medium

See Predefined Medium Types

Script Class WsfCommMedium

medium <name-or-type> <base-type-name> … end_medium

medium <name-or-type> <base-type-name>

   channels <integer-value>
   default_mode_name <mode-name>
   use_sharing <boolean-value>

   mode <mode-name>
      ...
   end_mode

   script string ModeOnTransmit ...

end_medium

Adding a medium to a valid communication framework object:

comm <name> <type>   # or edit comm <name>
   add medium <type>
     ...
   end_medium
end_comm

Editing a medium object on a valid communication framework object:

router <name> <type>   # or edit router <name>
   edit medium <type>
      ...
   end_medium
end_router

Deleting a medium object on a valid communication framework object:

comm <name> <type>   # or edit comm <name>
   delete medium <type>
end_comm

Note that deleting a medium replaces the existing definition with the default medium type with default settings for this object.

Overview

A medium is an object based representation of the means by which a communications device propagates data to another communication device.

Mediums provide a definable user type that can be utilized by various objects within the AFSIM communications framework. Mediums define the limitations imposed on communications by their implementation, working in conjunction with the limitations defined by the communications model that uses the medium. For example, even though a communication device may utilize a maximum transfer_rate, that rate may be further limited by the medium being used, or other characteristics dynamic to the medium (such as the number of channels being utilized in multiplexing).

Mediums are unique in that they may be shared between multiple communication objects in AFSIM. As such, every communication device using a shared medium is restricted by the limitations of such a medium. For example, a medium shared between four comm devices may have four channels available for transmission. If one comm is using all four of those channels, all other comm devices cannot transmit until one or more of those channels are available for usage. Particular models may implement their own restrictions based on concepts such as interference, congestion, etc.

Because mediums are shared objects, they are only definable in the global context. Any utilization of a medium specific to a comm object (such as a router or a comm) must refer to a medium defined in the global context, and only refers to such a medium by its type name.

Mediums may also contain multiple modes, indicating different states associated with that medium. Using the AFSIM scripting language, the state used for any transmission may be modified during runtime to provide a dynamic method to change transmission characteristics. While any object in AFSIM is limited to a single medium object, that medium may have any number of modes available for usage.

Commands

channels <integer-value>

Defines the number of channels available to a medium, in other words, if multiplexing is available. The number of channels determines how many concurrent transmissions may be handled by this medium, and subsequently by all communication objects utilizing this medium.

Default maximum integer value (no restriction on number of concurrent transmissions)

default_mode_name <mode-name>

Specifies the default mode to be used for transmissions over this medium. Every medium has a default mode named as “default” using default values. Unless this command is used, the “default” mode will be used during typical medium processing. Note that the default mode may be modified by explicitly defining the “default” mode using the mode command.

Default Use of the “default” mode

use_sharing <boolean-value>

By default, mediums are shared between every object that refers to a particular globally defined medium type. If use_sharing is indicated to be false, then this medium type definition will result in every usage of this medium instantiating their own instance. This allows the type definition to act as a simple template for each instance, while avoiding sharing the actual medium itself.

Default true (mediums are shared)

mode <mode-name> .. end_mode

The mode command is used to define an individual mode for this medium. It may be repeated any number of times, with the restriction that each mode must have a unique string name. The actual commands available for any given mode is determined by the medium type being used.

Note

Every medium has a “default” mode. Any usage of typical mode commands outside of the mode block refers to the “default” mode.

ModeOnTransmit (script)

script string ModeOnTransmit(WsfCommMessage aMessage, WsfComm aTransmitter, WsfComm aReceiver)
...
end_script

Defines an optional script method that is invoked every time a message is attempting transmission over this medium. A user may specify the mode intended for transmission over this medium by returning the string identifier for the mode.

By returning an empty string when this method is called, or a mode name that does not exist, the medium will use the currently specified default mode for this message transmission.