as) United States
`a2) Patent Application Publication 0) Pub. No.: US 2004/0142693 Al
`
`Federet al.
`(43) Pub. Date:
`Jul. 22, 2004
`
`US 20040142693A1
`
`(54) SYSTEM AND METHOD FOR
`ESTABLISHING AND/OR MAINTAINING A
`DATA SESSION ACROSS PACKET DATA
`NETWORKS
`
`(76)
`
`Inventors: Peretz Meshes Feder, Englewood, NJ
`(US); Gang Li, Bridgewater, NJ (US);
`Martin Howard Meyers, Montclair, NJ
`(US); Ajay Rajkumar, Morristown, NJ
`(US)
`Correspondence Address:
`HARNESS, DICKEY & PIERCE, P.L.C.
`PO. Box 8910
`Reston, VA 20195 (US)
`
`(21) Appl. No.:
`.
`(22)
`Filed:
`
`10/347,807
`Jan. 22, 2003
`Publication Classification
`
`(SV)
`
`Tint. C07 eee ececeeeeeescssnneeecereteeeeenneeeeees H04Q 7/20
`
`(52) US. C1. eeeeeecseessseseecsecnecneeeneess 455/443; 455/436
`
`(57)
`
`ABSTRACT
`
`A communication system selection algorithm (SSA) imple-
`mented by a mobile station chooses between available
`systems to select a system to serve the mobile station.
`During initialization, the SSA causes the mobile station to
`scan the environment and compare available communication
`systems to determine the best system to provide service.
`After an initial system is chosen, the SSA causes the mobile
`station to continuously,or at discrete time intervals, scan the
`environment for available systems,
`thus allowing for a
`seamless switch to an available system whenevera handoff
`is desired. The SSA choosesthe best available system based
`on measurements of each available system and applying
`preference rules defined by a service provider and/or user of
`the mobilestation.
`
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`1
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`

`

`Patent Application Publication
`
`Jul. 22,2004 Sheet 1 of 2
`
`US 2004/0142693 A1
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`

`Patent Application Publication Jul. 22,2004 Sheet 2 of 2
`
`US 2004/0142693 Al
`
`FIGURE2
`
`
`
`SCAN ENVIRONMENTFOR AVAILABLE SYSTEMS $10
`
`DETERMINE SET OF VALID SYSTEMS
`
`$20
`
`OBTAIN MEASUREMENTS FOR EACH VALID SYSTEM
`
`$30
`
`COMPARE MEASUREMENTSTO DETERMINE
`PREFERRED CANDIDATE FOR EACH AVAILABLE SYSTEM|
`TYPE
`
`S40
`
`S90
`INITIAL SYSTEM SELECTION MODE? SELECTED SYSTEM = CURRENTLY
`SERVING SYSTEM?
` IMPLEMENT SELECTED SYSTEM AS SERVING SYSTEM
`
`APPLY PREFERENCE RULES TO MEASUREMENTS TO
`SELECT SYSTEM FROM PREFERRED CANDIDATES
`
`
`
`
`S60
`
` HANDOFF CONDITIONS MET?
`
`
`390
`
`3
`
`

`

`US 2004/0142693 Al
`
`Jul. 22, 2004
`
`SYSTEM AND METHOD FOR ESTABLISHING
`AND/OR MAINTAINING A DATA SESSION
`ACROSS PACKET DATA NETWORKS
`
`session during the switch. The switch can therefore be
`seamless, so that the user does not realize a switch has
`occurred.
`
`BACKGROUND OF THE INVENTION
`
`[0001] The present invention relates to wireless and wire-
`line communications networks and, more particularly, to a
`method for a mobile client to choose amongst wireless and
`wireline service providers.
