Title of Invention

A WIRELESS COMMUNICATION SYSTEM FOR PROVIDING IMPROVED HANDOFFS IN WIRELESS COMMUNICATION NETWORKS AND A METHOD FOR PERFORMING A HANDOFF IN A MOBILE COMMUNICATION SYSTEM

Abstract FOR PERFORMING A HANDOFF IN A MOBILE COMMUNICATION SYSTEM Methods and systems are provided for using a packet data serving node (PDSN) (341) in a wireless communication network that includes multiple logical PDSNs (342-345) each of which is associated with a particular IP address and corresponding physical interface (352-355). Through the use of multiple logical PDSNs (342-345) and interfaces (352-355), the throughput of the PDSN may be substantially increased. Additionally, the multiple logical PDSNs (342-345) and interfaces (352-355) may be used to provide redundancy in order to protect against software or hardware failures. A problem with prior art systems are that the PDSNs cannot provide as much throughput nor can they reduce the likelihood of hard handoffs. According to the methods and systems of the invention, moreover, the risk of internal hard handoffs resulting from the use of a PDSN (341) having multiple logical PDSNs (342-345) is eliminated or at least substantially reduced.
Full Text

A Wireless Communication System For Providing Improved Handoffs
In Wireless Communication Networks And A Method For Performing
A Handoff In A Mobile Communication System"
Cross Reference to Related Application
[0001] This application claims the benefit under 35 U.S.C. ยง 119(e) of United States
Provisional Patent Application No. 60/488,152, filed July 17,2003, which is hereby
incorporated by reference herein in its entirety.
Field of the Invention
[0002] The present invention relates to wireless communication networks. More
particularly, this invention relates to improved handoffs in wireless communication networks
that use one or more packet data serving nodes (PDSNs) having multiple IP addresses.
Background of the Invention
[0003] Wireless communication systems and networks are used in connection with
many applications, including, for example, satellite communications systems, portable digital
assistants (PDAs), laptop computers, and portable communication devices (e.g., cellular
telephones). One significant benefit that wireless communication networks provide to a user
of such an application is the ability to connect, or stay connected to, a network (e.g., the
Internet) as long as the user is within range of the wireless communication network.
[0004] Three major access techniques have been developed which are used to share
the available bandwidth in a wireless communication system. Two of these techniques are
referred to as time division multiple access (TDMA) and frequency division multiple access
(RDMA). In TDMA systems, two or more signals (e.g., voice or data signals) share a single
channel. In particular, in TDMA systems, multiple signals are transmitted over the same
channel by allocating to the transmission of each signal a different time interval. InFDMA
systems, on the other hand, the available frequency spectrum is divided into narrow channels,
where each signal to be transmitted is assigned to a respective channel. The third technique,
which is most relevant to the invention and is described below, is referred to as code division
multiple access (CDMA).
[0005] CDMA systems operate by dividing a radio spectrum to be shared by multiple
users through the assignment of unique codes. CDMA systems assign a unique code to each
signal that is to be transmitted, and are thereby able to spread many simultaneous signals

across a wideband spread spectrum bandwidth. Using the respective codes, the signals can
then be detected and isolated from the other signals that are being transmitted over the same
bandwidth.
[0006] FIG. 1 is a simplified illustration of one embodiment of a CDMA wireless
communication system 100 in which the present invention may be implemented. As the main
features of wireless communication system 100 are well know to those versed in the art, only
a brief description of its components will now be provided. Further explanation will be
provided below as necessary to aid the understanding of the principles of the present
invention described herein.
[0007] As shown, wireless communication system 100 includes a plurality of mobile
subscribers (MSs) 101-109. Mobile MSs 101-109, which are also known as mobile stations,
mobile nodes, and by other names, each function as an Internet Protocol (IP) client (Simple
IP and/or Mobile IP, as explained below). MSs 101-109 may each be any suitable device that
is capable of communicating with a wireless network, such as a cellular telephone or a laptop
computer with a wireless modem.
[0008] Wireless communication system 100 also includes a plurality of base stations
or base transceiver stations (BTSs) 111-113 for managing wireless links to MSs 101-109.
BTSs 111-113 act as the interface between the network and MSs 101-109, in that they
convert digital data into radio signals and vice versa. Although not shown, each of
BTSs 111-113 generally has an associated radio tower or antenna and communicates with
various MSs 101-109 using radio links. In particular, BTSs 111-113 communicate with
various MSs 101-109 through the modulation and transmission of sets of forward signals,
while BTSs 111-113 receive and demodulate sets of reverse signals from various MSs 101 -
109 that are engaged in a wireless network activity (e.g., a telephone call, Web browsing
session, etc.).
[0009] As shown in FIG. 1, BTSs 111-113 connect to one or more base station
controllers (BSCs) 121-122 (e.g., using un-channelized Tl facilities or direct cables, although
this is not required). BSCs 121-122 are used to interface (aggregate) all radio frequency (RF)
traffic arriving from the antennas of BTS 111-113, and to provide this traffic to a mobile
switching center (MSC) 123. As known in the art, BSCs 121-122 are generally responsible
for managing the radio resources for one or more BTSs 111-113. For example, BSCs 121-


