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.