as) United States
`a2) Patent Application Publication co) Pub. No.: US 2005/0053034 Al
`Chiueh Mar.10, 2005 (43) Pub. Date:
`
`
`
`US 20050053034A1
`
`(54) SYSTEM AND METHOD FOR IP HANDOFF
`
`(52) US. Che ecceccesssscsseeseeseessesnseneesseenesnneeneees 370/331
`
`(76)
`
`Inventor: Tzi-cker Chiueh, East Setauket, NY
`(US)
`Correspondence Address:
`F. CHAU & ASSOCIATES, LLC
`130 WOODBURY ROAD
`
`WOODBURY, NY 11797 (US)
`(21) Appl. No.:
`10/815,443
`
`(22)
`
`Filed:
`
`Apr. 1, 2004
`
`Related U.S. Application Data
`(60) Provisional application No. 60/501,114,filed on Sep.
`8. 2003.
`,
`
`Publication Classification
`
`(SV) Tite C07 neceeccceecccceeeeesccenneeeececenneeeennee H04Q 7/00
`
`(57)
`
`ABSTRACT
`
`A seamless vertical handoff method allows the network
`applications and connections on a mobile node to continue
`without disruption as it moves within a wireless overlay
`network that comprises multiple possibly overlapping layers
`of wireless networks (e.g., a WLAN and a WWAN) with
`different underlying technologies, providing mobile roam-
`ing capabilities. The method comprises a WLAN access
`point signal strength monitor for determining whento switch
`between WLAN and WWAN,and a network connection
`migration scheme that can move an active network connec-
`tion from a wireless link of one technology to another
`wireless link of a different technology in a way that is
`transparent
`to the user,
`the remote end of the network
`connection, and the operator of the WWAN carrier.
`
`
`
`
`
`
`WWAN
`FOREIGN
`AGENT
`
`307
`
`~
`
`N
`
`‘“N
`
`
`WLAN
`
`
`
`
`FOREIGN
`WLAN
`|
`DEAD
`AGENT
`ZONE
`|
`‘ $06
`
`\
`
`
`MOBILE
`
`NODE
`7
`
`\
`
`\ X
`
`~~
`
`~—,
`
`—
`
`”
`
`\
`
`\
`
`\
`\
`|
`|
`/
`
`/
`
`/
`
`IPR2021-00297
`
`Bose Exhibit 1103
`Bose Exhibit 1103
`Bose v. Koss
`Bose v. Koss
`IPR2021-00297
`
`

`

`
`
`Input
`Devices
`
`
`
`Patent Application Publication Mar. 10,2005 Sheet 1 of 8
`
`US 2005/0053034 A1
`
`101
`
`
`
`
`

`

`Patent Application Publication Mar. 10,2005 Sheet 2 of 8
`
`US 2005/0053034 A1
`
`(/)APPLICATION 7PRESENTATION
`
`4
`tx ¥
`zOrZz<«
`wf
`9
`A
`VY
`Oo
`An
`2
`Ss
`NV
`9
`££ FE &
`Lu
`Ww
`FT
`non
`2
`fC
`
`kK
`
`fF
`
`
`
`
`
`
`
`
`
`
`<tc
`O
`
`
`
`CSV CS) GY) GY) CY)
`
`
`
`
`
`
`
`OSIPROTOCOLSTACK
`
`FIG.2(PriorArt)
`
`
`
`€
`

`

`Patent Application Publication Mar. 10,2005 Sheet 3 of 8
`
`US 2005/0053034 A1
`
`FOREIGN
`
`L
`
`=©L
`
`L
`or
`
`OL
`
`

`

`Patent Application Publication Mar. 10,2005 Sheet 4 of 8
`
`US 2005/0053034 A1
`
`/
`
`/
`
`/
`|
`
`S
`
`~
`
`yo
`
`~
`
`a
`
`x
`
`=
`
`
`
`zO
`Ww
`2
`
`\
`
`\
`
`\
`
`\
`
`]
`/
`/
`
`/
`
`ye
`eS
`~— 7 69
`us
`jon
`om
`
`ZONE
`
`=
`R
`
` FOREIGN
`
`

