How the Wizard Decides Who Opens Connections
When you click Next on the netmask and gateway step the Wizard has enough information to decide which side of the VSP-to-DS connection will be responsible for establishing data connections with the other side.
In doing this, the Wizard decides on the future values of the Routing Mode (RM) and Connection Mode (CM) settings of the DS, as well as the Routing Mode and Connection Mode properties of the VSP .
In general, the Wizard tries to follow the natural flow of data between the application and the serial device. In the initiator of the data exchange step you have already specified which side sends the data first, so the Wizard will have this side open a data connection to the other side as soon as the first data needs to be sent from this side of the connection.
For example, if you are dealing with the "slave terminal" type of serial device, then the first data is always sent by the application (and the VSP ). Therefore, the Wizard will set the Routing Mode property of the VSP to "client" and the Routing Mode (RM) setting of the DS to "slave".
Lines 1-3 of the following table illustrate what's just been said. Notice that the Connection Mode (CM) setting is always set to "on data". As the first data is received (by one side of the link) it triggers an attempt to open a data connection with the other side of the link:
| Which side can "see" the other side of the connection |
Which side sends the first data |
Routing Mode on the VSP |
Connection Mode on the VSP |
Routing Mode on the DS |
Connection Mode on the DS |
|
| 1 |
Both sides can see each other |
Application |
Client |
On data |
Server |
--- |
| 2 |
Both sides can see each other |
Serial device |
Server |
--- |
Client (server/client) |
On data |
| 3 |
Both sides can see each other |
Any side |
Server/client |
On data |
Server/client |
On data |
| 4 |
Only PC can see the DS |
Application |
Client |
On data |
Server |
--- |
| 5 |
Only PC can see the DS |
Serial device |
Client |
Immediately |
Server |
--- |
| 6 |
Only PC can see the DS |
Any side |
Client |
Immediately |
Server |
--- |
| 7 |
Only DS can see the PC |
Application |
Server |
--- |
Client |
Immediately |
| 8 |
Only DS can see the PC |
Serial device |
Server |
--- |
Client |
On data |
| 9 |
Only DS can see the PC |
Any side |
Server |
--- |
Client |
Immediately |
The situation becomes more complicated when only one side of the connection can "see" the other side. Consider the case in line 5 of the table. The serial device has to send the data first, but it cannot "see" the VSP . Therefore, even when the DS receives the first data into its serial port it will be unable to establish a connection to the VSP and send this data!
The way out is to have the VSP connect to the DS as soon as the VSP is opened (so, connection mode for the VSP is set to "immediately"). This way, by the time the DS needs to send the first data to the VSP the connection is already established. This kind of connections are called "reverse".
A special comment should be made on line 2 of the table, where the Routing Mode on the DS is designated to be either "client" or "server/client". The Wizard chooses "client" if DS programming is effected using out-of-band access method (you have selected this on the target DS step of the Wizard ). If inband access method was selected the Wizard will set the mode to "server/client". This is because choosing "client" would cause it DS to reject all incoming connections in the future and this means that you wouldn't be able to program the DS using inband access in the future!
* This is the case when you have specified that "the Device Server is not accessible from this PC" on the target DS step, or that "the PC is not accessible from this Device Server" on the netmask and gateway for the DS step of the Wizard.