`
`DESCRIPTION OF THE RELATED ART
`
`[0002] Currently, a subscriber using a mobile station, such
`as that shown in FIG.1, can connect to a wireless or wireline
`communication network in order to conduct a data session,
`e.g., an Internet session. For example, mobile stations such
`as personal digital assistants (PDAs) or laptop computers
`may be used to conduct a data session.
`
`[0003] The Mobile IP standard currently provides seam-
`less mobility in the IP layer by maintaining the same IP
`address across different systems. However, Mobile IP does
`not proactively seek another communication system until the
`current system cannot maintain a connection.
`
`SUMMARYOF THE INVENTION
`
`[0004] The present invention provides a system selection
`algorithm (SSA), which is run on the mobile client of a
`mobile station, to choose between available communication
`systems during initialization of the mobile station, or to
`seamlessly switch between systems while a data session is
`being conducted on the mobile station. The SSA continu-
`ously monitors the disparate wireless and wireline commu-
`nication systemsto initiate a “make before break” seamless
`handoff to the “best” system based on variouscriteria, in
`contrast to Mobile IP.
`
`invention will
`[0007] Other advantages of the present
`become more apparent from the detailed description given
`hereafter. However, it should be understood that the detailed
`description and specific examples, while indicating pre-
`ferred embodiments of the invention, are given by way of
`illustration only, since various changes and modifications
`within the spirit and scope of the invention will become
`apparent to those skilled in the art from this detailed descrip-
`tion.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`invention will become more fully
`[0008] The present
`understood from the detailed description given below and
`the accompanying drawing, which is given for purposes of
`illustration only, and thus do not limit the present invention.
`
`[0009] FIG. 1 illustrates a high level architecture of a
`generic network in which a mobile device is capable of
`conducting a data session using one of multiple types of
`communication systems.
`
`[0010] FIG. 2 is a flowchart illustrating the steps per-
`formed by the system selection algorithm (SSA) according
`to an exemplary embodiment of the present invention.
`
`DETAILED DESCRIPTION OF THE
`EXEMPLARY EMBODIMENTS
`
`[0011] The present invention relates to a system selection
`procedure (SSA) that is incorporated in a mobile client. A
`“mobile client” is defined as application software that runs
`on a mobile station. A mobile station may be any data
`processing device with wireless and wireline communica-
`tion capabilities, such as, but not limited to, laptop computer,
`personal digital assistant, etc. For wireless communication
`systems, radio frequency and baseband processing may be
`performed by a PCMCIA card or other RF front end cir-
`cuitry. Also, a mobile station may be capable of using data
`services from two or more different wireless and wireline
`systems, either one at a time or simultaneously.
`
`[0012] According to an exemplary embodiment, the SSA
`runs continuously in the mobile client, causing the mobile
`station to scan the environment and monitor available sys-
`tems, either continuously or at discrete time intervals. The
`mobile station collects measurementsin order to monitor the
`
`[0005] During initialization, the SSA causes the mobile
`station to scan the environment for available systems, and
`perform comparisons to determine the best system available
`for providing service. After a system is initially chosen, the
`mobile station continuously (or at configurable discrete
`intervals) scans available systems according to the SSA and
`performs comparisons to choose a best available system.
`The conditions of the currently serving system are also
`monitored, and the SSA initiates or assists in handoff to the
`chosen system whenevernecessary. According to this algo-
`rithm, the mobile station may be seamlessly handed off to
`conditions of each available system. The measurements are
`the best available system, regardless of whether or not the
`reported to the SSA,andaset of preference rules are applied
`best system is disparate from the current system. The SSA
`to these measurements to determine the best available sys-
`compares the available systems according to measurable
`tem. The SSA is configured to run according to the following
`conditions, which are monitored for each available system.
`three modes:
`While comparing systems, the SSA applies a set of prefer-
`encerules to the service provider preference rules, which are
`downloaded to the mobile client from the primary service
`provider with whom the user subscribes. These rules may
`also include preferences configured by the user.
