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{tikz}
   9 \usetikzlibrary{arrows}
  10 \usetikzlibrary{arrows}
  11 \usetikzlibrary{positioning}
  12 \usetikzlibrary{shapes.symbols}
  13 %\usepackage[usenames,dvipsnames]{color}
  14
  15 %\presetkeys{todonotes}{inline}{}
  16 \newcommand{\code}[1]{\texttt{#1}}
  17 \definecolor{green}{RGB}{137,164,0}  % from tubslatex
  18
  19 \title{Chatty Things}
  20 \subtitle{Making the Internet of Things Readily Usable for the Masses with XMPP}
  21 \author{Roland Hieber}
  22 \institute[IBR, TU-BS]{Institute of Operating Systems and Computer Networks}
  23 \date[SKM-13/14]{Seminar Communications and Multimedia, WS 2013/14}
  24
  25 \begin{document}
  26
  27 \begin{frame}[plain]
  28 \maketitle
  29 \end{frame}
  30
  31 \begin{frame}{Contents}
  32 \tableofcontents
  33 \end{frame}
  34
  35 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
  36 \section{Motivation}
  37 \begin{frame}{Motivation}
  38 \begin{block}{The IoT Vision}
  39         \begin{itemize}
  40                 \item plentitude of smart objects
  41                 \item interoperability between devices
  42                 \item easy accessibility for users
  43         \end{itemize}
  44 \end{block}
  45 \end{frame}
  46
  47 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
  48 \begin{frame}<1>[label=subgoals]{Motivation: Subgoals}
  49         \begin{block}{But how do we\ldots}
  50                 \begin{itemize}
  51                         \item configure our devices?
  52                                 \begin{itemize}
  53                                         \invisible<1-1>{\item[\color{green}\checkmark]\color{green}
  54                                                 Link-Local Addressing, Stateless Address Autoconfiguration}
  55                                 \end{itemize}
  56                         \item find other nodes to talk to?
  57                                 \begin{itemize}
  58                                         \invisible<1-2>{\item[\color{green}\checkmark]\color{green}
  59                                                 DNS-SD + mDNS}
  60                                 \end{itemize}
  61                         \item talk to other nodes or users?
  62                                 \begin{itemize}
  63                                         \invisible<1-3>{\item[\color{green}\checkmark]\color{green} XMPP
  64                                                 Serverless Messaging}
  65                                 \end{itemize}
  66                         \item filter relevant information?
  67                                 \begin{itemize}
  68                                         \invisible<1-4>{\item[\color{green}\checkmark]\color{green} ``Traffic
  69                                                 Lights'', Temporary Subscription for Presence}
  70                                 \end{itemize}
  71                 \end{itemize}
  72         \end{block}
  73 \end{frame}
  74
  75 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
  76 \section{Technologies for Distributed Networking}
  77 \begin{frame}{Address Allocation}
  78 IPv4 Link-Local Addessing (``APIPA'', ``Zeroconf'', RFC 3927)
  79 \begin{itemize}
  80         \item subnet \code{169.254.0.0/16}
  81 \end{itemize}
  82 IPv6 Stateless Address Autoconfiguration (RFC 4862)
  83 \begin{itemize}
  84         \item subnet \code{fe80::/64} (link-local)
  85         \item subnet \code{fc00::/11} (unique-local, if configured)
  86         \item or global address (if configured)
  87 \end{itemize}
  88
  89 \begin{block}{Algorithm}
  90 \begin{enumerate}
  91         \item choose (random) IP address in subnet
  92         \item ask if anyone uses that address
  93         \item if not, we're fine
  94         \item else, retry
  95 \end{enumerate}
  96 \end{block}
  97 \end{frame}
  98
  99 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 100 \againframe<2>{subgoals}
 101
 102 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 103 \begin{frame}{Multicast DNS (RFC 6762)}
 104 \begin{itemize}
 105 \item distributed DNS database
 106 \item uses multicast address \code{224.0.0.251} (IPv4) and \code{ff02::fb}
 107         (IPv6), UDP port 5353
 108 \item standard DNS packet format
 109 \item hosts announce their own resources
 110 \item hosts respond to queries if queried resource is known
 111 \end{itemize}
 112 \end{frame}
 113
 114 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 115 \begin{frame}{DNS-Based Service Discovery (RFC 6763)}
