The simulation model

A possible simulation model is shown in the first figure, where we can identify the following Omnet modules:

  1. gen: the generator module. It creates data packets at certain time interval. In this case the data packets can be considered to be IP packets, or they can be considered to be files, of a certain length. This depends also on the type of traffic that is modelled. For example, if we model an FTP session, it would be better to consider that the generator creates files.
  2. svr: the server. It is actually only a storage element, not a server. It stores the data packets created by the generator module. The packets can be stored in one queue, or in several queues, each queue corresponding to a traffic or to a QoS class.
  3. alg: the module that implements the VHO algorithm, i.e., the algorithm that decides on which of the available networks to send the next data packet.
  4. dest: the destination module. It is a sink type module, that only collects statistics and deletes the OMNeT++ messages that model the data packets. This module informs the server when a data packet has been completely sent, so that the server can send the next data packet.
  5. network1, network2: two different networks. The user can chose one of them in order to send the next data packet.
A possible general model for a network is shown here:

The module called databuffer stores the data packet received from the srv module. Then this data packet is send over the corresponding network. The modules genLoadCond and genRadioCond model the change of the load in the cell and respectively the change of the radio conditions.

The effective transfer of a data packet is modeled using the delay element (dly in the figure) and the loop module. If a part of the data packet (e.g. an IP packet) is send the length of the data packet will be decreased by the length of the data packet. When the length is zero, it means that the data packet (the file) has been completely sent, and the corresponding Omnet message will be sent to the sink (the destination module). The delay element models the time necessary to send an IP packet. This time depends on the network load, the radio conditions and on the type of the network (i.e. GPRS/EGPRS, UMTS, LTE, etc).

Basic (minimal) requirements

Realize a working model like above with only two networks and a dummy VHO algorithm (e.g. one network is chosen randomly), or with a simple algorithm (chose the fastest network, or the cheapest network), and collect results for the implemented algorithm.

Points for exam. Alternatives:

  1. Implement a VHO algorithm described in the literature. You can use for the VHO algorithm the Customer Surplus (CS) method proposed by Olga Ormond in [DCU05] or [DCU-PIMRC05] . (username: mcs passwd: mcs05 ) Compare the algorithm from literature with the simple one in terms of performance.

    Performance can be expressed by the average delay, the number of retransmitted files, the network utilization.