CHAPTER 4 ROUTING IN 6LoWPANshodhganga.inflibnet.ac.in/bitstream/10603/36007/4/...between 6LoWPAN and IPv6 In Link state routing, each node acquires complete information about the

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CHAPTER 4

ROUTING IN 6LoWPAN

4.1 INTRODUCTION

The IETF (Internet Engineering Task Force) standard 6LoWPAN,

together especially with the IEEE 802.15.4 for the physical and the MAC layer

becomes increasingly important for building efficient and interactive WSNs. Multi

hop data transfer over intermediate nodes serves to increase the covered area of the

network maintaining low transmit power of the sensor node. The proposed research

work provides an energy efficient routing solution for 6LoWPAN networks. This

chapter gives the overview of state-of-art in routing techniques for 6LoWPAN. Also

various requirements and challenges in designing routing protocol for 6LoWPAN

are discussed.

4.2 ROUTING IN 6LoWPAN

Routing is one of the main task of the network layer as defined by the

Open System Interconnection (OSI) model. Various other tasks include addressing

of nodes and creation and maintenance of network topology. 6LoWPAN

technology adopts the modified IPv6 protocol stack to achieve seamless

connectivity between IEEE 802.15.4 based networks and the IPv6 based

infrastructure.

Routing protocols for WSN are standardised by Zigbee. The most

commonly used is Zigbee AODV. However, as far as 6LoWPAN is concerned,

standardization is still under draft level. Several RFC (Request For Comments)

drafts have been released by IETF working group. 6LoWPAN routing protocol can

be grouped into two approaches namely, MANET (Mobile Adhoc Network) based

approach and ROLL based approach. (Zach Shelby and Carsten Bormann, 2009).

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4.2.1 MANET Based Approach

The MANET WG (Working Group) has produced a large number of

routing protocols. Based on the routing technique, they can be categorised as

distance-vector or link state and based on the route discovery process they can be

categorised as proactive or reactive (Prasant Mohapatra and Srikanth, 2005).

However MANET is mainly considered for routing in ad hoc mobile networks using

Wireless Local Area Network (WLAN) technology, where the majority of traffic is

peer-to-peer. Common MANET routing protocols are Ad hoc On Demand Distance

Vector (AODV), dynamic MANET on-demand (DYMO) and Optimised Link State

Routing (OLSR). A neighbour discovery protocol is developed for collecting route

information. In order to reduce the signalling overhead and to make suitable for

embedded applications, protocols of MANET need to be modified.

4.2.2 ROLL Based Approach

The IETFs Routing Over Low power Lossy Networks (ROLL) working

group analyses the requirements for embedded applications. It also standardizes a

routing protocol for these applications. Various ROLL based applications are

industrial automation, building automation and home automation. These Low-power

and Lossy networks (LLNs) are made up of embedded devices with limited

processing, memory and power resources. This WG focuses only on routing for

general IPv6 and 6LoWPAN networks. So ROLL differs from 6LoWPAN wherein

LLN is used for LoWPAN, LLN border router is used in 6LoWPAN instead of

LoWPAN Edge Router. Route metrics in ROLL are used for the path selection

process in a routing protocol. They are used to choose the best route. Different types

of route metrics considered in ROLL based approach are link, node, dynamic etc.,

where link metrics include throughput, latency and link reliability. Node metrics

deals with memory, processing load and residual energy. Dynamic metrics deals

with routing stabilities. The metric calculation should be consistent throughout the

routing domain as it is useful for the path calculation. The architecture of LLNs is

different from MANET. MANET is mainly meant for routing in ad hoc mobile

networks, where the majority of traffic is peer-to-peer. Various MANET based


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applications include nomadic computing, emergency and rescue networks and

military applications. Whereas ROLL protocol is a proactive distance-vector

algorithm with options for constrained-based routing, multi-topology routing and

traffic engineering.

4.3 MANET BASED ROUTING IN 6LoWPAN

Based on the application, 6LoWPAN routing protocols can be classified

into Mesh-under routing and Route-over routing as illustrated in Figure 4.1.

