Java in Simulation Time

Misc

Pitfalls

• Use Java 1.4 compatibility, BCel cannot handle Java 5.0
• If more than one node use the same NetAddress, the simulation aborts prematurely without any error message.
• All entity classes and related interfaces MUST be public.
• JiST does not support JUnit.Workaround: Write test code without JUnit support.
• Superclasses must be final. Otherwise the Rewriter generates invalid code (A java.verifier exception will occur). So a best practise is to mark all concrete classes as final to prevent this error.
• Since it is a discrete simulator, it is possible to schedule more than one event at exactly one point in time. In this particular case, the execution order is not predefined.
• Jist does not (fully) support polymorphism for implementation classes (entities), only for interfaces.

Interesting Things

computeAvgConnectivity

Collisions

• RadioNoiseIndep and RadioSimpleStochastic both do not implement packet collisions on radio level:

 RadioNoiseIndep.receive():

     case Constants.RADIO_MODE_RECEIVING:
       if(Main.ASSERT) Util.assertion(signals>0);
       if(power_mW >= radioInfo.shared.threshold_mW
           &&  power_mW > signalPower_mW*thresholdSNR)
       {
         lockSignal(msg, power_mW, duration);
       }
       break;

• RadioNoiseAdditive implements additive superposition of radio signals and packet collisions. A signal is received only if it is stronger than thresholdSNR multiplied with the sum of the power of all other signals. Otherwise all signals are scrambled.

 RadioNoiseAdditive.receive():

     case Constants.RADIO_MODE_RECEIVING:
       if(power_mW > signalPower_mW  &&  power_mW >= totalPower_mW*thresholdSNR)
       {
         lockSignal(msg, power_mW, duration);
         setMode(Constants.RADIO_MODE_RECEIVING);
       }
       else if(type == SNR  
           &&  signalPower_mW < (totalPower_mW-signalPower_mW+power_mW)*thresholdSNR)
       {
         unlockSignal();
         setMode(Constants.RADIO_MODE_SENSING);
       }
       break;

Multi-Channel Support for JiST

Architecture

RadioIf <|--- ChannelIf ---|> FieldIf

NetworkIf
   |
MacIf <|-- Mac802_11 <|-- MacMc802_11
   |                         |
RadioIf                      |
   |                         |
ChannelIf <|------------- Channel
   |
FieldIf

• Channels are realized through an additional channel layer
  • Has an active channel within a given set of channels
  • Discards packets on other channels
  • Delayed channel switching (only possible, when not transmitting)
  • TODO Cross-channel interference

ExOR Implementation in JiST

Frame Format

• Data Frame
• Acknowledgement Frame
  • 802.11 Frame Control
  • DstAddr: Data frame sender’s address
  • SrcAddr: Data frame receiver's address
  • The position within the candidate list of the node with the highest priority acknowledgment
  • 802.11 Frame Control Sequence

|------------------------|----------------------------------------------------|-----|
|                        | Mac Frame                                          |     |
|----------|-------------|---------------|---------|---------|----------|-----|-----|
| Preamble | PLCP Header | Frame Control | DstAddr | SrcAddr | Cand. ID | FCS | Pad |
|----------|-------------|---------------|---------|---------|----------|-----|-----|
Bytes                    | 2             | 6       | 6       | 1        | 4   |
                         |----------------------------------------------------|

References

• Opportunistic Routing in MultiHop Wireless Networks

Extensions

• Javis

Further Information

• JiST Website
• Presentation "Virtual Machine-based Simulation"
• Javis Network Animator for JiST/SWANS simulator