Mobile%20Computing

1
Mobile Computing

• Assistant Professor Jenhui Chen
• Office number 5990
• Homepage http//www.csie.cgu.edu.tw/jhchen

2
Textbooks and References

• W. Stallings, Wireless Communications Networks,
  Prentice Hall, August 2001.
• D.J. Goodman, Wireless Personal Communications
  Systems, Addison-Wesley, 1997.
• Selected journal articles and conference papers

3
Grading

• Midterm Report
• Oral presentation- over 15 pages (30)
• Final Project
• Oral presentation- over 15 pages (30)
• Report 10 pages (40)

4
Selected Papers

• Journals
• IEEE Transactions on Mobile Computing
• IEEE Journal on Selected Areas in Communications
• IEEE Transactions on Vehicular Technology
• ACM Computing Surveys
• Magazine
• IEEE Pervasive Computing
• IEEE Wireless (Personal) Communications
• IEEE Communications
• Communications of the ACM
• Conferences
• IEEE INFOCOM, IEEE GLOBECOM, IEEE ICC
• ACM SIGCOM, ACM MOBICOM

5
Related Topics

• Sensor Networks
• Pervasive Computing (Wireless LAN)
• Internet Computing
• Personal Communication System
• UMTS (Universal Mobile Telecommunications System)
• GPRS (General Packet Radio Service)

6
Chapter 1

• Introduction
• Why and who will be mobile?

7
Telecom Networks/Systems

• Wired Networks (Internet)
• Local Area Networks (LANs)
• Public Data Networks, i.e., WANs
• Wireless Networks
• Wireless LANs
• Mobile Data Networks
• Fixed Telephone Networks, i.e., Public Switched
  Telephone Networks (PSTNs)
• Mobile Phone Systems

8
Telecom Statistics
1995 1996 1997 1998 1999
2000
Note According to Jan. 2001 statistics, total
mobile phone subscribers are 18.3M in
which CHT 4.7M(25.7), and others 13.61M(74.3)
9
Some Forecasts

• In 3 years, Internet traffic will grow to 10,000
  times its current level.
• Global e-business revenue will grow 86 per year
  to 1.4 Trillion in 2003.
• Bandwidth consumption will grow by a factor of
  100 to 200 over the next four years.

10
What is Mobile Computing?

• Mobile Computing is also known as Ubiquitous
  Computing (anywhere, anytime and any device)
• The scope covered by Mobile Computing roughly
  includes Mobile Data, Wireless LANs and Ad Hoc
  Networks, etc.

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Mobile Computing Chart
Verticals
Horizontals
Applications
Mobile operation systems
Operating systems
Notebooks
PDAs
Phones
Others
Devices
WANs
LANs
Wireless networks
12
Application Layer

• Vertical applications those apply to a function
  part of an industry such as field sales and field
  service, or to specific market segment such as
  banking or health care
• Horizontal applications apply to many people
  across most market segments

13
Operation Systems Layer

• This layer provides tools for application
  programmers to access different mobile devices
  and different wireless networks
• A key layer to rapid growth of wireless
  networking and proliferation of applications

14
Device Layer

• All the mobile devices we carry with us
• Notebooks (NBs)
• Personal Digital Assistants (PDAs)
• Cellular phones
• Personal communicators
• Combination devices
• Combination devices are now rapidly emerging

15
Wireless Networks Layer

• The Wireless Wide Area Network (WAN) is also
  called Mobile Data including
• Packet networks RAM/Mobitex, ARDIS/Modacom
• Paging networks
• Data over cellular CDPD (over AMPS), GPRS (over
  GSM)
• Data over satellite
• Wireless LANs with much higher rate but smaller
  coverage than Mobile Data networks

16
Applications Market by 2005
17
Field Sales Application

• Sales quotation
• Inventory check
• Order entry
• Credit authorization
• Invoicing

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Field Service Application

• Obtaining a maintenance history of the item
  requiring service
• Performing complex diagnostics that require
  access to databases and applications at other
  locations
• Checking parts inventory if required
• Updating the maintenance database after the
  service is done
• Invoicing for the job
• Real-time dispatching of the field engineer

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Transportation Application

• The oldest application
• Including
• Automatically locating the vehicle
• Dispatching the vehicle to the next job
• Routing the vehicle if required
• Capturing data from the vehicle

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Personal Communications Application

• Messaging
• Calendaring
• Directories
• Info Systems
• Fax

21
Mobile Office Application

• Fax
• E-mail
• LAN access
• File transfer
• Database access

22
Vertical Market Examples

• Airlines
• Police
• Field sales
• Emergency
• Hospitals
• Maintenance
• Retail stores

• Stock exchanges
• Casinos
• Hotel
• Taxicabs
• Rental car agencies
• Transportation

23
Challenges

• Security
• User authentication
• Data privacy
• Privacy of user location
• Bandwidth
• Limited bandwidth (10K10M)

