Internetwork Mobility
`The CDPD Approach
`
`Mark S. Taylor
`William Waung
`Mohsen Banan
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`June 11, 1996
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`Samsung Ex. 1008, Page 1 of 334
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`Contents
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`1 Introduction to Mobility
`1.1 What is Mobility?
`1.2 Basic Approaches to Mobility
`1.2.1 Approach 1: Application Awareness
`1.2.2 Approach 2: Directory Lookup
`1.2.3 Approach 3: Mailbox Service
`1.2.4 Approach 4: Administrative Redirection
`1.3 Aspects of Mobile Communications
`1.3.1 Mobile Network Access
`1.3.2 Mobility Management
`1.4 The Essential Challenge of Mobility Management
`1.4.1 Knowing Where the Mobile is
`1.4.2 Routing Data to the Mobile
`1.5 Mobility Management is a Network Layer Function
`1.5.1 Network Layer Addresses
`1.5.2 Network Topology Changes
`1.5.3 Routing Table Updates
`1.6 Mobility Management Schemes
`1.6.1 Permanent Address Scheme (PAS)
`1.6.2 Temporary Address Scheme (TAS)
`1.6.3 Embedded Network Scheme (ENS)
`Steps in the Mobility Management Process
`1.7.1 Registration
`1.7.2 Usage
`1.7.3 De-registration
`1.8 A Simple Taxonomy of Mobility
`1.8.1 Type 0 Mobility: Stationarity
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`1.7
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`1.8.2 Type 1 Mobility: Location Independence
`1.8.3 Type 2 Mobility: Transience
`1.9 Range of Mobility
`1.9.1 Channel
`1.9.2 Cell
`1.9.3 Mobility Area
`1.9.4 Administrative Domain
`1.10 Mobility is not Wirelessness
`1.10.1 Wireless Considerations
`1.11 Challenges of Mobility
`1.11.1 Geography vs. Network Topology
`1.11.2 Part-time Destinations
`1.11.3 Moving Targets
`1.11.4 Application Transparency
`1.11.5 Name-to-Address Mapping
`1.11.6 Security
`1.11.7 Scale
`1.12 Summary
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`2 Introduction to Cellular Systems
`2.1 The Ubiquity of Cellular
`2.2 Radio Channels
`2.3 The Cellular Concept
`2.4 Cell Handoff
`2.5 Cellular Channel Quality
`2.6 Power Control
`2.7 Advanced Mobile Phone System (AMPS)
`2.7.1 AMPS Channels
`2.7.2 Roaming
`2.7.3 AMPS Cellular Operation
`2.7.4 AMPS Mobile Call Origination
`2.7.5 AMPS Mobile Call Termination
`2.7.6 AMPS Radio Resource Management (RRM)
`2.7.7 AMPS Mobility Management
`2.8 Data Transmission via AMPS
`2.9 Digital Cellular Technologies
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`CONTENTS
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`2.10 Europe: GSM and DCS 1800
`2.11 Japan: PDC
`2.12 North American Digital Standards
`2.13 TDMA (IS-54/13x)
`2.14 CDMA (IS-95,99)
`2.15 PCS: Back to the Future?
