Real networks often experience over_loaded traffic, congestion will occur due to the limited capacity and the process rate of network nodes, which will cause the networks the experience serious delays and performance degrade.

• 实际网络经常承受超负荷的流量；由于网络节点自身容量或者处理速度的限制；往往导致严重的拥塞产生；使得网络具有较大的时延并且性能下降.