Praise for Fundamentals of WiMAX

224 Chapter 7 • Networking and Services Aspects of Broadband WirelessThe purpose of this chapter is to provide an end-to-end network and services perspective tobroadband wireless. The first four sections attempt to answer the four questions listed earlier,which pertain to quality of service (QoS), multimedia session management, security, and mobilitymanagement.Since WiMAX is designed primarily to provide IP-based services—be it data, voice, video,messaging or multimedia—a good part of the discussion in this chapter is around IP-based protocolsand architecture and how they are used to meet the end-to-end service requirements. Aspointed out in Chapter 1, IP was designed primarily for survivability and not so much for efficiency.IP was also designed for best-effort data and not for supporting services that requireQoS. The need to support multimedia and other services with stringent QoS needs has led tonew developments in IP protocols and architecture. Developments have also occurred for optimizingIP over a capacity-constrained and unreliable wireless medium. Although significantprogress has been made over the past several years, adapting IP to the special challenges of wirelessand multimedia services continues to be an area of active research and development. Thischapter reviews some of these developments.The topics covered in this chapter have a very broad scope, and our intent is to provide onlya brief overview. More detailed exposition can be found in [5, 34, 48, 65].7.1 Quality of ServiceIn this section, we discuss QoS from an end-to-end network perspective. How is QoS providedfor communication between the two end points of a broadband wireless packet network, whichin addition to the wireless link may include several other links interconnected via routers,switches, and other network nodes? The links between intermediate nodes may use a variety oflayer 2 technologies, such as ATM, frame relay, and Ethernet, each of which may have its ownmethods to provide QoS. It is not our intent to cover how QoS is handled in each of these layer 2technologies. Instead, we provide a brief overview of the general requirements and methods forproviding QoS in packet networks and focus on how this is done end to end using emerginglayer 3 IP QoS technologies. Since WiMAX is envisioned to provide end-to-end IP services andwill likely be deployed using an IP core network, IP QoS and its interaction with the wirelesslink layer are what is most relevant to WiMAX network performance.First, what is QoS? This rather elusive term denotes some form of assurance that a servicewill perform to a certain level. The performance level is typically specified in terms of throughput,packet loss, delay, and jitter, and the requirements vary, based on the application and service.The form of assurance can also vary from a hard quantitative measure, such as a guaranteethat all voice packets will be delivered with less than 100ms delay 99 percent of the time—to asoft qualitative guarantee that certain applications and users will be given priority over others.Resource limitations in the network is what makes providing assurances a challenge.Although typically, the most-constrained resource is the wireless link, the other intermediatenodes and links that have to be traversed for an end-to-end service also have resource limitations.1 Each link has its own bandwidth-capacity limits, and each node has limited memory for