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An Effective QoS Differentiation scheme for wireless mesh networks IEEE Network Jan/Feb 2008

This paper presents a QoS differentiation scheme for wireless mesh networks, focusing on the interaction of cooperative transmission, scalability, and fairness. It proposes an effective strategy to achieve QoS differentiation in collocated and general topologies.

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An Effective QoS Differentiation scheme for wireless mesh networks IEEE Network Jan/Feb 2008

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  1. An Effective QoS Differentiation scheme for wireless mesh networksIEEE Network Jan/Feb 2008 Honglin Hu, Shanghai Research Center for Wireless Communications Yan Zhang, Simula Research Laboratory Hsiao-Hwa Chen, National Cheng Kung University Presented by Guan-Wei ,Chen NTU IM OPLAB

  2. About Authors- Honglin Hu • received his Ph.D. degree in communications and information system in January 2004 from the University of Science and Technology of China • Working for international standardization and other collaborative researches on next generation wireless communication systems NTU IM OPLAB

  3. About Authors- Yan Zhang • received his B.S. degree in communication engineering from Nanjing University of Post and Telecommunication, China. • received his M.S. degree in electrical engineering from Beijing University of Aeronautics and Astronautics, China. • received his Ph.D. degree from the school of Electrical and Electronics Engineering,Nanyang Technological University, Singapore. NTU IM OPLAB

  4. About Authors- Hsiao-Hwa Chen • received his B.S. and M.S. degrees in electrical engineering from Zhejiang Universityin 1982、1985 , China. • received his Ph.D. degree in electrical engineering from theUniversity of Ouluin 1990 , Finland. NTU IM OPLAB

  5. Today’s Agenda 1 - INTRODUCTION 2 - SYSTEM MODEL FOR MESH NETWORK 3 - QoS DIFFERENTIATION SCHEME 4 - DISSCUSSION AND FUTURE WORK 5 - CONCLUSION NTU IM OPLAB

  6. Today’s Agenda 1 - INTRODUCTION 2 - SYSTEM MODEL FOR MESH NETWORK 3 - QoS DIFFERENTIATION SCHEME 4 - DISSCUSSION AND FUTURE WORK 5 - CONCLUSION NTU IM OPLAB

  7. INTRODUCTION1.1-Background • Wireless mesh networks (WMNs) consists of mesh routers and clients • can be independently implemented • or integrated with other communications systems such as conventional cellular networks • be characterized by dynamic self-organization, self-configuration, and self-healing • Quick deployment ,easy maintenance, low cost, great scalability, and reliable NTU IM OPLAB

  8. INTRODUCTION1.1-Background • International standardization organizations are working on the specifications of mesh networking modes • IEEE 802.11、IEEE 802.15、IEEE 802.16 IEEE 802.20 • Wireless metropolitan area networks offer two standardizations • Point-to-multipoint (PMP) • Mesh network operations NTU IM OPLAB

  9. INTRODUCTION1.2-PMP mode • Base station (BS) • performs a central role to coordinate and replay all communications • Subscriber station (SS) • under the management of the BS • before transmitting data to other SSs has to communicate with BS NTU IM OPLAB

  10. INTRODUCTION 1.2-PMP mode • Wireless networks promise to support a variety of traffic types • High-data-rate delay-sensitive application • Video streaming • Low-data-rate delay-sensitive application • Web surfing • Smoothly handle bursty traffic over the Internet • need to deal with different types of traffic types NTU IM OPLAB

  11. INTRODUCTION 1.2-PMP mode • Various quality of service should be defined on PMP mode • Four connection-based QoS classes have been specified: • Unsolicited grant service (UGS) • Real-time polling service (rtPS) • Non-real-time polling service (nrtPS) • Best effort (BE) NTU IM OPLAB

  12. INTRODUCTION1.3-Mesh mode • Unlike PMP mode, mesh mode has no clearly separated downlink and uplink • Every SS can directly communicate with its neighbors without the BS • Typically, install one or several nodes as BS to connect to external backhaul link NTU IM OPLAB

