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The current architecture supporting data services to mobile devices is built below the network layer (IP) and users receive the payload at the application layer. Between them is the transport layer that can cause data consumption inflation due to the retransmission mechanism that provides reliable delivery. In this paper, we examine the accounting policies of five large cellular ISPs in the U.S. and South Korea. We look at their policies regarding the transport layer reliability mechanism with TCP's retransmission and show that the current implementation of accounting policies either fails to meet the billing fairness or is vulnerable to charge evasions. Three of the ISPs surveyed charge for all IP packets regardless of retransmission, allowing attackers to inflate a victim's bill by intentionally retransmitting packets. The other two ISPs deduct the retransmitted amount from the user's bill thus allowing tunneling through TCP retransmissions. We show that a "free-riding" attack is viable with these ISPs and discuss some of the mitigation techniques.

No abstract

WiBro (Wireless Broadband Internet), the Korean version of mobile WiMAX compatible standard, provides high-speed mobile data service. Although mobile WiMAX services are being deployed, there exist few reports about WiBro performance. In this work, we measure and analyze best-case performance of WiBro. In order to measure one-way delay, we develop a GPS synchronization device to measure one-way delay.Our measurement shows that the maximum throughput over the WiBro network is 10 Mbps in downlink and 2.5 Mbps in uplink. We estimate that both the base station and WiBro modems have large buffers up to 2 s and 500 ms and minimum one-way delay of 76 ms and 11 ms for uplink and downlink, respectively. We measure TCP throughput over WiBro by varying the send buffer and receive buffer sizes. To fully exploit the high bandwidth of Wibro, we conclude the TCP needs along with the minimum of 128 KB buffer size.