`
`[0006] By continuously determining a best available sys-
`tem according to the conditions and preference rules, while
`monitoring the conditions of the currently serving system,
`the mobile client is prepared to switch from the current
`system to another when necessary. Accordingly, the SSA of
`the present invention allows for the mobile station to switch
`to another network, while maintaining the current data
`
`1) Initial system selection mode: during initializa-
`[0013]
`tion of the mobile client, the SSA causes the mobile station
`to check the environment, scanning for available systems.
`The SSA then chooses one of the available system to serve
`the mobile station. The SSA may choose the best available
`system based on a comparison of monitored conditions, or
`a system mandated bythe service provider in a downloaded
`set of service provider preferences, described in more detail
`in the Preference Managementsection below.
`
`2) Normaltraffic mode: after initial service has
`[0014]
`been established, the SSA may then cause the mobilestation
`
`4
`
`

`

`US 2004/0142693 Al
`
`Jul. 22, 2004
`
`to initiate a handoff to a best available system (determined
`according to ongoing monitoring and comparison steps),
`whencertain conditions are met.
`
`3) Handoff Mode: if the SSA determines that the
`[0015]
`currently serving system cannot maintain the service, based
`on changes in monitored conditions (e.g., channel condi-
`tions) of the serving system, the SSAinitiates a handoff of
`the mobile station to the best available system (if the best
`available system is a better alternative to the current system).
`
`[0016] Exemplary embodiments of the present invention
`will be described below in connection with high-speed
`wireline systems, Third Generation (3G) systems, wireless
`local area network (WLAN) systems (including both IEEE
`802.11 systems and Bluetooth systems), and Bluetooth-
`based personal area network (PAN) systems. The term 3G
`system will be used to refer to different types of Third
`Generation
`systems,
`including
`cdma2000, UMTS,
`3G-EVDO, 3G-EVDV, HSDPA,as well as other evolving
`3G systems.
`
`It should be noted that 3G, WLAN, and PAN
`[0017]
`systems are merely examples of the types of systems, which
`may be used to service the mobile station in the present
`invention; and the present invention is not limited to these
`types of wireless systems. For instance, the mobile station
`may beserviced by various types of cellular communication
`systems including, but not
`limited to, 3G systems and
`various types of wireless packet data networks including,
`but not limited to, 802.11-based systems. Thus, according to
`an exemplary embodiment, the present invention may allow
`for seamless switching between cellular networks and wire-
`less packet data networks.
`
`[0018] Overview of the SSA
`
`FIG.2 is a flowchart of the steps performed by the
`[0019]
`SSAaccording to an exemplary embodimentof the present
`invention. For the purpose of explanation only, the process
`illustrated in FIG. 2 will be described as being implemented
`in the system shown in FIG. 1. However,
`the process
`illustrated in FIG.2 is not limited to such an implementa-
`tion. In step S10, the SSA instructs the mobilestation to scan
`the environment to detect available systems. The systems
`detected by the mobile station may include systems of a
`type, which is different than, and disparate (.e., not com-
`patible) with respect to, the system currently serving the
`mobile station.
`
`the SSA determines which of the
`In step S20,
`[0020]
`available systems detected in step $10 are valid, i.e., which
`systems the mobile station is authorized to use. This step
`may involve checking each available system detected in step
`S10 to a list of allowable systems in the mobile client.
`Accordingly, the SSA would determine a set of valid sys-
`tems as including the currently serving system (which must
`be valid since it was already selected by the SSA), and any
`system detected in step $10, whichis onthelist of allowable
`systems.
`
`In an exemplary embodiment,the list of allowable
`[0021]
`systemsincludes those systemseither operated by, or having
`a Service Level Agreement (SLA) with, the primary service
`provider. An SLA is a type of agreement whereby a wireless
`service provider (e.g., 802.11 hot spot operator) agrees to
`service subscribers of a primary service provider (e.g., a 3G
`
`network operator), usually in exchange for a share of the
`subscriber fees collected by the primary service provider.
