U.S. patent application number 15/153300 was filed with the patent office on 2016-09-08 for method for performing packet switched handover in a mobile communication system.
This patent application is currently assigned to VRINGO INFRASTRUCTURE INC.. The applicant listed for this patent is VRINGO INFRASTRUCTURE INC.. Invention is credited to Miikka HUOMO, Kari P. KAURANEN, Tuomas Niemela.
Application Number | 20160262076 15/153300 |
Document ID | / |
Family ID | 31725756 |
Filed Date | 2016-09-08 |
United States Patent
Application |
20160262076 |
Kind Code |
A1 |
Niemela; Tuomas ; et
al. |
September 8, 2016 |
Method for Performing Packet Switched Handover in a Mobile
Communication System
Abstract
A method and system for performing packet switched handover in a
mobile communication network. The system includes a mobile node, a
first and a second packet switching node. The method enables the
parallel sending of logical link layer frames from the first and
the second packet switching node. This is achieved so that the
mobile node does not reject incoming frames received from two
logical link layer entities having different states. The benefits
of the invention are related to improved quality of service and the
avoiding of gaps in received data during handover.
Inventors: |
Niemela; Tuomas; (Helsinki,
FI) ; KAURANEN; Kari P.; (Helsinki, FI) ;
HUOMO; Miikka; (Vantaa, FI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
VRINGO INFRASTRUCTURE INC. |
New York |
NY |
US |
|
|
Assignee: |
VRINGO INFRASTRUCTURE INC.
|
Family ID: |
31725756 |
Appl. No.: |
15/153300 |
Filed: |
May 12, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14582854 |
Dec 24, 2014 |
9402219 |
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15153300 |
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13618843 |
Sep 14, 2012 |
8942206 |
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14582854 |
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11898773 |
Sep 14, 2007 |
8804654 |
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13618843 |
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10816931 |
Apr 5, 2004 |
7333793 |
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11898773 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04W 36/30 20130101;
H04W 76/12 20180201; H04W 36/18 20130101; H04W 36/08 20130101; H04W
28/18 20130101; H04W 36/26 20130101 |
International
Class: |
H04W 36/26 20060101
H04W036/26; H04W 36/08 20060101 H04W036/08 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 23, 2004 |
FI |
20040280 |
Claims
1. A method of performing packet switched handover in a mobile
communication network, comprising a mobile node, a first and a
second packet switching node, the method comprising: forming a
first logical link layer entity in the mobile node; and detecting a
handover condition in the mobile node; receiving at least one
ciphering parameter from the first packet switching node to the
second packet switching node when the first packet switching node
requests handover preparation from the second packet switching
node; forming a second logical link layer entity in the mobile
node; sending logical link layer frames from the first and second
packet switching nodes to the mobile node during handover;
detecting a handover completion; and renegotiating logical link
layer parameters between the mobile node and the second packet
switching node after the detecting of the handover completion when
the logical link layer parameters are not suitable.
2. The method according to claim 1, further comprising: removing
the first logical link layer entity in the mobile node after the
detecting of the handover completion.
3. The method according to claim 1, further comprising: utilizing a
General Packet Radio Service (GPRS) network as the mobile
communication network, serving GPRS Support Nodes (SGSN) as the
first and second packet switching nodes, and GPRS Logical Link
Control (LLC) as at least one of the first and the second the
logical link layer.
4. An apparatus comprising at least one processor and a memory
including computer program code, the memory and the computer
program code configured to, with the at least one processor, direct
the apparatus at least to: cause communications with a remote
packet switching node, prior to receiving a data packet stream that
is routed from the remote packet switching node as a result of a
handover to the remote packet switching node, to receive an
indication of a packet-switched handover condition associated with
a mobile node, to request packet-switched handover preparation, to
send logical link layer information, and to receive logical link
layer information; form a first logical link layer control entity
in response to connection establishment and a second logical link
layer control entity in response to a packet-switched handover
condition; detect the packet-switched handover condition and a
packet-switched handover completion; and cause the second logical
link layer control entity to be configured to renegotiate logical
link layer parameters with a packet switched node after the
packet-switched handover completion when the logical link layer
parameters are not suitable.
