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