Topics in Wireless Networks

1
Topics in Wireless Networks

• Robert Turetsky
• rjt72_at_columbia.edu
• Columbia University
• 12/6/2000

2
Presentation Goals

• Introduce major wireless technologies
• Wireless Application Protocol (WAP)
• Metricom Ricochet
• Sun Microsystems JINI
• Bluetooth
• Identify issues in wireless network design
• Discuss recent research in wireless data/computer
  networks

3
Why Wireless?

• Freedom from the boundaries of space
• Instant access to data and applications
• Spontaneous (ad-hoc) networking
• Embedded communication in devices
• M-Commerce
• Play games and find stock quotes during lame
  status meetings

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So, whats the holdup?

• High communications, device cost
• Long latency period
• Low/uncertain bandwidth
• Unreliable channels
• Roaming/handoff issues
• Unique devices
• No accepted standards
• We want it NOW issues

5
Designing for wireless

• Lacks non-commercial testing grounds
• Goal Minimize download time, manual typing
• Content bytes
• Service oriented applications
• myCustomization
• Interaction with wired web
• Always consider different screen sizes

6
The present state of wireless

• WAP Web services on cellular phones
• iMode M-commerce overseas
• Ricochet 128 kbps wireless modems
• Connected PDAs / E-mail devices
• Transmeta Caruso Low-cost/power ?P
• Voice/Data network separate (WAP)
• Data over voice (cellular modems)

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WAP Wireless ApplicationProtocol
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WAP Introduction

• WAP Wireless Application Protocol
• Communications Protocol and Application
  Environment for deployment of information
  resources, advanced telephony services and
  Internet access from mobile devices
• WAP Forum Phone.com, Ericsson, Nokia and
  Motorola
• Check out my cool phone!

9
WAP Philosophy

• Simplicity in devices, complexity in gateways
• Base standards on wired web
• Designed for any mobile phone
• Designed for any wireless protocol

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WAP Applications

• Wireless Web Browsing, E-mail
• Remote LAN access
• Mobile Banking
• M-Commerce and prepayment
• Remote point of sale
• Wired workers, ie meter readers
• In the future Location-based services
• In the future Multimedia

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WAP Architecture

• WAP Gateway acts as intermediary between web
  server and mobile client

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WAP Terminology

• WAP Device
• WAP Client
• Microbrowser
• User Agent
• WAP Gateway
• Network Operator
• Bearer Services
• Origin Server

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WAP The Protocol Stack

• Mobile enhancements to OSI Protocol Stack

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WAP WAE Application Layer

• Provides an environment to execute and develop
  applications
• Building blocks
• WML Wireless Markup Language
• WLMScript Lightweight scripting language
• 2 User Agents
• WAE Microbrowser and text editor
• WTA Wireless Telephony Agent (in development)

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WAP WML Markup Language

• Optimized for narrowband pipes
• Based on early stages of HTML
• Defined as an XML document type
• Basic unit The Deck
• Made up of one or more Cards
• One deck downloaded at a time
• Variable exchange between cards
• How to display a deck is up to the browser

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WAP WML Supports

• Text editing and text formatting
• Bitmapped b/w images (WBMP)
• User input elements
• Variables
• Navigation and history stack
• Unicode

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WAP WML Example

• 1.1//EN" "http//www.wapforum.org/DTD/wml_1.1.xml"
  
• Hello world!

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WAP WMLScript

• Based on EMCAScript
• Adds intelligence to the client
• Math and string functions
• User input validation
• Access to device facilities
• Methods for interacting with user
• WMLScript files cannot be embedded in WML pages
  like JavaScript.

