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
Elements of a Wireless Network
3
Elements of a Wireless Network
4
Elements of a Wireless Network

• Wireless Link
• typically used to connect mobile(s) to base
  station
• also can be used as a backbone link
• multiple access protocol coordinates link access
• various data rates, transmission distance

5
Characteristics of Selected Wireless Link
Standards
200
802.11n
54
802.11a,g
802.11a,g point-to-point
Data
5-11
802.11b
802.16 (WiMAX)
3G cellular enhanced
4
UMTS/WCDMA-HSPDA, CDMA2000-1xEVDO
Data rate (Mbps)
1
802.15,
.384
UMTS/WCDMA, CDMA2000
3G
2G
.056
IS-95, CDMA, GSM
Indoor 10-30m
Outdoor 50-200m
Mid-range outdoor 200m 4 Km
Long-range outdoor 5Km 20 Km
6
Elements of a Wireless Network
7
Elements of a Wireless Network

• Ad hoc Mode
• no base stations
• nodes can only transmit to other nodes within
  link coverage
• nodes organize themselves into a network route
  among themselves

8
Wireless Network Taxonomy
Multiple hops
Single hop
Host may have to relay through several wireless
nodes to connect to larger Internet mesh net
Host connects to base station (WiFi, WiMAX,
cellular) which connects to larger Internet
Infrastructure (e.g., APs)
No base station, no connection to larger
Internet. May have to relay to reach a given
wireless node MANET, VANET
No infrastructure
No base station, no connection to larger
Internet (Bluetooth, ad hoc nets)
9
Wireless Link Characteristics

• Differences from wired link .
• Decreased signal strength radio signal
  attenuates as it propagates through matter (path
  loss).
• Interference from other sources standardized
  wireless network frequencies (e.g., 2.4 GHz)
  shared by other devices (e.g., phone) devices
  (motors, microwave ovens) interfere as well.
• Multipath propagation radio signal reflects off
  objects on the ground, arriving at destination at
  slightly different times.
• All this can make communication across (even a
  point to point) wireless link much more
  challenging.

10
Wireless Link Characteristics

• SNR signal-to-noise ratio
• Higher SNR easier to extract signal from noise
  (a good thing)
• SNR versus BER tradeoffs
• Given physical layer Increase power -gt increase
  SNR-gtdecrease BER
• But, increasing power consumes more energy and
  increases chances of interference
• Given SNR choose physical layer that meets BER
  requirements, giving highest throughput at the
  same time
• SNR may change with mobility dynamically adapt
  physical layer (modulation technique, rate)

10-1
10-2
10-3
10-4
BER
10-5
10-6
10-7
10
20
30
40
SNR(dB)
QAM256 (8 Mbps)
QAM16 (4 Mbps)
BPSK (1 Mbps)
11
Wireless Link Characteristics

• The multipath propagation problem
  illustrated
• Signal from omnidirectional antenna at A arrives
  twice at B, causing interference or confusion.
• But if we sent different data in different
  directions from A just right, we may be able to
  use the multipath effect to increase our
  effective bandwidth! People are looking into
  this kind of technology as we speak!

12
Wireless Network Characteristics

• Multiple wireless senders and receivers create
  additional problems (beyond multiple access)

• Hidden terminal problem
• B, A hear each other.
• B, C hear each other.
• A, C can not hear each other meaning A, C unaware
  of their interference at B.

• Signal fading
• B, A hear each other.
• B, C hear each other.
• A, C can not hear each other, and are interfering
  at B.

13
Code Division Multiple Access (CDMA)

• Used in several wireless broadcast channels
  (cellular, satellite, etc.) standards.
• Unique code assigned to each user i.e., code
  set partitioning.
• All users share same frequency, but each user has
  own chipping sequence (i.e., code) to encode
  data.
• encoded signal (original data) X (chipping
  sequence)
• decoding inner-product of encoded signal and
  chipping sequence
• Allows multiple users to coexist and transmit
  simultaneously with minimal interference (if
  codes are orthogonal).

