General Approaches for General Approaches for Implementing Seamless Implementing Seamless

HandoverHandover

Markus EndlerMarkus Endler

PUC-Rio - BrazilPUC-Rio - Brazil

endler@inf.puc-rio.brendler@inf.puc-rio.br

Vera NagamutaVera Nagamuta

IME/USP - BrazilIME/USP - Brazil

nagamuta@ime.usp.brnagamuta@ime.usp.br

POMC2002

OutlineOutline

MotivationMotivation Main ConceptsMain Concepts Bird Eye’s ViewBird Eye’s View General ApproachesGeneral Approaches Case StudiesCase Studies Architectural FrameworkArchitectural Framework Conclusions & Future ResearchConclusions & Future Research

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Motivation Motivation In mobile networks, migration is a central issue, with impact In mobile networks, migration is a central issue, with impact

on service performance, QoS, reliability, security,..on service performance, QoS, reliability, security,.. Handover is the process “behind the scene” that handles Handover is the process “behind the scene” that handles

all the necessary changes when switching (access) all the necessary changes when switching (access) domains.domains.

Types of migration:Types of migration: micro-migration: between access points within a wireless networkmicro-migration: between access points within a wireless network macro-migration: between distinct networksmacro-migration: between distinct networks

Common tasks in mobile/cellular networks:Common tasks in mobile/cellular networks: message re-routingmessage re-routing state transfer and context re-establishment (e.g. discovery of state transfer and context re-establishment (e.g. discovery of

servers)servers) The goal of The goal of Seamless HandoverSeamless Handover is to make migration is to make migration

transparent to the communicating parties.transparent to the communicating parties.

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Motivation Motivation Seamless Handover has been investigated in several contexts:Seamless Handover has been investigated in several contexts: Medium Access Layer of cellular networks Medium Access Layer of cellular networks

Goal: Switch channels with smallest possible traffic disruptionGoal: Switch channels with smallest possible traffic disruption IETF Mobile IP Route Optimization, IPv6IETF Mobile IP Route Optimization, IPv6

Goal: minimum loss of IP packetsGoal: minimum loss of IP packets Wireless ATM Wireless ATM

Goal: Fast re-establishment of a virtual circuitGoal: Fast re-establishment of a virtual circuit Mobile Objects/AgentsMobile Objects/Agents

Goal: Reliable interaction among objects (no message loss)Goal: Reliable interaction among objects (no message loss) Heterogeneous wireless NetworksHeterogeneous wireless Networks

Goal: Provide continuous service across multiple administrative domains Goal: Provide continuous service across multiple administrative domains and wireless technologiesand wireless technologies

Seamlesness is also an issue in other fields: e.g. virtual reality, Seamlesness is also an issue in other fields: e.g. virtual reality, human-computer interaction, etc.human-computer interaction, etc.

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Meanings of SeamlessMeanings of Seamless

The meaning of “seamless” depends on:The meaning of “seamless” depends on: QoS requirements of the upper network/application QoS requirements of the upper network/application

layers layers type of service (e.g. virtual circuit vs. packet switching)type of service (e.g. virtual circuit vs. packet switching) properties of the wireless network (e.g. degree of cell properties of the wireless network (e.g. degree of cell

overlay, network structure, etc.)overlay, network structure, etc.)

Examples: Examples: reliable message delivery in causal orderreliable message delivery in causal order delivery of data frames with max delay delivery of data frames with max delay

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Motivation Motivation Thesis: Despite the differences in the meaning of “Seamless” Thesis: Despite the differences in the meaning of “Seamless”

and the tasks of the Handover for a specific service/network, and the tasks of the Handover for a specific service/network, there exist common patterns of solutions, which could be there exist common patterns of solutions, which could be described in general terms.described in general terms.

