Spectroscopy of the packet radio interfaces: A case study with GSM/GPRS

In this paper we apply some ideas presented in [1] of network spectroscopy to the analysis of a packet radio interface. We analyze the IP packet interarrival time distribution of upstream traffic, taking into account also the packet sizes in the case where the IP packet trace is measured after the Time Division Multiple Access (TDMA) based radio interface of General Packet Radio Service (GPRS). When the Logical Link Control (LLC) layer works in unacknowledged mode and the Radio Link Control (RLC) layer works in acknowledged mode, we show that using the ideas of spectroscopy it is possible to some extent to detect the behaviour of the TDMA based radio interface of GPRS from the IP level packet data. More precisely, it is possible to extract the number of Packet Data Channels (PDCHs) and Channel Coding Scheme used for uplink traffic of a single mobile station (MS). Physical connections between the MS and the Base Station Subsystem (BSS), called Temporary Block Flows (TBFs), can be extracted also, and it is possible to indirectly detect some retransmissions of radio blocks within TBF. The general method is not restricted to TDMA and should give good results also for other packet radio interfaces like Code Division Multiple Access (CDMA) based packet radio interfaces or Carrier Sense Multiple Access (CSMA) based WLANs.