4.3.1 Mesh-under

In mesh-under routing, both the Extended Universal Identifier (EUI)-64

bit and 16 bit addressing schemes are used to send a packet to a particular

destination through the neighbouring nodes (Zach Shelby and Carsten Bormann,

2009). 6LoWPAN header consists of both the link layer originator and the final

destination address. Multiple link layer hops are used to complete a single IP hop

and hence it is called mesh-under.

The adaptation layer divides the IP packet into number of fragments and

these fragments are delivered to the destination in a hop by hop manner using mesh

routing. The divided fragments take different paths to reach the destination and they

are gathered together at the destination. After all the fragments reach the destination,

the adaptation layer of the destination node reassembles all the fragments and

creates an IP packet.

If any fragment is missed during the forwarding process, the entire IP

packet is transmitted to the destination. In mesh-under approach, no IP routing is

done within the LoWPAN. In this approach, forwarding of data is performed at the

link layer based on the IEEE 802.15.4 frame.


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4.3.2 Route-over

In Route-over, the decision of routing is taken at the network layer. Here

each 6LoWPAN node in the network acts as an IP router. In this approach, each link

layer hop is an IP hop by which packets are forwarded in the network. The routing

process in the network layer uses the encapsulated IP header and routing tables.

IPv6 packets are divided into IP packet fragments and forwarded. After all the IP

fragments reach the destination, the adaptation layer reassembles the IP packet and

sends it to the network layer. If the IP packet reaches the destination, the network

layer sends the IP packet to the transport layer, otherwise it forwards the packet to

the next hop based on the routing table information. Therefore route-over approach

performs IP routing. IP address is generated with a combination of IPv6 prefix and

interface identifier acquired through Stateless Address Auto configuration (SAA).

4.4 CHARACTERISTICS OF 6LoWPAN ROUTING

6LoWPAN routers perform forwarding on a single wireless interface.

They send and receive the information between nodes using the same interface. A

6LoWPAN has a flat address space, as all nodes in a LoWPAN share the same IPv6

prefix. 6LoWPANs are stub networks, and are not meant to be transit networks

between two different subnets, which simplifies the requirements for 6LoWPAN

routers (Chian-Wen Lu et al., 2011) as shown in the Figure 4.2.

APPLICATION LAYER APPLICATION LAYER

TRANSPORT LAYER TRANSPORT LAYER

IPv6 (or) NETWORK LAYER IPv6 (or) NETWORK LAYER

(Route-over Routing)

ADAPTATION LAYER (Mesh-under Routing)

ADAPTATION LAYER

DATA LINK LAYER DATA LINK LAYER

PHYSICAL LAYER PHYSICAL LAYER

(a) Mesh-under (b) Route-over

Figure 4.1 Mesh-under Vs Route-over Forwarding


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4.5 TAXONOMY OF 6LoWPAN ROUTING PROTOCOLS

6LoWPAN includes two main classes of routing protocols they are

distance vector routing and link state routing . In distance vector routing, each link is

assigned a cost based on the appropriate route metrics. The routing table of each

router keeps soft-state route entries for the destination, with the path cost. Routing

information is updated either proactively or reactively depending on the routing

algorithm (Zach Shelby and Carsten Bormann, 2009).

Distance vector routing is commonly applied to 6LoWPAN owing to its

simplicity, low signalling overhead and local adaptive in nature. The proposed

novel Location Based Routing Protocol (LBRP) falls under the class of distance

vector routing with an On- demand approach.

Figure 4.2 Stack View of Data Forwarding Supporting Interoperability between 6LoWPAN and IPv6

In Link state routing, each node acquires complete information about the

entire network, called graph. Link-state routing incurs a large amount of overhead,

especially in networks with frequent topology. Link state routing is not suitable for

distributed use among LoWPAN nodes because they incur a large amount of


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overhead, especially in networks with frequent topology change. Also they require

substantial memory resources to maintain the state of each node.

Constrained routing in 6LoWPAN networks uses compound route metrics,

local route recovery, flow labelling to achieve Multi Topology Routing (MTR),

forwarding on multiple paths with multipath routing, and traffic engineering.

Based on the network structure, the routing protocols for 6LoWPAN are

classified into data-centric, Hierarchical and Location-based. In data-centric

protocols, queries on particular data are sent from base station to the network. The

nodes holding the data related to the query alone send the reply. It helps in avoiding

redundant transmissions.

