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. Especially to simplify resource management, the PPI will take many configuration
58 objects by value. Even though this is not as efficient, it frees the user from most resource
59 management chores. This decision does not affect the runtime performance since it only affects
60 the configuration step.
62 \section packets Packets
64 The PPI processes packets and uses the <a href="@TOPDIR@/Packets/doc/html/index.html">Packet
65 library</a> to handle them. All packets are passed around as generic Packet::ptr's, the PPI
66 does not enforce any packet type restrictions.
68 \section modules Modules
70 A module is represented by a class type. Each module has several components:
72 \li It may have any number of connectors (inputs and outputs)
73 \li Each module declares flow information which details the route packets take within the
74 module. This information does not define how the information is processed, it only tells,
75 where data arriving on some input will be directed at.
76 \li The module might take additional parameters.
77 \li The module might also register additional events.
79 Modules are divided roughly in to two categories: I/O modules provide packet sources and sinks
80 (network connection, writing packets to disk, generating new packets) whereas processing modules
81 process packets internally. In the target scenario, <em>TAP</em>, <em>ASI Out</em>, <em>Raw
82 Socket</em> and in a limited way <em>Generator</em> are I/O modules whereas <em>PEP</em>,
83 <em>DiffServ</em>, <em>DVB Enc</em>, <em>GRE/UDLR</em>, <em>TCP Filter</em> and <em>Stuffer</em>
84 are processing modules. <em>ASI/MPEG</em> and <em>Net</em> are external I/O ports which are
85 integrated via the <em>TAP</em>, <em>ASI Out</em> and <em>Raw Sock</em> modules using external
88 The following example module declares three I/O connectors (see below): <tt>payload</tt>,
89 <tt>stuffing</tt> and <tt>output</tt>. These connectors are defined as <em>public</em> data
90 members so they can be accessed from the outside. This is important as we will see below.
94 : public senf::ppi::module::Module
96 senf::ppi::IntervalTimer timer_;
99 senf::ppi::connector::ActiveInput payload;
100 senf::ppi::connector::ActiveInput stuffing;
101 senf::ppi::connector::ActiveOutput output;
103 RateStuffer(unsigned packetsPerSecond)
104 : timer_(1000u, packetsPerSecond)
106 route(payload, output);
107 route(stuffing, output);
109 registerEvent(&RateStuffer::tick, timer_);
123 On module instantiation, it will declare it's flow information with <tt>route</tt> (which is
124 inherited from <tt>senf::ppi::module::Module</tt>). Then the module registers an interval timer
125 which will fire <tt>packetsPerSecond</tt> times every <tt>1000</tt> milliseconds.
127 The processing of the module is very simple: Whenever a timer tick arrives a packet is sent. If
128 the <tt>payload</tt> input is ready (see throttling below), a payload packet is sent, otherwise
129 a stuffing packet is sent. The module will therefore provide a constant stream of packets at a
130 fixed rate on <tt>output</tt>
132 An example module to generate the stuffing packets could be
135 class CopyPacketGenerator
136 : public senf::ppi::module::Module
139 senf::ppi::connector::PassiveOutput output;
141 CopyPacketGenerator(Packet::ptr template)
142 : template_ (template)
145 output.onRequest(&CopyPacketGenerator::makePacket);
149 Packet::ptr template_;
153 output(template_.clone());
158 This module just produces a copy of a given packet whenever output is requested.
160 \section connectors Connectors
162 Inputs and Outputs can be active and passive. An \e active I/O is <em>activated by the
163 module</em> to send data or to poll for available packets. A \e passive I/O is <em>signaled by
164 the framework</em> to fetch data from the module or to pass data into the module.
166 To send or receive a packet (either actively or after packet reception has been signaled), the
167 module just calls the connector. This allows to generate or process multiple packets in one
168 iteration. However, reading will only succeed, as long as packets are available from the
171 Since a module is free to generate more than a single packet on incoming packet requests, all
172 input connectors incorporate a packet queue. This queue is exposed to the module and allows the
173 module to process packets in batches.
175 \section connections Connections
177 \image html ratestuffer.png Simple RateStuffer
179 To make use of the modules, they have to be instantiated and connections have to be created
180 between the I/O connectors. It is possible to connect any pair of input/output connectors as
181 long as one of them is active and the other is passive.
183 It is possible to connect two active connectors with each other using a special adaptor
184 module. This Module has a passive input and a passive output. It will queue any incoming packets
185 and automatically handle throttling events (see below). This adaptor is automatically added by
186 the connect method if needed.
