A Survey of Limitations and Enhancements of the IPv6 Routing Protocol for Low-power and Lossy Networks: A Focus on Core Operations <s> D. LLNs Routing Requirements <s> This document presents home control and automation application ::: specific requirements for Routing Over Low power and Lossy networks ::: (ROLL). In the near future many homes will contain high numbers of ::: wireless devices for a wide set of purposes. Examples include ::: actuators (relay, light dimmer, heating valve), sensors (wall switch, ::: water leak, blood pressure) and advanced controllers (RF-based AV ::: remote control, Central server for light and heat control). Because ::: such devices only cover a limited radio range, routing is often ::: required. The aim of this document is to specify the routing ::: requirements for networks comprising such constrained devices in a ::: home control and automation environment. <s> BIB001 </s> A Survey of Limitations and Enhancements of the IPv6 Routing Protocol for Low-power and Lossy Networks: A Focus on Core Operations <s> D. LLNs Routing Requirements <s> The purpose of this document is to provide guidance in the selection ::: and use of protocols from the Routing Protocol for Low-Power and Lossy ::: Networks (RPL) protocol suite to implement the features required for ::: control in building and home environments. <s> BIB002 </s> A Survey of Limitations and Enhancements of the IPv6 Routing Protocol for Low-power and Lossy Networks: A Focus on Core Operations <s> D. LLNs Routing Requirements <s> This document discusses the applicability of the Routing Protocol for ::: Low-Power and Lossy Networks (RPL) in Advanced Metering Infrastructure ::: (AMI) networks. <s> BIB003
The introduction of 6LoWPAN emphasized the need for additional IPv6-based LLNs routing solutions , thus, soon afterwards, IETF commissioned the Routing over Low power and Lossy networks (ROLL) working group to design such routing solutions BIB001 . Hence, the ROLL working group recognized that a wide range of application areas exists in LLNs each with its own routing requirements. Its first objective, therefore, was to define the routing requirements for four anticipated application areas, namely, Home Automation BIB001 , Building Automation  Industrial LLNs  , and Urban LLNs  . A discussion of these areas is now presented and a summary of these areas routing requirements is shown in Table 1 . Home Automation: Recently, the usage of sensing devices and actuators has increased in smart home applications. A modern home automation application will typically encompass both sensors, such as gas detectors, and actuators, such as heating valves BIB001 BIB002 . These applications are designed to allow for the electrical devices at home to be connected to an IP-based system that controls these devices based on some input values from the end-users. Typical use-cases of home applications include: at-home health reporting and monitoring; lighting, central heating and air conditioning remote control; alarm systems (e.g. carbonmonoxide, smoke, fire detection, panic button, etc.) BIB001 . The majority of devices (sensors and actuators) in a homeoperated network are stationary; however, there are scenarios where mobile devices are present, such as the wearable healthcare devices used to collect bio-medical signals remotely and also home applications controlled using a remote controller that moves from one location to another at random BIB001 . Supporting mobility is, therefore, a necessary requirement for the successful deployment of home automation networks. The traffic patterns within this category vary widely BIB001 [58]. For example, the MP2P is used for communicating health conditions (e.g. blood pressure, temperature, insulin level, weight), while the P2MP model is appropriate for a lighting control system, where a central device sends control commands to associated devices BIB002 . However, the P2P traffic pattern has dominance here as most of the traffic in home-automation applications is generated by wall controllers and remote controls to their associated light or heat sources BIB001 BIB002 . It is envisioned that a typical home automation network will be composed of tens of nodes with a maximum hop separation of a few nodes, and typically network diameter of five hops BIB001 . Many devices will be battery-powered so power consumption should be kept minimal to prolong network lifetime BIB001 . The majority of devices in home automation networks are likely to be Class 0 nodes (e.g., wall switches) with the rest of typically Class 1 BIB001 . The routing protocol for stationary devices has convergence requirements of no more than half a second, relaxed to four seconds at the presence of mobility BIB001 . For instance, a remote control appears unresponsive if it takes more than a second to pause the music BIB001 BIB002 . Building Automation: These systems are deployed in a large set of commercial buildings such as hospitals, colleges, universities, high schools, governmental and manufacturing facilities  . They typically enable automatic control of a commercial building's lighting, air conditioning, ventilation, fireresponse and physical security among other systems  . The main purposes behind building automation are: reducing operating costs and energy consumption; enhancing occupant comfort; improving building service quality and the life cycle of utilities  . As with home automation, the majority of nodes in buildingautomation networks are Class 0 and Class 1 stationary devices with a small proportion of mobile nodes  BIB002 . It is expected that 30% of the traffic in building networks will be P2P with a typical frequency of one packet per minute BIB002 . For example, in a temperature-controlling application, a sensor will