e of established connections. Policing at the user-network interface is referred to as usage parameter control. Policing at the network-network Interface is referred to as network parameter control Discarded checksum error Computer unit counter counting for ingress cells discarded due to cells checksum errors Discarded UTOPIA Computer unit counter counting for ingress cells discarded due to parity interface cells errors at the UTOPIA interface. Count of cells when error was detected as a result of a parity check at the universal test and operations interface for ATM (UTOPIA) Discarded CRC error cells Computer unit counter counting for ingress cells discarded due to cyclic redundancy check (CRC) errors Transmission Network Planning and Optimisation on the physical layer is in terms of E1/T1/JT1 or VC-12/VC-4 in the case of fibre. On the ATM layer the bandwidth is leased in terms of kbps or cps. In one way or another, however, there is a granularity where the bandwidth is leased. Minimising the leased capacity to just meet the desired traffic scenario is the optimisation objective. The importance of this optimisation is especially large at narrowband links where a decision between leasing, for example, one or two E1 often means selecting between single and double costs. At more broadband links the effect decreases if, for example, the selection is made of whether eight or nine E1s should be leased. In the end the same maximisation of the usage principle applies as with owned capacity. When the leasing agreement is done and the transmission links are taken into use then obviously the transmission links should not be minimised but rather maximised within the leased bandwidth to get the most out of it. So far it might seem quite a simple objective, but the wild card of this minimisation task is to consider the time line. Sooner or later the needed capacity is supposed to exceed the installed or leased capacity. The trick is to optimise that moment. There are big installation and purchase costs involved in owned capaci