`2.15.1 PCS Licensing
`2.15.2 PCS Standards
`2.15.3 PCS Challenges
`2.16 Summary
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`3 Overview of CDPD
`3.1 CDPD Background
`3.1.1 CDPD Prototypes
`3.1.2
`"CDPD Lite"
`3.1.3 CDPD Forum
`3.1.4 CDPD Service Providers
`3.2 Relationship of CDPD to other Cellular Data Initiatives
`3.3 CDPD Services and Characteristics
`3.3.1 CDPD Network Services
`3.3.2 CDPD Network Support Services
`3.3.3 CDPD Network Application Services
`3.4 CDPD Design Goals and Considerations
`3.4.1 Location Independence
`3.4.2 Application Transparency
`3.4.3 Multiprotocol Support
`3.4.4
`Interoperability
`3.4.5 Minimal Invention
`3.4.6 Optimal Usage of RF
`3.4.7 Evolutionary Design
`3.4.8 Open
`3.4.9
`Secure
`3.4.10 Simple
`3.4.11 Transparent to the Existing Cellular Voice Network
`3.5 The CDPD Architectural Approach
`3.6 The Three Key CDPD Interfaces
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`3.6.1 The A-Interface
`3.6.2 The E-Interface
`3.6.3 The I-Interface
`3.7 CDPD Network Elements
`3.7.1 The Mobile End System (M-ES)
`3.7.2 The Mobile Data Base Station (MDBS)
`3.7.3 The Mobile Data Intermediate System (MD-IS)
`3.7.4 The Intermediate System (IS)
`3.7.5 The Fixed End System (F-ES)
`3.8 CDPD Mobility Management
`3.9 CDPD Radio Resource Management
`3.10 CDPD Security
`3.11 CDPD Accounting
`3.12 Summary
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`4 Mobility Management in Wide-Area Networks
`4.1 The CDPD Mobility Vision
`4.2 The CDPD Mobility Approach
`4.3 CDPD Mobility Management Scope
`4.4 CDPD Mobility Management Functions
`4.5 CDPD Routing Architecture
`4.6 CDPD Protocol Architecture
`4.7 CDPD Support Protocol Architecture
`4.8 CDPD Mobility Management Operation
`4.8.1 Mobile Identification to Network - End System Hello (ESH)
`4.8.2 Mobile Redirection Request (RDR)
`4.8.3 Confirmation of service - Redirect Confirm (RDC)
`4.8.4 Confirmation to M-ES - Intermediate System Confirm (ISC)
`4.9 CDPD Mobile Data Routing
`4.9.1 Home MD-IS
`4.9.2
`Serving MD-IS
`4.10 Intra-Area Mobility
`4.11 Inter-area Mobility
`4.12 Other Administrative Operations
`4.12.1 Redirect Flush
`4.12.2 Redirect Query and End System Query
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`CONTENTS
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`4.13 Support Data Structures
`4.13.1 Home Domain Directory
`4.13.2 Registration Directory
`4.13.3 Location Directory
`4.14 Multicast Group Management
`4.14.1 CDPD Multicast Service Definition
`4.14.2 Multicast Registration
`4.14.3 Multicast Authentication
`4.14.4 Multicast Data Redirection
`4.14.5 Multicast Data Forwarding
`4.14.6 Multicast Service Characteristics
`4.15 Broadcast Addresses
`4.16 Selection rationale
`4.16.1 CLNP
`4.16.2 Triangle routing
`4.17 Summary
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`5 Accessing the Mobile Network
`5.1 The A-Interface
`5.2 The Airlink Physical Layer
`5.3
`Shared Channel Environment
`5.3.1 Approach 1 - Token Passing
`5.3.2 Approach 2 - Demand Assigned with Reservation
`5.3.3 Approach 3 - Slotted Aloha
`5.3.4 Approach 4 - Carrier Sense Multiple Access with Collision Detection (CSMA/CD)
`5.4 The Airlink MAC Sublayer
`5.4.1 Reed-Solomon Blocks
`5.4.2 Busy/Idle Indicator
`5.4.3 Decode Status Flag
`5.5 M-ES State Machine
`5.6 Airlink MAC Parameters
`5.6.1 Min Idle Time
`5.6.2 Min count and Max count
`5.6.3 Max blocks Parameter
`5.7 Half Duplex Mobiles
`5.8 The Airlink Data Link Protocol
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`CONTENTS
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`5.9
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`Selective Reject
`5.8.1
`5.8.2 Removal of CRC
`5.8.3 Addition of ZAP
`5.8.4
`Sleep mode
`SNDCF - Protocol Convergence
`5.9.1
`Segmentation and Reassembly
`5.9.2 Multiplexing
`5.9.3 Header Compression
`5.9.4 V.42
`5.9.5 Data Encryption
`5.10 How Data Moves Through Layers.
