How to Build a Wireless Network

How to Build a Wireless Network Moving Beyond the WLAN Martin Roth Wireless Intelligent Systems Laboratory School of Electrical and Computer Engineering Cornell University Ithaca, NY, USA Tuesday, March 26, 2002 Wireless Networks A wireless network is a computer network in which communication between machines occurs over a wireless link.  Cellular networks  Verizon, DoCoMo, etc.  Satellite networks  Iridium, Inmarsat, etc.  Battlefield networks  Communication between tanks, soldiers, etc.  Wireless Local Area Networks (LAN)  IEEE 802.11 • a, b, g • Red Rover (802.11b) Wireless LAN A popular wireless networking system is 802.11b, also known as Wi-Fi.  Connectivity to the network is through Access Points (APs) Similar to cellular networks  Data rates up to 11 Mbps 1, 2, 5.5, 11 Mbps  Ranges up to 550 meters Much more with specialized equipment  20MHz channel @ 2.4GHz Direct Sequence Spread Spectrum (DSSS) How an 802.11 Network Works  Access Points (AP) are connected to a wired network  AP location never changes  Clients connect to one AP at a time over a wireless link  Clients communicate only with APs, not with any other clients  Clients may move between APs  Clients must remain within the coverage area of an AP to have access to the network •Basic Service Set (BSS) •Coverage by one AP •Extended Service Set (ESS) •Coverage by all APs Wireless LANs are too Limited!  Service is limited to some areas of some buildings  What if I want to walk from one building to the next and stay connected?  What if I want to surf the web while outside? From the Plantations?  What if I didn’t want to install APs all over campus??? Mobile Wireless Ad Hoc Networks Ad Hoc networks have no predefined structure. Machines may join and leave the network at any time Machines are mobile; movement is entirely unrestricted Each machine forwards data packets for other machines in the network Access to Network Resources Every computer is an access point to the network.  A connection to at least one machine is enough to maintain connectivity to the entire network.  A network exists even without a gateway to the Internet  A network is created as soon as two computers are within range of each other AP AP Wireless LAN Ad Hoc Network Issues in Ad Hoc Networks How to get information from A to B when everything in between is moving??? And what about… Delay Throughput Energy Consumption Path reliability Routing in Ad Hoc Networks Routing in Ad Hoc networks is an area of active research.  Flooding  Dynamic Source Routing (DSR)  Ad Hoc On demand Distance Vector Routing (AODV)  Zone Routing Protocol (ZRP)  Termite  …*! ? Flooding Flooding is the simplest of all routing protocols.  Send all information to everybody  If data is received that is not for you, send it to all of your neighbors!  Robust  Destination is guaranteed to receive data  Resource Intensive  Data is sent to many nonessential nodes  Network performance drops quickly under increasing load Dynamic Source Routing (DSR)  To find a route, the network is flooded with route request packets  Each packet records its path  The destination receives the first route request and returns a full path to the source  The source sends data over the returned path The discovered route can be saved for future use route request route reply Open Research Topics Energy Aware Routing Each computer has a limited power supply which needs to be conserved Multipath Routing The more paths used to send information, the more reliable the transmission Clustering (Hierarchical Routing) Dynamic management of subnetworks More Research Topics  Topology Control Adjustment of transmission power to simplify routing  Internetworking Managing communications between wired and wireless networks  Heterogeneous Networks Different devices on the network have different capabilities  Content Aware Networks Location of services within the network  Printers Conclusion Ad hoc networks provide flexibility in… Connectivity… Mobility… Resource Availability… …to any networking application. Research in the area is very active, and there is still a long way to go!