  13. INTRODUCTION1.3-Mesh mode • No similar studies have been done on QoS priority differentiation schemes • IEEE 802.16 standard define • centralized scheduling scheme has algorithms for real-time and non-real-time traffic • distributed scheduling scheme has not been fully addressed NTU IM OPLAB

  14. INTRODUCTION1.4-Our contribution • This paper propose an effective strategy to achieve QoS differentiation • Collocated and general topologies • Interaction of cooperative transmission, the scalability problem, and the fairness issue NTU IM OPLAB

  15. Today’s Agenda 1 - INTRODUCTION 2 - SYSTEM MODEL FOR MESH NETWORK 3 - QoS DIFFERENTIATION SCHEME 4 - DISSCUSSION AND FUTURE WORK 5 - CONCLUSION NTU IM OPLAB

  16. SYSTEM MODEL FOR MESH NETWORK2.1-Frame Structure in Mesh Mode • PMP mode supports both frequency-division duplex (FDD) and time-division duplex (TDD) • IEEE 802.16 mesh mode only supports TDD operation for transmission several MSSs have to share and compete in the common radio channel (TDMA) NTU IM OPLAB

  17. SYSTEM MODEL FOR MESH NETWORK2.1-Frame Structure in Mesh Mode • Mesh frame consists of • data subframe • consists of medium access control (MAC) protocol data units (PDUs) • generic MAC header, a mesh subheader, optional data • Divided into a number of minislot • Start with two OFDM symbols serving for synchronization, followed by several MAC PDUs NTU IM OPLAB

  18. SYSTEM MODEL FOR MESH NETWORK2.1-Frame Structure in Mesh Mode • Mesh frame consists of • control subframe • creation and maintenance of cohesion • coordinated scheduling of data transfer • The minislot of data subframe is Where MSH-CTRL-LEN has four bits(0~15) and its value is advertised in the Network Descriptor *OFDM=orthogonal frequency-division multiplexing NTU IM OPLAB

  19. SYSTEM MODEL FOR MESH NETWORK2.1-Frame Structure in Mesh Mode • Two different typies of control subframes and occurs in a frame exclusively • network control subframe primarily for new nodes to achieve synchronization and join a mesh network • schedule control subframe for centralized or distributed scheduling for sharing MSSs in common radio resource NTU IM OPLAB

  20. SYSTEM MODEL FOR MESH NETWORK2.1-Frame Structure in Mesh Mode • Network control subframe • first transmission opportunity is network entry component carrying MSH-NENT • remaining (MSH-CTRL-LEN -1) transmission opportunities are network configuration component • the length of the transmission opportunity is 7 OFDM symbols • so the length of the transmission opportunity carrying MSH-NCHG is equal to (MSH-CTRL-LEN -1)*7 OFDM symbols NTU IM OPLAB

  21. SYSTEM MODEL FOR MESH NETWORK2.1-Frame Structure in Mesh Mode NTU IM OPLAB

  22. SYSTEM MODEL FOR MESH NETWORK2.1-Frame Structure in Mesh Mode • Scheduling Frame field in the Network Descriptor defines • that the number of frames having a schedule control subframe between two frames with network control subframes in multiples of four frames • Ex: If Scheduling Frame is 3 , then there are 12 control subframes between network subframes NTU IM OPLAB

  23. SYSTEM MODEL FOR MESH NETWORK2.1-Frame Structure in Mesh Mode NTU IM OPLAB

  24. SYSTEM MODEL FOR MESH NETWORK2.2-Centralized Scheduling Scheme • transmission opportunities in control subframe and minislots in data subframe are separated • Contention consequences in control subframe does not affect on data transmission • used to transfer data between MBS and MSSs • MBS gathers resource requests through MSH-CSCH from MSSs within a certain hop range NTU IM OPLAB

  25. SYSTEM MODEL FOR MESH NETWORK2.2-Centralized Scheduling Scheme • MBS determine flow assignments from resource requests and send assignments to MSSs • MBS determine their own opportunities using a common predetermined algorithm • If requests change ,MBS will rebroadcast adjusted flow assignments • and MSSs recalculate their opportunities • Scheduling Algorithm NTU IM OPLAB

