4 // Fraunhofer Institute for Open Communication Systems (FOKUS)
6 // The contents of this file are subject to the Fraunhofer FOKUS Public License
7 // Version 1.0 (the "License"); you may not use this file except in compliance
8 // with the License. You may obtain a copy of the License at
9 // http://senf.berlios.de/license.html
11 // The Fraunhofer FOKUS Public License Version 1.0 is based on,
12 // but modifies the Mozilla Public License Version 1.1.
13 // See the full license text for the amendments.
15 // Software distributed under the License is distributed on an "AS IS" basis,
16 // WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
17 // for the specific language governing rights and limitations under the License.
19 // The Original Code is Fraunhofer FOKUS code.
21 // The Initial Developer of the Original Code is Fraunhofer-Gesellschaft e.V.
22 // (registered association), Hansastraße 27 c, 80686 Munich, Germany.
25 // Stefan Bund <g0dil@berlios.de>
28 using namespace senf::ppi::module;
30 /** \mainpage Example introducing the Packet Processing Infrastructure
32 This example application implements a simple PPI application: It will read UDP packets from an
33 input port and will forward them to another port at a fixed packet rate. If the input stream
34 does not provide enough packets, empty UDP packets will be sent instead.
36 \section run Running the example
38 Running the example is a little bit more complicated since we need to provide example UDP
39 packets so we can see the application at work. We do this using \c netcat. We open several shell
40 windows and run the following commands, each in it's own window
42 The first command listens for incoming UDP packets on port 44345:
47 The next command starts the \c ratestuffer
49 # cd .../Examples/RateStuffer
54 We should now see '<idle>' messages arriving in the first window once per second. We now can
55 start another \c netcat to send packets to the input port.
58 # nc -u localhost 44344
59 < type any text here >
62 Whenever we send out a packet with CR in the last window we should see it appear in the first
63 one. If we send out packets faster than 1 packet per second, they will start to be discarded if
64 more than two packets are in flight.
66 \image html screenshot.png
68 \section setup Module setup
70 \diaimage ratestuffer.dia
72 Above image depicts the module setup implementing the rate stuffer. A
73 senf::ppi::module::ActiveSocketSource reads the incoming UDP packets and sends them into a
74 senf::ppi::module::PassiveQueue (via a senf::ppi::module::ThrottleBarrier).
76 The \a queue feeds the packets into a senf::ppi::module::PriorityJoin. The CloneSource
77 \a generator is fed as second input into the \a join to provide the stuffing packets.
79 The RateFilter \a rateFilter reads packets from it's input at a fixed rate and writes them into
80 the senf::ppi::module::PassiveSocketSink \a udpSink. The senf::ppi::module::PriorityJoin
81 ensures that read requests of the RateStuffer's input are always serviced, either from the \a
82 queue or, if the \a queue output is throttled, from the \a generator.
84 The \a barrier is not strictly necessary. However, it makes the behavior of the RateStuffer
85 predictable in the case where packets need to be dropped. Without the
86 senf::ppi::module::ThrottleBarrier, the packets will be left in the kernel socket queue. Packets
87 will only start to be dropped when that queue fills up. The size of this queue cannot be easily
88 manipulated and it's initial size is immense. So to stop the kernel queue from filling up with
89 increasingly out-of-date packets, we add the \a barrier which will explicitly read and drop
92 \section code Example code
94 \dontinclude ratestuffer.cc
96 The code starts out including the necessary header files
102 We also define some namespace aliases
107 The RateStuffer application is based on one additional application module.
109 \subsection ratefilter The RateFilter module
111 The RateFilter module simply forwards packets at a fixed rate.
116 Both connectors of the RateFilter module are active. The module is driven by a
117 senf::ppi::IntervalTimer.
121 The event is initialized to fire every \a interval nanoseconds. The traffic is routed 'across'
122 the timer which controls the traffic. This routing lets the module automatically handle
123 throttling events. The timer is registered to call RateFilter::timeout().
127 The event handler is quite simple: Every \a interval nanoseconds a packet is read from \a input
128 and forwarded to \a output.
130 This is all there is to the RateFilter module. Due to the routing setup, the timer will
131 automatically be disabled should either \a input or \a output become throttled. However, in this
132 specific case this should never happen: The \a input is connected (via the \a join) to the
133 senf::ppi::module::CloneSource, which will never throttle. The \a output is connected to a UDP
134 socket which also never throttles.
136 \subsection ratestuffer The RateStuffer subnet
138 We decide to implement the RateStuffer as a subnet or collection. This is a simple struct or
139 class which contains all the modules necessary for a specific functionality. The modules are
140 initialized and connected in the class's constructor. External connectors are exported as
141 references to the corresponding module connectors:
146 First the needed modules are declared. We have
147 - the \a barrier to discard incoming packets sent to fast
148 - the \a queue to receive incoming packets and create throttling notifications
149 - the \a generator to create the stuffing packets
150 - the \a join to combine the input stream from the \a queue with the stuffing packet stream
151 - the \a rateFilter to generate the fixed rate output stream
155 Here we declare the external connectors. The subnetwork exports a single input and output
156 connector. The external connectors are declared as \e references.
160 The constructor now initializes all the local objects. We pass the template \a packet to the \a
161 generator and set the timing \a interval of the \a rateFilter.
163 The \a input and \a output connector references are bound to the corresponding connectors we
164 want to expose: \a input to the \a barrier's \a input and \a output to the \a rateFilter's \a
169 The constructor body sets up the connections within the subnetwork. Finally, we set the queueing
170 discipline of the \a queue. This Completes the RateStuffer. This subnetwork can now be used like
173 \subsection main Application setup
175 The applications main() method starts out by initializing the socket handles
180 The \a inputSocket is listening on port 44344 while the \a outputSocket will send packets to
181 port 44345 on localhost. The \a outputSocket uses the senf::ConnectedUDPv4SocketProtocol which
182 is compatible with the senf::ppi::module::PassiveSocketSink module.
186 Here we allocate the components:
188 - \a udpSource to read the packets from \a inputSocket
189 - \a stuffer for the real work and
190 - \a udpSink to send the packets to \a outputSocket
194 The \ref senf::ppi::connect() calls setup the necessary connections.
196 The module setup is complete, \ref senf::ppi::run() is called to enter the event loop.
205 // comment-column: 40
206 // c-file-style: "senf"
207 // indent-tabs-mode: nil
208 // ispell-local-dictionary: "american"
209 // compile-command: "scons -u doc"