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Subject: Brent: What's wrong with having devices communicate in their ownnative languages

FYI: An article I just read = Brent


6LoWPAN Goes Where ZigBee Can't

An IP-based protocol puts sensor applications on the Internet.

by Jon Titus, Senior Technical Editor

Jon TitusMany “standard” and proprietary protocols use the media-access controller (MAC) and the physical circuits (PHY) associated with IEEE 802.15.4 radios. Those protocols use their own arrangements of bits and bytes to transfer information between nodes, but none of them use the Internet Protocol (IP). So they cannot directly communicate with Internet-based devices and Web servers/browsers. The IPv6 over Low power Wireless Personal Area Networks (6LoWPAN) standard offers an alternative because it employs the IPv6 protocol and can operate equally well over wireless and wired connections.

To find out more about 6LowPAN, I talked with Geoff Mulligan, the chairman of the IP for Smart Objects (IPSO) Alliance and 6LoWPAN Working Group Chair. "When I worked for Invensys, we started a project to put wireless IPv6 communications in smoke alarms and appliances. The header and address information for IPv6 amounts to 40 bytes. But the 802.15.4 packets have only 127 bytes, so IPv6 would take much of the available space. Some bright engineers came up with the idea of compressing the IPv6 header information so it needs only three or four bytes on average."

03ECN-Titus ES 6LoWPAN Fig 1The compression is completely stateless, which means that it creates no binding state between the compressor-decompressor pair. Stateless compression gives nodes the flexibility to communicate with any neighbor in compact form at all times.(Ref 1.) In addition, the stateless compression gives a network multiple entry and exit points, whereas a "stateful" network is susceptible to single-point failures.
"As a result of stateless compression, the 6LoWPAN community has software 'stacks' that require less RAM and ROM than a ZigBee stack, for example," added Mulligan. "Instead of having a monolithic header, you only add the bits and bytes you need for, say, fragmentation or mesh routing. If you don't need those capabilities, the packet doesn't carry that type of information, thus reducing the overhead."

The Internet Engineering Task Force (IETF) oversees the 6LoWPAN standardization and specification work under Request for Comments (RFC) 4944. The specifications are open and developers can buy 6LoWPAN code, use open-source code, or write their own. But 6LoWPAN communications don't require a complete rewrite of an IEEE 802.15.4 radio stack. Instead, 6LoWPAN adds an adaptation layer that lets the radio stack and IPv6 communications operate together. 

"The beauty of 6LoWPAN communications is that they let people communicate with devices across the Internet without having to go through, say, a ZigBee-to-IP translation step," explained Mulligan. "If they have a network of sensors in Antarctica the Internet will connect them directly to it. When the sensor bridge-network connects to Internet, it 're-inflates' the compressed headers and puts back all the needed IPv6 information."

The lack of gateways that translate protocols also improves end-to-end communication security. If you use a gateway to connect a proprietary network to the Internet, you have two security "spheres;" one for the Internet and one for the proprietary network. That arrangement provides a potential point of attack that could destroy the integrity of the end-to-end link.

"Work on the 6LoWPAN specifications continues," stressed Mulligan. "Engineers are working to answer questions such as how do users commission a network and how do they establish good security so their network doesn't connect to a neighbor’s network?"

The 6LoWPAN hardware relies on the IEEE 802.15.4 radio-communication standard and although IPv6 is relatively new, the Internet Protocol has over 30 years of history behind it. So, 6LoWPAN equipment should not encounter any problems with the other type of IP--intellectual property. Large companies such as IBM, Sun, Cisco, and Microsoft have invested heavily in IP-based communications and would not have done so unless the believed the IP had no hidden patent liabilities.  Unfortunately, proprietary or emerging network hardware and software standards might run up against existing patents that engineers have yet to uncover.

Companies offer development kits that can help developers kick start a 6LoWPAN project or just investigate its capabilities. Sensinode (www.sensinode.com) offers a K210 6LoWPAN Devkit and Atmel (www.atmel.com) provides its 2.4 GHz Evaluation and Starter Kit (ATAVRRZRAVEN) that runs a port of the Contiki 2.2.2 OS, which contains the small uIPv6 stack and SICSlowpan 802.15.4-over-IPv6 compression (http://www.sics.se/contiki). Arch Rock (www.archrock.com) has a PhyNet OEM Development Kit (IE version) that comes configured with the PhyNet IE Engine that lets developers use direct C API calls to the Arch Rock IP/6LoWPAN linkable kernel library to access operating-system services and standard TCP/UDP/IP-based networks. Jennic (www.jennic.com) also offers a 6LoWPAN Network Protocol stack that operates with the company's JN5139 wireless microcontrollers and modules.

