6.3 Object hierarchy

The base class used to represent links is called Link. Methods for this class are listed in the next section. Other link objects derived from the base class are given as follows:

• SimpleLink Object A SimpleLink object is used to represent a simple unidirectional link. There are no state variables or configuration parameters associated with this object. Methods for this class are: $simplelink enable-mcast src dst
  This turns on multicast for the link by creating an incoming network interface for the destination and adds an outgoing interface for the source.

  $simplelink trace ns file optional:op
  Build trace objects for this link and update object linkage. If op is specified as "nam" create nam trace files.

  $simplelink nam-trace ns file
  Sets up nam tracing in the link.

  $simplelink trace-dynamics ns file optional:op
  This sets up tracing specially for dynamic links. <op> allows setting up of nam tracing as well.

  $simplelink init-monitor ns qtrace sampleInterval
  Insert objects that allow us to monitor the queue size of this link. Return the name of the object that can be queried to determine the average queue size.

  $simplelink attach-monitors insnoop outsnoop dropsnoop qmon
  This is similar to init-monitor, but allows for specification of more of the items.

  $simplelink dynamic
  Sets up the dynamic flag for this link.

  $simplelink errormodule args
  Inserts an error module before the queue.

  $simpleilnk insert-linkloss args
  Inserts the error module after the queue.

  //Other link objects derived from class SimpleLink are FQLink, CBQLink and IntServLink.

  Configuration parameters for FQLink are:

  queueManagement_

  The type of queue management used in the link. Default value is DropTail.

  No configuration parameters are specified for CBQLink and IntServLink objects.

• DelayLink Object The DelayLink Objects determine the amount of time required for a packet to traverse a link. This is defined to be size/bw + delay where size is the packet size, bw is the link bandwidth and delay is the link propagation delay. There are no methods or state variables associated with this object.

  Configuration Parameters are:

  bandwidth_

  Link bandwidth in bits per second.

  delay_

  Link propagation delay in seconds.