Teledesign Systems Inc TS4000EH Manuel D’Utilisation

 
AirNet is an embedded packet protocol available in some Teledesign Systems 
modems.  AirNet provides a complete protocol that manages the end to end data 
transfers of wireless networks.  The AirNet protocol is flexible and configurable 
so that it can be used with any host (user) system or network architecture. 
 
The basic purpose of the AirNet packet protocol is to ensure that data is reliably 
transferred between nodes in the network.  This means preventing data from 
being lost, repeated or corrupted at the receiving nodes.  This is accomplished 
by combining transmit data into packets which contain user data and control 
information.  The control information includes addressing, sequencing and error 
detection.  Addressing information allows receiving nodes to determine if a 
packet is intended for them and also who the source of the packet was.  
Sequence information is used so that the data can be reconstructed in the 
correct order, and so that repeated packets of the same data are not given to the 
user.  Error detection is provided by adding a CRC (Cyclic Redundancy Check) 
onto the packet so that any corruption of the packet can be detected. 
 
The key feature of any packet data protocol is its ability to identify and coordinate 
data transfers between individual nodes in a network.  In order to move data 
between nodes, each node is assigned a unique address.  With the AirNet 
protocol each node is assigned a unique individual and group address.  Group 
addresses allow the nodes in a network to be partitioned into classes of service 
or segmented into regions.  The AirNet protocol allows a data packet to be 
transferred to an individual node, to all nodes in a group (group broadcast), or to 
all nodes in all groups (network broadcast).  
 
The AirNet protocol also includes multicast reception.  Multicast reception is the 
ability of a node to receive group broadcasts for groups other than its own.  This 
allows a node to be a member of a number of different groups at the same time. 
 
Individual node to node data transfers can be sent with or without positive 
acknowledgment from the destination node.  Positive acknowledgment is the 
process where a destination node which receives an error free packet sends a 
return packet (without user data) to tell the source node that the packet was 
received correctly.  This allows the source node to be sure that the data has 
been transferred.  If the sending node does not receive an acknowledgment 
(ACK) packet within a preset period of time then it automatically re-sends (or 
retries) the data packet.   
 
Note that broadcast packets are never acknowledged and therefore the source 
node cannot be sure that they have been received correctly by all the destination 
nodes. 
 
For most wireless data networks, there is the possibility that more than one node 
will attempt to transmit simultaneously.  This is termed a collision and typically 
results in the data from both nodes being lost.  To minimize collisions, the nodes 
must have an orderly means of accessing the shared channel.  The AirNet 
protocol uses a CSMA/CA (Carrier Sense Multiple Access with Collision 
Avoidance) protocol to coordinate channel access (see CSMA System for 
details). 
 
In many networks some nodes are unable to directly communicate with all other 
nodes in the system due to insufficient RF coverage.  To combat this many 
systems use frequency translating repeaters that are located at advantaged