Effective counteraction to Distributed Denial-of-Services (DDoS) attacks is a pressing problem over the Internet. For this counteraction, it is considered important to locate the router interfaces closest to the attackers in order to effectively filter a great number of identification jammed packets with spoofed source addresses from widely distributed area. Edge sample (ES) based Probabilistic Packet Marking (PPM) is an encouraging method to cope with source IP spoofing, which usually accompanies DDoS attacks. But its fragmentation of path information leads to inefficiency in terms of necessary number of packets, path calculation time and identification accuracy. We propose Branch Label (BL) based PPM to solve the above inefficiency problem. In BL, a whole single path information is marked in a packet without fragmentation in contrast to ES based PPM. The whole path information in packets by the BL approach is expressed with branch information of each router interfaces. This brings the following three key advantages in the process of detecting the interfaces: quick increase in true-positives detected (efficiency), quick decrease in false-negatives detected (accuracy) and fast convergence (quickness).

In this paper, we consider the performance of QPSK systems using complex transversal filters with additional decision-feedback (DF) taps, in the presence of colored noise and single continuous wave (CW) interference. Both one-sided and two-sided transversal filters with DF are considered. The general analytic expressions for the optimum tap weights and minimum mean square errors are obtained. We calculate the output signal-to-noise ratio of the filters and compare the theoretical results with the computer simulated results. The relations between the spectrum of the colored noise as well as CW interference and the corresponding frequency response of the DF filters are considered. We also consider the transient behavior of the adaptive DF filters. It is shown that the DF filters can suppress not only CW interference but also colored noise and that the two-sided transversal filter with DF has best performance in the presence of the colored noise and CW interference, while the one-sided transversal filter with DF is preferred when the white Gaussian noise and CW interference are included in the system. It is also shown that the frequency response of the DF filters is changed according to the spectrum distribution of the colored noise and CW interference in order to suppress them more effectively. The simulated results are in good agreement with the theoretical results.