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WAP Session Layer

• Session services set up a communication channel
  between client and server
• Shares state between client and server
• Binary form of HTTP/1.1
• Two protocols like TCP and UDP
• Connection oriented, runs over WTP
• Connectionless, runs over WDP

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WAP Transaction Layer

• WTP Wireless Transaction Protocol
• Provides services to accomplish transactions with
  varying degree of reliability
• Operates over WDP or WTLS

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WAP Transaction reliability

• Unreliable request

• Reliable request

• Reliable request with result message

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WAP Security layer

• Based on HTTP security layers
• Meant to encourage development/use of sensitive
  wireless applications
• Ensures
• Privacy
• Server Authentication
• Client Authentication
• Data Integrity

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WAP Conclusions

• WAP extends the WWW to wireless
• WAP is still in its infancy
• WAP detractors abound
• 3G will provide new services and a test
• Patience is a virtue, but time is of the essence

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RICOCHET

• Wireless High-Speed WAN

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The Ricochet Network Infrastructure
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Ricochet Network Components

• Wireless Radio Modems
• Microcell Radios
• Wired Access Points (WAP)
• Regional Network Interface Facilities (NIFs)
• 2 Network Operations Center (NOC)

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Ricochet Infrastructure Take 2
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Ricochet Technology Overview

• Licensed 2.3GHz and Unlicensed ISM bands
• Packet switched to shared bandwidth
• Frequency hopping for multiplexing
• Microcells meshed together

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I DREAM OF JINI

• JINI Sun Microsystems

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JINI Goals

• Enabling users to share resources and services
  across a network
• Providing users easy access to resources anywhere
  on a network while allowing the network location
  of a user to change
• Simplifying the task of building, maintaining and
  altering a network of devices, software and users

31
Jini System Components

• A set of components that provides an
  infrastructure for federating services in a
  distributed system
• A programming model that encourages the
  production of reliable distributed services
• Services that can be made part of a federated
  Jini system which offer functionality to any
  other member of the federation
• End Result A network that allows shared services
  to join and detach from a network

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Jini and Wireless

• Jini can be run over any network that
• Has inter-service communication channels
• Supports the JVM
• Resource Discovery allows for embedded devices
  and ad-hoc networking

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Java and Jini

• Jini extends the JVM from one machine to a
  distributed network
• Why use Java?
• Bytecode and Data cross-platform
• Strong typing
• Java Security Manager
• Java RMI as framework for distributed object
  communication
• Because Sun Micro likes Java

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JINI Definitions

• Service
• Federation
• Service Protocol
• Lookup Service
• Discovery
• Lease
• Transaction
• Event

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JINI Components Infrastructure

• Discovery/join protocol
• Lookup services
• Distributed security system
• Built into Java RMI
• Principal agent accessing a service
• Access Control List

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JINI Components Programming Model

• Set of interfaces to be implemented by services
• Leasing Interface
• Event Notification Interface
• Transaction Interface
• 1) Voting Stage
• 2) Coordinated Commit Stage

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JINI Components Services

• Can be computation, storage, communication link,
  I/O devices, special hardware or another user
• Appear as objects written in Java
• Others dont care if service is software,
  hardware, on different machine,
  shared/distributed memory space
• Public interface for other services to access
• One service can be built of multiple services

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JINI Protocols

• Discovery A service looks for a Lookup Service
  to register with
• Join Connecting a service with a Lookup Service
• Lookup A client or user locates and invokes a
  service
• Discovery/Join takes place on device startup

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JINI Protocols in action
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KVM Java Everywhere!

• KVM Highly optimized VM for resource constrained
  user devices
• Idea Add profiles for optional features
• Implemented as 16,000 Lines of C
• Includes subset of java.lang and java.util, but
  no AWT
• Take it for a test drive!

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ROB TO BRIDGE BLUETOOTH

• The future is now.
• .whatever that means.

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Bluetooth What does it do?