`5.10.1 Radio Resource Management
`5.11 Channel Hopping
`5.12 Circuit Switch Cellular Digital Packet Data
`5.12.1 Circuit Switch CDPD Control Protocol
`5.13 Summary
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`6 Mobile Data Network Security
`6.1
`Introduction
`6.2
`Security Policy
`6.3
`Security Threats
`6.4
`Security Services and Mechanisms
`6.4.1 Encipherment and Data Confidentiality
`6.4.2 Digital Signatures
`6.4.3 Authentication
`6.4.4 Traffic Flow Confidentiality
`6.4.5 Data Integrity
`6.4.6 Key Management
`6.4.7 Access Control
`6.4.8 Network Layer Security Considerations
`6.5 CDPD Security
`6.5.1 CDPD Security Design Goals and Tradeoffs
`6.5.2 CDPD Authentication
`6.5.3 CDPD Confidentiality
`6.5.4 CDPD Privacy
`6.6 CDPD Security Design Rationale
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`6.6.1 CDPD Security Objectives
`6.6.2 One-Way vs. Two-Way Authentication
`6.6.3 The Tunnel’s Data Confidentiality and Authentication
`6.6.4 Considerations for Use of PKCS
`6.6.5 Consideration of Other Approaches
`6.6.6 End to end security services
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`7 Mobile Network Support Services
`7.1
`Support Services Overview
`7.2 CDPD Support Services
`7.3 Network Management
`7.3.1 Overview of System Management Framework
`7.3.2
`Systems Management Functional Areas
`7.3.3 Relationship of Management Specifications to Functional Areas
`7.3.4 CDPD Network Management
`7.4 Usage Accounting
`7.4.1 CDPD Usage Accounting
`7.4.2 The CDPD Accounting Model
`7.4.3 Accounting Meter
`7.4.4
`Serving Accounting Distributor (SAD)
`7.4.5 Home Accounting Distributor (HAD)
`7.4.6 Home Accounting Collector (HAC)
`7.4.7 Consolidation Accounting Collector (CAC)
`7.5 Message Handling Service
`7.5.1 Overview of Message Handling Services
`7.5.2 Message Structure
`7.5.3 Message Transfer Agent (MTA)
`7.5.4 User Agent (UA)
`7.5.5 Message Store (MS)
`7.6 Directory Services
`7.6.1 The Directory
`7.6.2 The Directory Model
`7.6.3 The CDPD Directory Service
`Summary
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`7.7
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`8 Mobile Applications
`8.1 Categories of Mobile Applications
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`8.1.1 Push or Pull: Mobile Application Information Access
`8.1.2 Vertical or Horizontal Nature of Mobile Applications
`8.2 Vertical Applications
`8.2.1
`Field Service
`8.2.2 Mobile Professional
`8.2.3 Transportation
`8.2.4 Point-of-Sale (POS)
`8.2.5 Telemetry
`8.2.6 Government
`8.3 Horizontal Applications
`8.3.1 Messaging and Email
`8.3.2 Limited Size Messaging
`8.4 Applications-Enabling Protocols
`8.4.1 Limited Size Remote Operation Service (LSROS)
`8.4.2
`Status Notification Service
`8.4.3
`Subscriber Area Location Service
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`9 Non-Cellular Approaches to Mobile Data Networking
`9.1 Background
`9.2 Wireless LANs and Metropolitan Networks
`9.2.1
`Infrared Systems
`9.2.2 Narrowband RF Systems
`9.2.3
`Spread Spectrum Systems
`9.2.4 Metricom Ricochet
`9.3 Paging Systems
`9.3.1 One-Way Paging Systems
`9.3.2 Two-Way Paging Systems
`9.4 Private Wireless Packet Data Systems
`9.5 Public Wireless Packet Data Services
`9.5.1 Advanced Radio Data Integrated System (Ardis)
`9.5.2 RAM Mobile Data (Mobitex)
`9.5.3 RadioMail
`Satellite-Based Systems
`Summary
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`9.6
`9.7
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`10 Future Directions in Mobility
`10.1 Mobility under IPv4
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`10.1.1 The Mobile IP Standards Process
`10.1.2 Overview of Draft Version 16 of the IETF IP Mobility Support
`10.1.3 Implementations Based on Mobile IP Drafts
`10.2 Mobility under IPv6
`10.2.1 The IPv6 Standards Process
`10.2.2 Overview of Mobility Support in IPv6
`10.3 Comparison of Mobile IP and CDPD
`10.3.1 Objectives, Goals and Assumptions
`10.3.2 Technical Architecture and Design
`10.3.3 Model and Terminology
`10.3.4 Operational Assumptions
`10.3.5 Standardization Process
`10.3.6 Potentials
