3GPP43.013Discontinuous Reception (DRX) in the GSM systemRelease 16TS
The MSC is almost transparent to DRX, since it has no real time knowledge of the absolute frame numbers on the air interface (refer to Technical Specification GSM 08.02).
It should be noted, however, that the MSC does define which cells are to be paged in order to locate a particular MS. Normally this will be a location area.
The MSC therefore constructs page requests and sends them to a specific set of BSSs. Each page request always includes the IMSI. The timer to detect non receipt of a page response may require alteration depending upon the number of page groups that are involved. If this is the case, then the timer will be set by O and M command at the same time as the number of paging groups at the cell is altered.