WIT2410P
© 2000- 2008 Cirronet™ Inc
14
M-2410P-0000 Rev G2
3. PROTOCOL MODES
In point-to-point applications, it is generally desired that the radios operate in a
transparent mode. That is, raw unformatted data is sent from the host to the radio and is
received as raw data from the receiving end. The addressing and error detection and
correction are still performed by the radios, but it is transparent to the user application.
To set up a point-to-point network, one radio has to be set up as a base station. When the
radios are powered on, the base station will send out the synchronization signal at the
beginning of each hop. The remote will synchronize with the base and automatically
request registration. Once the remote is registered, the radios can transmit data. Protocol
mode operation is available in point-to-point mode if desired.
If the base station is to be responsible for directing data to a specific remote in point-to-
multipoint mode, the data sent to the base station by the user application must adhere to a
packet format. This allows transmissions from the base station to be directed to a specific
remote. Data received by a base station from a remote is similarly formatted to identify
to the user application the remote that sent the transmission. The remotes may still use
transparent mode without formatting to send data to the base, if desired. The WIT2410
supports 10 protocol formats that are described in detail below. The protocol format is
selected through the
Set Protocol Mode
command.
Base and remote radios can use protocol modes to insure that a packet is transmitted to
the base without being broken up over multiple hops. The
data length
value in the data
packet becomes the effective
minimum packet length
and
maximum packet length
for that
packet. Note that if the remote
data length
is set to a number of bytes that is longer than
the number of bytes that can be transmitted by a remote on a single hop, the packet will
be discarded. For the base, this value is set by the
Set Base Slot Size
command. For
remotes this value is dynamically available through the
Get Maximum Data Length
command or may be calculated based on the maximum number of remotes that can ever
be registered at one time. See Sections 5.3 and 2.2.3 respectively. Also note that using
protocol modes effectively disables
Data Transmit Delay
. This means that a packet will
not be transmitted until the entire packet has been sent to the radio, regardless of the
amount of time it takes.
If the remote hosts can determine what data is directed to them in point-to-multipoint
mode, the data can be sent to the base station without using a packet format. In this
situation, broadcast mode is selected at the base station by using the
Set Default Handle
and selecting
3FH
as the default handle. In this mode, the automatic retransmission of
unsuccessful transmissions is disabled. This is required since all of the remote modems
will attempt to acknowledge each base transmission when ARQ is enabled.
Transmissions that are received with errors are discarded by the radio. The remote
devices must be able to detect a missing packet and request a retransmission by the base
device.
