Chapter 4 outline

1
Chapter 4 outline

• Introduction to mobile and wireless networking
• Mobile and wireless protocols and standards
• Mobile IP
• Wireless application protocol and related
  standards
• Wireless technologies
• 802.11
• Bluetooth
• Cellular (PCS, GSM, GPRS, etc.)
• Satellite

2
IEEE 802.11 Wireless LAN

• 802.11b
• 2.4 GHz unlicensed radio spectrum.
• Up to 11 Mbps.
• Widely deployed, using base stations.
• Currently deployed at Western in most public
  locations, and in a few departments (like
  Computer Science).

• 802.11a
• 5-6 GHz range.
• Up to 54 Mbps.
• 802.11g
• 2.4-5 GHz range.
• Up to 54 Mbps.
• All have base-station (access point based) and
  ad-hoc network versions.

3
Base Station Approach

• Wireless host communicates with a base station.
• base station access point (AP)
• Basic Service Set (BSS) (similar to a cell)
  contains
• Wireless hosts.
• An access point (AP), the base station.
• BSSs can be combined using a backbone
  Distribution System (DS) to form an Extended
  Service Set (ESS), which appears as a single
  logical LAN.

DS
ESS
4
Ad Hoc Network Approach

• No AP (i.e., base station).
• Wireless hosts communicate with each other.
• To get packet from wireless host A to B may need
  to route through wireless hosts X,Y,Z.
• Applications
• Laptop meeting in conference room, car.
• Interconnection of personal devices.
• Battlefield uses.
• IETF MANET (Mobile Ad hoc Networks) working
  group.

5
Distribution of Messages

• Distribution service
• The primary service used to exchange messages
  between wireless stations within the same ESS.
• Either within a single BSS (in which case the
  messages just go through the AP for that BSS), or
  from one BSS to another, in which the messages
  must traverse the DS.
• Integration service
• Transfer of data between a wireless station on an
  IEEE 802.11 LAN and a station on an integrated
  wired IEEE 802.x LAN attached to the DS through a
  portal.
• The integration service must take care of any
  address translation and media conversion logic.

6
Distribution of Messages
7
Associations

• Before the distribution service can deliver data
  to or accept data from a wireless station, that
  station must first be associated.
• It must be registered with an AP in a BSS, so
  that its identity and location is known to the
  network.
• Association service
• Establishes an initial association between a
  wireless station and an AP.
• Reassociation service
• Enables transfer of association from one AP to
  another, allowing a wireless station to move from
  one BSS to another.
• Disassociation service
• Association termination notice from a wireless
  station or AP.

8
Associations and Mobility

• There are different viewpoints of mobility within
  an 802.11 wireless LAN.
• No transition
• A wireless station is either stationary or moves
  only within a single BSS. Nothing special is
  needed.
• BSS transition
• The wireless station is moving from one BSS to
  another BSS inside the same ESS. Uses the
  reassociation service to support the move.
• ESS transition
• The wireless station is moving from BSS in one
  ESS to BSS within another ESS. Requires a
  disassociation and a new association in the new
  ESS. Upper layer connections cannot be
  guaranteed by 802.11 in this case, so Mobile IP
  would be necessary.

9
Access and Privacy Services

• To reasonably approximate a wired network, an
  802.11 network needs to provide access and
  privacy services to wireless stations.
• Access services
• Restricts which wireless stations can access the
  network, and can be done in a variety of ways.
• Service Set Identifiers (SSIDs) A station needs
  to know this to get access. Since most APs
  broadcast this (and if not, it is still
  accessible in plaintext from sniffed packets),
  this is not secure on its own.
• MAC address filtering Wireless stations with
  certain MAC addresses are allowed or disallowed.
• Wired Equivalent Privacy (WEP) A station needs
  to know the WEP key to get access. Again, not
  secure.
• Application level access control Includes a
  variety of mechanisms, like Bluesocket at UWO.

10
Access and Privacy Services

• Privacy services
• Prevents the contents of messages from being
  accessed by anyone other than the intended
  recipient.
• This usually entails some form of encryption, if
  you really want some measure of privacy.
• Wired Equivalent Privacy (WEP) A common, but
  broken, approach to encryption set in the
  standards.
• 802.1x A newer, but still not perfect, IEEE
  standard for access control for wireless and
  wired LANs, giving a means of authenticating and
  authorizing devices.
• EAP An 802.1x standard that uses a central
  authentication server to authenticate each user
  on the network. EAP has a number of variants,
  including EAP MD5, EAP-Tunneled TLS (EAP-TTLS),
  Lightweight EAP (LEAP), and Protected EAP (PEAP).
  
• Plus many, many others on the way!

11
Bluetooth Basics

• Low-power, small radius, wireless networking
  technology.
• 10-100 meters.
• Omnidirectional
• Not line-of-sight (like infrared).
• Interconnects gadgets
• PDAs.
• Cell phones.
• Gaming and music devices.
• Cameras.
• Printers.
• Keyboards/mice.
• Headphones and microphones.

• Bluetooth uses the 2.4-2.5 GHz unlicensed radio
  band.
• It supports data rates up to 721 kbps.
• Interference from 802.11 wireless LANs, digital
  cordless phones, microwave ovens
• Frequency hopping helps.

