presentation.tex

   1 \documentclass{beamer}
   2 \usepackage[utf8]{inputenc}
   3 \usepackage[english]{babel}
   4 \usepackage{todonotes}
   5 \usepackage{inconsolata}
   6 %\usepackage{multicol}
   7 \usepackage{array}
   8 \usepackage{cclicenses}
   9 \usepackage{tikz}
  10 \usetikzlibrary{arrows}
  11 \usetikzlibrary{arrows}
  12 \usetikzlibrary{positioning}
  13 \usetikzlibrary{shapes.symbols}
  14 %\usepackage[usenames,dvipsnames]{color}
  15
  16 %\presetkeys{todonotes}{inline}{}
  17 \newcommand{\code}[1]{\texttt{#1}}
  18 \definecolor{green}{RGB}{137,164,0}  % from tubslatex
  19
  20 \title{Chatty Things}
  21 \subtitle{Making the Internet of Things Readily Usable for the Masses with XMPP}
  22 \author{Roland Hieber}
  23 \institute[IBR, TU BS]{Institute of Operating Systems and Computer Networks, TU
  24         Braunschweig}
  25 \date[SKM-13/14]{Seminar Communications and Multimedia, WS 2013/14}
  26
  27 \begin{document}
  28
  29 \begin{frame}[plain]
  30 \maketitle
  31 \end{frame}
  32
  33 \begin{frame}{Contents}
  34 \tableofcontents
  35 \end{frame}
  36
  37 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
  38 \section{Motivation}
  39 \begin{frame}{Motivation}
  40 \begin{block}{The IoT Vision}
  41         \begin{itemize}
  42                 \item plentitude of smart objects
  43                 \item interoperability between devices
  44                 \item easy accessibility for users
  45         \end{itemize}
  46 \end{block}
  47 \end{frame}
  48
  49 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
  50 \begin{frame}<1>[label=subgoals]{Motivation: Subgoals}
  51         \begin{block}{But how do we\ldots}
  52                 \begin{itemize}
  53                         \item configure our devices?
  54                                 \begin{itemize}
  55                                         \invisible<1-1>{\item[\color{green}\checkmark]\color{green}
  56                                                 Link-Local Addressing, Stateless Address Autoconfiguration}
  57                                 \end{itemize}
  58                         \item find other nodes to talk to?
  59                                 \begin{itemize}
  60                                         \invisible<1-2>{\item[\color{green}\checkmark]\color{green}
  61                                                 DNS-SD + mDNS}
  62                                 \end{itemize}
  63                         \item talk to other nodes or users?
  64                                 \begin{itemize}
  65                                         \invisible<1-3>{\item[\color{green}\checkmark]\color{green} XMPP
  66                                                 Serverless Messaging}
  67                                 \end{itemize}
  68                         \item filter relevant information?
  69                                 \begin{itemize}
  70                                         \invisible<1-4>{\item[\color{green}\checkmark]\color{green} ``Traffic
  71                                                 Lights'', Temporary Subscription for Presence}
  72                                 \end{itemize}
  73                 \end{itemize}
  74         \end{block}
  75 \end{frame}
  76
  77 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
  78 \section{Technologies for Distributed Networking}
  79 \begin{frame}{Address Allocation}
  80 IPv4 Link-Local Addessing (``APIPA'', ``Zeroconf'', RFC 3927)
  81 \begin{itemize}
  82         \item subnet \code{169.254.0.0/16}
  83 \end{itemize}
  84 IPv6 Stateless Address Autoconfiguration (RFC 4862)
  85 \begin{itemize}
  86         \item subnet \code{fe80::/64} (link-local)
  87         \item subnet \code{fc00::/11} (unique-local, if configured)
  88         \item or global address (if configured)
  89 \end{itemize}
  90
  91 \begin{block}{Algorithm}
  92 \begin{enumerate}
  93         \item choose (random) IP address in subnet
  94         \item ask if anyone uses that address
  95         \item if not, we're fine
  96         \item else, retry
  97 \end{enumerate}
  98 \end{block}
  99 \end{frame}
 100
 101 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 102 \againframe<2>{subgoals}
 103
 104 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 105 \begin{frame}{Multicast DNS (RFC 6762)}
 106 \begin{itemize}
 107 \item distributed DNS database
 108 \item uses multicast address \code{224.0.0.251} (IPv4) and \code{ff02::fb}
 109         (IPv6), UDP port 5353
