Measuring the behavior between Internet hosts is critical for diagnosing current performance problems as well as for designing future distributed services. Unfortunately, the Internet architecture was not designed with performance measurement as a primary goal and therefore has few ``built-in'' services that support this need [Cla88]. Consequently, measurement tools must either ``make do'' with the services provided by the Internet, or deploy substantial new infrastructures geared towards measurement.
In this paper, we argue that the behavior of the commonly deployed Transmission Control Protocol (TCP) can be used as an implicit measurement service. We present a new tool, called sting, that uses TCP to measure the packet loss rates between a source host and some target host. Unlike traditional loss measurement tools, sting is able to precisely distinguish which losses occur in the forward direction on the path to the target and which occur in the reverse direction from the target back to the source. Moreover, the only requirement of the target host is that it run some TCP-based service, such as a Web server.
The remainder of this paper is organized as follows: In section 2 we review the current state of practice for measuring packet loss. Section 3 contains a description of the basic loss deduction algorithms used by sting, followed by extensions for variable packet size and inter-arrival times in section 4. We briefly discuss our implementation in section 5 and present some preliminary experiences using the tool in section 6.