l be satisfied following the priority of the users. In order to calculate the traffic offered by each cell, the following information is usually required: Total number of active users Distribution of users in the area of interest Average user traffic profile By using the above data the average number of users per cell and the traffic per cell can be calculated. In order to estimate the number of traffic channels per cell the following objectives should be specified: Grade of service Traffic model The grade of service (GoS) is a measure of the ability of a user to access a trunked system during the busiest hour. It is specified as the probability of a call being blocked or the probability of a call being delayed beyond a certain amount of time. The traffic model specifies the probability distribution of the calls in the time domain, the trunking system strategy, the time between successive calls, etc. The most common formula used to estimate the traffic channels was developed by Erlang. In cases where the blocked calls are delayed, the Erlang C formula will be used. Figure D.10 summarises the process to be applied for traffic channel estimations. Suggested Reading 3GPP, 3G TR 23.923 ver.3.0, 2000-05, Combined GSM and Mobile IP Mobility Handling in UMTS IP CN. 3GPP, 3G TS 22.796, ver.2.0.0, 2000-06, Study on Rel.2000 Services and Capabilities. 3GPP, TS 23.002, Rel.4 Network Architecture. 3GPP, TS 23.205, Rel.4 Bearer-Independent Circuit-Switched Core Network. 3GPP, TS 23.228, IP Multimedia Subsystem. 3GPP, TS 23.907, Services and System Aspects, QoS Concepts. 3GPP, TS 25.414, Rel.4 UTRAN Iu-Interface Data Transport and Transport Signalling. 3GPP, TS 29.414, Rel.4 Core Network Nb-Interface Data Transport and Transport Signalling. 3G TS 25.213, Spreading and Modulation (FDD). 3G TS 25.223, Spreading and Modulation (TDD). Agilent technologies (CDMA systems drive), http://cp.literature.agilent.com/litweb/pdf/5968-5554E.pdf. Allen, K.C., "Observation of specific attenuation of millimetre waves by rain", IEE A&P Conferen