All messages have to be assigned a sequence number for reliable message delivery. Each client requests sequence number to the server before sending a message. Each sequence number is based on the time of arrival to the message transmission server. The messages go through the process of being transmitted to each reliable message transmission client that wants to subscribe to the topic which is related to the messages. Each messenger client confirms whether or not the message is missing by checking the sequence number of the received message. Figure 3 shows the message data flow in reliable message transmission system. If a receiver client finds there is a missing message, the receiver client sends a message which is ‘‘request previous message’’ like Fig. 4.