Wireless Ad Hoc and Sensor Networks
Wireless Ad Hoc and Sensor Networks Wireless Ad Hoc and Sensor Networks
Background on Networking 9when to generate a busy signal. Proper resources may be reserved for anaccepted request based on its QoS specification, such as minimum bandwidthand buffer space. Chapter 4 introduces a recent algorithm foradmission control for packet-switched networks.1.2.2 Traffic Access ControlTraffic Access control (e.g., GCRA) shapes the behavior of data flows atthe entry and at specific points within the network. Once the connectionis accepted to the network, traffic to the network should comply with thetraffic descriptor. If not, the excess traffic can either be dropped or taggedto a lower priority, or delayed (i.e., shaped). Different scheduling andadmission control schemes have different limitations on the characteristics(e.g., rate, burstiness) of traffic that may enter the network. Traffic accesscontrol algorithms filter data flows to make them conform to the expectationsof the scheduling algorithms. For details on traffic access control,refer to Stallings (2002).1.2.3 Packet SchedulingPacket scheduling specifies the queue service discipline at a node — thatis, the order in which queued packets are actually transmitted. Becausepackets of many users may depart from the same outgoing node, packetscheduling also enforces a set of rules in sharing the link bandwidth. Forexample, if a user is given the highest priority to access the link, his or herpackets can always go first, whereas packets from others will be delayed;and this privileged user can have his or her packets marked through sometraffic access control algorithm when they enter the network.In other words, packet scheduling prioritizes a user’s traffic into twocategories: delay priority for real-time traffic and loss priority for datatypetraffic. One major concern is to ensure that the link bandwidth isfairly shared between connections and to protect the individual user’sshare from being corrupted by malicious users (i.e., put a firewall betweenconnections). In this respect, FPQ is very promising. Chapter 7 introducesvarious kinds of scheduling algorithms for wireless networks targeted atdifferent goals. Scheduling schemes for the wireless networks are quitesimilar to a wired network although unpredictable channel state becomesan issue in the design of the scheduling schemes for wireless networks.There is a challenging design issue in that FPQ’s packet reorderingand queue management impose increased computational overhead andforwarding burden on networks with large volumes of data and veryhigh-speed links. Chapter 7 presents the development and implementationof a weighted fair scheduler and how to assess the overhead due tothe scheduler for wireless ad hoc networks.
10 Wireless Ad Hoc and Sensor Networks1.2.4 Buffer ManagementThe problem of buffer sharing arises naturally in the design of high-speedcommunication devices such as packet switches, routers, and multiplexers,where several flows of packets may share a common pool of buffers.Buffer management sets the buffer-sharing policy and decides whichpacket should be discarded when the buffer overflows. Thus, the designof buffer-sharing strategies is also very critical to the performance of thenetworks. Because there are variable-length packets in routers andswitches, the per-time slot processing imposes a difficulty in handlinglarge volumes of data at high-speed links for both buffer managementand PFQ, as mentioned earlier. Buffer management is very critical evenfor congestion control. For details refer to Stallings (2002).1.2.5 Flow and Congestion ControlIn all networks, there are scenarios where the externally offered load ishigher than can be handled by the network. If no measures are taken tolimit the traffic entering into the network, queue sizes at bottleneck linkswill grow fast and packet delays will increase. Eventually, the buffer spacemay be exhausted, and then some of the incoming packets are discarded,possibly violating maximum-delay loss specifications. Flow control andcongestion control are necessary to regulate the packet population withinthe network. Flow control is also sometimes necessary between two usersfor speed matching, that is, for ensuring that a fast transmitter does notoverwhelm a slow receiver with more packets than the latter can handle.Chapter 3 presents the schemes for ATM and Internet, whereas Chapter 9details the congestion control for wireless networks.1.2.6 QoS RoutingThe current routing protocols used in IP networks are typically transparentto any QoS requirements that different packets or flows may have. As aresult, routing decisions are made by neglecting the resource availabilityand requirements. This means that flows are often routed over paths thatare unable to support their requirements although alternate paths withsufficient resources are available. This may result in significant deteriorationin performance, such as high call-blocking probability in the case of ATM.To meet the QoS requirements of the applications and improve thenetwork performance, strict resource constraints may have to be imposedon the paths being used. QoS routing refers to a set of routing algorithmsthat can identify paths that have sufficient residual (unused) resources tosatisfy the QoS constraints of a given connection (flow). Such a path iscalled a feasible path. In addition, most QoS routing algorithms also considerthe optimization of resource utilization measured by metrics, such
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10 <strong>Wireless</strong> <strong>Ad</strong> <strong>Hoc</strong> <strong>and</strong> <strong>Sensor</strong> <strong>Networks</strong>1.2.4 Buffer ManagementThe problem of buffer sharing arises naturally in the design of high-speedcommunication devices such as packet switches, routers, <strong>and</strong> multiplexers,where several flows of packets may share a common pool of buffers.Buffer management sets the buffer-sharing policy <strong>and</strong> decides whichpacket should be discarded when the buffer overflows. Thus, the designof buffer-sharing strategies is also very critical to the performance of thenetworks. Because there are variable-length packets in routers <strong>and</strong>switches, the per-time slot processing imposes a difficulty in h<strong>and</strong>linglarge volumes of data at high-speed links for both buffer management<strong>and</strong> PFQ, as mentioned earlier. Buffer management is very critical evenfor congestion control. For details refer to Stallings (2002).1.2.5 Flow <strong>and</strong> Congestion ControlIn all networks, there are scenarios where the externally offered load ishigher than can be h<strong>and</strong>led by the network. If no measures are taken tolimit the traffic entering into the network, queue sizes at bottleneck linkswill grow fast <strong>and</strong> packet delays will increase. Eventually, the buffer spacemay be exhausted, <strong>and</strong> then some of the incoming packets are discarded,possibly violating maximum-delay loss specifications. Flow control <strong>and</strong>congestion control are necessary to regulate the packet population withinthe network. Flow control is also sometimes necessary between two usersfor speed matching, that is, for ensuring that a fast transmitter does notoverwhelm a slow receiver with more packets than the latter can h<strong>and</strong>le.Chapter 3 presents the schemes for ATM <strong>and</strong> Internet, whereas Chapter 9details the congestion control for wireless networks.1.2.6 QoS RoutingThe current routing protocols used in IP networks are typically transparentto any QoS requirements that different packets or flows may have. As aresult, routing decisions are made by neglecting the resource availability<strong>and</strong> requirements. This means that flows are often routed over paths thatare unable to support their requirements although alternate paths withsufficient resources are available. This may result in significant deteriorationin performance, such as high call-blocking probability in the case of ATM.To meet the QoS requirements of the applications <strong>and</strong> improve thenetwork performance, strict resource constraints may have to be imposedon the paths being used. QoS routing refers to a set of routing algorithmsthat can identify paths that have sufficient residual (unused) resources tosatisfy the QoS constraints of a given connection (flow). Such a path iscalled a feasible path. In addition, most QoS routing algorithms also considerthe optimization of resource utilization measured by metrics, such
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