One document matched: draft-dokaspar-6lowpan-routreq-07.xml
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<front>
<title abbrev="6LoWPAN Routing Requirements">
Problem Statement and Requirements for 6LoWPAN Routing
</title>
<author initials="E." surname="Kim" fullname="Eunsook Eunah Kim">
<organization>ETRI</organization>
<address>
<postal>
<street>161 Gajeong-dong</street>
<street>Yuseong-gu</street>
<city>Daejeon</city>
<code>305-700</code>
<country>Korea</country>
</postal>
<phone>+82-42-860-6124</phone>
<email>eunah.ietf@gmail.com</email>
</address>
</author>
<author initials="D." surname="Kaspar" fullname="Dominik Kaspar">
<organization>Simula Research Laboratory</organization>
<address>
<postal>
<street>Martin Linges v 17</street>
<city>Snaroya</city>
<code>1367</code>
<country>Norway</country>
</postal>
<phone>+47-6782-8223</phone>
<email>dokaspar.ietf@gmail.com</email>
</address>
</author>
<author initials="C." surname="Gomez" fullname="Carles Gomez">
<organization>Tech. Univ. of Catalonia/i2CAT</organization>
<address>
<postal>
<street>Escola Politecnica Superior de Castelldefels</street>
<street>Avda. del Canal Olimpic, 15</street>
<city>Castelldefels</city>
<code>08860</code>
<country>Spain</country>
</postal>
<phone>+34-93-413-7206</phone>
<email>carlesgo@entel.upc.edu</email>
</address>
</author>
<author initials="C." surname="Bormann" fullname="Carsten Bormann">
<organization>Universität Bremen TZI</organization>
<address>
<postal>
<street>Postfach 330440</street>
<city>Bremen</city>
<code>D-28359</code>
<country>Germany</country>
</postal>
<phone>+49-421-218-63921</phone>
<facsimile>+49-421-218-7000</facsimile>
<email>cabo@tzi.org</email>
</address>
</author>
<date month="November" year="2008" />
<area>General</area>
<workgroup>6LoWPAN Working Group</workgroup>
<keyword>Internet-Draft</keyword>
<abstract>
<t>
This document provides the problem statement for 6LoWPAN
routing. It also defines the requirements for 6LoWPAN routing
considering the low-power characteristics of the network and its devices.
</t>
</abstract>
</front>
<middle>
<section anchor="problems" title="Problem Statement">
<t>
Low-power wireless personal area networks (LoWPANs) are formed by devices
complying to the IEEE 802.15.4 standard <xref target="refs.IEEE802.15.4"/>. LoWPAN devices
are distinguished by their low bandwidth, short range, scarce memory capacity, limited processing capability and other
attributes of inexpensive hardware. In this document, the characteristics of nodes participating in LoWPANs
are assumed to be those described in <xref target="RFC4919"/>.
</t>
<t>
IEEE 802.15.4 networks support star and mesh topologies and consist of two different device types:
reduced-function devices (RFDs) and full-function devices (FFDs). RFDs have the most limited capabilities
and are intended to perform only simple and basic tasks. RFDs may only associate with a single FFD at a time, but
FFDs may form arbitrary topologies and accomplish more advanced functions, such as multi-hop routing.
</t>
<t>
However, neither the IEEE 802.15.4 standard nor the 6LoWPAN format specification
("IPv6 over IEEE 802.15.4" <xref target="RFC4944"/>) specify how mesh topologies
could be obtained and maintained. Thus, the 6LoWPAN formation and multi-hop routing
should be supported by higher layer, either 6LoWPAN adaptation layer or IP layer.
In the IETF, a number of experimental protocols in IP layer have been developed in
many working groups. However, these existing routing protocols may not be satisfying
for mesh routing in a LoWPAN domain, for the following reasons:
<list style="symbols">
<t>
6LoWPAN nodes have special types and roles, such as primary battery-operated RFDs, battery-operated and mains-powered FFDs,
possibly various levels of RFDs and FFDs, mains-powered and high-performance gateways, data aggregators, etc. 6LoWPAN
routing protocols should support multiple device types and roles.
</t>
<t>
The more stringent requirements that apply to 6LoWPANs as opposed to higher performance or non-battery-operated networks.
6LoWPAN nodes are characterized by small memory sizes, low processing power, and are running on very limited power
supplied by primary non-rechargeable batteries (a few kBytes of RAM, a few dozens of KBytes of ROM/flash memory,
and a few MHz of CPU is typical). A node's lifetime is usually defined by the lifetime of its battery.
</t>
<t>
Handling sleeping nodes is very critical in 6LoWPANs, more than in traditional ad-hoc networks. 6LoWPAN nodes might stay
in sleep-mode for most of the time. Time synchronization is important for efficient forwarding of packets.
</t>
<t>
A possibly simpler routing problem; 6LoWPANs might be either transit-networks or stub-networks. We can focus
on stub networks first as existing 6LoWPAN documents (implicitly or explicitly) show the 6LoWPAN picture
under the configuration of stub networks at this moment
<xref target="RFC4944"/>, <xref target="refs.6lowpan.nd"/>. We can simplify
networks by an assumption of no transit networks. (based on the necessity, we may extend the network configuration
including transit network case)
</t>
<t>
A possibly harder routing problem; routing in 6LoWPANs requires to consider power-optimization, harsh environment,
data-aware routing, etc. These are not easy requirements to satisfy together.
</t>
</list>
This creates new challenges on obtaining robust and reliable routing within LoWPANs.
</t>
<t>
The 6LoWPAN problem statement document ("6LoWPAN Problems and Goals" <xref target="RFC4919"/>)
briefly mentions four requirements on routing protocols;
<list>
<t>(a) low overhead on data packets</t>
<t>(b) low routing overhead</t>
<t>(c) minimal memory and computation requirements</t>
<t>(d) support for sleeping nodes considering battery saving</t>
</list>
These four high-level requirements only describe the need for low overhead and power saving.