`

`Patent Application Publication Mar. 10,2005 Sheet 5 of 8
`
`US 2005/0053034 A1
`
`
`
`DETERMINING THE SIGNAL STRENGTH TO BE
`UNDESIRABLE AS COMPARED TO A THRESHOLD
`
`MONITORING WLAN SIGNAL STRENGTH
`
`
`
`
`
`INITIATING VERTICAL HANDOFF
`
`
`
`TUNNELING ACTIVE NETWORK CONNECTIONS
`
`
`
`CACHING AND REPLAYING INFORMATION
`OVER THE WWAN CONNECTION
`
`401
`
`402
`
`403
`
`404
`
`405
`
`408
`
`407
`
`ESTABLISHING A WWAN CONNECTION
`
`
`
`
`
`
`
`
`
`
`
`CACHING INFORMATION
`RECEIVED OVER THE WLAN
`
`
`FIG. 4B
`
`

`

`Patent Application Publication Mar. 10,2005 Sheet 6 of 8
`
`US 2005/0053034 A1
`
`403
`
`DETERMINE A SIGNAL STRENGTH OF SIGNAL OF A
`FIRST TYPE OF CONNECTIVITY TO BE LESS THAN
`OR EQUAL TO A THRESHOLD
`
`
`
`DETERMINE THAT A SIGNAL OF A SECOND
`TYPE OF CONNECTIVITY IS NEEDED
`
`
`
`REQUESTING A SIGNAL OF THE
`SECOND TYPE OF CONNECTIVITY
`
`01
`
`502
`
`503
`
`504
`
`SIGNAL OF THE SECOND TYPE OF CONNECTIVITY
`
`ESTABLISHING CONNECTIVITY THROUGH THE
`
`FIG. 5
`
`

`

`Patent Application Publication Mar. 10,2005 Sheet 7 of 8
`
`US 2005/0053034 Al
`
`06
`
`609
`
`
`
`
`
`
`
`dlalgo)dlaliqow
`
`909
`
`
`
`
`
`
`
`
`jouun,dOL-di—»/"
`
`
`
`jeuUunLdi-dl
`
`
`/uoleolunwwo5
`
`
`
`(“~~aeyiajuy[ENYA
`
`NVMPHOMENSd
`
`
`
`
`
` aoB}aqU]SYdO'.oP\AA
`
`9‘Old
`
`$09
`
`NVSS2[4I\\
`
`adepJa}U|
`
`Caen
`
`OMENSWOHd-
`
`
`
`
`
`

`

`Patent Application Publication Mar. 10,2005 Sheet 8 of 8
`
`
`
`
`
`NV1MO}SuduolsipedAquolsioeSud0}NVIMYOPUEH
`
`sinpow
`
`
`
`ysanbeyuoejysiGaydjSlgoy
`
`
`
`uondacedAQapousjiqo//\
`
`
`
`JeAJaqu!AYJIRH--feAuaqU!AGWBay
`
`ysanbayuonesjsibey4]aiqoyw
`
`
`
`SHdOuosjeyoedJapsojonO
`
`SWOQ0DL-SWD0P
`
`
`
`NVMUoJeyoedJsul4
`
`
`
`SUUQOL|-swoge
`
`
`Aideyuojedysibey|aIqow
`
`swood-suosebNV1Muouolssilusuel|
`
`
`
`
`
`
`
`Advjuabeublel0}SYd5payseg
`
`US 2005/0053034 Al
`
`LO14
`
`
`
`jeuun)qO4UOJeyoedJsuly
`
`
`
`
`
`
`
`A\dayuonedysibaydq]aIGoW
`
`
`

