In each other independent from the phys- ical

In this subsection, we provide a summary of major is-
sues that may affect the design of the routing protocols
for SG based on the applications discussed above. For each
issue, we discuss how it relates to routing in the context of
SG applications.

4.3.1. Node heterogeneity

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SG is conceived as a blend of communications technol-
ogies interconnecting various devices of different types,
from common networking technologies such as computers,
routers, switches to smart meters, home appliances, sen-
sors, synchrophasors, and EVs. The data generated from
these nodes will have different requirements in terms of
routing and thus this may lead to different type of service
(ToS) requirements for each type of data. Furthermore,
each of these devices will have different hardware restric-
tions in terms of CPU, memory, battery or storage and thus
routing protocol should consider these resource require-
ments as well. In addition to common resource variations
such as in computation capability, storage capacity, and
energy supply; a node in SG could be equipped with
multiple interfaces instead of a single interface in order
to exploit heterogeneous communications technology
environments (i.e., multiple radios, channels). Such addi-
tional interface will affect the design of the routing proto-
col by providing alternative routes. These issues can be
addressed by clustering the similar devices under a
network and using different standards/protocols based on

the cluster’s needs. This is also related to interoperability
which is discussed next.

4.3.2. Interoperability

The nodes and networks in SG may be owned and man-
aged by different entities. To prevent large-scale blackouts
and cascading failures, these utilities need to be able to
route information among each other. Therefore, interoper-
ability, the capability among different systems to exchange
and use information securely, efficiently, and easily, is very
important in a complex system such as the SG. The compo-
nents of each of these different systems will need a way to
communicate with each other independent from the phys-
ical medium used, type of devices, and manufacturers. One
of the solutions typically employed currently is to deploy
gateway nodes at certain edges of the communications
network which can communicate with different entities
via multiple interfaces. Gateway nodes will be able to rec-
ognize different protocols to provide interoperability
among different components. However, it may not be pos-
sible to deploy such gateway nodes in every part of the
networks. In addition, with the increasing variety of appli-
cation, interoperability requirements may force research-
ers to come up with standard protocols that can be
deployed in HANs, NANs and maybe WANs without any
bridge device such as a gateway. This leads the routing de-
sign to consider standardization for the used hardware as
well as used addressing architectures (e.g., IPv6 can be
used in all devices to provide interoperability).

4.3.3. Node placement

The network topology in SG HANs, NANs and WANs is
formed based on the nodes placement and their transmis-
sion range. Given that most of the nodes such as smart me-
ters, sensors and gateways are fixed and deployed at
specific locations across large geographic areas with vary-
ing density and transmission ranges, HANs, NANs or WANs
will have a wide variety of possible network topologies.
The decision for data collector or sensor location in a
NAN may affect the routing performance based on the sig-
nal quality, dynamically created links or interference from
within or outside the SG communications network. For in-
stance, in a HAN used for AMI applications, some bottle-
neck nodes may exist due to poor links and no other
nodes may be available as alternative routes 15. Further-
more, the collisions can be high at the data collector and its
nearest nodes since all packets are forwarded into the
direction of the collector. Therefore, the additional relay
nodes would be needed which may require significant up-
dates to the routing protocol to be used. The issue of node
deployment plays a significant role when sensors are de-
ployed for monitoring the SG devices. Careful planning of
node placement may help alleviate some problems of rout-
ing in terms of interference and reliability. The addition or
removal of new nodes should also be considered by the
routing protocols to update the existing routes.

4.3.4. Network dynamics

Most of nodes in SG are static. However, electric vehi-
cles, mobile workforce and some nodes in the Distribution
Grid Management application are considered mobile.

N. Saputro et al. / Computer Networks 56 (2012) 2742–2771 2749

2750 N. Saputro et al. / Computer Networks 56 (2012) 2742–2771

Mobile nodes introduce new challenges regarding the han-
dling of mobility and tractability of the nodes which can af-
fect the routing protocol.

