Path Diversity and its Effect over High Speed Wireless Mesh Backbone: Towards a New Routing Framework

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1 Path Diversity and its Effect over High Speed Wireless Mesh Backbone: Towards a New Routing Framework Sandip Chakraborty Department of Computer Science and Engineering Indian Institute of Technology Guwahati, Guwahati INDIA 18 March, 2014

2 Outline Mesh networks: An Introduction A brief preface of my research works and achievements IITGMesh: A Practical Mesh Testbed at IIT Guwahati Some Observations from IITGMesh: Towards the Motivation SGF: A New Routing Paradigm Performance of SGF The Future Directions

3 Preface: Wireless Mesh Networks Broad Area of Research Wireless Mesh Networks Some Practical Implementations: - IEEE Standardized in September More than thousands deployments of mesh networking technology, for commodity and commercial usage, - Freifunk.net, Communty Mesh for Germany Open Mesh - Canberra Wireless Network, Australia CanberraWirelessNetwork

4 Preface: Mesh Networking Standards IEEE : IEEE s - Most popular: Cost effective, deployment-ease, commercially available for wide ranges and varieties - Cons: Less coverage - works good inside an enterprise or in a small urban/rural area IEEE : IEEE e, IEEE m - Coverage for a large area - Devices are large and costly, mostly works on licensed spectrum Cellular architecture, LTE (Multi-hop cellular) Heterogeneous networks, IEEE

5 Preface: IEEE Mesh Networking Research Goals It is important to understand that these goals are in order of importance, and an entirely different network architecture would result if the order were changed. 1 1 D. Clark The design philosophy of the DARPA internet protocols. SIGCOMM Comput. Commun. Rev. 18, 4 (August 1988),

6 Preface: IEEE Mesh Networking Research Goals Capacity vs Interference: Works in unlicensed band, self-interference as well as interference from external devices - End-to-end flow control fails to achieve the desired goal - they only count for congestion losses, not the contention or interference losses (a fundamental problem why convention TCP shows negative impact over wireless channel) - Heterogeneous traffic demands and the level of interference: Client traffic vs the Router traffic - Multi-channel and multi-interface : Cost vs Performance

7 Preface: IEEE Mesh Networking Research Goals Quality of Service (QoS) and Quality of Experience (QoE): The Internet was designed to meet the needs of users, and so any evaluative criteria must reduce, in essence, to the following question: how happy does this architecture make the users? 2 2 S. Shenker Fundamental design issues for the future Internet. IEEE J.Sel. A. Commun. 13, 7 (September 2006),

8 Preface: IEEE Mesh Networking Research Goals Fairness - End-user fairness : Equal fairness for equal priority users - Router fairness : Proportional fairness - ensures a router with more traffic load gets more (proportional) channel share - Fairness vs throughput trade-off - does it hold for a mesh network?

9 Preface: IEEE Mesh Networking Research Challenges Path Diversity: Multiple paths from a source to a destination; - Different path metrics give different best paths - Is there any BEST or OPTIMUM path at all? - Routing/forwarding strategy Vs Path metric

10 Preface: IEEE Mesh Networking Research Challenges Path Diversity: Multiple paths from a source to a destination; - Different path metrics give different best paths - Is there any BEST or OPTIMUM path at all? - Routing/forwarding strategy Vs Path metric Traffic Diversity: - Best or optimum policy is time dependent - Network evolves as it learns from the environment (cognitive network?)

11 Preface: IEEE Mesh Networking Research Challenges Data Rate Diversity: Varies from 2 Mbps to 600 Mbps with IEEE n - High data rate may not always reflect high user satisfaction. - Channel error is almost four times more for 600 Mbps compared to 300 Mbps - introduces jitter in the network (poor video streaming)

12 IITGMesh: An IEEE n+s Mesh Networking Testbed N3 N 2 N 1 50 m G RS Lab 2 RS Lab 1 N4 N9 N10 N 8 Security Lab N5 N 6 N 7