`
`It should be noted that even though the primary
`[0022]
`service provider permits the mobile station to roam to other
`systems having an SLA,the primary service providerstill
`“owns” (controls the rights of)
`the roaming subscriber.
`Accordingly, the primary service provider sets the service
`provider rules for the mobile unit of the subscriber.
`
`[0023] The SSA receives measurement reports for each
`valid system for the mobile station in step S30. Accordingly,
`step S30 allows the SSA to monitor conditions, e.g., radio
`link conditions for each valid wireless system and the
`availability of high-speed wireline system. The types of
`measurements and conditions monitored by the SSA will be
`described in the section below entitled Monitoring Condi-
`tions for Available Systems.
`
`[0024] The scanning and monitoring processes of steps
`$10-S30 may be performed continuously while the mobile
`station is operating. Alternatively, the SSA may be config-
`ured to repeat steps S10-S30 after a particular time duration
`has passed.
`
`[0025] While steps S10-S30 illustrate exemplary steps to
`allow the mobile station to find available systems,
`the
`present invention should not be construed as being limited to
`these scanningsteps. Instead of relying on the mobile station
`to frequently scan the environment for signals from avail-
`able systems, the present invention may utilize a message-
`based approach to notify the mobile client of other valid
`systems, which are available in an alternative embodiment.
`In this embodiment, the serving wireless system sends a
`message to the mobile unit identifying other valid wireless
`systems when they becomeavailable.
`
`[0026] For example, in 3G systems such as cdma2000,
`system parameters are broadcast over the cell to mobile
`units. The cdma2000 system could notify mobile stations of
`the presence of a valid alternative system, e.g., a valid
`802.11 hot spot,
`in the broadcast message.
`In another
`example, if the mobile station is currently being served by
`a 802.11 system, a broadcast message can be added to the
`802.11 beacon to identify valid 3G systemsavailable in the
`area.
`
`[0027] Referring back to FIG. 2, in step S40, the SSA
`compares the various measurements in order to determine a
`preferred candidate system for each of the disparate types of
`networks available. The preferred candidate system repre-
`sents the “best” available network for each network accord-
`
`ing to the measurements. For example, when multiple valid
`3G service providers are detected in the environment, along
`with a set of valid 802.11 WLANs and a set of valid
`
`Bluetooth WLANs,a preferred candidate system is selected
`for each of the set of 3G systems, the set of 802.11 systems,
`and the set of Bluetooth systems.
`
`In an exemplary embodiment, the SSA assigns a
`[0028]
`score to each available system based on the measurements,
`and compares these scores to determine the preferred can-
`didate for each network type. The preference rules may
`include rules defining how measurementsrelating to differ-
`ent conditions (e.g., radio link, system performance, high-
`speed wireline availability, etc.) are scored. The scoring will
`be described further below in the Preference Management
`section.
`
`5
`
`

`

`US 2004/0142693 Al
`
`Jul. 22, 2004
`
`[0029] Whenthe serving system is a wireline system, the
`relevant measurement may be whether an active connection
`to the serving wireline system still exists. In an exemplary
`embodiment, if the SSA determines that the connection is
`still active,
`the serving wireline system may be selected
`according to the preference rules to continue to serve the
`mobile unit, regardless of the scores of the other available
`systems.
`
`the preference rules are
`[0030] According to step S50,
`applied by the SSAto select one of the preferred candidate
`systems. The preference rules are used to compare different
`types of networks according to both the measurements (i.e.,
`monitored conditions) and the preferences of the primary
`service provider and/or user.
`
`[0031] For certain types of conditions, a direct comparison
`of disparate types of networks can be made based on the
`measurements performed. For example, a signal strength
`indicator (RSSI) for each system can be measured for each
`wireless system type in order to compare the radio coverage
`areas of the disparate systems. However, for other types of
`monitored conditions, different types of measurements must
`be taken from the disparate systems, for which a direct
`comparison cannot be made.