• Software
• Still in its infancy
• The main/ biggest reason for late data
  implementations
• Safety
• Radiation is harmful to human beings
• Trends low power, thus less radiation

24
Application/Technology Matrix
Sector Application Technology Technology Technology Technology
Sector Application Cellular Paging Mobile Data WLANs
Private (corporate) Service engineering
Private (corporate) Order entry 0
Private (corporate) Vehicle routing 0
Private (corporate) Incident control 0
Public Network Services Facsimile 0 0
Public Network Services Text messaging
Public Network Services Info services
Public Network Services News 0
Public Network Services Market 0
Public Network Services Financial 0
Public Network Services Location tracking 0 0 0
Public Network Services Traffic alerts 0
25
Horizontal Application Examples

• Near term horizontal applications (LAN app.)
• Dynamic work environment
• Trade show
• conference
• Difficult to wire areas
• New employees who need immediate service
• Broad-based horizontal applications (WAN app.)
• Wireless meeting
• Wireless traveler
• Interactive TV

26
Positioning of Wireless Networking
Wireless Data Today Future
Mobile Data 10 Kbps 100 Kbps
Wireless LANs 1 Mbps 10 Mbps
Wired Data Today Future
Wired Data 100 Kbps gt1 Mbps
Wired LANs 10 Mbps gt100 Mbps

• Comparison between wireless data wired data
  capacities
• Position of wireless networks relative to wired
  networks
• Not a replacement but an extension to wired
  networks

27
CDPDCellular Digital Packet Data

• Daniel Grobe Sachs
• Quji Guo

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What is CDPD?

• Motivation Packet data over AMPS
• AMPS is unsuited for packet data
• Long call setup times
• Modem handshaking required
• Analog providers have AMPS allocation.
• Use AMPS channels to provide data service.
• Cellular digital packet data
• Cant interfere with existing analog service.
• CDPD is cheap no new spectrum license needed!

29
Design Goals

• Goals
• Low speed, high latency data service
• Primarily intended for paging and email.
• Provide broadcast and multiple-access service.
• Dynamically shared media, always online.
• Share channels with AMPS allocation
• Transparency to existing AMPS service.

30
CDPD History

• Standard released Jan, 1995 (v1.1)
• Initially used by police (1996)
• Wide service availability around 2000
• Omnisky, Verizon Wireless, others.
• Covers most US population centers
• Champaign-Urbana now covered.
• Rural area coverage poor.

31
CDPD Market

• CDPD is used primarily for
• Law enforcement
• Handheld/laptop IP access
• Main competition Wireless Web phones.
• CDPD costs
• Wireless modems 300 (Omnisky Palm V)
• Service 30-40 per month (handheld)
• 40-80 per month (laptop)

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Omnisky Coverage Map
Source Omnisky (http//www.omnisky.com)
33
CDPD Infrastructure
Source A. Salkintzis, Packet Data over Cellular
Networks The CDPD Approach
34
CDPD - Layering
IP/CLNP
Connectionless Network Protocol Subnetwork
Dependant Convergence Protocol Mobile Data Link
Protocol Media Access Control Physical
SNDCP
MDLP
MAC
Physical
Network layer CDPD Layer
35
CDPD Physical Layer

• 30KHz BW channels, shared with AMPS
• Separate forward and reverse channels
• Forward channel is continuous
• Reverse channel is multiple access.
• Gaussian Minimum-Shift Keying-GMSK
• GMSK compromises between channel bandwidth and
  decoder complexity.
• 19.2kbps per channel.

IP/CLNP
SNDCP
MDLP
MAC
Physical
36
AMPS and CDPD

• CDPD runs alongside AMPS
• AMPS system is unaware of CDPD system
• CDPD system watches AMPS behavior
• AMPS generally has unused channels.
• Blocked calls when all channels are allocated.
• 1 block probability gt all channels used only 1
  of the time.

37
CDPD Channel Usage

• CDPD uses unused AMPS channels.
• Usually are several available.
• Each 30KHz channel 19.2kbps up and down
• CDPD channel hopping.
• Forced AMPS must be vacated within 40ms of
  allocation for voice use.
• Planned Regular hops prevent AMPS system from
  identifying channel as unusable.

38
Channel Scanning

• 1. Check signal levels from nearby cells.
• Use a list of reference channels distributed by
  the CDPD infrastructure to find levels.
• 2. Select cell with best signal.
• If non-critical and no cell is significantly
  better than current, no handoff is done
  (hysteresis)
• 3. Scan RF channels in cell for CDPD.
• Stop when an acceptable channel is found.

39
Handoff in CDPD

• Critical handoffs Must choose new channel
• High error rate is observed or BS signal lost.
• Received signal strength below a threshold.
• Base station does not receive data from mobile.
• Noncritical handoffs
• Channel rescan interval expires.
• Signal strength changes significantly.

