Chapter 5 Ad Hoc Wireless Network. Jang Ping Sheu

Transcription

1 Chapter 5 Ad Hoc Wireless Network Jang Ping Sheu

2 Introduction Ad Hoc Network is a multi-hop relaying network ALOHAnet developed in 1970 Ethernet developed in 1980 In 1994, Bluetooth proposed by Ericsson to develop a short-range, low-power, lowcomplexity, and inexpensive radio inteface WLAN spec. is proposed in /11/2 2

3 Cellular and Ad Hoc Wireless Networks Cellular Wireless Networks: infrastructure dependent network Ad Hoc Networks: multi-hop radio relaying and without support of infrastructure Wireless Mesh Networks Wireless Sensor Networks The major differences between cellular networks and ad hoc networks as summarized in Table /11/2 3

4 Wireless Mesh Networks Cellular Wireless Networks Hybrid Wireless Networks Wireless Sensor Networks Infrastructure Dependent (Single-Hop Wireless Networks) Ad Hoc Wireless Networks (Multi-Hop Wireless Networks) Figure 5.1. Cellular and ad hoc wireless networks. 2009/11/2 4

5 A B C E D Switching Center + Gateway Base Station Mobile Node Path from C to E 2009/11/2 5 Figure 5.2. A cellular networks.

6 A B F C E D Mobile Node Wireless Link Path from C to E 2009/11/2 6 Figure 5.3. An ad hoc wireless networks

7 Table 5.1 Differences between cellular networks and ad hoc wireless networks Cellular Networks Ad Hoc Wireless Networks Fixed infrastructure-based Single-hop wireless links Guaranteed bandwidth (designed for voice traffic) Centralized routing Infrastructure-less Multi-hop wireless links Shared radio channel (more suitable for best-effort data traffic) Distributed routing Circuit-switched (evolving toward packet switching) Seamless connectivity (low call drops during handoffs) High cost and time of deployment Reuse of frequency spectrum through geographical channel reuse Packet-switched (evolving toward emulation of circuit switching) Frequency path break due to mobility Quick and cost-effective deployment Dynamic frequency reuse based on carrier sense mechanism 2009/11/2 7

8 Table 5.1 Differences between cellular networks and ad hoc wireless networks (cont.) Easier to achieve time synchronization Easier to employ bandwidth reservation Application domains include mainly civilian and commercial sector High cost of network maintenance (backup power source, staffing, etc.) Mobile hosts are of relatively low complexity Major goals of routing and call admission are to maximize the call acceptance ratio and minimize the call drop ratio Time synchronization is difficult and consumes bandwidth Bandwidth reservation requires complex medium access control protocols Application domains include battlefields, emergency search and rescue operation, and collaborative computing Self-organization and maintenance properties are built into the network Mobile hosts require more intelligence (should have a transceiver as well as routing/switching capacity) Man aim of routing is to find paths with minimum overhead and also quick reconfiguration of broken paths Widely deployed and currently in the third generation Several issues are to be addressed for successful commercial deployment even though widespread use exists in defense 2009/11/2 8

9 Applications of Ad Hoc Wireless Networks Military Applications Establishing communication among a group of soldiers for tactical operations Coordination of military object moving at high speeds such as fleets of airplanes or ships Requirements: reliability, efficiency, secure communication, and multicasting routing, Collaborative and Distributed Computing Conference, distributed files sharing Emergency Operations 2009/11/2 Search, rescue, crowd control, and commando operations Support real-time and fault-tolerant communication paths 9

10 Wireless Mesh Networks An alternate communication infrastructure for mobile or fixed nodes/users Provides many alternate paths for a data transfer session between a source and destination Advantages of Wireless Mesh Networks High data rate, quick and low cost of deployment, enhanced services, high scalability, easy extendability, high availability, and low cost per bit 2009/11/2 10

11 Wired Network Gateway node Transmission range A house with rooftop transceiver Wired link to the Internet Wireless link Figure 5.4. Wireless mesh networks operating in a residential zone 2009/11/2 11

12 Internet Radio relay node Multi-hop radio relay link Wired link to the Internet Lamp Coverage area Figure 5.5 Wireless mesh network covering a highway 2009/11/2 12

