In ITU-T Recommendation I.371, the Generic Cell Rate Algorithm (GCRA) is used to define Peak Cell Rate for the ATM network. It is further applied by the ATM Forum '93 to define Sustainable Cell Rate and Burst Tolerance so as to facilitate Usage Parameter Control and Network Parameter Control. To judge the validity of a cell according to declared GCRA parameters, the enforcer must read the clock time when the cell arrives. However, the clock of the enforcer would roll over frequently and accordingly the judgment would be incorrect. On the other hand, for a shaper in a customer premise node to dispatch cells conforming to the declared GCRA parameters, the clock would also roll over and the cell would not be dispatched correctly. To overcome the problems induced by clock roll-over, based on "time difference" concept, we propose two modified GCRA's for the enforcer and shaper, respectively. According to the proposed algorithms, we design a feasible architecture for a multi-connection shaper and simplify it for an enforcer. They are proven to perform well in spite of the inherent clock roll-over characteristics. By simulation, we evaluate the delay in the shaper and the loss in the enforcer. The features of the architectures are also discussed.

This paper presents a pseudo glottal excitation model for the type of linear prediction vocoders with speech being coded at 1.6 kbps. While unvoiced speech and silence intervals are processed with a stochastic codebook of 512 entries, a glottal codebook with 32 entries for voiced excitation is used to describe the glottal phase characteristics. Steps of formulating the pseudo glottal excitation for one pitch period consist of 1) applying a polynomial model to simulate the low-frequency constituent of the residual, 2) inserting a magnitude-adjustable pulse sequence to characterize the main excitation, and 3) introducing turbulent noise in series with the resulting excitation. Procedures are described for codebook construction in addition to analysis and synthesis of the pseudo glottal excitation. Results in a mean opinion score (MOS) test show that the quality produced by the proposed coder is almost as good as that by 4.8 kbps CELP coder for male utterances, but the quality for female utterances is yet somewhat inferior.

Due to the Cell Delay Variation (CDV) at User Network Interface (UNI), it is very hard for an ATM network to perform Usage Parameter Control (UPC), which is an important job for congestion control. Based on the Generic Cell Rate Algorithm (GCRA), ATM Forum has proposed a procedure to perform the UPC. However, the severe problem is that a user has to specify the CDV Tolerance at the UNI by itself. Such a nearly unreachable constraint makes the GCRA unsuitable for UPC. In this paper, we point out that the CDV comprises two parts in which the customer and a network provider should be responsible. Thus, we propose a concept of Innocent Public Network and an Agent Protocol to realize the principle and facilitate UPC. In addition, a shaper is suggested for the customer to employ so as to prevent its performance degradation. In the proposed system, the network is no longer suffered from CDV at the UNI and the UPC can be easily preformed.

In ATM networks, two main functions for achieving traffic control and congestion control are Call Admission Control (CAC) and Usage Parameter Control (UPC). Among various UPC schemes, Leaky Bucket is a popular one. In this paper, we study the characteristics of the system in which every traffic source is regulated by an enhanced leaky-bucket before entering the multiplexer at the edge node of the ATM network. In addition to the factor of mean cell rate, peak cell rate is also taken into consideration. Based on the criteria of average waiting time at the multiplexer, we derive the performance bounds expressed as the functions of the LB parameters and numbers of connections.