 2 . Default RTR-10 Buffer Configuration
Queue Count
Size
(Bytes) Total Bytes
Input Buffer Queue 2 66 132
Priority Output Buffer Queue 2 66 132
Non-Priority Output Buffer Queue 15 66 990
Total 1254
The default buffer size of 66 bytes allows the router to handle packets with
maximum address overhead and data size for any network variable message and
explicit messages with up to 40 bytes of data; this size is large enough for any
network management or network diagnostic message. In applications that must
route large explicit messages with more than 40 bytes of data, the buffer size