But, based on the fundamental features of LoWPAN, more detailed routing requirements are presented in this document,
which can lead to further analysis and protocol design.
</t>
<t>
Using the 6LoWPAN header format[6], there are two layers routing protocols can be defined at, commonly referred to
as "mesh-under" and "route-over". The mesh-under approach supports routing under the IP link and is directly based
on the link-layer IEEE 802.15.4 standard, therefore using (64-bit or 16-bit short) MAC addresses. On the other hand,
the route-over approach relies on IP routing and therefore supports routing over possibly various types of
interconnected links (see also <xref target="NetworkStack"/>). Most statements in this document consider
both the mesh-under and route-over cases.
<vspace/>
[Note] ROLL WG is now working on the protocol survey for Low power and Lossy Networks (LLNs),
not specifically for 6LoWPAN. It will decide whether new solution will be developed or not, after that survey.
This document is focused on 6LoWPAN specific requirements, in alignment with ROLL WG.
</t>
<t>
Considering the problems above, The detailed 6LoWPAN routing requirements must be defined.
Application-specific features affect the design of 6lowpan routing requirements and the corresponding solutions.
However, various applications can be profiled by similar technical characteristics, although the detail requirements differ.
(e.g., a few dozens nodes for home lighting system needs appropriate 'scalability' for the applications,
while billions of nodes for highway infrastructure system also needs appropriate 'scalability'.)
This document states the routing requirements to consider the features of 6LoWPAN applications in general, while
trying to give example cases for different cases of routing.
It is noted that this one routing requirement document does not mean that
having a single routing solution may be the best one for all 6LoWPAN applications.
</t>
</section><!-- end of Chapter 1:problem statement-->
<section title="Design Space">
<t>
Apart from a wide variety of routing algorithms possible for 6LoWPAN, the question remains as to whether routing should
be performed mesh-under (in the adaptation layer defined by the 6lowpan format document <xref target="RFC4944"/>), or
in the IP-layer using a route-over approach. The most significant consequence of mesh-under routing is that routing would
be directly based on the IEEE 802.15.4 standard, therefore using (64-bit or 16-bit short) MAC addresses instead of IP
addresses, and a LoWPAN would be seen as a single IP link. In case a route-over mechanism is to be applied to a LoWPAN it
must also support 6LoWPAN's unique properties using global IPv6 addressing.
One radio hop would be seen as a single IP link <xref target="refs.6lowpan.nd"/>.
</t>
<figure anchor='NetworkStack' title="Mesh-under (left) and route-over routing (right)">
<preamble>
<xref target="NetworkStack"/> shows the place of 6LoWPAN routing in the entire network stack;
</preamble>
<artwork>
+-----------------------------+ +-----------------------------+
| Application Layer | | Application Layer |
+-----------------------------+ +-----------------------------+
| Transport Layer (TCP/UDP) | | Transport Layer (TCP/UDP) |
+-----------------------------+ +-----------------------------+
| Network Layer (IPv6) | | Network +---------+ |
+-----------------------------+ | Layer | Routing | |
| 6LoWPAN +---------+ | | (IPv6) +---------+ |
| Adaptation | Routing | | +-----------------------------+
| Layer +---------+ | | 6LoWPAN Adaptation Layer |
+-----------------------------+ +-----------------------------+
| IEEE 802.15.4 (MAC) | | IEEE 802.15.4 (MAC) |
+-----------------------------+ +-----------------------------+
| IEEE 802.15.4 (PHY) | | IEEE 802.15.4 (PHY) |
+-----------------------------+ +-----------------------------+
</artwork>
<postamble/>
</figure>
<t>
In order to avoid packet fragmentation and the overhead for reassembly, routing packets should fit into
a single IEEE 802.15.4 physical frame and application data should not be expanded to an extent that they
no longer fit.
<t>
</t>
If a mesh-under routing protocol is built for operation in 6LoWPAN's adaptation layer,
routing control packets are placed after the 6LoWPAN Dispatch, unless a new code type is assigned for
mesh-under routing. Multiple routing protocols can be supported by the usage of different Dispatch bit sequences.
In a specific use-case can use mesh-header in <xref target="RFC4944"/>for pre-defined L2 forwarding.
When a route-over protocol is built in the IPv6 layer, the Dispatch value can be chosen as one of the Dispatch patterns
for 6LoWPAN compressed or uncompressed IPv6, followed by the IPv6 header.
</t>
<t>
If a 6LoWPAN is formed like the <xref target="6LoWPAN-conf"/> , the PnC is the only IPv6 router in the LoWPAN
in the assumption of <xref target="RFC4944"/>.
The mesh-under routing mechanism MUST be provided to forward packets which require multi-hop forwarding.
</t>
<t>
If route-over routing is used in the stub-network, not only the PnC but also other intermediate nodes
become LoWPAN router and set up IPv6 paths for multi-hop transmission.
</t>
<figure anchor='6LoWPAN-conf' title="An example of a 6LoWPAN">
<preamble></preamble>
<artwork>
O X
/ | PnC: PAN Coordinator
PnC --- O --- O --- X O: Intermediate node (FFD)
/ \ X: End host (FFD or RFD)
X O --- X
|
/ \
O - O -- X
</artwork>
</figure>
<t>
If multiple 6LoPWANs are formed with globally unique IPv6 addresses in the 6LoWPANs,
and node (a) of 6LoWPAN [A] wants to communicate with node (b) of 6LoWPAN [B],
the PnC (= IPv6 router at the edge of the LoWPAN) will be always the default router for the outgoing packet
of the 6LoWPAN.
</t>
</section> <!-- end of Chapter2:Design space-->
<!-- start of section 3.scenario and parameters -->
<section anchor="scenarios" title="Scenario Considerations and Parameters for 6LoWPAN Routing">
<t>
IP-based low-power WPAN technology is still in its early stage of development, but the range of conceivable usage
scenarios is tremendous. The numerous possible applications of sensor networks make it obvious that mesh
topologies will be prevalent in LoWPAN environments and routing will be a necessity for expedient communication.