14
CDMA Encode/Decode
channel output Zi,m
Zi,m di.cm
data bits
sender
slot 0 channel output
slot 1 channel output
code
slot 1
slot 0
received input
slot 0 channel output
slot 1 channel output
code
receiver
slot 1
slot 0
15
CDMA Two-sender Interference
16
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

17
IEEE 802.11 Wireless LAN

• 802.11g
• 2.4 GHz range
• Up to 54 Mbps
• Some multi-channel variants exist too
• 802.11n multiple input, multiple output (MIMO)
  antennas
• 2.4-5 GHz range
• Up to 248 Mbps
• Still in draft form, with standardization on-going

• 802.11a
• 5-6 GHz range
• Up to 54 Mbps
• 802.11b
• 2.4 GHz unlicensed spectrum
• Up to 11 Mbps
• Direct sequence spread spectrum (DSSS) in
  physical layer
• All hosts use same chipping code

• All use CSMA/CA for multiple access
• All have base-station and ad-hoc network versions

18
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
19
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.
• IETF MANET (Mobile Ad hoc Networks) working
  group.

20
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.

21
Distribution of Messages
22
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.

23
The Association Process

• Again, each host must associate with an AP to be
  part of the wireless network.
• The host scans channels, listening for beacon
  frames containing APs name (SSID) and MAC
  address.
• It then selects the AP to associate with, based
  on what it finds.
• It may perform authentication, depending on the
  configuration of the AP and its network.
• Typically, the host will run DHCP to get an IP
  address in APs subnet.

24
Associations Passive/Active Scanning
BBS 1
BBS 1
BBS 2
BBS 2
AP 1
AP 2
AP 1
AP 2
H1
H1

• Active Scanning
• Probe Request frame broadcast from H1
• Probes Response frame sent from APs
• Association Request frame sent H1 to selected AP
  
• Association Response frame sent H1 to selected AP

• Passive Scanning
• Beacon frames sent from APs
• Association Request frame sent H1 to selected AP
  
• Association Response frame sent H1 to selected AP

25
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.

26
Mobility BSS Transition Example

• H1 remains in same IP subnet IP address can
  remain same.
• Switch which AP is associated with H1?
• Self-learning switch will see frame from H1 and
  remember which switch port can be used to reach
  H1.
• With right infrastructure,reassociation service
  can be quite simple.

hub or switch
BSS 1
AP 1
AP 2
H1
BSS 2
27
802.11b Channels

• 802.11b Frequency spectrum divided into 14
  channels at different frequencies.
• In North America, 1-11 are used. Most of Europe
  allows 1-13, while Japan allows only 14.
• AP admin chooses frequency for AP.
• Interference is possible!
• Channel can be same as that chosen by neighboring
  AP!
• Channels also overlap with one another!
• 5 MHz between centers of channels, but an 802.11b
  signal requires about 30 MHz of the frequency
  spectrum.
• Consequently, a channel will overlap with its
  neighbours.
• In North America, this leaves you with 3 safe
  channels without interference 1, 6, and 11.

28
IEEE 802.11 Multiple Access

• Avoid collisions 2 nodes transmitting at same
  time.
• 802.11 CSMA (Carrier Sense Multiple Access) -
  sense before transmitting
• Dont collide with ongoing transmission by other
  nodes.
• 802.11 No collision detection!
• Difficult to receive (sense collisions) when
  transmitting due to weak received signals
  (fading).
• Cant sense all collisions in any case hidden
  terminal, fading.
• Goal avoid collisions CSMA/C(ollision)A(voidance
  )

29
IEEE 802.11 MAC Protocol CSMA/CA

• 802.11 sender
• 1 if sense channel idle for DIFS then
• transmit entire frame (no CD)
• 2 if sense channel busy then
• start random backoff time
• timer counts down while channel idle
• transmit when timer expires
• if no ACK, increase random backoff interval,
  repeat 2
• 802.11 receiver
• - if frame received OK
• return ACK after SIFS (ACK needed due to
  hidden terminal problem)

sender
receiver
Distributed Inter Frame Space
Short Inter Frame Space
30
Avoiding Collisions (More)

• Idea allow sender to reserve channel rather
  than random access of data frames avoid
  collisions of long data frames.
• Sender first transmits small request-to-send
  (RTS) packets to BS using CSMA.
• RTSs may still collide with each other (but
  theyre short).
• BS broadcasts clear-to-send CTS in response to
  RTS.
• CTS heard by all nodes.
• Sender transmits data frame.
• Other stations defer transmissions.

