6LoWPAN Working Group D. Kaspar
Internet-Draft Simula Research Laboratory
Expires: October 4, 2008 E. Kim
ETRI
C. Gomez
Technical University of
Catalonia/i2CAT
C. Bormann
Universitaet Bremen TZI
April 2, 2008
Problem Statement and Requirements for 6LoWPAN Mesh Routing
draft-dokaspar-6lowpan-routreq-05
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Abstract
This document provides the problem statement for 6LoWPAN mesh
routing. It also defines the requirements for 6LoWPAN mesh routing
considering the low-power characteristics of the network and its
devices.
Table of Contents
1. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 3
2. Design Space . . . . . . . . . . . . . . . . . . . . . . . . . 6
3. Scenario Considerations . . . . . . . . . . . . . . . . . . . 8
4. 6LoWPAN Routing Requirements . . . . . . . . . . . . . . . . . 11
4.1. Routing Requirements depending on the 6LoWPAN Device
Properties . . . . . . . . . . . . . . . . . . . . . . . . 11
4.2. Routing Requirements depending on Types of 6LoWPAN
Applications . . . . . . . . . . . . . . . . . . . . . . . 14
4.3. MAC-coupled Requirements . . . . . . . . . . . . . . . . . 16
5. Security Considerations . . . . . . . . . . . . . . . . . . . 19
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 20
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 21
7.1. Normative References . . . . . . . . . . . . . . . . . . . 21
7.2. Informative References . . . . . . . . . . . . . . . . . . 21
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 23
Intellectual Property and Copyright Statements . . . . . . . . . . 24
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1. Problem Statement
Low-power wireless personal area networks (LoWPANs) are formed by
devices complying to the IEEE 802.15.4 standard [7][8]. 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
[5].
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.
However, neither the IEEE 802.15.4 standard nor the 6LoWPAN format
specification ("IPv6 over IEEE 802.15.4" [6]) specify how mesh
topologies could be obtained and maintained. Routing in mesh
networks has been the subject of much research. Also in the IETF, a
number of experimental protocols have been developed in the Mobile
Ad-hoc Networks (MANET) working group, such as AODV [2], OLSR [3], or
DYMO [11]. However, these existing routing protocols may not be
satisfying for mesh routing in a LoWPAN domain, for the following
reasons:
o 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.
o The more stringent requirements that apply to LoWPANs as opposed
to higher performance or non-battery-operated networks. LoWPAN
nodes are characterized by small memory sizes, low processing
power, and are running on very limited power supplied by primary
non-rechargeable batteries. A node's lifetime is usually defined
by the lifetime of its battery.
o 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.
o A possibly simpler routing problem; 6LoWPANs might be either
transit-networks or stub-networks. However, we can focus on stub
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networks first as many practical 6LoWPANs are configured with stub
networks at this moment. We can simplify networks by an
assumption of no transit networks.
o 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.
This creates new challenges on obtaining robust and reliable mesh
routing within LoWPANs.
Using the 6LoWPAN header format, 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 Figure 1).
Most statements in this draft apply to both the mesh-under and route-
over cases.
The 6LoWPAN problem statement document ("6LoWPAN Problems and Goals"
[5]) briefly mentions four requirements on routing protocols;
(a) low overhead on data packets
(b) low routing overhead
(c) minimal memory and computation requirements
(d) support for sleeping nodes considering battery saving
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.
In summary, the main problems of mesh routing in LoWPANs are:
1. Existing routing solutions do not operate in 6LoWPAN's adaptation
layer (and do not support the addressing scheme defined by IEEE
802.15.4). If a routing protocol for 6LoWPAN is designed to run
in the IP layer, it should be adapted to meet the 6LoWPAN-
specific requirements. It must be evaluated which layer is most
suitable for 6LoWPAN routing.
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2. The precise 6LoWPAN routing requirements must be defined.
3. It needs to be clarified how existing routing solutions can be
adapted to meet the low-power requirements presented in
Section 4.
Considering the problems above, this draft addresses mesh routing
requirements for 6LoWPANs for both mesh-under and route-over routing
protocol design.
Application-specific features affect the design of 6lowpan routing
requirements and the corresponding solutions. However, various
applications can be profiled by similar technical characteristics.
This document states the requirements to consider the general
features of all categories of 6LoWPAN applications. However, one
single routing solution may not be the best one for all 6LoWPAN
applications.
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2. Design Space
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
[6]), 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 shortened) 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.
Additionally, because of the low-performance characteristics of
LoWPANs, a light-weight routing protocol must be produced that meets
the design goals and requirements presented in this document.