Research efforts in the area of sensor networking have put forth a large variety of multi-hop routing algorithms
<xref target="refs.bulusu"/>. Most related work focuses on optimizing routing for specific application scenarios,
which can largely be categorized into several models of communication, including the following ones:
<list style="symbols">
<t>Flooding (in very small networks)</t>
<t>Data-aware routing (dissemination vs. gathering)</t>
<t>Event-driven vs. query-based routing</t>
<t>Geographic routing</t>
<t>Probabilistic routing</t>
<t>Hierarchical routing</t>
</list>
Depending on the topology of a 6LoWPAN and the application(s) running over it, different types of routing
may be used. However, this document abstracts from application-specific communication and describes
general routing requirements valid for overall routing in 6LoWPANs.
</t>
<t>
The following parameters can be used to describe specific scenarios in which the candidate routing protocols could
be evaluated.
</t>
<list style="letters">
<t>Network Properties:</t>
<list style="symbols">
<t>
Number of Devices, Density and Network Diameter: <vspace/>
These parameters usually affect the routing state directly
(e.g. the number of entries in a routing table or neighbor
list). Especially in large and dense networks, policies must
be applied for discarding "low-quality" and stale routing
entries in order to prevent memory overflow.
</t>
<t>
Connectivity: <vspace/>
Due to external factors or programmed disconnections, a 6LoWPAN
can be in several states of connectivity; anything in the
range from "always connected" to "rarely connected". This
poses great challenges to the dynamic discovery of routes
across a LoWPAN.
</t>
<t>
Dynamicity (include mobility): <vspace/>
Location changes can be induced by unpredictable external
factors or by controlled motion, which may in turn cause route
changes. Also, nodes may dynamically be introduced into a
LoWPAN and removed from it later. The routing state and the
volume of control messages is heavily dependent on the number
of moving nodes in a LoWPAN and their speed.
</t>
<t>
Deployment: <vspace/>
In a LoWPAN, it is possible for nodes to be scattered randomly
or to be deployed in an organized manner. The deployment can
occur at once, or as an iterative process, which may also
affect the routing state.
</t>
<t>
Spatial Distribution of Nodes and Gateways: <vspace/>
Network connectivity depends on node spatial distribution besides
other factors like device number, density and transmission range. For
instance, nodes can be placed on a grid, or can be randomly placed in
an area (bidimensional Poisson distribution), etc.
In addition, if the LoWPAN is connected to other networks through
infrastructure nodes called gateways, the number and spatial
distribution of gateways affects network congestion and available
bandwidth, among others.
</t>
<t>
Traffic Patterns, Topology and Applications: <vspace/>
The design of a LoWPAN and the requirements on its application
have a big impact on the network topology and the most efficient routing type to be
used. For different traffic patterns (point-to-point,
multipoint-to-point, point-to-multipoint) and network
architectures, various routing mechanisms have been
introduced, such as data-aware, event-driven, address-centric,
and geographic routing.
</t>
<t>
Quality of Service (QoS): <vspace/>
For mission-critical applications, support of QoS is mandatory
in resource-constrained LoWPANs and cannot be achieved without
a certain degree of routing protocol overhead.
</t>
<t>
Security: <vspace/>
LoWPANs may carry sensitive information and require a high
level of security support where the availability, integrity,
and confidentiality of data are primordial. Secured messages
cause overhead and affect the power consumption of LoWPAN
routing protocols.
</t>
</list> <!-- end of network parameters-->
<t>Node Parameters:</t>
<list style="symbols">
<t>
Processing Speed and Memory Size: <vspace/>
These basic parameters define the maximum size of the routing
state. LoWPAN nodes may have different performance
characteristics beyond the common RFD/FFD distinction.
</t>
<t>
Power Consumption and Power Source: <vspace/>
The number and topology of battery- and mains-powered nodes in
a LoWPAN affect routing protocols in their selection of
optimal paths for network lifetime maximization.
</t>
<t>
Transmission Range: <vspace/>
This parameter affects routing. For example, a
high transmission range may cause a dense network, which in
turn results in more direct neighbors of a node, higher
connectivity and a larger routing state.
</t>
<t>
Traffic Pattern:
This parameter affects routing since high-loaded nodes (either
because they are the source of packets to be transmitted or due
to forwarding) may incur a greater contribution to delivery
delays than low-loaded nodes. This applies to both data
packets and routing control messages themselves.
