t-side text bloc refers to downlink messages and the right-side one refers to uplink messages. Possible identifiers of calls on an Abis trace, for example, are called IMSI and ISDN numbers. When ciphering is active on the network, it is not possible to identify the calling party because of the use of the TMSI instead of the IMSI. Offline Observation Observations are handled at the BSC level in the same way as measurements. According to the setup definition, specific reports start to be updated only if the 'observed' event happens. For example, if the focus is on drop calls in one BTS, the observation report will give a history only on drop calls and only on this BTS. Observations help identify possible causes for the event. The main ones give reports on SDCCH/TCH seizures/releases, DCR and BSC outgoing handovers. The procedure idea of an observation is generation of reports immediately after an event is captured, such as a handover request or a channel seizure. In Figure 2.48 an SDCCH observation file is presented. This example gives the statistical sharing between different SDCCH release causes in each call phase where the SDCCH is involved (example: basic assignment, internal handover, etc.). Alarm Monitoring The BSS holds a certain intelligence that helps operators to understand better and to dialog with the machine. Generally, it reports a set of alarms that help maintenance engineers identify, diagnose and Radio Network Optimisation * NetHawk GSM Analyser File Edit Monitor View Tools Help States Traps - IMEI included Conn:1 Line:1 TS:29 Subch: 0 542399 21:05:09.949 VALID FRAME: 02 13 01 SC RECEIVER READY SAPI: o (Oh) THI: 9 (9h) C/R: 1 D/F: o N(R): 2KH Conn:2 Line:1 TS:26 Subch:0 542400 21:05:10.025 VALID FRAME 02 07 30 A6 OC 15 01 90 OE 00 OC 08 29 80 10 28 10 31 71 63 SAPI: 0 (Oh) THI: 3 (3h) C/R: 1 P/F: 0 N(R): 53H N(S): 18H OC 15 01 90 OH 00 OC 08 29 80 10 28 10 31 71 63 PAGING CHD (CCH) T=O Channel Nr - downlink CCCH (PCH + AGCH) - timeslot o Paging Group value : 0 (00h) ns Identity IMSI 208018201131736