 116 Two-step process:
 117 \begin{enumerate}
 118         \item Service Instance Enumeration
 119         \begin{itemize}
 120                 \item query PTR records of form \code{\_service.\_proto.domain}
 121                 \item results: instance names of form \code{name.\_service.\_proto.domain}
 122         \end{itemize}
 123         \item Service Instance Resolution
 124         \begin{itemize}
 125                 \item query instance names as SRV records
 126                 \item result gives host name, port, priority, weight
 127         \end{itemize}
 128 \end{enumerate}
 129 \end{frame}
 130
 131 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 132 \begin{frame}[fragile]{mDNS + DNS-SD}
 133 \tikzset{font=\fontsize{7.5pt}{1em}\selectfont, >=latex, thick, y=3.5em}
 134 %\tikzstyle{iconlabel}=[text width=2cm, align=center,
 135         %font=\fontsize{7.5pt}{1em}\selectfont]
 136 \tikzstyle{label}=[font=\fontsize{7pt}{1em}\selectfont]
 137 \tikzstyle{pkt}=[font=\fontsize{7pt}{1em}\selectfont,
 138         draw,fill=white,dash pattern=on 2pt off 2pt, align=center,
 139         inner sep=2pt]
 140 \def\xhalf{.45\textwidth}
 141 \def\nodeskip{2.2em}
 142 \begin{enumerate}
 143         \item Service Instance Enumeration
 144         \begin{tikzpicture}
 145                 \node[cloud,draw,fill=gray!20,aspect=2] (thecloud) at (0,0) {multicast};
 146                 \def\nodelist{
 147                         node/{(-\xhalf,0)}/{},
 148                         juliet/{(\xhalf,0)}/juliet,
 149                         romeo/{(\xhalf,-1)}/romeo,
 150                         mercutio/{(\xhalf,1)}/mercutio%
 151                 }
 152                 \foreach \name/\pos/\text in \nodelist {
 153                         \node (\name) at \pos { \includegraphics[width=3em]{icon-computer.pdf} };
 154                         \node[below=\nodeskip of \name.north,label] (\name text) { \text };
 155                 }
 156                 \draw[->] (node) -- (thecloud) node[pkt,pos=0.5]{
 157                         \verb+_presence._tcp.local+\\PTR? };
 158                 \draw[->] (juliet) -- (thecloud) node[pkt,pos=0.35]{
 159                         \verb+juliet._presence.+\\\verb+_tcp.local+ };
 160                 \draw[->] (romeo) -- (thecloud) node[pkt,pos=0.35]{
 161                         \verb+romeo._presence.+\\\verb+_tcp.local+ };
 162                 \draw[->] (mercutio) -- (thecloud) node[pkt,pos=0.35]{
 163                         \verb+mercutio._presence.+\\\verb+_tcp.local+ };
 164         \end{tikzpicture}
 165
 166         \item Service Instance Resolution
 167         \begin{tikzpicture}
 168                 \node[cloud,draw,fill=gray!20,aspect=2] (thecloud) at (0,0) {multicast};
 169                 \node (node) at (-\xhalf,0) { \includegraphics[width=3em]{icon-computer.pdf} };
 170                 \node (juliet) at (\xhalf,0) { \includegraphics[width=3em]{icon-computer.pdf} };
 171                 \node[below=\nodeskip of juliet.north,label] (juliet text) { juliet };
 172                 \draw[->] (node) -- (thecloud) node[pkt,pos=0.5]{
 173                         \verb+juliet._presence._tcp.local+\\SRV? };
 174                 \draw[->] (juliet) -- (thecloud) node[pkt,pos=0.5]{
 175                         \verb+juliet.local, port 5222,+\\\verb+prio 0, weight 0+ };
 176
 177
 178         %\node[draw] (resptr) at (0,-4) {\code{juliet.\_presence.\_tcp.local} SRV?};
 179         %\node[draw] (resres) at (16em,-4) {\code{juliet.local, port 5222, prio 0, weight 0}};
 180
 181         %\draw[->] (enumptr) -- (enumres);
 182         %\draw[->] (resptr) -- (resres);
 183 \end{tikzpicture}
 184 \end{enumerate}
 185 \end{frame}
 186
 187 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 188 \againframe<3>{subgoals}
 189
 190 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 191 \begin{frame}{XMPP (RFC 6122)}
 192 \begin{columns}[c]
 193         \column{.55\textwidth}
 194         \begin{onlyenv}<1>
 195                 \begin{block}{Extensible Messaging and Presence Protocol}
 196                 \begin{itemize}
 197                         \item XML-based
 198                         \item Federated architecture
 199                         \begin{itemize}
 200                                 \item modeled after E-Mail
 201                         \end{itemize}
 202                         \item publish-subscribe mechanism
 203                         \item XMPP Extension Protocols (XEPs), e.\,g.
