Transcript Slide 1 - Community College of Rhode Island

Introduction Wireless Networking
Wireless Networking Topologies
Module-05B
Jerry Bernardini
Community College of Rhode Island
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Presentation Reference Material
• CWNA Certified Wireless Network
Administration Official Study Guide
(PWO-104), David Coleman, David Westcott,
2009, Chapter-7
• The California Regional Consortium for
Engineering Advances in Technological
Education (CREATE) project
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Network Topologies
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Topologies are physical or logical layouts of nodes
Topology-How things are interconnected
Basic Networking Topologies - Bus Ring Star Mesh
Wireless Topologies are based upon coverage area
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Wireless wide area networks (WWAN)
Wireless metropolitan area networks(WMAN)
Wireless personal area networks (WPAM)
Wireless local area networks (WLAN)
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Wireless Wide Area Networks (WWAN)
• Networks with ten’s of miles of coverage
• Wireline WANs
– T1, Frame Relay, ATM, MPLS
• WLANs
– Cellular, T-Mobile, Verizon
– GPRS, CDMA, TDMA, GSM technologies
• Wireless point-to-point networks
• IEEE 802.11 was not designed for WWAN
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Wireless Metropolitan Area Network (WMAN)
• Networks with miles of coverage
• Networks for metropolitan areas
– Around Washington DC
– Around Boston
– DC government network
• WMAN technologies
– IEEE 802.16
– WiMAX
• Can provide “the last mile” coverage
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Wireless Personal Area Network (WPAN)
• Networks with feet (meters) of coverage
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Between Laptops
Between PDAs
Between wireless phones
Headsets
• Technologies used
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Bluetooth
Infrared
ZigBee
Radio
FHSS
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Wireless Local Area Network (WLAN)
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Networks with hundred’s of feet of coverage
Provides end user access to LANs
Coverage for buildings and campuses
Great fit for 802.11 technology
802.11 WLAN provides balance of:
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Performance
Cost
Availability
Technology evolution
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IEEE 802.11 Topologies
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The purpose of 802.11 is to interconnect radio cards
Every wireless device has a radio card
All wireless devices are referred to as Stations (STA)
Three topologies defined by 802.11 – Service Sets
– Basic Service Set (BSS)
– Extended Service Set (ESS)
– Independent Basic Service Set (IBSS)
• Nonstandard Topologies
– Bridging, Repeating, Workgroup bridging
– Mesh networking (growing in importance)
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Network Communication Modes
• Modes or how STAs can communicate
• Simplex Communications
– One STA transmits, one STA receives
– One way communications
• Half-Duplex Communications
– Both STAs can transmit and receive but not at the same time – must
take turns
– Walkie-talkies
– 802.11 networks
• Full-Duplex Communications
– Both STAs can transmit and receive at the same time
– Requires two radio channels
– 802.11 does not support full-duplex
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Basic 802.11 Components
• Wireless Client stations or Wireless devices –STAs
• Wireless Access Points - APs
• Wireless Bridges
• Wireless Repeaters
• Wireless Controllers
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Access Points
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The Access Point (AP) is the device that provides access to
the WLAN
Each BSS has one AP and multiple Aps make an ESS
Two categories of APs are Fat and Thin Access Points
Thin AP’s are paired with a wireless LAN switch or controller
to offer additional functionality and centralization over Fat
AP’s.
Fat (Thick or Smart) AP’s are "fat" because they operate
autonomously as members of a decentralized WLAN.
3Com Wireless LAN Switch WX1200
3Com AP3750 MAP
Access Points Market
Belkin APs
Buffalo APs
Cisco APs
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Linksys APs
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Autonomous or FAT Access Points
• Traditional wireless LANs use decentralized Fat
access points
• Manual configuration required to set the power
level, channel, security and other configurable
parameters.
• Each access point is individually configured
• Third party software solutions are often needed for
additional security and management capabilities
• For large networks which quickly add to the total
cost of ownership.
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Autonomous AP Implementation
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Lightweight or Thin Access Points
• Centralized WLANs use a wireless controller to manage,
process, and configure the RF environment
• Centralized WLANs use called thin or lightweight APs
• APs communicate directly with the central controller with the
wired network
• All the functionality and intelligence is offloaded to the
controller
• This provides a single point of administration for various
policies relating to security, intrusion detection, user roles,
and software upgrades..
