QoS Associated Path Selection in Wireless Mesh Networks

Transcription

1 QoS Associated Path Selection in Wireless Mesh Networks Sandip Chakraborty, Sukumar Nandi Department of CSE IIIT Guwahati, Guwahati INDIA Department of CSE IIT Guwahati, Guwahati INDIA 16 December, 2014

2 Preface: Wireless Mesh Networks Wireless Mesh Networks Some Practical Implementations: - Thousands of practical deployments of mesh networking technology (municipal networks, community networks), for commodity and commercial usage, community_networks_by_region

3 Introduction: Path Selection Frameworks for Mesh Four types of basic path selection mechanisms, - Proactive Path Selection - Reactive Path Selection - Hybrid Path Selection - Opportunistic Path Selection

4 Basic Path Selection Frameworks: Proactive and Reactive Proactive path selection: - Precomputed path selection information - A path selection table is built based on the information obtained from path selection packet broadcast - Optimized Link State Routing (OLSR) - Network topology is formed from link state path selection packet broadcast - Shortest path algorithm over network topology - pre-compute path selection paths Reactive path selection: - 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)

5 Other Path Selection Protocols Hybrid Path Selection - Proactive + Reactive Opportunistic Path Selection - 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

6 IEEE s Mesh Standardization Standardized in September, 2011 Provides MAC layer functionalities to a mesh backbone network IEEE s mesh nodes, - Mesh Stations (STA) - Mesh Gates

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

8 HWMP: Path Quality Measurement Airtime Link Metric (ALM): [ 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)

9 Effect of Channel Fluctuation over Airtime Link Metric ALM depends significantly on the channel quality (in terms of received signal strength) and packet error rates. In a backbone mesh network with high data rate support, the airtime link value changes very frequently. Proactive HWMP fails to adopt to this changes because of its long lifetime. Therefore for most of the cases in a time-variant noisy channel, a stale link metric value is used to find out the mesh path. Path selection protocol performance significantly depends on the channel interference and MAC layer scheduling informations. However, HWMP along with ALM does not consider interference during path selection. It can be noted that the physical data rate is used in ALM calculation, rather that the actual or expected data rate.

10 Why ALM does not Perform Well for Delay Sensitive Traffics? The size of ALM test packets is very low. Therefore it frequently overlooks the delay introduced by inter-flow interference. The ALM test packets are periodic broadcast packets. Therefore they do not account for interference during channel access. ALM gives only the transmission delay. It does not include queuing delay. In a mesh network, majority of mesh path delay is contributed by the queuing delay.

11 IITGMesh: An IEEE n+s Mesh Networking Testbed Internet STA-1 STA-3 STA-5 STA-8 STA-13/Gate STA-6 STA-9 STA-12 STA-2 STA-4 STA-7 STA-10 STA-11

12 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 -

13 Effect of Data Packet Size Over Path Delay Average Mesh Path Delay (ms) Delay Estimation from ALM Transmission Delay Transmission + Queuing Delay Data Packet Size (Kb)

14 Queuing Estimated Airtime Link Metric (QE-ALM) Let p i denotes transmission failure probability and κ is the maximum number of retransmissions according to IEEE EDCA channel access. Further assume that L is the data packet length including the protocol overheads and B is the channel bandwidth. Let T is the expected service time for a data packet. Then, ( 1 p κ ) E[T ] = i L 1 p i B + E[B] where E[B] is the expected back-off time.

15 Queuing Estimated Airtime Link Metric (QE-ALM) The expected queuing delay E[D q ] can be estimated as follows, E[D q ] = N +1 i=1 E[T i ] where E[T i ] is the expected service time for data packet i. When a new packet P e (P d ) is enqueued (dequeued) in the interface queue, the expected queuing delay is computed as, E[D q (t + 1)] = E[D q (t)] + E[T Pe ] E[D q (t + 1)] = E[D q (t)] E[T Pd ] QE-ALM C d a is defined as, C d a = C a + E[D q ]

16 Validation of QE-ALM Average Mesh Path Delay (ms) Average Mesh Path Delay QE-ALM Data Packet Size (Kb)

17 QE-ALM over Selective Greedy Path Selection Selective Greedy (SelG) Path Selection 1 - a two phase mesh path selection protocol. First Phase: Select a set of potential forwarders. Second Phase: Select one of the nodes as a next hop from the set of potential forwarders based on statistical analysis. SelG+ : QE-ALM + SelG 1 Chakraborty, Sandip, and Sukumar Nandi. Selective greedy routing: exploring the path diversity in backbone mesh networks. Wireless Networks, October 2014, Volume 20, Issue 7, pp

18 QE-ALM: Effect of reactive path selection timeout MOS (a) MOS for Voice Traffic 3 SelG+ 2.8 SelG 2.6 HWMP Reactive Path Selection Timeout (TU) SSIM (b) SSIM for Video Traffic 0.65 SelG+ SelG 0.6 HWMP Reactive Path Selection Timeout (TU)

19 QE-ALM: Performance of background (CBR) traffic Throughput (Kbps) (a) Throughput for CBR Traffic SelG+ SelG HWMP Data Generation Rate (Kbps) End-to-end Delay (ms) SelG+ SelG HWMP (b) Delay for CBR Traffic Data Generation Rate (Kbps)

20 QE-ALM: Performance of best effort (FTP) traffic (a) Throughput for FTP Traffic SelG+ SelG HWMP SelG+ SelG HWMP (b) Delay for FTP Traffic Throughput (Kbps) End-to-end Delay (ms) Number of FTP Flows Number of FTP Flows

21 Conclusion A QoS associated mesh path selection protocol for wireless mesh network built over IEEE s standard. The proposed improvements over the selective greedy path selection mechanism uses an advanced path selection metric, that considers mesh path delay at its core. Delay sensitive traffics can use a minimum delay path for traffic forwarding, that significantly improves their QoS parameters. The performance of the proposed SelG+ protocol is evaluated from a practical mesh networking testbed, and compared with SelG and the standard HWMP protocols for mesh path selection.

22 Thank You