In hierarchical protocols, nodes are grouped in clusters. A node is elected

as a Cluster Head (CH). CH performs aggregation of data transmitted by its cluster

member using standard information fusion technique. In Location-based protocols,

position information of nodes is utilised to relay the data to the desired destination.

Power optimisation can be achieved in Location-based routing protocols and control

overheads can be minimized. By utilising the location information of nodes, the

place of occurrence of the phenomenon can be easily determined which reduces the

control overhead involved in locating the node. Power optimisation can be achieved

by selecting the node which has highest Cost over Progress Ratio (CPR) towards the

destination node, as the forwarding node.

Based on the route discovery process, the routing protocols can be

classified into three categories namely proactive, reactive and hybrid (Jamal Al

Karaki et al., 2004). In proactive routing protocols, all the routes are computed in

advance. Hence they are best suited for static network. In reactive routing protocols

routes are computed on demand, so they are best suited for dynamic network

environment. Hybrid protocols use the combination of these two protocols. Another

class of routing protocols is called co-operative wherein sensor nodes send data to

the central node which aggregates and processes the data. Proactive routing comes

with the cost of increased signalling overhead especially with frequent topology


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changes and increase state for routers. The advantage of reactive routing is that

signalling and route state increases only when and as needed and it is well suited for

ad hoc networks with frequent topological changes.

4.6 REQUIREMENTS FOR ROUTING IN 6LoWPAN

This section defines a list of requirements for 6LoWPAN routing. An

important design requirement is that LoWPANs have to support multiple node types

and roles as mentioned below (Kim et al., 2011):

Power-constrained nodes - Nodes drawing their power from primary

batteries or using energy harvesting

Power affluent nodes - mains-powered nodes

High Performance gateway(s)

Nodes with multiple functionalities (data aggregators, relays, local

manager/coordinators, etc.)

Due to these different device types and roles, LoWPANs need to consider

the following two primary attributes:

Power conservation: Some devices are mains-powered, but many are

battery-operated and need to last from several months to a few years

with a single AA battery.

Low performance: tiny devices, small memory sizes, low-

performance processors, low bandwidth, high loss rates, etc.

These fundamental attributes of LoWPANs affect the design of routing

solutions. In order to fit the requirements of LoWPANs, the existing routing

protocols need to meet the following requirements:


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1. Support of 6LoWPAN Device Properties

2. Support of 6LoWPAN link Properties

3. Support of 6LoWPAN Network Characteristics

4. Support of Security

5. Support of Mesh Under Forwarding

4.7 PARAMETERS INFLUENCING ROUTING IN 6LoWPAN

4.7.1 Network Parameters

Following are the various network parameters influencing routing scenario

in 6LoWPAN (Kim et al., 2011):

1. Node density:

It is defined as the number of nodes in the network. This parameter has a

direct impact on the routing state, especially in large and dense network. Further to

avoid memory overflow, certain policies need to be applied in discarding "low-

quality" and stale routing entries in the routing table.

2. Connectivity:

Status of the wireless link between the nodes provides several state of

connectivity in 6LoWPAN. It may range from “always connected” to “rarely

connect”. This in turn imposes a great challenge in dynamic route discovery

mechanism.

3. Dynamicity :

It is experienced in 6LoWPAN due to various factors namely mobility of

the nodes, medium characteristics influenced by multipath radio propagation and

lifetime of the nodes. These factors need to be considered carefully to avoid data

loss in the network.


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4. Deployment:

Deployment of nodes in LoWPAN can be regular or random, static or dynamic. The

organization of nodes in the network can influence the performance of routing in

6LoWPAN.

5. Spatial Distribution of Nodes and Gateways:

Network connectivity depends on the spatial distribution of the nodes and

on other factors, such as node density and transmission range. In addition, if the

LoWPAN is connected to other networks through infrastructure nodes called

gateways, the number and spatial distribution of gateways also affects network

congestion and availability of data rate among other networks.

6. Traffic Patterns, Topology and Applications:

Generally LoWPAN are application specific. The traffic pattern can either

be event driven or periodic. The type of routing mechanism is also influenced based

on the application.

4.7.2 Node Parameters

Following are the various node parameters influencing routing scenario in

6LoWPAN (Kim et al., 2011):

1. Processing Speed and Memory Size:

It defines the maximum size of the routing state and maximum complexity

of its processing.