13 IITGMesh: Configuration Details RT3352 Router-on-Chip 300 Mbps IEEE b/g/n complaint Lanbowan ANT0627D8S-XP 2x2 directional MIMO antennas Embedded MIPS24KEc (400 MHz) with 32K I-Cache and 16K D-Cache 16/32-bit SDRAM DRAM up to 128 Mbytes 5 Ports 10/100 SW and RGMII Mesh Network: IEEE s protocol stack: MPM (mesh peer management) + EDCA (channel access) + HWMP (mesh forwarding) Linux kernel open80211s : Network monitoring and traffic generation tools: - Netflow Analyzer iperf Wireshark tcpdump Seagull Multi-protocol Traffic Generator -

14 However, interference among the communicating pairs can not be mitigated completely (maximum number of non-overlapping channels available in IEEE b/g/n is three only) 3 P. Dutta, S. Jaiswal, D. Panigrahi, and R. Rastogi, A new channel assignment mechanism for rural wireless mesh networks, in proceedings of The 27th IEEE IITGMesh: An Important Design Aspect IITGMesh relies on simultaneous transmission and reception (STAR) at a single router - to support spatial diversity (effective use of directional communication) In a single channel network, STAR is not possible due to self-interference and side-lobe interference. Use a channel assignment strategy, proposed by Dutta et al. 3 to enable STAR. - Use different non-overlapping channels to different interfaces of the same router.

15 Routing Strategies for Mesh Network and Their Evaluation over IITGMesh

16 Introduction: Routing Frameworks for Mesh Four types of basic routing mechanisms, - Proactive Routing - Reactive Routing - Hybrid Routing - Opportunistic Routing

17 Basic Routing Frameworks: Proactive and Reactive Proactive routing: - Precomputed routing information - A routing table is built based on the information obtained from routing packet broadcast - Optimized Link State Routing (OLSR) - Network topology is formed from link state routing packet broadcast - Shortest path algorithm over network topology - pre-compute routing paths Reactive routing: - On-demand information gathering - Ad-Hoc On-demand Distance Vector Routing (AODV) - Route Request (RREQ) broadcast when a path is necessary - RREQ eventually reaches at the destination - Reverse path establishment through Route Reply (RREP)

18 Other Routing Protocols Hybrid Routing - Proactive + Reactive Opportunistic Routing - Advantage of wireless broadcast - Every data packet is broadcast to the one-hop neighborhoods - Neighbors coordinate among themselves to decide who will forward (broadcast) the packet next. - Neighbor coordination is hard to design

19 IEEE s Mesh Standardization Standardized in September, 2011 Provides MAC layer functionalities to a mesh backbone network IEEE s mesh terminologies, - Mesh Points (MP): Mesh access points (routers and gateways) - Mesh Access Points (MAP) - Mesh Portal Points (MPP): Mesh gateways - Mesh Stations (STA): Client nodes

20 IEEE s Mesh Forwarding: Hybrid Wireless Mesh Protocol (HWMP) The standard routing protocol for IEEE s mesh networks Operates at MAC layer (considers lower layer forwarding path establishments) A hybrid routing protocol Operates in two modes - proactive tree based forwarding and reactive on-demand forwarding

21 HWMP: Path Quality Measurement Airtime Link Metric: [ Test Packet Size C = O ca +O p + Bit Rate Parameter a b O ca 75µs 355µs O p 110µs 364µs B t ] 1 (1 Channel Error Rate)

22 Proactive Tree Based Forwarding MPP periodically broadcast Route Announcement (RANN) (or Proactive Route Request (PRREQ)) message On receiving the RANN (or PRREQ) message, every MP selects the source as the tree parent (if it have not done so already), and rebroadcast the message.