If 6LoWPAN sounds interesting, but you have a ZigBee or other 802.15.4 project in the works you can still implement 6LoWPAN communications later. Just ensure you can "reflash" your firmware in the field so it can accept code for a 6LoWPAN stack. According to Mulligan, at least one utility company will take this approach with its first meter-reading equipment.  



From: Edward Koch [mailto:ed@akuacom.com]
Sent: Thursday, April 02, 2009 10:14 AM
To: Considine, Toby (Campus Services IT); smartgrid-interest@lists.oasis-open.org
Subject: [smartgrid-interest] RE: What's wrong with having devices communicate in their own native languages


OK guys.  I hesitate to pontificate too much since we are getting a bit off track here, but as someone who built a company back in the 90’s who developed BOTH routers and gateways specifically for connecting control networks to IP networks I can’t help but wade in on a topic that I am very intimate with.  Although I tend to agree that that gateways are better than tunneling routers in most cases where you have heterogeneous networks I do feel the need to play the devil’s advocate a bit here.


To say that system boundaries should be dictated by network boundaries is a bit too simplistic for me.  While I will admit that it is often very difficult to tunnel control/device network protocols over IP I don’t think that just because a packet is entering a tunnel it is necessarily crossing a system boundary.  I also think that saying tunneling should never be used is akin to saying things like “late night romantic phone calls  should never be conducted over packet switched networks like the internet, i.e. VOIP.”  I prefer to draw system boundaries based upon functional responsibilities and ease of moving information across the boundaries.


There is no doubt that network boundaries should play a part in deciding where to draw system boundaries, but if by system boundary you mean that you have to put in a gateway and do semantic mapping across that gateway then you also have to be very careful.  Everywhere you put a gateway you have to deal with the so called “binding” problem and when the binding problem starts to get distributed across your network the complexity can grow sharply.  This can be especially true when you have to go back and start swapping out already commissioned equipment or reconfiguring your network. With tunnels the binding problem is isolated to both ends of the tunnel. For every anecdote of someone having a problem using a tunneling router I can probably give you one where the a gateway and the binding problem bit someone in the ass.


Again I’m not trying to advocate tunnels and routers over semantic mappings and gateways I’m just trying to point out that each has their place and neither should be condemned outright.  The fact is that transporting information across heterogeneous networks is not for kids and there is no magic bullet.


All that being said – of course we need to have semantically consistent data models that can “hopefully” be both transported and mapped to a variety of networks, protocols, and end devices that have to consume the information.



-ed koch



From: Considine, Toby (Campus Services IT) [mailto:Toby.Considine@unc.edu]
Sent: Thursday, April 02, 2009 7:42 AM
To: smartgrid-interest@lists.oasis-open.org
Subject: [smartgrid-interest] What's wrong with having devices communicate in their own native languages


Subject changed because discussion was veering far from EMIE


It all depends on where you define the system boundaries.


I don’t care if you and your family walk around naked in your house. When you go on the street, and expect to interact with others, then societal expectations for behavior and dress kick in. I don’t care if you create small naturist clubs where you can walk around naked with a larger group. Every naturist camp always has a sign by the door “Did you remember to put on clothes?” Streaking, though, is always disruptive. As someone who has managed any number of “native protocols” interacting on a campus backbone, I know that those are much more disruptive then the kids who streak the library each semester before exams.


Tunneling protocols over IP is the like late night explicit romantic phone call. It may be an expedient solution to a short term problem in a niche situation, but it is no architecture. If the communication style extends to other phone calls, you get social problems, and potential law suits. Tunneling protocols, xxxx over IP, are just  problematic. They are barriers to interoperability. They often don’t recognize external costs. I have seen dozens of man hours expended to avoid a second $500 gateway. I’ve seen similar amounts of man hours expended again and again by network operations staff to sustain the protections that these tunneled protocols need.


The great wide internet is non-deterministic – which causes problems in lots of native protocols. Native protocols have all sorts of untested and undefined dependencies. I can regale you with stories of control protocols over IP disrupted by  replacement of a router blade…and of broadcast storms stopped only by unplugging all building system gateways, and then rebooting all routers, and then letting things stabilize, and then turning on each building gateway one at a time…why? Because the makers of that proprietary “it’s our own variant of UDP” control protocols over IP just didn’t anticipate the obscure interaction, and even extensive use of VLANs could not protect these systems.


At another University located near UNC, almost a year was spent figuring out that merely putting an un-configured HP Jet Direct card on-line would take the control system of the coal plant off line. Now that was fun.


The net of these experiences is a few principles that *I* hold dear…


-           Systems should be small and coherent, and should not have the internet in the middle. If the internet is in the middle, or perhaps even if IP is in the middle, it should be defined as two systems.