Main Goals:Main Goals: Investigate Handover protocols for micro-mobility Investigate Handover protocols for micro-mobility

they are a fundamental component of distributed algorithms for they are a fundamental component of distributed algorithms for Mobile NetworksMobile Networks

Identify and classify the canonic solution approachesIdentify and classify the canonic solution approaches may be re-used for different networks/applicationsmay be re-used for different networks/applications

Define an unifying Framework and identify the common used Define an unifying Framework and identify the common used techniquestechniques gives support for developing distributed services for mobile networksgives support for developing distributed services for mobile networks

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Main ConceptsMain Concepts A A Migrating Element (ME)Migrating Element (ME) moves between moves between DomainsDomains (e.g. from (e.g. from

DomDomoo to Dom to Domnn), while it is interacting with one or more ), while it is interacting with one or more Correspondent Elements (CE)Correspondent Elements (CE)

In each Domain, a In each Domain, a Domain Representative (DomRep)Domain Representative (DomRep) is is responsible for serving ME when it is within its Domainresponsible for serving ME when it is within its Domain

DomRep is a network access point which delivers DomRep is a network access point which delivers Downstream EventsDownstream Events from the network to ME and from the network to ME and Upstream Upstream EventsEvents from ME to network (e.g. signals, packets, messages, from ME to network (e.g. signals, packets, messages, etc.)etc.)

Handover is a distributed protocol between DomRepHandover is a distributed protocol between DomRepoo, DomRep, DomRepnn (and propably other network nodes) that(and propably other network nodes) that creates alternative/replicated routes for data, creates alternative/replicated routes for data, establishes the execution context at DomRepestablishes the execution context at DomRepnn, and , and updates ME´s network-resident stateupdates ME´s network-resident state

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Bird Eye’s View: Bird Eye’s View: Major EventsMajor Events

{m,h}p : preparation for a migration/handover{m,h}p : preparation for a migration/handover{m,h}i : initiation of a migration/handover{m,h}i : initiation of a migration/handover{m,h}c: completion of a migration/handover{m,h}c: completion of a migration/handoverODx: old Domain exitODx: old Domain exitNDy: new Domain entryNDy: new Domain entry

network

ME

ODx

NDy

hi

mi

hc

mc

hp

mp hi-ack

(serviced by either DomRepo or DomRepn)

How to provide the service (event delivery) in the migration interval

[mi,mc] like before and after migration?

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General ApproachesGeneral ApproachesApproaches:Approaches: Non-Coordinated Redundant ServiceNon-Coordinated Redundant Service Coordinated Redundant ServiceCoordinated Redundant Service New Domain ServiceNew Domain Service Old Domain ServiceOld Domain Service Interrupted Service with ExceptionsInterrupted Service with Exceptions

Main Differences: Main Differences: if DomRepif DomRepoo or DomRep or DomRepnn (or both) will serve ME and (or both) will serve ME and if (and how) they synchronize the switching of service if (and how) they synchronize the switching of service

responsibilityresponsibility

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General Approach General Approach #1#1

Non-Coordinated Redundant ServiceNon-Coordinated Redundant Serviceboth DomRepboth DomRepoo or DomRep or DomRepnn deliver/receive eventsdeliver/receive events requires access to either DomReprequires access to either DomRepoo OR DomRep OR DomRepnn during during

the migration intervalthe migration interval redundant events must be identified & filtered outredundant events must be identified & filtered outnon-optimal use of resourcesnon-optimal use of resources

DomRepo DomRepn

ME

CE

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General Approach General Approach #2#2 Coordinated Redundant ServiceCoordinated Redundant Service

both DomRepboth DomRepoo or DomRep or DomRepn n could serve ME, but agree on a could serve ME, but agree on a precise moment to switch service (“switching point”)precise moment to switch service (“switching point”)

switching point must be synchronized with update of ME´s switching point must be synchronized with update of ME´s network-resident statenetwork-resident state

saves resources and avoids filtering of redundant eventssaves resources and avoids filtering of redundant events

DomRepo DomRepn

ME

CE

synch

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General Approach General Approach #3#3 New Domain Service New Domain Service

only DomReponly DomRepnn serves ME during migration intervalserves ME during migration interval requires NDy requires NDy mi mi (( = happens before) = happens before)DomRepDomRepoo must forward events to DomRep must forward events to DomRepnn

DomRepDomRepn n must merge direct and forwarded eventsmust merge direct and forwarded events