2. Power Consumption and Power Source:

The nodes in LoWPAN are mostly driven by battery, hence these

parameter become significant in designing an efficient routing protocol.


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3. Transmission Range:

This parameter is directly related to the energy availability in the node.

High transmission range increases the connectivity and number of neighbouring

nodes, but reduces the lifetime of the node. Low transmission range increases the

routing overhead as the number of nodes involved in routing increase. Thus

selection of optimal range is more challenging.

4. Traffic Pattern:

Distribution of traffic in the network influences the delay and energy

consumption involved in forwarding data in the network. Thus, Load Balancing is a

necessary factor that needs to be considered in designing a routing protocol.

4.7.3 Link Parameters

Following are the various link parameters influencing routing scenario in

6LoWPAN (Kim et al., 2011):

1. Throughput:

Table 4.1 illustrates various data rates adopted in 6LoWPAN.

Table 4.1 Data Rate in Ideal 2.4 GHz Channel

MAC address Legacy Mode Data Rate

16-bit Unreliable 151.6kbit/s

16-bit Reliable 139.0 kbit/s

64-bit Unreliable 135.6 kbit/s

2. Latency:

Table 4.2 illustrates the range of latency experienced in an ideal 2.4 GHz

channel of 6LoWPAN.


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4.8 EXISTING PROTOCOLS

From the literature survey, it is found that IP-based LoWPAN technology

(6LoWPAN) is still in its early stages of development, hence developing new

routing protocols meeting the above mentioned requirements are still an open

research problem (Gee Kenqg Ee et al., 2010). Some of the routing protocols

developed for 6LoWPAN includes LOAD (Kim et al., 2007), MLOAD (Jian Ming

Chang et al., 2010), DYMO-Low (Kim et al., 2007), Hi-Low (Kim and Yoo et al.,

2007), Improved Hi-Low (Hong Yu and Jingsha he, 2011), S-AODV (Zhongyu Cao

and Gang Lu, 2010), SPN (Gee Keng Ee et al., 2010), TA-HiLow (Tree Avoiding

technique for hierarchical routing) (Hun-Jung Lim and Tai-Myoung Chung, 2009),

SPEED (Stefano Bochhino et al., 2011), Extended Hierarchical routing (Choong-

Sun Nam et al., 2008), Bias child node avoidance in 6LoWPAN routing (Lingeswari

et al., 2010). The taxonomy of existing 6LoWPAN routing protocols are presented

in Figure 4.3. The existing routing protocols can be classified into three category

namely flat routing, hierarchical routing and location-based routing.

Table 4.2 Range of Latency in Ideal 2.4 GHz Channel

MAC address Legacy Mode Delay

16-bit Unreliable [1.92ms, 6.02ms]

16-bit Reliable [2.46ms, 6.56ms]

64-bit Unreliable [2.75ms, 6.02ms]

64-bit Reliable [3.30ms, 6.56ms]

AODV has been considered a strong candidate for 6LoWPAN due to its

simplicity in finding routes (Perkins et al., 2003). Some modifications are required

in AODV to suit 6LoWPAN environments. LOAD (Kim and Daniel Park et al.,

2007) enhances the AODV protocol according to 6LoWPAN requirements.


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4.8.1 LOAD

A 6LoWPAN routing protocol based on AODV is proposed in (Kim and

Daniel Park et al., 2007). The developed LOAD reduces the implementation

complexity and provides load balancing in the network as compared to AODV. It

maintains the routing table and route request table that are used only during route

discovery phase. LOAD does not use the precursor list of AODV because Route

Error (RERR) message is sent only to the source. Further the protocol does not use

the destination sequence number which results in reduction of packet size and

simplifies the route discovery process. The reply for the Route Request (RREQ)

message is sent only from the destination node which ensures loop free condition.

LOAD uses the Link Quality Indicator (LQI) of 6LoWPAN MAC layer as a routing

cost metric to determine the strongest route. It uses Acknowledge (ACK) message to

ensure guaranteed delivery of packets.

4.8.2 MLOAD

MLOAD stands for Multipath 6LoWPAN ad-hoc On-demand distance

vector routing protocol (Jian Ming Chang et al., 2010). The limitation of LOAD

identified is increase in energy consumption by repeated broadcast of RREQ for

route discovery process. MLOAD is developed to reduce network overhead.