 110 \item standard DNS packet format
 111 \item hosts announce their own resources
 112 \item hosts respond to queries if queried resource is known
 113 \end{itemize}
 114 \end{frame}
 115
 116 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 117 \begin{frame}{DNS-Based Service Discovery (RFC 6763)}
 118 Two-step process:
 119 \begin{enumerate}
 120         \item Service Instance Enumeration
 121         \begin{itemize}
 122                 \item query PTR records of form \code{\_service.\_proto.domain}
 123                 \item results: instance names of form \code{name.\_service.\_proto.domain}
 124         \end{itemize}
 125         \item Service Instance Resolution
 126         \begin{itemize}
 127                 \item query instance names as SRV records
 128                 \item result gives host name, port, priority, weight
 129         \end{itemize}
 130 \end{enumerate}
 131 \end{frame}
 132
 133 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 134 \begin{frame}[fragile]{Example: mDNS + DNS-SD}
 135 \tikzset{font=\fontsize{7.5pt}{1em}\selectfont, >=latex, thick, y=3.5em}
 136 %\tikzstyle{iconlabel}=[text width=2cm, align=center,
 137         %font=\fontsize{7.5pt}{1em}\selectfont]
 138 \tikzstyle{label}=[font=\fontsize{7pt}{1em}\selectfont]
 139 \tikzstyle{pkt}=[font=\fontsize{6pt}{0.7em}\selectfont,
 140         draw,fill=white,dash pattern=on 2pt off 2pt, align=center,
 141         inner sep=2pt]
 142 \def\xhalf{.45\textwidth}
 143 \def\nodeskip{2.2em}
 144 \begin{enumerate}
 145         \item Service Instance Enumeration
 146         \begin{tikzpicture}
 147                 \node[cloud,draw,fill=gray!20,aspect=2] (thecloud) at (0,0) {multicast};
 148                 \def\nodelist{
 149                         node/{(-\xhalf,0)}/{},
 150                         juliet/{(\xhalf,0)}/juliet,
 151                         romeo/{(\xhalf,-1)}/romeo,
 152                         mercutio/{(\xhalf,1)}/mercutio%
 153                 }
 154                 \foreach \name/\pos/\text in \nodelist {
 155                         \node (\name) at \pos { \includegraphics[width=3em]{icon-computer.pdf} };
 156                         \node[below=\nodeskip of \name.north,label] (\name text) { \text };
 157                 }
 158                 \draw[->] (node) -- (thecloud) node[pkt,pos=0.5]{
 159                         \verb+_presence._tcp.local+\\PTR? };
 160                 \draw[->] (juliet) -- (thecloud) node[pkt,pos=0.4]{
 161                         \verb+juliet._presence.+\\\verb+_tcp.local+ };
 162                 \draw[->] (romeo) -- (thecloud) node[pkt,pos=0.4]{
 163                         \verb+romeo._presence.+\\\verb+_tcp.local+ };
 164                 \draw[->] (mercutio) -- (thecloud) node[pkt,pos=0.4]{
 165                         \verb+mercutio._presence.+\\\verb+_tcp.local+ };
 166         \end{tikzpicture}
 167
 168         \item Service Instance Resolution
 169         \begin{tikzpicture}
 170                 \node[cloud,draw,fill=gray!20,aspect=2] (thecloud) at (0,0) {multicast};
 171                 \node (node) at (-\xhalf,0) { \includegraphics[width=3em]{icon-computer.pdf} };
 172                 \node (juliet) at (\xhalf,0) { \includegraphics[width=3em]{icon-computer.pdf} };
 173                 \node[below=\nodeskip of juliet.north,label] (juliet text) { juliet };
 174                 \draw[->] (node) -- (thecloud) node[pkt,pos=0.5]{
 175                         \verb+juliet._presence._tcp.local+\\SRV? };
 176                 \draw[->] (juliet) -- (thecloud) node[pkt,pos=0.5]{
 177                         \verb+juliet.local, port 5222,+\\\verb+prio 0, weight 0+ };
 178         \end{tikzpicture}
 179 \end{enumerate}
 180 \end{frame}
 181
 182 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 183 \againframe<3>{subgoals}
 184
 185 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 186 \begin{frame}{XMPP (RFC 6122)}
 187 \begin{columns}[c]
 188         \column{.55\textwidth}
 189         \begin{onlyenv}<1>
 190                 \begin{block}{Extensible Messaging and Presence Protocol}
 191                 \begin{itemize}
 192                         \item XML-based
 193                         \item Federated architecture
 194                         \begin{itemize}
 195                                 \item modeled after E-Mail
 196                         \end{itemize}
 197                         \item publish-subscribe mechanism
 198                         \item XMPP Extension Protocols (XEPs), e.\,g.
