O. Pfeiffer 
   Internet Draft                                             ESAcademy 
   Document: draft-pfeiffer-remoteaccess-00.txt             P. Lukowicz 
   Expires: July 2003                                               ETH 
   Category: Best Current Practice                         January 2003 
    
    
                     Remote Access to Embedded Devices 
    
    
Status of this Memo 
    
   This document is an Internet-Draft and is in full conformance with 
   all provisions of Section 10 of RFC2026 [1].  
    
   Internet-Drafts are working documents of the Internet Engineering 
   Task Force (IETF), its areas, and its working groups.  Note that      
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   Drafts. 
    
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   material or to cite them other than as "work in progress." 
    
   The list of current Internet-Drafts can be accessed at 
        http://www.ietf.org/ietf/1id-abstracts.txt 
   The list of Internet-Draft Shadow Directories can be accessed at 
        http://www.ietf.org/shadow.html. 
    
    
Abstract 
    
   The aim of this document is to standardize remote access options to 
   parameters of embedded devices with limited resources.  Typically 
   such devices are based on 8-bit or 16-bit microcontrollers with 
   limited memory (64K or less) and a low operating frequency (20 MHz or 
   less).  The protocol described in this document uses existing markup 
   formats to specify modifiable parameters of embedded devices and 
   existing protocols to transfer these parameters between clients and 
   servers. 
    
    
Conventions used in this document 
    
   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 
   "SHOULD", "SHOULD NOT", "RECOMMENDED",  "MAY", and "OPTIONAL" in this 
   document are to be interpreted as described in RFC-2119 [2]. 
    
 
 
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Table of Contents 
    
   1. Introduction...................................................2 
      1.1 Terminology and Abbreviations..............................3 
   2. Remote Access Parameter Description Format (RAPDF).............5 
      2.1 RAPDF Outline..............................................5 
      2.2 Storing the RAPDF..........................................6 
   3. Protocols and Formats Used.....................................7 
   4. General RAPDF Usage Example....................................7 
   Security Considerations...........................................8 
   References........................................................8 
   Appendix A û RAPDF Examples.......................................9 
   Author's Addresses...............................................12 
    
    
1. Introduction 
    
   Remote access to embedded devices in our homes, factories, and 
   vehicles or to personal mobile electronic appliances becomes reality. 
   The RFC2324 [3] published on April 1st, 1998 was a humorous approach: 
   getting a coffee machine online and needing a Hyper Text Coffee Pot 
   Control Protocol (HTCPCP/1.0) seemed to be funny at that time. 
    
   Today RFC2324 does not sound as funny anymore - it is closer to 
   reality today than it was on its publishing date.  There is a clear 
   drive in the industry to Internet-enable embedded device like climate 
   control units and appliances - and coffee machines. 
    
   There are attempts by several companies to Internet-enable their 
   products û with some companies inventing their own proprietary 
   protocols and methods on how to allow remote access via the Internet. 
    
   Unfortunately this approach is not user-friendly.  Users have to get 
   acquainted with different methods and tools on how to access their 
   devices via email, web or other services û and none of them are 
   compatible with each other. 
    
   The goal of this document is to find a common ground for remote 
   access functionality û from the client viewpoint.  No matter what 
   kind of embedded system is connected to the Internet the client 
   should be able to expect some standardized methods for the remote 
   access using common services like email, regular web browsers or 
   minimized web browsers for PDAs or mobile phones,. 
    
   This document does not invent any new Internet technologies - it just 
   RECOMMENDS how existing protocols and methods should be used to offer 
   users standardized methods for remote access. 
    

 
 
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   For the scope of this document it does not matter how an embedded 
   device is connected to the Internet.  Connection can be directly or 
   via a specialized gateway for embedded devices that might use a 
   simple serial link or other lower cost network or fieldbus to 
   exchange information with the embedded devices.  However, this 
   document assumes that there is at least one Internet node that 
   manages one or more embedded device(s) and that offers the 
   standardized protocols and methods described in this document to 
   allow remote access to the embedded device(s).  We distinguish 
   between three types of devices: 
    
   1) Remote Access Client (RAC): the system that attempts to access an 
      embedded device over the Internet. 
   2) Remote Access Server (RAS): the system that manages the internet 
      access to one or multiple embedded device and  
   3) Remote Access Device (RAD): the device that is to be accessed 
      through the Internet. 
    