188 To complete our simplified example: Lets say we have an <tt>ActiveSocketInput</tt> and a
189 <tt>PassiveUdpOutput</tt> module. We can then use our <tt>RateStuffer</tt> module to build an
190 application which will create a fixed-rate UDP stream:
193 RateStuffer rateStuffer (10);
195 senf::Packet::ptr stuffingPacket = senf::Packet::create<...>(...);
196 CopyPacketGenerator generator (stuffingPacket);
198 senf::UDPv4ClientSocketHandle inputSocket (1111);
199 senf::ppi::module::ActiveSocketReader udpInput (inputSocket);
201 senf::UDPv4ClientSocketHandle outputSocket ("2.3.4.5:2222");
202 senf::ppi::module::PassiveSocketWriter udpOutput (outputSocket);
204 senf::ppi::module::PassiveQueue adaptor;
206 senf::ppi::connect(udpInput.output, adaptor.input);
207 senf::ppi::connect(adaptor.output, rateStuffer.payload);
208 adaptor.qdisc(ThresholdQueueing(10,5));
209 senf::ppi::connect(generator.output, rateStuffer.stuffing);
210 senf::ppi::connect(rateStuffer.output, udpOutput.input);
215 First all necessary modules are created. Then the connections between these modules are set
216 up. The buffering on the udpInput <-> rateStuffer adaptor is changed so the queue will begin to
217 throttle only if more than 10 packets are in the queue. The connection will be unthrottled as
218 soon as there are no more than 5 packets left in the queue. This application will read
219 udp-packets coming in on port 1111 and will forward them to port 2222 on host 2.3.4.5 with a
220 fixed rate of 10 packets / second.
222 \section throttling Throttling
224 If a passive connector cannot handle incoming requests, this connector may be \e
225 throttled. Throttling a request will forward a throttle notification to the module connected
226 to that connector. The module then must handle this throttle notification. If automatic
227 throttling is enabled for the module (which is the default), the notification will automatically
228 be forwarded to all dependent connectors as taken from the flow information. For there it will
229 be forwarded to further modules and so on.
231 A throttle notification reaching an I/O module will normally disable the input/output by
232 disabling any external I/O events registered by the module. When the passive connector which
233 originated the notification becomes active again, it creates an unthrottle notification which
234 will be forwarded in the same way. This notification will re-enable any registered I/O events.
236 The above discussion shows, that throttle events are always generated on passive connectors and
237 received on active connectors. To differentiate further, the throttling originating from a
238 passive input is called <em>backward throttling</em> since it is forwarded in the direction \e
239 opposite to the data flow. Backward throttling notifications are sent towards the input
240 modules. On the other hand, the throttling originating from a passive output is called
241 <em>forward throttling</em> since it is forwarded along the \e same direction the data
242 is. Forward throttling notifications are therefore sent towards the output modules.
244 Since throttling a passive input may not disable all further packet delivery immediately, all
245 inputs contains an input queue. In it's default configuration, the queue will send out throttle
246 notifications when it becomes non-empty and unthrottle notifications when it becomes empty
247 again. This automatic behavior may however be disabled. This allows a module to collect incoming
248 packets in it's input queue before processing a bunch of them in one go.
250 \section events Events
252 Modules may register additional events. These external events are very important since they
253 drive the PPI framework. Possible event sources are
254 \li time based events
255 \li file descriptors.
256 \li internal events (e.g. IdleEvent)
258 Here some example code implementing the ActiveSocketInput Module:
261 class ActiveSocketReader
262 : public senf::ppi::module::Module
264 typedef senf::ClientSocketHandle<
265 senf::MakeSocketPolicy< senf::ReadablePolicy,
266 senf::DatagramFramingPolicy > > SocketHandle;
267 SocketHandle socket_;
268 DataParser const & parser_;
269 senf::ppi:IOSignaler event_;
271 static PacketParser<senf::DataPacket> defaultParser_;
274 senf::ppi::connector::ActiveOutput output;
276 // I hestitate taking parser by const & since a const & can be bound to
277 // a temporary even though a const & is all we need. The real implementation
278 // will probably make this a template arg. This simplifies the memory management
279 // from the users pov.
280 ActiveSocketReader(SocketHandle socket,
281 DataParser & parser = ActiveSocketReader::defaultParser_)
284 event_ (socket, senf::ppi::IOSignaler::Read)
286 registerEvent( &ActiveSocketReader::data, event_ );
287 route(event_, output);
296 output(parser_(data));
301 First we declare our own socket handle type which allows us to read packets. The constructor
302 then takes two arguments: A compatible socket and a parser object. This parser object gets
303 passed the packet data as read from the socket (an \c std::string) and returns a
304 senf::Packet::ptr. The \c PacketParser is a simple parser which interprets the data as specified
305 by the template argument.