 199                         \begin{itemize}
 200                                 \item Multi-User Chats % (XEP-0045)
 201                                 \item Serverless Messaging %(XEP-0174)
 202                                 \item recently, also XEPs for the IoT %(XEP-0323 through -0326)
 203                         \end{itemize}
 204                 \end{itemize}
 205                 \end{block}
 206         \end{onlyenv}
 207         \begin{onlyenv}<2>
 208                 \begin{block}{Serverless XMPP (XEP-0174)}
 209                 \begin{itemize}
 210                         \item Clients communicate directly, no server needed
 211                         \item service discovery via mDNS/DNS-SD
 212                 \end{itemize}
 213                 \end{block}
 214         \end{onlyenv}
 215
 216         \column{.45\textwidth}
 217         \tikzset{node distance=0pt, >=stealth, thick, x=3.5em, y=2.8em}
 218         \tikzstyle{iconlabel}=[text width=2.5cm, align=center,
 219                 font=\fontsize{7.5pt}{1em}\selectfont]
 220         \tikzstyle{label}=[font=\fontsize{7pt}{1em}\selectfont]
 221         \begin{overprint}
 222                 \begin{figure}
 223                 \begin{tikzpicture}[remember picture]
 224                         \input{fig-xmpparch.tex}
 225                 \end{tikzpicture}
 226                 \end{figure}
 227                 \tikz[remember picture,overlay]
 228                         \draw<2>[<->,dotted] (juliet) -- node[anchor=south,label]{serverless} (romeo);
 229         \end{overprint}
 230 \end{columns}
 231 \end{frame}
 232
 233 \begin{frame}{XMPP (RFC 6122)}
 234         \begin{block}{XEPs for the Internet of Things}
 235                 \begin{itemize}
 236                         \item XEP-0323 Sensor Data
 237                         \begin{itemize}
 238                                 \item format for sensor data, query modes
 239                         \end{itemize}
 240                         \item XEP-0324 Provisioning
 241                         \begin{itemize}
 242                                 \item defining access rights and user privileges
 243                         \end{itemize}
 244                         \item XEP-0325 Control
 245                         \begin{itemize}
 246                                 \item get/set control prameters on a (group of) sensor node(s)
 247                         \end{itemize}
 248                         \item XEP-0326 Concentrators
 249                         \begin{itemize}
 250                                 \item implement proxies for a subnet of the WSN
 251                         \end{itemize}
 252                 \end{itemize}
 253         \end{block}
 254 \end{frame}
 255
 256 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 257 \againframe<4>{subgoals}
 258
 259 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 260 \section{Chatty Things}
 261 \begin{frame}{Chatty Things}
 262 \begin{itemize}
 263         \item use serverless XMPP + mDNS + DNS-SD for communication
 264         \item interaction using a standard XMPP client
 265         \item prevent information overflow
 266         \begin{itemize}
 267                 \item ``Traffic lights'': status icon in roster represents threshold value
 268                 \item \emph{Temporary Subscription for Presence (TSP)}
 269         \end{itemize}
 270         %\item working prototype for Contiki on MSP430
 271 \end{itemize}
 272 \begin{block}{Prototype}
 273         \begin{itemize}
 274                 \item \emph{uBonjour} for mDNS + DNS-SD
 275                 \item \emph{uXMPP} for XMPP