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`A Glossary of Terms
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`B Bibliography
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`CONTENTS
`CONTENTS
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`List of Figures
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`0.1 Basic Communication Model
`0.2
`Indirect Message Conveyance
`0.3 ARQ Message Acknowledgment
`0.4 Windowing-Based Message Acknowledgement
`0.5 Ethernet MAC System
`0.6 Token Ring MAC System
`0.7 Network Layer “Cloud” Diagram
`0.8 Layer (N) Protocol Primitives
`0.9 Protocol and Service Data Units
`0.10 Roles in Mobility and Message Flow
`0.11 Directions of Mobile Transmission
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`1.1 The Application Awareness Approach to Mobility
`1.2 The Directory Lookup Approach to Mobility
`1.3 The Mailbox Service Approach to Mobility
`1.4 The Administrative Redirection Approach to Mobility
`1.5 Two Basic Aspects of Mobile Communications
`1.6
`IP Network Address
`1.7 Conventional Data Network Routing
`1.8 Permanent Address Scheme (PAS)
`1.9 Temporary Address Scheme (TAS)
`1.10 Embedded Network Scheme (ENS)
`1.11 Packet Encapsulation in CDPD
`1.12 Address Substitution in Mobile IPX
`1.13 The Mobility Cube
`1.14 Range of Mobility
`1.15 Radio Frequency Spectrum
`1.16 The Protocol Hour-Glass
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`LISTOFFIGURES
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`2.1 AMPS Architecture
`2.2 Frequency Reuse
`2.3 Cell Handoff Strategies
`2.4 MCI’s Xstream Air Network
`2.5 Time vs. Frequency for an FDMA System (e.g., AMPS)
`2.6 Time vs. Frequency for a TDMA System (e.g., IS-54/136)
`2.7 Time vs. Frequency for a FH-CDMA System
`2.8 Time vs. Frequency for a DS-CDMA System (e.g., IS-95)
`2.9 LAPDm Frame Format
`2.10 LAPDm Address Field
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`3.1 CDPD coverage at year-end 1995
`3.2 The CDPD System
`3.3 CDPD Interface Model
`3.4 CDPD Network Layer Reference Model
`3.5 CDPD Example Interface Profiles for Network Services
`3.6 CDPD Network Elements
`3.7 CDPD Reference Architecture
`3.8 Mobile End System Architecture
`3.9 CDPD Traffic Flows
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`4.1 CDPD Cellular Network Overlay
`4.2 CDPD Network Routing Architecture
`4.3 CDPD Protocol Architecture
`4.4 CDPD Support Protocol Architecture
`4.5 M-ES Registration
`4.6 End System Hello (ESH) Message Format
`4.7 Redirect Request (RDR) Message Format
`4.8 Redirect Confirm (RDC) Message Format
`4.9 MD-IS Hello Confirm (ISC) Message Format
`4.10 Home MD-IS and serving MD-IS
`4.11 CDPD Data Routing
`4.12 Intra-area Mobility
`4.13 Intra-area Cell Transfer Protocol Events
`4.14 Inter-area Mobility
`4.15 Inter-area Cell Transfer Protocol Events
`4.16 Redirect Flush (RDF) Message Format
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`LISTOFFIGURES
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`4.17 Configuration Timer Expiry Protocol Events
`4.18 Redirect Query Protocol Events
`4.19 Example Home Domain Directory–Initial State
`4.20 Example Home Domain Directory–Updated State
`4.21 Registration Directory
`4.22 Location Directory
`4.23 Multicast Data Redirection and Forwarding
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`5.1 Airlink Protocol Profile
`5.2 Physical RF channels
`5.3 Token Passing Networks
`5.4 Time Based Demand Assigned with Reservation Example
`5.5 Frequency Based Demand Assigned with Reservation Example
`5.6 Forward Channel Transmission Structure
`5.7 M-ES Procedure for Reverse Channel Access
`5.8 Reverse Channel Transmission Structure
`5.9 Decode Status Flag Timing Relationship
`5.10 MDLP Frame Format
`5.11 Overview of States of the Point-to-Point Procedures
`5.12 Sleep Mode Operation
`5.13 Encoding of SN-Data PDU
`5.14 Encoding of SN-Unitdata PDU
`5.15 Encoding of Compressed TCP/IP Protocol Header
`5.16 Typical Uncompressed CLNP PDU Header
`5.17 Encoding of Compressed CLNP Header
`5.18 SNDCP Model for use of Acknowledged Data Link Services
`5.19 Packet Transformation Data Flow