5. The apparatus according to claim 4, wherein being directed to
form the second logical link layer control entity includes being
directed to perform the logical link parameter renegotiation using
exchange identification (XID) negotiation.
6. A method of performing packet switched handover in a mobile
communication network comprising a mobile node, a first and a
second packet switching node, the method comprising: detecting a
handover condition associated with the mobile node in the first
packet switching node; requesting handover preparation by the first
packet switching node from the second packet switching node,
receiving at least one ciphering parameter from the first packet
switching node to the second packet switching node when the first
packet switching node requests handover preparation from the second
packet switching node; receiving a packet at the first packet
switching node; forming a logical link layer Protocol Data Unit
(PDU) from data in the packet; sending a first frame containing the
logical link layer Protocol Data Unit (PDU) to the mobile node from
the first packet switching node; sending the logical link Protocol
data Unit (PDU) from the first packet switching node to the second
packet switching node; and sending a second frame containing the
logical link layer Protocol Data Unit (PDU) to the mobile node from
the second packet switching node.
7. The method according to claim 6, further comprising: utilizing a
General Packet Radio Service (GPRS) network as the mobile
communication network, Serving GPRS Support Nodes (SGSN) as the
first and second packet switching nodes, and GPRS Logical Link
Control (LLC) as a logical link layer.
8. The method according to claim 7, further comprising: utilizing a
General Packet Radio Service (GPRS) network as the mobile
communication network, a Serving GPRS Support Node (SGSN) as the
first packet switching node, a Base Station Subsystem (BSS) node as
the second packet switching node, and GPRS Logical Link Control
(LLC) as the logical link layer.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 14/582,854 which was filed with the U.S.
Patent and Trademark Office on Dec. 24, 2014 and Ser. No.
13/618,843 which was filed with the U.S. Patent and Trademark
Office on Sep. 14, 2012 and Ser. No. 11/898,773 filed on Sep. 14,
2007 and Ser. No. 10/816,931 filed on Apr. 5, 2004. Priority is
claimed for this invention and application, corresponding
application(s) having been filed in Finland on Feb. 23, 2004, No.
20040280.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The invention relates to mobile communication systems.
Particularly, the invention relates to the performing of packet
switched handover in a mobile communication system.
[0004] 2. Description of the Related Art
[0005] The introduction of conversational and streaming services in
Global System of Mobile Communications (GSM) has created a demand
for efficient hand-overs from user perspective in GSM/Edge Radio
Access Network (GERAN). The General Packet Radio Service (GPRS) and
the IP Multimedia System (IMS) support the conversational and
streaming services on their side and impose requirements on the
GERAN side. It is necessary to be able to perform Packet Switched
(PS) handovers frequently enough and to be able to minimize
interruptions in a constant packet stream to a mobile terminal. The
interruptions must preferably be short enough to enable a packet
buffering mechanism in the mobile terminal to hide the
interruptions. Previously in GPRS it was sufficient to provide a
loss-free link layer service for interactive applications such as
Wireless Application Protocol (WAP) browsing. In browsing
applications moderate extra delays caused by handovers are
acceptable. However, in streaming or conversational class services
interruptions in the supposedly constant packet stream are
immediately noticeable unless, of course, they can be hidden using
large enough buffers in the receiving ends. However, such buffering
introduces always a delay in the media streams provided to the
user. In the case of conversational voice services any significant
delays are unallowable, especially considering other factors
already introducing a delay in the speech path such as noise
filtering and speech coding.
