erlying transport technology is changed from ATM to IP and as well the employed QoS scheme is adapted from ATM QoS to IP QoS, the M/G/R-PS model is still valid and applicable for modeling the IP-based lub link. As due to the behavior of TCP protocol, all elastic traffic flows going over the same IP-based lub link will share the IP bandwidth resources equally, and thus the system is still essentially behaving as a Processor Sharing queue. This section further extends the M/G/R-PS model to dimension the IP-based lub link for elastic traffic, where the DiffServ-based QoS structure is deployed on the IP transport. As seen in the IP DiffServ-based QoS architecture described in section 3.4.2.3, the elastic traffic is accommodated by Assured Forwarding (AF) or Best Effort (BE) PHBs, whereas the circuit-switched traffic is carried by the Expedited Forwarding (EF) PHB. The elastic traffic is corresponding to Non Real Time (NRT) traffic and the circuit-switched traffic corresponds to Real Time (RT) traffic. The bandwidth allocations among different AF and BE PHB classes are controlled by the WFQ scheduling. If each AF/BE PHB queue is continuously sending data, then the kth queue receives its share of the available bandwidth BWk as calculated in formula (3.1). That means, a fraction of the total capacity is supposed to be allocated to each PHB. But if one PHB queue does not have data to send (i.e. not utilizing its allocated bandwidth), then in accordance with the concept of WFQ, its spare bandwidth shall be fairly shared among the other queues according to their weights. The concept of dimensioning for elastic traffic over AF or BE PHBs is illustrated in Figure 7.1. The total IP bandwidth is divided into two parts: the bandwidth reserved or used by the RT traffic over EF PHB; and the remaining bandwidth to transmit the NRT traffic with various priorities by means of different AF and BE PHBs. As mentioned in section 4.4, two cases are considered for the bandwidth allocation between the RT and the NRT traffic: (1) bandwidth 