Wireless Networks

1
Wireless Networks

• Introduction to Wireless Networks.
• Overview
• Wireless Specifications
• Advantages / disadvantages of Wireless

2
Types of Wireless Networks

• Infra Red
• LED transmitter TV Controller technology
• Line of sight
• Very Low capacity (100Kbit is high speed)
• BlueTooth
• Personal Network
• Short Distance (within a room)
• Low Capacity (lt3 Mbits)
• WiFi

3
Bluetooth

• 802.15.1
• Uses short range radio frequency 2.4 gigahertz
• frequency hopping spread spectrum technique
• Very Short range lt10m (Class 1 lt1m
  Class2lt10mltClass 3lt100m
• Does allow 1 M relationships Piconets upto 8
  devices
• Low bandwith
• 1.0 Started at 1Mbit per second
• 2.0 is now 3Mbit per second
• Each Bluethooth device has
• 48 bit device address
• 24 bit device identifier
• Can have 4 digit pin number for securing link
  between devices
• Three major versions
• 1.1 and 1. 2 increase transmission speed
• 2.0 ITS and reduced power consumption

4
Overview of Operation

• A Physical radio channel is shared by a group of
  devices (Piconet).
• They are synchronised
• to a common clock and
• frequency hopping pattern
• Algorithmically determined by certain fields in
  the specification address and clock of the
  master device
• FH pattern is pseudo random ordering of the 79
  frequencies.
• Adaptive FH means can exclude in use frequencies.
• Improves co-existence with static (non
  hopping)ISM systems
• All other devices on the piconet are slaves.

5
Channel Segmentation

• Physical channel divided into time units called
  slots
• Data is transmitted in packets in these slots
• Packets can span several slots
• Frequency hopping takes place between
  transmission and reception of packets
• Full duplex (comms in both directions) achieve by
  a time division duplex (TDD) scheme)
• Each channel can be used for multiple services
  (profiles)

6
Layering of links and channels

• Physical Channel
• Physical Link
• Logical Transport
• Logical Link
• L2CAP Channel

Piconet
Master
Slave
Slave
Slave
1234
0000
9999
7
How does wireless Work

• Uses radio signals to transmit data.
• As it is a radio wave transmitted in all
  directions.
• Line of sight not required.
• Can travel through physical barriers (walls etc)
  but High density objects or large volumes of
  physical barriers will degrade signal.
• Radio bandwidths are licensed by governments.
• 2.4 and 5 gigahetz (US also allows 4.9 gHz)
• 14 channels available
• Short range 100 metres in good conditions.
• To create a link between two devices
• Need 2 of transceivers (a transmitter and a
  receiver).
• Each extra device requires another transceiver.
• Communication is between the base station (access
  point) and remote device(s).
• Remote devices cannot communicate with each other.

8
IEE Wireless Standard 802

• 802.11a - 54 Mbps standard, 5 GHz signaling
  (ratified 1999)
• 802.11b - 11 Mbps standard, 2.4 GHz signaling
  (1999)
• 802.11c - operation of bridge connections (moved
  to 802.1)
• 802.11d - worldwide compliance with regulations
  for use of wireless signal spectrum (2001)
• 802.11e - Quality of Service (QoS) support (not
  yet ratified)
• 802.11f - protocol for communication between
  access points to support roaming clients (2003)
• 802.11g - 54 Mbps standard, 2.4 GHz signaling
  (2003)
• 802.11h - enhanced version of 802.11a to support
  European regulatory requirements (2003)
• 802.11i - security improvements for the 802.11
  family (2004)
• 802.11j - enhancements to 5 GHz signaling to
  support Japan regulatory requirements (2004)
• 802.11k - WLAN system management (in progress)
• 802.11l - skipped to avoid confusion with 802.11i
  
• 802.11m - maintenance of 802.11 family
  documentation
• 802.11n - future 100 Mbps standard (in progress)
  

9
Wireless Advantages

• Easier physical Installation.
• Not limited to line of sight (ie Infrared).
• Device can be moved without significantly
  affecting link (within range).

10
Wireless Disadvantages

• Range
• 100m radius per access point.
• Obstructions e.g .walls etc reduce range.
• Reliability
• The further away from the access point the lower
  the speed for contact.
• Interference e.g.
• 802.11b 2.5 gHertz is subject to interference
  from electrical devices such as Microwaves
• electrical burst noise
• Weather conditions affect transmission of radio
  waves.

11
Wireless Disadvantages

• Bandwidth
• Limited by the medium!
• Theoretical Effective
• 802.11a 2Mbit lt1Mbit FHSS
• 802.11b 11Mbit 2-3 Mbit DHSS
• 802.11g 54 Mbit 10 Mbit ??
• 802.11n 320Mbit ???
• Limited by access points connection to the
  network
• Several devices linking through a single access
  point share the bandwidth.

12
Wireless Problems

• Security.
• As signal is broadcast in all directions it can
  be picked up by anyone so-
• Legitimate connections can be heard.
• Unauthorised access can be attempted by Hostile
  agents.
• First problem can be dealt with by encryption
• The second by authentication.

13
Security Solutions for Wireless

• Encryption
• WEP (wired equivalent protocol) based on RC4
  cipher
• TKIP - temporal key integrity protocol
• Authentication
• WPA Wifi protected Access
• LEAP / PEAP service
• RADIUS (Remote Authentication Dial In User
  Service)
• is an AAA (authentication, authorization and
  accounting) protocol
• Set up a VPN (Virtual Private network)
• Other barriers
• Not broadcasting SSID
• Mac Filtering checking the mac address of the
  wireless device
• Use fixed IP rather than DHCP

14
Improving Security on Wireless

• Always update your wireless router firmware
• Change the default SSID
• Use WPA2/802.11i if possible
• Authenticate your wireless LAN users using
  protocols like EAP-TLS, EAP-TTLS, PEAP, and
  EAP-SIM
• Disable SSID Broadcast
• Use FreeRADIUS for Unix systems for more
  authentication
• Turn off DHCP on the router or access point, set
  a fixed IP address range
• Log every inbound/outbound traffic of your
  network
• Run pen tests against your wireless router using
  wireless hackers tools
• Place your wireless antennas and routers far from
  external walls.
• Use wireless access point sniffers from outside
  your room and check the signal
• Do not rely upon MAC authentication
• Use a firewall that supports VPN connectivity
  requiring users to log on as if they were dialing
  in remote

15
Wireless Security

• Can you protect wireless systems?
• http//blogs.zdnet.com/Ou/index.php?p43