[0006] Reference is now made to FIG. 1, which is a block diagram
illustrating the architecture and the protocol stacks in a GPRS
system in association with the GERAN. The GPRS system is specified,
for example, in the 3GPP specification 23.060. The protocol stacks
are illustrated from the user plane point of view. In FIG. 1 there
is a Gateway GPRS Support Node (GGSN) 106. GGSN 106 is connected to
an external network (not shown) via a Gi interface. The external
network may be an arbitrary IP network, for example, the Internet
or an intranet. In FIG. 1 there is also a Serving GPRS Support Node
(SGSN) 104. GGSN 106 communicates with SGSN 104, which routes
packets to and from Mobile Station (MS) 100 via a Base Station
Subsystem (BSS). SGSN 104 takes care of the mobility related tasks
such as the maintaining of mobile station 100 location information,
network registrations, routing area and location updating, Packet
Data Context (PDP) activation and deactivation, handovers and the
paging of mobile station 100. Part of the above mentioned tasks are
naturally done in other network elements with which SGSN 104 is
communicating. The GGSN is responsible for routing and tunneling
packets to and from a number of SGSN 104 and other SGSNs. The
routing is based on SGSN address information maintained in a PDP
context information held by GGSN 106 for each network address
activated for MS 100, for example, an IP address or an X.25 address
or a PPP link.
[0007] In FIG. 1, the uppermost protocol layer in MS 100 is the
application layer (APPL). The application layer may be any
protocol, for example, a WAP protocol or Transmission Control
Protocol (TCP) or Universal Datagram Protocol (UDP). Over TCP/IP
may be carried, for example, Hypertext Transfer Protocol (HTTP).
The application layer communication is exchanged with a peer host,
which may be located behind the Gi interface, for example, in the
Internet. Below the application layer there is the IP layer or
alternatively X.25 layer, which in GPRS is supported by both MS 100
and GGSN 106. The IP address for packets addressed to MS 100 points
to GGSN 106. An IP packet 114 is conveyed to MS 100 using GPRS user
plane protocols below the IP layer. Between GGSN 106 and SGSN 104
IP packet 114 is conveyed using the GPRS Tunneling Protocol (GTP).
A GTP packet carried further over UDP/IP.
[0008] In SGSN IP packet 114 data is routed based on MS 100
location information and passed to Sub-Network Dependent
Convergence Protocol (SNDCP) layer. SNDCP is specified in the 3GPP
specification 44.065. SNDCP layer maps network-level
characteristics onto the characteristics of the underlying network.
For example, SNDCP takes care of the transmission and reception of
Network layer Protocol Data Units (N-PDU) carrying IP packets. For
example, IP packet 114 is carried in N-PDU 112. SNDCP multiplexes
several packet data protocol packets for the same MS. It segments
IP packet 114 to LLC frames, for example, LLC frame 110. It also
reassembles packets from LLC frames. Header compression and packet
payload compression is also performed at SNDCP layer. SNDCP
performs parameter negotiation between MS 100 and SGSN 104. SNDCP
buffers N-PDUs in the case of acknowledged mode services.
[0009] The Logical Link Control (LLC) layer provides a highly
reliable link between MS 100 and SGSN 104. The LLC is specified in
3GPP specifications 44.064 and 04.64. The LLC is independent of the
underlying radio protocols and hides the BSS and radio interface
related tasks from the LLC layer users. LLC supports
variable-length information frames. LLC supports both acknowledged
and unacknowledged data transfers, that is, acknowledged and
unacknowledged modes of operation. LLC provides services typical to
a link layer comprising parameter negotiation, flow control in the
Asynchronous Balanced Mode (ABM), sequence control to maintain the
ordering of LLC-frames, expedited delivery for high-priority data,
error detection, error recovery and indication. LLC performs data
confidentiality by means of the ciphering of LLC-frame contents.
LLC also supports user identity confidentiality by means of the use
of Temporary Logical Link Identity (TLLI) instead of International
Mobile Subscriber Identity (IMSI).