</t>
</list> <!--end of node parameters-->
<t>Link Parameters:</t>
<list style="symbols">
<t>
Throughput:
<vspace/>
<vspace/>
The maximum user data throughput of a bulk data transmission between a single sender and
a single receiver through an unslotted IEEE 802.15.4 2.4 GHz channel in ideal conditions is
as follows <xref target="refs.Latre"/>:
<list style="symbols">
<t>16-bit MAC addresses, unreliable mode: 151.6 kbps </t>
<t>16-bit MAC addresses, reliable mode: 139.0 kbps </t>
<t>64-bit MAC addresses, unreliable mode: 135.6 kbps </t>
<t>64-bit MAC addresses, reliable mode: 124.4 kbps </t>
</list>
<vspace/>
<vspace/>
In the case of 915 MHz band:
<list style="symbols">
<t> 16-bit MAC addresses, unreliable mode: 31.1 kbps </t>
<t> 16-bit MAC addresses, reliable mode: 28.6 kbps </t>
<t> 64-bit MAC addresses, unreliable mode: 27.8 kbps </t>
<t> 64-bit MAC addresses, reliable mode: 25.6 kbps </t>
</list>
<vspace/>
<vspace/>
In the case of 868 MHz band:
<list style="symbols">
<t> 16-bit MAC addresses, unreliable mode: 15.5 kbps </t>
<t> 16-bit MAC addresses, reliable mode: 14.3 kbps </t>
<t> 64-bit MAC addresses, unreliable mode: 13.9 kbps </t>
<t> 64-bit MAC addresses, reliable mode: 12.8 kbps </t>
</list>
</t>
<t>
Latency: <vspace/>
The range of latencies of a frame transmission between a single sender and
a single receiver through an unslotted IEEE 802.15.4 2.4 GHz channel in ideal conditions
are as follows [20]:
<list style="symbols">
<t> 16-bit MAC addresses, unreliable mode: [1.92 ms, 6.02 ms] </t>
<t> 16-bit MAC addresses, reliable mode: [2.46 ms, 6.56 ms] </t>
<t> 64-bit MAC addresses, unreliable mode: [2.75 ms, 6.02 ms] </t>
<t> 64-bit MAC addresses, reliable mode: [3.30 ms, 6.56 ms] </t>
</list>
<vspace/>
In the case of 915 MHz band:
<list style="symbols">
<t> 16-bit MAC addresses, unreliable mode: [5.85 ms, 29.35 ms] </t>
<t> 16-bit MAC addresses, reliable mode: [8.35 ms, 31.85 ms] </t>
<t> 64-bit MAC addresses, unreliable mode: [8.95 ms, 29.35 ms] </t>
<t> 64-bit MAC addresses, reliable mode: [11.45 ms, 31.82 ms] </t>
</list>
<vspace/>
In the case of 868 MHz band:
<list style="symbols">
<t> 16-bit MAC addresses, unreliable mode: [11.7 ms, 58.7 ms] </t>
<t> 16-bit MAC addresses, reliable mode: [16.7 ms, 63.7 ms] </t>
<t> 64-bit MAC addresses, unreliable mode: [17.9 ms, 58.7 ms] </t>
<t> 64-bit MAC addresses, reliable mode: [22.9 ms, 63.7 ms] </t>
</list>
</t>
</list> <!-- end of link parameters-->
</list> <!-- end of parameter list-->
</section> <!-- end of Chapter3: Scenarios and Parameters-->
<!-- start of section 4.routing requirements -->
<section anchor="Requirements" title="6LoWPAN Routing Requirements">
<t>
This section defines a list of requirements for 6LoWPAN routing. The
most important design property unique to low-power networks is that 6LoWPANs
have to support multiple device types and roles, for example:
<list style="symbols">
<t>primarily battery-operated host nodes</t>
<t>mains-powered host nodes</t>
<t>possibly various levels of nodes (data aggregators, relayers, etc.)</t>
<t>mains-powered, high-performance gateway(s)</t>
</list>
<t>
Due to these unique device types and roles 6LoWPANs need to consider
the following two primary features:
</t>
<list style="symbols">
<t>
Power conservation: some devices are mains-powered, but most are
battery-operated and need to last several months to a few years
with a single AA battery. Many devices are mains-powered most of
the time, but still need to function for possibly extended periods
from batteries (e.g. on a construction site before building power
is switched on for the first time).
</t>
<t>
Low performance: tiny devices, small memory sizes, low-performance processors,
low bandwidth, high loss rates, etc.
</t>
</list>
These fundamental features of LoWPANs affect the design of routing
solutions, so that existing routing specifications should be
simplified and modified to the smallest extent possible when there are appropriate solutions to adapt,
otherwise, new solutions should be introduced in order to
fit the low-power requirements of LoWPANs, meeting the following
requirements:
</t>
<!-- start of Section 4.1: Device -->
<section anchor="reqs1" title="Support of 6LoWPAN Device Properties">
<t>
The general objectives listed in this subsection should be followed
by 6LoWPAN routing protocols. The importance of each requirement is
dependent on what device type the protocol is running on and what
the role of the device is. The following requirements are based on battery-powered LoWPAN devices.
</t>
<t>
[R01] 6LoWPAN routing protocols SHOULD have small code size of routing protocol stack
and require low routing state to fit the typical 6LoWPAN node capacity.
(e.g., code size considering its typical flash memory size, and routing table less than 32 entries)
</t>
<list>
<t> <!-- R01: small code-->
A LoWPAN routing protocol solution should consider the limited memory size
typically starting at 4KB.
RAM size of 6LoWPAN nodes often ranges between 2KB and 10KB,
and program flash memory normally consists of 48KB to 128KB.
(e.g., in the current market, MICAz has 128KB program flash,
4KB EEPROM, 512KB external flash ROM; TIP700CM has 48KB program
flash, 10KB RAM, 1MB external flash ROM).
</t>
<t>
Due to these hardware restrictions, code length should be considered to
fit within a small memory size; no more than 48KB to 128KB of flash memory including
at least a few tens of KB of application code size.
A routing protocol of low complexity helps to achieve
the goal of reducing power consumption, improves robustness,
requires lower routing state, is easier to analyze, and may be
implicitly less prone to security attacks.
</t>
<t>
In addition, operation with low routing state (such as routing tables and neighbor lists)
SHOULD be maintained since some typical memory sizes preclude to store
state of a large number of nodes. For instance, industrial monitoring applications
need to support at maximum 20 hops <xref target="refs.roll.industry"/>.
Small networks, can be designed to support a smaller number of hops.
It is highly dependent on network architecture,
but considering the 6LoWPAN device properties, there should be at least one mode of operation that can
function with 32 forwarding entries or less.
</t>
</list> <!-- end of R01-->
<t> <!-- R02: no fragmentation-->
[R02] 6LoWPAN routing protocol control messages SHOULD not create
fragmentation of physical layer (PHY) frames.</t>
<list>
<t>
In order to save energy, routing overhead should be minimized
to prevent fragmentation of frames on the physical layer
(PHY). Therefore, 6LoWPAN routing should not cause packets to
exceed the IEEE 802.15.4 frame size. This reduces the energy
required for transmission, avoids unnecessary waste of bandwidth,
and prevents the need for packet reassembly. As calculated in
RFC4944 <xref target="RFC4944"/>, the maximum size of a 6LoWPAN
frame, in order not to cause fragmentation on the PHY layer, is
81 octets.
