There is a conservation law [l] that states that the sum of the average queuing delays within a set of multiplexed flow is independent of priority control.However with reference to ARQ specifically, we can adopt the idea of "goodput" [2] (normalized throughthis, we discover that there are cases when the goodput of high-prioritized and low-prioritized flows can both improve at the same time. To achieve this, we will need routers that are able to handle priority control adaptively. This is confirmed theoretically in this paper, which wthout pnonty control put) to evaluate the efficiency of the transmission. With packe-s w,thpnontycontro, uses a simple Go-back-N model as a basis for calculation. I1 Problem AnalysisThe "throughput" of a transmission channel is a measurement of the traffic load transmitted across the channel in a unit time. However for ARQ to provide a reliable connection between the endpoints, it must also include ACK, NAK, and other packets which do not contribute to the transmission of productive data. A worse offender is the case of retransmitted packet, in which the same amount of data takes a longer time to be sent, and yet consumes more network resources at the same time. Hence, we see the need for the measurement of the productive rate of transmission in evaluation of networks, and this is normally referred to as the "normalized throughput", or simply "goodput"[2].To see how priority control can lead to improved in goodputs of both the high-prioritized and lowprioritized flows, we refer to the below Figure 1.In the former case without priority control, we can see that repeat, or retransmitted packets are interspaced within the regular packets on the server (router) queue. Figure 1: result of priority control By applying priority control and eliminating these repeat packets (from the bottom high-prioritized flow), itis quite obvious that the throughput of this flow will improve. If we look inside the server queue, we can see that the space previously occupied by these repeat packets has been freed. Both the high-priority and lowpriority flows will utilize this leftover bandwidth, resulting in an improved goodputs for both cases. Preparation AIn this paper, we analyze a simply situation in which there are the only two flows, A and B, on a network.The two flows have different source and destination nodes, and there is one and only one common link on the two paths. Here we set link 3-4 to be the common link, and the other links are simulated as 1-3, 2-3, 4 5 , and 4 6 , as shown in Fig. 2.