`5.20 Theoritical Cell Selection
`5.21 Example of Absolute Received Signal Strength Based Selection
`5.22 Example of Comparative Received Signal Strength Selection
`5.23 Example of Hysteresis Region of 10 dB
`5.24 Example of Received Signal Strength Parameter of -10 dB
`5.25 Channel Stream Identification Message
`5.26 Cell Configuration Message
`5.27 Channel Quality Parameters Message
`5.28 Channel Access Parameters Message
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`LISTOFFIGURES
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`5.29 Cellular Channel Assignment
`5.30 Channel Hopping example
`5.31 Circuit Switched CDPD Components
`5.32 CM-ES Initial Connection
`5.33 CM-ES Initiated Reconnection
`5.34 CMD-IS Initiated Reconnection
`5.35 Redirect to Local Modem Bank
`5.36 Redirect to Local CMD-IS
`5.37 CSCCP Link Reset Procedure
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`6.1 A Public Key Cryptographic System (PKCS)
`6.2 A Digital Signature Mechanism
`6.3 CDPD Security Protocol Events
`6.4 CDPD Key Exchange
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`7.1 CDPD Network Management Model
`7.2 CDPD Accounting Model
`7.3 Message Structure
`7.4 MHS Architecture
`7.5 Directory and Users
`7.6 Directory Model
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`8.1 LSM World with Global Messaging World
`8.2 Messaging Communication Stack and LSM
`8.3
`Status Notification System Architecture
`8.4 Example of messaging to an OC-ES
`8.5 CDPD Subscriber Area Location Service
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`9.1 Metricom Ricochet
`9.2 Telocator Data Protocol
`9.3 ARDIS Architecture
`9.4 ARDIS Communications Architecture
`9.5 RAM Architecture
`9.6 Mobitex Communications Architecture
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`10.1 Mobile IP Routing to Mobile Node
`10.2 Mobile IP Routing to Correspondent Node
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`List of Tables
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`0.1 OSI Reference Model
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`1.1 Routing Table Entries for Host 1
`1.2 PAS Routing Table prior to Mobile 2 Movement
`1.3 PAS Routing Table following Mobile 2 Movement
`1.4 TAS Routing Table prior to Mobile X.1 Movement
`1.5 TAS Routing Table following Mobile Z.2 Movement
`1.6 ENS Routing Table prior to Mobile X.1 Movement
`1.7 TAS Routing Table following Mobile X.1 Movement
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`2.1 Growth of AMPS Subscriber Base
`2.2 AMPS Frequency Allocations
`2.3 GSM Frequency Allocations
`2.4 PDC Frequency Allocations
`2.5 Cellular System Comparison
`2.6 PCS Frequency Allocations
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`5.1 Network Layer Protocol Identification
`5.2 Changes Mask Bit Definitions
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`9.1 Wireless LAN Technology Characteristics
`9.2 Narrowband PCS Channels
`9.3 The Motorola FLEX
`Protocol Family
`9.4 CDPD, RAM and ARDIS Feature Comparison
`9.5 Comparison of “Big LEO” Systems
`9.6 Comparison of non-“Big LEO” Systems
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`10.1 Comparative Glossary
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`Preface
`
`This book discusses user mobility in a wide area network (WAN) environment. In this discussion, a mobile
`data device is one which can receive WAN services from essentially any location without requiring any
`special actions by the user of the device. User mobility is described in the context of the Cellular Digital
`Packet Data (CDPD) standard, developed by ourselves and others on behalf of the North American cellular
`industry.
`Two trends provide a backdrop for this subject matter. The first of these is the rapid growth of the
`Internet1. Both in terms of numbers of users and traffic, this growth has been nothing short of phenomenal.
`What was once strictly the domain of highly technically-literate people has now become headline news.
`Censorship of the World-Wide Web is now discussed by politicians and URLs are commonly displayed in
`advertisements.