</t>
</list> <!-- end of R02: no fragmentation-->
<t> <!-- R03: minimal power -->
[R03] 6LoWPAN routing protocols SHOULD cause minimal power
consumption by the efficient use of control packets
(e.g., minimize expensive multicast which cause broadcast to the entire LoWPAN).
</t>
<list>
<t>
Routing protocol design for 6LoWPAN should consider IEEE 802.15.4
link layer feedback on energy consumption. Power-aware routing is
a non-trivial task, because it is affected by many mutually
conflicting goals:
<list style="symbols">
<t>Minimization of total energy consumed in the network</t>
<t>Maximization of the time until a network partition occurs</t>
<t>Minimizing the energy variance at each node</t>
<t>Minimizing the cost per packet</t>
</list>
while maintaining packet delivery ratio, latency or other requirements
depending on each application.
</t>
<t>
One way of battery lifetime optimization is by achieving a minimal
control message overhead. Compared to functions such as in many devices,
computational operations or taking sensor samples, radio communications
is by far the dominant factor of power consumption <xref target="refs.SmartDust"/>.
Power consumption of transmission and/or reception depends linearly
on the length of data units and on the frequency of transmission
and reception of the data units <xref target="refs.Shih"/>.
</t>
<t>
In <xref target="refs.Hill"/> the energy consumption of two
example RF controllers for low-power nodes is shown. The TR1000
radio consumes 21mW on transmitting at 0.75mW, and 15mW on reception
(with a receiver sensitivity of -85dBm). The CC1000 consumes 31.6mW on
transmitting 0.75mW, and 20mW for receiving (with a receiver sensitivity of -105dBm).
<xref target="refs.Hill"/> explains the power continuation under the concept of
an idealized power source: based on the energy of idealized AA battery,
the CC1000 can transmit for approximately 4 days straight
or receive for 9 days straight.
</t>
<t>
One multicast packet causes reception of the entire nodes in the LoWPAN, while
only the nodes in the path use the reception energy at unicast. Thus, 6LoWPAN routing
protocol SHOULD minimize the control cost by the routing packets.
</t>
</list> <!-- end of R03-->
</section> <!-- end of section 4.1 -->
<!-- start of section 4.2 : Link -->
<section anchor="reqs2" title="Support of 6LoWPAN Link Properties">
<t>
6LoWPAN links have the characteristics of low bandwidth and possibliy high loss rates.
The routing requirements described in this subsection are from the link properties.
</t>
<t> <!-- start of R04: NEWLY added on Nov. 3, by EUNAH-->
[R04] The design of routing protocols for 6LoWPANs must consider the fact that
packets are to be delivered with reasonable probability.
</t>
<list>
<t>
Latency requirements may differ from a few hundreds milliseconds to minutes, depending on the
type of application.
Real-time building automation applications usually need response times below 500 ms between ingress and egress, while
forced entry securty alerts must be routed to one or more fixed or mobile user devices
within 5 seconds <xref target="refs.roll.building"/>.
Non-critical closed loop applications for industrial automation
have latency requirements that can be as low as 100 ms but many control loops are
tolerant of latencies above 1s <xref target="refs.roll.industry"/>. In contrast to this,
urban monitoring applications allow latencies smaller than the typical intervals used for
reporting sensed information; for instance, in the order of seconds or
minutes <xref target="refs.roll.urban"/>.
</t>
<t>
The range of latencies of a frame transmission between a single sender and
a single receiver through an unslotted IEEE 802.15.4 2.4 GHz channel is between 2.46ms and 6.02ms
in 64 bit MAC address unreliable mode and 2.20 ms to 6.56ms in 64 bit address reliable mode.
The range of latencies of 868 MHz band is from 11.7 ms to 63.7 ms, different from address types and
reliable/unreliable mode.
</t>
<t>
Considering the 6LoWPAN link latency, routing protocols can calculate the
probable delivering time of the control packets in a normal case not more than a few hundred ms
between two nodes.
</t>
</list> <!-- end of R04 -->
<t> <!-- start of R05-->
[R05] 6LoWPAN routing protocols SHOULD be robust to dynamic loss
caused by link failure or device unavailability either in short-term
(e.g. due to RSSI variation, interference variation, noise and asynchrony)
or in long-term (e.g. due to a depleted power source, hardware breakdown,
operating system misbehavior, etc).
</t>
<list>
<t>
An important trait of 6LoWPAN devices is their unreliability due to
limited system capabilities, and also because they might be closely
coupled to the physical world with all its unpredictable variation.
In harsh environments, LoWPANs easily suffer from
link failure. Collision or link failure easily increases Send
Queue/Receive Queue (SQ/RQ) and it can lead to queue overflow and
packet losses.
</t>
<t>
For home applications, where users expect feedback after carrying out actions
(such as handling a remote control while moving around), routing protocols must converge
within 2 seconds if the destination node of the packet has moved <xref target="refs.roll.home"/>.
The tolerance of the recovery time can vary dependent on the application,
however, the routing protocol must provide the detection of short-term unavailability
and long-term disappearance.
The routing protocol has to exploit network resources (e.g. path redundancy)
to offer good network behavior despite of node failure.
</t>
</list> <!-- end of R05-->
</section>
<!-- end of section 4.2: link -->
<!-- start of section 4.3 : Network-->
<section anchor="reqs3" title="Support of 6LoWPAN Network Characteristics">
<t>
6LoWPAN can be deployed with different tolerance levels, network scales,
topologies, levels of mobility, etc.
In any case, 6LoWPAN must be maintain low energy consumption.
The requirements described in the following subsection are derived from the network feature of
6LoWPANs.
