2 // Fraunhofer Institut fuer offene Kommunikationssysteme (FOKUS)
3 // Kompetenzzentrum fuer Satelitenkommunikation (SatCom)
4 // Stefan Bund <g0dil@berlios.de>
6 // This program is free software; you can redistribute it and/or modify
7 // it under the terms of the GNU General Public License as published by
8 // the Free Software Foundation; either version 2 of the License, or
9 // (at your option) any later version.
11 // This program is distributed in the hope that it will be useful,
12 // but WITHOUT ANY WARRANTY; without even the implied warranty of
13 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 // GNU General Public License for more details.
16 // You should have received a copy of the GNU General Public License
17 // along with this program; if not, write to the
18 // Free Software Foundation, Inc.,
19 // 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
21 /** \mainpage libPPI : The Packet Processing Infrastructure
23 The PPI provides an infrastructure to create packet oriented network processing applications. A
24 PPI application is built by combining processing modules in a very flexible manner.
26 \image html scenario.png Target Scenario
28 The PPI concept is built around some key concepts
30 \li The PPI is based on processing \ref packets. It does not handle stream oriented channels.
31 \li The PPI is built around reusable \ref modules. Each module is completely independent.
32 \li Each module has an arbitrary number of \ref connectors, inputs and outputs.
33 \li The modules are connected to each other using flexible \ref connections.
34 \li Data flow throughout the network is governed via flexible automatic or manual \ref
36 \li Modules may register additional external \ref events (file descriptor events or timers).
38 The PPI thereby builds on the facilities provided by the other components of the SENF
39 framework. The target scenario above depicts a diffserv capable UDLR/ULE router including
40 performance optimizations for TCP traffic (PEP). This router is built by combining several
44 <a href="../../../Examples/RateStuffer/doc/html/index.html">PPI Example Application:
46 \ref senf::ppi::module "Modules" \n
47 \ref senf::ppi::connector "Connectors" \n
51 /** \page overview PPI Overview and Concepts
53 \section design Design considerations
55 The PPI interface is designed to be as simple as possible. It provides sane defaults for all
56 configurable parameters to simplify getting started. It also automates all resource
57 management. The throttling infrastructure handles blocking conditions (like input exhaustion)
60 \section packets Packets
62 The PPI processes packets and uses the <a href="@TOPDIR@/Packets/doc/html/index.html">Packet
63 library</a> to handle them. All packets are passed around as generic Packet::ptr's, the PPI
64 does not enforce any packet type restrictions.
66 \section modules Modules
68 A module is represented by a class type. Each module has several components:
70 \li It may have any number of connectors (inputs and outputs)
71 \li Each module declares flow information which details the route packets take within the
72 module. This information does not define how the information is processed, it only tells,
73 where data arriving on some input will be directed at.
74 \li The module might take additional parameters.
75 \li The module might also register additional events.
77 Modules are divided roughly in to two categories: I/O modules provide packet sources and sinks
78 (network connection, writing packets to disk, generating new packets) whereas processing modules
79 process packets internally. In the target scenario, <em>TAP</em>, <em>ASI Out</em>, <em>Raw
80 Socket</em> and in a limited way <em>Generator</em> are I/O modules whereas <em>PEP</em>,
81 <em>DiffServ</em>, <em>DVB Enc</em>, <em>GRE/UDLR</em>, <em>TCP Filter</em> and <em>Stuffer</em>
82 are processing modules. <em>ASI/MPEG</em> and <em>Net</em> are external I/O ports which are
83 integrated via the <em>TAP</em>, <em>ASI Out</em> and <em>Raw Sock</em> modules using external
86 The following example module declares three I/O connectors (see below): <tt>payload</tt>,
87 <tt>stuffing</tt> and <tt>output</tt>. These connectors are defined as <em>public</em> data
88 members so they can be accessed from the outside. This is important as we will see below.
