Algorithms for effective variable bit rate traffic smoothing

The transfer of prerecorded, compressed variable-bit-rate video requires multimedia services to support large fluctuations in bandwidth requirements on multiple time scales. Bandwidth smoothing techniques can reduce the burstiness of a VBR (variable bit rate) stream by transmitting data at a series of fixed rates, simplifying the allocation of resources in video servers and the communication network. The RCBR (renegotiated constant bit rate) service model seems ideally suited for smoothed VBR traffic which is piece-wise CBR. Zhimei Jiang (see Proc. IEEE Infocomm 98, p.676, 1998) proposed a dynamic programming algorithm to compute the optimal renegotiation schedule given the relative cost of renegotiation and client buffer size. We show that the schedule produced by his algorithm has high peak rates and frequent renegotiations. We propose another algorithm that computes a renegotiation schedule that has a slightly higher cost than the optimal schedule, but has other desirable properties, such as lower peak rate and lower frequency of renegotiations. We also consider proxy-based online smoothing, and propose an adaptive heuristic algorithm to generate renegotiation schedules at runtime without knowledge of future frame size information. We compare the schedule computed by the algorithm to the optimal schedule computed with full knowledge of future frame sizes.