The estimation algorithm of Pathload is based on the SLoPS methodology,
which is described in:
Pathload : A measurement tool for end-to-end available bandwidth" ,
by Manish Jain and Constantine Dovrolis, published at PAM 2002.
A more extensive study of available bandwidth is given in:
"End-to-End Available Bandwidth: Measurement methodology, Dynamics, and
Relation with TCP Throughput", to appear at the IEEE/ACM Transactions on Networking, August 2003 (journal version of the ACM SIGCOMM 2002 paper).
Briefly, Pathload is based on the following key idea:
When a process at S sends a periodic stream of UDP packet
at a rate higher than the available bandwidth in the path,
the relative one-way packet delays show an increasing trend.
When the stream rate is lower than the available bandwidth, the
relative one-way packet delays show no consistent trend.
Pathload consists of a process running at S and a process running at R.
S sends periodic streams of UDP packets from S to R at a certain rate.
Pathload does not determine whether a particular rate (Tr) is
greater than available bandwidth (A) based on just one stream.
Instead, it sends "a fleet of N streams", so that it has N samples
to decide whether Tr > A, or not.
Upon the receipt of a complete fleet, R checks if there is an increasing
trend in the relative one-way packet delays in each stream.
If a large fraction f of the N streams in a fleet show increasing trend,
then the entire fleet is said to have increasing trend and the
next fleet rate is lower than Tr.
If a large fraction f of streams in a fleet show no trend, then the
entire fleet is said to have no trend and the next fleet rate is higher
than Tr.
A certain fleet rate falls into the `grey region' when less than f x N
streams of the fleet show increasing trend, and less than f x N streams
show no trend.
The iterative estimation algorithm of Pathload terminates when:
1. Overview of Pathload
Pathload is a tool for estimating the available bandwidth
of an end-to-end path from a host S (sender) to a host R (receiver).
The available bandwidth is the maximum IP-layer
throughput that a flow can get in the path from S to R,
without reducing the rate of the rest of the traffic in the path.
This can happen when the available bandwidth was more than fleet rate
for some streams and less than the fleet rate for some other streams.
In other words, the available bandwidth during the fleet duration varied
above and below the fleet rate, causing some streams to show increasing
trend and others to show no trend.
-q | : quite mode | |
-H|-h | : print this help and exit | |
-i | : run sender in iterative (persistent) mode |
-s | : hostname/ipaddress of sender | |
-q | : quite mode | |
-v | : verbose mode | |
-w | : user specified bandwidth resolution | |
-o <file> | : write log to user specified file [default is pathload.log] | |
-O <file> | : append log to user specified file [default is pathload.log] | |
-N <file> | : append output in netlogger format to <file> | |
-H|-h | : print this help and exit |
[-o] By default, receiver always appends detailed output to file "pathload.log". The output file can be changed by specifying a filename with -o switch. Note that if the specified file already exits, it will be over-written.
[-O] Similar to -o except that the log is appended to the file.
[-q,-v] By default, receiver sends minimal output (fleet rate and final result) to terminal (stdout). To completely disable any message on stdout, use -q (quite mode). To enable detailed output on screen, use -v (Verbose mode). Note that, log file (user specified or "pathload.log") contains exactly the same output as -v.
[-N] Specify a file name to store output in netlogger compatible format.
[-w] By default, bandwidth resolution (bw-resol) is set to a fraction of the Average Dispersion Rate (ADR) in the path. To change default bw-resol use -w. bw-resol allows the user to select the precision with which Pathload should try to estimate the available bandwidth. Keep in mind that the available bandwidth is a dynamically varying metric, and so its variation range may be wider than the user-specified resolution. In that case, Pathload will report the "grey region", which is an estimate of the variation range of the available bandwidth.
6. References
Manish Jain and Constantine Dovrolis
PAM 2002.
Manish Jain and Constantine Dovrolis
To appear at the IEEE/ACM Transactions on Networking, August 2003 (journal version of the ACM SIGCOMM 2002 paper).