</t>
<t> <!-- R06: sleep node-->
[R06] 6LoWPAN routing protocols SHOULD be reliable despite unresponsive nodes
due to periodic hibernation. (e.g., management with the duty cycle)
</t>
<list>
<t>
Many nodes in 6LoWPAN environments might periodically hibernate
(i.e. disable their transceiver activity) in order to save energy.
Therefore, routing protocols must ensure robust packet
delivery despite nodes frequently shutting off their radio
transmission interface. Feedback, for instance from periodic
beacons, from the lower IEEE 802.15.4 layer may be considered
to enhance the power-awareness of 6LoWPAN routing protocols.
</t>
<t>
In <xref target="refs.Hill"/> it is explained that CC1000-based nodes must operate at a duty cycle
of approximately 2% to survive for one year from idealized AA battery power source. For home automation purposes, it is suggested that
that the devices have to maximize the sleep phase with a duty cycle lower
than 1% <xref target="refs.roll.home"/>, while in building automation, batteries must be operational
for at least 5 years when the sensing devices are transmitting data (e.g. 64 bytes) once
per minute <xref target="refs.roll.building"/>.
</t>
<t>
Dependent on the application in use, packet rates differ from 1/sec to 1/day.
Routing protocols need to know the cycle of the packet transmission
and utilize the information to calculate routing pathes.
</t>
</list> <!-- end of R06-->
<t> <!-- R07: metrics -->
[R07] The metric used by 6LoWPAN routing protocols MAY utilize
a combination of the inputs provided by the MAC layer and other measures
to obtain optimal path considering energy balance and link quality.
</t>
<list>
<t>
Simple hop-count-only mechanisms may be inefficient in 6LoWPANs.
In home, buildings, or infrastructure, some nodes will be installed
with mains-powered. Such power-installed node MUST be considered
as a relay point for more roles in packet delivery.
6LoWPAN routing protocols MUST know the power source of the nodes.
</t>
<t>
There is a Link Quality Indicator (LQI), Link Delivery Ratio (LDR), or/and RSSI from
IEEE 802.15.4 that may be taken into account for better metrics.
The metric to be used (and its goal) may depend on
application and requirements.
</t>
<t>
The numbers in <xref target="LDR"/> represent the Link Delivery Ratio (LDR)
between each pair of nodes. There are studies that show a piecewise linear dependence between LQI and
LDR <xref target="refs.Chen"/>.
</t>
<figure anchor='LDR' title="An example network">
<preamble></preamble>
<artwork>
0.6
A-------C
\ /
0.9 \ / 0.9
\ /
B
</artwork>
</figure>
<t>
In this simple example, there are two options in routing from node A to node C:
</t>
<list style="letters">
<t>Path AC:</t>
<list style="symbols">
<t>(1/0.6) = 1.67 avg. transmissions needed for each packet</t>
<t>one-hop path</t>
<t>good in energy consumption, bad in delivery ratio (0.6)</t>
</list>
<t>Path ABC</t>
<list style="symbols">
<t>2*(1/0.81) = 2.47 avg. transmissions needed for each packet</t>
<t>two-hop path</t>
<t>bad in energy consumption, good in delivery ratio (0.81)</t>
</list>
</list>
<t>
If energy consumption of the network must be minimized, path AC
is the best (this path would be chosen by hop count metric).
However, if delivery ratio in that case is not sufficient, best
path is ABC (it would be chosen by an LQI based metric).
Combinations of both of metrics can be used.
</t>
</list> <!-- end of R07:metrics-->
<t> <!-- R08-->
[R08] 6LoWPAN routing protocols SHOULD be designed to achieve both
scalability from a few nodes to millions of nodes and minimality in terms of used system resources.
</t>
<list>
<t>
A 6LoWPAN may consist of just a couple of nodes (for instance in
a body-area network), but may expand to much higher numbers of
devices (e.g. monitoring of a city infrastructure or a highway).
For home automation applications it is envisioned that the routing protocol
must support 250 devices in the network <xref target="refs.roll.home"/>,
while routing protocols for metropolitan-scale sensor networks must be capable of clustering
a large number of sensing nodes into regions
containing on the order of 10^2 to 10^4 sensing nodes each <xref target="refs.roll.urban"/>.
It is therefore necessary that routing mechanisms are designed
to be scalable for operation in various network sizes. However,
due to a lack of memory size and computational power, 6LoWPAN
routing might limit forwarding entries to a small number, such
as at maximum 32 routing table entries.
</t>
</list> <!--end of R08-->
<t> <!--R09 -->
[R09] The procedure of route repair and related control messages
should not harm overall energy consumption from the routing protocols.
</t>
<list>
<t>
Local repair improves throughput and end-to-end latency, especially
in large networks. Since routes are repaired quickly, fewer data
packets are dropped, and a smaller number of routing protocol
packet transmissions is needed since routes can be repaired without
source initiated Route Discovery <xref target="refs.Lee"/>.
</t>
</list> <!-- end of R09-->
<t> <!-- R10-->
[R10] 6LoWPAN routing protocols SHOULD allow for dynamically adaptive
topologies and mobile nodes. When supporting dynamic topologies and
mobile nodes, route maintenance should be managed by keeping in mind
the goal of a minimal routing state.
</t>
<list>
<t>
Building monitoring applications, for instance, require that the mobile devices
SHOULD be capable of unjoining (handing-off) from an old network joining
onto a new network within 15 seconds <xref target="refs.roll.building"/>.
More interactive applications such as used in home automation systems, where users are giving input
and expect instant feedback, mobility requirements are also stricter and
a convergence time below 0.5 seconds is commonly required <xref target="refs.roll.home"/>.
In industrial environments, where mobile equipment such as cranes move around,
vehicular speeds of up to 35 kmph are required to be supported by the routing protocol
<xref target="refs.roll.industry"/>. Currently, 6LoWPANs are not being used for such a fast mobility
cases, but dynamic association and deassociation MUST be supported in 6LoWPAN.