122 may handle radio-channel setup, frequency hopping, and handovers (which are described
below). Moreover, MSC 123 is responsible for providing the interface between the radio
access network (RAN), which includes BTSs 111-113, BSCs 121-122, and PCFs 131-132,
and a public switched telephone network (PSTN). In particular, MSC 123 controls the
signaling required to establish calls, and allocates RF resources to BSCs 121-121 and packet
control functions (PCFs) 131-132.
[0010] PCFs 131-132 are used to route IP packet data between MSs 101-109 (when
within range of one of BTSs 111-113) and packet data service nodes (PDSNs) 141-143.
PDSNs 141-143, in turn, are used to provide access to one or more IP networks 151-153,
which may be, for example, the Internet, intranets, applications servers, or corporate virtual
private networks (VPNs). In this manner, PDSNs 141-143 acts as an access gateway.
Although not shown in FIG. 1, PDSNs 141-143 generally also act as a client for
Authentication, Authorization, and Accounting (AAA) AAA servers. As known in the art,
AAA servers are used to authenticate and authorize MSs 101-109 before access is granted to
one of IP networks 151-153.
[0011] It will be understood that nine MSs 101-109, three BTSs 111-113, two
BSCs 121, two PCFs 131-132, and three PDSNs 141-143 have been shown in FIG. 1 solely
for the sake of adding clarity to the description of the present invention. Persons versed in
the art will appreciate, however, that the invention is not limited by the particular number of
these components that exist in wireless communication system 100. Moreover, it will be
understood that, although not shown in FIG. 1, various MSs 101-109 may have radio
connections with more than one of BTSs 111-113. Similarly, a single PCF 131-132 may
support more than one of BSCs 121-133 in wireless communication system 100. Persons
versed in the art will also appreciate that, although the invention is described with reference
to PDSNs 141-143, the principles of the present invention discussed herein can be used with
other types of network access servers (NASs). In particular, it should be understood that the
invention is applicable to any current or future access technologies where MSs 101-109 use
the point-to-point (PPP) protocol as a client access protocol with an access gateway.
[0012] As known by those versed in the art, two modes of operation are typically
offered by a PDSN 141-143. These two modes of operation are often referred to as the
"Simple IP" mode and the "Mobile IP" mode, both of which are described in greater detail
below. In either mode, the act of an MS 101-109 moving between different PCFs 131-132

and keeping the same PDSN 141-143 is termed a "soft handoff." The act of an MS 101-109
moving between PCFs 131-132 and also switching physical PDSNs 141-143, on the other
hand, is termed a "hard handoff." Similarly, in prior wireless communication systems, a
"hard handoff will result anytime the IP address of a PDSN 141-143 changes for a call (even
if the same physical PDSN 141-143 remains in use).
[0013] In general, hard handoffs are undesirable in both the Simple IP mode and the
Mobile IP mode. In the case of Simple IP, a hard handoff requires the renegotiation of all
call-related access processing parameters (e.g., Al 1, PPP, and IP). As known by those versed
in the art, renegotiation of such parameters is both time consuming and disruptive to data
applications that may be running on the MS 101-109. In the case of Mobile IP, a hard
handoff requires the same renegotiation of the call processing parameters as in the Simple IP
case plus Mobile IP parameters. However, this procedure is less disruptive to data
applications as the MS 101-109 is able to retain the same assigned IP address, and mere is no
disruption of the data path for the MS 101-109.
[0014] Due to the undesirability of hard handoffs, PDSNs 141-143 have typically
been designed to have only a single IP address and a single corresponding physical (layer 3)
interface. This is due in large part to prevent the occurrence of an "internal hard handoff,"
which refers to the case where a hard handoff is thought to have occurred (and the handoff is
treated as such) even though an MS 101-109 has not moved to a new PDSN 141-143. For
example, in the case of a PDSN 141-143 having multiple IP addresses, an internal hard
handoff may occur when an MS 101-109 roams from a first PCF 131-132 to a second
PCF 132, and the second PCF 132 mistakenly uses a the wrong (i.e., a different) IP address of
the same PDSN 141-143. However, the use of only a single IP address and interface for a
PDSN 141-143 significantly and undesirably limits the throughput of the PDSN 141-143.
That is, the throughput of the PDSN 141-143 is limited to the bandwidth provided by the
single physical interface. Additionally, the use of only a single IP address and interface for a
given PDSN 141-143 makes it impossible (or at least much more difficult) to provide a
desired level of redundancy to protect against the effects of software or hardware failures.
[0015] Accordingly, it is desirable to provide systems and methods for using
PDSNs 141-143 in a wireless communication system 100 that include multiple IP addresses,
and multiple corresponding physical interfaces, while eliminating or at least substantially
reducing the likelihood of internal hard handoffs.