`
`[0032] As indicated in decision block S60, if the SSA is
`running in initial system selection mode(i.e., no system is
`currently serving the mobile station), the SSA jumps ahead
`to step S90 where the system selected in step S50 is
`implemented as the serving system, 1.e., the mobile station
`connects to the selected system, and a data session may be
`initiated.
`
`[0033] However, if the SSA is running either in the normal
`traffic mode or the handoff mode, it is determined whether
`the currently serving system has been selected, as shown in
`decision block S70. If the currently serving system has been
`selected, no handoff is required by the SSA, which once
`again starts scanning for available systems according to step
`S10.
`
`[0034] However, if another system is selected, a determi-
`nation is made as to whether the conditions for initiating a
`handoff have been met, as indicated by decision block S80.
`These handoff conditions may be contained in one or more
`preference rules, which apply thresholds to the monitored
`conditions of the selected system and/or the currently serv-
`ing system, as described in the Preference Management
`section below. For example,
`if the serving system is a
`wireline system, the condition for initiating the handoff may
`be met when the SSA detects that the mobile unit is no
`
`longer actively connected to the serving wireline system.
`
`If the handoff conditions are not met, no handoff is
`[0035]
`performed, and the SSA returnsto its scanning modein step
`S10. If the handoff conditions are met, the SSA implements
`the selected system to service the mobile station in step $90,
`by initiating or assisting in the handoff of the mobile station
`to the selected system. Then, the SSA returns to step S10.
`
`[0036] The SSArunscontinuously while the mobile unit is
`conducting a data session. The SSA therefore continuously
`determines a best available system (i.e., preferred candidate
`system) based on monitored conditions and the preferences
`of the primary service provider and/or user. By having
`already determined the best available system, the mobile
`unit is prepared to perform a handoff whenever the condi-
`
`tions associated with the currently serving system make it
`necessary to switch systems. Thus,
`the handoff proceeds
`seamlessly, even when the mobile unitis being handed off to
`a disparate type of network.
`
`[0037] Monitoring Conditions for Available Systems
`
`[0038] The SSA can makeits decisions for system selec-
`tion according to various types of information collected at
`the mobile receivers and/or each system. Specifically, the
`SSA may take into consideration one or more of the fol-
`lowing factors:
`
`1) Availability of a high-speed wireline connection.
`[0039]
`This information is available to the mobile client software
`
`through the standard operating system interface.
`
`2) Radio link conditions (e.g., radio coverage area
`[0040]
`and forward link interference). This type of information can
`be gathered using measurements obtained at the mobile unit.
`A further description of radio link conditions is provided
`below.
`
`3) System loading conditions (e.g., forward and
`[0041]
`reverse link loading). Such information may be measured
`and communicated by each available system.
`
`4) Service quality (e.g., data bit rate). Direct per-
`[0042]
`formance measurements for each system may be obtained
`using short “probe” sessions. When a mobile station
`includes multiple RF front-ends, multiple parallel probe
`sessions may be used for multiple wireless systems. If only
`one RF front-end is available, probe sessions can be per-
`formed sequentially. Similarly,for currently serving wireline
`systems, probe sessions can determine whethera particular
`connection is active or not.
`
`[0043] Radio Link Conditions
`
`[0044] The SSA can monitor radio link conditions through
`measurementreports from the radio receivers of the mobile
`client. In order to compare radio link conditions, the SSA
`receives measurements from radio receivers within the
`
`mobile station. For example, a received signal strength
`indication (RSS]) measurement may be used by the SSA to
`compare the radio coverage area of each system. The SSA
`mayalso use different types of measurements to compare a
`commonradio link condition in different types of wireless
`systems.