</t>
<t>
There are several challenges that should be addressed by a 6LoWPAN
routing protocol in order to create robust routing in dynamic
environments:
<list style="symbols">
<t> Mobile nodes changing their location inside a 6LoWPAN:
<vspace/>
If the nodes' movement pattern is unknown, mobility cannot
easily be detected or distinguished from the routing protocols.
Mobile nodes can be treated as nodes that disappear and re-appear
in another place. Movement pattern tracking increases complexity and can be
avoided by handling moving nodes using reactive route updates.
</t>
<t> Movement of a 6LoWPAN with respect to other (inter)connected 6LoWPANs:
<vspace/>
Within stub networks, more powerful gateway nodes need to be
configured to handle moving 6LoWPANs.
</t>
<t> Nodes permanently joining or leaving the 6LoWPAN:
<vspace/>
In order to ease routing table updates and reduce error
control messages, it would be helpful if nodes leaving the network inform
their coordinator about their intention to disassociate.
</t>
</list> <!--end of symbol list-->
</t>
</list> <!-- end of R10-->
<t> <!-- R11: traffic pattern -->
[R11] 6LoWPAN routing protocol SHOULD support various traffic patterns;
point-to-point, point-to-multipoint, and multipoint-to-point,
while avoid excessive multicast traffic (broadcast in Link) in 6LoWPAN.
</t>
<list>
<t>
6LoWPANs often have point-to-multipoint or multipoint-to-point
traffic patterns. Many emerging applications include point-to-point
communication as well. 6LoWPAN routing protocols should
be designed with the consideration of forwarding packets from/to
multiple sources/destinations. Current WG drafts in the ROLL working group
explain that the workload or traffic pattern of use cases for
6LoWPANs tend to be highly structured, unlike the any-to-any data
transfers that dominate typical client and server workloads. In many
cases, exploiting such structure may simplify difficult problems
arising from resource constraints or variation in connectivity.
</t>
</list> <!-- end of R11-->
</section>
<!-- end of section 4.3-->
<!-- start of section :4.4 security -->
<section anchor="reqs4" title="Support of Security">
<t>
The routing requirement described in this subsection allow secure
transmission of routing messages. Solutions may take into account the
specific features of IEEE 802.15.4 MAC layers.
</t>
<t> <!-- R12: security-->
[R12] 6LoWPAN protocols SHOULD support secure delivery of control messages.
A minimal security level can be achieved by utilizing AES-based mechanism
provided by IEEE 802.15.4.
</t>
<list>
<t>
Security threats within LoWPANs may be different from existing
threat models in ad-hoc network environments. Neighbor Discovery
in IEEE 802.15.4 links may be susceptible to threats as listed in
RFC3756 <xref target="RFC3756"/>. Bootstrapping may also impose additional threats.
Security is also very important for designing robust routing
protocols, but it should not cause significant transmission
overhead. While there are applications which require very high security,
such as in traffic control, other applications are less easily harmed by
wrong node behavior, such as a home entertainment system.
</t>
<t>
The IEEE 802.15.4 MAC provides an AES-based security mechanism. Routing
protocols need to define how this mechanism can be used to obtain
the intended security. Byte overhead of the mechanism, which depends
on the security services selected, must be considered. In the worst
case in terms of overhead, the mechanism consumes 21 bytes of MAC
payload.
</t>
</list> <!-- end of R12 -->
</section>
<!-- end of section: 4.4 secuirty -->
<!-- start of section: 4.5 mesh-under -->
<section anchor="reqs5" title="Support of Mesh-under Forwarding">
<t>
One 6LoWPAN may be built as one IPv6 link. In this case, mesh-under
forwarding/routing must be supported.
The routing requirements described in this subsection allow
optimization and correct operation of routing solutions taking into
account the specific features mesh-under routing.
</t>
<t>
[R13] In case a routing protocol operates in 6LoWPAN's adaptation layer,
then routing tables and neighbor lists MUST support 16-bit short and
64-bit extended addresses.
</t>
<t>
[R14] For neighbor discovery, 6LoWPAN devices SHOULD avoid sending
"Hello" messages. Instead, link-layer mechanisms (such as
acknowledgments or beacon responses) MAY be utilized to keep track of
active neighbors.
</t>
<list>
<t>
After an IEEE 802.15.4 PAN coordinator permits a device to join, the
new device adds the PAN coordinator to its neighbor list and starts
transmitting periodic beacons. These beacons can be used as an
indication of current neighbors.
</t>
</list>
<t>
[R15] In case there are one or more alternative PAN coordinators,
the coordinators MAY take the role of keeping track of node association and
de-association within the LoWPAN.
</t>
<t>
[R16] Alternative PAN coordinators, if any, MAY be a relay point of
group-targeting message instead of using multicast (broadcast in the link layer).
</t>
<list>
<t>
For example, RS and RA can be only sent to the coordinators,
instead of being multicast. The coordinators take the role to pass the packets
to their own neighbors.
</t>
</list>
</section>
<!-- end of mesh-under req -->
</section>
<!-- end of Requirement section-->
<section title="Security Considerations">
<t>Security issues are described in <xref target="reqs4"/>. More security considerations will follow
the 6LoWPAN security analysis work.</t>
</section>
<section title="Acknowledgements">
<t>The authors thank Myung-Ki Shin for giving the idea of writing this draft.
