sations' - we still use the Erlang as a unit of measurement to dimension Node B, RNC and core network capacity and (rather dangerously) use Erlang traffic-arrival formula to design network processor components. Reproduced from 3G Handset and Network, Design Varrall and Belcher, Page 406, Figure 17.1, John Wiley, ISBN 0471 22936-9. Making Telecoms Work The good thing about voice traffic is that it is reasonably predictable. Multimedia traffic is also quite predictable though we have less experience and knowledge of 'mixed' me- dia/'rich' media traffic-arrival patterns (and less experience of how we should treat the traffic). This means that networks don't always behave as expected - their behaviour is not con- sistent with traditional queuing theory. The anecdotal experience is that as we move from voice to a mix of voice, data and multimedia, networks become progressively more badly behaved. One reason for this bad behaviour is the increasing burstiness of the offered traffic that effectively puts network components (network processing and network router buffers) into compression. This results in packet loss and (if using TCP) transmission retries. These 'bandwidth effects' can be due to transmission bandwidth constraints, buffer band- width constraints and/or signalling bandwidth constraints. Traffic-shaping protocols (TCP, RSVP, MPLS, etc.) may help to modulate these effects or may make matters worse! It is thus quite difficult sometimes to know whether we are measuring cause or effect when we try and match traffic-arrival and traffic-throughput patterns. Benoit Mandelbrot (1982), 2 and subsequently Kihong Park, Willinger and others have characterised network traffic in terms of a series of multiplicative processes and cascades - the end result is a turbulent network. Whether using TCP or UDP, the network effectively behaves as a filter, including bulk delay and group delay effects and creates backpressure when presented with too much traffic or bursty traffic (which puts the network into compression). The effe