[0010] The relay layer relays LLC PDUs between the Um and Gb
interfaces in the BSS. The Base Station System GPRS Protocol
(BSSGP) layer specified in 3GPP specification 08.18 conveys routing
and QoS-related information between the BSS and the SGSN. For
example, it carries radio resource related requests from the SGSN
to the BSS 102. It also carries LLC frames between the BSS and the
SGSN. In addition to LLC frames it also carries signaling PDUs
associated with GRPS mobility management. The Network Service (NS)
layer transports BSSGP PDUs between BSS and SGSN. NS may be based
on Frame Relay (FR). The RLC sub-layer within the RLC/MAC layer
provides a radio technology dependent reliable link between MS 100
and BSS 102. The MAC sub-layer performs the requesting and
reservation of radio resources and maps LLC frames onto the GSM
physical channels. The task of the MAC layer is to ensure efficient
sharing of common radio resources by several mobile stations. The
RLC/MAC layer is defined in the 3GPP specification GSM 04.60.
[0011] The standardization organization 3G Partnership Project
(3GPP) is currently specifying the packet switched handover for
GERAN A/Gb mode. One of the key aspects of the packet switched
handover is duplicated packet forwarding to both a source BSS and a
target BSS during handover, which has not yet been thoroughly
covered in the specifications.
[0012] Reference is now made to FIG. 2, which is a block diagram of
GPRS architecture illustrating problems in prior art associated
with duplicated packet forwarding. According to current GPRS
specifications, an LLC entity in a new SGSN can only be started so
that an LLC connection is establishing at the request of an SNDCP
entity or the peer LLC entity. An LLC entity can only be created in
its initial state where the LLC connection variables have their
initial values. In FIG. 2 there is an MS 100, Base Transceiver
Stations (BTS) 224-228 and Base Controller Stations (BSC) 210-214
in BSS 216. There is a GGSN 200, which is connected to IP network
201. From IP network 201 is received a downlink packet stream 246
for which a real-time service is required. Initially, downlink
packet stream 246 is tunneled to SGSN 202 as packet stream 240.
Initially, SGSN 202 routes packet stream 240 to MS 100 via BSC 212
and BTS 222 as packet stream 242 using an LLC connection
terminating at an LLC entity 230, which is located in MS 100. BSC
212 and BTS 222 are referred to as source BSS 262. MS 100
communicates with BSC 212 via BTS 222. BSC 212 performs handover
related tasks including the handover determination algorithms and
decisions. In handover related signaling an SGSN communicates with
a BSC within a BSS. Similarly, in handover related signaling an MS
communicates with a BSC within a BSS. The signaling between an MS
and a BSC goes via a BTS.
[0013] However, when MS 100 receives a report indicating that a
cell served by BTS 224 has better radio quality, it must start
performing handover to the cell served by BTS 224. The new cell is
under the area of a new SGSN 204. After the handover, packet stream
246 should be routed to MS 100 from GGSN 200 via SGSN 204, BSC 214
and BTS 224. BSC 214 and BTS 224 are also referred to as a target
BSS 264. While the handover is not fully complete, SGSN 202 must
forward packets to both BSC 212 and SGSN 204. In order to be able
to process packets from packet stream 240 SGSN 204 must receive
them as a GTP tunneled packet stream 241 from SGSN 202. Packets
from GTP tunneled packet stream 241 are forwarded in SGSN 204 to
its LLC entity 254. The LLC entity is started from initial state
with initial LLC connection variables. GTP tunneled packet stream
241 is routed from SGSN 204 as packet stream 244 carried over an
LLC connection. The problem in the packet duplicated forwarding
mechanism described above is that LLC entity 254 in the new SGSN,
namely SGSN 204, has different state compared to LLC entity 252 and
LLC entity 230. This means that LLC entity 230 in MS 100 receives
packets from two different independent LLC entities. The
corresponding peer LLC entity 230 in MS 100 is not capable of
receiving simultaneously packets from two different LLC entities,
if the states of the LLC entities comprising the LLC variables are
not synchronized. The different states essentially lead to the
rejection of LLC frames carrying packet stream 244 or the receiving
of duplicate LLC frames in an uncontrolled manner.