Avoid data frame collisions completely using
small reservation packets!
31
Collision Avoidance RTS-CTS Exchange
A
B
AP
defer
time
32
802.11 Frame Addressing
Address 4 used only in ad hoc mode.
Address 1 MAC address of wireless host or AP to
receive this frame.
Address 3 MAC address of router interface to
which AP is attached.
Address 2 MAC address of wireless host or AP
transmitting this frame.
33
802.11 Frame Addressing
H1
R1
34
802.11 Frame More
frame seq
duration of reserved transmission time (RTS/CTS)
frame type (RTS, CTS, ACK, data)
35
802.11 Advanced Capabilities

• Rate Adaptation
• Base station, mobile dynamically change
  transmission rate (physical layer modulation
  technique) as mobile moves, SNR varies

10-1
10-2
10-3
BER
10-4
10-5
10-6
10-7
10
20
30
40
SNR(dB)
1. SNR decreases, BER increase as node moves away
from base station
QAM256 (8 Mbps)
QAM16 (4 Mbps)
2. When BER becomes too high, switch to lower
transmission rate but with lower BER
BPSK (1 Mbps)
operating point
36
802.11 Advanced Capabilities

• Power Management
• Node-to-AP I am going to sleep until next
  beacon frame
• AP knows not to transmit frames to this node, and
  buffers them for later transmission
• The node sets and timer, and wakes up before the
  next beacon frame
• Beacon frame from AP contains list of mobile
  nodes with AP-to-mobile frames buffered and
  waiting to be sent to them
• The node will stay awake if AP-to-mobile frames
  to need to be received otherwise it sleeps again
  until next beacon frame

37
802.15 Personal Area Network

• Less than 10 m diameter.
• Replacement for cables (mouse, keyboard,
  headphones).
• Ad hoc no infrastructure.
• Master/slaves
• Slaves request permission to send (to master).
• Master grants requests.
• 802.15 evolved from Bluetooth specification.
• 2.4-2.5 GHz radio band.
• Up to 721 kbps.
• More on Bluetooth soon!

radius of coverage
38
802.16 WiMAX
point-to-point

• Worldwide Interoperability for Microwave Access
• Like 802.11 and cellular base station model
• Transmissions to/from base station by hosts with
  omnidirectional antenna
• Base station-to-base station backhaul with
  point-to-point antenna
• Unlike 802.11
• Can deliver over 70 Mbps over 50 km, but not
  simultaneously!
• Best expectations are 10 Mbps over 10km,
  depending on line of sight and other issues

point-to-multipoint
39
802.11 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.

40
802.11 Access and Privacy Services

• More access services
• Wired Equivalent Privacy (WEP) A station needs
  to know the WEP key to get access. Again, not
  secure.
• Wi-Fi Protected Access (WPA) An improved access
  mechanism, designed to work with 802.1x for
  authentication (also known as enterprise mode) or
  using pre-shared keys or pass-phrases (also known
  as personal mode). Now have version WPA2 (a
  complete implementation of 802.11i the original
  WPA was only a subset of the standard).
• Application level access control Includes a
  variety of mechanisms, like Bluesocket at UWO.

41
802.11 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!

42
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

43
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. Newer
  versions with higher speeds are on the way!
• Interference from 802.11 wireless LANs, digital
  cordless phones, microwave ovens
• Frequency hopping helps.

44
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.

45
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.

46
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.

47
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.

48
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.

49
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.

50
Piconets and Scatternets
51
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.

52
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.

53
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.

54
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 enforced before devices are even
  allowed to link together.

55
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.

56
Bluetooth Protocol Stack
57
Bluetooth Protocol Stack

• Bluetooth Radio
• Defines the requirements for a Bluetooth
  transceiver in the 2.4GHz frequency band.
• Bluetooth Baseband
• The physical layer of Bluetooth, managing
  physical channels and low level links, providing
  a Bluetooth Link Controller (LC).
• LMP (Link Manager Protocol)
• The Link Manager carries out link setup,
  authentication, link configuration and other
  protocols. It discovers other remote LMs and
  communicates with them via the LMP.

58
Bluetooth Protocol Stack

• HCI (Host Controller Interface)
• Provides a standard communications protocol
  between the stack and the lower layers. HCI
  communication packets can be transmitted using
  UART, RS232 or USB interfaces.
• L2CAP (Logical Link Control and Adaptation
  Protocol Layer)
• This layer allows multiple channels to share a
  single Bluetooth link. It also handles
  segmentation and assembly of long messages, group
  management, and quality of service
  functionalities.

59
Bluetooth Protocol Stack

• RFCOMM
• This layer implements the functionalities of a
  virtual RS232 link. Most of the application
  profiles use RFCOMM as a means of transmitting
  and receiving data.
• SDP (Service Discovery Protocol)
• This layer provides functionalities to publish
  supported Bluetooth functionalities (SDP server),
  as well as for querying remote Bluetooth devices
  for supported functionalities (SDP client).
• OBEX (OBject EXchange)
• A communication protocol that facilitates the
  exchange of binary objects between devices.