Wireless Sensor Network
University of Babylon
Mehdi Ebady Manaa
College of IT
2rd class – Department of Network
Routing protocols in WSN
1.1 WSN Routing Scheme
Data collected by sensor nodes in a WSN is typically propagated
toward a base station (gateway) that links the WSN with other networks
where the data can be visualized and analyzed.
In small sensor networks where sensor nodes and a gateway are in close
proximity, direct (single-hop) communication between all sensor nodes
and the gateway may be feasible. However, most WSN applications require
large numbers of sensor nodes that cover large areas, necessitating an
indirect (multi-hop) communication approach.
That is, sensor nodes must not only generate and disseminate their own
information, but also serve as relays or forwarding nodes for other sensor
nodes.
The process of establishing paths from a source to a sink (e.g., a gateway
device) across one or more relays is called routing and is a key
responsibility of the network layer of the communication protocol stack.
A. When the nodes of a WSN are deployed in a deterministic manner
(i.e., they are placed at certain predetermined locations),
communication between them and the gateway can occur using
predetermined routes.
B. When the nodes are deployed in a randomized fashion (i.e., they are
scattered into an environment randomly), the resulting topologies
are nonuniform and unpredictable. In this case, it is essential for
these nodes to do the following:- self-organize, that is, they must cooperate to determine their
positions
- Identify their neighbors, and discover paths to the gateway
device.
In the following figure (1): it shows the single and multi-hop routing model
1Page
Date: September 19, 2013
Wireless Sensor Network
University of Babylon
Mehdi Ebady Manaa
College of IT
2rd class – Department of Network
Figure (1): Single-hop routing model (left) versus multi-hop routing
model (right).
This design of a routing protocol is challenging due to the unique
characteristics of WSNs, including resource scarcity or the unreliability
of the wireless medium. For example, the limited processing, storage,
bandwidth, and energy capacities require routing solutions that are
lightweight, while the frequent dynamic changes in a WSN (e.g., topology
changes due to node failures) require routing solutions that are adaptive
and flexible.
1.2 WSN Routing Classification
There are various ways to classify routing protocols. Figure (2)
presents three different classifications based on the network structure or
organization, the route discovery process, and the protocol operation
2Page
Date: September 19, 2013
Wireless Sensor Network
University of Babylon
Mehdi Ebady Manaa
College of IT
2rd class – Department of Network
A. Network Organization Protocol
Most routing protocols fit into one of three classes.
 Flat-based routing protocols consider all nodes of equal
functionality or role.
 hierarchical-based routing protocols, different nodes may assume
different roles in the routing process, that is, some nodes may
forward data on behalf of others, while other nodes only generate
and propagate their own sensor data.
 Location-based routing protocols rely on the location information
from nodes to make routing decisions.
B. Route Discovery Protocol
It can use for route discovery and to distinguish between different types of
routing protocols.
 Reactive protocols discover routes on-demand that is, whenever a
source wants to send data to a receiver and does not already have a
route established. A reactive route discovery incurs ( ‫ ) تعاني‬delays
before actual data transmission can occur, proactive routing
protocols establish routes before they are actually needed
 Proactive Protocols (table driven). This category of protocols is
also often described as table-driven, because local forwarding
decisions are based on the
a) Contents of a routing table that contains a list of destinations,
combined with one or more next-hop neighbors that lead toward
these destinations and
b) Costs associated with each next hop option.
In this type the disadvantages are: routes are established that may
never be needed. Further, the time interval between route discovery
and actual use of the route can be very large, potentially leading to
outdated routes (e.g., a link along the route may have broken in the
meantime).
 Hybrid protocol: it exhibits characteristics of both reactive and
proactive protocols.
c) Protocol Operation
 Negotiation-based protocols aim to reduce redundant data
transmissions by relying on the exchange of negotiation messages
between neighboring sensor nodes before actual data transfers occur.
3Page
Date: September 19, 2013
Wireless Sensor Network
University of Babylon
Mehdi Ebady Manaa
College of IT
2rd class – Department of Network
 Multipath-based protocols use multiple routes simultaneously to
achieve higher performance or fault tolerance.
 Query-based routing protocols are receiver-initiated, that is, sensor
nodes send data in response to queries issued by the destination
node.
 QoS-based routing protocols is to satisfy a certain Quality ofService (QoS) metric (or a combination of multiple metrics), such as
low latency, low energy consumption, or low packet loss.
 Coherent-based protocols perform only a minimum amount of
processing (e.g., eliminating duplicates, time-stamping) before
sensor data is sent to receivers and data aggregators. However, in
noncoherent-based protocols, nodes may perform significant local
processing of the raw data before it is sent to other nodes for further
processing.
