A teletraffic analysis of dial-up connections over PSTN

Although new technologies such as xDSL and PONs will soon permit a direct and continuous access to global information infrastructures, such as the Internet, of residential and SOHO (small office-home office) users, dial-up access via analog modems over PSTN remains the most frequent approach. The ever increasing number of Internet users adopting this access modality is leading to two kind of problems: (1) a dimensioning problem for the ISPs which have to properly define the number of modems to guarantee a low refuse probability for the incoming traffic (dial-up connections); (2) terrible implications on dimensioning problems of the PSTN which was designed on the basis of assumptions strongly modified by the new statistical nature of ISP access connections. The paper presents an extensive measurement analysis carried out collecting traffic data offered to an Internet dial-up access server. The characterisation of the arrival process and the call holding time (CHT) distribution is presented. The analyses have pointed out the tail heaviness of the CHT distribution and a non-negligible correlation of the arrival process. The impact of these features on a loss queueing system corresponding to the ISP modem pool is analysed.