23 Reactive On-Demand Forwarding Similar to Ad-Hoc On Demand Distance Vector Routing (AODV) Route Request (RREQ) broadcast at the source MP Reverse path establishment through Route Reply (RREP) message, when the destination MP receives the RREQ

24 Effect of Channel Fluctuation over Airtime Link Metric With 20% SINR fluctuation, there is approximately 40% fluctuation in airtime link metric (ALM) value. Traffic load slowly impacts ALM, however impact of SINR fluctuation is dominant. ALM fluctuation results in frequent route changes, called the route flapping. Receive Power (dbm) Load ALM (ms) Time (Hrs)

25 Route Flapping: Impact over Performance High Route Flapping: Network inconsistency Low Route Flapping: Network fails to adopt with channel variation

26 Route Flapping for the Conventional Protocols Route flapping is very less for the proactive HWMP: Fails to adopt with the link quality changes Route flapping is very high for the reactive HWMP: frequent path changes, control overhead is very high. SINR Variation (dbm) Route Flapping Low Load Route Flapping High Load Reactive HWMP Proactive HWMP Reactive HWMP Proactive HWMP Router Number

27 Selective Greedy Forwarding (SGF): A New Routing Paradigm A two step routing protocol: Selection of a set of potential forwarders (Proactive approach) Selection of the next hop from the set of potential forwarders (Greedy/Opportunistic Approach) - Effect of the variation in link information over the path information S

28 SGF: Selection of the Set of Potential Forwarders PPREQ Broadcast Reception of PPREP - Select the first best m neighbors, store the interface information along with the link metric and path metric - Update information if it is already there.

29 SGF: Greedy Selection of the Best Candidate Interference Estimation Estimation of the effect of current link metric value over the path metric value used during proactive computation Select the best candidate

30 SGF: Interference Estimation The Protocol Interference Model: Two nodes interfere with each other if they are within the interference range, R I (more than the communication range, R c, assume R I = q R c ) Refer to the figure: Either MP i can transmit, or a set of nodes within its interference range can transmit, provide they does not interfere with each other qxr c MP i MP u 1.5xqxR c MP v qxr c 2

31 SGF: Interference Estimation Two nodes does not interfere with each other if they are q R c distance apart Model the problem as a circle packing problem: How many circles of radius 0.5 q R c can be packed within a circle of radius 1.5 q R c? qxr c MP i MP u 1.5xqxR c MP v qxr c 2

32 SGF: Interference Estimation For every interface I k i Γ i of MP i, following condition must hold true for minimum interference data communication, Z(I k i )+ I m j H(I k i ) Z(I m j ) α Beam direction for k Interface I i MP u qxr c 2 Z(Ii k ) is a indicator that denotes whether interface Ii k is currently being used. α: Beamwidth of the interface H(I k i ): Set of interfering interfaces MP i MP v qxr c 1.5xqxR c

33 SGF: Utilization for Greedy Selection U(MP j,ii k ) = 1+ 1 P k ij ; (Ck ij) 2 ( ) 2 C k ij ( ) 2 C k ij ( ) 2 (C C k k ij ij ) 2 ( C k ij P k ij ; if Ck ij < Ck ij ) 2 P k ij ; if Ck ij > Ck ij if Ck ij = Ck ij C k ij : The link metric during the construction of the set of potential forwarders P k ij : The path metric during construction of the set of potential forwarders

34 SGF: Greedy Selection min MP j,i k i s.t. U(MP j,i k i ) Z(I k i )+ e H(I k i ) Z(e ) α MP j F i I k i Γ i The selection problem can be solved within O( F i Γ i ) time complexity. - F: Set of potential forwarders - Γ i : Set of interfaces

35 SGF: Routing performance A P 1 P 2 B Z(P 1 ) <= Z(P 2 ) C L 1 P 1 P 1 A P 2 B A P 2 B L 2 C Z(L 1 +P 1 ) <= Z(L 1 +P 2 ) Z(P 1 +L 2 ) <= Z(P 2 +L 2 )

36 SGF: Routing performance A P 1 P 2 B C Z(P 1 ) <= Z(P 2 ) L 1 P 1 P 1 A P 2 B A P 2 Ensures stable routing The utility function supports isotonicity. L 2 B C Z(L 1 +P 1 ) <= Z(L 1 +P 2 ) Z(P 1 +L 2 ) <= Z(P 2 +L 2 )

37 Forwarder Percentage MP j,ii k in included in F i, if and only if following condition is satisfied, ( ) 2 ) 2 P k ij ( Pk ij ) 2 δ ( Pk ij where, P k ij = min{pr il MP l,i r i F i } δ is called the Forwarder Percentage