Summary of the Invention
[0016] In accordance with the principles of the present invention, systems and
methods are provided for using PDSNs 141-143 in a wireless communication network 100
that include multiple IP addresses and multiple corresponding physical interfaces. Through
the use of multiple IP addresses and interfaces, the throughput of a PDSN 141-143 may be
substantially increased. Additionally, the multiple P addresses and interfaces may be used to
provide redundancy in order to protect against software or hardware failures. According to
the systems and methods of the invention, moreover, the risk of internal hard handoffs
resulting from the use of a PDSN having multiple IP addresses and interfaces is eliminated or
at least substantially reduced.
[0017] In one embodiment, the invention provides a wireless communication system
that includes a first BTS that is associated with a first PCF and a second BTS that is
associated with a second PCF, a PDSN having multiple IP addresses, and an MS mat uses the
first PCF to establish a first session using a first IP address of the PDSN when in an area
being served by the first BTS and that uses the second PCF to establish a second session with
a second IP address of the PDSN when in an area served by the second BTS, where the
handoff between the first IP address and the second IP address of the PDSN is treated as a
soft handoff.
[0018] In a second embodiment, the invention provides systems and methods for
performing a handoff in a mobile communication system that uses a PDSN having more than
one IP address, wherein the method includes establishing a first session, for a MS in the
mobile communication system, using a first IP address of the PDSN, and establishing a
second session, for the MS, using a second IP address of the PDSN, where the handoff
between the first IP address and the second IP address of the PDSN is treated as a soft
handoff.
[0019] In a third embodiment, the invention provides a wireless communication
system that includes means for establishing a first session, for a mobile station (MS) in the
mobile communication system, using a first IP address of the PDSN, means for establishing a
second session, for the MS, using a first IP address of the PDSN, and means for treating the
handoff between the first IP address and the second IP address of the PDSN as a soft handoff.


[0020] In a fourth embodiment, the invention provides a PDSN having multiple IP
addresses for use in a wireless communication system, the PDSN having a first session with a
mobile station (MS) using a first of its IP addresses and a second session with the same MS
using a second of its IP addresses, wherein the handoff between the first IP address and the
second IP address of the PDSN is treated as a soft handoff.
[0021] Additional embodiments of the invention, its nature and various advantages,
will be more apparent upon consideration of the following detailed description, taken in
conjunction with the accompanying drawings, in which like reference characters refer to like
parts throughout:
[0022] FIG. 1 is a simplified illustration of one embodiment of a CDMA wireless
communication system 100 in which the present invention may be implemented;
[0023] FIG. 2 is a simplified illustration showing the data flow associated with a
typical Mobile IP session;
[0024] FIG. 3 is a simplified illustration of a single physical PDSN with n different IP
addresses;
[0025] FIG. 4 is a flow chart illustrating the steps performed according to one
embodiment of the present invention in eliminating or at least substantially reducing the
likelihood of internal hard handoffs when using a PDSN such as the one illustrated in FIG. 3;
and
[0026] FIG. 5 is a more detailed flow chart of the fourth step depicted in FIG. 4
according to one embodiment of the present invention.
Detailed Description of the Invention
[0027] An important goal in wireless communication system 100 is to provide
MSs 101-109 with a durable IP address that persists even as an MS 101-109 moves with from
one cell, which refers to the area covered by a BTS 111-113, to another cell (thus breaking a
point-to-point radio connection and making a new one). PDSNs 141-142 offer two modes of
operation relating to IP address mobility. These two modes, as mentioned above, are Simple
IP and Mobile IP. As the systems and methods described herein according to the present


invention are useful to enhance the operation of both the Simple IP and the Mobile IP modes,
a summary of these modes is first provided.
[0028] Simple IP, which provides a relatively low level of IP address mobility, is
specified in IS-835, which is hereby incorporated by reference herein in its entirety. In
general, Simple IP allows multiple cells to be connected to a single PDSN 141-143. Thus, as
long as MS 101-109 moves only among these cells (i.e., within a restricted geographic
region), the PDSN 141-143 is able to keep track of the MS 101-109 and assign it the same IP
address each time it reconnects via a new cell. For example, if one of MSs 101-109 moves
from one PCF 131-132 to another PCF 131-132 but remains with the same PDSN 141-143
(as in the case of a soft handoff), then the MS 101-109 is able to retain the same IP address
when it reconnects to the PDSN 141-143 using the second PCF 131-132. However, if an
MS 101-109 moves to a cell that is handled by a different PDSN 131-132 (as in the case of a
hard handoff), a new IP address will need to be assigned, resulting in a temporary loss of
network connection. As mentioned above, in prior wireless communication systems, a
similar result may be obtained when the MS 101-109 remains with the same physical
PDSN 141-143 but has been assigned to a different one of the multiple IP addresses of the
PDSN 141-143.
[0029] Mobile IP, which unlike Simple IP provides mobility even across service
providers and PDSNs, is specified in IS-835 and RFC-2002, which are hereby incorporated
by reference herein in their entirety. In general, Mobile IP enables an MS 101-109 to move
from cell to cell, even into cells supported by different PDSNs 141-143, while maintaining a
single IP address such that network connectivity is substantially continuous. This is unlike
the Simple IP, in which an MS 101-109 must always obtain a new IP address when roaming
across different PDSNs 141-143.
[0030] The above is accomplished in Mobile IP using two mobility agents which are
referred to as the Home Agent (HA) and the Foreign Agent (FA). In general, the FA is held
with (contained in) a PDSN 141-143, and the HA is a standalone entity. In general, the home
provider of an MS 101-109 provides a static home IP address and an HA which maintains
this IP address for the MS 101-109. It will be understood that the "home provider" may be
any suitable entity that operates the home network where the HA is attached. For example,
the home provider may be a corporation or Internet Service Provider (ISP) that operates the
HA and assigns addresses to MSs 101-109. Then, as the MS 101-109 connects to a new