[0014] The rejection is due to the fact that LLC entity 252 sends
LLC frames with sequence numbers that are overlapping with the
sequence numbers sent by LLC entity 254 even though they are
different LLC frames. Frames are rejected in LLC entity 230 also
due to the fact that LLC entity 254 sends LLC frames using
different ciphering parameters. Because the ciphering parameters
are different, LLC entity 230 is unable to decipher the LLC frames
and discards them due to failing Frame Check Sequence (FCS)
verification. A further problem is that SGSN 204 is unaware of the
LLC frame sizes negotiated between MS 100 and SGSN 202. If SGSN 204
uses values that exceed the maximum values supported by MS 100, it
discards all LLC frames. This in turn may lead to the releasing of
the PDP context carrying packets streams 240, 241, 242 and 244. MS
100 may additionally also perform reset.
[0015] As explained in the 3GPP specification 44.064, the ciphering
parameters for LLC frames comprise IOV, LFN, OC and SX. IOV is an
Input Offset Value, which is a 32 bit random value generated by the
SGSN. LFN is the LLC Frame Number (LFN) in the LLC frame header. OC
is an overflow counter that is calculated and maintained
independently at the sending and the receiving sides. An OC for
acknowledged operation must be set to 0 whenever asynchronous
balanced mode operation is re-established for the corresponding
Data Link Connection Identifier (DLCI). An LLC layer connection is
identified using DLCI, which consists of Service Access Point
Identifier (SAPI) and the TLLI associated with MS 100. OC shall be
incremented by 512 every time when the corresponding LFN rolls
over. Due to this fact, OC is never sent directly in LLC frames.
The aim of OC is to add variation to the ciphering process in order
to make it more robust. SX is an XOR mask calculated from the LLC
entity identifier. There are two IOV values, one for numbered
information frames associated with acknowledged operation and
another for unconfirmed information frames associated with
unacknowledged operation. There are also two LFN values, one for
acknowledged operation and another for unacknowledged operation.
There are four OC counters associated with each DLCI. There is one
OC counter per operation mode, which is either unacknowledged or
acknowledged, and direction of transmission, which is either uplink
or downlink.
[0016] Naturally, the session key K.sub.c used in the ciphering
algorithm is one of the ciphering parameters.
[0017] Reference is now made to FIG. 3, which is a signaling
diagram illustrating signaling during a packet switched handover in
accordance with the current 3GPP proposals. The current proposals
are described in TSG document GP-032710 "Packet Switched Handover
for GERAN A/Gb mode, Stage 2", version 0.2.0, 2004-01. The
architecture associated with the signaling is as illustrated in
FIG. 2. MS 100 sends radio quality measurement information
pertaining to neighboring cells to source BSS 262 using message
301. Based on the measurement information source BSS 262 determines
that handover is required. At time t.sub.0 source BSS 262
determines that handover is to be performed to a new cell, which is
in the area of a new SGSN, which is SGSN 204. Source BSS 262 sends
a PS Handover Required message 302 to old SGSN 202. The message
comprises, for instance, the source cell, the target cell, TLLI,
cause and a transparent container. SGSN 202 determines based on the
target cell if the handover is an intra- or inter-SGSN handover.
SGSN 202 determines the identity of the new SGSN and sends a
Prepare PS Handover Request message 303 to SGSN 204. SGSN 204 sends
a PS Handover Required message 304, which requests target BSS 264
to reserve radio resources for MS 100 in the target cell. When
radio resources have been successfully allocated, target BSS 264
sends a PS Handover Request Acknowledge message 305 indicating
successful allocation. SGSN 204 sends a Prepare PS Handover
Response message 306 to SGSN 202, which tells, among other things,
that SGSN 202 may issue to MS 100 a command to complete handover to
the new cell. SGSN 202 receives message 306 at time t.sub.1.