Figure 1 shows the place of 6LoWPAN mesh routing in the entire
network stack;
+-----------------------------+ +-----------------------------+
| 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) |
+-----------------------------+ +-----------------------------+
Figure 1: Mesh-under (left) and route-over routing (right)
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.
If a mesh-under routing protocol is built for operation in 6LoWPAN's
adaptation layer, routing control packets are placed after the
6LoWPAN Dispatch. Multiple routing protocols can be supported by the
usage of different Dispatch bit sequences. When a route-over
protocol is built in the IPv6 layer, the Dispatch value can be chosen
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as one of the Dispatch patterns for 6LoWPAN compressed or
uncompressed IPv6, followed by the IPv6 header.
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3. Scenario Considerations
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 [9].
Most related work focuses on optimizing routing for specific
application scenarios, which can largely be categorized into the
following models of communication:
o Flooding (in very small networks)
o Data-aware routing (dissemination vs. gathering)
o Event-driven vs. query-based routing
o Geographic routing
o Probabilistic routing
o Hierarchical routing
Depending on the topology of a LoWPAN and the application(s) running
over it, these different types of routing may be used. However, this
draft abstracts from application-specific communication and describes
general routing requirements valid for any type of routing in
LoWPANs.
The following parameters can be used to describe specific scenarios
in which the candidate routing protocols could be evaluated.
a. Network Properties:
* Device Number, Density and Network Diameter:
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.
* Connectivity:
Due to external factors or programmed disconnections, a LoWPAN
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
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across a LoWPAN.
* Dynamicity (incl. mobility):
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.
* Deployment:
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.
* Spatial Distribution of Nodes and Gateways:
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.
* Traffic Patterns, Topology and Applications:
The design of a LoWPAN and the requirements on its application
have a big impact on 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.
* Quality of Service (QoS):
For mission-critical applications, support of QoS is mandatory
in resource-constrained LoWPANs and cannot be achieved without
a certain degree of control message overhead.
* Security:
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.
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b. Node Parameters:
* Processing Speed and Memory Size:
These basic parameters define the maximum size of the routing
state. LoWPAN nodes may have different performance
characteristics beyond the common RFD/FFD distinction.
* Power Consumption and Power Source:
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.
* Transmission Range:
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.
* 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.
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4. 6LoWPAN Routing Requirements
This section defines a list of requirements for 6LoWPAN routing. The
most important design property unique to low-power networks is that
6LoWPANs support multiple device types and roles, for example:
o primary battery-operated RFDs
o battery-operated and mains-powered FFDs
o possibly various levels of RFDs and FFDs
o mains-powered, high-performance gateway(s)
o data aggregators, etc.
Due to these unique device types and roles 6LoWPANs need to consider
the following two primary features:
o 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 possible extended periods
from batteries (e.g. on a construction site before building power
is switched on for the first time).
o Low performance: tiny devices, small memory sizes, low-performance
processors, low bandwidth, high loss rates, etc.
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, in order to
fit the low-power requirements of LoWPANs, meeting the following
requirements:
4.1. Routing Requirements depending on the 6LoWPAN Device Properties
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.
[R01] A LoWPAN routing protocol SHOULD be designed to minimize the
required computational and algorithmical complexity.
The lifetime of a wireless sensor node depends on the energy it
can store and harvest. However, one major factor of power
consumption in LoWPAN nodes is caused by the microcontroller.
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Power consumption of microcontrollers varies from family to
family, but typical low power sensor nodes have 8 or 16 bit
microcontrollers. They consume between 0.250 mA and 2.5 mA per
MHz [13]. Low power microcontrollers can have a significant
impact on system performance. A routing protocol of low
complexity helps to achieve the goal of reducing power
consumption, improves robustness, requires lower routing state, is
more easy to analyze, and is implicitly less prone to security
attacks. 6LoWPAN routing protocols SHOULD be simple and of low
computational complexity.
[R02] 6LoWPAN routing protocols SHOULD have a low routing state to
fit the typical 6LoWPAN node capacity.
Typical RAM size of LoWPAN nodes 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). Operation with low routing state
(such as routing tables and neighbor lists) SHOULD be maintained.
For example, devices may have only 32 forwarding entries
available. A LoWPAN routing protocol solution should consider the
limited memory size typically starting at 4KB, in which it is hard
to store neighbor state of hundreds of nodes) and computation
capabilities of participating devices; due to these hardware
restrictions, code length should be considered to fit within a
small memory size. In addition, it should be taken into account
that, while power consumption for RAM is almost negligible, flash
writing/reading is energy expensive. For instance, in MICA motes,
writing and reading consumes 1.1 nAh/byte and 83.3 nAh/byte,
respectively.