`The popularityof the Internetreflects a change in the mediaof choice for peoplewishing tocommunicate.
`Email allows the thoughtfulness of a letter while providing the potential immediacy of the telephone.
`Complex ideas can be conveyed in an organized manner, then further developed by the receiving party.
`Several rounds of a discussion can take place in a matter of minutes, quickly resolving issues that might be
`difficult to present orally. The CDPD specification was itself rapidly developed by remote parties largely
`via Email discussion.
`The second trend is that of mobile communications. The cellular industry is experiencing explosive
`growth, with over 32 million subscribers in North America at year-end 1995. The paging industry has also
`experienced rapid growth; the advent of new two-way messaging services is likely to extend that growth
`in the face of competition from low cost (to the subscriber) mobile cellular handsets.
`The next step in this evolution of communications is that of mobile data communications. Mobile
`data is expected to grow from 200 thousand subscribers in 1990 and 1.1 million in mid1995, to 5.2 million
`subscribers in 2000.2 Several technology developments aimed at mobile data communications are in various
`stages of progress or completion.
`The Mobile IP Task Force of the IETF has been addressing the requirements for mobility in data com-
`munications. Their charter is to define the protocols necessary for a correspondent to send and receive data
`anywhere. The media to be used is unspecified. Presumably one will in the future be able to find an Internet
`"socket" in the wall of a hotel room as readily as they currently find electrical outlets. However, many "real
`world" considerations such as usage accounting remain unaddressed by this group.
`The Ram and ARDIS mobile data services, supported by RadioMail, provide gateway connections
`between proprietary radio technology and the Internet or other wide-area networks. However, the need
`to port applications to nonstandard proprietary mobile devices and APIs limits the generality and user
`1. In this book we use the convention of ("big-I") "Internet" meaning the worldwide interconnection of networks. We use ("little-i")
`"internet" to mean either an internetwork (collection of networks) or a protocol suite (typified by TCP/IP).
`2. Source: Economic and Management Consultants, Inc., estimate [EMCI95].
`
`1
`
`Samsung Ex. 1008, Page 17 of 334
`
`

`

`2
`
`LISTOFTABLES
`
`adoption of these service offerings.
`Rather than using gateways between proprietary radio technology and the Internet, CDPD defines an
`open standard which allows mobile devices to be as directly accessible as any other IP host. Standard APIs
`allow the immediate use of current data applications such as Email on mobile devices. We have done this
`many times.
`This book is intended to complement the CDPD specification but not replace it. Our emphasis is on
`the data networking aspects of CDPD and its solution to the mobility problem. CDPD is a data network
`which happens to have an RF-based data link resembling Ethernet (but at a lower speed). The fixed end
`of the radio link, called the Mobile Data Base Station or MDBS, is little more than a LAN hub from a data
`networking perspective.
`This book is clearly focused on CDPD as the preeminent wide area mobile data solution. We don’t
`apologize for our bias–we were highly involved in the creation of CDPD. However, no systemor technology
`lasts forever; one of our design goal was that CDPD be readily amenable to evolution. CDPD is much more
`than an airlink–it is an architecture that supports host mobility over a wide area.
`The chapters which follow describe the CDPD solution to the challenge of mobility in wide-area net-
`works. A discussion of mobility (of which wirelessness is a special case) is followed by a summary of
`cellular technology, an overview of CDPD, a description of CDPD architecture and how it supports mo-
`bility, a description of security and other support services provided by CDPD (and needed by anypublic
`mobile data network!), a survey of other (noncellular) mobile systems and finally, a discussion of future
`directions in mobility in the wide-area environment. For readers unfamiliar with data networking concepts,
`a primer on this subject precedes the first chapter.
`The target audience for this book is any individual interested in mobile data communications or, more
`specifically, the rationale behind the design of CDPD. The discussion of technical issues avoids the jargon
`and abstractions necessary and typical in technical specifications. Because we are not radio engineers, we
`focus on the system and networking aspects of CDPD rather than the radio technologies, which are better
`described elsewhere. Our goal is to explain mobility and CDPD in plain English. Please let us know
`whether we succeeded at mark.taylor@airdata.com, wwaung@direct.ca and mohsen@neda.com.