[0018] However, simultaneously a packet from GTP packet stream 307
is received by SGSN 202. SGSN 202 forwards packets one by one from
GTP packet stream 307 to SGSN 204 as packet stream 308. SGSN 204
sends packets from packet stream 308 further to target BSS 264 as
packet stream 309. Target BSS forwards packets from packet stream
308 to MS 100 as packet stream 310. There is a delay before MS 100
is able to receive packets from SGSN 204 via target BSS 264. SGSN
202 sends PS Handover Command message 311 to source BSS 262. Source
BSS sends further PS Handover Command message to MS 100. Thereupon,
MS 100 tunes to the radio channel and timeslot allocated in the
target cell by target BSS 264. This is illustrated using arrow 312.
Target BSS 264 sends Physical information to MS 100 for MS 100 to
synchronize. After MS 100 has synchronized, it sends a PS Handover
Complete message 314 to target BSS 264 at time t.sub.2. Only after
time t.sub.2 MS 100 is prepared to receive packets via target BSS
264 normally, which shows that there is an intolerable delay unless
MS 100 receives packets via both target BSS 264 and source BSS 262.
Target BSS 264 sends a PS Handover Complete message 315 to SGSN
204. Thereupon, SGSN 204 performs PDP context update messaging
represented using arrows 316 and 317 with GGSN 200. PDP context
update indicates to GGSN 200 the address of current SGSN 204. After
having received PDP context update at time t.sub.3, GGSN 200 is
able to start routing GTP packet stream 318 to right SGSN, which is
now SGSN 204. Thereupon, MS 100 receives packet stream 320 from
target BSS 264, which has received it from SGSN 204 as packet
stream 319.
[0019] Reference is now made to FIG. 4, which is signaling diagram
illustrating the delay associated with a solution, which merely
forwards packets from a source node to a target node during
handover processing. The solution is similar to the solution
utilized in UMTS in association with Serving Radio Network Server
SRNS relocation. SRNS relocation is explained in 3GPP 23.060. In
FIG. 4 a source node 452 receives a packet stream 401 sent by an
upper node 450, which is connected to an IP network 451. At time to
upper node sends a specific packet 460 in packet stream 401. Source
node forwards packet stream further 402 to MS 100 via an access
network 456. At time t.sub.1 MS 100 decides to start using a target
node 454 instead of source node 452 for receiving packet streams.
At time t.sub.1 MS 100 acknowledges last frame received via source
node 452 using message 403. Packet 460 has not been completely
received, for example the last frame from packet 460 may be
pending. MS 100 sends a request message 403 for source node 452
indicating the abandoning of source node 452 for MS 100 traffic.
After receiving message 403, source node 452 starts forwarding all
packets addressed to MS 100 via target node 454 as packet stream
405. Packet stream 405 is forwarded by target node 454 to MS 100 as
packet stream 406. At time t.sub.2 MS 100 receives a first packet
since MS 100 received the last frame via source node 452 at time
t.sub.1. The time difference between t.sub.1 and t.sub.2 represents
the gap in the receiving of packets at MS 100, whereas the time
difference between t.sub.0 and t.sub.2 represent a delay in
receiving packet 460 from upper node 450 to MS 100. The delays
explained above are intolerable for real-time services.
[0020] As has been illustrated in association with FIGS. 2, 3 and
4, there are problems in performing packet switched handover using
current GPRS architecture and the solutions proposed in prior art.
On the one hand, it must be possible for an MS to receive packets
simultaneously from a source node and a target node during the
handover signaling. On the other hand, this is not possible in
current GPRS specifications and leads to the rejection of forwarded
frames at the MS side.