   In some implementations, the RAS might be implemented directly with 
   one RAD. In others, one RAS will be able to handle multiple RADs. 
    
 
1.1 Terminology and Abbreviations 
    
   RAD û Remote Access Device 
   The embedded device(s) that can be accessed via the Internet. 
    
   RAS û Remote Access Server 
   This is the access point for the Remote Access Client.  The RAS 
   manages one or multiple Remote Access Devices and provides the 
   Internet connectivity.  The RAS can be part of an embedded device or 
   part of a gateway connecting several Remote Access Devices to the 
   Internet. 
    
   RAC û Remote Access Client 
   A software or hardware client used to provide remote access to a 
   Remote Access Server.  This can be a web browser, email client, PDA 
   or any other internet connected device.   
    
   RAPDF û Remote Access Parameter Description Format 
   A format that describes all Remote Access Devices and their 
   configurable parameters connected to a single Remote Access Server. 







 
 
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                                     +------------+ 
   +------------+                    !   RAS A    ! 
   !    RAC     ! <--> INTERNET <--> ! with RAPDF ! 
   +------------+                    +------------+ 
                                     !   RAD 1    ! 
                                     +------------+ 
    
   FIGURE 1 û Remote Access to a RAS/RAD combination device 
    
   Figure 1 shows a Remote Access Device (RAD 1) that directly 
   implements a Remote Access Server (RAS A).  The RAS A can directly 
   serve RAPDF information to a Remote Access Client (RAC). 
    
    
                                     +------------+ 
   +------------+                    ! Web server ! 
   !   RAS B    ! <--> INTERNET <--> ! with RAPDF ! 
   +------------+                    ! info from  ! 
         !                           ! RAD 2-4    ! 
     E N !   +------------+          +------------+ 
     m e +---!   RAD 2    ! 
     b t !   +------------! 
     e w !                
     d o !   +------------+    
     d r +---!   RAD 3    ! 
     e k !   +------------! 
     d   !                
         !   +------------+    
         +---!   RAD 4    ! 
             +------------! 
    
   FIGURE 2 û Remote Access to devices on a local, embedded network 
    
   Figure 2 shows how one Remote Access Server (RAS B) can handle 
   multiple Remote Access Devices (RAD 2-4).  The RADs can be connected 
   to the RAS via a local, low-cost serial network or fieldbus. 
   Depending on resources available to RAS and RAD, the RAS MAY retrieve 
   the RAPDF information from a web server instead from the RAD itself, 
   after the appropriate URL was reported to the RAS by each RAD. 
    
    






 
 
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2. Remote Access Parameter Description Format (RAPDF) 
    
   Every remote access devices has certain parameters/variables that we 
   want to be able to read or write through an Internet connection. 
    
   All accessible parameters (both, read and write) of a certain device 
   MUST be defined using the Remote Access Parameter Description Format 
   (RAPDF). 
    
    
2.1 RAPDF Outline 
    
   RAPDF is based on HTML 4.0 [4] and obeys the following rules: 
    
   1.)   The header section MUST include the META tag 
    
   <META name=ötypeö content=öRAPDF 1.0ö> 
    
    
   2.)   The body section MUST include AT LEAST ONE HTML FORM. The name 
   of the form and the action identifies exactly one RAD (Remote Access 
   Device). For example: 
    
   <FORM name=öRemote Access to MyHomeDeviceö 
   action="mailto:remote@mail.com?subject=RAPDF" method="post"> 
   ... 
   </FORM> 
    
   Additionally, it is RECOMMENDED to use the <LABEL> tag to ensure 
   proper display of the formsÆ name: 
    
   <LABEL for=öra_my_formö>MyHomeDevice</LABEL> 
   <FORM name=öRemote Access to MyHomeDeviceö 
   action="mailto:remote@mail.com?subject=RAPDF" method="post" 
   id=öra_my_formö> 
   ... 
   </FORM> 
    
    
   3.)   For every parameter of the embedded device the form contains a 
   dedicated field The tags LABEL and ID MUST be used to associate a 
   name with the corresponding parameter: 
    