  26. INTRODUCTIONcentralized scheduling scheme (con’t) Transmission-Tree Scheduling (TSS) Algorithm NTU IM OPLAB

  27. SYSTEM MODEL FOR MESH NETWORK2.3-Distributed Scheduling Scheme • Divided into coordinated and uncoordinated • the difference lies in whether scheduling messages are coordinated or uncoordinated in competing for shared radio channel • we address coordinated distributed scheduling due to tunable and predicative performance • MSH-DSCH throughout the scheduling process NTU IM OPLAB

  28. SYSTEM MODEL FOR MESH NETWORK2.3-Distributed Scheduling Scheme • MSH-DSCH field • Availabilities IE • starting frame number, starting minislot within frames,and number of available minislot for the granter to assign • Scheduling IE • Show next MSH-DSCH transmission time NextXmtTime and XmtHoldoffExponent of the node and also its neighbor nodes • Request IE • the resource demand of the node • Grants IE • conveys the granted starting frame number, the granted starting minislot within the frame, and the granted minislots range NTU IM OPLAB

  29. SYSTEM MODEL FOR MESH NETWORK2.3-Distributed Scheduling Scheme • Decide NextXmtTime of MSH-DSCH during its current trasmission time • There are two parameters, NextXmtMx and XmtHoldoffExponent in MSH-NCFG • Determine the next eligibility interval • Node can transmit in any slot in this interval NTU IM OPLAB

  30. SYSTEM MODEL FOR MESH NETWORK2.3-Distributed Scheduling Scheme • before a new transmission , the node needs to holdoff time • node choices temporary transmission opportunity after the holdoff time • Se is set of eligible competing nodes • is built for a specific node, and has pseudo-random mixing function to calculate value for each node NTU IM OPLAB

  31. SYSTEM MODEL FOR MESH NETWORK2.3-Distributed Scheduling Scheme • If the node has the biggest value, then it win competition • NextXmtTime is set as TempXmtTime • broadcasts to its neighbors in MSH-NCFG • otherwise, set TempXmtTime as the next transmission slot and repeat until it wins NTU IM OPLAB

  32. SYSTEM MODEL FOR MESH NETWORK2.3-Distributed Scheduling Scheme • Notations: • Nk : set of 2-hop neighbors • Nkunknown : 2-hop neighbors with unknown schedule • Nkknown = Nk \ Nkunkown • xk : holdoff exponent of node k • Hk = 2^(xk +4) : holdoff time • Vk = 2^(xk) : eligibility interval • Sk = number of slots node k fails the competition • τk = Hk + Sk : interval between successive TOs • M(s) : expected number of competing nodes in slot s NTU IM OPLAB

  33. SYSTEM MODEL FOR MESH NETWORK2.3-Distributed Scheduling Scheme Identical holdoff Exponent eligibility interval holdoff time Non-identical holdoff Exponent NTU IM OPLAB

  34. SYSTEM MODEL FOR MESH NETWORK2.3-Distributed Scheduling Scheme Proof: has (N-1) neighbors and is binomial distributed EX: By the assumption of independence (non-identical): identical holdoff exponent non-identical holdoff exponent NTU IM OPLAB

  35. SYSTEM MODEL FOR MESH NETWORK2.3-Distributed Scheduling Scheme P(Compete|S)= Assume Sj are geometrical distributed. To estimate pk: H+E(S) E(S)=1/p P(Compete|S)= NTU IM OPLAB

  36. SYSTEM MODEL FOR MESH NETWORK2.3-Distributed Scheduling Scheme directly give the approximation combining (27) and (28), NTU IM OPLAB

  37. Today’s Agenda 1 - INTRODUCTION 2 - SYSTEM MODEL FOR MESH NETWORK 3 - QoS DIFFERENTIATION SCHEME 4 - DISSCUSSION AND FUTURE WORK 5 - CONCLUSION NTU IM OPLAB

  38. QoS DIFFERENTIATION SCHEME • real-time QoS • non-real-time QoS • transmission interval in MSH-DSCH • eligibility interval and its length define generalized • αdenote XmtHoldoffExponent • a real numberβdenote length of eligibility interval Next transmission time: NTU IM OPLAB

