User`s guide

11 - 8 Ethernet or Token Ring Bridge
The Ethernet or Token Ring Bridge may be set up to monitor and record
the list of protocols currently being forwarded over the radio. It will
record the protocols found, how may packets were encountered and
whether the packet came from the LAN or the radio.
To set up the protocol filters, start the monitor and let it run for a while
under normal use. Add filters by selecting the protocols from the
monitor list.
There is a default action for those protocols not in the list of explicitly
filtered protocols. If you know exactly which protocols are going to be
used by the radio nodes, set the default action to discard and add filters
to forward only those protocols that will be used. If you are not sure of
all the protocols that will be used but you know that there are certain
protocols you will not use, you would set the default to forward and add
filters to discard only those protocols you will not use.
For filtering purposes the Bridge assumes that the data portion of the
packets is in one of two forms:
n The first 16 bits of the data portion contains a value that is greater
than the maximum data size (1518). The value is assumed to be a
protocol identifier that may be used to determine which protocol is
being used within the packet.
n The first 16 bits of the data portion contains a value that is less than
the maximum data size. The value is interpreted as a frame length
and it is assumed that a IEEE 802.2 Logical Link Control (LLC)
header follows the length.
The format of the LLC header is as follows:
DSAP, 8 bits, Destination Service Access Point (DSAP)
SSAP, 8 bits, Source Service Access Point (SSAP)
CTL, 8 bits, Control field
If the control field has a value 3 (for an un-numbered information
frame), then this header may be followed by:
OUI, 24 bits, Organization Unique Identifier (OUI)
SAP-PROT, 16 bits, Protocol Identifier