12
Bluetooth Application Areas

• Bluetooth provides support for three general
  application areas using short-range wireless
  connectivity.
• Data and voice access points
• Real-time voice and data transmissions by
  wireless connection of portable and stationary
  devices.
• Cable replacement
• Eliminates need for numerous cable attachments
  for connection of practically any kind of
  communications device.
• Ad hoc networking
• Devices with Bluetooth radio can easily establish
  connections with one another as soon as they come
  in range.

13
Bluetooth Standards Documents

• The Bluetooth standards are huge over 1500
  pages divided into two key groups.
• Core specifications
• Contain details of various layers of the
  Bluetooth protocol architecture, from the radio
  interface to link control.
• Profile specifications
• Discuss the use of Bluetooth technology to
  support various applications.
• Each profile specification discusses the use of
  the technology defined in the core specification
  to implement a particular usage model.

14
Bluetooth Usage Models

• Some of the key usage models defined in the
  Bluetooth profile specifications
• File transfer
• Supports the transfer of directories, files,
  documents, images, and streaming media.
• Internet bridge
• Allows a mobile phone or cordless modem to
  provide dial-up networking and fax capabilities
  to other Bluetooth enabled devices.
• LAN access
• Enables devices on a Bluetooth network to access
  a LAN as if they were wired devices directly
  connected to it.

15
Bluetooth Usage Models

• Synchronization
• Provides device-to-device synchronization of PIM
  (personal information management) data, such as a
  phone book, calendar, message, and note
  information.
• Three-in-one phone
• Telephone headsets that implement this model act
  as a cordless phone with a base station, an
  intercom device, and a cellular phone.
• Headset
• Allows a headset to act as a remote devices
  audio input and output interface.

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Bluetooth Usage Models

• Audio-video remote control
• Allows a Bluetooth device to function as a remote
  control for audio/video devices.
• Basic imaging
• Provides basic support for capturing,
  transferring, and manipulating images. (Good for
  digital cameras and video recorders.)
• Basic printing
• Provides support for the queuing and printing of
  documents to a Bluetooth enabled printer without
  fussing around with complex printer drivers.
• And many, many more!
• Complete lists available on the Internet.

17
Piconets and Scatternets

• Bluetooth is designed to operate in an
  environment of many users.
• Up to eight devices (one master and one to seven
  active slave devices) can communicate in a small
  network called a piconet. Ten such piconets can
  coexist in the same coverage area.
• Devices in one piconet can function as masters or
  slaves in other piconets in the same coverage
  area, giving an overlapping network called a
  scatternet.
• To provide security, each link is encoded and
  protected against eavesdropping and interference.

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Piconets and Scatternets
19
Piconets and Scatternets

• A Bluetooth master device determines the channel
  (frequency hopping sequence) and phase (timing
  offset, i.e. when to transmit) used by all
  devices in a piconet.
• Slaves may only communicate with the master, and
  may only communicate when granted permission by
  the master.
• This approach is similar to a base station mode
  of communication in other wireless networks.
• There is also a peer-to-peer mode, which is
  closer in functioning to a typical ad hoc
  wireless network.

20
Frequency Hopping

• Frequency hopping in Bluetooth serves two main
  purposes
• It provides resistance to interference.
• It provides a form of multiple access among
  co-located devices in different piconets.
• How it works
• The total Bluetooth bandwidth is divided into 79
  different channels (in most countries).
• Frequency hopping occurs by jumping from one
  channel to another in a pseudo-random sequence.
• The same sequence is used by all devices on a
  single piconet, as determined by the master.
• Occasionally, there may be collisions in
  co-located piconets, but these are infrequent,
  and are handled easily with forward error
  correction and other techniques.

21
Bluetooth Security

• Bluetooth specifies facilities for security
  between any two Bluetooth devices, with support
  for authentication, encryption (for privacy), and
  key management.
• It works reasonably well, but once again, is not
  perfect either.
• A common practice for Bluetooth devices is
  pairing, which sets up a secure channel between
  two devices based on a shared secret key that
  only the devices know about.
• Most devices allow you to enter a PIN or
  alphanumeric pass code used to authenticate
  theBluetooth devices in the pairing.

22
Bluetooth Security Modes

• Bluetooth specifications define three different
  possible security modes for a device
• Security Mode 1
• No security is provided. Essentially, the device
  is in a promiscuous or discovery mode in which
  any other Bluetooth device can communicate with
  it.
• Security Mode 2
• Security is enforced after devices are linked
  together and a communications channel is
  established.
• Security Mode 3
• Security is enforce before devices are even
  allowed to link together.

23
Other Bluetooth Security Notes

• Frequency hopping helps prevent casual or
  accidental eavesdropping.
• Frequency hopping occurs 1600 times per second.
• Unless a device is in sync with the sequence
  established by the master of a piconet, it is
  hard to recover much in the way of useful data.
• It is not very hard to get in sync, however.
• Many devices allow themselves to be hidden from
  Bluetooth discovery scans, so they only appear to
  devices that explicitly know their names or
  addresses on the network, as another measure of
  security.