   <LABEL for="ra_temp_lr">Living Room Temperature</LABEL> 
   <INPUT name="temp_living_room" type="text" id="ra_temp_lr"> 
    
   <INPUT name="light_living" type="checkbox" value="Living Room" 
   id="ra_light_lr"> 
   <LABEL for="ra_light_lr">Living Room Lights</LABEL> 
 
 
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   <LABEL for="ra_safety">Select the device to shut off</LABEL> 
   <SELECT name="safety_shutoff" id="ra_safety"> 
     <OPTION>None</OPTION> 
     <OPTION>Water Heater</OPTION> 
     <OPTION>Furnace</OPTION> 
     <OPTION>Stove</OPTION> 
   </SELECT> 
    
    
   4.)   The usage of formatting tags such as paragraphs, tables, inline 
   graphics or tables has no effect on the automatic interpretation of 
   an RAPDF.  Devices or processing tools that work automatically on a 
   RAPDF MAY ignore all formatting tags (especially if implemented on 
   medium to low performance systems). 
    
    
   5.)   It is recommended to use FIELDSET and LEGEND where appropriate. 
   See the Appendix for examples. 
    
    
   6.)   The ôreadonlyö tag is supported for inputs and marks parameters 
   of the embedded device that cannot be changed. Example: 
    
   <LABEL for="ra_temp">Current Temperature</LABEL> 
   <INPUT name="temp" type="text" id="ra_temp_lr" readonly> 
    
   Note that there is no particular language specified for an RAPDF.  
   The description in the <LABEL> section can be provided in any 
   language.  
    
   The primary identifier to match a parameter to the RAPDF is the 
   ônameö of each <FORM>, <INPUT> or <SELECT> element.  These variable 
   names MUST remain the same in any language, as these would be most 
   likely hard-coded into the firmware of the RAD. 
    
   Also note that any other HTML tags for formatting or links may be 
   used outside or within a FORM. However, each FORM MUST be associated 
   with a RAD. 
    
    
2.2 Storing the RAPDF 
    
   Manufacturers of Remote Access Devices MUST provide the RAPDF 
   information along with their devices.  
    
   As code and data space in many embedded devices is limited, it is 
   recommended to provide the RAPDF information on HTTP servers [5] on 
   the Internet.  This way an embedded device does not need to store the 

 
 
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   entire RAPDF information locally.  Storing the URL indicating where 
   to find the RAPDF is sufficient for such cases. 
    
   If the embedded device integrates a Remote Access Server (RAS) 
   directly and its CPU performance and disk storage capacity is 
   sufficient in size, the RAPDF MAY be stored and made available by the 
   device itself. 
    
    
3. Protocols and Formats Used 
 
   Which protocols are used to exchange the RAPDF information between 
   the RAD, RAS and RAC is not specified in this document.  Depending on 
   the application a variation of existing email or web protocols MAY be 
   used.  Also depending on the application additional security 
   protocols should be used to prohibit unauthorized access. 
    
   The information flow and formats used are: 
    
   Information sent from the RAS to the RAC MUST be in RAPDF.  This 
   ensures support of a wide variety of existing and future clients. 
    
   Information sent from the RAC to the RAS MUST be the regular POST 
   reply used for HTML forms (see [4] and [5]). 
    
   Information flow between RAD and RAS is application and manufacturer 
   specific.  Either the RAD provides the RAS with the entire RAPDF or 
   it provides the RAS with information where to get the RAPDF (for 
   example by giving it a URL to the RAPDF info) 
    
    
4. General RAPDF Usage Example 
 
   To illustrate how Remote Access MAY be implemented in accordance to 
   this document, here is an example: 
    
   In an automated home, one RAS provides access to several RAD, such as 
   thermostats, light controls, etc.  The RAS is configured to recognize 
   a list of authorized users. 
    
   Using a RAC, an authorized user requests the RAPDF from the RAS.  The 
   RAS assembles the RAPDF information by either getting the data from 
   the RAD themselves û or if they are minimal implementations, 
   retrieves the RAPDF information from the manufacturerÆs web page 
   (using a URL reported by the RAD). 
    