-          Internal “native” protocols should not be used to communication between systems.

-          Anything that can be attached to the internet, will be. This means that it will be exposed to unanticipated protocols, hostile interactions, and even accidental DOS attacks. We should define interfaces to systems accordingly.

-          The communication stack at the edge of a system should be well tested and well debugged, and have been used in as many open scenarios as possible so that all exceptionalism will have been eliminated. I never want to find that “unanticipated interaction”

-          When any combination of systems gets to a sufficient size, interoperability (or the lack thereof) becomes the most significant determinant of expense. (Every now and then, someone turns to me and says “wouldn’t it be easier if we just picked one vendor, one brand, and…I point out that if we did that, it would take us 20 years to get the “one true protocol” installed, and by that time, we would be unable to buy the legacy systems any more.


At the edge of the system, we should have well defined discoverable interfaces. There will be circumstances, few and rare, in which we legitimately need to split a system in half – but not many. Does this mean I want IP everywhere? Well, almost. Zigbee is not IP, but for purposes of this conversation it might be.


Take my PC. It has two IP addresses for its two interfaces (wired and wireless). I do not need an IP address on my mouse, nor on my screen. See, I don’t want IP everywhere. But I uses KVM to access my servers, with an IP based communications from my mouse keyboard, and display. KVM is a special case, with special needs, and special costs, and I can break that one IP per system rule because I can articulate the reasons, and support the special security requirements this requires. My KVM also has no interoperability requirements.


How do you define system?

What is the interoperability requirement?

Do you want the integration to scale?

Will one integrator be responsible for all systems, and all systems that interact with them?


On one side of those questions is “native protocols” and “xxx over IP”

On the other side IP is not enough, and you have services and discoverability and mature security and…


Take your pick. Answer all 4 questions. Then, and only then, is it time to listen to the justification of the native protocol. It would be interesting if to see how many want to put *that* explanation into the sales literature for the product…





"A man should never be ashamed to own that he has been in the wrong, which is but saying ... that he is wiser today than yesterday." -- Jonathan Swift

Toby Considine

Facilities Technology Office
University of North Carolina
Chapel Hill, NC


Email: Toby.Considine@ unc.edu
Phone: (919)962-9073


blog: www.NewDaedalus.com



From: Michel Kohanim [mailto:michel@universal-devices.com]
Sent: Thursday, April 02, 2009 1:41 AM
To: smartgrid-interest@lists.oasis-open.orgSubject: RE: [smartgrid-interest] Draft Charter - Energy Market Information Exchange


Hi Brian, I had to think about this for a day! Perhaps my statements are going to cause a heated debate, but, here I go:


I really do not see why everything has to communicate IP. What’s wrong with having devices communicate in their own native languages and over their desired (most optimal) media? What do we gain by having all devices communicate IP if – and as you (Brian) suggested – we do not first come up with the abstract model? We have a hammer?


With kind regards,



Michel Kohanim, C.E.O

Universal Devices, Inc.


(p) 818.631.0333

(f) 818.708.0755




From: Brian Frank [mailto:brian@skyfoundry.com]
Sent: Tuesday, March 31, 2009 11:11 AM
To: smartgrid-interest@lists.oasis-open.org
Subject: Re: [smartgrid-interest] Draft Charter - Energy Market Information Exchange


Couple of my thoughts since Toby cross-posted some of my oBIX ideas...

I don't suspect that many in this group need to be convinced that technologies like 6LoWPAN create the opportunity to communicate IP all the way out to the edge.  In fact, it is hard to imagine using anything but IP for communication these days - even for sub $10 devices (legacy devices excluded of course).

But just because a 6LoWPAN device speaks IP doesn't necessarily mean that it going to run a SOAP stack:
  - These are typically sub-3$ dollar microprocessors with less than 100KB of memory
  - Low end wireless networks don't run TCP well,  only UDP; this means common techniques for end-to-end security such as TLS are not available
  - Payload size on a 6LoWPAN packet is ideally less than ~80 bytes
  - 6LoWPAN nodes spend most of their time sleeping which makes communication difficult

But these are all surmountable problems if you define an information model which works well end-to-end.  Translating between protocols (HTTP-to-UDP) is pretty easy.  Translating between data encodings is also easy (XML-to-Binary).  But translating between data models is really, really hard and almost always results in a degradation of information.

So my perspective is that the most important task is define the abstract model.  Then you can apply different protocols and encoding as needed as long as everyone is working off the same basic ontology. 

This is exactly what oBIX does.  It defines a very simple, but powerful meta-model for building models.  The oBIX meta-model is based on type theory that embraces the notion that modeling the real-world is a messy and inexact science.  But it turns out to work really well for simple sensors all the way up to million point SCADA systems.


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