`

`US 2005/0053034 Al
`
`Mar. 10, 2005
`
`SYSTEM AND METHOD FOR IP HANDOFF
`
`[0001] This application claims the benefit of U.S. Provi-
`sional Application No. 60/501,114, filed Sep. 8, 2003.
`
`BACKGROUNDOF THE INVENTION
`
`[0002]
`
`1. Field of the Invention
`
`[0003] The present disclosure relates to wireless roaming,
`and more particularly to a system and method for vertical
`handoff in a wireless network.
`
`[0004]
`
`2. Discussion of Related Art
`
`[0005] Wireless connectivity is a burgeoning market in
`which consumers are coming to expect network access in a
`variety of venues, such as malls, hotels, public spaces,etc.
`Wireless Local Area Networks (WLAN) are providing the
`connectivity.
`
`[0006] Within these venues dead zones are a problem.
`Dead zones are pockets within a WLAN having reduced or
`no wireless signal for connecting to the network. As a
`mobile node movesinto a dead zone, any connection to the
`network will be substantially degraded or dropped. The dead
`zones detract from the users experience of wireless connec-
`tivity.
`
`[0007] One method of limiting dead zonesis to implement
`a network comprising different wireless technologies having
`different capabilities in a given geographic area. For a
`wireless device to move within such a network, a handoff is
`needed between wireless network cells to provide continu-
`ous connections to the network.
`
`[0008] Handoffs in wireless mobile networks can be char-
`acterized into two categories, horizontal handoff and vertical
`handoff. Horizontal handoff allows mobile nodes to move
`
`among wireless networkcells that support the same wireless
`link technology. Vertical handoff allows device movement
`within a network environmentthat comprises heterogeneous
`wireless links.
`
`[0009] Because vertical handoff involvesdifferent types of
`connections, e.g., 802.11 and General Packet Radio Service
`(GPRS), handing a connection from one cell to another is
`slow as compared to horizontal handoff, and detracts from a
`user’s wireless experience. For example, until
`the new
`connectionis established, the mobile nodeis cut off from the
`network. Further, packet
`loss or delay during a handoff
`interval can incorrectly trigger a congestion control mecha-
`nism at the senderside of any Transmission Control Protocol
`(TCP) connections in which the mobile node is involved,
`thus greatly slowing down the throughput.
`
`[0010] No known system or method exists for seamless
`vertical handoff between different wireless technologies.
`Therefore, a need exists for a system and method for
`performing a seamless vertical handoff.
`
`SUMMARYOF THE INVENTION
`
`[0011] According to an embodimentofthe present disclo-
`sure, a vertical handoff system comprises a first foreign
`agent providing connectivity to a network,the first foreign
`agent broadcasting a wireless local area network signal, and
`a second foreign agent providing connectivity to the network
`via a wireless wide area network signal. The system further
`comprises a mobile node comprising executable code for
`
`seamlessly performing a vertical handoff betweenthefirst
`foreign agent and the second foreign agent, and a home
`agent routing information to the mobile node through one of
`the first foreign agent and the second foreign agent accord-
`ing to an established connection of the mobile node.
`
`signal
`a
`{0012] The mobile node further comprises
`strength monitor. The mobile node comprises a buffer for
`caching information received throughthefirst foreign agent
`prior to establishing a connection with the second foreign
`agent.
`
`[0013] The second foreign agent comprises a buffer for
`caching information to be transmitted to the mobile node.
`
`[0014] The home agent comprises a router for routing
`information transmitted from the mobile node.
`
`[0015] The executable code for performing the vertical
`handoff includes a link status monitor for monitoring a
`signal strength of the wireless local area network signal. The
`link status monitor further includes a communication dae-
`
`monfor initiating the vertical handoff upon determining the
`signal strength to be undesirable and for establishing con-
`nectivity between a mobile internet protocol module of the
`mobile node and the second foreign agent.
`
`(0016] The wireless local area network connects wire-
`lessly to the mobile node via radio frequency electromag-
`netic airwaves.
`
`{0017] The wireless wide area network connects wire-
`lessly to the mobile node via one of Code Division Multiple
`Access, Global System for Mobile Communications, Gen-
`eral Packet Radio Service, Enhanced Data rate for Global
`Evolution, or Wideband Code Division Multiple Access.
`
`[0018] According to an embodimentof the present disclo-
`sure, a seamless vertical handoff method comprises estab-
`lishing a network connection to a networkhost via a wireless
`local area network, determining a strength of the wireless
`local area network connection to be at or below a threshold
`strength, and moving, seamlessly, the network connection to
`a wireless wide area network.
`
`Thetransition is transparent to a user and a remote
`[0019]
`end of the network connection.
`
`[0020] The moving comprises buffering packets at a home
`agent and pacing packets sent to a mobile node, wherein the
`network connection exists between the home agent and the
`mobile node.
`
`{0021] According to an embodimentofthe present disclo-
`sure, a method for vertical handoff in a wireless network
`vertical comprises monitoring a wireless local area network
`signal carrying an active network connection,
`initiating
`vertical handoff to a wireless wide area network signal upon
`determining that the wireless local area network signal is
`undesirable, tunneling the active network connection over
`the wireless wide area network signal, and caching and
`replaying information over the wireless wide area network
`signal.
`
`Initiating the vertical handoff comprises establish-
`[0022]
`ing a wireless wide area network connection to a mobile
`node. Initiating the vertical handoff comprises caching infor-
`mation received by a mobile node over the wireless local
`area network signal. The caching of information received
`
`