• Facilitate fast and secure wireless
  communications
• Replace cables for everything
• Handle voice/data communication for spontaneous
  (ad-hoc) networks
• Provide a medium for embedded devices to
  communicate

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Bluetooth Potential applications

• Syncing multiple devices
• Creating Spontaneous LANs
• Building Internet Bridges
• Smart appliances (embedded everything)
• Three-in-one phones
• Instant peer-to-peer document exchange
• Making geeks rich again

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Bluetooth The numbers

• Transmits up to 30 ft
• 2.4GHz frequency band (ISM)
• Data transfer rate near 1Mb/s
• Duplex communication
• Asymmetric 721kb/s one way, 57.6kb/s other way
• Symmetric 423.6k/s

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Bluetooth More Numbers

• Combination Circuit / Packet Switching
• Circuit switching 1 packet send, 1 packet
  receive
• Packet Switching 1600 hops/sec, 1, 3 or 5 slot
  packets
• Power Consumption 3 of Cellular phones
• Synchronous/Asynchronous communication
• 1 Asynchronous packet switched Data channel
• 3 Synchronous circuit switched voice channels
• 1 shared data/voice channel
• Receiver interconnections point to point and
  multipoint

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Bluetooth Data Integrity

• Works under heavy radio noise/interference
• Fast hops with short packets
• Switches frequency after each packet
• Error Correction Code FEC
• Protects against noise from long distance
• Protects against interference from microwaves
• Built in encryption/authentication schemes
• 09/2000 Lucent researches cracked security codes

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Bluetooth Piconets

• Piconets A collection of bluetooth devices
  connected together in an ad-hoc fashion.
• Between 2-8 devices per piconet
• One device in the piconet acts as the master the
  rest are slaves.
• Any device can be the master
• Connect piconets together to form scatternets

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Bluetooth Access Procedures

• Use page and inquiry protocols to establish and
  maintain connections between devices

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Bluetooth Link Manager

• Responsible for the following services
• Sending and receiving data
• Name request
• Link address inquiries
• Connection setup
• Authentication
• Link mode (data/voice) negotiation
• Discovers and communicates with other LMs via
  Link Manager Protocol (LMC)

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Bluetooth Connection Mode

• In connection mode, packets can be sent from the
  master to slave devices.
• 4 modes of operation Active, Sniff, Hold and Park

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Bluetooth Packets

• Access code can be CAC, DAC, IAC
• Packet header has the following fields AM_ADDR,
  FLOW, SEQN, TYPE, ARQN, HEC
• Payload can be voice, data or both

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Bluetooth No Handoffs?

• Raison D'être Cable, not cellular replacement
• To keep costs
• Piconets are dynamic and fast
• Can connect to a new piconet in 1-5s
• Solutions do exist, but they are proprietary (and
  incompatible)

53
Bluetooth vs. Jini

• Different layers of the protocol stack
• Bluetooth Physical and transport layer
• Jini Resource discovery protocol
• Different approaches to device discovery
• Bluetooth Simple and fast
• Jini Robust
• Jini over Bluetooth?
• Not yet. Jini is TCP/IP based. Bluetooth is
  not. But it is in the works )

54
Bluetooth SIG

• Promoter companies 3Com, Ericsson, IBM, Intel,
  Lucent, Microsoft, Motorola, Nokia and Toshiba
• SIG members can develop (royalty-free) Bluetooth
  devices and products
• Any incorporated company can join for free
• 2000 member companies

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Cool Bluetooth Products

• National Semiconductor demos
• Ericsson Bluetooth cellular phone
• Motorola others Bluetooth cards
• Connected Library
• Lots more to come.

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WIRELESS PAPERSURVEY

• 1994 to 2000

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Paper Survey Topics

• Wireless Andrew
• MobileIP and IEEE 802.11
• A Cordless Distributed System
• Optimizing HTTP for wireless
• Predictive Mobility Management
• Routing Protocol Evaluation

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Wireless Andrew (CMU 1997)

• Deals with issues in setting up a campus-wide
  wireless WAN
• Infrastructure choices
• Business decisions
• Which technology to use
• Dealing with holes in service, interference
• Manageability, maintainability of the network
• Comparison to the wired Andrew file system