 204                         \begin{itemize}
 205                                 \item Multi-User Chats % (XEP-0045)
 206                                 \item Serverless Messaging %(XEP-0174)
 207                                 \item recently, also XEPs for the IoT %(XEP-0323 through -0326)
 208                         \end{itemize}
 209                 \end{itemize}
 210                 \end{block}
 211         \end{onlyenv}
 212         \begin{onlyenv}<2>
 213                 \begin{block}{Serverless XMPP (XEP-0174)}
 214                 \begin{itemize}
 215                         \item Clients communicate directly, no server needed
 216                         \item service discovery via mDNS/DNS-SD
 217                 \end{itemize}
 218                 \end{block}
 219         \end{onlyenv}
 220
 221         \column{.45\textwidth}
 222         \tikzset{node distance=0pt, >=stealth, thick, x=3.5em, y=2.8em}
 223         \tikzstyle{iconlabel}=[text width=2.5cm, align=center,
 224                 font=\fontsize{7.5pt}{1em}\selectfont]
 225         \tikzstyle{label}=[font=\fontsize{7pt}{1em}\selectfont]
 226         \begin{overprint}
 227                 \begin{figure}
 228                 \begin{tikzpicture}[remember picture]
 229                         \input{fig-xmpparch.tex}
 230                 \end{tikzpicture}
 231                 \end{figure}
 232                 \tikz[remember picture,overlay]
 233                         \draw<2>[<->,dotted] (juliet) -- node[anchor=south,label]{serverless} (romeo);
 234         \end{overprint}
 235 \end{columns}
 236 \end{frame}
 237
 238 \begin{frame}{XMPP (RFC 6122)}
 239         \begin{block}{XEPs for the Internet of Things}
 240                 \begin{itemize}
 241                         \item XEP-0323 Sensor Data
 242                         \begin{itemize}
 243                                 \item format for sensor data, query modes
 244                         \end{itemize}
 245                         \item XEP-0324 Provisioning
 246                         \begin{itemize}
 247                                 \item defining access rights and user privileges
 248                         \end{itemize}
 249                         \item XEP-0325 Control
 250                         \begin{itemize}
 251                                 \item get/set control prameters on a (group of) sensor node(s)
 252                         \end{itemize}
 253                         \item XEP-0326 Concentrators
 254                         \begin{itemize}
 255                                 \item implement proxies for a subnet of the WSN
 256                         \end{itemize}
 257                 \end{itemize}
 258         \end{block}
 259 \end{frame}
 260
 261 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 262 \againframe<4>{subgoals}
 263
 264 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 265 \section{Chatty Things}
 266 \begin{frame}{Chatty Things}
 267 \begin{itemize}
 268         \item use serverless XMPP + mDNS + DNS-SD for communication
 269         \item interaction using a standard XMPP client
 270         \item prevent information overflow
 271         \begin{itemize}
 272                 \item ``Traffic lights'': status icon in roster represents threshold value
 273                 \item \emph{Temporary Subscription for Presence (TSP)}
 274         \end{itemize}
 275         %\item working prototype for Contiki on MSP430
 276 \end{itemize}
 277 \begin{block}{Prototype}
 278         \begin{itemize}
 279                 \item \emph{uBonjour} for mDNS + DNS-SD