38 Effect of Forwarder Percentage (δ) Route Flapping Low Load Route Flapping High Load δ = 60% δ = 40% δ = 20% δ = 60% δ = 40% δ = 20% Router Number An interplay of two factors - contention (or interference) and channel effect Contention for channel access increases as the traffic load increases. At low traffic load: Effect of channel fluctuation is more compared to contention effect Increased route flapping At high traffic load: Effect of contention oversuites the effect due to channel fluctuation Less route flapping (traffic follows the path with less contention)

39 SGF: Performance Average Per User MAC Throughput (Mbps) HWMP: Proactive HWMP: Reactive SGF: δ=30% SGF: δ=40% SGF: δ=50% Average End-to-End Delay (ms) HWMP: Proactive HWMP: Reactive SGF: δ=30% SGF: δ=40% SGF: δ=50% Average Number of Users Average Number of Users MAC Throughput Forwarding Delay Throughput increases with the increase in δ, and attains maximum (or gets saturated) with δ = 50%. The minimum delay path is a function of traffic load and SGF. When the traffic load is high, higher SGF results in less delay (as a result of load-contention dependency)

40 SGF: Performance Average Jitter (ms) HWMP: Proactive HWMP: Reactive SGF: δ=30% SGF: δ=40% SGF: δ=50% Average Number of Users Average Jitter MOS HWMP: Proactive HWMP: Reactive SGF: δ=30% SGF: δ=40% SGF: δ=50% Average Number of Users Mean Opinion Score for Voice Traffic

41 SGF: Performance for Video Traffic HWMP: Proactive HWMP: Reactive SGF: δ=30% SGF: δ=40% HWMP: Proactive HWMP: Reactive SGF: δ=30% SGF: δ=40% 25 SGF: δ=50% 0.9 SGF: δ=50% PSNR (db) 20 SSIM Average Number of Users Peak Signal to Interference Noise Ratio (PSNR) Average Number of Users Structural Similarity Index (SSIM)

42 SGF: Channel Fluctuation vs MOS SINR Variation (dbm) Load MOS HWMP Proactive HWMP Reactive SGF Time (Hrs)

43 Moving Forward... Though SGF significantly improves performance, compared to the conventional routing paradigm, however, we can not guarantee optimum/best performance always Performance depends heavily on channel condition fluctuation, which is random and unpredictable. Learn from the Environment: - What would be the traffic demand at a given time of the day? (varies from organization to organization) - What is the best response for a specific channel condition? (if the network can learn it from the past experience) - What can be the next step, according to the experience gained from the current step? (opportunistic approach) - If I execute a selfish behavior (that seems best for me), how much it effect others? (for some strategies, selfish behavior results best Nash bargaining)

44 Cognitive Mesh Network (CogMesh) Different from cognitive radio network (a subset of cognitive network) - not only deals with spectrum sharing Network learns from the environment gives the best possible response (may not be the globally best response) based on environment conditions Learning improves gradually best possible response tends to be the best response Network gradually evolves as it goes with time - Future Wireless Internet Architecture 4 4 Zorzi, M., Gluhak, A., Lange, S., & Bassi, A. (2010). From today s Intranet of things to a future Internet of things: a wireless-and mobility-related view. Wireless Communications, IEEE, 17(6), 44-51

45 CogMesh: How Learning Improves Performance - An Example HWMP: Proactive HWMP: Reactive SGF + Adaptive SPF HWMP: Proactive HWMP: Reactive SGF + Adaptive SPF 28 4 Average Jitter (ms) MOS Average Number of Users Average Number of Users

46 Performance Distortion in High Speed Mesh Networks: An Example Wireless data rate shows a quantum lap: 600 Mbps with IEEE n, and 6.77 Gbps with IEEE ac Very much suitable and attractive for backbone mesh networks. However, high data rate is not always good, an example: Average TCP Goodput (Mbps) MHz 20 MHz MCS TCP over IITGMesh MCS Bandwidth Data Rate

47 Thank You