DomRepo DomRepn

ME

CE

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General Approach General Approach #4#4 Old Domain ServiceOld Domain Service

only DomReponly DomRepn n serves ME during migration intervalserves ME during migration interval requires hc requires hc ODx ODx if DomRepif DomRepnn receives Downstream events directly it either receives Downstream events directly it either

buffers them or redirects them to DomRepbuffers them or redirects them to DomRepnn

may be required ifmay be required if context establishment at DomRepcontext establishment at DomRepnn is is time-consuming, ortime-consuming, or if DomRepif DomRepoo DomRep DomRepnn forwarding is forwarding is not cost-effectivenot cost-effective

DomRepo DomRepn

ME

CE

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General Approach General Approach #5#5 Interrupted Service with ExceptionsInterrupted Service with Exceptions

ME is not served by any DomRep during migration ME is not served by any DomRep during migration interval (i.e. delivery is interrupted)interval (i.e. delivery is interrupted)

Correspondent Element (or proxy) gets an exception Correspondent Element (or proxy) gets an exception and is requested to re-send events and is requested to re-send events

Feasible only if:Feasible only if:There are no upstream Events (e.g. ME is quiescent during

migration) or proxy at ME buffer events, and There is no requirement about timely delivery

Major advantage: does not require overlapping access Major advantage: does not require overlapping access areasareas

DomRepo DomRepn

ME

CENot found

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Case StudiesCase Studies Wireless LANs Wireless LANs Non-Coordinated Reduntant Non-Coordinated Reduntant

DomReps are AccessPoints (hubs)DomReps are AccessPoints (hubs) all frames are received by all DomReps, which transcode them to the all frames are received by all DomReps, which transcode them to the

wireless linkwireless link ME must filter out redundant frames ME must filter out redundant frames

Multicast-based Handover Multicast-based Handover Non-Coordinated Reduntant Non-Coordinated Reduntant ME has a IP multicast address, and registers with a multicast routerME has a IP multicast address, and registers with a multicast router DomRepDomRepoo and DomRep and DomRepnn are included in the multicast tree are included in the multicast tree multicast router forwards any IP packets to both DomReps, which relay multicast router forwards any IP packets to both DomReps, which relay

them to MEthem to ME

Mobile IP Seamless Handover Mobile IP Seamless Handover New Domain New Domain ME informs new Care-of Address to DomRepME informs new Care-of Address to DomRepo, o, which forwards IP packets to which forwards IP packets to

DomRepDomRepnn

forwarding pointer expires after some timeforwarding pointer expires after some time

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Case StudiesCase Studies Mobile Database Transaction Mobile Database Transaction Old Domain Old Domain

a ME requests read locks at the current DomRep, and even after migration a ME requests read locks at the current DomRep, and even after migration locks are maintained at DomReplocks are maintained at DomRepoo

before granting any new lock DomRepbefore granting any new lock DomRepnn checks for confliciting locks at checks for confliciting locks at previous DomReps (i.e. DomRepprevious DomReps (i.e. DomRepoo))

from concurrency control point of view, ME is still at DomRepfrom concurrency control point of view, ME is still at DomRep oo

Wireless ATM Wireless ATM Coordinated Redundant Coordinated Redundant handover is responsible for switching connection between CE and handover is responsible for switching connection between CE and

DomRepDomRepoo to DomRep to DomRepnn (path redirection at a (path redirection at a ATM crossover switchATM crossover switch)) switching point = when new path is set at ATM crossover switchswitching point = when new path is set at ATM crossover switch

Mobile Agent Systems Mobile Agent Systems Interrupted Service & Exceptions Interrupted Service & Exceptions proxies hold the bindings to the mobile objectsproxies hold the bindings to the mobile objects if proxy attempts to communicate through a stale binding, this raises an if proxy attempts to communicate through a stale binding, this raises an

exception, and proxy transparently, gets new location, updates binding, exception, and proxy transparently, gets new location, updates binding, and re-submits requestand re-submits request

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Elements involvedElements involved

Interactions and Alternative Paths in a Interactions and Alternative Paths in a Downstream Downstream