PDSN 141-143 (which functions as an FA), a tunnel is established between the FA and the
HA to carry the traffic for MS 101-109. As the MS 101-109 connects to another PDSN 141-
143, also functioning as an FA, a new tunnel is established from the new FA to the same HA
through which traffic is routed.
[0031] More specifically, each time an MS 101-109 is out of range from its home
provider, it uses the FA of a PDSN 141-143 in order to obtain a "care-of" address. The care-
of address, which serves to identify the current location of the MS 101-109, is discovered
using either agent advertisement or agent solicitation, both of which are known in the art. In
general, FAs broadcast agent advertisements at regular intervals. If an MS 101-109 does not
wish to wait for the periodic advertisement, it can broadcast (or multicast) a solicitation that
will be answered by any FA that receives the solicitation.
[0032] Once a care-of address has been obtained by the MS 101-109, it must be
registered by the MS 101-109 with its HA. This process begins with the MS 101-109
sending a registration request to the FA (PDSN 141-143), which in turn generates a
corresponding Mobile IP (MIP) Registration Request to the HA with the care-of address.
Once the request is received by the HA, it typically adds the necessary information to its
routing table, approves the request, and sends a registration reply back to the FA (PDSN 141-
143) which in turn forwards it back to the MS 101-109. Upon accepting the request, the HA
also begins to associate the home address of the MS 101-109 with the care-of address that
was received from the MS 101-109. The HA maintains mis address for the "lifetime" of the
registration (e.g., for a predetermined period of time). It will be understood that, although not
described, the registration process generally also requires the HA to obtain authentication of
the registration information from MS 101-109.
[0033] After the registration has been completed as described above, the HA
intercepts any traffic destined to the static IP address (home address) of the MS 101-109 and
tunnels it to the care-of address registered with it. The FA unencapsulates the traffic and
forwards it to the MS 101-109. Traffic from the MS 101-109, on the other hand, can either
be directly delivered to its destination, or reverse-tunneled (by the FA) to the HA for delivery
to its final destination.
[0034] FIG. 2 is an illustration of a typical Mobile IP data flow involving MS 101,
radio network 210 (which includes, for example, BTS 111, BSC121, and PCF131), FA


(PSDN) 141, HA 211, and IP network 151. As shown, data flow (e.g., datagrams, which are
logical groupings of information sent as a network layer unit over the Internet) being sent
from IP network 151 using standard IP routing to MS 101 is intercepted by HA 211. The
data flow is then tunneled to the care-of address for MS 101 that has been registered. This
data flow is then de-tunneled and delivered to MS 101 using radio network 210. For data
flow sent by MS 101, standard IP routing may be used for delivery to its final destination, or
the data may be forwarded by the PDSN 141 over a reverse-tunnel to the HA.
[0035] As mentioned above, hard handoffs are undesirable in both the Simple IP and
the Mobile IP. In particular, in the case of the Simple IP, a hard handoff requires the
renegotiation of all access parameters (including PPP) because the new PDSN 141-143 is
unaware of the previous PPP session state (as mandated by IS-835). This includes assigning
MS 101-109 a new IP address, as well as data compression dictionaries, packets filters, a
firewall state, network-side tunnels, etc., before traffic can flow again to and from MS 101-
109. As a result of this required renegotiation of call parameters, data applications that may
be running on the MS 101-109 may be disrupted, essentially requiring the applications to
terminate their service.
[0036] Hard handoffs in Mobile IP are less disruptive in Mobile IP compared to
Simple IP because network-layer (IP) parameters are not renegotiated. However, there can
be significant delays in reestablishing a Mobile DP tunnel between the PDSN (FA) and the
HA for a given MS 101-109. As known in the art, such delays can be disruptive to packets in
transit to the MS 101-109.
[0037] One problem with using PDSNs 141-143 that have multiple IP addresses and
multiple corresponding physical interfaces is that hard handoffs might result even when a call
is being switched within the same physical PDSN 141-143. For example, PCFs 131-132 will
normally try to avoid the generation of hard handoffs by maintaining the same PDSN 141-
143 for a given MS 101-109, but this requires that the PCFs 131-132 exchange information
among themselves regarding which PDSN 141-143 should handle a given call. This process
is often impossible in a large multi-vendor network. Nevertheless, there are many situations
for which it would be desirable to use PDSNs 141-143 having multiple IP addresses. For
example, a PDSN 141-143 with multiple IP addresses and interfaces is typically able to
achieve much greater throughput (bandwidth) than a PDSN 141-143 having only a single IP
address and interface. In particular, the existence of multiple P addresses and interfaces