`
`[0045] For example, an appropriate measure of the inter-
`ference level of the forward link (downlink) in an 802.11-
`based system is signal to noise ratio (SNR). However, to
`measure downlink interference in a 3G network, the mobile
`station must measure a signal energy to interference ratio
`(E/1,) of a received pilot signal. In order to perform a
`comparison, the SNR and E,/I, can each be converted to a
`common parameter by the SSA.
`
`In one embodiment, the different types of measure-
`[0046]
`ments may be compared by mapping each into a maximum
`available data bit rate. Accordingly, in the above example
`where the available systems include a 802.11 network and a
`3G network, the SSA may calculate the maximum data bit
`rate allowed for the 802.11 network based on the measured
`SNR,and the maximum data rate for the 3G network based
`on the measured E,/I,.
`
`[0047] While E,/I, provides an exemplary method of
`determining data rate for 3G networks, one of ordinary skill
`
`6
`
`

`

`US 2004/0142693 Al
`
`Jul. 22, 2004
`
`in the art will realize that the maximum available data rate
`for 3G systems can be determined by other means. In a
`further exemplary embodiment, the available data rate of a
`3G network may be obtained from a data rate field in a
`message sent from the 3G network to the mobile unit.
`
`[0048] Also, there are various other methods of determin-
`ing a maximum available data rate for systems such as
`802.11 and Bluetooth networks, as will be apparent to those
`ordinarily skilled in the art. The present
`invention thus
`covers all means for determiningthe available datarate ofall
`various types of wireless and wireline networks, as will be
`contemplated by one of ordinary skill in theart.
`
`In an alternative exemplary embodiment,different
`[0049]
`measurement types for a common radio link condition do
`not need to be converted to a common parameter type such
`as data bit rate. Instead, preference rules may be defined and
`used to classify each measurementinto one of a variety of
`service level categories for a particular radio link condition.
`The systems can therefore be compared with each other
`based on their corresponding service level category. A more
`complete description of the different types of preference
`rules will be given below in the Preference Management
`section.
`
`[0050] Preference Management
`
`[0051] The basic idea behind configuration of the mobile
`client software is preference management—thespecification
`of various preferences, and the construction of a set of
`preference rules for a user according to these preferences.
`There are generally two types of preferences: 1) service
`provider preferences, and 2) mobile user preferences. The
`service provider preferences are determined by the primary
`service provider, subscribed to by the mobile user.
`
`[0052] For example, 3G systems generally provide wide-
`scale coverage and mobility, as opposed to WLANs and
`PANs. Therefore, a user would likely subscribe to a 3G
`service provider for primary service coverage, and receive
`the credentials needed for accessing both 3G and WLAN
`systems from the 3G service provider. In such a situation,
`“service provider preferences” are defined to be the prefer-
`ences provided by a 3G service provider. It should be noted,
`however, that the same service provider could operate a 3G
`and one or more types of WLANs.
`
`[0053] According to an exemplary embodiment, the pri-
`mary service provider downloadsthe set of service provider
`preferences to the mobile client as a configurationfile at the
`time the user initially subscribes, or signs up, to the primary
`service provider. The primary service provider may
`remotely download these rules via a wireless networkat the
`time of activation. Alternatively, the primary service pro-
`vider may download the service provider preference rules
`using a wireline connection (or may directly program the
`rules into the mobile client), for example,if the user acquires
`an activated mobile station directly from the primary service
`provider.
`
`the primary
`[0054] After the user initially subscribes,
`service provider may remotely upgrade the service provider
`preference rules in the mobile client. Such upgrades may be
`performed whenever the primary service provider decides
`that new criteria should be established for selecting a best
`available system, determining whether the conditions for
`handoff have been satisfied, etc.
`
`[0055] According to a further embodiment, each of the
`settable preferences may also have a default value built into
`the mobile client software, which is overridden by the values
`provided by the primary service provider in the configura-
`tion file. For example, the mobile client software would use
`these default values if the configuration file containing the
`service provider preference rules has not been downloaded.
