// $Id$ // // Copyright (C) 2007 // Fraunhofer Institute for Open Communication Systems (FOKUS) // // The contents of this file are subject to the Fraunhofer FOKUS Public License // Version 1.0 (the "License"); you may not use this file except in compliance // with the License. You may obtain a copy of the License at // http://senf.berlios.de/license.html // // The Fraunhofer FOKUS Public License Version 1.0 is based on, // but modifies the Mozilla Public License Version 1.1. // See the full license text for the amendments. // // Software distributed under the License is distributed on an "AS IS" basis, // WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License // for the specific language governing rights and limitations under the License. // // The Original Code is Fraunhofer FOKUS code. // // The Initial Developer of the Original Code is Fraunhofer-Gesellschaft e.V. // (registered association), Hansastraße 27 c, 80686 Munich, Germany. // // Contributor(s): // Stefan Bund using namespace senf::ppi::module; /** \mainpage Example introducing 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 following 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 second, they will start to be discarded if more than two packets are in flight. \image html screenshot.png \section setup Module setup \diaimage ratestuffer.dia Above image depicts the module setup implementing the rate stuffer. A senf::ppi::module::ActiveSocketSource reads the incoming UDP packets and sends them into a senf::ppi::module::PassiveQueue (via a senf::ppi::module::ThrottleBarrier). The \a queue feeds the packets into a senf::ppi::module::PriorityJoin. The CloneSource \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::PassiveSocketSink \a udpSink. 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. The \a barrier is not strictly necessary. However, it makes the behavior of the RateStuffer predictable in the case where packets need to be dropped. Without the senf::ppi::module::ThrottleBarrier, the packets will be left in the kernel socket queue. Packets will only start to be dropped when that queue fills up. The size of this queue cannot be easily manipulated and it's initial size is immense. So to stop the kernel queue from filling up with increasingly out-of-date packets, we add the \a barrier which will explicitly read and drop excess packets. \section code Example code \dontinclude ratestuffer.cc The code starts out including the necessary header files \skip Custom \skip #include \until PPI We also define some namespace aliases \skip namespace \until senf::ppi; The RateStuffer application is based on one additional application module. \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 every \a interval nanoseconds. The traffic is routed 'across' the timer which controls the traffic. This routing lets the module automatically handle throttling events. The timer is 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 should either \a input or \a output become throttled. However, in this specific case this should never happen: The \a input is connected (via the \a join) to the senf::ppi::module::CloneSource, which will never throttle. The \a output is connected to a UDP socket which also never throttles. \subsection ratestuffer The RateStuffer subnet We decide to implement the RateStuffer as a subnet or collection. This is a simple struct or class which contains all the modules necessary for a specific functionality. The modules are initialized and connected in the class's constructor. External connectors are exported as references to the corresponding module connectors: \skip class \until rateFilter First the needed modules are declared. We have - the \a barrier to discard incoming packets sent to fast - the \a queue to receive incoming packets and create throttling notifications - the \a generator to create the stuffing packets - the \a join to combine the input stream from the \a queue with the stuffing packet stream - the \a rateFilter to generate the fixed rate output stream \until output Here we declare the external connectors. The subnetwork exports a single input and output connector. The external connectors are declared as \e references. \until output The constructor now initializes all the local objects. We pass the template \a packet to the \a generator and set the timing \a interval of the \a rateFilter. The \a input and \a output connector references are bound to the corresponding connectors we want to expose: \a input to the \a barrier's \a input and \a output to the \a rateFilter's \a output. \until }; The constructor body sets up the connections within the subnetwork. Finally, we set the queueing discipline of the \a queue. This Completes the RateStuffer. This subnetwork can now be used like a module. \subsection main Application setup 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 the senf::ConnectedUDPv4SocketProtocol which is compatible with the senf::ppi::module::PassiveSocketSink module. \until udpSink Here we allocate the components: - \a udpSource to read the packets from \a inputSocket - \a stuffer for the real work and - \a udpSink to send the packets to \a outputSocket \until udpSink The \ref senf::ppi::connect() calls setup the necessary connections. 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: