Add New Application and Agent



  • Objective
  • We want to build a multimedia application that runs over a UDP connection, which simulates the behavior of an imaginary multimedia application that implements "five rate media scaling" that can respond to network congestion to some extent by changing encoding and transmission policy pairs associated with scale parameter values.


  • Application Description
  • In this implementation, it is assumed that when a connection is established, the sender and the receiver agree on 5 different sets of encoding and transmission policy pairs, and associate them with 5 scale values (0-4). For simplicity reasons, it is also assumed that a constant transmission rate is determined for each of the encoding and transmission policy pairs, and every pair uses packets of the same size regardless of the encoding scheme.

    Basically, "five rate media scaling" works as follow. The sender starts with transmission rate associated with scale 0, and changes transmission rates according to the scale value that the receiver notifies. The receiver is responsible for monitoring network congestion and determining the scale factor. For congestion monitoring, a simple periodical (for every RTT second) packet loss monitoring is used, and even a single packet loss for each period is regarded as network congestion. If congestion is detected, the receiver reduces the scale parameter value to half and notifies the sender of this value. If no packet loss is detected, the receiver increases the value by one and notifies the sender.


  • Problem Analysis
  • Before implementing this application, the UDP agent implementation is examined and one major problem is found. Since a UDP agent allocates and sends network packets, all the information needed for application level communication should be handed to the UDP agent as a data stream. However, the UDP implementation allocates packets that only have a header stack. Therefore, we need to modify the UDP implementation to add a mechanism to send the data received from the application. It is also noted that we might want to use this application for further research on IP router queue management mechanisms. Therefore, we need a way to distinguish this type of multimedia stream from other types of streams. That is, we also need to modify UDP agent to record data type in one of IP header fields that is currently not used.