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596 MOBILE APPLICATION PART19.4.3 Message ContentsThis section introduces the main parameters in the invokes and return-result for theoperations described earlier [5]. The reference numbers (Par.1, etc.) point to parameterdescriptions in Section 19.5.4. It is helpful to look up the descriptionswhen reading this section.HandoffMeasurementRequest Invoke (HOMEAS). See Fig. 19.4-2. Par.22(ServingCellID) identifies the cell that currently serves MS. Par.24 (StationClass-Mark) lists the transmission characteristics of the MS (Section 12.4.8).If the mobile is currently using an analog voice channel, the invoke includes Par.8(ChannelData), which contains the channel number, and the attenuation and colorcodes with which the MS is transmitting.If the mobile is currently using a digital traffic channel, the invoke also includesPar.10 (DigitalChannelData) and Par.7 (CallMode).On receiving a HOMEAS invoke, a MSC determines which cells are neighbors tothe current serving cell of the MS (from Par.22). These cells can be “target” cells forthe handoff. The MSC orders the target cells to measure the signal strengths receivedfrom MS.HandoffMeasurementRequest Return-Result (homeas). See Fig. 19.4-2.After receiving the measurement results, the MSC calculates the “quality” of thereceived signals. Cells in which the signal quality is above a predetermined levelare target cells for the handoff. The return-result is a list of target cells. Eachentry consists of a Par.23 (SignalQuality) and a Par.25 (TargetCellID).Figure 19.4-2. Parameters in handoff measurement messages. (From IS-41.5-B. Reproducedwith permission of TIA.)