Freddy Duarte

WLANs use radio or infrared frequencies to transmit signals using air as the transmission medium (instead of cables).

Basic Categories

• 802.1x Family of Standards (aka, Wi-Fi)
• Infrared/Optical Frequencies

Components of WLANs

• Network Interface Cards
• Available for laptops as PCMCIA cards
• Available for desktops as standard cards
• Many laptops come with WLAN built in
• About 100-500 feet max transmission range
• Access Points (APs)
• Used instead of hubs; act as repeater
• Must hear all computers in WLAN
• Message transmitted twice: Sender -> AP ; AP -> Receiver

Antenas used in WLANs

• Omni directional antennas:
• Most common
• Transmit in all directions simultaneously
• Directional antennas:
• Project signal only in one direction
• Stronger signals
• More secure

IEEE 802 Standards

• IEEE 802.1 Bridging (networking) and Network Management
• IEEE 802.2 Logical link control
• IEEE 802.3 Ethernet
• IEEE 802.4 Token bus (disbanded)
• IEEE 802.5 Defines the MAC layer for a Token Ring
• IEEE 802.6 Metropolitan Area Networks (disbanded)
• IEEE 802.7 Broadband LAN using Coaxial Cable (disbanded)
• IEEE 802.8 Fiber Optic TAG (disbanded)
• IEEE 802.9 Integrated Services LAN (disbanded)
• IEEE 802.10 Interoperable LAN Security (disbanded)
• IEEE 802.11 Wireless LAN & Mesh (Wi-Fi certification)
• IEEE 802.12 demand priority
• IEEE 802.13 Cat.6 – 10Gb lan (new founded)
• IEEE 802.14 Cable modems (disbanded)
• IEEE 802.15 Wireless PAN
• IEEE 802.15.1 (Bluetooth certification)
• IEEE 802.15.4 (ZigBee certification)
• IEEE 802.16 Broadband Wireless Access (WiMAX certification)
• IEEE 802.16e (Mobile) Broadband Wireless Access
• IEEE 802.17 Resilient packet ring
• IEEE 802.18 Radio Regulatory TAG
• IEEE 802.19 Coexistence TAG
• IEEE 802.20 Mobile Broadband Wireless Access
• IEEE 802.21 Media Independent Handoff
• IEEE 802.22 Wireless Regional Area Network

WLAN Security

• Service Set Identifier (SSID)
• Wired Equivalent Privacy (WEP)
• Extensible Authentication Protocol (EAP)
• Wi-Fi Protected Access (WPA)
• 802.11i

Implications for Management

• Access to internal data, any time, any place
• Public access through WLAN hotspots
• Drastic price drops of WLAN devices
• Development of new Internet applications
• Drastic increase in the amount of data flowing around

Sources

http://en.wikipedia.org/wiki/IEEE_802

ISM2727 – WLANs (PPT)

Tech

In Telecommunications, Multiplexing consists of a process in which several signals (analog or digital) are combined into one single signal over a shared medium.

Types of Connections:

• Synchronous vs Asynchronous (temporal)
• Duplex vs Simplex (directional)
• Multiplexing: Frequency and Time (spatial)

Multiplexing Techniques:

• FDM: Frequency Division Multiplexing
• TDM: Time Division Multiplexing
• WDM: Wavelength Division Multiplexing
• CDM: Code Division Multiplexing

Frequency Division Multiplexing

• All signals are transmitted at the same time using different frequencies.
• Oldest Multiplexing technique. The signals are all transmitted in analog; hence, the signals are more susceptible to noise.
• Examples: Broadcast Radio, Cable Television.

Time Division Multiplexing

• Only digital signals are used; hence, less noise.
• Transmission time is divided among users.
• Two Types of TDM: Synchronous TDM and Asynchronous TDM.
• Synchronous TDM is the most popular these days, but Asynchronous TDM uses bandwidth much more efficiently. With Synchronous TDM, it is assumed all sources will transmit all the time, but Asynchronous only works when there’s actually a need to.
• Synchronous TDM Examples: T1, ISDN, SONET.

Wave Division Multiplexing

• Each signal has a different frequency (wavelength).
• DWDM: Dense Wavelength Division Multiplexing allows multiple data streams onto a single optic line. Each signal carried on the fiber can be transmitted at a different rate from the other signals.

Code Division Multiplexing (aka CDMA)

• Advanced technique that allows multiple devices to transmit on the same frequencies at the same time using different codes.
• Used for mobile communications.

Advantages and Disadvantages of Multiplexing Techniques

Tech

I just watched this movie last week, I thought it was pretty decent. It was nominated for several Oscar categories, so it’s probably worth watching.

Oscar.com
“When one of the star attorneys at a powerful corporate law firm suffers a guilt-fueled breakdown that threatens to derail a planned merger, the firm’s fixer, Michael Clayton, is called in to take care of the situation. As he delves into the facts behind the multimillion dollar lawsuit at the center of the conflict, Michael finds himself making moral and ethical decisions that will place his life in danger. ”

IMDB.com
“An attorney known as the Fixer in his law firm comes across the biggest case of his career that could produce disastrous results for those involved.”

Movies