MLOAD enhances the LOAD by implementing the Ad hoc-on-demand multipath

distance vector routing (AOMDV) on LOAD, to find multipath routes during route

discovery process.

4.8.3 Hi-Low

Hi-Low stands for hierarchical routing in 6LoWPAN (Kim and Yoo et al.,

2007). It is developed to increase network scalability. One of the distinctive features

of 6LoWPAN is the assignment of 16-bit short addresses to the IEEE 802.15.4

devices. HiLow uses 16-bit short addresses as interface identifier for memory saving

and larger scalability. HiLow exhibits parent – child model by initiating scanning

procedures. Each node in the network, discovers its parent by sending a broadcast


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signal. If it finds a 6LoWPAN parent node within its Personal Operating Space

(POS), then it gets associated with the 6LoWPAN parent node using 16-bit short

address, otherwise it configures itself as a coordinator (parent). Every child node in

the network receives its 16 bit short address from the 6LoWPAN parent node

provided the following rule is satisfied

0

*

0

i f N M Cth e nC M C A P Ne ls eA P (4.1)

Where

C = address of the child node

MC = maximum number of children a parent can poses

AP = address of the Parent

N = nth child node

When the current node wants to send the packet to the destination, it

determines the next hop node to forward the packet. Whenever link failure is

encountered, no route recovery path mechanism is performed to repair the route that

was carried out in LOAD. This results in unguaranteed delivery of packets in the

network.

4.8.4 DYMO-Low

DYMO-low (Kim and Park et al., 2007) stands for dynamic MANET On-

demand routing for 6LoWPAN. The DYMO-low protocol provides an effective and

simple method to implement routing protocol based on AODV. DYMO performs

route discovery and maintenance by using Route Request (RREQ), Route Reply

(RREP) and Route Error (RERR) messages. It operates on top of IP layer and not on

the link layer. DYMO protocol cannot be applied directly in 6LoWPAN routing due


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to its increased memory and power consumption. DYMO-low is a routing protocol

developed for 6LoWPAN which operates on link layer directly to create a mesh

topology with 6LoWPAN devices, so that IP views the WPAN as a single link.

DYMO-low uses both the 16-bit link layer short address and 64-bit extended

address.

4.8.5 S-AODV

S-AODV (Sink Routing Table over AODV) protocol is developed for

6LoWPAN. This protocol provides load balancing in the network, minimises the

power consumption and prolongs network lifetime. In this S-AODV protocol, the

routing table is maintained only in the sink node. Sink using the routing table

forwards the query packets to a specific internal node. The destined node responds

to the query of the sink node through the optimal neighbouring node.

The developed S-AODV (Zhongyu Cao and Gang Lu, 2010) protocol

consists of set-up phase and a steady state phase. Initially the sink node broadcasts

its status to the nodes in the network. In set-up phase, every node establishes its path

to the sink node through optimal neighbour node. Using this information, the sink

node constructs a Sink Routing Table (SRT). In the steady-state phase, data transfer

is carried out between the sink node and the destined common node. The delay and

the energy consumption in the network for data forwarding is minimised by

adopting this mechanism.

4.8.6 Step Parent Node (SPN)

A new path recovery algorithm called Step Parent Node (SPN) algorithm

is developed to the existing HiLow protocol. In SPN (Gee Keng Ee et al., 2010)

algorithm, every node knows its MC (Maximum Child) value (MC=4). When there

is a link break, the child node of the failure parent node broadcasts a step parent

request message to the neighbouring nodes. The neighbouring node which has the

existing number of child nodes that is less than its MC value, unicast a step parent

node reply to the request sender. If the requesting node receives more reply


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messages, then it will check the address and the Path Quality Indication (PQI) of the

various sender. It

Figure 4.3 Taxonomy of Routing Protocols in 6LoWPAN

get associated with the neighbouring node that is not the descending node of the

sender and posses high PQI.

After association the neighbour node becomes the new parent node of the

child node from the failure node. In this algorithm only 16-bit short addresses are

used to improve the network scalability. Path recovery mechanism in conventional

HiLow is solved by applying SPN algorithm in HiLow. This algorithm provides a

sustainable connection along the 6LoWPAN routing path.