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Thin Access Points Implementation
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Access Point Modes
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APs are small computers with one or more radios
The AP operating systems are Linux or propriety
IEEE 802.11 defines three Operational Modes
Root Mode
– The default mode for most APs
– Provides wireless clients access to the WLAN
• Bridge Mode
– Used to create a link between two or more APs
• Repeater Mode
– Used to extend the range of a WLAN beyond
normal boundaries
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Access Point Features
• Support of various IEEE 802.11 standards
– FHSS, DSSS, OFDM, 802.11a,b, g, n
• Support for various security standards
– IEEE 802.11i, WEP, WPA, WPA2, PSK, RADIUS
• Support for QoS extensions
– Wireless Multimedia (WMM), VoWLAN
• Fixed or Detachable Antenna
– Omni-directional, Directional
• Filtering
– MAC, Protocol
• Variable Power
– Percent of Max or Actual Levels
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Power Over Ethernet (PoE) Support
• Found on Enterprise and not on SOHO APs
• Primary benefit is ability to install APs where no AC
power is present
• IEEE 802.3af standard for PoE
• PoE is supply by injectors or switches
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PoE Options and Power Source Equipment(PSE)
Pins 4-5 +Power(48v)
Pins 7-8 –Power
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Active/PSE
Switch
PD Access Point
DC Power
CAT-5e Ethernet
PD Access Point
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Switch
AC Power
DC Power
PSE Injector
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Switch
CAT-5e Ethernet
DC
Power
AC Power
DC Power
PSE Injector
CAT-5e Ethernet
Tap/Splitter
Access Point
Wireless Bridges
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Provides a link between two WLAN segments
Not full described by IEEE 802.11
Vendor dependent
Two Modes – Root and Non-root
Non-Root
Point-to-Point
Non-Root
Root
Non-Root
Point-to-Mulitpoint
Root
WLAN Bridge Modes and Components
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Root Mode – A bridge that acts as the hub to a group of
bridges.
– Only One Root-Bridge for PtP or PtMP links
(important for tests)
– For PtP link one Root-Bridge and one Non-Root
Bridge
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Non-Root Mode – A member bridge of a group that is not the
Root Bridge.
– Can also function as a standard AP
– Can function as a repeater
3Com WLAN Bridge
Cisco Aironet 1400
Proxim Quick Bridge 11
Bridge Application: School
District
Richardson
Elementary
Yagi
Bode
Elementary
Yagi
Roberts
Middle School
Dish
High School 2
Bridges
One 12 dBi omni
One Dish
Channel #1
Channel #6
Channel #11
Price
Elementary
Yagi
WeaverSpecial
Education
Dish
UNIVERSITY
Administration
2 Bridges
One 12 dBi omni
One Yagi
Lincoln
Elementary
Yagi
Bolich
Dewitt Elementary Middle
School
Yagi
Yagi
Residential WLAN Gateways
• Same as SOHO wireless routers
• Support of various IEEE 802.11 standards
– FHSS, DSSS, OFDM, 802.11a,b,
g, n
• Support for various security standards
– IEEE 802.11i, WEP, WPA, WPA2,
PSK, RADIUS
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Built in firewall features
Packet and MAC Filtering
Switched Ethernet ports
DHCP
NAT and PAT
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Enterprise WLAN
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Enterprise Wireless Gateways
• Enterprise Wireless Gateway – is a powerful device that interfaces
between the enterprise network and the corporate firewall.
– HTML  WML
– Authentication, Filtering, and Security
– Traffic Management, QoS
– Mobile Addressing
Vernier IS 6500p
BlueSecure Controller
BSC 2100
Enterprise Wireless Gateways
Internet
Enterprise
Server
Enterprise
Gateway
Router
Switch
Access
Points
Wireless
Clients
Voice Over IP WLAN (VoWLAN)
• Telephone communication using a WLAN requires latency and
QoS considerations
• Special equipment is required
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VoWLAN phone (phones that will connect to WLAN)
WLAN infrastructure with QoS (low latency and Protocol management)
Call management (PBX for IP phones)
Voice gateway for outside calls
• IP phones associate with APs rather than cellular towers
Siemens Linksys
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Client Stations and Adapters
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Service Set Identifiers - SSID and BSSID
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SSID -Service Set Identifier is a 1-32 byte alphanumeric
sequence that uniquely names an ESS (the network name).
• Any SSID or Null SSID is a blank SSID used to associate with
anyone.
• BSSID- Basic Service Set Identifier is a 48-bits that uniquely
identifies a BSS
Wired LAN
BSA
Basic service Area
–Physical
Coverage Area
AP
ESS
Id = SSID
BSS
Id = BSSID
Basic Service Set (BSS)