`

`US 2005/0053034 Al
`
`Mar. 10, 2005
`
`over the wireless local area network is performed before a
`wireless wide area network connection is established.
`
`[0036] FIG.3B is a diagram of a network according to an
`embodiment of the present disclosure;
`
`determining
`comprises
`further
`[0023] The method
`whether a second wireless local area network signal
`is
`desirable prior to initiating the vertical handoff. The method
`comprises initiating a horizontal handoff upon determining
`that the second wireless local area network signal is desir-
`able.
`
`[0024] The method comprises initiating vertical handoff
`from the wireless wide area network signal to the wireless
`local area network signal upon determiningthat the wireless
`local area network signal is desirable.
`
`[0025] Desirability corresponds to a threshold for measur-
`ing strength of a wireless signal.
`
`[0026] Tunneling includes redirecting a signal of a client
`side mobile internet protocol implementation from the wire-
`less local area network signal to the wireless wide area
`networksignal.
`
`[0027] Tunneling includes providing a communication
`agent using a protocol to talk to home agent and mobile
`node.
`
`[0028] Tunneling includes providing a mobile internet
`protocol foreign agent for communicating with a mobile
`node and a home agent, establishing a forwarding tunnel
`between the home agent and the mobile node, authenticating
`the mobile node, and updating a routing table to route
`packets.
`
`[0029] Tunneling includes tunneling packets from a home
`agent directly to a mobile node.
`
`[0030] Tunneling includes intercepting traffic going to a
`mobile node belonging to an enterprise, and establishing a
`tunnel between the mobile node and a network address
`
`translation gateway, wherein communications between a
`mobile node and a communicating party is via the network
`address translation gateway.
`
`[0031] According to an embodimentof the present disclo-
`sure, a program storage device is provided, readable by
`machine,
`tangibly embodying a program of instructions
`executable by the machine to perform method steps for
`vertical handoff in a wireless network. The method steps
`comprising monitoring a wireless local area network signal
`carrying an active network connection, initiating vertical
`handoff to a wireless wide area network signal upon deter-
`mining that the wireless local area network signal is unde-
`sirable, tunneling the active network connection over the
`wireless wide area network signal, and caching and replay-
`ing information over the wireless wide area network signal.
`
`BRIEF DESCRIPTION OF THE FIGURES
`
`[0032] Preferred embodiments of the present invention
`will be described below in more detail, with reference to the
`accompanying drawings:
`
`[0033] FIG. 1 is a diagram of a system according to an
`embodimentof the present disclosure;
`
`[0034] FIG. 2 is a diagram of an OSIstack;
`
`[0035] FIG. 3A is a diagram of a network according to an
`embodimentof the present disclosure;
`
`[0037] FIG. 4Ais a flow chart of a method according to
`an embodimentof the present disclosure;
`
`[0038] FIG. 4B is a flow chart of a method according to
`an embodimentof the present disclosure;
`
`[0039] FIG.5 is a flow chart of a method according to an
`embodimentof the present disclosure;
`
`[0040] FIG.6 is an illustration of a system architecture
`according to an embodimentof the present disclosure; and
`
`{0041] FIG.7 is a Gant chart according to an embodiment
`of the present disclosure.
`
`DETAILED DESCRIPTION OF PREFERRED
`EMBODIMENTS
`
`[0042] To support seamless vertical handoff between a
`wireless wide area network (WWAN), such as GPRS, and a
`wireless local area network (WLAN), a WLAN linkstatusis
`monitored to determine whether to use WLAN technology
`or a WWAN link. A Mobile IP (internet protocol) imple-
`mentation is provided for establishing connectivity to the
`WLAN link, and packet scheduling and buffering mecha-
`nisms arc supported to accommodate transmission charac-
`teristics of the WWAN link. Link monitoring may be carried
`out by an external software module, which in turn triggers
`network-layer handoff supported by Mobile IP when a
`vertical handoff is needed. The Mobile IP implementation
`may be used whetheror not a foreign agent for WWAN link
`and a mobile node are on the same subnet.
`
`[0043] According to an embodimentofthe present disclo-
`sure a heterogeneous wireless network comprises two for-
`eign agents using different, possibly overlapping, wireless
`transmission technologies. A first foreign agent is based on
`a WLAN.In a WLAN there are no physical connection
`wires needed between the mode node andthe infrastructure.
`
`The signals are sent using radio frequency electromagnetic
`airwaves. The Institute of Electrical and Electronics Engi-
`neers (IEEE) 802.11a, b, and g are WLAN standards and
`may bereferred to as Wi-Fi.
`
`[0044] Asecond foreign agent provides connectivity via a
`WWAN,
`for example, Code Division Multiple Access
`(CDMA), Global System for Mobile Communications
`(GSM), GPRS, Enhanced Data rate for Global (or GSM)
`Evolution (EDGE) and Wideband-CDMA.
`
`[0045] An example of a heterogeneous wireless networkis
`a wireless overlay network,
`in which different wireless
`technologies co-exist in the same geographical area, for
`example, infrared/Bluetooth for personal area networking,
`802.11 based WLAN forlocal area networking, and cellular
`communication networks for wide area networking. A wire-
`less overlay network permits a user to chooseto use the most
`appropriate wireless link technology to satisfy a need.
`Throughout
`the disclosure the term connection includes
`wired and/or wireless communications links unless other-
`wise specified.
`
`[0046] Each foreign agent is connected to a home agent
`across an IP network, such as the Internet. A mobile node,
`such as a laptop computer, is capable of connecting to the
`first foreign agent and/or the second foreign agent. Further,
`
`

