Transport Protocol & Listening Ports
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On this step you select the protocol that will be used for exchanging the data between the application and the DS. You also choose the listening port number on the side(s) of the link that will be receiving incoming connections from the other side.
In general, we recommend you to stick to the TCP/IP, unless the application requires that the UDP/IP protocol is used. Since the Wizard can only setup the transport protocol on the DS side of this connection, it is your responsibility to setup the application side accordingly.
There is one case when the UDP/IP selection is not available and the TCP protocol is pre-selected for you- this is when you have specified an inband access method on the target DS step of the Wizard. Since inband access requires a TCP/IP data connection with the DS you must use TCP/IP transport protocol!
Under What Circumstances Transport Protocol & Port Selection Is Disabled
As noted above, when you use Inband access mode for the wizard, you must use TCP/IP as the transport protocol. Also, port selection will be disabled in this case. At this stage of the Connection Wizard you are already in communication with a DS. The communication is done via the data transport channel of the DS (as opposed to a separate command channel, like in Telnet or out-of-band mode).
The DS is usually far away (somewhere on a WAN), otherwise you would not use inband access to reach it. Thus, there are all sorts of firewalls and gateways between yourself and the DS. Firewalls only allow traffic on certain ports to go through, and UDP packets are often dropped on WANs.
If you change the protocol to UDP now, or change the listening port on the DS, you may render it completely inaccessible. The change will occur, because the Wizard is in communication with the DS (on the proper port which you configured in the beginning). But at the end of the Wizard run, you'll have an unpleasant surprise - the DS may suddenly disappear.
Thus, when selecting Inband Access mode in the beginning of the Wizard, you cannot later change the Transport Protocol or Listening Port.
This screen also provides an option of entering the port number on the listening side(s) of application-to-DS link. By now the Wizard has already decided which side opens the connections. Connecting side needs to know the number of the listening port on the other side. For example, if it is the PC application that will always be connecting to the DS, then you only have to specify the listening port on the DS side. Consequently, the listening port on the DS textbox will be enabled, and the listening port on the PC textbox will be disabled. If both sides will need to establish the connection, then you have to specify the listening ports on both sides too, and both textboxes will be active.
There is one case when the listening port on the DS side is fixed and pre-selected for you- this is when you have specified an inband access method for this DS. In this case you have already specified the listening port (as the access port) on the target DS stepof the Wizard (listening port and the access port are the same for inband mode).
Once again, proper setup of the application side is your responsibility. For example, if you choose the listening port on the DS to be 1001 the Wizard will program this number into the Port Number (PN) setting on the DS automatically, and your job will be to set the destination port number on the application side to 1001. Likewise, if you choose the listening port on the application side to be 3500, then the Wizard will automatically set the Destination Port (DP) setting of the DS to 3500, but you need to make sure that the same listening number is actually selected in the application.
How the listening port numbers are chosen
You can choose any port numbers of your liking. The only limitations are:
The DS can be adjusted to use any destination and local port numbers. The only limitation is that the Port Number (PN) setting cannot be programmed to 65535 (this is a special command port number).