 280                 \item \emph{uXMPP} for XMPP
 281                 \item 12~kB of ROM, 0.6 kB of RAM with Contiki on MSP-430
 282         \end{itemize}
 283 \end{block}
 284 \end{frame}
 285
 286 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 287 \begin{frame}{Temporary Subscription for Presence}
 288         \begin{block}{Problem}
 289                 \begin{itemize}
 290                         \item node must manually subscribe to get information
 291                         \item users can move quickly out of the network
 292                         \item subscriptions become outdated
 293                         \item renewing/canceling subscriptions needs bandwidth
 294                         \item data publishers also get updates
 295                 \end{itemize}
 296         \end{block}
 297 \end{frame}
 298
 299 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 300 \begin{frame}{Temporary Subscription for Presence}
 301 \begin{block}{Solution: Multi-User Chats}
 302         \begin{itemize}
 303                 \item create one chat room per topic
 304                 \item users subscribe to information by entering the chat room
 305                 \item server only sends information to nodes who want it
 306                 \begin{itemize}
 307                         \item Chatty Things send a flag that they're uninterested
 308                 \end{itemize}
 309         \end{itemize}
 310 \end{block}
 311 \begin{block}{Drawbacks}
 312         \begin{itemize}
 313                 \item only works with central XMPP server
 314                 \begin{itemize}
 315                         \item XEP-0045 is not (yet) specified for serverless XMPP
 316                 \end{itemize}
 317                 \item XMPP server needs to handle TSP
 318         \end{itemize}
 319 \end{block}
 320 \end{frame}
 321
 322 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 323 \begin{frame}{Bootstrapping}
 324 \begin{block}{At Boot}
 325         \begin{enumerate}
 326                 \item activate uBonjour
 327                 \item try to discover a central XMPP server
 328                 \begin{itemize}
 329                         \item DNS-SD: \code{\_xmpp-client.\_tcp.local}
 330                 \end{itemize}
 331                 \item if an XMPP server is discovered: \emph{Infrastructure mode}
 332                 \begin{itemize}
 333                         \item connect with ANONYMOUS login (XEP-0175)
 334                         \item join topic-based chats
 335                         \item deactivate uBonjour
 336                 \end{itemize}
 337                 \item if no server is found: \emph{Ad hoc mode}
 338                 \begin{itemize}
 339                         \item activate serverless messaging
 340                 \end{itemize}
 341         \end{enumerate}
 342 \end{block}
 343 \end{frame}
 344 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 345 \begin{frame}{Bootstrapping}
 346 \begin{block}{During Runtime}
 347         \begin{itemize}
 348                 \item if server is lost, change to Ad hoc mode
 349                 \item if new server is found in Ad hod mode, try changing to Infrastructure
 350                         mode
 351                 \begin{itemize}
 352                         \item if that fails, stay in Ad hoc mode
 353                 \end{itemize}
 354         \end{itemize}
 355 \end{block}
 356 \end{frame}
 357
 358 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 359 \againframe<5>{subgoals}
 360
 361 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 362 \section{Related Approaches}
