e between a measure of cell transfer delay and the mean cell transfer delay on the same connection. Cell error ratio (CER): This is the ratio of the cell(s) delivered with an error to the total number of cells. Severely errored cell block ratio (SECBR): This is the ratio of SES blocks (of cells) received to the total number of blocks transmitted. Cell mis-insertion ratio (CMR): Owing to errors in some headers, the cells may end up at the wrong destination. The CMR is the total number of mis-inserted cells observed during a specified time interval divided by the time interval duration (equivalently, the number of mis-inserted cells per connection second). Mis-inserted cells and time intervals associated with severely errored cell blocks are excluded from the calculation of cell mis-insertion rate. ATM traffic parameters are related to the services offered by the ATM network. This is shown in Table 8.1. Table 8.1 ATM service categories Parameter traffic type Traffic parameter QoS parameter CDV, CTD, CLR RT-VBR PCR, SCR, MBS CDV, CTD, CLR NRT-VBR PCR, SCR, MBS Connection Admission Control (CAC) CAC algorithms determine whether a new connection is to be accepted or rejected (similar to AC in Chapter 7). A connection request is accepted only if sufficient resources are available and if connection will not affect the existing QoS. Some factors that are considered for a new connection request are: traffic parameters of new connections and QoS requirements existing traffic contracts and connections bandwidth, both allocated and unallocated. DETAILED PLANNING Conformance Monitoring and Control Conformance definition is responsible for indicating when a traffic contract is broken, e.g. if the network is not able to provide a bandwidth that is agreed, or a user exceeds the requested bit rate. This is done through two mechanisms: policing and traffic shaping. Policing is a usage parameter function (UPF) which ensures that, during the connection, the network uses the traffic contract defined for the connection to check that i