   Once the RAPDF is assembled and the current data values / settings 
   inserted, the RAS transmits the RAPDF to the RAC who requested it. 
    
 
 
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   If the user requests changes to the data values / settings, the new 
   values are transmitted back to the RAS who is in charge of applying 
   them. 
    
    
Security Considerations 
    
   This document does not address the security issue, as it focuses on 
   the data format exchanged between the RAC and RAS, not on the 
   protocols used to exchange the data. Depending on the security level 
   required by the application, an appropriate secure transmission 
   protocol SHOULD be used. 
    
    
References 
    
                     
   1  Bradner, S., "The Internet Standards Process -- Revision 3", BCP 
      9, RFC 2026, October 1996. 
    
   2  Bradner, S., "Key words for use in RFCs to Indicate Requirement 
      Levels", BCP 14, RFC 2119, March 1997. 
    
   3  L. Masinter, ôHyper Text Coffee Pot Control Protocol 
      (HTCPCP/1.0)ö, RFC2324, April 1998. 
    
   4  Dave Ragget, Arnaud Le Hors, Ian Jacobs, ôHTML 4.01ö, 
      www.w3.org/TR/html4, December 1999. 
    
   5  R. Fielding, J. Gettys, J. Mogul, H. Frystyk, L. Masinter, P. 
      Leach, T. Berners-Lee, ôHypertext Transfer Protocol -- HTTP/1.1ô, 
      RFC2616, June 1999. 
    
    
    














 
 
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Appendix A û RAPDF Examples 
    
   NOTE: Additional examples are available at: 
   http://www.embeddedinternetworking.com/remoteaccess/ 
    
    
   A.1 RAPDF Example with minimal formatting 
    
   <HTML> 
    
   <HEAD> 
   <meta http-equiv="Content-Type" content="text/html; charset=windows-
   1252"> 
   <META name=ötypeö content=öRAPDF 1.0ö> 
   <TITLE>Remote Access to Home Control Center</TITLE> 
   </HEAD> 
    
   <BODY> 
    
   <LABEL for="ra_form_name">Remote Access to Home Control 
   Center</LABEL> 
   <FORM name=öRemote Access to MyDeviceö 
   action="remote@mail.com?subject=RAPDF%20Command%20Set" method="post" 
   id="ra_form_name"> 
   <P> 
     <LABEL for="ra_temp_lr">Living Room Temperature</LABEL> 
     <INPUT name="temp_living_room" type="text" id="ra_temp_lr"><br> 
     <LABEL for="ra_temp_mb">Master Bedroom Temperature</LABEL> 
     <INPUT name="temp_master_bedroom" type="text" id="ra_temp_mb"><br> 
     <LABEL for="ra_temp_gr">Guest Room Temperature</LABEL> 
     <INPUT name="temp_guest_bedroom" type="text" id="ra_temp_gr"><br> 
   </P> 
   <P> 
     <INPUT name="light_living" type="checkbox" value="Living Room" 
   id="ra_light_lr">  
     <LABEL for="ra_light_lr">Living Room Lights</LABEL><br> 
     <INPUT name="light_kitchen" type="checkbox" value="Kitchen" 
   id="ra_light_ki">  
     <LABEL for="ra_light_ki">Kitchen Lights</LABEL><br> 
     <INPUT name="light_bath" type="checkbox" value="Bathroom" 
   id="ra_light_ba">  
     <LABEL for="ra_light_ba">Bathroom Lights</LABEL><br> 
   </P> 
   <P> 
     <LABEL for="ra_safety">Safety Shut-off</LABEL><br> 
     <SELECT name="safety_shutoff" id="ra_safety"> 
      <OPTION>None</OPTION> 
      <OPTION>Water Heater</OPTION> 
      <OPTION>Furnace</OPTION> 
 
 
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      <OPTION>Stove</OPTION> 
     </SELECT> 
   </P> 
   <P> 
     <INPUT name="time_method" type="radio" value="Once"> 
     <LABEL for="ra_time_now">Activate settings now</LABEL><br> 
     <INPUT name="time_method" type="radio" value="Daily"> 
     <LABEL for="ra_time_daily">Activate settings every 24 
   hours</LABEL><br> 
     <INPUT name="time_method" type="radio" value="Weekly"> 
     <LABEL for="ra_time_weekly">Activate settings every 7 
   days</LABEL><br> 
   </P> 
   <P> 
    <INPUT type="submit" value="Send Settings"> <INPUT type="reset" 
   value="Reset Values"> 
   </P>  
   </FORM> 
    