1.3 Routing Metrics
Routing is considered node-centric when sensor data is explicitly sent
to one or more receivers. Most routing protocols focus on unicast routing,
that is, forwarding of sensor data to exactly one receiver. Multicast and
broadcast routing approaches, on the other hand, disseminate data to
multiple or all nodes, respectively.
Data-centric routing is used when nodes are not explicitly addressed,
but instead receivers are implicitly described by certain attributes. For
example, a query issued by the gateway device may request temperature
readings and only sensors that can collect such information respond to the
query.
Sensor networks can vary widely in scale, the geographic areas they
cover, and their position-awareness. Global addressing schemes (such as
IP addresses used on the Internet) may be unavailable and even non
feasible, particularly in networks with heterogeneous nodes and node
mobility.
Routing metrics are used to express a variety of objectives of a routing
protocol with respect to the consumption of these resources or the
performance an application perceives. This section provides a brief
overview of commonly used routing metrics in WSNs.
1.3.1 Minimum Hop
4Page
Date: September 19, 2013
Wireless Sensor Network
University of Babylon
Mehdi Ebady Manaa
College of IT
2rd class – Department of Network
The most common metric used in routing protocols is minimum hop
(or shortest hop), that is, the routing protocol attempts to find the path
from the sender to the destination that requires the smallest number of
relay nodes (hops) in figure (3). In this simple technique, every link
has the same cost and a minimum-hop routing protocol selects the
path that minimizes the total cost of data propagation from source
to destination to reduce end-to-end delay.
Figure 3: Choosing of optimal path
For example, The format of the setup packet is defined as
“Setup.ID.hop.energylevel”, where the “Setup” indicates that it is a setup
packet and should be flooded throughout the entire network, “ID” is the ID
number of the sending node, “hop” represents the hop count between the
sending node and the sink node, and “energylevel” is the battery energy
level of the sending node. For the setup packet broadcasted by sink node,
the hop count value is set to 0 and the “energylevel” value is set to a very
large value in figure (4).
Figure 4: Single and Multi-hop in WSN’s
5Page
Date: September 19, 2013
Wireless Sensor Network
University of Babylon
Mehdi Ebady Manaa
College of IT
2rd class – Department of Network
1.3.2 Minimum energy consumed per packet:
The goal is to minimize the total amount of energy expended for the
propagation of a single packet from the source to the destination. The total
energy is then the sum of the energy consumed by each node along a
route for receiving and transmitting the packet. Figure (5) shows an
example of a small sensor network, where a source node wishes to transmit
a packet to a destination node using a route that minimizes the packet’s
energy overheads. The number on each link indicates the cost of
propagating the packet over this link. As a consequence, the packet will
travel via nodes A–D–G (with a total cost of 5). Note that this is different
from the minimum-hop route (B–G).
Figure (5): Comparison of routing choices using different energy
metrics.
1.3.3 Minimum variance in node power levels:
All nodes within the network are considered equally important and
the challenge is to distribute the energy consumption across all nodes in
the network as equally as possible. The goal of such an approach could be
to maximize the lifetime of the entire network.
1.3.4 Maximum (average) energy capacity:
The focus in this manner is the energy capacity (i.e., the current
battery charge level) of the nodes. A routing protocol that uses this metric
would then favor routes that have the largest total energy capacity from
source to destination. In Figure 5, the numbers in parentheses below the
nodes indicate the nodes’ remaining energy capacity. In this example, a
routing protocol could select path C–E–G, which has the largest total
6Page
Date: September 19, 2013
Wireless Sensor Network
University of Babylon
Mehdi Ebady Manaa
College of IT
2rd class – Department of Network
capacity (i.e., 8). A routing protocol that uses this metric must be carefully
designed to avoid the pitfall of choosing unnecessarily long routes in order
to maximize the total energy capacity.
1.3.5 Maximum minimum energy capacity:
The primary routing goal could be to select the path with the largest
minimum energy capacity. This technique also favors routes with larger
energy reserves, but also protects low-capacity nodes from premature
)‫ (مبكرا‬expiration. In Figure 5, a protocol using this metric would choose
B–G, since the minimum capacity along this route is 2, which is larger than
the minimum capacities of all other possible routes.
Question#1
For the network topology shown in Figure 6, identify the optimal
routes for source A to sink M according to the following criteria (describe
how you compute the cost for the optimal route). The numbers X/Y along
each link indicate the latency (X) and energy cost (Y) for transmitting a
single packet over the link. The number Z under each node indicates the
node’s remaining energy capacity.
(a) Minimum number of hops
(b) Minimum energy consumed per packet
(c) Maximum average energy capacity (eliminate hops that would
result in a higher average but unnecessarily add to the route
length!)
(d) Maximum minimum energy capacity
Figure 6: Topology of Question 1
7Page
Date: September 19, 2013
Wireless Sensor Network
University of Babylon
Mehdi Ebady Manaa
College of IT
2rd class – Department of Network
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Date: September 19, 2013