Real-Time Communication in IEEE Wireless Mesh Networks: A Prospective Study

Transcription

1 in IEEE : A Prospective Study January 2011 Faculty of Engineering of the University of Porto

2 Outline 1 Introduction in IEEE : A Prospective Study 2 / 28

3 Initial Considerations Introduction Motivation & Objectives 1 Introduction in IEEE : A Prospective Study 3 / 28

4 Initial Considerations Initial Considerations Introduction Motivation & Objectives Prospective Study Kind of a Survey Study Real-Time communication in IEEE Wireless Mesh Networks Still in progress Ph.D research topic/area in IEEE : A Prospective Study 4 / 28

5 Introduction Initial Considerations Introduction Motivation & Objectives IEEE Standard Wireless LAN dominant solution High performance Low cost Fast deployment Set of nodes connected without a central infrastructure Relay frames from one node to another Why Mesh? Enables rapid deployment Easy to provide coverage in hard-to-wire areas Self-healing, resilient, extensible in IEEE : A Prospective Study 5 / 28

6 Initial Considerations Introduction Motivation & Objectives Introduction (cont.) The traffic should respect a set of QoS requirements Real-time streams have well-defined periodicity, deadline and execution time in IEEE : A Prospective Study 6 / 28

7 Motivation & Objectives Initial Considerations Introduction Motivation & Objectives Motivation IEEE Demand for wireless broadband access and higher speed rates Medium Access mechanisms are not feasible to wireless mesh networks challenge in providing Real-Time communication Lack of central infrastructure High level of heterogeneity Node mobility Multi-hop characteristics in IEEE : A Prospective Study 7 / 28

8 Initial Considerations Introduction Motivation & Objectives Motivation & Objectives (cont.) Objectives Investigate the Real Time constraints in IEEE Evaluate the proposed techniques in IEEE : A Prospective Study 8 / 28

9 1 Introduction in IEEE : A Prospective Study 9 / 28

10 Extend the network communication coverage without any additional infrastructure Use multi-hop technique Nodes can relay traffic by traversing multiple hops Support a larger number of nodes IEEE s Wireless Mesh Standard Integrates mesh networking services and protocols with at the MAC Layer Allows the support of a larger diversity of wireless technologies in IEEE : A Prospective Study 10 / 28

11 (cont.) STA STA MP STA MAP MP MP MP MPP wired network Internet STA MAP MP MAP MP Meshcloud MPP MP Mesh Point MPP MAP Mesh Portal Point MeshAccess Point STA Legacy Station STA STA Mesh link Legacy link Wired link Figure: Elements of a IEEE s Network. in IEEE : A Prospective Study 11 / 28

12 RT Communication in Real-Time Techniques 1 Introduction in IEEE : A Prospective Study 12 / 28

13 RT Communication in Real-Time Techniques in IEEE s has some real-time constraints The medium access control was designed to single hop networks Not well-suited for multi-hop networks For an absolute QoS guarantee may be required: Resources reservation Maintenance the required/negotiated delay and jitter values in IEEE : A Prospective Study 13 / 28

14 Real-Time Techniques RT Communication in Real-Time Techniques Integrated Services Provides per-flow QoS guarantees to individual applications Several services classes are defined Each application should be able to choose a class based on their QoS requirements Uses RSVP (Resource reservation Protocol) to allocate resources to the links along the data path in IEEE : A Prospective Study 14 / 28

15 RT Communication in Real-Time Techniques Real-Time Techniques (cont.) Differentiated Services Specifies a restricted communication domain with determined requirements Boundary routers delimit/control the ingress/egress network traffic Classify the traffic according to a service level specification The traffic inside the domain is transmitted at maximum available speed in IEEE : A Prospective Study 15 / 28

16 RT Communication in Real-Time Techniques Real-Time Techniques (cont.) Resources Reservation DARE (Distributed end-to-end Allocation of time slots for REal-time) Periodically reserves time slots in all nodes along a path between source and destination Uses RTR/CTR frames (modified RTS/CTS model) to reservervation Request to Reserve / Clear to Reserve RTR includes requested duration and periodicity of a time slot After the reservation is done and during the amount of reserved time the frames may be transmitted in IEEE : A Prospective Study 16 / 28

