| Having dealt with in-depth analysis of SS#7, GSM and GPRS networks I started to monitor UTRAN interfaces approximately four years ago. Monitoring interfaces means decoding the data captured on the links and analysing how the different data segments and messages are related to each other. In general I wanted to trace all messages belonging to a single call to prove if the network elements and protocol entities involved worked fine or if there had been failures or if any kind of suspicious events had influenced the normal call proceeding or the call’s quality of service. Cases showing normal network behaviour have been documented in Kreher and Ruedebusch (UMTS Signaling. John Wiley & Sons, Ltd, 2005), which provides examples for technical experts investigating call flows and network procedures.
While still writing the last paragraphs of UMTS Signaling it became obvious that the focus of leading UMTS technology experts was changing more and more from the investigation of functional behaviour to the analysis of huge data streams supplied by signalling information and user data/payload. As a result the idea of a second book was already born before the first one was ready to be published. Some major customer projects I have been involved in pushed my ideas and knowledge further into this field. Indeed, if one compares radio-related information in UMTS and GSM radio access network protocols, e.g. the contents of measurement reports sent to the network by mobile stations and base stations, it is obvious that in UMTS much more radio-specific measurements are executed. Reports are sent more frequently and by using more sophisticated methods than in GSM to guarantee the quality of service in UMTS networks.
The radio technology behind UMTS is seen in two different varieties: frequency duplex division (FDD, also known as WCDMA), where uplink and downlink data is transmitted on two different frequency bands; and time division duplex (TDD), where uplink and downlink channels are separated using timeslots. TDD is actually beyond the scope of this book, because it has not been introduced in European and North American networks so far. The Chinese solution of a low chip rate TDD (TD-SCDMA) has not yet been deployed in the field, and although deployment may start during 2006 it will take a while before performance measurement becomes crucial for TD-SCDMA operators. First they have to set emphasis on the execution of functional tests. Nevertheless, many measurement definitions and key performance indicators presented in this book will also be valid in TDD networks apart from mostly radio-related measurements and soft handover analysis, because there is no soft handover in TDD. |