Ramakrishna Gummadi, Ramesh Govindan, Konstantinos Psounis Interference-Aware Fair Rate Control in Wireless Sensor Networks (IFRC) Sumit Rangwala Ramakrishna Gummadi, Ramesh Govindan, Konstantinos Psounis

Problem Definition Wireless network of N nodes Data transmission over multiple hops to a single node “Design a distributed algorithm to dynamically allocate fair and efficient rate to each flow” f20 f19 f15 f11 f13 10 Neighbor 11 12 13 14 15 16 17 18 19 20 21

Motivation: A Wireless Sensor Network for Collecting Structural Vibrations Nodes measured vibrations and transmitted it to a central node Over multiple hops Preconfigured rates for each flow Led to congestion More than an hour to receive 10 min of vibration data in a 15 node network

Assumptions consistent with current practice in sensornets CSMA MAC (without RTS/CTS) Link-layer retransmissions Routing Tree One flow originating per node f20 f19 f15 f11 f13 10 Neighbor 11 12 13 14 15 16 17 18 19 20 21 Assumptions consistent with current practice in sensornets

Challenges Goal Max-min allocation Wireless Networks Transmission rate from a node to its neighbor depends on neighborhood traffic Flows affecting this transmission rate are not merely flows traversing a node. fi fj A m n B Flows that affect each others' rate may not traverse a common link or node

Challenges Transmission rate along 16 →14 Dependent on traffic on various other links 20 → 16 (a) , 21 → 16 (b), 14 → 12 (c) 17 →14, 13 →11, 12 →10 Transmission rate along 16 →14 Dependent on traffic on various other links 20 → 16 (a) , 21 → 16 (b), 14 → 12 (c) 17 →14 (d), 13 →11 (e), 12 →10 (f) Transmission rate along 16 →14 Dependent on traffic on various other links 20 → 16, 21 → 16, 14 → 12 17 →14, 13 →11, 12 →10 Transmission rate along 16 →14 Dependent on traffic on various other links 20 → 16 (a) , 21 → 16 (b), 14 → 12 (c) 17 →14 (d), 13 →11 (e), 12 →10 (f) 10 Neighbor Child/Parent f 11 12 e c 13 14 15 d The rate of flows traversing 16 →14 (flows from 20, 21, and 16) … is affected by rate of: Flows originating from 17, 14, 13, 12, As well as 15, 18, 19 16 17 18 19 a b 20 21

Definition: Potential Interferer Interfering links l1 interferes with a link l2 if transmission along l1 prevents initiation of a transmission along l2 or successful reception of a transmission along l2. Potential interferer Node n1 is a potential interferer of node n2 if flow originating from node n1 uses a link that interferes with the link n2 → parent(n2). 10 Neighbor Child/Parent f 11 12 e c 13 14 15 d For CSMA and many-to-one traffic potential interferer (ni) includes neighbors of ni neighbors of parent(ni) Descendents of all the above nodes 16 17 18 19 a b 20 21

IFRC Design Congestion Detection Congestion Sharing Rate Adaptation Based on avg. queue length Congestion Sharing To all the potential interferers Rate Adaptation AIMD rlocal (rate of flow from this node) Forwarding Traffic Queue at each node Packet transmitted until queue is empty (with retransmission) IFRC adapts rate of flow originating at a node, not the rate of flows traversing the node

Congestion Detection and Rate Adaptation Based on queue length calculated as qavg = wq * qinst + (1- wq) * qavg Thresholding Rate Adaptation Every 1/rate sec (Additive Increase) rate = rate + δ / rate On local congestion (Multiplicative Decrease) rate = rate/2

Congestion Sharing Each node piggybacks on every transmitted packet Its own rate (rlocal) and its congestion state Rate and congestion state of its most congested child

These rules are sufficient to signal all potential interferers Congestion Sharing Rule 1: Local rate of a node should not be greater than that of its parent (rlocal < rparent) Rule 2: For any congested neighbor or congested child of a neighbor Local rate should not be greater than the rate of the congested node (rlocal < rcongested node) 10 Neighbor Child/Parent 11 12 13 14 15 16 17 18 19 20 21 These rules are sufficient to signal all potential interferers

Parameter Selection Additive Increase δ = rate of increase Analytically characterize δ to ensure stability Queue Threshold Network size and topology Avg. depth of the tree