13 Wireless Sensor Networks A collection of a large number of sensor nodes that are deployed in a particular region Applications: military, health care, home security, and environmental monitoring Differences with the ad hoc wireless networks: Mobility of nodes, size of network, density of deployment, power constraints, data/information fusion, traffic distribution 2009/11/2 13

14 Hybrid Wireless Networks HWN such as Multi-hop cellular networks and integrated cellular ad hoc relay networks The base station maintains the information about the topology of the network for efficient routing The capacity of a cellular network can be increased if the network incorporates the properties of multi-hop relaying along with the support of existing fixed infrastructure Advantages: Higher capacity than cellular networks due to better channel reuse Increased flexibility and reliability in routing Better coverage and connectivity in holes 2009/11/2 14

15 A B C D E Switching Center + Gateway Base Station Mobile Node MCN communication Figure 5.6. MCN architecture. 2009/11/2 15

16 Issues in Ad Hoc Wireless Networks Medium access scheme Routing, Multicasting, TPC protocol Pricing scheme, QoS, Self-organization Security, Energy management Addressing and service discovery Deployment considerations 2009/11/2 16

17 Medium Access Scheme Distributed operation fully distributed involving minimum control overhead Synchronization Mandatory for TDMA-based systems Hidden terminals Can significantly reduce the throughput of a MAC protocol Exposed terminals To improve the efficiency of the MAC protocol, the exposed nodes should be allowed to transmit in a controlled fashion without causing collision to the on-going data transfer Access delay 2009/11/2 17

18 The Major Issues of MAC Scheme Throughput and access delay To minimize the occurrence of collision, maximize channel utilization, and minimize controloverhead Fairness Equal share or weighted share of the bandwidth to all competing nodes Real-time traffic support Resource reservation Such as BW, buffer space, and processing power Capability for power control Adaptive rate control Use of directional antennas 2009/11/2 18

19 The Major Challenge of Routing Protocol Mobility result in frequent path break, packet collision, and difficulty in resource reservation Bandwidth constraint: BW is shared by every node Error-prone and share channel: high bit error rate Location-dependent contention: distributing the network load uniformly across the network Other resource constraint: computing power, battery power, and buffer storage 2009/11/2 19

20 The Major Requirement of Routing Protocol Minimum route acquisition delay Quick route reconfiguration: to handle path breaks Loop-free routing Distributed routing approach Minimum control overhead Scalability Provisioning of QoS: supporting differentiated classes of services Support for time-sensitive traffic Security and privacy 2009/11/2 20

21 The Major Issues in Multicast Routing Robustness Protocols recover and reconfigure quickly from link breaks Efficiency minimum number of transmissions to deliver a data packet to all the group members Minimal Control overhead QoS support Efficient group management Scalability Security 2009/11/2 21

22 Transport Layer Protocols Objectives: setting up and maintaining End-to-end connections, reliable end-to-end data delivery, flow control, and congestion control Major performance degradation: Frequent path breaks, presence of old routing information, high channel error rate, and frequent network partitions 2009/11/2 22

23 Quality of Service Provisioning QoS often requires negotiation between the host and the network, resource reservation schemes, priority scheduling and call admission control QoS in Ad hoc wireless networks can be on a per flow, per link, or per node Qos Parameters: different applications have different requirements Multimedia: bandwidth and delay are the key parameters Military: BW, delay, security and reliability Emergency search and-rescue: availability is the key parameters, multiple link disjoint paths WSN: battery life, minimum energy consumption 2009/11/2 23

24 Quality of Service Provisioning QoS-aware routing: To have the routing use QoS parameters for finding a path The parameters are network through put, packet delivery ratio, reliability, delay, delay jitter, packet lost rate, bit error rate, and path loss QoS framework: A frame work for QoS is a complete system that attempts to provide the promised service The QoS modules such as routing protocol, signaling protocol, and resource management should react promptly according to changes in the network state 2009/11/2 24

25 Self-Organization An important property that an ad hoc wireless network should exhibit is organizing and maintaining the network by itself Major activities: neighbor discovery, topology organization, and topology reorganization Ad hoc wireless networks should be able to perform self-organization quickly and efficiently 2009/11/2 25

26 Security The attack against ad hoc wireless networks are classified into two types: passive and active attacks Passive attack: malicious nodes to observe the nature of activities and to obtain information in the network without disrupting the operation Active attack: disrupt the operation of the network Internal attack: nodes belong to the same network External attack: nodes outside the network 2009/11/2 26