[R03] 6LoWPAN routing protocols SHOULD cause minimal power
consumption, both in the efficient use of control packet and also in
the process of packet forwarding after route establishment.
Saving energy is crucially important to LoWPAN devices that are
not mains-powered. In fact, 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
[15].
Compared to functions such as computational operations or taking
sensor samples, radio communications is by far the dominant factor
of power consumption [12]. In [13] the energy consumption of two
example RF controllers for low-power nodes is shown. The TR1000
radio consumes 21mW of energy when transmitting at 0.75mW. During
reception, the TR1000 consumes 15mW and has a receiver sensitivity
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of -85dBm. The CC1000 consumes 50mW to transmit at 3mW and
consumes 20mW to have a receiver sensitivity of -105dBm. When
transmitting 0.75mW, CC1000 consumes 31.6mW. On an idealized
power source, the CC1000 can transmit for approximately 4 days
straight or remain in receive mode for 9 days straight. In order
to last for one year, the CC1000 must operate at a duty cycle of
approximately 2%. It is shown that a node must consume less than
200uA on average to last for one year on a pair of AA batteries.
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:
* Minimization of total energy consumed in the network
* Maximization of the time until a network partition occurs
* Minimizing the energy variance at each node
* Minimizing the cost per packet
while keeping packet delivery ratio, latency or other requirements
depending on each application.
One way of battery lifetime optimization is by achieving a minimal
control message overhead.
[R04] The procedure of route repair and related control messages
should not harm overall energy consumption from the routing
protocols.
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 [14].
[R05] Neighbor discovery for 6LoWPAN routing SHOULD be energy-
efficient.
Neighbor discovery is a major precondition to allow routing in a
network. Especially in a low-power environment, where nodes might
be in periodic sleeping states, it is difficult to define whether
a node is a neighbor of another or not. Mesh-under neighbor
discovery for 6LoWPANs is currently still in progress and
described more detailed in [10]. In case of a route-over
protocol, IPv6 neighbor discovery should be operated energy-
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efficiently. For example, multicast may be needed if IPv6 ND
cannot be optimized well to suit for 6LoWPAN device.
[R06] 6LoWPAN routing protocols SHOULD be reliable despite
unresponsive nodes due to periodic hibernation.
Many nodes in LoWPAN environments might periodically hibernate
(i.e. disable their transceiver activity) in order to save energy.
Therefore, mesh 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.
4.2. Routing Requirements depending on Types of 6LoWPAN Applications
The routing requirements described in this subsection are heavily
dependent on application needs.
[R07] 6LoWPAN routing protocol SHOULD support various traffic
patterns; point-to-point, point-to-multipoint, and multipoint-to-
point.
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 personal 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.
[R08] 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).
An important trait of LoWPAN 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. For instance, in case of structural health monitoring,
hundreds of nodes could be placed on 20 bridge pillars spanning
over a river. Once the nodes are distributed, they are hardly
accessible for maintenance and in case of single node failure, the
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network should not break down. 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.
The design of mesh routing protocols must consider the fact that
packets are to be delivered with reasonable probability despite
unreliable and unresponsive nodes.
[R09] 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.
There are several challenges that should be addressed by a 6LoWPAN
routing protocol in order to create robust routing in dynamic
environments:
* Mobile nodes changing their location inside a LoWPAN:
If the nodes' movement pattern is unknown, mobility cannot
easily be detected or distinguished from routing in 6LoWPAN's
adaptation layer. 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.
* Movement of a LoWPAN with respect to other (inter)connected
LoWPANs:
Within stub networks, more powerful gateway nodes need to be
configured to handle moving 6LoWPANs.
* Nodes permanently joining or leaving the LoWPAN:
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.
[R10] 6LoWPAN routing protocols SHOULD be designed to achieve both
scalability and minimality in terms of used system resources.
A LoWPAN 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).
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 32
routing table entries.
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[R11] 6LoWPAN protocols SHOULD support secure delivery of control
messages. A minimal security level can be achieved by utilizing an
AES-based mechanism.
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 [4]. 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.
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.
4.3. MAC-coupled Requirements
The routing requirements described in this subsection allow
optimization and correct operation of routing solutions taking into
account the specific features of IEEE 802.15.4 physical and MAC
layers.
[R12] 6LoWPAN routing protocol control messages SHOULD not create
fragmentation of physical layer (PHY) frames.