`

`US 2005/0053034 Al
`
`Mar. 10, 2005
`
`the mobile node comprises functionality for monitoring the
`signal strength of packets from the foreign agent on the
`WLAN,and upon determining a weakening signal, seam-
`lessly moving the user’s on-going network connections to
`another foreign agent
`that has a more desirable signal,
`without disrupting the continuity of these connections. Sig-
`nal strength can be measured in decibels compared to one
`milliwatt (or dBm). Various known techniques exist for
`measuring signal strength, and typically client software for
`operating a wireless network interface comprises a signal
`strength monitor. The desirability of the signal is related to
`signal strength. The mobile node determinessignal strength
`for one or more available signals provided by respective
`foreign agents, and selects a signal among the one or more
`signals according to strength. Othercriteria for selecting a
`signal can include, for example, signal strength over time,
`e.g., whether the signal is becoming stronger or weaker over
`time, and user preferences for particular foreign agents.
`
`[0047] According to an embodimentof the present disclo-
`sure, the seamless vertical handoff occurs without user input.
`The user does not need to be aware that a handoff has
`happened. Further, upon detecting that the signalof the first
`foreign agent, or any other WLAN foreign agent, has
`reached a desirable strength, the mobile node can perform a
`handoff back to the WLAN signal.
`
`[0048] Further, connectivity providers, e.g., WWAN ser-
`vice providers operating WWAN foreign agents, may not
`need to implement changes to accommodate the mobile
`node. The system and/or method of the mobile node may be
`independent of the WWAN service provider.
`
`[0049] The ability to automatically and seamlessly switch
`between different foreign agents, regardless of their under-
`lying connectivity technology and their operators, enables a
`mobile node to maintain connectivity at all times and at a
`lowercost. That is, cellular network usage is typically more
`expensive than that of WLAN connectivity. Seamless hand-
`off makes it possible for users to use WLAN connectivity
`whenit is determined to be desirable while enjoying con-
`tinuous connectivity.
`
`general-purpose computer system that becomes a specific
`purpose computer system when executing the routine 107 of
`the present invention.
`[0052] The mobile node 101 also includes an operating
`system and micro instruction code. The various processes
`and functions described herein may either be part of the
`micro instruction code orpart of the application program (or
`a combination thereof), which is executed via the operating
`system. In addition, various other peripheral devices may be
`connected to the computer platform such as an additional
`data storage device and a printing device.
`[0053]
`It is to be further understood that, because some of
`the constituent system components and method steps
`depicted in the accompanying figures may be implemented
`in software,
`the actual connections between the system
`components (or the process steps) may differ depending
`upon the manner in which the present invention is pro-
`grammed. Given the teachings of the present
`invention
`provided herein, one of ordinary skill in the related art will
`be able to contemplate these and similar implementations or
`configurations of the present invention.
`[0054] According to an embodimentofthe present disclo-
`sure, handoff can take place at different layers of the Open
`Standards Interconnect (OSI) protocol stack. An example of
`the OSI protocol stack is shown in FIG.2. The functions of
`each layer of the OSI are well known in the art. When a
`mobile node switches from one WLAN cell
`to another
`
`WLAN cell, the network interface hardware performs the
`link-layer handoff, which changes the association of the
`mobile node from one access point to another. To maintain
`un-disrupted network service, the mobile node performs a
`network-layer handoff, which ensures that the device can
`continue to communicate with other Internet hosts even
`when the mobile node movesinto a different subnet.
`
`[0055] According to an embodimentofthe present disclo-
`sure, and referring to FIG. 3A, a homeagent 301 and foreign
`agents 302-303 are connected on a wired network. The
`WLAN foreign agent 302 periodically broadcasts Mobile IP
`advertisements on the WLAN to which a mobile node 101
`is attached.
`
`It is to be understood that the present invention
`[0050]
`[0056] For horizontal handoff in the network, whenever a
`may be implemented in various forms of hardware, soft-
`mobile node migrates fromafirst subnet to a second subnet,
`ware, firmware, special purpose processors, or a combina-
`it starts receiving the Mobile IP advertisements from the
`tion thereof. In one embodiment, the present invention may
`second subnet’s corresponding WLAN foreign agent. The
`be implemented in software as an application program
`Mobile IP software running on the mobile node intercepts
`tangibly embodied on a program storage device. The appli-
`these advertisements and sends a registration request to a
`cation program maybe uploaded to, and executed by, a
`newly discovered WLAN foreign agent of the second sub-
`machine comprising any suitable architecture.
`net. After authentication and consultation with the home
`
`[0051] Referring to FIG. 1, a mobile node 101, such as a
`laptop computer or handheld device, for implementing the
`present invention can comprise, inter alia, a central process-
`ing unit (CPU) 102, a memory 103 and an input/output(I/O)
`interface 104. The computer system 101 is generally coupled
`through the I/O interface 104 to a display 105 and various
`input devices 106 such as a mouse and keyboard. The
`support circuits can include circuits such as cache, power
`supplies, clock circuits, and a communications bus. The
`memory 103 can include random access memory (RAM),
`read only memory (ROM), disk drive, tape drive, etc., or a
`combination thereof. The present invention can be imple-
`mented as a routine 107 that is stored in memory 103 and
`executed by the CPU 102 to process the signal from the
`signal source 108. As such,
`the mobile node 101 is a
`
`agent, an IP-over-IP tunnelis established between the home
`agent and the new WLAN foreign agent. Tunneling
`includes,
`for example, encapsulating one packet within
`another packet. Various methods for tunneling exist, includ-
`ing, for example, the Layer 2 Tunneling Protocol and the
`Point-to-Point Tunneling Protocol. More generally, tunnel-
`ing is described in RFC 1853, wherein an outer IP headeris
`added before the original IP header. Between the outer IP
`header and the original IP header any other headers for the
`path, such as security headers specific to the tunnel configu-
`ration may be added. The outer IP header includes source
`and destination information identifying the endpoints of the
`tunnel. The inner IP header includes source and destination
`information identifying the original sender and recipient of
`the datagram.
`
`