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Mobile IP and IEEE 802.11

• Network layer solution for wireless LANs
• Main Idea Forward mobile users location
  information to home base
• 2 types of network configuration
• Ad-hoc
• Infrastructure
• Good Works with IPv4
• Bad Doesnt work with IPv6

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Mobile IP Networks

• Ad-hoc
• Usually fully-connected network
• Ways of discovering peers
• SEA Spokesman Election Algorithm
• Flood (broadcast) to anyone who can listen
• Infrastructure
• Fixed access points
• Can be easily connected to wired networks
• Handoff at overlaps between access points

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IEEE 802.11 Physical Layer

• 2.4 GHz frequency band (ISM)
• Direct sequence spread spectrum
• frequency hopping spread spectrum
• 300-428,000 GHz (Infrared)
• Bad Line of sight only
• Good More secure

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802.11 MAC Layer Spex

• MAC Layer Medium Access Control
• Responsible for collision avoidance
• CSMA/CA Carrier Sense Multiple Access with
  collision avoidance
• Check to make sure a node is free
• If free, transmit. Else random backoff
• Ethernets collision detection scheme can not be
  used.

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802.11 Hidden Node Problem
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802.11 Handshaking Protocol

• Sender sends RTS (ready to send) packet with
  CONTENT_LENGTH
• Receiver replies with CTS (clear to send) packet
• Sender sends packet CRC
• Receiver checks CRC. If OK, confirm with an ACK

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BlueSky Cordless Net for Palmtops

• Protoype Personal Area cordless network
• Built from cordless phone radio modules
• Mobile users plug adapter into serial ports
• AccessPoint Bridge to wired nets
• Uses PPP but keeps connections open during
  handoffs
• Can have 10-15 clients sharing 150kbps
• IBM, Bourns College of Engineering 1999

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BlueSky Properties of a Good Cordless Network

• Low Power consumption
• Large number of short-range Access Points
• Forget packet-based wireless LANs (ie 802.11)
• Low Control traffic
• Security Authentication at each handoff
• Low Connection-related overhead (ie not 802.11)

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BlueSky Access Points

• Responsible for
• Sharing bandwidth
• Registering new devices
• Performing handoffs

• One communication channel per AP
• Neighboring APs use different channels to avoid
  interference

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BlueSky Cordless Modules

• Why Cordless?
• Cheap and mass-produced
• Circuit-based
• Low Power Consumption

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BlueSky Layers PPP

• BlueSky uses PPP as its communications protocol
• Everyone already has it on their laptops/palmtops
• Can leverage existing dialup programs (ie Dialup
  Networking for Win98/2000)
• Both Serial line and cordless link are circuit
  oriented
• Can easily tunnel packets to wired networks

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BlueSky Layers MAC

• Packet Based for multiplexing
• One device can communicate at a time
• All other devices must turn of transmitters
• Polling-Based (moves complexity from device to
  Access Point)

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WebExpress Wireless Web Browsing (IBM 1996)

• Idea Improve HTTP performance over wireless
  networks
• Inhibitors to wireless HTTP
• High Latency (Oracle 15s for TCP/IP request)
• High Cost (1996 1 per 10k)
• Low bandwidth (4800bps-19.2kbps)
• High unreliability

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WebExpress More HTTP Woes

• Connection overhead must open new connection for
  every HTTP object
• Basically Stateless Browsers must re-send their
  capabilities
• No support for caching dynamic documents
• HTTP is verbose

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WebExpress The main idea

• WebExpress Intercept Layer
• Runs between wireless link and HTTP
• Client Side (CSI) and Server Side (SSI)
  Intercepts
• No need to reconfigure browsers or web server

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WebExpress Optimizations

• Caching on server and client side
• Differencing cache dynamic documents and only
  transmit differences
• Protocol Reduction a CSI maintains its TCP/IP
  connection to the SSI for all HTTP requests.
• Header Reduction transmit browser capabilities
  only once

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WebExpress Caching

• Differences between wired and wireless
• Cost of communication
• Persistence
• Applicability
• Scope