 276                 \item 12~kB of ROM, 0.6 kB of RAM with Contiki on MSP-430
 277         \end{itemize}
 278 \end{block}
 279 \end{frame}
 280
 281 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 282 \begin{frame}{Temporary Subscription for Presence}
 283         \begin{block}{Problem}
 284                 \begin{itemize}
 285                         \item node must manually subscribe to get information
 286                         \item users can move quickly out of the network
 287                         \item subscriptions become outdated
 288                         \item renewing/canceling subscriptions needs bandwidth
 289                         \item data publishers also get updates
 290                 \end{itemize}
 291         \end{block}
 292 \end{frame}
 293
 294 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 295 \begin{frame}{Temporary Subscription for Presence}
 296 \begin{block}{Solution: Multi-User Chats}
 297         \begin{itemize}
 298                 \item create one chat room per topic
 299                 \item users subscribe to information by entering the chat room
 300                 \item server only sends information to nodes who want it
 301                 \begin{itemize}
 302                         \item Chatty Things send a flag that they're uninterested
 303                 \end{itemize}
 304         \end{itemize}
 305 \end{block}
 306 \begin{block}{Drawbacks}
 307         \begin{itemize}
 308                 \item only works with central XMPP server
 309                 \begin{itemize}
 310                         \item XEP-0045 is not (yet) specified for serverless XMPP
 311                 \end{itemize}
 312                 \item XMPP server needs to handle TSP
 313         \end{itemize}
 314 \end{block}
 315 \end{frame}
 316
 317 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 318 \begin{frame}{Bootstrapping}
 319 \begin{block}{At Boot}
 320         \begin{enumerate}
 321                 \item activate uBonjour
 322                 \item try to discover a central XMPP server
 323                 \begin{itemize}
 324                         \item DNS-SD: \code{\_xmpp-client.\_tcp.local}
 325                 \end{itemize}
 326                 \item if an XMPP server is discovered: \emph{Infrastructure mode}
 327                 \begin{itemize}
 328                         \item connect with ANONYMOUS login (XEP-0175)
 329                         \item join topic-based chats
 330                         \item deactivate uBonjour
 331                 \end{itemize}
 332                 \item if no server is found: \emph{Ad hoc mode}
 333                 \begin{itemize}
 334                         \item activate serverless messaging
 335                 \end{itemize}
 336         \end{enumerate}
 337 \end{block}
 338 \end{frame}
 339 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 340 \begin{frame}{Bootstrapping}
 341 \begin{block}{During Runtime}
 342         \begin{itemize}
 343                 \item if server is lost, change to Ad hoc mode
 344                 \item if new server is found in Ad hod mode, try changing to Infrastructure
 345                         mode
 346                 \begin{itemize}
 347                         \item if that fails, stay in Ad hoc mode
 348                 \end{itemize}
 349         \end{itemize}
 350 \end{block}
 351 \end{frame}
 352
 353 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 354 \againframe<5>{subgoals}
 355
 356 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 357 \section{Related Approaches}
 358 \begin{frame}{Related Approaches}
 359 \begin{overprint}
 360         \onslide<1>
