Skip to Main Content
This paper investigates the SIP based Presence traffic impact on the VoIP capacity, assuming an HSPA system. The results show that 2000 subscribers per cell with VoIP and presence enabled can be accommodated with a minor capacity loss of 5%. The uplink is the bottleneck for the system. The major reason for the capacity decrease is not the presence packet itself, rather the control channel overhead from DPCCH in UL and A-DPCH in DL due to the channel release delay. The paper investigates different priority based scheduling schemes. The simulations show that the best performance is achieved when VOIP and SIP (including presence and call setup) have equal priority. Prioritizing SIP over VoIP decreases SIP call control setup delay at the expense of lower VoIP capacity. Prioritizing VoIP over SIP or granting Presence the lowest priority results in very large overhead from the control channels, especially the uplink DPCCH. This leads to both decreased VoIP capacity and increased SIP setup delay. However, when UL DPCCH gating is applied, the performance of the scheme to prioritize VoIP over SIP call control and Presence is improved quite a lot and achieves the best trade-off between VoIP capacity and SIP setup delay.