`
`In another embodiment, a mobile user can specify
`[0056]
`a set of preferences, e.g., through a user interface provided
`by the mobile client. Preferably, the service provider pref-
`erence rules have priority over the user-defined preference
`rules. However,
`the user may be allowed to specify a
`preference for a certain type of systems according to certain
`criteria or conditions not addressed by the service provider
`preference rules.
`
`[0057] According to an exemplary embodiment, a service
`provider can set one or more of the following preferences:
`
`1) Preference for an initial system amongdifferent
`[0058]
`types of systems: This is applicable only if more than one
`system is available at
`the time a data session is being
`established; otherwise the mobile station would establish a
`data session with whichever system is available. (Example
`A:
`if both a valid 3G system and a 802.11 system is
`available, the 3G system is given preference; Example B: if
`both a high-speed wireline service and wireless system is
`available, the high-speed wireline is selected).
`
`2) Service level classifications: The service pro-
`[0059]
`vider preference rules may define a set of ranges to classify
`3G pilot El, into various service level categories (e.g.,
`“High,“Medium,’“Low,” and “Unavailable”). A set of
`sample rangesto classify 3G pilot E,/l, measurements (E,/I,
`meas) into various categories is listed below:
`[0060] High: 0 dB>=E,/I
`>=-4 dB
`
`[0061] Medium: -4 dB>=E,/I, ,..4.2=-7 dB
`[0062] Low: -7 dB>=E,,, meas? =—10 dB
`[0063] Unavailable: -10 dB>=E./1, jneas
`
`3) Data Bit Rate Classifications: As discussed
`[0064]
`above, E./I, and SNR measurements can each be converted
`into one of a set of maximum allowable databit rates for 3G
`
`and 802.11 systems, respectively. A preference rule may be
`defined by the service provider to classify the bit rates into
`various categories. An exampleof a rule classifying 802.11
`data bit rates is listed below:
`
`[0065] High: 11 Mbits/second
`
`[0066] Medium: 5.5 Mbits/second
`
`[0067] Low: 2 Mbits/second and 1 Mbits/second
`[0068] Unavailable: No service available.
`[0069]
`4) Preference for handoff among different types of
`systems: When more than one type of system is simulta-
`neously available, each of which are classified in the same
`service level category, a service provider rule may determine
`which type is preferred for handoff. For example, when the
`available systemsare limited to 802.11 and 3G networks, the
`following preference rule may be specified:
`[0070] 802.11);is preferred over 3Gy;.n3
`[0071]
`802.11,,.aium Is preferred over 3Gy,.ainm3 and
`Low
`Low:
`(0072]
`802.11,,,,,
`is preferred over 3G
`
`7
`
`

`

`US 2004/0142693 Al
`
`Jul. 22, 2004
`
`[0073] Such rules may be configuredas tablesstored in the
`mobile client. Three examples are given below with respect
`to Tables 1-3:
`
`EXAMPLE 1
`
`[0074] Rule: 802.11,4;,., is preferred over 3Gy5;.43
`
`[0075]
`
`[0076]
`
`802.11 \eaium Is preferred over 3Gy,.aium3 and
`802.11,,,,, is preferred over 3GLow’
`
`looking to handoff from a 3G system to an 802.11 system,
`a threshold may be set by the preference rules indicating a
`minimum RSSI (as measured by the mobile unit), which the
`selected 802.11 system must achieve in order to perform the
`handoff.
`
`[0084] However, if only one threshold is defined, a “ping-
`pong effect” may occur whereby the mobile station is
`repeatedly handed off between the two systems as the
`measured RSSI of the 802.11 network fluctuates above and
`below this threshold.
`
`TABLE1
`
`Rule Table for Example 1.