 361         \begin{block}{Chatty Things}
 362         \end{block}
 363         \onslide<2>
 364         \begin{block}{Constrained Application Protocol (CoAP)}
 365                 \begin{itemize}
 366                         \item binary mapping to HTTP
 367                         \item UDP with confirmation and congestion control
 368                 \end{itemize}
 369         \end{block}
 370         \onslide<3>
 371         \begin{block}{MQ Telemetry Transport (MQTT)}
 372                 \begin{itemize}
 373                         \item binary, only 2-byte header
 374                         \item focused on M2M communication
 375                 \end{itemize}
 376         \end{block}
 377         \onslide<4>
 378         \begin{block}{Web Service for Devices (WS4D)}
 379                 \begin{itemize}
 380                         \item SOAP (XML-based) over HTTP
 381                 \end{itemize}
 382         \end{block}
 383 \end{overprint}
 384 \begin{table}
 385         \small\centering
 386         \begin{tabular}{|>{\onslide<1->}l||>{\onslide<1->}l|>{\onslide<2->}l|
 387                 >{\onslide<3->}l|>{\onslide<4->}l<{\onslide}|}
 388                 \hline
 389                 Feature & Chatty Things & CoAP & MQTT & WS4D \\
 390          \hline\hline
 391                 application gateways & - & yes & yes & - \\ \hline
 392                 usable with standard clients & yes & - & - & (yes) \\ \hline
 393                 discovery support & yes & yes & - & yes\\ \hline
 394                 IPv6/6LoWPAN ready & yes & yes & ? & partial \\ \hline
 395                 asynchronous messages & yes & yes & ? & ? \\ \hline
 396                 protocol overhead & moderate & low & low & high \\ \hline
 397         \end{tabular}
 398 \end{table}
 399 \end{frame}
 400
 401 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 402 \section{Conclusion}
 403 \begin{frame}{Conclusion}
 404 \begin{block}{Advantages of Chatty Things}
 405         \begin{itemize}
 406                 \item no need for central infrastructure
 407                 \item self-configuration and auto-discovery
 408                 \item interaction over standard chat clients
 409                 \item protocol flexibility for enhancements
 410         \end{itemize}
 411 \end{block}
 412 \begin{block}{Disadvantages of Chatty Things}
 413         \begin{itemize}
 414                 \item XMPP introduces some complexity
 415                 \item topic filtering only possible with central server
 416         \end{itemize}
 417 \end{block}
 418 \end{frame}
 419
 420 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 421 \begin{frame}
 422 \begin{center}
 423 \vfill
 424 \LARGE{Questions?}
 425 \vfill
 426 \vfill
 427 \footnotesize
 428 \cc\bysa\\
 429 This presentation is licensed under the terms of the \\
 430 Creative Commons Attribution-ShareAlike 3.0 Unported license\\
 431 and builds on public domain icons from the Tango Desktop Project
 432 \end{center}
 433 \end{frame}
 434
 435 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 436 \section*{Example}
 437 \def\bot{-7.5}
 438 \def\nearlybot{-7}
 439 \def\top{0}
 440 \def\nearlytop{-0.5}
 441 \def\dev{-5}
 442 \def\cli{5}
 443 \newlength{\ypos}
 444 \newlength{\yypos}
 445 \newcommand{\advanceby}[1]{%
 446         \addtolength{\ypos}{#1}%
 447         \addtolength{\yypos}{#1}%
 448         \global\ypos=\ypos% // see https://tex.stackexchange.com/questions/119730
 449         \global\yypos=\yypos%
 450 }
 451 \tikzstyle{pkt}=[
 452   fill,
 453   below=-.5\baselineskip,
 454   font=\scriptsize,
 455   draw,
 456   dash pattern=on 2pt off 2pt,
 457 ]
 458 \tikzstyle{clipkt}=[pkt,
