文档介绍：Accounting for Roaming Users on Mobile Data Access: Issues and Root Causes Guan-Hua Tu, Chunyi Peng, Chi-Yu Li, Xingyu Ma, Hongyi Wang, Tao Wang +, Songwu Lu puter Science, Los Angeles, CA 90095, USA; CECA, School of EECS, Peking University, Beijing 100871, China + {ghtu, chunyip, lichiyu, maxy12, hywang, slu}***@, ******@pku. + ABSTRACT In this paper, we study how mobility affects mobile data account- ing, which records the usage volume for each roaming user. We ?nd out that, current 2G/3G/4G systems have well-tested mobility support solutions and generally work well. However, under cer- tain biased, mon yet possible scenarios, accounting gap between the operator’s log and the user’s observation indeed exists. The gap can be as large as 69 . 6% in our road tests. We further discover that the root causes are diversi ?ed. In addition to the no- signal case reported in the prior work [23], they also include hand- offs, as well as insuf ?cient coverage of hybrid 2G/3G/4G systems. Inter-system handoffs (that migrate user devices between radio ac- cess technologies of 2G, 3G, and 4G) may incur non-negligible accounting discrepancy. Categories and Subject Descriptors [ works ]: Network Archi- tecture and Design— work ;[ Performance of Sys- tems ]:Design Studies General Terms Measurement, Experimentation, Performance Keywords works, Mobile Data Services, Data Accounting 1. INTRODUCTION Mobile data accounting records the data usage volume for each roaming user over wireless works. It has e an increasingly important problem in recent years. On one hand, most cellular carriers use metered accounting, which charges mo- bile users based on the data volume they consume. It thus departs from the typical, ?at-rate based charging over the wired and requires accurate accounting. On the other hand, user mobil- ity is prevalent in reality and mobile data traf ?c increases with the popularity of smartphones [22, 27]. The global mobile data traf ? c Permission to mak