Packet Engine Pro Help

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Sound Card Use
     . Sound Card Interface
     . HF Operations
     . 9600 Operations
     . Receive Problems
     . Transmit Problems

 

Help Date: 21 June 2004

 

 

Editing Port Properties: TNC Commands (Parameters)

On the Properties screen for any radio port (TNCs, modems, sound cards), there is a second tab entitled TNC Commands. Selecting that tab brings up a screen where you can edit various timing parameters.

Your most important decision is to choose who will set the TNC's traffic flow parameters: you or the program?

Program Adjusts Parameters - this is the default choice and provides a valuable feature: PE Pro monitors the packet traffic level and will automatically adjust all TNC traffic flow parameters every two minutes to match traffic level. Hint: Use the Port Activity screen to see the current traffic level and the current program settings.

Note: The 'on air' baud rate field below this radio button is no longer used by the program.

If you choose "program adjusts parameters", the five parameters that deal with traffic flow will be 'grayed-out' and inaccessible, as will the Default 1200 and Default 9600 buttons. You will only be able to adjust a few parameters (see Parameters information below) and the screen will look like this (default values for all fields are shown):

 

Let me adjust Parameters - this choice lets you alter the five traffic flow parameters: Persist, SlotTime, MaxFrame, Retries, Frack, RespTime, and Check Every (see Parameters information below).  You should only make this choice if the program is not handling the timing parameters to your satisfaction and you understand channel traffic symptoms and the intended affect of each parameter.

The screen will look like this (default values for all fields are shown) :


 

Parameters - Here is more information about each of the parameters:

  • Persist - works with the SlotTime parameter to determine the frequency of transmissions. SlotTime sets the time between slots (transmission opportunities). Persist sets the odds (the number of times in 255) that PE Pro will actually transmit when a slot come up. Use lower Persist numbers during heavy traffic (so PE Pro misses some turns and lets other stations transmit). Try higher numbers if traffic is light (PE Pro will transmit at most slots). Persist can be from 1 to 255. Default is 128 (50%) for 1200 baud; 190 (75%) for 9600 baud.
  • SlotTime - works with the Persist parameter to determine the frequency of transmissions. After detecting a clear channel, the SlotTime is the time in 10 milliseconds that PE Pro waits for the next slot (transmission opportunity). The Persist parameter sets the odds that a transmission will actually be made at that slot. Default is 10 for 1200 baud; 5 for 9600 baud.
  • MaxFrame: the number of packets (frames) of unacknowledged packets that  can be outstanding at one time. When MaxFrame is reached, PE Pro will stop sending packets and wait for an acknowledgement from the other station that ALL packets were received. If traffic is light, use a higher MaxFrame -- packets will get through more quickly. If traffic is heavy, use a lower value. Otherwise, a lost frame will result in a request from the receiving station to re-send ALL frames after the lost frame. This adds traffic to the channel. The maximum MaxFrame value is 7.
  • Retries: if a packet is not acknowledged by the receiving station, PE Pro will re-send the packet up to the maximum number specified by Retries. After that, the connection with the other station is assumed to be broken and it is closed. Default is 10 for 1200 baud; 15 for 9600 baud..
  • Frack: increment to wait for an acknowledgement from the other station before re-sending the packet.  Allow more time if you have more VIA stations in your packet address path. Default is 10 for 1200 baud; 8 for 9600 baud.
  • RespTime: the minimum delay to wait after a clear channel before sending an acknowledgement packet. This delay helps ensure all the sending station's  frames have been sent. Increments of 100 milliseconds. Default is 5 for 1200 baud; 3 for 9600 baud. Increase this if your ACK packets may be colliding with the other station's last info packets.
  • Check Every: the amount of time to wait after hearing nothing from a 'connected' station before sending a 'check' ("are you still there?") frame. Default is 180 (3 minutes) for 1200 baud; 120 (2 minutes) for 9600 baud.

Note: PacLen, the number of characters to place in each packet, is determined by your application program, not PE Pro. PE Pro can sent 255 characters per packet. If traffic is light (collision risk is low), you can send more characters per packet and exchanges will be quicker. If traffic is heavy, use less characters per packet because shorter packets will have a better chance of getting through without collision. This means the need for retries will be less and exchanges will be quicker in heavy traffic situations.

Other TNC parameters - You can adjust these parameters, even if PE Pro is automatically adjusting the timing parameters above.

  • DAMA Slave - check this if you are working with DAMA stations. It will put the port in DAMA mode when it detects that the station you have connected to is a DAMA node or BBS (DAMA Master). DAMA is common only in Germany/Europe. DAMA replaces SlotTime and Persist timing.
  • EAX25 Decoding -  if there another station is operating in EAX25 mode, then checking this box will allow you to monitor its traffic correctly. EAx25 is not a standard protocol and many stations don't support it. Incorrectly activating EAX25 decoding could result in problems.
  • TXDelay - the time in 10ths of a millisecond between when the PTT circuit is activated and packet data is sent. This delay gives your radio's transmitter time to come up to full power and gives the receiving radio time to switch from 'transmit' to 'receive'. A minimum delay increases traffic flow, but too little delay may result in the loss of the beginning of the packet and thus retries and decreased traffic flow. The default is 35 for 1200 baud; 20 for 9600 baud. Older radios may need a bit more; newer radios may need 15 or less.
  • TXTail - the time in 10ths of milliseconds between the end of packet data and the closing of the PTT circuit. Only needed on some modems. Can be set to zero for most TNCs. Default is 4.
  • Soft DCD - DCD is Data Carrier Detect. Some TNCs/modems must rely entirely on the radio's squelch to sense when there is a carrier/packet on the air (hardware DCD). If your radio does this, leave this unchecked. Other TNCs have software logic to detect when there is a carrier/packet in the noise, so you can leave the radio squelch open (software DCD). In fact, many TNCs are designed to run open squelch and use soft DCD automatically. Still other TNCs/modems let you choose which method to use. Check mark this box this if you want software DCD. The relative signal-to-noise threshold amount to the right can be changed. The default is 64.
  • Full Duplex - default is OFF, which means PE Pro uses the DCD signal to determine when the frequency is clear and when to acknowledge packets. When turned ON, PE Pro ignores the DCD signal and sends acknowledgements immediately; may be useful in split frequency operations such as through satellites or when doing loop-back tests, but only if both stations are operating full duplex.
  • Default 1200 Button - will set all the parameters to PE Pro's default settings for 1200 baud 'on air' packet.
  • Default 9600 Button - will set all the parameters to PE Pro's default settings for 9600 baud 'on air' packet.
     

Go to TNC Properties Help page

Go to Sound Card Properties Help page

 

Copyright 2004 SV2AGW George Rossopoulos . All rights reserved.