 459   below left=-.5\baselineskip and 0cm,
 460   pos=0.05,
 461 ]
 462 \tikzstyle{devpkt}=[pkt,
 463   below right=-.5\baselineskip and 0cm,
 464   pos=0.05,
 465 ]
 466 %%%%%%%%%
 467 \begin{frame}[fragile,plain,t]{Example: Sensor Data}
 468 \begin{tikzpicture}[
 469   every node/.style={fill=white, font=\small},
 470   every picture/.style=ultra thin,
 471   >=latex,
 472   semithick
 473 ]
 474 \setlength{\ypos}{0cm}
 475 \setlength{\yypos}{.5cm}
 476 %% Header
 477 \draw (\cli,\top) node[draw]{Client} -- (\cli,\nearlybot);
 478 \draw[dashed] (\cli,\nearlybot) -- (\cli,\bot);
 479 \draw (\dev,\top) node[draw]{Device} -- (\dev,\nearlybot);
 480 \draw[dashed] (\dev,\nearlybot) -- (\dev,\bot);
 481
 482 \advanceby{.75cm}
 483 \draw[->] (\cli,-\ypos) -- (\dev,-\yypos) node[clipkt]{\verb+<stream>+};
 484 \advanceby{1cm}
 485 \draw[->] (\dev,-\ypos) -- (\cli,-\yypos) node[devpkt]{\verb+<stream>+};
 486
 487 \advanceby{1cm}
 488 \draw[->] (\cli,-\ypos) -- (\dev,-\yypos) node[clipkt,align=left]{
 489 \verb+<iq type='get' id='1'+\\
 490 \verb+    to='dev@device.local/res'+\\
 491 \verb+    from='client@client.local'>+\\
 492 \verb+  <req xmlns='urn:xmpp:sn' seqnr='1'+\\
 493 \verb+      momentary='true'>+\\
 494 \verb+    <node nodeId='Device04'/>+\\
 495 \verb+    <field name='+{\color{red}\code{Energy}}\verb+'/>+\\
 496 \verb+    <field name='+{\color{blue}\code{Power}}\verb+'/>+\\
 497 \verb+  </req> </iq>+
 498 %\end{verbatim}
 499 \advanceby{9\baselineskip}
 500 };
 501
 502 \advanceby{0.3cm}
 503 \draw[->] (\dev,-\ypos) -- (\cli,-\yypos) node[devpkt,align=left]{
 504 \verb+<iq type='result' id='1'+\\
 505 \verb+    from='dev@device.local'+\\
 506 \verb+    to='client@client.local/res'>+\\
 507 \verb+  <accepted xmlns='urn:xmpp:sn' seqnr='1'/>+\\
 508 \verb+</iq>+
 509 \advanceby{4\baselineskip}
 510 };
 511 \end{tikzpicture}
 512 \end{frame}
 513
 514 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 515 \begin{frame}[fragile,plain,t]{Example: Sensor Data (cont.)}
 516 \begin{tikzpicture}[
 517   every node/.style={fill=white, font=\small},
 518   every picture/.style=ultra thin,
 519   >=latex,
 520   semithick
 521 ]
 522 \setlength{\ypos}{0cm}
 523 \setlength{\yypos}{.5cm}
 524 %% Header
 525 \draw[dashed] (\cli,\top) node[draw]{Client} -- (\cli,\nearlytop);
 526 \draw (\cli,\nearlytop) -- (\cli,\bot);
 527 \draw[dashed] (\dev,\top) node[draw]{Device} -- (\dev,\nearlytop);
 528 \draw (\dev,\nearlytop) -- (\dev,\bot);
 529
 530 \advanceby{.75cm}
 531 %\advanceby{1cm}
 532 \draw[->] (\dev,-\ypos) -- (\cli,-\yypos) node[devpkt,align=left]{
 533 \verb+<message from='dev@device.local'+\\
 534 \verb+    to='client@client.local/res'>+\\
 535 \verb+  <fields xmlns='urn:xmpp:sn' seqnr='1' done='true'>+\\
 536 \verb+    <node nodeId='Device04'>+\\
 537 \verb+      <timestamp value='2013-03-07T22:03:15'>+\\
 538 \verb+        <numeric name='+{\color{red}\code{Energy}}\verb+' momentary='true'+\\
 539 \verb+          value='+{\color{red}\code{167.5}}\verb+' unit='+{\color{red}\code{kWh}}\verb+'/>+\\
 540 \verb+        <numeric name='+{\color{blue}\code{Power}}\verb+' momentary='true'+\\
 541 \verb+          value='+{\color{blue}\code{239.4}}\verb+' unit='+{\color{blue}\code{W}}\verb+'/>+\\
 542 \verb+      </timestamp>+\\
 543 \verb+    </node>+\\
 544 \verb+  </fields>+\\
 545 \verb+</message>+
 546 \advanceby{12\baselineskip}
 547 };
 548
 549 \advanceby{1cm}
 550 \draw[->] (\cli,-\ypos) -- (\dev,-\yypos) node[clipkt]{\verb+</stream>+};
 551 \advanceby{1cm}
 552 \draw[->] (\dev,-\ypos) -- (\cli,-\yypos) node[devpkt]{\verb+</stream>+};
 553 \end{tikzpicture}
 554 \end{frame}
 555 \end{document}