`Bellevue, Washington
`June 11, 1996
`
`Samsung Ex. 1008, Page 18 of 334
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`

`

`Preliminaries
`
`Basically,onealwaysgetsintotroubletryingtodefinethesethingstoopreciselybecausethey
`aren’treallycleanconcepts.
`
`–Radia Perlman, 1996.
`
`This chapter introduces some of the standard data networking terminology and concepts used through-
`out this book. Those readers already familiar with data networking technology could begin with Chapter
`1, which is the realfirst chapter, with no loss of continuity.
`Familiarity with the concepts presented in this chapter is important to understanding the issues of
`mobility and is assumed in the chapters that follow. Topics discussed in this overview include the com-
`munications channel, protocols, connection-oriented and connectionless protocols, the OSI reference model
`and it layers, protocol data units and networking entities.
`This chapter is presented as a survey and is no substitute for the real thing–it is necessarily brief. Many
`fine texts, such as [STAL93], [PERL92] and [TANN95], are devoted to teaching data networking and cover
`this subject much more rigorously. Of course, true expertise comes only with study of actual standards
`documents.
`
`Basic Data Communication Model
`Communication is the conveyance of a messagefrom one entity, called the sourceortransmitter, to another,
`called the destinationor receiver, via a channel3 of some sort. A simple example of such a communication
`systemis conversation; people commonly exchange verbal messages, with the channel consisting of waves
`of compressed air molecules at frequencies which are audible to the human ear.4 This is depicted in Figure
`0.1.
`The conveyance of a message could be followed by a reciprocal responsemessage from the original
`destination (now a source) to the original source (now a destination) to complete one cycle in a dialogue
`betweencorrespondingentities. Depending on the application or need for the information exchange, either
`atomic one-way transactionsor a two-way dialogue could be appropriate.
`The only way that a messagesource can be certain thatthedestination properly received the messageis by
`some kind of acknowledgmentresponse from the destination. Conversing people might say "I understand"
`3. "Channel" is one of those words whose meaning varies with the context and the level of "source" and "destination." It could
`consist of a physical medium or a logical data path.
`4. Of course, many messages are conveyed more or less explicitly in the form of body language, in which the channel is the visual
`medium of electromagnetic radiation commonly known as reflected light. Difficulties arise when these visual messages conflict with
`the verbal messages they accompany.
`
`3
`
`Samsung Ex. 1008, Page 19 of 334
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`

`4
`
`LISTOFTABLES
`
`Message
`
`Hello!
`
`I just
`heard
`“Hello!”
`
`Channel
`
`Source
`
`Destination
`
`Figure 0.1: Basic Communication Model
`
`or nod their head in response to a statement made by their peer. This acknowledged form of dialogue is
`the basis of reliable communications–somehow the source must get feedback that the destination correctly
`received the message.5
`
`Variations on a Theme
`The conveyance of a message could be directbetween the corresponding entities or it could be indirect,
`with one or more intermediaries participating in the message transport. The presence or absence of an
`intermediary depends on the definition of the source and destination entities and the channel used to
`communicate; data communication between entities at one level might be considered to be direct and at
`another level to be indirect.
`Consideringthedirectnessorindirectnessofthecommunicatingentitiessimplydependsontherelevance
`of any intermediaries to the discussion. In Figure 0.2, the translator is important but should not really be
`a factor in the communication between the source and destination. Perhaps in a twist on the old parents’
`saying, a good translator is heard but not seen.
`Communication can be from a source to a single destination, known as point-to-pointor unicast, or
`to multiple destinations, known as point-to-multipointor multicast. A special case of multicast is the
`conveyance of a message from a source to every possible destination, which is referred to as broadcast; the
`broadcast can be local or global in scope.
`The primary difference between multicast and broadcast is that multicast communication is targeted
`at specific destinations, regardless of location, while broadcast communication is targeted at all possible
`destinationswithin the range (location)of the source. Multicast and broadcast communicationsare typically
`one-way "best efforts" modes of communication which are unacknowledged.6
`5. Correct message reception is one thing, agreement with the message content is another thing entirely. Cultural variances in
`acknowledgment responses have often led to difficulties in international relationships between people.
