Computer Networking: Notes of "Select" Lectures (Chapter 7: Wireless and Mobile Networks)
作者：互联网
a Top-Down Approach (8th ed.):
7.1 Introduction
Elements in a wireless network
• Wireless hosts.
• A wireless host (无线主机) might be a smartphone, tablet, or laptop, or it could be an Internet of Things (IoT) device.
• The hosts themselves may or may not be mobile.
• Wireless links.
• A host connects to a base station or to another wireless host through a wireless communication link (无线通信链路).
• Different wireless link technologies have different transmission rates and can transmit over different distances. 
• Base station.
• The base station (基站) is a key part of the wireless network infrastructure.
• A base station is responsible for sending and receiving data (e.g., packets) to and from a wireless host that is associated with that base station.
• "associated":
• the host is within the wireless communication distance of the base station
• the host uses that base station to relay data between it and the larger network. Examples:
• cell towers (蜂窝塔) in cellular networks
• access points (接入点) in 802.11 wireless LANs
• Hosts associated with a base station: operating in infrastructure mode (基础设施模式)
• since all traditional network services are provided by the network to which a host is connected via the base station.
• In ad hoc networks (自组织网络), no such infrastructure. The hosts themselves must provide for services.
• Handoff (切换) or handover (切换):
• When a mobile host moves beyond the range of one base station and into the range of another, it will change its point of attachment into the larger network.
• Network infrastructure. This is the larger network with which a wireless host may wish to communicate.
Taxonomy (分类学) of different types of wireless networks
Two criteria:
(i) one wireless hop or multiple wireless hops
(ii) infrastructure.
• Single-hop, infrastructure-based.
• A base station is connected to a larger wired network (e.g., the Internet).
• All communication is between this base station and a wireless host over a single wireless hop.
• 802.11 networks; 4G LTE data networks. The vast majority of our daily interactions are with them.
• Single-hop, infrastructure-less.
• No base station is connected to a wireless network.
• One node may coordinate the transmissions of the others.
• Bluetooth networks.
• Multi-hop, infrastructure-based.
• A base station is present that is wired to the larger network.
• Some nodes may have to relay in order to communicate via the base station.
• Some wireless sensor networks; wireless mesh networks (无线网状网络).
• Multi-hop, infrastructure-less.
• No base station.
• Nodes may have to relay to reach a destination.
• Mobile ad hoc networks (MANETs, 移动自组织网络); vehicular ad hoc network (VANET, 车载自组织网络).
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