`

`US 2005/0053034 Al
`
`Mar. 10, 2005
`
`[0057] For a mobile node to move across IP subnets and
`maintain all the active network connections, an indirection
`mechanism is needed to channel packets between the mobile
`node and the parties it is communicating with. The packet
`indirection mechanism enables a mobile node to keep its IP
`address unchanged regardless of its geographic location.
`The packet indirection mechanism is notified whenever the
`mobile node movesinto a different subnet, wherein it can
`adjust the redirection parameter accordingly.
`
`[0058] Mobile IP is an example of a packet indirection
`mechanism. Mobile IP has been extended to implement
`vertical handoff. The extension includes a WLAN link
`
`status-monitoring module to the mobile node. In the Mobile
`IP framework, a foreign agent channels packets between a
`mobile node and its home agent, and a mobile nodeandits
`foreign agent typically reside on the same subnet. Unlike
`WLAN,it is unlikely that the GPRSlink’s foreign agent can
`reside on the same site as mobile node, because the GPRS
`service provider does not necessarily support Mobile IP. A
`tunnel may be established between a mobile node andits
`GPRS link’s foreign agent
`to channel
`traffic between a
`mobile node and its communicating parties. Note that this is
`in addition to the IP-IP channel between a foreign agent and
`home agent in Mobile IP.
`
`[0059] While one end of this tunnel alwaysresides in the
`mobile node,
`there are at
`least
`three possible ways to
`implement the other end of the tunnel. First, it could be a
`special communication agent, which uses a proprietary
`protocol to talk to home agent and mobile node. Second,it
`could be a generic Mobile IP foreign agent that communi-
`cates with mobile node and home agent in a standard way,
`and sets up a forwarding tunnel between home agent and
`mobile node, authenticates the mobile node, and updatesits
`ownrouting table to route packets appropriately. Support is
`added for tunneling with mobile nodeto the existing foreign
`agent implementation. Third, the home agent can directly
`tunnel packets to a mobile node without the help of any
`intermediate agent.
`
`It is also possible to implement vertical handoff in
`[0060]
`a waythat is independent of Mobile IP. For example, within
`network address translation (NAT) technology for packet
`interception and redirection an enterprise-wide NAT gate-
`way may be usedto intercept traffic going to mobile nodes
`belonging to the enterprise. A tunnelis set up between each
`mobile node and the NAT gateway so that the communica-
`tions between a mobile node and its communicating parties
`always go through the NAT gateway. Whenever a mobile
`node changesits IP address, it informs the NAT gateway so
`that the old tunnel can be torn down and a new tunnel can
`be established. Since this tunnel can run over a WLAN,as
`well as a GPRSlink, this architecture provides a unified
`framework for both vertical and horizontal handoff. A new
`
`IP address may be acquired through DHCP for example.
`Further, an authentication protocolis issued between mobile
`node and NAT gateway.
`
`[0061] For a Mobile IP implementation for vertical hand-
`off the access point of a WWAN linkis typically a layer-3
`dial-up server, rather than a layer-2 bridge, as in the case of
`a WLAN accesspoint. As shown in FIG. 3B, as the mobile
`node 101 exits the service area 306 of the WLAN foreign
`agent, it detects that the signal strength of the WLAN is
