Routing Metrics used for Path Calculation in Low Power and Lossy Networks

1. Routing Metrics used for Path Calculation in Low Power and Lossy Networks draft-mjkim-roll-routing-metrics-00 IETF-72 - Dublin - July 2008 Mijeom Kim (mjkim@kt.com ) JP Vasseur (jpv@cisco.com) Hakjin Chong (hjchong@kt.com)

2. Introduction-1 • Motivation of the document • Unique characteristics of LLNs • Typical routing metrics such as hop counts or link metrics are not sufficient for LLNs • A new set of required link and node metrics suitable to LLNs needs to be specified • ROLL WG item • Nov 2008  Submit Routing metrics for LLNs document to the IESG to be considered as a Proposed Standard. • Classification of routing metrics • Link versus Node metrics • Qualitative versus quantitative • Dynamic or static IETF 72 – July 2008 - Dublin

3. Introduction-2 • Routing metrics for LLNs is a critical topic • Need to be cautious !!! May be tempting to define a plethora of metrics … but not always implementable and usable in a deployed network • Use of dynamic metrics have been studied and experimented in the past (ARPANET: first average delays, revised metrics) • Dynamic metrics => Use of energy … • The challenge is not to define metrics but to compute these metrics. • This first revision list potential candidates IETF 72 – July 2008 - Dublin

4. A first list of Node and Link Routing Attributes • Node metric • Computational resources • Residual Energy (dynamic) • Current workload (dynamic) • Node latency • Data Aggregation attribute • Node degree Dynamicity • Node reliability • Link metrics • Bandwidth • Reliability (Quality) • Propagation delay • Set of costs (missing from the ID) IETF 72 – July 2008 - Dublin

5. Node Metrics/Attributes • Most node attributes may be taken as static in LLN • Require quite resources to get exact values and update them periodically • Use of dynamic metrics is subject to routing instabilities • Critical parameters like residual power • Need to be considered dynamic and monitored continuously • Need multi-threshold schemes to avoid constant routing changes • Highly heterogeneous nodes in LLNs • More capable and stable nodes need to assist the most constrained ones for network lifetime extension and efficient network operations • Node metrics SHOULD be carefully maintained and utilized • Need constrained-based routing IETF-72 – July 2008 - Dublin

6. Open Issues • Consideration of routing efficiency and stability • Routing should be lightweight for resource saving in constrained networks • Need to care about the dynamic nature of some metrics and their implication on routing stability • Traffic flow requirement • Applicable metrics are dependent on application and traffic flow requirements • Different applications or Service Level Agreement (SLA) might demand different routing metric combination • May need Multi-topology routing based on the traffic flow requirements using different set of metrics • Metric weights exploitation • Metric weights should be decided according to applications and data flows • Applicable metrics or optimized weights may need to be changed on demand • Metrics related to security IETF-72 – July 2008 - Dublin

7. Next Steps • Too soon to ask for WG adoption • Please review and comment • Proposed approach: • Any metric missing • Be very cautious of not mandating metrics if not required (think protocol !). • Define the MUST, SHOULD, MAY, … IETF-72 – July 2008 - Dublin

8. Back-up slides

9. Residual Energy (Node metric) • Why • Power is highly precious resource in battery powered LLNs • To maintain energy balance among nodes for maximum network lifetime • Treated as a relative value • Considering statistical node lifetime and role of the node in the network • Constrained-based routing is needed • Generally, taken as a dynamic metric • Most battery operated devices have ability to estimate the remaining energy • Initial energy status can be considered as a static metric when monitoring energy status demands quite resources IETF-72 – July 2008 - Dublin

10. Current workload (Node Metric) • Why • Data processing along the data path is required • Queuing delays must be minimized for highly sensitive traffic • Difficult to be measured and compared • Also difficult to express in a quantitative form • Putting the workload as a "heavy" or "light" one bit metric can be good IETF-72 – July 2008 - Dublin

11. Node latency (Node Metric) • The time span from the arrival time to the departure time of a given packet at a node • Primarily made up of packet processing time and packet transmission time • High correlation with other metrics • Heavy workload increases node latency • Abundant computational resources reduce node latency IETF-72 – July 2008 - Dublin

12. Data Aggregation attribute • Data aggregation and fusion • Aggregation aims to reduce the amount of data • Fusion involves more complicated processing to improve accuracy of data • Data aggregation/fusion can be performed • Due to data correlation • Especially in urban applications where sensor nodes collect environmental information • High directional data flow is expected in a regular basis • Challenges • Capturing time and location dependent correlation among sensed data from nodes on the possible routes • In-network processing may have high complexity IETF-72 – July 2008 - Dublin

13. Node degree (Node Metric) • Node degree • Number of neighbors that can send a message to the node directly • Neighbors are nodes located within the transmission range of the node • A high node degree, generally • Is helpful for quick route recovery when the next hop node on the route cannot be accessible • Node degree has to be carefully utilized in routing decision • A node with a high degree has a high possibility to have heavy workload in a busy network IETF-72 – July 2008 - Dublin

14. Dynamicity (Node Metric) • Measured by many different factors such as • Mobility • Transmission range • Duty cycle • The rate at which node joins and leaves the network • Directly affects the network topology and connectivity • May trigger route reestablishment process • Less dynamic nodes should be preferred for path selection • Classifying nodes into static and dynamic can be helpful • May be a static or dynamic metric • When dynamic, the network administrator will have to use consistent metric values IETF-72 – July 2008 - Dublin

15. Node reliability (Node Metric) • Deeply related to node dynamicity • Node reliability deteriorates as node dynamicity increases • Node reliability is a wider concept than node dynamicity • Node dynamicity metric can be covered by node reliability metric • A crucial metric • Nodes in LLNs may stay in a sleep mode most of the time • A sleeping node should not be an intermediate node • Status of a node must be monitored or can be anticipated • Residual energy of a node should be predictable • To avoid the node’s battery out during routing process • Hard to be estimated or monitored • A specific function needs to be defined IETF-72 – July 2008 - Dublin

16. Link Attributes • Link attributes in static LLNs • Can be considered as static ones • Challenging to update them in a real-time manner • Quite time- and energy-consuming work • Static LLNs have also variables like appearance of obstacles and signal interference • Link attributes in dynamic LLNs • May need to take these attributes as dynamic metrics • Values of dynamic metrics • Cannot be obtained easily • To use historical data and average them within a specified time window. IETF-72 – July 2008 - Dublin

17. Bandwidth (Link Metric) • Can be taken as a link capacity metric • In case of wireless link, the link capacity is shared among nodes in a single wireless link • Can be evaluated as nodes’ communicational capability IETF-72 – July 2008 - Dublin

18. Reliability – Quality (Link Metric) • Can be measured by • Bit Error Rate (BER) • Mean Time Between Failures (MTBF) • Link churn (the rate at which links change between good and bad) • Closely related to node reliability especially in wireless LLNs • Two nodes which form a link affect directly to the link reliability • Also influenced by other factors like • Unexpected obstacles • Temporary interference • An essential routing metric • Change of link quality directly affects network connectivity • Increasing link and node reliability together enhances route robustness IETF-72 – July 2008 - Dublin

19. Propagation delay (Link Metric) • Is the time taken for the packet to traverse the link from the source node to the target node • Path (route) latency is made up of nodes’ latency and links’ propagation delay on the path • Can be obtained by making average from historical data IETF-72 – July 2008 - Dublin