307 We register an IOSignaler event. This event will be signaled whenever the socket is
308 readable. This event is routed to the output. This routing automates throttling for the socket:
309 Whenever the output receives a throttle notifications, the event will be temporarily disabled.
311 Processing arriving packets happens in the \c data() member: This member simple reads a packet
312 from the socket. It passes this packet to the \c parser_ and sends the generated packet out.
314 \section flows Information Flow
316 The above description conceptually introduces three different flow levels:
318 \li The <em>data flow</em> is, where the packets are flowing. This flow always goes from output
320 \li The <em>execution flow</em> describes the flow of execution from one module to another. This
321 flow always proceeds from active to passive connector.
322 \li The <em>control flow</em> is the flow of throttling notifications. This flow always proceeds
323 \e opposite to the execution flow, from passive to active connector.
325 This is the outside view, from without any module. These flows are set up using
326 senf::ppi::connect() statements.
328 Within a module, the different flow levels are defined differently depending on the type of
331 \li The <em>data flow</em> is defined by how data is processed. The different event and
332 connector callbacks will pass packets around and thereby define the data flow
333 \li Likewise, the <em>execution flow</em> is defined parallel to the data flow (however possible
334 in opposite direction) by how the handler of one connector calls other connectors.
335 \li The <em>control flow</em> is set up using senf::ppi::Module::route statements (as long as
336 automatic throttling is used. Manual throttling defines the control flow within the
337 respective callbacks).
339 In nearly all cases, these flows will be parallel. Therefore it makes sense to define the \c
340 route statement as defining the 'conceptual data flow' since this is also how control messages
341 should flow (sans the direction, which is defined by the connectors active/passive property).
343 \see \ref ppi_implementation
346 /** \page ppi_implementation Implementation Notes
348 \section processing Data Processing
350 The processing in the PPI is driven by events. Without events <em>nothing will happen</em>. When
351 an event is generated, the called module will probably call one of it's active connectors.
353 Calling an active connector will directly call the handler registered at the connected passive
354 connector. This way the call and data are handed across the connections until an I/O module will
355 finally handle the request (by not calling any other connectors).
357 Throttling is handled in the same way: Throttling a passive connector will call a corresponding
358 (internal) method of the connected active connector. This method will call registered handlers
359 and will analyze the routing information of the module for other (passive) connectors to call
360 and throttle. This will again create a call chain which terminates at the I/O modules. An event
361 which is called to be throttled will disable the event temporarily. Unthrottling works in the
364 This simple structure is complicated by the existence of the input queues. This affects both
365 data forwarding and throttling:
366 \li A data request will only be forwarded, if no data is available in the queue
367 \li The connection will only be throttled when the queue is empty
368 \li Handlers of passive input connectors must be called repeatedly until either the queue is
369 empty or the handler does not take any packets from the queue
372 \section logistics Managing the Data Structures
374 The PPI itself is a singleton. This simplifies many of the interfaces (We do not need to pass
375 the PPI instance). Should it be necessary to have several PPI systems working in parallel
376 (either by registering all events with the same event handler or by utilizing multiple threads),
377 we can still extend the API by adding an optional PPI instance argument.
379 Every module manages a collection of all it's connectors and every connector has a reference to
380 it's containing module. In addition, every connector maintains a collection of all it's routing
383 All this data is initialized via the routing statements. This is, why \e every connector must
384 appear in at least one routing statement: These statements will as a side effect initialize the
385 connector with it's containing module.
387 Since all access to the PPI via the module is via it's base class, unbound member function
388 pointers can be provided as handler arguments: They will automatically be bound to the current
389 instance. This simplifies the PPI usage considerably. The same is true for the connectors: Since
390 they know the containing module, they can explicitly bind unbound member function pointers to
394 \section random_notes Random implementation notes
396 Generation of throttle notifications: Backward throttling notifications are automatically
397 generated (if this is not disabled) whenever the input queue is non-empty \e after the event
398 handler has finished processing. Forward throttling notifications are not generated
399 automatically within the connector. However, the Passive-Passive adaptor will generate
400 Forward-throttling notifications whenever the input queue is empty.
402 \section class_diagram Class Diagram
404 \image html classes.png
406 \fixme Implement Spliters: PassiveSplitter, PrioritySplitter, CloneSplitter
407 \fixme Implement DiscardSink, CloneSource
408 \fixme Implement ThrottleBarrier
415 // c-file-style: "senf"
416 // indent-tabs-mode: nil
417 // ispell-local-dictionary: "american"