associated with a single PDSN 141-143 makes it possible to feed data through multiple
interfaces (rather than only a single interface), thereby enabling greater bandwidth.
Additionally, for example, it may be desirable to have a PDSN 141-143 be known by
multiple addresses in order to provide redundancy (and therefore, greater reliability). For
example, multiple addresses are useful in cases where a network connected between a
PCF 131-132 and a PDSN 141-143 becomes unavailable (e.g., due to a software or hardware
failure). In this situation, assuming there is redundancy, a different network (associated with
a different address of PDSN 141-143) can be used.
[0038] The present invention is useful (in both Simple IP and Mobile IP) in allowing
the use of PDSNs 141-143 having multiple IP addresses, and multiple physical interfaces,
while eliminating or substantially reducing the likelihood of internal hard handoff s as an
MS 101-109 moves from one PCF 131 to another PCF 132 in wireless communication
system 100. FIG. 3 illustrates such a PDSN 341 having multiple IP addresses that may be
used in accordance with the principles of the present invention. As shown, PDSN 341
includes n logical PDSNs 342-345 (i.e., logical PDSN(l) through logical PDSN(n)). It will
be understood that the term "logical PDSN" as used herein merely refers to the functions in
PDSN 341 that are associated with a particular IP address and its corresponding physical
(layer 3) interface. Accordingly, PDSN 341 is "known by" n different IP addresses, where
each IP address has its own physical (or logical) interface. As also shown in FIG. 3,
PDSN 341 includes physical interfaces 352-355, corresponding to logical PDSNs 342-345,
respectively. It will be understood that, alternatively, logical interfaces (not shown) may be
used.
[0039] In prior art communication systems, the transfer of a call from one logical
PDSNs 342-345 to another (e.g., when an MS 101-109 moves to a different PCF 131-132 that
fails to reconnect the MS 101-109 with the correct logical PDSN 342-345) is generally
treated as a hard handoff. In turn, this handoff would undesirably require renegotiation of all
call parameters, such as PPP, Quality of Service (QoS) state (traffic policing/shaping/marking
state), MIP state, tunneling state (L2TP, IPSEC, IP/IP, IP/GRE), and security parameters such
as packet filtering and firewall state. However, according to the principles of the present
invention, when a call arrives at a logical PDSN 342-345 of the single physical PDSN 341,
and the previous PDSN for the call was one of the other logical PDSNs 342-345, the higher-
layer (also referred to as "upper-layer") call functions are maintained between the calls and


the PPP is not renegotiated. Accordingly, the only things that need to be changed are the low
level transfer parameters. This is accomplished in accordance with the invention by
permitting the higher-layer call functions associated with an established A10/A11 layer (e.g.,
PPP) to be moved between services associated with one IP address in a PDSN 341 and
another IP address in the same physical PDSN 341. (Although aot described in detail herein
because it is known in the art, it should be understood that Al 1 protocols are used to set up an
A10 tunnel over which all the data associated with a mobile subscriber is routed.)
[0040] FIG. 4 is a flow chart illustrating the steps performed according to one
embodiment of the present invention in eliminating or at least substantially reducing the
likelihood of internal hard handoffs when using a PDSN 341 such as shown in FIG. 3. In
describing the steps of the flow chart shown in FIG. 4 (as well as the flow chart shown in
FIG. 5, which is described further below), for simplicity, the mobile station of interest will be
referred to as "MS1," the first PCF that MS1 uses will be referred to as "PCF(1)," while the
second PCF (to which MS1 roams) will be referred to as "PCF(2)." Additionally, the first
and second logical PDSNs being discussed will be referred to as 'TDSN(1)" and "PDSN(2)."
[0041] In step 402, MS 1 uses PCF(1) to establish an A10/A11 session to PDSN(1).
In particular, PCF(1) sends an A1 registration request (REG-REQ) to PDSN(1) using any
method that is known in the art. In response to the REG-REQ of PCF(1), PDSN(1) sends an
A11 registration response (REG-RSP) back to PCF(1). Next, in step 404, MS1 negotiates the
necessary PPP parameters with PDSN(1) and an IP address is assigned to MS 1. Again,
because this negotiation is know in the art, it is not described in detail herein.
[0042] In step 406, MS 1 roams to a new area that is served by PCF(2), which tries to
establish a new connection for MS1. For some reason (e.g., configuration problems), at this
time, PCF(2) selects PDSN(2), rather than the proper PDSN(1). Next, in step 408, MS uses
PCF(2) to establish a new A10/A11 session with PDSN(2) (which was selected by PCF(2)).
[0043] Generally speaking, in prior art wireless communication systems, establishing
a new session with PDSN(2) would be similar in terms of requirements (e.g., renegotiation of
PPP, etc.) to a hard handoff that occurs when using a new physical PDSN. According to the
present invention, however, this hard handoff is "turned into" a soft handoff. In other words,
the many or all of the problems associated with conventional hard handoffs (compared to