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4.8.7 I-HiLow (Improved HiLow)

The efficiency of routing is increased by improved Hierarchical routing.

In this improved HiLow, the current node can acquire the information about its

neighbouring nodes by broadcasting “Hello” messages in its Personal Operating

Space (POS). After receiving a packet, the current node “C” calculates its Parent

address using the equation given below (Hong Yu and Jingsha He, 2011):

[( 1) / ]AP AC MC (4.2)

Where

AP = address of the parent node

AC = address of the current node

MC = maximum number of children allowed

When a packet is received by a current node C, it checks for the

destination ‘D’. If it is the destined node ‘D’, the packet is delivered to the upper

layer. If not, it checks to see its descendants or ascendant by using the condition

discussed below.

1,

1,

,

If C is a member of SAThen next hop node is AA DC DIf C is a member of SDThen next hop node is AA DC COtherwise the 1, next hop nodes is AA DC C

Where

C = Current node

D = destination node

AD = address of the destination node


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SA = set of ascendant nodes of the destination node

SD = set of descendant nodes of the destination node

DD = depth of the destination node

DC = depth of the current node

Compared to the existing hierarchical routing, improved hierarchical

routing takes minimum hop counts to reach its destination. This scheme reduces the

hop-counts for communication between a node and a nearby node.

4.8.8 The Bias Routing Tree Avoiding Technique for Hierarchical Routing

Protocol for 6LoWPAN (TA-HiLow)

The hierarchical routing protocol is well known for light-weight address

allocation and addressing scheme. It is designed to establish a hierarchical tree with

parent and child nodes to transmit packets. The problems present in the existing

hierarchical routing protocol are address allocation and routing mechanism. But in

TA-HiLow (Hun-Jung Lim and Tai-Myoung Chung, 2009), a mechanism is

suggested to avoid the bias routing tree that could happen if the child nodes do not

attach to the parent nodes evenly. The bias routing tree problem is avoided by

transmitting attached child number information.

4.8.9 SPEED Routing Protocol in 6LoWPAN Networks

SPEED protocol is designed to provide soft real time communication in

6LoWPAN networks. In this protocol, the geographic location of nodes are

considered for packet forwarding in the network. A packet is sent to the destination

identified by its geographic position and global address. The destination area is

identified by its central position and radius. In this mechanism all the packets are

sent towards the destination using the shortest path. SPEED supports for soft

real-time, load balancing and flow shaping mechanisms making itself an

effective solution in supporting packet routing in 6LoWPAN networks

(Stefano Bochhino et al., 2011).


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4.8.10 Extended Hierarchical Routing

A hierarchical routing tree is configured by this extended hierarchical

routing mechanism. The routing tree structure cannot be maintained if a sensor

parent or child node fails due to some reasons. When a new child node is set to the

new parent then the packet delivery is done based on steps given below (Choong-

Sun Nam et al., 2008).

Step 1 : Source node sends a packet and destination node ID to its own parent

node.

Step 2 : The parent node sends the path request information of the destination to

the coordinator node.

Step 3 : The coordinator node receives the requests and sends the information to

the router nodes to check their Neighbour Added Child (NAC) in their

routing table.

Step 4 : The router node which has the answer for the request given by the

coordinator and sends a reply to the coordinator

Step 5 : After that the new child node transmits the packet to the destination

through its own new parent node.

4.8.11 Bias Child Node Association Avoidance Mechanism for Hierarchical

Routing Protocol in 6LoWPAN

The hierarchical routing protocol does not address the scenario where

there could be more than one potential parent node. If the child node attaches to the

first responding parent when there are more than one potential parent, then this leads

to bias or uneven distribution of the child node. Bias could lead to a short life span

of the 6LoWPAN network. The idea of the developed protocol is to avoid a bias

routing hierarchical tree structure considering potential parent nodes' signal strength,

depth and energy level. In the existing routing mechanism, the new potential parent

node provides the child node with its existing child node count (child number). By


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looking at the child node number, the new node selects the parent which has less

child nodes. The suggested mechanism performs well if the parent node has same

depth, same energy level and a different number of child nodes. If it is same would

again it lead to bias child node association.

