UMTS Assumptions

For user satisfaction the mobile terminal, the RNC and the S/GGSN need to be in states that enable long battery lifetime when not sending or receiving data, but with intact PS connectivity to the IMS.

Basically there are three such state combinations:

• PMM-CONNECTED, RRC: CelLPCH and SM: ACTIVE.

From an IMS session setup delay perspective, the first state combination gives the longest delay, while the last state combination gives the fastest Multimedia Telephony session setup times. As a compromise between speed and battery lifetime the second state combination was chosen to be used in this analysis. It can be assumed that the battery consumption in URA_PCH is about 3 mA h (as a comparison when transmitting in CELL_DCH the mobile terminal consumes about 300 mA h). Given a battery with 800-1000 mA h a mobile terminal should be able to camp in URA_PCH for days.

No transmission of SIP messages can be done in URA_PCH. Instead the mobile terminal and the RNC must switch to the Cell_DCH state before transmission of SIP messages can start. The state transition between URA_PCH and Cell_DCH needs two RRC procedures on the originating side and paging plus two RRC procedures on the terminating side. The two RRC procedures are: cell update and channel up switch. The technology potential of HSPA make the following delays possible.

• Channel up switch, mobile terminal initiated: 260 ms.

• Channel up switch, UTRAN initiated: 150 ms.

As described in Chapter 3, the Multimedia Telephony communication service uses a dedicated Interactive RAB for the SIP signaling. This means that a second RAB and thus a second PDP context is needed to convey the media of the Multimedia Telephony session. It should be noted that, after the secondary PDP context has been established, the SIP signaling is still sent over the primary PDP context.

It is assumed that the signaling radio bearers that carry e.g. GPRS SM messages and RRC messages are mapped onto E-DCH and HS-DSCH. This makes it possible to do the PDP context activation in about 350 ms.

The radio conditions are assumed to be good, enabling a maximum throughput of 0.5 Mbps in the UL and 2 Mbps in the DL. The transmission time of SIP messages assumes no RLC retransmissions but it assumes that on average 10% of the MAC-hs PDUs and the MAC-e PDUs are retransmitted using H-ARQ instead. On average approximately 1 ms is added to the delay for each SIP message sent over HSPA in UL and DL.

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