   </BODY> 
    
   </HTML> 
    
    
   A.2 RAPDF Example with FIELDSET and LEGEND 
    
   <HTML> 
    
   <HEAD> 
   <META http-equiv="Content-Type" content="text/html; charset=windows-
   1252"> 
   <META name=ötypeö content=öRAPDF 1.0ö> 
   <TITLE>Remote Access to Home Control Center</TITLE> 
   </HEAD> 
    
   <BODY> 
    
   <LABEL for="ra_form_name">Remote Access to Home Control 
   Center</LABEL> 
   <FORM name=öRemote Access to MyDeviceö 
   action="mailto:ra@mail.com?subject=RAPDF%20Command%20Set" 
   method="post" id="ra_form_name"> 
    
    <FIELDSET> 
     <LEGEND>Climate Control Settings</LEGEND> 
     <LABEL for="ra_temp_lr">Living Room Temperature</LABEL> 
     <INPUT name="temp_living_room" type="text" id="ra_temp_lr"><br> 
     <LABEL for="ra_temp_mb">Master Bedroom Temperature</LABEL> 
     <INPUT name="temp_master_bedroom" type="text" id="ra_temp_mb"><br> 
 
 
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     <LABEL for="ra_temp_gr">Guest Room Temperature</LABEL> 
     <INPUT name="temp_guest_bedroom" type="text" id="ra_temp_gr"><br> 
    </FIELDSET> 
    
    <FIELDSET> 
     <LEGEND>Light Controls</LEGEND> 
     <INPUT name="light_living" type="checkbox" value="Living Room" 
   id="ra_light_lr">  
     <LABEL for="ra_light_lr">Living Room Lights</LABEL><br> 
     <INPUT name="light_kitchen" type="checkbox" value="Kitchen" 
   id="ra_light_ki">  
     <LABEL for="ra_light_ki">Kitchen Lights</LABEL><br> 
     <INPUT name="light_bath" type="checkbox" value="Bathroom" 
   id="ra_light_ba">  
     <LABEL for="ra_light_ba">Bathroom Lights</LABEL><br> 
    </FIELDSET> 
    
    <FIELDSET> 
     <LEGEND>Safety Shut Off</LEGEND> 
     <LABEL for="ra_safety">Select the device to shut off</LABEL><br> 
     <SELECT name="safety_shutoff" id="ra_safety"> 
      <OPTION>None</OPTION> 
      <OPTION>Water Heater</OPTION> 
      <OPTION>Furnace</OPTION> 
      <OPTION>Stove</OPTION> 
     </SELECT> 
    </FIELDSET> 
    
    <FIELDSET> 
     <LEGEND>Timing Information</LEGEND> 
     <INPUT name="time_method" type="radio" value="Once"> 
     <LABEL for="ra_time_now">Activate settings now</LABEL><br> 
     <INPUT name="time_method" type="radio" value="Daily"> 
     <LABEL for="ra_time_daily">Activate settings every 24 
   hours</LABEL><br> 
     <INPUT name="time_method" type="radio" value="Weekly"> 
     <LABEL for="ra_time_weekly">Activate settings every 7 
   days</LABEL><br> 
    </FIELDSET> 
    
    <INPUT type="submit" value="Send Settings"> <INPUT type="reset" 
   value="Reset Values"> 
     
   </FORM> 
    
   </BODY> 
    
   </HTML> 
    
 
 
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Author's Addresses 
    
   Olaf Pfeiffer 
   Embedded Systems Academy 
   50 Airport Parkway 
   San Jose, California 95110 
   Email: opfeiffer@esacademy.com 
    
   Dr. Paul (Pawel) Lukowicz 
   ETH (swiss Federal Institute of Technology) Zurich 
   Wearable Computing Lab 
   Gloriastrasse 35 
   CH-8092 Zurich 
   Email: lukowicz@ife.ee.ethz.ch 
    

































 
 
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