`decreasing. Upon determining that the signal strength is
`
`equal to or less than a first threshold strength, the mobile
`node initiates a handoff. If no WLAN foreign agents are
`present with a signal strength above a secondthreshold,e.g.,
`a 10% abovethefirst threshold, the mobile node initiates a
`vertical handoff. The mobile node 101 establishes a new
`
`connection with the WWAN foreign agent 303 (e.g.,a GPRS
`foreign agent), and tunnelsall its active network connections
`on this new connection while maintaining its IP address.
`Because the WWAN interface of the mobile nodeis typically
`behind a NAT gateway,the tunnel between the mobile node
`and the WWAN foreign agent is a TCP tunnel, rather than
`the [P-over-IP tunnel. The round-trip delay on a WWAN
`link, such as GPRS, may be long; the numberofinteraction
`messages between a mobile node and the WWAN foreign
`agent should be reduced to the minimum. WWAN foreign
`agent advertisements are cached and replayed to the mobile
`node so that interactions between the WWAN foreign agent
`and the mobile node conform to a Mobile IP specification.
`Thus, the vertical handoff latency is reduced to one round-
`trip delay on the WWAN link. To minimize packet loss
`during a vertical handoff interval, a mobile node mayinitiate
`a vertical handoff anticipatively so that it can buffer addi-
`tional packets from the WLAN foreign agent while it
`switches to the WWAN foreign agent.
`In addition,
`the
`WWAN foreign agent also buffers packets from the home
`agent. The packets are paced at a controlled rate on the
`WWAN link so that packet drops are mimimized. Through
`both buffering andtraffic shaping, packet loss is reduced to
`substantially zero.
`
`[0062] When a mobile node uses a GPRSlink,it needs to
`obtain an IP addressfor its GPRS device. Because of lack of
`
`public IP addresses, the GPRS service provider typically
`uses an NAT gateway to translate between public IP
`addresses and addresses assigned to mobile nodes’ GPRS
`devices. Thus, a mobile node initiates all network connec-
`tions it has with the outside world through GPRS. A mobile
`node decapsulation mode and co-located care of address
`mechanism are not used whenthereis no foreign agentin the
`infrastructure. In mobile node decapsulation mode, an IP-
`over-IP tunnel is established directly between a mobile node
`and the home agent without an intermediate foreign agent.
`Oneend point of the tunnel is bound to the IP address of a
`mobile node, which is typically obtained through a standard
`protocol such as DHCP or someotherstatic address assign-
`ment mechanism.
`
`inbound packets to reach a mobile node
`[0063] For
`through an NAT gateway, they need to be part of a connec-
`tion initiated by the mobile node. An IP-over-TCPtunneling
`mechanism may be used. The mobile nodeinitiates the TCP
`tunnel so that the NAT gateway on the GPRS network can
`allow bidirectionaltraffic in this connection. Use of TCP for
`tunneling ensures that the tunneled data reaches the desti-
`nation in a reliable manner.
`
`[0064] A virtual network device, tcptun, is used that is
`exposed to Mobile IP software. This virtual device imple-
`ments the TCP tunneling mechanism overan already estab-
`lished TCP connection with the GPRS foreign agent. It also
`emulates the activities of a network interface for all inbound
`
`packets received over the TCP connection, thus enabling
`connectivity over a LAN with the GPRS foreign agent.
`Whena vertical handoff between the WLAN interface and
`
`