Correspondent/proxy

AddressRegistry

DomRepN

DomRepO

MERouter/Switch

Lookup Update

Context Forward

setNewPath

Buffer/Merge

Buffer/Merge

Filter

Not Found

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Core Tasks and MechanismsCore Tasks and Mechanisms Context EstablishmentContext Establishment

prepare/update network for interaction at new Domain prepare/update network for interaction at new Domain

e.g. update router, address registry, discover servicese.g. update router, address registry, discover services

Stream UniformnessStream Uniformness mechanisms to guarantee less disruption of event streamsmechanisms to guarantee less disruption of event streams

e.g. replication, redirection, retransmissione.g. replication, redirection, retransmission

Delivery ControlDelivery Control mechanisms to control/synchronize delivery of events by DomRepsmechanisms to control/synchronize delivery of events by DomReps

e.g. bufferingOn/Off, Enable/Disable delivery, etc. e.g. bufferingOn/Off, Enable/Disable delivery, etc.

Stream UnificationStream Unification mechanisms to merge streams (over different paths) to single streammechanisms to merge streams (over different paths) to single stream

e.g. Event forwarding, Stream merge, filtering, etc. e.g. Event forwarding, Stream merge, filtering, etc.

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Architectural FrameworkArchitectural Framework

The five General Approaches differ in how the mechanisms The five General Approaches differ in how the mechanisms & tasks are assigned to the several elements and how & tasks are assigned to the several elements and how they are synchronized.they are synchronized.

Hence, we are building an unifying architectural Hence, we are building an unifying architectural framework, where the mechanisms are the hot spots.framework, where the mechanisms are the hot spots.

Framework instantiation will depend on:Framework instantiation will depend on: the application requirementsthe application requirements specifics of the mobile network/system specifics of the mobile network/system specific meaning of “seamless” (e.g. set of properties to specific meaning of “seamless” (e.g. set of properties to

be satisfied in the migration interval)be satisfied in the migration interval)

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ConclusionConclusion

Handover is a fundamental part of distributed protocols in any Handover is a fundamental part of distributed protocols in any network with mobility.network with mobility.

For micro-mobility fast handover is desirable, but usually For micro-mobility fast handover is desirable, but usually provided only as “best effort”.provided only as “best effort”.

Seamless/Transparent Handover is required for applications Seamless/Transparent Handover is required for applications which have strict requirements of Quality of Service.which have strict requirements of Quality of Service.

Although there are several implementations of “seamless Although there are several implementations of “seamless handover” for different networks/services/applications most handover” for different networks/services/applications most solutions employ similar, general approaches.solutions employ similar, general approaches.

Our framework shall be useful for designing new protocols for Our framework shall be useful for designing new protocols for seamless handover for a wide range of networks and seamless handover for a wide range of networks and services.services.

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Future ResearchFuture ResearchBut there are still many open questions…But there are still many open questions… Are there other general approaches? Can the approaches be Are there other general approaches? Can the approaches be

further detailed? further detailed? Is it possible to describe each approach as a composition of Is it possible to describe each approach as a composition of

sub-approaches for each of the core tasks?sub-approaches for each of the core tasks? Is it possible to derive new protocols for seamless handover Is it possible to derive new protocols for seamless handover

by combining known protocols/mechanisms?by combining known protocols/mechanisms? How does location management affect handover protocols?How does location management affect handover protocols? How to formalize some of the intuitive meanings of seamless How to formalize some of the intuitive meanings of seamless

handover?handover? Are there other meanings of seamless from other application Are there other meanings of seamless from other application

areas?areas?

General Approaches for General Approaches for Implementing Seamless Implementing Seamless

HandoverHandover

Questions?Questions?

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Cellular IP (CIP)Cellular IP (CIP)

Routers have cache with soft-state entries (cleared by timeouts)Routers have cache with soft-state entries (cleared by timeouts) Entries are updated or refreshed by data (or Route-update) packets Entries are updated or refreshed by data (or Route-update) packets

sent by the MEsent by the ME In the overlapping area, packets from both DomReps are received In the overlapping area, packets from both DomReps are received

DomRepN

DomRepO

MECIP Gateway

Filter

Route-UpdatePacket

Route-UpdatePacket

CE