Mixed TDM and packet technologies as a best compromise solution to ensure a cost-effective bandwidth use with the current traffic evolution

Nowadays, transport networks are mainly based on SDH/SONET whereas the traffic becomes more Ethernet/IP oriented. The trend is to make the transport infrastructure more packet-aware, using for example multi-service transport platforms (MSTP). For transport infrastructure, such MSTP solutions are in competition with pure TDM platforms and pure packets ones. The paper demonstrates that, considering a network evolution in which the users' access rates increase faster than their mean rates, introduction of MSTP is justified when one considers the efficiency of the bandwidth use in the links of the networks. For this comparison, we developed an equivalent bandwidth model, including non-Gaussian characteristics, uncertainty and variability of the traffic. We defined the equivalent access rate, and the corresponding equivalent number of active flows, which is the key parameter to dimension the links. This new model may have some limitations. But it is simple, and it is realistic enough to understand the general trends between packet and TDM solutions in the transport networks.