`6. The primary reason for using broadcast and multicast is to gain channel efficiency by communicating with multiple entities
`via a single common message. However, the complexity of matching acknowledgments with intended message recipients at the
`source quickly overrides any efficiencies gained in a reliable multicast scenario. Depending on the number of channels, the number
`of members in the multicast group, etc., a set of unicast messages might be equally efficient for reliable communications. It really
`depends on where you want to handle reliability–in the networking technology transporting the message or in the application itself.
`We’ll talk more about reliability later.
`
`Samsung Ex. 1008, Page 20 of 334
`
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`

`LISTOFTABLES
`
`5
`
`Hello!
`
`I just
`heard
`“Hello!”
`
`I’ll
`translate.
`
`Guten
`Tag!
`
`I habe
`“Guten Tag!”
`gehoren.
`
`Channel
`
`Source
`
`Translator assisting
`communication between
`English and German
`speaking individuals.
`
`Destination
`
`Figure 0.2: Indirect Message Conveyance
`
`Communication can also be described in terms of the relative timeframes of the corresponding entities.
`Depending on the definitions of source,destination and channel, the communication could be asynchronous,
`synchronous or isochronous.
`In asynchronouscommunication, there is a minimal assumed timing relationship between the source
`and destination.
`In such a typically byte-orientedsystem, each character or byte is transmitted and re-
`ceived individually as a message. Asynchronous protocols were predominant in the early days of data
`communications because of limited processing capability and low quality transmission infrastructure.
`In synchronouscommunication, the relative bit timing of the source and destination is similar, allowing
`transmission and reception of relatively large groups of bits in a single message; the source and destination
`must be "in sync." This bit-orientedmode of communication can be much more efficient than asynchronous
`communications, but places requirements on the source (processing), channel (quality) and destination
`(more processing). Synchronous data communications are predominant today.
`Isochronouscommunication is the extreme case of synchronous communication–source and destination
`are "in sync" in the absolutesense of real time, allowingcontinual transmissionof bits. An everyday example
`of isochronous communication is a telephone conversation; if such a conversation occurs across a large
`distance (such as trans-Atlantic), the delays introduced can be disconcerting because the isochronicity which
`people are accustomed to has been negatively impacted. Effective isochronous communication depends
`on both transmission delays which are inconsequential to the corresponding entities and a consistent high
`quality transmission.
`
`The Communications Channel
`A communication channel can be simplex, in which only one party can transmit, full-duplex, in which
`both correspondents can transmit and receive simultaneously, or half-duplex, in which the correspondents
`alternate between transmitting and receiving states (such as conversing adults). Even though the channel
`might be capable of supporting full-duplex communication, if the corresponding entities are not capable
`of transmitting and receiving simultaneously, the communications system will be half-duplex (as in the
`example of the conversing adults).
`Communication between two entities can be considered either in-band or out-of-band, depending on
`
`Samsung Ex. 1008, Page 21 of 334
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`

`6
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`LISTOFTABLES
`
`context. In-bandcommunication is communication which occurs via the primary channel between the
`communicating entities. Out-of-band communication occurs via an alternative channel, which is not
`considered to be the primary channel between the entities.
`Which channel is primary and which is an alternate depends on context and the existence of an alternative
`channel. In the case of a conversation between two people, the primary channel could consist of verbal
`communication while the alternate channel consists of visual body language. Of course, if emotions rise,
`these two channels might reverse roles, with body language becoming the primary channel!
`
`Channel Characteristics
`
`A communications channel may be described in terms of its characteristic properties. These channel
`characteristicsincludebandwidth(how much information can be conveyed across the channel in a unit of
`time, commonly expressed in bits per second orbps7 ),quality(how reliably can the information be correctly
`conveyed across the channel, commonly in terms of bit error rate or BER8 )andwhetherthechannelis
`dedicated(to a single source) or shared(by multiple sources).
`Obviously a higher bandwidth is usually a good thing in a channel because it allows more information to
`be conveyed per unit of time. High bandwidths mean that more users can share the channel, depending on
`their means of accessing it. High bandwidths also allow more demanding applications (such as graphics)
`to be supported for each user of the channel.
`The capability of a channel to be shared depends of course on the medium used. A shared channel
`could be likened to a school classroom, where multiple students might attempt to si