 363 \begin{frame}{Related Approaches}
 364 \begin{overprint}
 365         \onslide<1>
 366         \begin{block}{Chatty Things}
 367         \end{block}
 368         \onslide<2>
 369         \begin{block}{Constrained Application Protocol (CoAP)}
 370                 \begin{itemize}
 371                         \item binary mapping to HTTP
 372                         \item UDP with confirmation and congestion control
 373                 \end{itemize}
 374         \end{block}
 375         \onslide<3>
 376         \begin{block}{MQ Telemetry Transport (MQTT)}
 377                 \begin{itemize}
 378                         \item binary, only 2-byte header
 379                         \item focused on M2M communication
 380                 \end{itemize}
 381         \end{block}
 382         \onslide<4>
 383         \begin{block}{Web Service for Devices (WS4D)}
 384                 \begin{itemize}
 385                         \item SOAP (XML-based) over HTTP
 386                 \end{itemize}
 387         \end{block}
 388 \end{overprint}
 389 \begin{table}
 390         \small\centering
 391         \begin{tabular}{|>{\onslide<1->}l||>{\onslide<1->}l|>{\onslide<2->}l|
 392                 >{\onslide<3->}l|>{\onslide<4->}l<{\onslide}|}
 393                 \hline
 394                 Feature & Chatty Things & CoAP & MQTT & WS4D \\
 395          \hline\hline
 396                 application gateways & - & yes & yes & - \\ \hline
 397                 usable with standard clients & yes & - & - & (yes) \\ \hline
 398                 discovery support & yes & yes & - & yes\\ \hline
 399                 IPv6/6LoWPAN ready & yes & yes & ? & partial \\ \hline
 400                 asynchronous messages & yes & yes & ? & ? \\ \hline
 401                 protocol overhead & moderate & low & low & high \\ \hline
 402         \end{tabular}
 403 \end{table}
 404 \end{frame}
 405
 406 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 407 \section{Conclusion}
 408 \begin{frame}{Conclusion}
 409 \begin{block}{Advantages of Chatty Things}
 410         \begin{itemize}
 411                 \item no need for central infrastructure
 412                 \item self-configuration and auto-discovery
 413                 \item interaction over standard chat clients
 414                 \item protocol flexibility for enhancements
 415         \end{itemize}
 416 \end{block}
 417 \begin{block}{Disadvantages of Chatty Things}
 418         \begin{itemize}
 419                 \item XMPP introduces some complexity
 420                 \item topic filtering only possible with central server
 421         \end{itemize}
 422 \end{block}
 423 \end{frame}
 424
 425 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 426 \begin{frame}
 427 \vfill
 428 \centering\LARGE{Questions?}
 429 \vfill
 430 \end{frame}
 431
 432 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 433 \section*{Example}
 434 \def\bot{-7.5}
 435 \def\nearlybot{-7}
 436 \def\top{0}
 437 \def\nearlytop{-0.5}
 438 \def\dev{-5}
 439 \def\cli{5}
 440 \newlength{\ypos}
 441 \newlength{\yypos}
 442 \newcommand{\advanceby}[1]{%
 443         \addtolength{\ypos}{#1}%
 444         \addtolength{\yypos}{#1}%
 445         \global\ypos=\ypos% // see https://tex.stackexchange.com/questions/119730
 446         \global\yypos=\yypos%
 447 }
 448 \tikzstyle{pkt}=[
 449   fill,
 450   below=-.5\baselineskip,
 451   font=\scriptsize,
 452   draw,
 453   dash pattern=on 2pt off 2pt,
 454 ]
 455 \tikzstyle{clipkt}=[pkt,
 456   below left=-.5\baselineskip and 0cm,
 457   pos=0.05,
