Connection Rerouting Strategies for Mobile Networks Bruce A. Mah - - PowerPoint PPT Presentation

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Connection Rerouting Strategies for Mobile Networks

Bruce A. Mah

bmah@CS.Berkeley.EDU

The Tenet Group University of California at Berkeley and International Computer Science Institute Hitachi-Tenet Meeting 6 July 1993

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Synopsis

Motivation The Problem Connection Rerouting Strategies Conclusions Future Work The Infopad

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Motivation

Mobile Computing Devices ⇒ Mobile Networks Multimedia Applications ⇒ Real-Time Network Services

Tenet Real-Time Scheme/Protocol Suite

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Mobile Networks

Mobile Hosts with wireless network interfaces Base Stations: Gateways between wireless and wired networks Backbone network: Conventional wired network or internetwork Base Station Mobile Host Switch Server Room-sized Microcell

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The Tenet Real-Time Scheme

Multimedia applications need hard real-time guarantees on network parameters, for example...

Delay Delay jitter Bandwidth Buffer allocation

Guarantee performance using...

Admission control Network resource allocation Work on level of individual network conversations

Requires a connection-oriented network layer

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The Tenet Real-Time Protocol Suite

Performance-Guaranteed Network Communication Continuous Media Transport Protocol (CMTP) Real-Time Message Transport Protocol (RMTP) Real-Time Internet Protocol (RTIP) Real-Time Channel Administration Protocol (RCAP)

Application CMTP RMTP RTIP RCAP Device Drivers

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The Tenet Real-Time Protocol Suite

Tenet Suite I

Performance-guaranteed, unreliable, connection-oriented, unicast real-time channels

Tenet Suite II: The Sequel

Performance-guaranteed, unreliable, connection-oriented, multicast real-time channels

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The Problem

How to re-route network connections when a host moves between cells?

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More of the Problem

What to do

Determine crossover point Forward data (optionally) Reroute connection

Information on impending handoffs

Use as hints...don’t always have them Radio networks may have “dead spots” Infrared networks may have line-of-sight problems

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Full Re-Establishment

Establish new connection for every existing network connection. Problem: Long paths mean long handoff latencies.

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Incremental Re-Establishment

Only create the disjoint part of the connection to the new base station. Key: Find the crossover point!

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Multicast-Based Re-Establishment

Use multicast facilities of the network to support handoff Use lots of network bandwidth to reduce handoff latency Easy to build

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Preliminary Analysis

Compute values of metrics...

Service disruption time (mobile host cannot receive downlink data) Buffer usage Excess bandwidth utilization in the network

For different connection types...

Distance to crossover point Distance between (physically) adjacent base stations

For a given technology point...

Latency, bandwidth of wireless and wired links Protocol processing time Control and data packet sizes Acquisition time during host migration Speed of cell transition

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Results of Preliminary Analysis

Service disruption time and downlink buffering in the base station vary linearly with forwarding path length (except for Multicast-Based re- establishment with hints). Uplink buffering on the mobile hosts is identical for all algorithms. Using hints trades excess allocation of resources in channels against needing to forward data. Multicast-Based re-establishment uses fewer network resources than Incremental Re-Establishment or Full Re-Establishment. For long base station-to-crossover point paths, all algorithms are about the same. Total path length only affects Full Re-Establishment.

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Conclusions

Hints are good We should investigate other multicast-based schemes, they look promising Considerations of network topology are important (want crossover point as close to the handoff site as possible)

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Future Work

Simulation using Ptolemy

Capture dynamics of the network Attempt to measure network capacity

Verification of handoff protocols

Hint-based protocols Unreliable message delivery

Implementation

Infopad

Implications of mobility on semantics of real-time guarantees?

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The Infopad

A Portable Multimedia Terminal University of California at Berkeley Faculty

Bob Brodersen (electronics) Dave Messerschmitt (display server, video coding) Domenico Ferrari (backbone network and network protocols) Randy Katz (storage servers) Jean-Paul Linnartz (radio links)

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Key Features of the Infopad

Portable Terminals

Lightweight: Size dictated by display Low power: battery operated

Multimedia I/O

Speech (input/output) Full Motion Video (output) Graphics/Text (output) Pen (input)

Micro-Cellular Network

1-3 GHz band Cell size of ~30 feet in diameter Low power transmission(1-10 mW) “High” bit rate (1-2 MBps)

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Applications

Video on demand: Movies, news, programming Print media databases: Books, newspapers Supercomputer simulation and display Driver information and safety systems Videophone Home and office information services Remote sensing and actuation Emergency services

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The Infopad Environment

VIDEO DATABASE Compressed Video

Fiber Optic Backbone 100 Mbps - 1 Gbps

WIRELESS BASE STATION COMMERCIAL

SPEECH RECOGNITION

DATABASE LARGE COMPUTE SERVERS

• Video
• Speech
• X-terminal

INFOPAD (A Portable Multimedia Terminal) PERSONAL COMMUNICATORS

• Personal numbers
• World wide coverage

Airline schedule, Newspaper, ...

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What’s Special About Infopad?

Power consumption is key

No processor on Infopad: Too much power Connection endpoints may be on base stations Applications run on compute servers in the backbone network Process migration of display server during handoff?!?

X as a display server

Is this a Good Thing™?

Asymmetric uplink/downlink channels

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Plans for the Infopad

Implement real-time protocols on Infopad backbone network Implement mobility on Infopad when prototype hardware is available

Experiment on a virtual mobile network first?