92 : public senf::ppi::module::Module
94 senf::ppi::IntervalTimer timer_;
97 senf::ppi::connector::ActiveInput payload;
98 senf::ppi::connector::ActiveInput stuffing;
99 senf::ppi::connector::ActiveOutput output;
101 RateStuffer(unsigned packetsPerSecond)
102 : timer_(1000u, packetsPerSecond)
104 route(payload, output);
105 route(stuffing, output);
107 registerEvent(&RateStuffer::tick, timer_);
121 On module instantiation, it will declare it's flow information with <tt>route</tt> (which is
122 inherited from <tt>senf::ppi::module::Module</tt>). Then the module registers an interval timer
123 which will fire <tt>packetsPerSecond</tt> times every <tt>1000</tt> milliseconds.
125 The processing of the module is very simple: Whenever a timer tick arrives a packet is sent. If
126 the <tt>payload</tt> input is ready (see throttling below), a payload packet is sent, otherwise
127 a stuffing packet is sent. The module will therefore provide a constant stream of packets at a
128 fixed rate on <tt>output</tt>
130 An example module to generate the stuffing packets could be
133 class CopyPacketGenerator
134 : public senf::ppi::module::Module
137 senf::ppi::connector::PassiveOutput output;
139 CopyPacketGenerator(Packet::ptr template)
140 : template_ (template)
143 output.onRequest(&CopyPacketGenerator::makePacket);
147 Packet::ptr template_;
151 output(template_.clone());
156 This module just produces a copy of a given packet whenever output is requested.
158 \section connectors Connectors
160 Inputs and Outputs can be active and passive. An \e active I/O is <em>activated by the
161 module</em> to send data or to poll for available packets. A \e passive I/O is <em>signaled by
162 the framework</em> to fetch data from the module or to pass data into the module.
164 To send or receive a packet (either actively or after packet reception has been signaled), the
165 module just calls the connector. This allows to generate or process multiple packets in one
166 iteration. However, reading will only succeed, as long as packets are available from the
169 Since a module is free to generate more than a single packet on incoming packet requests, all
170 input connectors incorporate a packet queue. This queue is exposed to the module and allows the
171 module to process packets in batches.
173 \section connections Connections
175 \image html ratestuffer.png Simple RateStuffer
177 To make use of the modules, they have to be instantiated and connections have to be created
178 between the I/O connectors. It is possible to connect any pair of input/output connectors as
179 long as one of them is active and the other is passive.
181 It is possible to connect two active connectors with each other using a special adaptor
182 module. This Module has a passive input and a passive output. It will queue any incoming packets
183 and automatically handle throttling events (see below). This adaptor is automatically added by
184 the connect method if needed.
186 To complete our simplified example: Lets say we have an <tt>ActiveSocketInput</tt> and a
187 <tt>PassiveUdpOutput</tt> module. We can then use our <tt>RateStuffer</tt> module to build an
188 application which will create a fixed-rate UDP stream:
191 RateStuffer rateStuffer (10);
193 senf::Packet::ptr stuffingPacket = senf::Packet::create<...>(...);
194 CopyPacketGenerator generator (stuffingPacket);
196 senf::UDPv4ClientSocketHandle inputSocket (1111);
197 senf::ppi::module::ActiveSocketReader udpInput (inputSocket);
199 senf::UDPv4ClientSocketHandle outputSocket ("2.3.4.5:2222");
200 senf::ppi::module::PassiveSocketWriter udpOutput (outputSocket);
202 senf::ppi::module::PassiveQueue adaptor;
204 senf::ppi::connect(udpInput.output, adaptor.input);
205 senf::ppi::connect(adaptor.output, rateStuffer.payload);
206 adaptor.qdisc(ThresholdQueueing(10,5));
207 senf::ppi::connect(generator.output, rateStuffer.stuffing);
208 senf::ppi::connect(rateStuffer.output, udpOutput.input);
213 First all necessary modules are created. Then the connections between these modules are set
214 up. The buffering on the udpInput <-> rateStuffer adaptor is changed so the queue will begin to
215 throttle only if more than 10 packets are in the queue. The connection will be unthrottled as
216 soon as there are no more than 5 packets left in the queue. This application will read
217 udp-packets coming in on port 1111 and will forward them to port 2222 on host 2.3.4.5 with a
218 fixed rate of 10 packets / second.