 458 ]
 459 \tikzstyle{devpkt}=[pkt,
 460   below right=-.5\baselineskip and 0cm,
 461   pos=0.05,
 462 ]
 463 %%%%%%%%%
 464 \begin{frame}[fragile,plain,t]{Example: Sensor Data}
 465 \begin{tikzpicture}[
 466   every node/.style={fill=white, font=\small},
 467   every picture/.style=ultra thin,
 468   >=latex,
 469   semithick
 470 ]
 471 \setlength{\ypos}{0cm}
 472 \setlength{\yypos}{.5cm}
 473 %% Header
 474 \draw (\cli,\top) node[draw]{Client} -- (\cli,\nearlybot);
 475 \draw[dashed] (\cli,\nearlybot) -- (\cli,\bot);
 476 \draw (\dev,\top) node[draw]{Device} -- (\dev,\nearlybot);
 477 \draw[dashed] (\dev,\nearlybot) -- (\dev,\bot);
 478
 479 \advanceby{.75cm}
 480 \draw[->] (\cli,-\ypos) -- (\dev,-\yypos) node[clipkt]{\verb+<stream>+};
 481 \advanceby{1cm}
 482 \draw[->] (\dev,-\ypos) -- (\cli,-\yypos) node[devpkt]{\verb+<stream>+};
 483
 484 \advanceby{1cm}
 485 \draw[->] (\cli,-\ypos) -- (\dev,-\yypos) node[clipkt,align=left]{
 486 \verb+<iq type='get' id='1'+\\
 487 \verb+    to='dev@device.local/res'+\\
 488 \verb+    from='client@client.local'>+\\
 489 \verb+  <req xmlns='urn:xmpp:sn' seqnr='1'+\\
 490 \verb+      momentary='true'>+\\
 491 \verb+    <node nodeId='Device04'/>+\\
 492 \verb+    <field name='+{\color{red}\code{Energy}}\verb+'/>+\\
 493 \verb+    <field name='+{\color{blue}\code{Power}}\verb+'/>+\\
 494 \verb+  </req> </iq>+
 495 %\end{verbatim}
 496 \advanceby{9\baselineskip}
 497 };
 498
 499 \advanceby{0.3cm}
 500 \draw[->] (\dev,-\ypos) -- (\cli,-\yypos) node[devpkt,align=left]{
 501 \verb+<iq type='result' id='1'+\\
 502 \verb+    from='dev@device.local'+\\
 503 \verb+    to='client@client.local/res'>+\\
 504 \verb+  <accepted xmlns='urn:xmpp:sn' seqnr='1'/>+\\
 505 \verb+</iq>+
 506 \advanceby{4\baselineskip}
 507 };
 508 \end{tikzpicture}
 509 \end{frame}
 510
 511 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 512 \begin{frame}[fragile,plain,t]{Example: Sensor Data (cont.)}
 513 \begin{tikzpicture}[
 514   every node/.style={fill=white, font=\small},
 515   every picture/.style=ultra thin,
 516   >=latex,
 517   semithick
 518 ]
 519 \setlength{\ypos}{0cm}
 520 \setlength{\yypos}{.5cm}
 521 %% Header
 522 \draw[dashed] (\cli,\top) node[draw]{Client} -- (\cli,\nearlytop);
 523 \draw (\cli,\nearlytop) -- (\cli,\bot);
 524 \draw[dashed] (\dev,\top) node[draw]{Device} -- (\dev,\nearlytop);
 525 \draw (\dev,\nearlytop) -- (\dev,\bot);
 526
 527 \advanceby{.75cm}
 528 %\advanceby{1cm}
 529 \draw[->] (\dev,-\ypos) -- (\cli,-\yypos) node[devpkt,align=left]{
 530 \verb+<message from='dev@device.local'+\\
 531 \verb+    to='client@client.local/res'>+\\
 532 \verb+  <fields xmlns='urn:xmpp:sn' seqnr='1' done='true'>+\\
 533 \verb+    <node nodeId='Device04'>+\\
 534 \verb+      <timestamp value='2013-03-07T22:03:15'>+\\
 535 \verb+        <numeric name='+{\color{red}\code{Energy}}\verb+' momentary='true'+\\
 536 \verb+          value='+{\color{red}\code{167.5}}\verb+' unit='+{\color{red}\code{kWh}}\verb+'/>+\\
 537 \verb+        <numeric name='+{\color{blue}\code{Power}}\verb+' momentary='true'+\\
 538 \verb+          value='+{\color{blue}\code{239.4}}\verb+' unit='+{\color{blue}\code{W}}\verb+'/>+\\
 539 \verb+      </timestamp>+\\
 540 \verb+    </node>+\\
 541 \verb+  </fields>+\\
 542 \verb+</message>+
 543 \advanceby{12\baselineskip}
 544 };
 545
 546 \advanceby{1cm}
 547 \draw[->] (\cli,-\ypos) -- (\dev,-\yypos) node[clipkt]{\verb+</stream>+};
 548 \advanceby{1cm}
 549 \draw[->] (\dev,-\ypos) -- (\cli,-\yypos) node[devpkt]{\verb+</stream>+};
 550 \end{tikzpicture}
 551 \end{frame}
 552 \end{document}