conventional soft handoffs) are eliminated. This is accomplished in step 408, which is
described in more detail with reference to the flow chart shown in FIG. 5.
[0044] Referring now to FIG. 5, the step of the MS1 establishing a new A10/A11
session with PDSN(2) (step 408, FIG. 4) preferably includes the following steps. In step 502,
PCF(2) sends an A11 REG-REQ (which includes the previous PCF IP address) to PDSN(2).
It should be noted that, as explained above with reference to FIG. 3, PDSN(2) is within the
same physical PDSN as PDSN(1).
[0045] In step 504, the physical PDSN is able to recognize that an A11 session is
already established for MS1. In particular, the PDSN reviews the subscriber ID and the
connection ID of MS1 signaled via an Al 1 Registration Request (both of these types of
identification are known in the art). Upon realizing that PCF(1) was previously
communicating with it (only at a different logical PDSN), the physical PDSN converts the
hard handoff into a soft handoff.
[0046] Next, in step 506, PDSN(1) sends a REG-UPDATE to PCF(1) to tear down
the old A11 session. In particular, PCF(1) "acks" the update (i.e. sends an Acknowledgment
packet) and sends a REG-REQ to PDSN(1) with a lifetime of zero (instructing the call to be
torn down). PDSN(1) acknowledges with an A11 REQ-RSP, and the original session is
closed. It should be noted that step 506 occurs at the same time that PDSN(2) is sending a
REG-RSP back to PCF(2) (in response to the REG-REQ sent according to step 502).
[0047] In step 508, PDSN(2) takes the upper call state (which includes, for example,
QoS state (traffic policing/shaping/marking state), MIP state, tunneling state (L2TP, IPSEC,
IP/IP, IP/GRE), and security parameters such as packet filtering and firewall state) associated
with the previous matching session, and PDSN(2) proceeds as if a soft handoff had occurred
(e.g., it does not renegotiate PPP with MS1). As will be understood by persons versed in the
art, this upper call information that is used by PDSN(2) may include, in addition to PPP
parameters, all the policy information on how to handle MS1, such as traffic policing, as well
as compression state, tunneling parameters, QoS parameters, security parameters (such as
packet filters, firewall state, IPSEC state), and Mobile IP state.
[0048] It will be appreciated that, in the manner described above, many of the
problems associated with using a PDSN 341 having multiple IP addresses and interfaces are
resolved. In particular, the risk of internal hard handoffs is eliminated or at least substantially


reduced. This, in turn, increases the ability to use such a PDSN 341, in order to achieve
higher throughput and redundancy, for example, without risking the effects of internal hard
handoffs.
[0049] Although the invention has been described and illustrated in the foregoing
illustrative embodiments, it is understood that the present disclosure has been made only by
way of example, and that numerous changes in the details of implementation of the invention
can be made without departing from the spirit and scope of the invention. Moreover, it will
be understood that certain features which are well known in the art have not been described in
order to avoid complication of the subject matter of the present invention. The present
invention is limited only by the claims which follow.


WE CLAIM:
1. A wireless communication system comprising:
means for establishing a first A10/A11 session, for a mobile station, MS, (101) in
the mobile communication system, using a first IP address of a packet data service
nodes, PDSN, (141),
the first A10/A11 session being established via a first packet control function,
PCF, (131) adapted to route IP packet data between the MS (101) and the PDSN (141)
when the MS (101) is in an area served by the first PCF (131), and the MS (101)
negotiating call parameters, including upper-layer call functions including point-to-point
radio connection, PPP, parameters, with the PDSN (141);
means for storing at the PDSN (141) a plurality of call parameters negotiated in
connection with the first A10/A11 session;
means for receiving, at a second IP address of the PDSN, after the MS (101)
moves to an area no longer being served by the first PCF (131) or after a failure in the
wireless communication system requires termination of the first session, the area being
served by a second packet control function, PCF, (132), an All Registration Request for
establishment of a second A10/A11 session, for the MS, using the second IP address of
the PDSN, the request being sent by the second PCF (132) and including a subscriber ID
and a connection ID associated with the MS; and
means at the second IP address of the PDSN for recognizing that the first
A10/A11 session is established for the MS, using the subscriber ID and the connection
ID;
means at the second IP address of the PDSN for using at least some of the stored
plurality of call parameters associated with the first A10/A11 session and maintaining
the upper-layer call functions in the PDSN (141), including the PPP parameters, during
the handoff between the first IP address and the second IP address of the PDSN (141) in
establishing the second A10/A11 session, without renegotiating the PPP parameters with
the MS (101), by using All protocols to set up an A10 tunnel between the first IP
address and the second IP address of the PDSN (141) for routing the upper-layer call
functions in the PDSN (141), including the PPP parameters, to the second IP address of
the PDSN (141).


