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General Approaches for General Approaches for Implementing Seamless Implementing Seamless
HandoverHandover
Markus EndlerMarkus Endler
PUC-Rio - BrazilPUC-Rio - Brazil
[email protected]@inf.puc-rio.br
Vera NagamutaVera Nagamuta
IME/USP - BrazilIME/USP - Brazil
[email protected]@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
POMC2002
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.
POMC2002
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.
POMC2002
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
POMC2002
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
POMC2002
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
POMC2002
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?
POMC2002
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
POMC2002
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
POMC2002
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
POMC2002
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
POMC2002
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
POMC2002
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
POMC2002
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
POMC2002
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
POMC2002
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
POMC2002
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.
POMC2002
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)
POMC2002
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.
POMC2002
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?
POMC2002
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