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