2. The system as claimed in claim 1, wherein the system is a code division multiple
access, CDMA, communication system.
3. The system as claimed in claim 1, wherein the PDSN (141) comprises a separate
physical interface (342, 343) for each IP address.
4. The system as claimed in claim 1, wherein the system operates in Simple IP
mode.
5. The system as claimed in claim 1, wherein the system operates in Mobile IP
mode.
6. A method for performing a handoff of a mobile station, MS, (101) in a mobile
communication system that uses a packet data serving node, PDSN, (141) having more
than one internet protocol, IP, address, the method comprising:
establishing a first A10/A11 session (402), for a mobile station, MS, in the
mobile communication system, using a first IP address of the PDSN;
the first A10/A11 session being established via a first packet control
function, PCF, (131) adapted to route IP packet data between the MS (101) and the
PDSN (141) when the MS (101) is in an area served by the first PCF (131), and the MS
(101) negotiating call parameters, including upper-layer call functions including point-
to-point radio connection, PPP, parameters, with the PDSN (141);
storing at the PDSN a plurality of call parameters negotiated in connection with
the first A10/A11 session;
receiving, at a second IP address of the PDSN, after the MS (101) moves to an
area no longer being served by the first PCF (131) or after a failure in the wireless
communication system requires termination of the first session, the area being served by
a second packet control function, PCF, (132) , an All Registration Request for
establishment of a second A10/A11 session, for the MS, using the second IP address of
the PDSN, the request being sent by the second PCF (132) and including a subscriber ID
and a connection ID associated with the MS;
recognizing at the second IP address of the PDSN that the first A10/A11 session
is established for the MS using the subscriber ID and the connection ID; and


using at the second IP address of the PDSN at least some of the stored plurality
of call parameters associated with the first A10/A11 session and maintaining the upper-
layer call functions in the PDSN (141), including the PPP parameters, during the
handoff between the first IP address and the second IP address of the PDSN (141) in
establishing the A10/A11 second session, without renegotiating the PPP parameters with
the MS (101), by using A11 protocols to set up an A10 tunnel between the first IP
address and the second IP address of the PDSN (141) for routing the upper-layer call
functions in the PDSN (141), including the PPP parameters, to the second IP address of
the PDSN (141).
7. The memod as claimed in claim 6, wherein the mobile communication system is
a code division multiple access (CDMA) communication system.
8. The method as claimed in claim 6, comprising establishing multiple sessions
witii multiple MSs (101, 102) using respective IP addresses of the PDSN.
9. The method of claim 6, comprising configuring a separate physical interface for
each IP address of the PDSN.
10. The method as claimed in claim 6, wherein the mobile communication system
operates in Simple IP mode.
11. The method as claimed in claim 6, wherein the mobile communication system
operates in Mobile IP mode.
12. The method as claimed in claim 6, wherein each of the IP addresses of the PDSN
are associated with a separate logical PDSN (342, 343).
13. A packet data serving node, PDSN, (341) having multiple internet protocol, IP,
addresses for use in a wireless communication system, the PDSN having a first A10/A11
session with a mobile station, MS, (101) using a first of its IP addresses and a second
A10/A11 session with the same MS using a second of its IP addresses,
the first A10/A11 session being established via a first packet control function,
PCF, (131) adapted to route IP packet data between the MS (101) and the PDSN (141)


when the 30 MS (101) is in an area served by the first PCF (131), and the MS (101)
negotiating call parameters, including upper-layer call functions including point-to-point
radio connection, PPP, parameters, with the PDSN (141)
the PDSN (341) comprising:
means for storing a plurality of call parameters negotiated in connection with the
first A10/A11 session;
means for receiving at a second IP address of the PDSN, after the MS (101)
moves to an area no longer being served by the first PCF (131) or after a failure in the
wireless 5 communication system requires termination of the first session, the area being
served by a second packet control function, PCF, (132) , an All Registration Request for
establishment of the second A10/A11 session, for the MS, using the second IP address
of the PDSN, the request being sent by the second PCF (132) and including a subscriber
ID and a connection ID associated with the MS;
means for recognizing that the first A10/A11 session is established for the MS,
using the subscriber ID and the connection ID;
means for using at least some of the stored plurality of call parameters associated
witii the first A10/A11 session and maintaining the upper-layer call functions in the
PDSN (141), including the PPP parameters, during the handoff between the first IP
address and 15 the second IP address of the PDSN (141) in establishing the A10/A11
second session, without renegotiating the PPP parameters with the MS (101), by using
A11 protocols to set up an A10 tunnel between the first IP address and the second IP
address of the PDSN (141) for routing the upper-layer call functions in the PDSN (141),
including the PPP parameters, to the second IP address of the PDSN (141).
14. The PDSN as claimed in claim 13, wherein each of the IP addresses of the PDSN
(341) are associated with a separate logical PDSN (342, 343).
15. The PDSN as claimed in claim 13, wherein the PDSN (341) comprises a separate
physical interface for each IP address.