220 \section throttling Throttling
222 If a passive connector cannot handle incoming requests, this connector may be \e
223 throttled. Throttling a request will forward a throttle notification to the module connected
224 to that connector. The module then must handle this throttle notification. If automatic
225 throttling is enabled for the module (which is the default), the notification will automatically
226 be forwarded to all dependent connectors as taken from the flow information. For there it will
227 be forwarded to further modules and so on.
229 A throttle notification reaching an I/O module will normally disable the input/output by
230 disabling any external I/O events registered by the module. When the passive connector which
231 originated the notification becomes active again, it creates an unthrottle notification which
232 will be forwarded in the same way. This notification will re-enable any registered I/O events.
234 The above discussion shows, that throttle events are always generated on passive connectors and
235 received on active connectors. To differentiate further, the throttling originating from a
236 passive input is called <em>backward throttling</em> since it is forwarded in the direction \e
237 opposite to the data flow. Backward throttling notifications are sent towards the input
238 modules. On the other hand, the throttling originating from a passive output is called
239 <em>forward throttling</em> since it is forwarded along the \e same direction the data
240 is. Forward throttling notifications are therefore sent towards the output modules.
242 Since throttling a passive input may not disable all further packet delivery immediately, all
243 inputs contains an input queue. In it's default configuration, the queue will send out throttle
244 notifications when it becomes non-empty and unthrottle notifications when it becomes empty
245 again. This automatic behavior may however be disabled. This allows a module to collect incoming
246 packets in it's input queue before processing a bunch of them in one go.
248 \section events Events
250 Modules may register additional events. These external events are very important since they
251 drive the PPI framework. Possible event sources are
252 \li time based events
253 \li file descriptors.
254 \li internal events (e.g. IdleEvent)
256 Here some example code implementing the ActiveSocketInput Module:
259 class ActiveSocketReader
260 : public senf::ppi::module::Module
262 typedef senf::ClientSocketHandle<
263 senf::MakeSocketPolicy< senf::ReadablePolicy,
264 senf::DatagramFramingPolicy > > SocketHandle;
265 SocketHandle socket_;
266 DataParser const & parser_;
267 senf::ppi:IOSignaler event_;
269 static PacketParser<senf::DataPacket> defaultParser_;
272 senf::ppi::connector::ActiveOutput output;
274 // I hestitate taking parser by const & since a const & can be bound to
275 // a temporary even though a const & is all we need. The real implementation
276 // will probably make this a template arg. This simplifies the memory management
277 // from the users pov.
278 ActiveSocketReader(SocketHandle socket,
279 DataParser & parser = ActiveSocketReader::defaultParser_)
282 event_ (socket, senf::ppi::IOSignaler::Read)
284 registerEvent( &ActiveSocketReader::data, event_ );
285 route(event_, output);
294 output(parser_(data));
299 First we declare our own socket handle type which allows us to read packets. The constructor
300 then takes two arguments: A compatible socket and a parser object. This parser object gets
301 passed the packet data as read from the socket (an \c std::string) and returns a
302 senf::Packet::ptr. The \c PacketParser is a simple parser which interprets the data as specified
303 by the template argument.
305 We register an IOSignaler event. This event will be signaled whenever the socket is
306 readable. This event is routed to the output. This routing automates throttling for the socket:
307 Whenever the output receives a throttle notifications, the event will be temporarily disabled.
309 Processing arriving packets happens in the \c data() member: This member simple reads a packet
310 from the socket. It passes this packet to the \c parser_ and sends the generated packet out.
