Wireless LAN

Foundation Concepts and Design

Types of Wireless Networks

  • Personal Area Network (PAN)

  • Local Area Network (LAN)

  • Metropolitan Area Network (MAN)

  • Wide Area Network (MAN)

Wireless LAN Facts

  • A Wireless Access Point (WAP) communicates like a hub

    • Shared signal

    • Half duplex

  • Uses unlicensed bands of radio frequency (RF)

  • Wireless is a physicall and data link standard

  • Uses CSMA/CA instead of CSMA/CD

  • Faces connectivity issues because of interference

Understanding the SSID

  • The Service Set Identifier (SSID) uniquely identifies and seperates wireless networks

  • When a wireless client is enabled:

    1. Client issues a proble

    2. Access Point(s) respond with a beacon

    3. Client associates with chosen SSID

    4. Access Point adds client MAC to association table

Correct Design of a WLAN

  • RF service areas should have 10-15% overlap

  • Repeaters should have 50% overlap

  • Bordering access points should use different channels

Client Roaming

  • As more mobile devices are released, client roaming becomes a big deal

  • True roaming allows seamless movement between access points

  • Not a feature ‘Joe-Shmo’ access points can support

  • Provides solid coverage and better battery life

  • Can be costly

Two Flavors or Roaming

Layer 2 Roaming

Requirement: same SSID, same VLAN, same Subnet

Layer 3 Roaming (AKA Mobile IP)

Requirement: same SSID

How a Client Roams

  • Beacons are missed

  • Data reaches maximum retry count

  • Data rate shifts down

  • Periodic intervals

Wireless VLAN Support

Multiple VLANs provide support for:

  • Multiple security levels

  • Multiple subnets

  • Multiple access privileges

Frequencies and 802.11 Standards

Unlicensed Frequencies

  • 900MHz Range: 902 - 928

  • 2.4GHz Range: 2.400 - 2.483

  • 5GhZ Range: 5.150 to 5.350

Understanding RF

  • RF waves are absorbed (passing through walls) or reflected (by metal)

  • Higher data rates have shorter ranges

  • Higher frequencies of RF have higher data rates

  • Higher frequencies of RF have shorter ranges

The 802.11 Lineup

  • 802.11b

    • Official as of september 1999

    • up to 11 mbps (1, 2, 5.5, 11 data rates)

    • most popular standard

    • three ‘clean’ channels

  • 802.11g

    • Official as of june 2003

    • Backwards compatible with 802.11b

    • Up to 54 Mbps (12 data rates)

    • Three ‘clean’ channels

  • 802.11a

    • Official as of september 1999

    • Up to 54 Mbps

    • Not cross-compatible with 802.11b/g

    • 12 to 23 ‘clean’ channels

Wireless Range

  • The further you go, the lower your speed

  • Example: 802.11g does 54Mbps if you’re 40ft from the AP

  • Example: 802.11a does 54Mbps if you’re 20 from the AP

  • Example: 802.11b does 11Mbps if you’re 110ft from the AP

Wireless LAN Security

  • Wireless has added a whole new paradigm to security

  • The wireless security evolution:

    • 1997 - Wired Equivalent Privacy (WEP)

    • 2001 - 802.1x EAP

    • 2003 - Wi-Fi protected Access (WPA)

    • 2004 - IEEE 802.11i (WPA2)

Understanding the Hardware

Understanding the AP Categories

  • Autonomous APs

    • Stand alone system

    • Cisco IoS-based

    • Can be centrally controlled using Wireless Domain Services (WDS)

    • Managed using Ciscoworks WLAN Solution Engine (WLSE)

  • Lightweight APs

    • Server-dependant system

    • Zero-configuration access points

    • Can be centrally controlled using Wireless LAN Controller (WLC)

    • Managed using Cisco Wireless Control System (WCS) - optional

Understanding Lightweight Access Points

  • Lightweight Access Point Protocol (LWAPP) used between controller and WAPs

  • Controller has all the intellegence for communication

  • Access point acts as “dumb terminal” that processes packets

  • Referred to as “split mac” design

Wireless LAN Controllers

  • 2100 series controller

    • Designed for SMB

    • Currently supports up to 6 access points

  • 4400 series controller

  • 4402 supports 12, 25, or 50 access points

  • 4404 supports 100 access points

Cisco Wireless Indoor Access Points

  • 1130AG

    • Indoor design

    • Slick, glowing plastic enclosure

    • Designed for cubicle/office environment

  • 1240AG

    • Indoor design

    • Durable metal enclosure

    • Handle larger temperature swings

    • Manufacturing, warehouses, etc

  • 1300 series

    • Outdoor design

    • your typical “put it there, get wireless” sort of AP

    • Handles outdoor temperatures (-22 to 131)

    • Can be configured as a bridge

  • 1400 series

    • Outdoor design

    • Point-to-point or multipoint bridging

    • Handles outdoor temperatures

    • 8.5 mile (p2p) pr 2.75 mile (p2m) range

Power Over Ethernet

  • Two Standards:

    • 802.3af

    • Cisco proprietary PoE

  • Comes in many forms

    • Cisco PoE switches

    • Switch router cards

    • SOHO firewalls and routers

    • Power patch panel

    • Inline power injector

Understanding Antennas

  • Omni-Directional Antenna: Provides even spread of wireless signal in a radius around the access point

  • Directional Antenna: Allows you to point antennas to get more radius and range in a specific direction

  • Yagi Antenna: Provides dual adjustments of direction and focus. The more streamlined focus gets intense reach/range.