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WebExpress Cache Improvelments

• Cross-session cache persistance
• Age-based coherency algorithms
• User-configurable options
• Digital-signature based modification verification

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WebExpress Differencing
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Mobile Distributed System Architecure

• Ericsson and Swedish Inst. Of Technology, 1995
• Main Idea To improve performance and mobility of
  wireless distributed systems
• Location sensitive information management
• Use agents to track and predict user mobility
• Forward user state to other agents to minimize
  handoff time delays, traffic

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TLAs Three Letter Acronyms

• MDSP Mobile Distributed System Protocol
• LSIM Location Sensitive Information Management
• PMM Predictive Mobility Management (also called
  MMP)
• Agent a space on Access Point that is
  synchronized with mobile users file system,
  memory space and cache

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Agents The Main Idea

• Use mobility prediction to have data ready for a
  user once he arrives in a cell

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Three Not-so-secret Agents

• M-Agent representative of the mobile user to the
  network
• Creates and deletes MF-Agents
• M-Agent the same through entire session
• MF-Agent Mobile floating
• Temporary agent set up before users arrival into
  a cell.
• Becomes AM-Agent when user arrives
• AM-Agent Active agent
• delivers resources to the user

82
Pre-assignment procedure

• Mobile terminal sends assignment request to
  M-Agent or AM-agent
• M-Agent registers the request and forwards it to
  the MSDP base
• MSDP tries to create new MF-Agent
• New MF-Agent asks foreign agent if it is OK to
  reside there

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Pre-assignment Contd

• If OK, new MF-Agent sends mobile terminal a
  success message
• The new MF-Agent will maintain variable data
  consistency with the AM-Agent
• Now, MF-Agent will be ready for the mobile
  agents arrival
• If MF-Agent creation fails, an error message is
  sent.

84
MMP Mobility Prediction

• Goal To have an MF-Agent waiting for the mobile
  user without wasting resources
• The proposal Predict where the user is likely to
  go, and set up MF-Agents there.
• 2 types of movement
• Regular Can be predicted
• Random Cannot be predicted

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MC/MT/d assignment protocol

• Tries to predict two types of movement
• MC Movement Cycle (cyclical)
• MT Movement Track (unidirectional)
• Benefits of MC/MT/d
• Less overhead than assigning MF-Agents to all
  neighbors (PTP protocol)
• Avoids computation-intensive stochastic models
• Prediction accuracy of 95

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MF/MC/d method

• Calculate mobility during ?m
• Define circle of radius d floor(hm?m)
• h hierarchic factor
• m mobility density during time ?m
• Assign MF-Agents to MC/MT predicted cells within
  radius d
• Repeat when user reaches the boundary of the
  circle

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MC/MF/d The Bottom Line

• Compare MC/MF/d to
• Standard Without MF-Agents
• PTP Assign MF-Agents to all cells within d
• Performance reduced latency - increased
  overhead
• PTP has performance gain of 25 over Standard
• MC/MF/d performance gains
• Heavy load, good prediction 45
• Low load, bad prediction 65

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Routing Algorithms Evaluated

• Uses simulation to assess performance of various
  routing algorithms
• Link-state protocol
• Distance Vector protocols
• Extended Bellman-Ford
• Destination Sequenced Distance Vector (DSDV)
• TORA Multipath protocol
• On-demand protocols
• DSR
• AODV

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Routing protocol evaluation

• Proactive approaches led to low delays and high
  delivery rates, but increased traffic
• On-demand protocol led to worse delays and
  delivery rates, but reduced load
• TORA did not perform well
• As user count increased, routing traffic varied
  less and less among protocols

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Wireless Networks Conclusion

• Bill Joys six webs Wireless is one key to the
  connected future
• This is only the beginning..
• You can reach me at rjt72_at_columbia.edu
• A copy of this presentation is athttp//www.caip.
  rutgers.edu/robjt/wireless.ppt