The authors also thank to S. Chakrabarti who gave valuable comments for mesh-under requirements.</t>
</section>
</middle>
<back>
<references title='Normative References'>&RFC2119;&RFC3756;&RFC4919;&RFC4944;
<reference anchor="refs.IEEE802.15.4">
<front>
<title>IEEE Std. 802.15.4-2006 (as amended)</title>
<author><organization>IEEE Computer Society</organization></author>
<date month="" year="2007"/>
</front>
</reference>
<!-- previously used references to IEEE 802.15.4 standard (before draft-dokaspar-6lowpan-routreq-07)
<reference anchor="refs.IEEE802.15.4">
<front>
<title>IEEE Std. 802.15.4-2003</title>
<author><organization>IEEE Computer Society</organization></author>
<date month="October" year="2003"/>
</front>
</reference>
<reference anchor="refs.IEEE802.15.4-2006">
<front>
<title>IEEE Std. 802.15.4-2006</title>
<author><organization>IEEE Computer Society</organization></author>
<date month="September" year="2006"/>
</front>
</reference>-->
</references>
<references title='Informative References'>
<reference anchor="refs.bulusu">
<front>
<title>Wireless Sensor Networks</title>
<author initials="N." surname="Bulusu" fullname="Nirupama Bulusu"></author>
<author initials="S." surname="Jha" fullname="Sanjay Jha"></author>
<date month="July" year="2005"/>
</front>
</reference>
<reference anchor="refs.6lowpan.nd">
<front>
<title>LoWPAN Neighbor Discovery Extensions, draft-shelby-6lowpan-nd-00 (work in progress)</title>
<author initials="Z." surname="Shelby" fullname=""></author>
<author initials="P." surname="Thubert" fullname=""></author>
<author initials="J." surname="Hui" fullname=""></author>
<author initials="S." surname="Chakrabarti" fullname=""></author>
<author initials="E." surname="Nordmark" fullname=""></author>
<date month="October" year="2008"/>
</front>
</reference>
<reference anchor="refs.SmartDust">
<front>
<title>Smart Dust: Wireless Networks of Millimeter-Scale Sensor Nodes</title>
<author initials="K. S. J." surname="Pister" fullname=""></author>
<author initials="B. E." surname="Boser" fullname=""></author>
<date month="" year=""/>
</front>
</reference>
<reference anchor="refs.Hill">
<front>
<title>System Architecture for Wireless Sensor Networks</title>
<author initials="J." surname="Hill" fullname="J. Hill"></author>
<date month="" year=""/>
</front>
</reference>
<reference anchor="refs.Lee">
<front>
<title>Scalability Study of the Ad Hoc On-Demand Distance-Vector Routing Protocol</title>
<author initials="S. J." surname="Lee" fullname=""></author>
<author initials="E. M." surname="Belding-Royer" fullname=""></author>
<author initials="C. E." surname="Perkins" fullname=""></author>
<date month="March" year="2003"/>
</front>
</reference>
<reference anchor="refs.Shih">
<front>
<title>Physical Layer Driven Protocols and Algorithm Design for Energy-Efficient Wireless Sensor Networks</title>
<author initials="E." surname="Shih" fullname=""></author>
<date month="July" year="2001"/>
</front>
</reference>
<reference anchor="refs.Chen">
<front>
<title>Ad-Hoc Multicast Routing on Resource-Limited Sensor Nodes</title>
<author initials="B." surname="Chen" fullname=""></author>
<author initials="K. K." surname="Muniswamy-Reddy" fullname=""></author>
<author initials="M." surname="Welsh" fullname=""></author>
<date month="" year="2006"/>
</front>
</reference>
<reference anchor="refs.roll.home">
<front>
<title>Home Automation Routing Requirement in Low Power and Lossy Networks, draft-ietf-roll-home-routing-reqs-04 (work in progress)</title>
<author initials="A." surname="Brandt" fullname="Anders Brandt"></author>
<author initials="J." surname="Buron" fullname="Jakob Buron"></author>
<author initials="G." surname="Porcu" fullname="Giorgio Porcu"></author>
<date month="October" year="2008"/>
</front>
</reference>
<reference anchor="refs.roll.industry">
<front>
<title>Industrial Routing Requirements in Low Power and Lossy Networks, draft-ietf-roll-indus-routing-reqs-01 (work in progress)</title>
<author initials="K." surname="Pister" fullname="Kris Pister"></author>
<author initials="P." surname="Thubert" fullname="Pascal Thubert"></author>
<author initials="S." surname="Dwars" fullname="Sicco Dwars"></author>
<author initials="T." surname="Phinney" fullname="Tom Phinney"></author>
<date month="July" year="2008"/>
</front>
</reference>
<reference anchor="refs.roll.urban">
<front>
<title>Urban WSNs Routing Requirements in Low Power and Lossy Networks, draft-ietf-roll-urban-routing-reqs-02 (work in progress)</title>
<author initials="M." surname="Dohler" fullname="Mischa Dohler"></author>
<author initials="T." surname="Watteyne" fullname="Thomas Watteyne"></author>
<author initials="T." surname="Winter" fullname="Tim Winter"></author>
<author initials="D." surname="Barthel" fullname="Dominique Barthel"></author>
<author initials="C." surname="Jacquenet" fullname="Christian Jacquenet"></author>
<date month="October" year="2008"/>
</front>
</reference>
<reference anchor="refs.roll.building">
<front>
<title> Building Automation Routing Requirements in Low Power and Lossy Networks, draft-ietf-roll-building-routing-reqs-01 (work in progress)</title>
<author initials="J." surname="Martocci" fullname=""></author>
<author initials="P." surname="De Mil" fullname=""></author>
<author initials="W." surname="Vermeylen" fullname=""></author>
<author initials="N." surname="Riou" fullname=""></author>
</front>
</reference>
<reference anchor="refs.Latre">
<front>
<title>Throughput and Delay Analysis of Unslotted IEEE 802.15.4</title>
<author initials="M." surname="Latre" fullname=""></author>
<author initials="P." surname="De Mil" fullname=""></author>
<author initials="I." surname="Moerman" fullname=""></author>
<author initials="B." surname="Dhoedt" fullname=""></author>
<author initials="P." surname="Demeester" fullname=""></author>
<date month="May" year="2006"/>
</front>
</reference>
</references>
</back>
</rfc>| PAFTECH AB 2003-2026 | 2026-04-24 04:23:24 |