unicast periodically (e.g. each minute) of temperature readings to its associated controller and expects an acknowledgment unicasted from that controller. The MP2P and P2MP will account for 70% of traffic in this domain  BIB002 . This is because that most of the messages in building applications are directed toward an aggregation point and then routed off the LLN for further processing (MP2P). In addition, an acknowledgment is unicasted from the destination to the respective sender (P2MP). The number of nodes in a building network is likely to be of larger size than in the domestic equivalent. However, a large building network would typically be divided into subnetworks of no more than 255 nodes to ensure that critical systems such as air conditioning and light systems are not vulnerable to global failures BIB002 . The latency requirements in building automation systems is somehow similar to the latency requirements in home-automation applications. However, many of the applications in this category are mission-critical (e.g., security fire) that are very sensitive to delay and require in-time delivery of messages BIB002 . Network devices (sensors and actuators) might be mains-powered, batteryless, or battery-powered  . Industrial LLNs: Industrial applications of LLNs enable plant and factory workers to manage remotely multiple control units at the site as well collect large amounts of information. Many application scenarios fall under this category, and they can be roughly classified into two different segments known as Factory Automation and Process Control  . Process Control applications target fluid products such as liquid chemicals, gas and oil, whereas Factory Automation is concerned with individual products such as cars, toys and screws  . All three communications patterns (P2MP, P2P and MP2P) will usually be present; however, the predominant traffic pattern is expected to be MP2P. The majority of applications will comprise tens of field devices and forwarders with a few hop to reach a backbone router  . LLN devices in industrial networks may use a variety of sources to provide power: while some will be line-powered, the majority will be battery-operated with lifetime requirements of at least five years  . The issue of mobility in this category is more complicated than in the home and building scenarios and velocities of up to 35kph are possible  . For instance, some field devices may be located on moving objects such as cranes. Since critical classes within this category are not expected to be handled by LLN routing protocols, the requirement of rapid convergence is somewhat relaxed  . It is stated in  that a routing protocol should converge within a few minutes of adding a new node with a latency of no more than ten seconds when delivering packets via established routes. Urban LLNs (U-LLNs): These networks are dedicated to measuring and reporting a wide gamut of data in outdoor urban environments with the primary goal is to improve inhabitants' living conditions and monitoring compliance with environmental present; however, the predominant traffic pattern is likely to be MP2P  . Typical applications include the monitoring of meteorological conditions or pollution and allergen concentration in specific regions. The dominant communication paradigm is the MP2P, as most of the traffic in this category will be generated by the sensor nodes and directed to the LBRs  . For example, the sensing nodes that gather temperature readings could communicate data every hour or every day. The P2MP model is also present: for instance, a query statement can be launched by a central unit to request pollution level readings from a group of sensors in a specific region  . Although most sensing devices in this category are expected to be stationary, the dynamicity of the network is not negligible, due to node disappearance, disassociation and association, in addition to perturbations of node interconnects BIB003 . Scalability represents the biggest concern in this category as the extensive measurement spaces in urban environments can result in very large networks. As currently imagined, an urban network will comprise more than a hundred nodes but sizes of tens of thousands, perhaps even millions of nodes, may be reached in the future  BIB003 . Although an urban network node cardinality is expected to be of the order of 5 to 10, examples of nodes with hundreds of neighbors may be encountered  . In addition, the physical distances between network devices can span from hundreds of meters to as much as a kilometer. Thus, it is unlikely that any field device will be able to reach its border router in a single hop and multi-hop distributions composed of as many as tens of hops may be unavoidable  . A mix of sparse and dense deployments in urban networks is expected: for instance, hundreds of devices may be presented in close proximity within one building in an urban area, whereas sparse node distributions, with low cardinality, would be the norm in sparsely built-up areas BIB003 . Devices may be powered using a variety of mechanisms, including: non-rechargeable batteries; rechargeable batteries with irregular or regular recharging; inductive/capacitive energy provision; or always-on (e.g. a powered electricity meter)  . It is likely, however, that the majority of nodes will use nonrechargeable batteries with lifetime requirements of 10-15 years  . Latency requirements in urban applications vary widely. For instance, for periodic traffic, latencies of up to a fraction of the reporting interval may be acceptable, while query-based applications will have somewhat more stringent requirements. Alert traffic is highly sensitive to delay and cannot tolerate a wait of more than a few seconds in the vast majority of cases  .