ABSTRACT


A WIRELESS COMMUNICATION SYSTEM FOR PROVIDING IMPROVED
HANDOFFS IN WIRELESS COMMUNICATION NETWORKS AND A METHOD
FOR PERFORMING A HANDOFF IN A MOBILE COMMUNICATION SYSTEM
Methods and systems are provided for using a packet data serving node (PDSN) (341)
in a wireless communication network that includes multiple logical PDSNs (342-345) each of
which is associated with a particular IP address and corresponding physical interface (352-355).
Through the use of multiple logical PDSNs (342-345) and interfaces (352-355), the throughput
of the PDSN may be substantially increased. Additionally, the multiple logical PDSNs (342-345)
and interfaces (352-355) may be used to provide redundancy in order to protect against
software or hardware failures. A problem with prior art systems are that the PDSNs cannot
provide as much throughput nor can they reduce the likelihood of hard handoffs. According to
the methods and systems of the invention, moreover, the risk of internal hard handoffs resulting
from the use of a PDSN (341) having multiple logical PDSNs (342-345) is eliminated or at least
substantially reduced.

Documents:

00215-kolnp-2006-abstract.pdf

00215-kolnp-2006-claims.pdf

00215-kolnp-2006-description complete.pdf

00215-kolnp-2006-drawings.pdf

00215-kolnp-2006-form 1.pdf

00215-kolnp-2006-form 3.pdf

00215-kolnp-2006-form 5.pdf

00215-kolnp-2006-gfa.pdf

00215-kolnp-2006-international publication.pdf

00215-kolnp-2006-pct forms.pdf

00215-kolnp-2006-priority document.pdf

215-KOLNP-2006-(02-01-2012)-CORRESPONDENCE.pdf

215-KOLNP-2006-(02-01-2012)-OTHERS.pdf

215-KOLNP-2006-(26-02-2013)-AMANDED PAGES OF SPECIFICATION.pdf

215-KOLNP-2006-(26-02-2013)-ANNEXURE TO FORM-3.pdf

215-KOLNP-2006-(26-02-2013)-CORRESPONDENCE.pdf

215-KOLNP-2006-ABSTRACT 1.1.pdf

215-KOLNP-2006-ANNEXURE FORM 3.pdf

215-KOLNP-2006-ASSIGNMENT.pdf

215-KOLNP-2006-ASSIGNMENT1.1.pdf

215-KOLNP-2006-CANCELLED PAGES.pdf

215-KOLNP-2006-CLAIMS 1.1.pdf

215-KOLNP-2006-CORRESPONDENCE.pdf

215-KOLNP-2006-DESCRIPTION (COMPLETE) 1.1.pdf

215-KOLNP-2006-DRAWINGS 1.1.pdf

215-KOLNP-2006-EXAMINATION REPORT.pdf

215-KOLNP-2006-FORM 1.1.1.pdf

215-KOLNP-2006-FORM 13.pdf

215-KOLNP-2006-FORM 18.pdf

215-KOLNP-2006-FORM 2.pdf

215-KOLNP-2006-FORM 3.pdf

215-KOLNP-2006-FORM 5.pdf

215-KOLNP-2006-GPA.pdf

215-KOLNP-2006-GRANTED-ABSTRACT.pdf

215-KOLNP-2006-GRANTED-CLAIMS.pdf

215-KOLNP-2006-GRANTED-DESCRIPTION (COMPLETE).pdf

215-KOLNP-2006-GRANTED-DRAWINGS.pdf

215-KOLNP-2006-GRANTED-FORM 1.pdf

215-KOLNP-2006-GRANTED-FORM 2.pdf

215-KOLNP-2006-GRANTED-FORM 3.pdf

215-KOLNP-2006-GRANTED-FORM 5.pdf

215-KOLNP-2006-GRANTED-SPECIFICATION-COMPLETE.pdf

215-KOLNP-2006-OTHERS.pdf

215-KOLNP-2006-OTHERS1.1.pdf

215-KOLNP-2006-PA.pdf

215-KOLNP-2006-PETITION UNDER RULE 137.pdf

215-KOLNP-2006-REPLY TO EXAMINATION REPORT.pdf


Patent Number 255699
Indian Patent Application Number 215/KOLNP/2006
PG Journal Number 12/2013
Publication Date 22-Mar-2013
Grant Date 15-Mar-2013
Date of Filing 30-Jan-2006
Name of Patentee STARENT NETWORKS CORPORATION
Applicant Address 30 INTERNATIONL PLACE, TEWKSBURY, MA 01876, UNITED STATES OF AMERICA
Inventors:
# Inventor's Name Inventor's Address
1 HARPER MATTHEW H 22 TICKLEFANCY LANE, SALEM, NEW HAMPSHIRE 03079, UNITED STATES OF AMERICA
2 SENTHILNATHAN JANAKIRAMAN 28 CODOGAN WAY, NASHUA, NH 03062, UNITED STATES OF AMERICA
PCT International Classification Number G06F
PCT International Application Number PCT/US2004/023338
PCT International Filing date 2004-07-19
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 60/488,152 2003-07-17 U.S.A.