are switch. Figure 17.3 illustrates this shift. Network Software - The User Experience Soft Switching Hardware Switching Figure 17.3 Hardware switching increases as packet length reduces. 17.7.4 Fixed Routing As session length increases, we move progressively towards providing less rather than more routing flexibility. Traditionally in an IP network, routing flexibility has been promoted due to its ability to improve transmission bandwidth utilisation and increase network resilience. However, the cost is delay (first-order effect) and delay variability (second-order effect). As traffic becomes more inelastic over time we become less tolerant to any change in routing trajectory. Routing flexibility is antithetical to network determinism. Conversely, if we have fixed routing we don't need to have routing tables, thus saving on CAM memory. If we don't need packet-by-packet classification we don't need classifiers (saving on S-RAM). If we also decide we don't need or cannot tolerate buffering because delay and delay variability compromises our inelastic traffic then we can also get rid of all or at least some of that expensive S-DRAM and DDR DRAM. Also, as we reduce the buffering used in network components we reduce the need to manage memory - the software processes implicit in memory management introduce delay and delay variability in the end-to-end communications channel. So it may be that the need for flexibility and the benefits of flexibility in next-generation networks are overstated. What is really needed is predictable and stable end-to-end performance that can be mapped to clearly defined quality of experience metrics. The easiest and lowest-cost way to achieve this may be to overdimension network delivery bandwidth. So the thesis is that as session lengths increase and as we move towards fixed-length packets and fixed routing trajectories it makes more sense to hardware switch and less sense to software switch. This goes against the present trend in which a number of vendors are promoting general- purpose n