1. Design Considerations & Emerging Standards

3.  Carrier Sense Multiple Access / Collision Detect.  Practical limit on 802.3 Nodes per collision domain

4.  Listen before you talk.

6. All stations share (access) the common media.

7.  Each station must wait at least 9.6 microseconds between packets ◦ InterPacket Gap (IPG) ◦ Allows receiver to process packet ◦ Also allows everyone a chance to use the medium.

11.  The first station to detect a collision sends a 32 bit ‘Jam’ signal. ◦ All stations stop sending for at least 9.6 microseconds  The two stations that caused the collision then calculate a “Backoff Period” Before retrying.

12.  There are a certain number of availble values for the random backoff period.  Once networks get to about 30 devices, the backoff periods become congested.

13.  CSMA/CD  Send and Receive share the same bus Half Duplex Collision Domain

14.  Switches Required  Switches create 2 virtual bus’s per connection Collision Domain

15.  802.11 is Half Duplex ◦ Tx and Rx uses SAME space ◦ A radio can not Transmit and Receive Simultaneously. ◦ Therefore, Collision Detection is not an option.

16.  Waits for each frame to be ACKd  If ACK not received, Collusion Assumed ◦ Takes LONGER then CD. ◦ More devices -> More Collisions -> More Wait Time

17.  Back to the rules of Shared Media  Each section of air is Shared Media  Each Channel is a segment (at a certain point.)

19.  Radio Frequency  2.6 Ghz, 5.2 Ghz

20.  Knows no boundaries  Unprotected from outside signals  Distance Sensitive ◦ Law of Inverse Square  Regulated differently in each country.

21.  More power = More Distance. ◦ Sorta.

23.  LOTS of interference ◦ Devices operating in the 2.4 GHz range include:  Microwave ovens.  Bluetooth devices.  Baby monitors.  Cordless telephones.  Building Security Systems

24.  NO Overlap between Channels 1, 6, and 11.  All other channels, to bad!

26.  Relatively unused.  Less Interference.  More Available Channels  Shorter Wavelength = ½ theoretical coverage  Absorbed more readily by solid objects.

31.  Pros ◦ More Bandwidth ◦ More Channels ◦ Less Interference  Cons ◦ Less Coverage Area ◦ Lower Penetration The Drawbacks” of 5 Ghz actually HELP K-12

36.  Uses Different Frequency Hopping to pack more of the RF Space.  Therefore, the faster the network, the more “attack surface” for interference it has.

37.  802.11a up to 54 Mbps in 5 Ghz Band  802.11b up to 11 Mbps in 2.4 Ghz Band.  802.11g up to 54 Mbps in 2.4 Ghz Band.  802.11n up to 600 Mbps via MIMO ◦ Technically supported in 2.4 GHZ.  802.11ac MultiGbps via MU-MIMO

42.  802.11n ◦ 20 Mhz Channels X 3 Streams = 300 MB ◦ 40 Mhz Channels X 3 Streams = 600 MB  802.11ac ◦ 80 Mhz Channels x 4 streams = 1.7 Gb ◦ 160 Mhz Channels X 8 Streams = 6.9 Gb  (No chipsets yet bond 160Mhz)

44. Room 106Room 108

45.  IEEE 802.11 RTS/CTS mechanism helps to solve this problem only if the nodes are synchronized and packet sizes and data rates are the same for both the transmitting nodes. When a node hears an RTS from a neighboring node, but not the corresponding CTS, that node can deduce that it is an exposed node and is permitted to transmit to other neighboring nodes IEEE 802.11 RTS/CTS

46.  Limit Association Rates  Try for uniform Device Radio Types

52. http://www.nojitter.com/post/240000795/rf- interference-when-things-go-bump-in-the- air

54.  Bluetooth hops across the 2.4 GHz 1,600 times a second,

55.  Interference – What’s already there?  Building Construction – Brick Walls?  Area to Cover  Type of service ◦ (VoIP/Wifi?)  Number of potential Clients  Total Bandwidth required

56. ◦ 5 GHZ Devices ◦ 802.11n or 802.11ac ◦ One AP : Traditional classroom ◦ One AP : 30 Students 802.1x authentication on WiFi Limiting “casual” associations

57.  Dual Band Devices ◦ 802.11 abgn ◦ List “preferred” devices with abgn support

58.  Probes – frames advertise the WLAN network  Beacons – frames locate the WLAN network of the client  Authentication – access and entry into the WLAN network  Association – set up of a link between the AP and WLAN client

59.  War Drivers: Scanning devices are used to discover and exploit networks.  Hackers (Crackers): Where the hacker understands the complexity of the system and exploits its weaknesses.  Employees: End users make changes to the security of the system leaving it vulnerable to intrusion.

62.  PAN  LAN  MAN  WAN