Evaluation of a picture archiving and communication system with combined voice and data traffic

The importance of providing voice communication between picture archiving and communication system (PACS) users has been realized by many researchers. In particular, voice communication can aid in the diagnosis of a patient by geographically separated radiologists and physicians. The voice dialogue can also be stored for later review. This work reports the results of a study to investigate the feasibility of introducing packetized voice to a particular PACS network. It is based on a multiplexed passive star local area network with wavelength-division multiplexing to provide separate logical channels for transfer of control and image data. It consists of an image network (INET) for image transfer at a rate of 140 Mbps, and a control network (CNET) operating at 10 Mbps, for controlling the flow of image transfers. The CNET employs the CSMA/CD protocol for bus arbitration. Previous simulation studies have shown that the CNET remains extremely underutilized even under conditions that overload the INET. This suggests that the CNET could be used to carry packetized voice as well as the control data currently carried. Use of the CNET for this purpose must be considered carefully, however, since the CSMA/CD protocol suffers long packet delays at heavy loads. At an early design phase, detailed modeling can be used to determine whether this will occur at various loads for this PACS. Stochastic activity networks provide the modeling framework necessary to carry out a detailed evaluation of this type. In this research, we represent the modified PACS network and the hypothesized voice, control, and image workload as stochastic activity networks. We verify that the network can support packetized voice in CNET while providing a reasonable service to control traffic.