VC link Virtual channel connection Virtual channel level VP link Virtual path connection Virtual level Transmission path Transmission level Digital section Digital section level Regenerator section Regenerator section level Endpoint of the corresponding levels Connecting point of the corresponding levels Figure 41.18 OAM hierarchical levels (Fig. 3/1.610) Quality of service performance requirements 41/19 Network performance parameter values are required to give net- work providers a view of the performance they must provide to meet Table 41.5 Bearer services and applications the users' needs and to provide manufacturing industry with perfor- mance targets upon which to base equipment designs. They are Bearer service Application defined against the following assumptions: 64kbit/s 8kHz structured Telephony; data; 1. All ATM connections maintain cell sequence integrity. (CCITT Rec. I.231 videotelephony 2. Each teleservice is supported by a single ATM bearer service. 1961.231.4) 3. Each ATM bearer service is supported by one virtual circuit. 2x64kbit/s unrestricted, 8kHz Videotelephony 4. ATM bearer services are regarded as different if at least one of structured (CCITT Rec. their attributes differs. 1.231.5) 64kbit/s Access to server for The QoS of an ATM Layer service can be characterised by a connectionless services. number of parameters: cell insertion rate due to header errors; cell These services include loss rate due to header errors; cell loss rate due to buffer overflow; mean/maximum delay; delay dispersion/burst diffusion; connection 'Remote process control' set-up delay; reliability/availability; information field error-rate. 64kbit/s Interoffice signalling between These correspond to the attribute network performance for con- signalling points in public nection types and in the following section definitions are given for networks or between two a set of network performance parameters based on the CCITT PABXs attribute description method which characterises the requirements 384kbit/s unrestricted, 8kHz Vid