27 Major Security Threats Denial of service: either consume the network BW or overloading the system Resource consumption Energy depletion: by directing unnecessary traffic through nodes Buffer overflow: filling unwanted data, routing table attack (filling nonexistent destinations) Host impersonation: A compromised node can act as another node and respond control packets to create wrong route entries and terminate the traffic Information disclosure: support useful traffic pattern Interference: create wide-spectrum noise 2009/11/2 27

28 Addressing and Service Discovery An address that is globally unique is required for a node to participate communication Auto-configuration of address is required to allocate nonduplicate address to the nodes In networks frequent partitioning and merging of network components require duplicate address detection mechanisms Nodes in the network should be able to locate services that other nodes provide 2009/11/2 28

29 Energy Management Transmission power management: RF hardware design ensure minimum power consumption Uses variable power MAC protocol Load balance in network layer Reducing the number of retransmissions at the transport layer Application software developed for mobile computers 2009/11/2 29

30 Energy Management (cont.) Battery energy management: extending the battery life by taking chemical properties, discharge patterns, and by the selection of a battery from a set of batteries that is available for redundancy Processor power management: CPU can be put into different power saving modes during low processing load conditions Devices power management: can be done by OS by selectively powering down interface devices that are not used or by putting devices into different powersaving modes 2009/11/2 30

31 Scalability The latency of path-finding involved with an on-demand routing protocol in a large ad hoc wireless network may be unacceptably high A hierarchical topology-based system and addressing may be more suitable for large ad hoc wireless networks 2009/11/2 31

32 Deployment Considerations The deployment of a commercial ad hoc wireless network has the following benefits Low cost of deployment Incremental deployment Short deployment time Re-configurability 2009/11/2 32

33 Major Issues for Deployment Scenario of deployment Military deployment Data-centric (e.g. WSN) User-centric (soldiers or vehicles carrying with wireless communication devices) Emergency operations deployment Commercial wide-area deployment Home network deployment Required longevity of network: regenerative power source can be deployed when the connectivityis required for a longer duration of time Area of coverage 2009/11/2 33

34 Major Issues for Deployment Service availability: redundant nodes can be deployed to against nodes failure Operational integrationwith other infrastructure: can be considered for improve the performance or gathering additional information, or for providing better QoS Choice of protocols: the choices of protocols at different layers of the protocol stack is to be done taking into consideration the deployment scenario 2009/11/2 34

35 Ad Hoc Wireless in Internet Similar to wireless internet, the ad hoc wireless internet extends the service of the Internet to the end user over an ad hoc wireless network Gateways: entry points to the wired Internet Address mobility: similar to the Mobile IP Routing: major problem in ad hoc wireless Internet Transport layer protocol Load balancing, pricing/billing, security, QoS Service, address, and location discovery 2009/11/2 35

36 TCP/IP protocol stack Application Layer (HTTP, TELNET, SMTP, etc.) Transport Layer (TCP/UDP) TCP/IP protocol stack Application Layer (HTTP, TELNET, SMTP, etc.) Transport Layer (TCP/UDP) TCP/IP protocol stack Application Layer (HTTP, TELNET, SMTP, etc.) Transport Layer (TCP/UDP) Network Layer (IPv4/IPv6) Network Layer (IPv4/IPv6) Network Layer (IPv4/IPv6) Network Layer (IPv4/IPv6) /HIPERLAN /HIPERLAN HIPERLAN 802.3/802.4/ /802.4/802.5 Mobile node that can be connected to any AP running ad hoc wireless routing protocol Mobile node that can relay packets to any mobile node running ad hoc wireless routing protocol Multi-hop wireless part of ad hoc wireless Internet Ad hoc wireless Internet gateway connected to a subnet of the Internet Internet Traditional wired Internet Flow of an IP packet from the wired Internet to a mobile node Transceiver antenna 2009/11/2 36 Figure 5.7. A schematic diagram of the ad hoc wireless Internet

37 A Internet Gateway Node A house with rooftop transceiver Path 1 Path 2 Transmission range Wired link to the Internet Wireless link Figure 5.8. An illustration of the ad hoc wireless Internet implemented by a wireless mesh network 2009/11/2 37

38 Home Work 4, 8, 11, /11/2 38