multaneously. HSPA technology is integrated directly into the existing UMTS nodes, i.e. Node B and RNC, via software/hardware updates. Thus, the lub interface between the RNC and Node B carries both HSPA and Rel99 traffic. Rel99 and HSPA traffic have different delay requirements on the transport network. There is an extremely strict delay constraint on the lub interface for DCH channels of Rel99, not only due to the delay requirements of the user traffic itself but also because of the requirements derived from supporting radio control functions such as outer-loop power control and soft handover. The excessively delayed Frame Protocol packets (their delay is larger than predefined delay boundaries) will be discarded at the Node B as they become too late to be sent over the air interface for the allocated time slot. However, HSPA traffic has significantly lower delay requirement on the lub interface. Because for both HSDPA and HSUPA a fast scheduling is introduced at the Node B which reserves the time slot on the air interface replacing the scheduling at RNC in Re199, and furthermore there is buffering in the Node B which supports fast HARQ. Thus, the delay requirements for HSPA are essentially only due to the service itself, which are mainly delay-tolerant best effort services that have loose constraints on the delay and delay variations. Thanks to the Rel99 traffic having a much more stringent delay requirement on the lub interface, the Rel99 traffic is usually given a higher priority to transmit over the HSPA traffic. UMTS R99 combined with HSPA (HSUPA/HSDPA) Cell phone Cell phone HSDPA Time (second) ce 100 Laptop HSDPA Laptop HSUPA Node B Cell phone IIIII WCDMA Figure A.21: UMTS Network supporting Rel99 and HSPA traffic In the currently deployed UMTS system, the UTRAN transport network is ATM-based. In the case without using traffic separation at the lub interface, the Re199 traffic and HSPA traffic are carried within a single ATM CBR (Constant Bit Rate) VP (Virtual Path). In this Appendix case, it is assumed t