ons of VoIP packets. At the end of the talk spurt, persistent resource allo- cation is released. Thus, the released resource can be allocated to some other VoIP user, which enables efficient usage of PDSCH bandwidth. © 2009 by Taylor & Francis Group, LLC Radio Access Network VoIP Optimization 20 ms DL allocation: DL VolP packet: Retransmission: Reserved resource: Figure 10.10 Talk spurt based persistent allocation in downlink. The persistent allocation at the beginning of the talk spurt is signaled by using L1/L2 signaling. RRC signaling is used to signal some semi-static parameters such as the periodicity of the allocation. A slow, talk spurt based link adaptation is pos- sible since the modulation scheme as well as the amount of resources are signaled with L1/L2 signaling. The release of the persistent allocation at the end of the talk spurt is done via explicit signaling from the eNodeB with L1/L2 signaling. It is still open whether implicit release (without signaling) of DL semi-persistent resources is supported, too. DL operation for the talk spurt based persistent allocation is illustrated in Figure 10.10. In the UL direction, the UE should send a scheduling request (SR) to the eNodeB at the beginning of a talk spurt to get the radio resource allocated for it. Similarly, as in DL, the allocated radio resource is used to carry initial transmis- sions of VoIP packets without any scheduling related L1/L2 signaling in DL. SID frames can be allocated dynamically (thus requiring SR for each SID). The required signaling in the UL direction is similar to the DL. The persistent UL allocation at the beginning of the talk spurt is signaled by using L1/L2 signaling. When the talk spurt ends, the resource is released either explicitly with release signaling or implicitly by noticing that no more data is coming. Thus, the released resource can be allocated to some other VoIP user. Figure 10.11 shows the required UL and DL signaling as well as the transmis- sion resources. Here we assume that SID frames are scheduled dyna