312 \section flows Information Flow
314 The above description conceptually introduces three different flow levels:
316 \li The <em>data flow</em> is, where the packets are flowing. This flow always goes from output
318 \li The <em>execution flow</em> describes the flow of execution from one module to another. This
319 flow always proceeds from active to passive connector.
320 \li The <em>control flow</em> is the flow of throttling notifications. This flow always proceeds
321 \e opposite to the execution flow, from passive to active connector.
323 This is the outside view, from without any module. These flows are set up using
324 senf::ppi::connect() statements.
326 Within a module, the different flow levels are defined differently depending on the type of
329 \li The <em>data flow</em> is defined by how data is processed. The different event and
330 connector callbacks will pass packets around and thereby define the data flow
331 \li Likewise, the <em>execution flow</em> is defined parallel to the data flow (however possible
332 in opposite direction) by how the handler of one connector calls other connectors.
333 \li The <em>control flow</em> is set up using senf::ppi::Module::route statements (as long as
334 automatic throttling is used. Manual throttling defines the control flow within the
335 respective callbacks).
337 In nearly all cases, these flows will be parallel. Therefore it makes sense to define the \c
338 route statement as defining the 'conceptual data flow' since this is also how control messages
339 should flow (sans the direction, which is defined by the connectors active/passive property).
341 \see \ref ppi_implementation
344 /** \page ppi_implementation Implementation Notes
346 \section processing Data Processing
348 The processing in the PPI is driven by events. Without events <em>nothing will happen</em>. When
349 an event is generated, the called module will probably call one of it's active connectors.
351 Calling an active connector will directly call the handler registered at the connected passive
352 connector. This way the call and data are handed across the connections until an I/O module will
353 finally handle the request (by not calling any other connectors).
355 Throttling is handled in the same way: Throttling a passive connector will call a corresponding
356 (internal) method of the connected active connector. This method will call registered handlers
357 and will analyze the routing information of the module for other (passive) connectors to call
358 and throttle. This will again create a call chain which terminates at the I/O modules. An event
359 which is called to be throttled will disable the event temporarily. Unthrottling works in the
362 This simple structure is complicated by the existence of the input queues. This affects both
363 data forwarding and throttling:
364 \li A data request will only be forwarded, if no data is available in the queue
365 \li The connection will only be throttled when the queue is empty
366 \li Handlers of passive input connectors must be called repeatedly until either the queue is
367 empty or the handler does not take any packets from the queue
370 \section logistics Managing the Data Structures
372 The PPI itself is a singleton. This simplifies many of the interfaces (We do not need to pass
373 the PPI instance). Should it be necessary to have several PPI systems working in parallel
374 (either by registering all events with the same event handler or by utilizing multiple threads),
375 we can still extend the API by adding an optional PPI instance argument.
377 Every module manages a collection of all it's connectors and every connector has a reference to
378 it's containing module. In addition, every connector maintains a collection of all it's routing
381 All this data is initialized via the routing statements. This is, why \e every connector must
382 appear in at least one routing statement: These statements will as a side effect initialize the
383 connector with it's containing module.
385 Since all access to the PPI via the module is via it's base class, unbound member function
386 pointers can be provided as handler arguments: They will automatically be bound to the current
387 instance. This simplifies the PPI usage considerably. The same is true for the connectors: Since
388 they know the containing module, they can explicitly bind unbound member function pointers to
392 \section random_notes Random implementation notes
394 Generation of throttle notifications: Backward throttling notifications are automatically
395 generated (if this is not disabled) whenever the input queue is non-empty \e after the event
396 handler has finished processing. Forward throttling notifications are not generated
397 automatically within the connector. However, the Passive-Passive adaptor will generate
398 Forward-throttling notifications whenever the input queue is empty.
400 \section class_diagram Class Diagram
402 \image html classes.png
409 // c-file-style: "senf"
410 // indent-tabs-mode: nil
411 // ispell-local-dictionary: "american"