In the new Bias Child node association mechanism, the new child node

is provided with two forms of information namely the depth of the parent node

and the average amount of power the parent node possesses. The average amount

of power of the parent node is calculated using the equation given below

(Lingeswari et al., 2010).

/ ( 2)Avg CBP CC (4.3)

Where

CBP is the current battery power of the potential parent.

CC is the current child node.

Avg is the Average amount of power.

4.9 COMPARISON OF ROUTING PROTOCOLS IN

6LoWPAN

The comparisons of different 6LoWPAN routing protocols are presented

in Table 4.3. It is found that RERR message is utilised in the LOAD, DYMO-Low,

M-LOAD and S-AODV protocols to indicate the link breakage in the networks,

while the other protocols have not utilised this feature. The Energy consumption in

all the protocols is low. Broadcasting of RREQ for route discovery is used in

LOAD, DYMO-Low, Hi-Low, SPN and MLOAD whereas it is not used in other

protocols. The use of sequence number, elides loop freedom in DYMO-Low

whereas it is not adopted in other protocols.


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The concept of hop count is used as routing metric in Hi-Low, MLOAD,

S-AODV, I-Low and ELBRP. The Hello message is used only in the DYMO-Low

and I-Low to constantly track the information about neighbouring nodes. Whenever

there is a break in the link of the network, the process of local repair is adopted in

LOAD to determine alternate link for data forwarding. In case of M-LOAD,

alternate path is identified for data forwarding.

The support for mobility of sink is addressed in S-AODV protocols in

contrast to other protocols. Node mobility is supported by all other protocols except

SPEED. Scalability analysis has been performed for HiLow, SPN, I-Low,

TA-HiLow, Ex-HiLow and BC-HiLow in comparison to other protocols. Routing

delay is found to be high in DYMO-low when compared to other protocols.

Convergence to varying topology is slow in HiLow, SPN and SPEED compared to

other protocols. Path Quality Indication (PQI) is utilised as a routing parameter in

SPN and ELBRP protocols when compared to other protocols.


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Table 4.3 Comparisons of 6LoWPAN Routing Protocols

Features LOAD DYMO-

Low Hi-Low

M-LOAD

S-AODV SPN I-Low TA-HiLow SPEED Ex-HiLow BC-HiLow ELBRP

RERR Msg. Use Use No Use Use Use No Use No Use No use No Use No use No use No use

Energy Usage Low Low Low Low Low Low Low Low Low Low Low VeryLow

Broadcasting RREQ High High High High Reduced High Reduced Reduced Reduced Reduced Reduced Reduced

Sequence Number No use Use No use Use No use No use No use No use No use No use No use No use

Hop count Optional Optional Use Use Use No Use Use No Use Use No use No use Use

Hello Msg. No use Use No Use No use No use No Use Use No Use No Use No Use No Use No use

Local repair Use No use No Use No use No use No Use No Use No Use No Use No Use No Use No use

Multiple path to destination

No use No use No Use Use No use No Use No Use No Use No Use No Use No Use No use

Sink Mobility Static Static Static Static Mobile Static Static Static Static Static Static Static

Node Mobility Mobile Mobile Static Mobile Mobile Mobile Mobile Mobile Static Mobile Mobile Mobile

Scalability Low Low High Low Low High High High Low High High Low

Routing delay Low High Low Low Low Low Low Low Low Low Low Low

Convergence to topology

Fast Fast Slow Fast Fast Slow Fast Fast Slow Fast Fast Fast

Path quality Indication(PQI)

No use No

Use No Use No use No use Use No Use No Use No Use No Use No Use Use


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4.10 ADVANTAGES OF LOCATION BASED ROUTING

PROTOCOLS

Location-based routing protocols utilize the position information of nodes

to relay the data to the desired regions only rather than to the whole network (Young

Bae Ko and Nitin Vaidya, 2000). The 6LoWPAN based WSN is an autonomous

monitoring system which consists of large number of micro sensor nodes with

communication and computing capabilities deployed in the unattended monitoring

regions. Therefore adding location information in the routing algorithms helps in

guiding route discovery and maintenance as well as data forwarding, enabling

directional transmission of the information and avoids flooding in the network. As a

result, control overhead of the algorithm is reduced and routing is optimised.

Network management becomes simple (Elizabeth Royer and Charles Perkins, 2000).

