basic wireless infrastructure and · pdf filebasic wireless infrastructure and topologies ......
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Basic Wireless Infrastructure and Topologies
Developed by Sebastian Buettrich
and Alberto Escudero Pascual
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Goals
• To be aware of the most common wireless topologies
• To be able to identify and plan suitable topologies for real scenarios
• To give a brief introduction to practical setup
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Table of Contents• Basic Network Topologies
• Topologies in wireless networking
• Wireless Components (AP, clients)
• Wireless Modes (ad hoc, infrastructure)
• Practical cases (incl. setup)– Ad hoc, Star, PtP, Repeating and Mesh
• Real life examples
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Basic Network Topologies
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Topologies Relevant for Wireless Networking
• Star Yes, standard wireless topology
• Tree Yes (a combination of star and line)
• Line Yes, with two or more elements (PtP)
• Mesh Yes, mainly partial mesh
• Ring Possible, but rarely found
• Bus Not applicable. Why?
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Some General Remarks• Wireless communication needs no medium
– EM waves travel through “nothing”
– The “line” in a network diagram is the connection that is being made
• Wireless communication is always 2way
– Except for passive sniffing
– Applies to transmitters/receivers, clients/masters
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Wireless Components• Access Point
– Wireless transmitter/receiver that bridges between wireless nodes and a wired network
– IEEE 802.11 + Wired Ethernet connection
• Wireless clients– Any computer with a wireless network adapter card
that transmits and receives RF signals
– Laptop, PDA, surveillance equipment, VoIP phone
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Two Basic Wireless Modes1.Ad Hoc (IBSS)
2.Infrastructure (BSS)
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Mode 1: Ad hoc (Peertopeer)• Independent Basic Service Set (IBSS)
• No need of central access point
• All nodes need to use the same SSID and channel
• Not scalable
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Mode 2: Infrastructure• Extended Service Set (ESS)
• Central access point is needed
• “Connects“ a WLAN to an Ethernet network
• Clients and AP's must use the same SSID
• Channel is set in AP and discovered by clients
• Scalable
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Remarks about Wireless Modes• In both modes, the SSID identifies the network
• Consider the SSID as the “label” of a Ethernet jack on the wall
• Modes (modes of operation) can be hidden and not noticeable in a topology
– ex: A PtP link can be ad hoc or infrastructure
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Ad hoc case 1: Pointtopoint
• Connecting two wireless clients directly
• Building to building (when one has Internet connection and the other one does not)
• Inside an office
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Ad hoc Case 1: PointtopointSetting Node 1 Node 2
Mode ad hoc ad hoc
SSID MY_SSID MY_SSID
Channel Need to agree and know eachothers
Need to agree and know eachothers
IP address Typically fixed Typically fixed
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Infrastructure Case 1: Star
• Hotspots, Telecenters, Offices and WISP's
• Point to Multipoint
• The most common infrastructure in wireless networking
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Infrastructure Case 1: StarSetting AP/Gateway Node x
Mode Infrastructure Infrastructure
SSID Sets MY_SSID Connects to MY_SSID
Channel Sets channel x Discovers channel from AP
IP address Typically runs DHCP server Typically gets IP via DHCP lease
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Infrastructure Case 2: Point to Point• Standard element of wireless infrastructure
• A PtP link may be part of
– a star, a tree, a two point line or other topology
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Infrastructure Case 2: Point to PointSetting Node 1 Node 2
Mode Any Any
SSID MY_SSID MY_SSID
Channel Set the Channel Discovers the channel
IP address Typically fixed Typically fixed
MAC address Might be fixed to one another's MAC Might be fixed to one another's MAC
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Infrastructure Case 3: Repeating
• Necessary when direct line of sight (LOS) is obstructed
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Infrastructure case 3: Repeating• The repeating unit consist of
• One or two physical devices
• Two radios or one radio and “isolated antennas”
• Can be seen as a “receiving client and a retransmitting access point”
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Infrastructure Case 4: Mesh
• Mesh topologies are an interesting option mainly in
– dynamic environments (urban areas)
– where central infrastructure is hard to implement
– when redundancy is desired
• Typical cases are: municipal networks, campus networks and neighborhood communities
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Infrastructure Case 4: Mesh• Full mesh topology (each node is direct connected
to all other nodes)
• Partial mesh topology (each node is direct connected to some but not all nodes)
• Nothing is necessarily dynamic in a mesh
• Used as synonym for "ad hoc" or "mobile" network
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Infrastructure case 4: Mesh
• All mesh nodes need to run the same mesh routing protocol
• The nodes can be of different operating
systems and hardware types
if they comply with the mesh
protocol specification
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Infrastructure Case 4: MeshSetting Node x1 Node x2
Mode ad hoc ad hoc
SSID MY_SSID MY_SSID
Channel Channel x Channel x
IP address Typically static and manually set Typically static and manually set
MAC address Might be fixed to one another'sMAC
Might be fixed to one another'sMAC
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Real Life Examples of Wireless Infrastructure
• Real life wireless networks are very often combinations of more than one topology
• Graphical representations are totally arbitrary and different from one another
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Typical office network
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Widearea Wireless backbone
5
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Nepalwireless.net Backbone Topology
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Mesh Network (OLSR) Berlin Wizards of OS 2004
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Wireless Backbone, rural Nigeria
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Conclusions• Most wireless implementations are based on
– Star, tree or line topology
• In implementations we can find two modes:
– Ad hoc or infrastructure (more common)
• The basics of any setup includes:
– Mode, SSID, Channel + MAC/auth + IP
• Many wireless implementations are based on more than one topology