`
`[0085] Accordingly, the service provider preference rules
`may define two thresholds for the measured RSSI of the
`selected 802.11 system. A “high watermark” Twlan,, indi-
`cates an RSSI threshold at which the 802.11 system is
`
`deemed available for handoff. After satisfying the Twlan,,
`threshold, if the 802.11 system dips below a “low water-
`mark” Twlan,,, it is deemed no longeravailable for handoff.
`In an exemplary embodiment, these two thresholds can be
`defined as any values between -10 dBm to -120 dBm,
`where Twlan,, is greater than Twlan,,.
`
`3Grign—3GMedium=3Grow 3GUnavailable
`
`802.11sich
`802.11 sredium
`802.11;ow
`802.11unavailable
`
`802.11
`3G
`3G
`3G
`
`802.11
`802.11
`3G
`3G
`
`802.11
`802.11
`802.11
`3G
`
`802.11
`802.11
`802.11
`Work offline or sleep
`
`EXAMPLE2
`
`[0077] Rule: 802.11\,.aium 18 preferred over 3G)4;43 and
`
`[0078]
`
`802.11,,,,, is preferred over 3Gy,.aium-
`
`TABLE 2
`
`Rule Table for Example 2.
`
`6) Thresholds for handoff from an 802.11 system to
`[0086]
`a 3G system: A threshold may also be defined for the
`measured RSSI of a 3G system in order to effectuate a
`handoff from an 802.11 system to the 3G system. Further, in
`order to counter the ping-pong effect, a high watermark
`T3g,, and a low watermark T3g,,, may be defined for the 3G
`system. According to an exemplary embodiment, each
`watermark may be defined as any value between -10 dBm
`to -120 dBm,such that T3¢,;>T3¢,,.
`
`[0087]
`7) Time for monitoring systems: This preference
`defines T.,, a timer for monitoring the “channel quality and
`availability” of the channels of the available and serving
`wireless systems.
`
`
`
`3Gyignh 3Géedium=3Grow 3Gunavailable
`
`802.11seh
`802.11 Medium
`802.11,ow
`802.11pynavailable
`
`802.11
`802.11
`3G
`3G
`
`802.11
`802.11
`802.11
`3G
`
`802.11
`802.11
`802.11
`3G
`
`802.11
`802.11
`802.11
`Work offline or sleep
`
`EXAMPLE3
`
`[0079] Rule: 3G,y;.1 is preferred over 802.11pin
`
`[0080]
`
`[0081]
`
`3Gyjyeaium 1S preferred over 802.11 \jeaium
`Low
`Low
`
`is preferred over 802.11
`
`3G,,.,
`
`8) List of SLAs: A list ESSIDs for WLAN systems
`[0088]
`identify valid networks operators who have an SLA with the
`primary service provider to provide service for the mobile
`station. This list could either be dynamically loaded to the
`mobile client when the SLAs change, or statically down-
`loaded at the time of the mobile client configuration. Simi-
`larly, for wireline operators it may bea list of valid network
`operator IDs.
`
`TABLE 3
`
`Rule Table for Example 3.
`
`
`
`3Gyignh 3Géedium=3Grow 3GUnavailable
`
`It should be noted that the above list is not exhaus-
`[0089]
`tive, and may include rules regarding any other preferences
`that will be contemplated by those of ordinary skill in the art.
`For example, a service provider may define preferences with
`
`respect to the system loading conditions and/or network
`throughput of each system monitored by the SSA.
`
`802.11seh
`802.11 Medium
`802.11,ow
`802.11pynavailable
`
`3G
`3G
`3G
`3G
`
`802.11
`3G
`3G
`3G
`
`802.11
`802.11
`3G
`3G
`
`802.11
`802.11
`802.11
`Work offline or sleep
`
`these rule tables can be constructed
`[0082] Note that
`without knowingthe specific ranges for 802.11pions 3Gutigh>
`etc. Also, note that since these examples discuss two dis-
`parate systems
`they describe two dimensional
`tables.
`Depending on the number of disparate system