eve its QoS goals. 2. Policing Function: Given that a switch at the edge of the network has accepted a virtual circuit request, it must ensure that the customer equipment fulfils its side of the traffic contract. The policing function estimates the parameters of incom- ing traffic and takes action if they measure traffic exceeding agreed parameters. This action could be to drop the cells or to mark them as low cell-loss priority. 3. Charging Function: This function computes a charge from the estimated and agreed traffic parameters. 4. Traffic-shaping Function: Traffic shaping occurs in the customer equipment. A common analogy is, if the policing function is the policeman and the charging function is the judge, then the traffic shaper is a lawyer. Like a lawyer, it allows the service to go as close as possible to the minimum QoS line in the sand without crossing it, and at the least cost. In particular, the traffic shaper uses information about the policing and charging functions to change traffic charac- teristics of the customer's stream to ensure lowest charge, smallest cell loss, etc. In Chapter 6, we briefly introduced Service Level Agreements (SLAs). An SLA also specified the Traffic Conditioning Agreement (TCA) by the rules needed to realise the service which is specified in the SLA, and this specifies both what the service provider and client agree to do so that the promised quality of service is delivered. A TCA specifies classifier rules, traffic profiles and shaping rules that are to be applied to each traffic classification. A TCA encompasses all traffic conditioning rules that are explicitly given in the SLA, and also makes explicit the rules that must be satisfied to achieve the service requirements. In the TCA, the traffic profile com- prises the properties of a traffic stream in time, that is, bits per second, burstiness specification. As a traffic stream enters the domain to which the TCA applies, packets are classified into a traffic aggregate by a filter on the relevant router at the edge of OSS