40
CDPD effects on AMPS

• CDPD logically transparent to AMPS
• Can reduce AMPS service quality
• More channel usage gt increased interference.
• If AMPS system is close to SIR margin, CDPD can
  push it below.
• Full CDPD usage can push SIR down 2dB
• 19 channels/cell, Pblock 0.02, 12.3 Erlangs
• Limiting channels used reduces SIR cost..

41
Data Transmission Format

• All links are base to mobile.
• Mobile to mobile goes through base station.
• Full-duplex separate forward and reverse links.
• Forward link
• Continuous transmission by BS
• Reverse link
• Shared multiple access for mobiles.
• Reverse link activity indicated by BS.

IP/CLNP
SNDCP
MDLP
MAC
Physical
42
Forward Link Structure
Source A. Salkintzis, Packet Data over Cellular
Networks The CDPD Approach
43
Reverse Link Structure
Source A. Salkintzis, Packet Data over Cellular
Networks The CDPD Approach
44
Reverse Link MAC

• Near/Far problem
• Mobile may not detect a faraway transmitter.
• Base station must report busy status.
• Protocol
• Digital Sense Multiple Access
• Nonpersistant Checks once for busy state.
• Slotted Can only start when BS reports state.
• Similar to Ethernet MAC.

IP/CLNP
SNDCP
MDLP
MAC
Physical
45
Reverse Link MAC
Source J. Agostsa et al., CDPD Cellular Data
Packet Standards and Technoloy
46
Reverse Link MAC

• Reverse link idle gt can transmit.
• Busy status checked before transmission starts..
• Continue burst unless error is indicated.
• If BS indicates error, assume collision
  exponential backoff is used.
• Reverse link busy
• Delay for a random number of slots.
• Check busy status again.

47
Mobile Data Link Protocol
IP/CLNP
SNDCP
MDLP
MAC
Physical
Source J. Agostsa et al., CDPD Cellular Data
Packet Standards and Technoloy
48
CDPD - MDLP

• Mobile Data Link Layer Protocol (MDLP)
• High-level data link control (HDLC)
• Similar to ISDN HDLC.
• Mobile (M-ES) to Infrastructure (MD-IS)
• In this layer, air link and BS become transparent
• Connection oriented
• MDLP Frame (message structure)
• Address, control field, information field
• No checksum MAC discards incorrect packets.

49
CDPD - MDLP

• Temporary equipment identifier (TEI)
• Identifies destination mobile - virtual address.
• Assigned by infrastructure.
• Packet types
• Unacknowledged information
• Sequenced information
• Sequence number, ack, timeout
• Sliding window
• Selective rejection supported.

50
CDPD - SNDCP

• Subnetwork-Dependent Convergence Protocol (SNDCP)
• Between IP or CLNP and MDLP
• In both mobile and infrastructure (MD-IS)
• Segmentation, compression, encryption
• Questions
• Where and how to segment data?
• Where and how to compress data?

IP/CLNP
SNDCP
MDLP
MAC
Physical
51
CDPD - SNDCP

• Segmentation
• Goal to fit the size of underlying frames
• Two type of headers
• Sequenced headers
• For compressed, encrypted, and segmented user
  data.
• Unnumbered headers Control information.
• Efficiency consideration (similar to X.25)
• Which layer should segment/assemble messages?
• Use More indicator to avoid IP fragmentation.

52
CDPD - SNDCP

• Compression
• Header compression
• To send the Delta information
• Data compression
• V.42bis a dictionary-based compression
• Which layer should compress data?
• Source-dependent compression higher layer
• Source-independent compression lower layer

53
CDPD - Registration

• Low-level protocols ignore authentication.
• Registration and Authentication
• M-ES, serving MD-IS, home MD-IS
• Base station (MDBS) has no network function.
• Network Equipment identifier (IP, etc.)
• Forwarding database in home MD-IS
• Deregistration
• Table maintenance timer

54
Problems with CDPD

• Limited bandwidth
• 19.2kbps shared per channel
• Modern applications demand more bandwidth.
• Security
• Man in the middle identity theft attack
• IP network attacks
• Denial of Service attacks easy.

55
Potential Improvements

• Multichannel / multicarrier transmission
• Would allow faster rates with AMPS compatibility.
• Security Improvements
• Secure against man-in-the-middle attacks.
• Switch to CDMA/GSM.
• Digital cellular services are more able to
  accommodate data services.

56
References

• J. Agosta and T. Russell, CDPD Cellular Packet
  Data Standards and Technology, McGraw Hill, 1996.
• Y. Frankel et al., Security Issues in a CDPD
  Wireless Network, IEEE Personal Communications,
  August 1995, pp. 16-26.
• D. Saha and S. Kay, Cellular Digital Packet Data
  Network, IEEE Transactions on Vehicular
  Technology, August 1997, pp. 697-706.
• A. Salkintzis, Packet Data over Cellular
  Networks The CDPD Approach, IEEE Communication
  Magazine, June 1999, pp. 152-159.
• A. Salkintzis, Radio Resource Management in
  Cellular Digital Packet Data Networks, IEEE
  Personal Communications, December 1999, pp. 28-36