// $Id$ // // Copyright (C) 2007 // Fraunhofer Institut fuer offene Kommunikationssysteme (FOKUS) // Kompetenzzentrum fuer Satelitenkommunikation (SatCom) // Stefan Bund // // This program is free software; you can redistribute it and/or modify // it under the terms of the GNU General Public License as published by // the Free Software Foundation; either version 2 of the License, or // (at your option) any later version. // // This program is distributed in the hope that it will be useful, // but WITHOUT ANY WARRANTY; without even the implied warranty of // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the // GNU General Public License for more details. // // You should have received a copy of the GNU General Public License // along with this program; if not, write to the // Free Software Foundation, Inc., // 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. /** \mainpage RateStuffer: A simple example featuring the Packet Processing Infrastructure This example application implements a simple PPI application: It will read UDP packets from an input port and will forward them to another port at a fixed packet rate. If the input stream does not provide enough packets, empty UDP packets will be sent instead. \section run Running the example Running the example is a little bit more complicated since we need to provide example UDP packets so we can see the application at work. We do this using \c netcat. We open several shell windows and run the folling commands, each in it's own window The first command listens for incoming UDP packets on port 44345: 
    # nc -u -l -p 44345
The next command starts the \c ratestuffer 
    # cd .../Examples/RateStuffer
    # scons -u
    # ./ratestuffer
We should now see '' messages arriving in the first window once per second. We now can start another \c netcat to send packets to the input port. 
    # nc -u localhost 44344
    < type any text here >
Whenever we send out a packet with CR in the last window we should see it appear in the first one. If we send out packets faster than 1 packet per seccond, they will still only be forwarded with a speed of 1 packet / seccond. If the kernel UDP buffer overflows, packets would be dropped (however, this buffer is prohibitively large) \image html screenshot.png \section setup Module setup \image html ratestuffer.png Above image depicts the module setup implementing the rate stuffer. A senf::ppi::module::ActiveSocketReader reads the incoming UDP packets and sends them into a senf::ppi::module::PassiveQueue. The \a queue feeds the packets into a senf::ppi::module::PriorityJoin. The CopyPacketGenerator \a generator is fed as second input into the \a join to provide the stuffing packets. The RateFilter \a rateFilter reads packets from it's input at a fixed rate and writes them into the senf::ppi::module::PassiveSocketWriter \a udpWriter. The senf::ppi::module::PriorityJoin ensures that read requests of the RateStuffer's input are always serviced, either from the \a queue or, if the \a queue output is throttled, from the \a generator. \section code Example code \dontinclude ratestuffer.cc The code starts out including the necessary header files \skip Custom \skip #include \until Setup We also define some namepsace aliases \skip namespace \until senf::ppi; The RateStuffer application is based on two additional modules. \subsection ratefilter The RateFilter module The RateFilter module simply forwards packets at a fixed rate. \skip class \until }; Both connectors of the RateFilter module are active. The module is driven by a senf::ppi::IntervalTimer. \until } The event is initialized to fire eery \a interval nanoseconds. The traffic is routed 'accross' the timer which controls the traffic. The timer is then registered to call RateFilter::timeout(). \until } The event handler is quite simple: Every \a interval nanoseconds a packet is read from \a input and forwarded to \a output. This is all there is to the RateFilter module. Due to the routing setup, the timer will automatically be disabled if either \a input or \a output become throttled (which is not even needed here). \subsection generator The CopyPacketGenerator We need an additional module to provide the stuffing packets. The CopyPacketGenerator provides an unlimited stream of clone's of a template packet. \skip class \until }; This module is very simple. \until } We save the template packet and initialize the \a output connector to call CopyPacketGenerator::request() whenever a packet is requested. \until } The handler just provides \a packet on each request. This is ok as long as the packets are not changed, in which case we would return packet->clone() instead. \subsection main Connecting the modules The applications main() method starts out by initializing the socket handles \skip main \until 44345 The \a inputSocket is listening on port 44344 while the \a outputSocket will send packets to port 44345 on localhost. The \a outputSocket uses a ConnectedUDPv4SocketHandle which is compatible with the senf::ppi::module::PassiveSocketWriter module. \until udpWriter Next all the modules are allocated: \li \a udpReader to read the packets from \a inputSocket \li \a queue to convert the active output of senf::ppi::module::ActiveSocketReader into a passive output \li \a generator to provide the stuffing in the form of packets containing "\n" \li \a join to combine the two packet streams (from \a udpReader and from \a generator) into a single stream \li \a rateFilter to generate the fixed rate packet stream of 1 packet every 1000000000 nanoseconds and \li \a udpWriter to send the packets to \a outputSocket \until udpWriter The \ref senf::ppi::connect() calls now setup the necessary connections. \until run The module setup is complete, \ref senf::ppi::run() is called to enter the event loop. \until } */ // Local Variables: // mode: c++ // fill-column: 100 // comment-column: 40 // c-file-style: "senf" // indent-tabs-mode: nil // ispell-local-dictionary: "american" // compile-command: "scons -u doc" // mode: flyspell // mode: auto-fill // End: