Integration Guide

WIT2410

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.