ct is a network cross-traffic generator implementation using NodeJS.

In order to test custom software-defined networks built using mininet, I needed a tool to stress test the network data plane capacity in terms of latency and throughput. The tools I found so far on the web either measure latency or throughput, but not both of them simultaneously over the same data flow. Hence, I came up with my own implementation, called ct.

In a nutshell, ct provides a server and a set of client applications, where each type of client conveys a different type of flow generation scheme. In the overall picture, multiple clients continuously pump data to the given servers over TCP. In the meantime, servers collect throughput and latency statistics on a per client basis.

ct is written in CoffeeScript on top of NodeJS framework for efficient stream handling and low system overhead. You need to have npm, cake, and node to install, compile and run the program, respectively. On a GNU/Linux Ubuntu system you can install this toolset as follows.

$ sudo apt-get install nodejs npm
$ sudo npm install -g coffee-script
$ sudo ln -s /usr/bin/nodejs /usr/bin/node

First, you need to clone the repository to your local machine.

~$ git clone https://github.com/vy/ct.git
~$ cd ct
~/ct$ _

Next, run npm to install dependencies.

~/ct$ npm install

Finally, compile the CoffeeScript sources.

~/ct$ cake compile

Further, you can run unit tests to verify the integrity of the installation.

~/ct$ cake test

For a complete list of all available build options, run cake without any parameters.

~/ct$ cake
Cakefile defines the following tasks:

cake compile              # Compile CoffeeScript sources in 'src' to 'out'
cake watch                # Watch 'src' for changes
cake doc                  # Create the documentation from sources
cake test                 # Run test suites

ct ships a single server executable: server.exec.js.

$ node out/exec/server.exec.js
Start the cross-traffic server.
Usage: node ./out/exec/server.exec.js

Options:
  -f, --reportFile  report output file  [required]

Missing required arguments: f

By default there are two types of clients shipped as follows.

periodicClient.exec.js generates (and maintains) given number of concurrent connections to the specified set of servers. Generated flows has a constant lifetime with a parametrized variation.

$ node out/exec/periodicClient.exec.js
Start the periodic cross-traffic client.
Usage: node ./out/exec/periodicClient.exec.js

Options:
  -f, --serverAddressFile        file containing list of server addresses in JSON        [required]
  -x, --excludedServerAddresses  whitespace separated list of excluded server addresses  [default: ""]
  -c, --nConns                   number of concurrent connections                        [required]
  -h, --hostId                   host id                                                 [required]
  -l, --lifetime                 flow lifetime                                           [required]
  -v, --lifetimeVariance         variation window of the flow lifetime                   [required]

Missing required arguments: f, c, h, l, v

You can employ periodicClient.exec.js in your mininet setup as follows. First, start a set of ct servers on server hosts:

$ node out/exec/server.exec.js --reportFile /tmp/server.dat

Next, write down the list of server IP addresses to a file.

$ echo '["127.0.0.1"]' >/tmp/serverAddresses.json

Finally, start clients by providing necessary command line arguments.

$ node out/exec/periodicClient.exec.js \
	--serverAddressFile /tmp/serverAddresses.json
	--nConns 10 \
	--hostId 1 \
	--lifetime 10000 \
	--lifetimeVariance 3000

Here, we start a client that is supposed to connect to a single server running at 127.0.0.1. Client will try to maintain nConns=10 concurrent connections at a time. (The server for each connection will be picked randomly.) hostId is the identifier of the current client. Server will use this information to differentiate statistics for each client in the reports. lifetime=10000 and lifetimeVariance=3000 instructs client to generate flows with a lifetime of 10±3 seconds.

A client continuously pushes data over TCP to the servers using given number of concurrent connections. When you interrupt a server (via ^C) it will write down the statistics collected so far to the specified reportFile as follows.

$ cat /tmp/server.dat
data throughput to host 1: 46126.948121987814 bytes/ms
data latency to host 1: 171.35418041643547 ms
total data throughput: 455082.68570153916 bytes/ms
total data latency: 171.35418041643547 ms
total connection throughput: 0.0010692720563569272 conns/ms

Note that data throughput to host 1 is nearly 10-times less than the total data throughput. This is due to the fact that, first we compute the throughput of each flow individually and then take the mean of these individual throughputs to compute the throughput of a single host. Hence, since there are 10 concurrent connections, (data throughput to host 1) x 10 ~= total data throughput.

randomClient.exec.js generates instantaneous flows to the specified set of servers. While doing so, flow inter-arrival time is set to be exponentially distributed and flow lifetimes are picked randomly from the range [0, 10).

$ node out/exec/randomClient.exec.js
Start the random cross-traffic client.
Usage: node ./out/exec/randomClient.exec.js

Options:
  -f, --serverAddressFile        file containing list of server addresses in JSON        [required]
  -x, --excludedServerAddresses  whitespace separated list of excluded server addresses  [default: ""]
  -h, --hostId                   host id                                                 [required]

Missing required arguments: f, h

While periodic client keeps the socket creation rate at a regular pace, random clients can quickly exhaust the available port space due to TIME-WAIT sockets in a few seconds. In order to alleviate this problem, you might consider enabling TCP time-wait socket recycling (that is, net.ipv4.tcp_tw_recycle) in the kernel.

Copyright © 2014, Volkan Yazıcı

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