A good example for mobility is the involvement of mo-
bile workforce in the SG. While on the way, the mobile
workforce may perform a machine-to-machine communi-
cations to the sensors at the faulty location for online diag-
nostics. Sensor could be part of a Wireless Sensor Network
(WSN) and they can communicate with mobile workforce
devices via another network. In this case, routing message
from and to the mobile workforce vehicle is more challeng-
ing since route stability becomes an important issue. Effi-
cient routing with relatively low latency, high reliability,
high security and support for mobility is required for this
application. In addition, the network topology may change
over time due to link and node failures, intra-network
interference, as well as interference from the SG.

Tracking the vehicles could be another application where
the field vehicle is being tracked and directed to the faulty
SG location. The tracking information for the vehicles needs
to be routed via the communications network of the SG. For
instance a fleet management approach as in 13 could be
followed to route the tracking information.

4.3.5. Security and privacy

Security as a major requirement covers all aspects of the
SG, from physical devices to routing protocol operations to
ensure the availability and reliability of the whole net-
work. Many end-point devices in power transmission and
distribution networks, and power generation networks
are located in an open, potentially insecure environment
which makes them prone to malicious physical attacks.
These devices must be protected properly against unautho-
rized access such as modifying the routing table or some
network information stored in the compromised device.
These actions as well as spoofing, altering or replaying
routing information during information exchange between
nodes are examples of attacks against routing protocols.

Another major concern in the routing would be the pri-
vacy of the power data. Many customers would be reluc-
tant to expose their power usage data (as well as the
electric vehicle locations) and thus confidentiality and ano-
nymity should be provided at all times. This may require
additional mechanisms other than confidentiality when
routing the data. For instance, if the customers may not
even trust the utility company, the usage data may need
to be routed to a third-party escrow service to provide
the billing service. Non-repudiation is also required in
some electricity transaction applications such as in the fu-
ture electricity trade-market, and electric vehicle’s power
usage in public or private charging stations.

As a result, routing protocols should be designed by tak-
ing into account the security and privacy requirements of
the specific SG applications considered. Wherever needed,
confidentiality, integrity, authentication, and data valida-
tion should be provided as part of the routing process.

4.3.6. Quality of Service (QoS)

QoS, a guarantee by the network to provide certain per-
formance in terms of bandwidth, reliability, delay, and
jitter, etc., is also important in the SG. SG applications

require QoS to provide high reliability and availability,
especially for system control and situational awareness.
For instance, the information concerning power networks
incidents or disturbances, pricing of electricity, electricity
load balancing, and electricity generation failures need to
be delivered in real-time or near real time. The video sur-
veillance for securing critical assets requires a high band-
width. The power consumption data from each
household can be generated at different pace and size. Bill-
ing application requires low frequency data reporting
(weekly/monthly) and an aggregation of appliance-level
data while demand response and managing load applica-
tions require much higher frequency (seconds/minutes/
hours) of power consumption data reporting for more
accurate information.

Besides the application, there are challenges that arise
from the underlying low level protocols. Due to the specific
features of their access and physical layers, different wire-
less communications technologies usually provide diverse
QoS which impact the performance of routing protocol
16. For example, IEEE 802.11 wireless LAN offers rela-
tively high bit rate but the service is best effort since the
access to medium is based on carrier sensing and random
access. On the other hand, cellular networks offer better
coverage and stability but at the lower data rates.

To provide QoS at the network layer in the SG, all QoS
requirements from the application as well as the heteroge-
neity of the network with various resource constraints and
underlying communications technologies should be con-
sidered. This is sometimes referred to as cross-layer design
where one takes into account the constraints from applica-
tion, MAC and physical layers when designing the routing
protocol. QoS routing will not only consider finding a path
to the destination but also ensure certain characteristics on
such a path.

4.3.7. Scalability

Routing scalability or the ability to provide an accept-
able level of service even with a sheer number of nodes
is very crucial for the SG. Millions of smart meters will
be attached to communications network to deliver power
usage data from each household to utility companies.
Nonetheless, the number of nodes connected to the net-
work at a certain location would vary depending on the
population density in that area. For instance, while urban
areas will have a high density of customers, rural areas will
be sparsely distributed with low number of customers.
Therefore, any proposed routing protocol for the SG should
be able to scale under a variety of use cases with their dis-
tinct operational requirements. Route discovery, mainte-
nance and key distribution in case of secure routing will
grow rapidly with the network size. This design issue
may significantly affect the way the routing protocols are
designed depending on the application and underlying net-
work and the link metrics used.