Mobile Computing Assistant Professor: Jenhui Chen Office number: 5990 Homepage: http://www.csie.cgu.edu.tw/jhchen 2018/12/6 Dr. Jenhui Chen

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 2018/12/6 Dr. Jenhui Chen

Grading Midterm Report Oral presentation- over 15 pages (30%) Final Project Report 10 pages (40%) 2018/12/6 Dr. Jenhui Chen

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 2018/12/6 Dr. Jenhui Chen

Related Topics Sensor Networks Pervasive Computing (Wireless LAN) Internet Computing Personal Communication System UMTS (Universal Mobile Telecommunications System) GPRS (General Packet Radio Service) 2018/12/6 Dr. Jenhui Chen

Introduction: Why and who will be mobile? Chapter 1 Introduction: Why and who will be mobile? 2018/12/6 Dr. Jenhui Chen

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 2018/12/6 Dr. Jenhui Chen

Telecom Statistics 1995 1996 1997 1998 1999 2000 (1) Telephone (M) 1995 1996 1997 1998 1999 2000 (1) Telephone (M) (2) Mobile phone (K) (3) Radio paging (K) (4) Internet (K) 9.17 (7.9%) 770 (31.8%) 2,083 (20.5%) 21 10.01 (9.2%) 970 (26.0%) 2,301 (10.5%) 165 (686.0%) 10.86 (8.5%) 1,492 (53.8%) 2,641 (14.8%) 429 (160%) 11.50 (5.9%) 4,727 (217.0%) 4,261 (61.3%) 1,665 (288%) 12.04 (4.7%) 11,541 (144.0%) 3,873 (-9.1%) 2,874 (72.6%) 12.64 (5.0%) 17,743 (53.7%) 2,867 (-26.0%) 4,650 (61.8%) 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%) 2018/12/6 Dr. Jenhui Chen

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. 2018/12/6 Dr. Jenhui Chen

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. 2018/12/6 Dr. Jenhui Chen

Mobile Computing Chart Verticals Horizontals Applications Operating systems Mobile operation systems Devices Notebooks PDAs Phones Others WANs LANs Wireless networks 2018/12/6 Dr. Jenhui Chen

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 2018/12/6 Dr. Jenhui Chen

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 2018/12/6 Dr. Jenhui Chen

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 2018/12/6 Dr. Jenhui Chen

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 2018/12/6 Dr. Jenhui Chen

Applications Market by 2005 2018/12/6 Dr. Jenhui Chen

Field Sales Application Sales quotation Inventory check Order entry Credit authorization Invoicing 2018/12/6 Dr. Jenhui Chen

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 2018/12/6 Dr. Jenhui Chen

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 2018/12/6 Dr. Jenhui Chen

Personal Communications Application Messaging Calendaring Directories Info Systems Fax 2018/12/6 Dr. Jenhui Chen

Mobile Office Application Fax E-mail LAN access File transfer Database access 2018/12/6 Dr. Jenhui Chen

Vertical Market Examples Airlines Police Field sales Emergency Hospitals Maintenance Retail stores Stock exchanges Casinos Hotel Taxicabs Rental car agencies Transportation 2018/12/6 Dr. Jenhui Chen

Challenges Security User authentication Data privacy Privacy of user location Bandwidth Limited bandwidth (10K~10M) 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 2018/12/6 Dr. Jenhui Chen

Application/Technology Matrix Sector Application Technology Cellular Paging Mobile Data WLANs Private (corporate) Service engineering ** * Order entry Vehicle routing *** Incident control Public Network Services Facsimile Text messaging Info services News Market Financial Location tracking Traffic alerts 2018/12/6 Dr. Jenhui Chen

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 2018/12/6 Dr. Jenhui Chen

Positioning of Wireless Networking Wireless Data Today Future Mobile Data 10 Kbps 100 Kbps Wireless LANs 1 Mbps 10 Mbps Wired Data Today Future 100 Kbps >1 Mbps Wired LANs 10 Mbps >100 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 2018/12/6 Dr. Jenhui Chen

CDPD: Cellular Digital Packet Data Daniel Grobe Sachs Quji Guo 2018/12/6 Dr. Jenhui Chen

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” Can’t interfere with existing analog service. CDPD is cheap: no new spectrum license needed! 2018/12/6 Dr. Jenhui Chen

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. 2018/12/6 Dr. Jenhui Chen

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. 2018/12/6 Dr. Jenhui Chen

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) 2018/12/6 Dr. Jenhui Chen

Omnisky Coverage Map Source: Omnisky (http://www.omnisky.com) 2018/12/6 Dr. Jenhui Chen Source: Omnisky (http://www.omnisky.com)

CDPD Infrastructure 2018/12/6 Dr. Jenhui Chen Source: A. Salkintzis, “Packet Data over Cellular Networks: The CDPD Approach”

CDPD - Layering Application Transport Network Data link Physical 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 2018/12/6 Dr. Jenhui Chen

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 2018/12/6 Dr. Jenhui Chen Physical

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 => all channels used only 1% of the time. 2018/12/6 Dr. Jenhui Chen

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. 2018/12/6 Dr. Jenhui Chen

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. 2018/12/6 Dr. Jenhui Chen

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. 2018/12/6 Dr. Jenhui Chen

CDPD effects on AMPS CDPD logically transparent to AMPS Can reduce AMPS service quality More channel usage => 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.. 2018/12/6 Dr. Jenhui Chen

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 2018/12/6 Dr. Jenhui Chen Physical

Forward Link Structure 2018/12/6 Dr. Jenhui Chen Source: A. Salkintzis, “Packet Data over Cellular Networks: The CDPD Approach”

Reverse Link Structure 2018/12/6 Dr. Jenhui Chen Source: A. Salkintzis, “Packet Data over Cellular Networks: The CDPD Approach”

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 2018/12/6 Dr. Jenhui Chen Physical

Reverse Link MAC 2018/12/6 Dr. Jenhui Chen Source: J. Agostsa et al., “CDPD: Cellular Data Packet Standards and Technoloy”

Reverse Link MAC Reverse link idle => 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. 2018/12/6 Dr. Jenhui Chen

Mobile Data Link Protocol IP/CLNP SNDCP MDLP MAC 2018/12/6 Dr. Jenhui Chen Source: J. Agostsa et al., “CDPD: Cellular Data Packet Standards and Technoloy” Physical

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. 2018/12/6 Dr. Jenhui Chen

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. 2018/12/6 Dr. Jenhui Chen

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 2018/12/6 Dr. Jenhui Chen Physical

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. 2018/12/6 Dr. Jenhui Chen

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 2018/12/6 Dr. Jenhui Chen

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 2018/12/6 Dr. Jenhui Chen

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. 2018/12/6 Dr. Jenhui Chen

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. 2018/12/6 Dr. Jenhui Chen

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 2018/12/6 Dr. Jenhui Chen