Based on the nodes' location information, global network optimisation can be

achieved.

Location based routing algorithm makes use of location information to

reduce energy consumption. Location based routing can be categorised into three

types according to location information base (Paolo Baronti et al., 2007). The first is

the localised routing algorithm in which the node uses its own location, its

neighbouring nodes and the destination to forward packets to the next hop. In this

type of routing, greedy forwarding technique is followed in which the packet make

progress at each step along the path. Each node forwards the packets to a neighbour

closer to the destination, until the packet reaches the destination. If the nodes have

consistent location information, greedy forwarding is guaranteed to be loop free.

The second type of location based routing is the grid based routing. Here

the algorithm divides the network into many smaller grids based on the location

information of the nodes. All the nodes in the same grid send the data packet

to their grid leader. Grid leader routes the data packets by grids. They are suitable

for large and dense networks due to the reduction of routing complexity.


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GAF (Xu et al., 2001) and GRID are two typical grid based routing protocol (Wen-

Hwa Liao et al., 2001) and (Sinchan Roychowdhury et al., 2010).

The third type is the location-aided routing algorithm, which uses

the location information of nodes for route discovery and limits the route discovery

flooding to a geographic area around the destination. AODVjr, LBM,LAR

and DREAM are examples of those which use flooding for route discovery

(Xiao Hui Li et al., 2011)

From the literature survey, it is observed that very few energy aware

location based routing protocols exist. Hence, this research work exploits the use of

location information of the node to achieve energy efficient routing.

4.11 PROBLEM STATEMENT

The repeated broadcast of RREQ message for route discovery process in

LOAD resulted in increased energy consumption (Kim and Daniel park et al., 2007).

To address this limitation, MLOAD (Jian Ming Chang et al., 2010) has been

developed which computes multiple routes during the route discovery process so

that alternate paths are used whenever path failure occurs. This has resulted in

reduction of control overhead during route discovery process which in turn has

minimized energy consumption. The Hello messages used in DYMO-Low ensures

more reliable data forwarding but results in increase in delay during packet

forwarding.

The developed LOAD reduces the implementation complexity and

provides load balancing in the network when compared to Ad hoc on demand

Distance Vector (AODV) (Perkins et al., 2003). The various modifications carried

out in AODV as an enhancement resulting in a new protocol LOAD are presented

below. It maintains the routing table and route request table that was used only

during route discovery phase. LOAD does not maintain the precursor list as used in

AODV. Whenever a link failure occurs, the Route Error (RERR) message is sent

only to the source node which results reduction in routing overhead. Further, the


85

route discovery process is simplified by avoiding the use of destination sequence

number. To ensure loop free condition, only the destination node generates Route

Reply (RREP) message. LOAD uses the Link Quality as a new routing metric as

compared to AODV. Guaranteed delivery of packets in LOAD is achieved through

the use of Acknowledgement (ACK) message. The limitation of LOAD includes

increase in energy consumption due to repeated broadcast of Route Request (RREQ)

message during route discovery process. Whenever the link breakage is indicated re-

establishment of alternate route is mandatory. This leads to increase in energy

consumption.

4.12 MOTIVATION OF THE PROPOSED WORK

Location based routing is the suitable scheme for the 6LoWPAN based

WSN, as the information about the place of occurrence of event is needed for quick

remedial measures. But, the challenging issues in the design of such protocols is the

energy, delay and link quality issues. The existing 6LoWPAN based schemes do not

consider all these issues. Hence a novel location based routing protocol is proposed

in this research work. It is an extended version of existing LOAD protocol.

The limitations of LOAD protocol addressed above are considered as the

motivation for the proposed work. In this thesis, a novel Location Based Routing

Protocol (LBRP) is proposed for 6LoWPAN networks. The proposed LBRP

considers distance and residual energy as the new routing matrices in addition to

Link Quality Indicator (LQI) of existing LOAD. To determine the distance, all

nodes are assumed to be location aware. Further to minimize the use of constraint

resources energy and bandwidth, two tiered hierarchical structure is adopted.

Thus in this chapter the state-of-art in routing techniques for 6LoWPAN

has been discussed. The challenges and requirements for designing a routing

protocol in 6LoWPAN has also been discussed.


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