We have started a long-term experiment of end-to-end active measurements along a number of Internet paths, while such kinds of distributed measurement infrastructures have been developed on the Internet and a number of experiments on them have already been reported. Our objective is to explore correlations among various properties of an individual path measured within a period in which the path state does not change, which have not yet been clearly covered. A PC-based measurement system has been developed to
measure a set of path properties in sequence or in parallel for this purpose.
In our preliminary experiment over several Internet paths in Japan,
loss (rate and pattern) and delay (RTT and queuing delay) statistics;
bottleneck bandwidths (the capacity and available bandwidth); and TCP throughput as well as the end-to-end route (to validate no changes of itself) are measured. Some interesting correlations (and no-correlation) among those properties are shown, which indicate the potential of efficient and/or reliable measurement of some path property utilizing the multiple properties measured on the path.
Emerging delay-sensitive applications on the Internet increase awareness of the Quality of Service (QoS) parameters of a path for Internet Service Providers (ISPs) as well as users, However, it is costly to frequently monitor delays along individual paths among every edge-router in the ISP. The most widely used way of estimating such statistics is by actively sending probe packets along each path, despite the increased transmission of wasteful traffic introduced by the probe packets itself for frequent and accurate estimations. On the other hand, each router can passively observe local queuing delays experienced at the router. However, while the mean delays can
always be concatenated concentrating simply by summing those at tandem routers along a path, the statistics (other than the mean) such as the 90-percentile cannot be estimated accurately by such a simple-sum scheme because of dependence among delays at such routers on the Internet. In this work, a novel scheme to estimate the QoS parameters of a path is proposed, which combines statistics
gatherd at each router and data obtained from a small number of sampling along the path. For delays, considering an unknown joint discrete distribution of quantized queuing delays on routers along a path, we find the maximum likelihood estimator for the unknown distribution (under the constraints of the marginal distributions measured at each router) from the samples. Theoretical analysis and numerical simulations indicate that this scheme effectively estimates the delay statistics along a path even with a small number of samples, which allows continual measurements capturing statistics with a broad range of time-scales.
The recent evolution on the network tomography have successfully provided
principles and methodologies of inferring network-internal (local)
from only end-to-end measurements,
which should be followed by deployment in practical use.
In this paper, we propose two types of
user-oriented tools for inferring one-way
packet losses on paths from/to an user-host (a client) to/from a specified target
host (a server or router)
without any measurement on the target,
which utilize a method based on the network tomography.
One is a stand-alone tool running on the client, and
the other is a client-server style tool running on both the client
and proxy measurement server(s) distributed in the Internet.
Both of them can infer one-way packet loss rates not only on a
path between the client and an application server, but on
a path segment (a portion of the path)
between the client and any router residing in the path, and thus
can find the congested area along the path.
We have developed prototypes of the tools
and have evaluated them in experiments in the Internet environment,
which showed that
the tools could infer one-way packet loss rates
within 1% errors in various network conditions.