Teledesign TS4000 - AirNet CSMA MAC Calculations and Control Strings

TS4000 Radio Modem User’s Manual AirNet Packet Protocol 38
Control Description
Min Idle Slots This sets the minimum number of idle slots before a
modem attempts transmission (see Setting Min Idle Slots).
If the minimum number of idle slots is set to zero the
modem randomizes its transmission attempts with the first
slot after the channel becomes idle. For values greater
than zero, the modem waits that many slots before
randomizing its transmission attempts.
Tx Index The transmission index (TI) is the inverse of the probability
of transmitting in an idle slot. An index of 4 corresponds to
a 1/4 or 25% chance of transmitting in an idle slot. The
goal of setting TI is to maximize efficiency on the channel.
If TI is set too low then transmissions collide too often. If TI
is set too high then there is excessive unused channel time
in the system (see Setting Transmission Index).
CSMA MAC Setup
Min Idle Slots and Tx Index can be set differently for different types of packets.
The following table describes the different packet types.
Type Description
Data Packets These are any packets that carry user data. These include
data packets for all the different types of transfers (i.e.
Individual, Individual w/o ACK, Broadcast).
ACK Packets These are the acknowledgment packets for the individually
addressed data packets.
Relay Packets These are any packets that are repeated with the store and
forward repeater option. Both data packets and ACK
packets can be repeated. These values are set on the
Packet General tab.
Control strings are used to control the operation of the modem. Status strings
are used to provide status information from the modem. Status strings from the
modem can be disabled if they are not needed for a given application. All control
and status strings begin with the ASCII string “+TS”, followed by specific ASCII
letters and numbers corresponding to the particular control field or status value
provided (See Appendix B - ASCII Character Set).
Control and Status
Strings
All numbers are formatted as ASCII digits and sent most significant digit first.
iii - Represents a three digit individual address.
gg - Represents a two digit group address.
nn - Represents a two digit packet number.
Control String Description
+TSI Set for individual transfer.
+TSIAiii Set for individual transfer with address change. The three
address characters change the individual destination
address.
+TSICggiii Set for individual transfer with complete address change.
The first two characters are for the group address and the
remaining three are for the individual destination address.
+TSN Set for individual without acknowledgment transfer.
+TSNAiii Set for individual without acknowledgment transfer with
address change. The three address characters change the
Control Strings