17 RT Communication in Real-Time Techniques Real-Time Techniques (cont.) Rate Adaptation MTOP (Multi-hop Transmission Opportunity) Multi-rate adaptation mechanism for IEEE Acts when a given Transmission Opportunity cannot allows frames to be transmitted in that opportunity Takes advantage of different defer thresholds to send frames to next hops Different transmission rates (1 Mbps and 11 Mbps), has different defer thresholds ( dbm and dbm) The defer threshold difference is 8.9 db This difference is the multi-rate margin that MTOP exploits to allow a frame to travel 1 or 2 more hops in IEEE : A Prospective Study 17 / 28

18 RT Communication in Real-Time Techniques Real-Time Techniques (cont.) Multi-Channel Communication FFMAC (Fast Forward Medium Access Control) Provides real-time guarantees through multiple communication channels Initially defines a path between source and destination HWMP (Hybrid Wireless Mesh Protocol) Reserves one channel to exchange control frames (control channel) and the remainder channels to exchange data frames (data channels) Proposes a Forwarding Model to exchange packets Uses RREQ/RREP (Route Request/Route Reply) in the control channel to establish a route between source and destination After path establishment the nodes exchange packets in IEEE : A Prospective Study 18 / 28

19 Handoff Procedures Reducing IEEE Handoff Delays 1 Introduction in IEEE : A Prospective Study 19 / 28

20 Handoff Procedures Handoff Procedures Reducing IEEE Handoff Delays Handoff Mobility process which allows a mobile station to move from one access point to another The communication is interrupted during an interval The stations are unable to transmit frames during the AP transition Occurs when received power signal is lower than a threshold Can occur in single layer or in multiple layers Data Link/MAC layer (2) Network layer (3) Application layer (5) in IEEE : A Prospective Study 20 / 28

21 Handoff Procedures Reducing IEEE Handoff Delays Handoff Procedures (cont.) IEEE Handoff process Scanning Authentication (Re)association IEEE Handoff delays Scanning phase is the responsible for consume most of the delay time in IEEE : A Prospective Study 21 / 28

22 Handoff Procedures Reducing IEEE Handoff Delays Handoff Procedures (cont.) Subnet 1 Router Subnet 2 Bridge 1 Bridge 2 AP 1.1 AP 1.2 AP 2.1 AP 2.2 Layer 2 Handoff Layer 3 Handoff Moving... Moving... Station A Station A Station A Figure: A mobile station in handoff process. in IEEE : A Prospective Study 22 / 28

23 Handoff Procedures Reducing IEEE Handoff Delays Handoff Procedures (cont.) Handoff Station Scanning Reassociation Probe Request (Broadcast) Probe Response. Probe Request (Broadcast) Probe Response Authentication Request Authentication Response (Re)association Request (Re)association Response AP2 AP1... AP(x) New AP Figure: IEEE handoff process. in IEEE : A Prospective Study 23 / 28

24 Handoff Procedures Reducing IEEE Handoff Delays Reducing IEEE Handoff Delays Cross-layer Techniques Off-line / Online phase Off-line phase Pre-computes a ratio of data frames relayed to a target MAP based on Contention Window (MAC layer) and Received Signal Strength (PHY layer) values Online phase Uses pre-computed transmission ratio to control data relaying during the handoff process There is an anchor node that will start transmitting frames from source to destination (in advance) using that transmission ratio in IEEE : A Prospective Study 24 / 28

25 Handoff Procedures Reducing IEEE Handoff Delays Reducing IEEE Handoff Delays (cont.) Explicit Multicast (XCast) Architecture proposed to facilitate inter-gateway handoff Enables a parallel execution of multi-layers Instead of sequential execution (as usual in traditional approaches) Uses a caching mechanism to minimize packet loss during handoff Packets are cached in advance in IEEE : A Prospective Study 25 / 28

26 Future Work 1 Introduction in IEEE : A Prospective Study 26 / 28

27 Future Work Preliminary study of techniques to guarantee real-time communication in wireless mesh networks Resources Reservation and Handoff Management techniques Brief and initial state-of-the-art for my Ph.D research A combination of these techniques seems to be promising in IEEE : A Prospective Study 27 / 28

28 Future Work Introduction Future Work Extend to a survey Further research in Real-Time techniques Combine resource reservation with improved handoff management techniques Implement and compare these techniques Through a simulator software Analyze their viability to support real-time communication Propose and evaluate new techniques to improve Real-Time communication Return in IEEE : A Prospective Study 28 / 28