BSS - The Basic Service Set is a term used to describe the
collection of Stations which may communicate together within an
802.11 WLAN.
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Basic Service Set (BSS): Group of
wireless devices served by single AP
– infrastructure mode
BSS must be assigned unique identifier
– Service Set Identifier (SSID)
• Serves as “network name” for
BSS
Basic Service Area (BSA): Geographical
area of a BSS
– Max BSA for a WLAN depends on
many factors
Dynamic rate shifting: As mobile
devices move away from AP,
transmission speed decreases
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Basic Independent Basic Service Set (BSSID)
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Independent Basic Service Set (IBSS):
Wireless network that does not use an
AP
– Wireless devices communicate
between themselves
– Peer-to-peer or ad hoc mode
BSS more flexible than IBSS in being
able to connect to other wired or
wireless networks
IBSS useful for quickly and easily
setting up wireless network
– When no connection to Internet or
external network needed
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Extended Service Set (ESS)
• ESS - is comprised of a number BSS’s
• ESS stations must have the same SSID
• The BSSID is the “name” of the BSS (not same as SSID)
• APs can be positioned so that cells overlap to facilitate roaming
– Wireless devices choose AP based on signal strength
– Stations going from one BSS to another will deal with Handoff
Wired LAN
ESS
SSID
BSS2
(BSSID2)
BSS1
(BSSID1)
BSS3
(BSSID3)
Wireless Mesh Access Points
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Mesh APs associate with multiple APs
Association between APs is limited by vendor (3-5)
Currently vendor dependent
Clients can reach destinations thru multiple APs
APs route packets to ovoid failures and optimal paths
Mesh Networks are more resilient
Not every AP has to be connected to a wired network
Self-Healing, Self-Configuring using Layer-2 Protocol
New standard IEEE 802.11s will allow interoperability
between vendors
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Wireless Mesh Network Implementation
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Reassociation
Wired LAN
Access Points
Link Fading
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Wireless Clients
Reassociation
Request
Load Balancing or Sharing
Wired LAN
Access Points
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Wireless Clients
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WLAN IP Addressing
• In standard networking, IP protocol
responsible for moving frames between
computers
– Network layer protocol
• TCP/IP works on principle that each network
host has unique IP address
– Used to locate path to specific host
– Routers use IP address to forward packets
– Prohibits mobile users from switching to another network and using same IP
number
• Users who want to roam need new IP address on every
network
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Infrastructure Mode
CWNA Guide to Wireless
LANs, Second Edition
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Channel reuse
CWNA Guide to Wireless
LANs, Second Edition
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Flip flop between access points
CWNA Guide to Wireless
LANs, Second Edition
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WLAN Design Models
•Point-to-Point (PtP)
•Point-to-Multipoint (PtMP)
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WLAN Modes
• Single MAC Model
– Edge, Autonomous, Stand-Alone, Fat-AP
• Split MAC Model
– Centralized, Thin-AP
• Mesh Network
– Distributed, Multipath, IEEE 802.11s
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Single MAC Model
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Split MAC Model
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WLAN Model Evolution
• Intelligent Edge(Distribution)
– Quick to setup but for small-medium networks
– Difficult to mage for large networks
• WLAN Network Management Systems
– Centralized Management Distribution Processing
– For large networks
• Centralized WLAN Architecture (Split MAC)
– For large networks with centralized controller
– Large amount of wiring needed
• Distributed Data Forwarding (DDF) WLAN
– Similar to Split MAC but uses Fat-AP
• Unified WLAN Architecture
– Wireless built in to every thing including switches
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WLAN Power Management
Features
• Active Mode
– No power saving but improved station and AP
performance
– For desktops and line powered laptops
• Power Save Mode
– Dozing and Wake modes
– Switches to wake to check for frames
• WMM Power Save
– U-APSD Unscheduled Automatic Power-Save Delivery
– This is an industry certification
– IEEE 802.11e-2005
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Power Management
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A WLAN laptop must remain “awake” in order to receive network transmissions
– Original IEEE 802 standard assumes stations always ready to receive network
messages
Power management: Allows mobile devices to conserve battery life without
missing transmissions
– Transparent to all protocols
– Differs based on WLAN configuration
– AP records which stations awake and sleeping
– Buffering: If sleeping, AP temporarily stores frames
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Power Management
• At set times AP send out beacon to all stations
– Contains traffic indication map (TIM)
– At same time, all sleeping stations switch into active listening mode
• Power management in ad hoc mode:
– Ad hoc traffic indication message (ATIM) window: Time at which all stations
must be awake
• Wireless device sends beacon to all other devices
– Devices that previously attempted to send a frame to a
sleeping device will send ATIM frame indicating that receiving
device has data to receive and must remain awake
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Continuous Aware Mode
• Constantly Awake Mode provides the best
performance allowing the client a strong
connection between the wireless card and the
AP; however, it also rapidly drains the client’s
battery, resulting in shorter battery life.
Power Management with TIM/DTIM/ATIM
• Traffic Indication Map (TIM)
– A table stored on the AP of all STA’s in Power Save mode
– TIM is used to determine which STA’s require frame
buffering
– Every Beacon contains a TIM
• Delivery Traffic Indication Message (DTIM)
– Used to manage STAs and to program wakeup
– Sent on every few (third or some interval)Beacon
• Ad Hoc Traffic Indication Message (ATIM)
– Use to power manage IBSS
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