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 [6], the
maximum size of a 6LoWPAN frame, in order not to cause
fragmentation on the PHY layer, is 81 octets.
[R13] 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.
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
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starts transmitting periodic beacons. These beacons can be used
as an indication of current neighbors.
[R14] In order to optimize the delivery ratio by using energy-optimal
routing paths, LoWPAN mesh routing protocols should minimize power
consumption by utilizing a combination of the metrics provided by the
MAC layer and other measures.
Simple hop-count-only mechanisms may be inefficient in LoWPANs.
There is an 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.
The numbers in Figure 2 represent the Link Delivery Ratio (LDR)
between a pair of nodes. There are studies that show a linear
dependence between LQI and LDR [16].
0.6
A-------C
\ /
0.9 \ / 0.9
\ /
B
Figure 2: An example network
In this simple example, there are two options in routing from node
A to node C:
A. Path AC:
+ (1/0.6) = 1.67 avg. transmissions needed for each packet
+ one-hop path
+ good in energy consumption, bad in delivery ratio (0.6)
B. Path ABC
+ 2*(1/0.81) = 2.47 avg. transmissions needed for each packet
+ two-hop path
+ bad in energy consumption, good in delivery ratio (0.81)
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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.
[R15] 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.
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5. Security Considerations
Security issues are described in Section 4.2
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6. Acknowledgements
The authors would like to thank Myung-Ki Shin for giving the idea of
writing this draft.
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7. References
7.1. Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[2] Perkins, C., Belding-Royer, E., and S. Das, "Ad hoc On-Demand
Distance Vector (AODV) Routing", RFC 3561, July 2003.
[3] Clausen, T. and P. Jacquet, "Optimized Link State Routing
Protocol (OLSR)", RFC 3626, October 2003.
[4] Nikander, P., Kempf, J., and E. Nordmark, "IPv6 Neighbor
Discovery (ND) Trust Models and Threats", RFC 3756, May 2004.
[5] Kushalnagar, N., Montenegro, G., and C. Schumacher, "IPv6 over
Low-Power Wireless Personal Area Networks (6LoWPANs): Overview,
Assumptions, Problem Statement, and Goals", RFC 4919,
August 2007.
[6] Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler,
"Transmission of IPv6 Packets over IEEE 802.15.4 Networks",
RFC 4944, September 2007.
[7] IEEE Computer Society, "IEEE Std. 802.15.4-2003", October 2003.
[8] IEEE Computer Society, "IEEE Std. 802.15.4-2006",
September 2006.
7.2. Informative References
[9] Bulusu, N. and S. Jha, "Wireless Sensor Networks", July 2005.
[10] Chakrabarti, S. and E. Nordmark, "LoWPAN Neighbor Discovery
Extensions, draft-chakrabarti-6lowpan-ipv6-nd-04 (work in
progress)", November 2007.
[11] Chakeres, I. and C. Perkins, "Dynamic MANET On-demand (DYMO)
Routing, draft-ietf-manet-dymo-12 (work in progress)",
June 2005.
[12] Pister, K. and B. Boser, "Smart Dust: Wireless Networks of
Millimeter-Scale Sensor Nodes".
[13] Hill, J., "System Architecture for Wireless Sensor Networks".
[14] Lee, S., Belding-Royer, E., and C. Perkins, "Scalability Study
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of the Ad Hoc On-Demand Distance-Vector Routing Protocol",
March 2003.
[15] Shih, E., "Physical Layer Driven Protocols and Algorithm Design
for Energy-Efficient Wireless Sensor Networks", July 2001.
[16] Chen, B., Muniswamy-Reddy, K., and M. Welsh, "Ad-Hoc Multicast
Routing on Resource-Limited Sensor Nodes", 2006.
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Authors' Addresses
Dominik Kaspar
Simula Research Laboratory
Martin Linges v 17
Snaroya 1367
Norway
Phone: +47-6782-8223
Email: dokaspar.ietf@gmail.com
Eunsook Kim
ETRI
161 Gajeong-dong
Yuseong-gu
Daejeon 305-700
Korea
Phone: +82-42-860-6124
Email: eunah.ietf@gmail.com
Carles Gomez
Technical University of Catalonia/i2CAT
Escola Politecnica Superior de Castelldefels
Avda. del Canal Olimpic, 15
Castelldefels 08860
Spain
Phone: +34-93-413-7206
Email: carlesgo@entel.upc.edu
Carsten Bormann
Universitaet Bremen TZI
Postfach 330440
Bremen D-28359
Germany
Phone: +49-421-218-63921
Fax: +49-421-218-7000
Email: cabo@tzi.org
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