`

`US 2005/0053034 Al
`
`Mar. 10, 2005
`
`the GPRSinterface is needed, a horizontal handoff is trig-
`gered between the WLAN interface and the virtual device
`for GPRSinterface.
`
`[0065] The homeagent 301 acts as a proxy for the mobile
`node 101, intercepting incoming packets intended for the
`mobile node 101 and transmitting the incoming packets to
`the WLAN foreign agent 302 over an [P-over-IP tunnel. The
`foreign agent decapsulates the packets coming from the
`tunnel and forwards the packets to the mobile node. Simi-
`larly, packets that a mobile node transmits are received by
`the WLAN foreign agent and are tunneled over to the home
`agent 301, which further routes them to the true destination
`on the Internet 305.
`
`[0066] The home agent 301 is a node in the home subnet
`that provides a fixed IP address abstraction for mobile nodes.
`Each foreign agent 302-303 is an indirection point for
`routing. The tunnel is between the home agent and a foreign
`agent. A WLAN foreign agent is associated with a wireless
`access network, and periodically broadcasts advertisements
`to announce its presence to mobile nodes. Accordingly, the
`mobile nodes are mobility aware of the WLAN environ-
`ment. When a mobile nodeis in a foreign subnet, the mobile
`node communicates with Internet hosts through triangle
`routing.
`
`[0067] Triangle routing is a process of sending and receiv-
`ing packets to the mobile node. Although a mobile node does
`not need to send packets via its home agent,
`tunneling
`out-going packets to the home agentis a preferred mode of
`routing because it avoids various issues such as ingress and
`egress filtering that the firewalls at the foreign and home
`sites perform. Whenever a mobile node migrates to a new
`foreign subnet, it binds with the foreign agent of the new
`foreign subnet, and tears down the association with the
`foreign agent in the old subnet. When a mobile node returns
`to its home subnet, standard routing is resumed. The process
`of switching from one foreign agent to another as a mobile
`node movesacross adjacent wireless IP subnets is Mobile IP
`handoff.
`
`[0068] The mobile node preserves its own IP address
`while roaming between horizontal and vertical agent. No
`modification may be needed for non-mobile nodes, e.g.,
`other devices connected to the network, to communicate
`with the mobile node.
`
`there could be multiple network
`In Mobile IP,
`[0069]
`interfaces in a mobile node, but only one of the active
`interfaces may be used for external communication. An
`interface is active if advertisements from some mobile agent
`are received on that interface. The mobile node assumesthe
`
`task of triggering a Mobile IP handoff, where a mobile node
`switches from WLAN interface to the virtual interface or
`vice versa.
`
`[0070] To make effective use of WLAN bandwidth and
`GPRS link bandwidth, the mobile node makes the handoff
`decisions