Sender delay comparison of IP-based reliable synchronous collaboration communication

Synchronous collaboration is one of the most important fields of CSCW (computer supported cooperative work). IP multicasting is becoming the main trend of synchronous collaboration. But little of the current synchronous collaboration literature pays attention to the conditional superiority of IP multicasting over IP unicasting under a certain packet error rate. In this paper, we compare the sender delay performance of two reliable synchronous collaboration schemes which are based on IP unicasting and IP multicasting and show that IP multicasting is not always superior to IP unicasting in synchronous collaboration. In networks with low packet error rate and to a certain range of number of receivers, IP multicasting has the lower sender delay and superior scalability; while in networks with high packet loss rate and to a large user number, IP multicasting is inferior to the IP unicasting. In addition, we also conclude the communication principle which is to apply IP multicasting in low packet-error-rate environment and to apply IP unicasting in high packet-error-rate environment.