ter error rate by means of channel coding 3.3 UMTS Release 99 and retransmission. But traffic in the Interactive class has higher priority in scheduling than Background class traffic, SO background applications use transmission resources only when interactive applications do not need them. Traffic class Fundamental characteristics Preserve time relation (variation) between information entities of the stream Conversational class Conversational pattern (stringent and low delay) Example: speech, video Preserve time relation (variation) between information entities Streaming class of the stream (i.e. some but constant delay) Example: streaming audio and video Request response pattern Interactive class Preserve payload content Example: web browsing Destination is not expecting the data within a certain time Background Preserve payload content Example: background download of emails or file downloads Table 3.1: Traffic classes [3GP06c] Maximum bitrate (kbps) is the peak data rate a user/application can transmit. It is defined as maximum number of bits delivered by UMTS and to UMTS at a Service Access Point (SAP) within a period of time, divided by the duration of the period. Guaranteed bitrate (kbps) is defined as guaranteed number of bits delivered by UMTS at a SAP within a period of time (provided that there is data to deliver), divided by the duration of the period. It describes the bitrate the UMTS bearer service must guarantee to the user or application. That means, UMTS bearer service attributes such as delay and reliability attributes are guaranteed for traffic up to the Guaranteed bitrate. The Guaranteed bitrate may be used to facilitate admission control based on available resources, and for resource allocation within UMTS. Maximum SDU Size (octets) defines the maximum allowed SDU size. It is used for admission control and policing, and/or optimizing transport. Other important RAB service attributes such as SDU error ratio, residual bit error ratio, delivery of erroneous SDUs, transfer delay, traffic handling p