Evaluation on Sensor Testbed Platform Tmote Sky TinyOS 1.1.15 Setup 40 node testbed Network diameter = 8 hops Static routing tree Depth of the Tree = 9 hops Link quality varied from 66% to 96% Each experiment was conducted for an hour 3 5 1 4 8 6 7 14 10 11 12 13 9 18 20 21 16 15 24 17 26 22 25 27 28 30 31 23 32 36 34 29 35 33 39 37 38 41 40 42 2 19 4th Floor Base Station

Topology Base Station

Per Flow Goodput and Packet Reception Average goodput as well as the instantaneous goodput is fair

Comparison with Optimal IFRC achieves 80% of the optimal fair rate IFRC achieves 60% of the optimal fair rate IFRC achieves 60-80% of the optimal fair rate

Rate Adaptation and Instantaneous Queue Length Max Buffer Size = 64 Not a single drop due to queue overflow

Weighted Fairness IFRC works without modification Sending rate = weight* rlocal pkts/sec w = 1 w = 2 w = 1 IFRC assigns rate proportional to node weight

Multiple Sink Two base stations rooted at 1 and 41 IFRC is efficient Nodes get rates that are fair across trees IFRC is efficient Node 4,5 and 6 get greater (but equal) rates Their flows don’t traverse the most congested region.

Conclusions Analysis of set of flows that share congestion at a node Potential interferers Design and implementation of low-overhead rate control mechanism Analysis of IFRC’s steady-state behavior Provide guidelines for parameters selection

Thank You For more Information Code http://enl.usc.edu/~srangwal/projects/ifrc.html Code Tinyos contrib tinyos-1.x/contrib/usc-ifrc ENL public CVS http://enl.usc.edu/cgi-bin/viewcvs/viewcvs.cgi/ifrc

Backup Slides

Definition: Fair and Efficient Allocation fi flow originating from node i Fi flows routed through node I At each node i, define Ғi to be the union of Fi and all sets Fj where j is either a neighbor of i, or a neighbor of i’s parent. These flows are flows from i’s potential interferers. Allocate to each flow in Ғi a fair and efficient share of the nominal bandwidth B. Denote by fl,i the rate allocated at node i to flow l. Repeat this calculation for each node. Assign to fl the minimum of fl,i over all nodes i. 10 Neighbor Child/Parent 11 12 13 14 15 16 17 18 19 20 21

Related Work Sensornets Graceful, fair, degradation under load [Hull et al. (Fusion), Wan et al. (CODA)] Centralized rate allocation [Sankarasubramaniam et al. (ESRT), Ee et al.] AIMD-based rate adaptation without congestion sharing [Woo et al.] Unlike prior work, we precisely identify the set of potential interferers Wireless ad-hoc networks Congestion sharing heuristics for any-to-any communication [Xu et al. (NRED)] These heuristics don’t precisely identify the set of potential interferers

Congestion Detection Based on queue length calculated as EWMA qavg = wq * qinst + (1- wq) * qavg Multiple thresholds Lower threshold L Upper thresholds U(k) = U(k-1) + I/2k-1 U(0) = U Local Congestion L U U + I U + 3I/2 Local Congestion

Rate Adaptation Slow start Slow start ends when Starts with rate = rinit Every 1/ rate sec rate = rate + Φ Slow start ends when node itself get congested constrained by other nodes to reduce its rate Congestion sharing

Congestion Detection and Rate Adaptation ri remains unchanged L U every 1/ri sec ri = ri+δ/ri ri = ri /2 U + I U + 3I/2 Rate adaptation with changing queue size

Base Station Maintains rbase station, like rlocal of any other node, to share congestion across nodes Follows the same algorithm for rate adaptation with one exception Decreases rbase station only when a child of base station is congested. It does not decreases its rate when any other neighbor is congested or any child of a neighbor is congested.

Parameter Selection (Steady State) Additive increase Constraint on ε U0 and U1 based on [Floyd et al.] Rule of thumb for Fj (n = size of network)

Evaluation (Tree)

Parameters Used

Comparison with Optimal Max Queue Length IFRC achieves 60-80% of the optimal fair rate

Node Addition Nodes join

Node Deletion Nodes leave

IFRC (No Link Layer Retransmissions)

Subset of node Special case of weighted fairness nodes with no data to send ≡ weight = 0

Multiple Sink (Trees) Base Stations