  39. QoS DIFFERENTIATION SCHEME • γdenote real-time base value • λdenote holdoff exponent • XmtHoldoffTime is given as • Denote the set of QoS differentiated parameters node k as: • Sk denote the number of slots which node K fails before it wins NTU IM OPLAB

  40. QoS DIFFERENTIATION SCHEME • τk the interval between two consecutive MSH-DSCH transmission opportunities for node K • τk is the summation of the holdoff transmission time and Sk • Expected value is +E(Sk) • two scenarios collocated topology and general topology NTU IM OPLAB

  41. QoS DIFFERENTIATION SCHEME3.1-Collocate topology implement • Mk(s) denote the expected number of nodes competing with node k during slot s • the probability node k in pesudo-random election algorithm is 1/ Mk(s) • each node has the same probability to win a slot • the expected transmission interval of MSH-DSCH for any k can be derived • QoS different XmtHoldoffExponent was considered NTU IM OPLAB

  42. QoS DIFFERENTIATION SCHEME3.1-Collocate topology implement • for demonstration simplicity, N nodes are partitioned into three classes • set [α(i) ; β(i) ; λ(i); γ(i)] (i=1,2,3) • each node belongs to a class exclusively • EX: • [α(1) ; α(2); α(3) ]=[ 2 ; 2 ; 2 ] • [β(1) ; β(2); β(3) ]=[ 1.7 ; 2 ; 2.3 ] • [λ(1) ; λ(2); λ(3) ]=[ 1.7 ; 2 ; 2.3 ] • [γ(1) ; γ(2); γ(3) ]=[ 1 ; 2 ; 3 ] NTU IM OPLAB

  43. QoS DIFFERENTIATION SCHEME3.1-Collocate topology implement • evaluate the efficiency of parameters α, β, λ, γ to differentiate QoS • To examine α, set parameters β=2, λ=2, γ=2 • αis insignificant contribution to QoS assurance NTU IM OPLAB

  44. QoS DIFFERENTIATION SCHEME3.1-Collocate topology implement • To examine β, set parameters α=2, λ=2, γ=2 • β is insignificant contribution in achieving service differentiation for small or large N NTU IM OPLAB

  45. QoS DIFFERENTIATION SCHEME3.1-Collocate topology implement • To examine λ, set parameters α=2, β=2, γ=2 • E(τ) increases with λ • λ is significant contribution in achieving service differentiation both small or large N NTU IM OPLAB

  46. QoS DIFFERENTIATION SCHEME3.1-Collocate topology implement • To examine γ, set parameters α=2, β=2, λ=2 • E(τ) increases with γ • holdoff transmission time become longer and consequently the transmission interval become larger • γand λ can achieve service differentiation effectively but α,β are not obvious NTU IM OPLAB

  47. QoS DIFFERENTIATION SCHEME 3.2-General topology implement • denote set of known node • denote set of unknown node • E[τk] = • E[Sk] is affect both known and unknown nodes • challenge include node movement and topology changes NTU IM OPLAB

  48. QoS DIFFERENTIATION SCHEME 3.2-General topology implement • untimely delivery of the latest scheduling message to two-hop neighborhood • MAC layer some nodes may experience unexpected collision • out-of-date scheduling information while the underlying factors for unknown nodes are actually not available • analyze this issue from a probabilistic point of view to evaluate the scheduling performance NTU IM OPLAB

  49. QoS DIFFERENTIATION SCHEME 3.2-General topology implement • Denote be the probability that node is an unknown node of node k at instant t • If node k and node j do not know each other , and equal 1 • otherwise, they are zero • after network become stable • characteristics matrix Q [ ] NTU IM OPLAB

  50. QoS DIFFERENTIATION SCHEME 3.2-General topology implement • Base on matrix Q in general topology , the expected value of Skand expected transmission interval of an MSH-DSCH message τk can be calculated. • can use this probabilistic model to apply other network topologies to investigate the scheduling performance NTU IM OPLAB

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