) in order to alleviate any short term over- Constant bit-rate services: bit-rates negotiated at call set-up load conditions that may occur. time to ensure resources are fully allocated for duration of call. Variable bit-rate services: expressed by a number of parameters 41.4.4 I.211: B-ISDN service aspects related to traffic characteristics (see Rec. 1.311). Parameters negotiated at call set-up time are supported for duration of call. Provides a general classification of the standardised services to be Maximum service bit-rate supported by the 155 Mbit/s inter- supported by a B-ISDN and gives guidance on important network face: UNI (SDH) payload = 155.52 X 260/270 = 149.760 aspects which need to be taken into account when supporting Mbit/s. With ATM cell format, cell payloads carry 149.76 X services for B-ISDN. In particular, gives consideration to video 48/53 = 135.631 Mbit/s (= maximum possible service bit-rate). coding aspects in relation to ATM. May in fact be less due to: transfer capacity required for OAM and signalling cells; ATM adaptation layer overheads; the time period associated with the 'structure' attribute for CBR service- 41.4.4.1 Service classification 4. Maximum service bit-rate supported by the 622 Mbit/s inter- The classification separates services into two main categories: in- face: for further study. teractive and distribution services. Interactive services are sub- divided into: Service timing/synchronisation aspects: 1. Conversational, which permit bilateral communication with 1. End-to-end methods: use of an adaptive clock; use of a syn- real-time, end-to-end information transfer from user to user. chronisataion pattern; and time stamping. 2. Messaging, which permit user-to-user communication via stor- 2. Network methods: mechanisms to be provided to support ser- age units with store and forward, mailbox and/or message vices with 8kHz integrity. Examples are network sourced time- handling functions. stamped cells; timing information from the T-interface. 3. Retrieval, which permit retrie