SUMMARY OF THE INVENTION
[0021] The invention relates to a method of performing handover in
a mobile communication system comprising a mobile node, a first and
a second packet switching node. In the method a handover condition
associated with the mobile node is detected in the first packet
switching node; the first packet switching node requests handover
preparation from the second packet switching node; logical link
layer information is received from the first packet switching node
to the second packet switching node; the state in a logical link
layer entity is set in the second packet switching node based on
the logical link layer state information; and logical link layer
frames are sent from the first and second packet switching nodes to
the mobile node during handover.
[0022] The invention relates also to a method performing handover
in a mobile communication system comprising a mobile node, a first
and a second packet switching node. In the method a handover
condition associated with the mobile node is detected in the first
packet switching node; the first packet switching node requests
handover preparation from the second packet switching node; a
packet is received at the first packet switching node; a logical
link layer Protocol Data Unit (PDU) is formed from data in the
packet; a first frame containing the logical link layer Protocol
Data Unit (PDU) is sent to the mobile node from the first packet
switching node; the logical link Protocol data Unit (PDU) is sent
from the first packet switching node to the second packet switching
node; and a second frame containing the logical link layer Protocol
Data Unit (PDU) is sent to the mobile node from the second packet
switching node.
[0023] The invention relates also to a method performing handover
in a mobile communication system comprising a mobile node, a first
and a second packet switching node. In the method a handover
condition associated with the mobile node is detected in the first
packet switching node; the first packet switching node requests
handover preparation from the second packet switching node; at
least one ciphering parameter is received from the first packet
switching node to the second packet switching node; a logical link
parameter exchange is performed between the mobile node and the
first packet switching node; and logical link layer frames are sent
from the first and second packet switching nodes to the mobile node
during handover.
[0024] The invention relates also to a method performing handover
in a mobile communication system comprising a mobile node, a first
and a second packet switching node. In the method a first logical
link layer entity is formed in the mobile node; a handover
condition is detected in the mobile node; a second logical link
layer entity is formed in the mobile node; logical link layer
frames are sent from the first and second packet switching nodes to
the mobile node during handover; handover completion is detected;
and logical link layer parameters between the mobile node and the
second packet switching node are renegotiated after the detecting
of the handover completion if the logical link layer parameters are
not suitable.
[0025] The invention relates also to a system, which comprises a
mobile node, a first and a second packet switching node. The system
further comprises: signaling means in the first packet switching
node for detecting a handover condition associated with the mobile
node, requesting handover preparation from the second packet
switching node and sending logical link layer information to the
second packet switching node; signaling means in the second packet
switching node for receiving logical link layer information from
the first packet switching node; control means in the second packet
switching node arranged to set the state in a logical link layer
entity based on logical link layer information from the first
packet switching node; and control means in the first packet
switching node arranged to send logical link layer frames to the
mobile node during handover
[0026] The invention relates also to a system, which comprises a
mobile node, a first and a second packet switching node. The system
further comprises: signaling means in the first packet switching
node for detecting a handover condition associated with the mobile
node and requesting handover preparation from the second packet
switching node; logical link layer means in said first packet
switching node for forming logical link layer Protocol Data Units
(PDU) and sending said logical link layer Protocol Data Units (PDU)
to said second packet switching node; and logical link layer means
in said second packet switching node for sending said logical link
layer Protocol Data Units (PDU) transparently to said mobile
node.
[0027] The invention relates also to a system, which comprises a
mobile node, a first and a second packet switching node. The system
further comprises: signaling means in the first packet switching
node for detecting a handover condition associated with the mobile
node, requesting handover preparation from the second packet
switching node and sending at least one ciphering parameter to the
second packet switching node; signaling means in the second packet
switching node for receiving at least one ciphering parameter from
the first packet switching node; logical link layer means in the
first packet switching node for performing a logical link parameter
exchange with the mobile node.
[0028] The invention relates also to a system, which comprises a
mobile node, a first and a second packet switching node. The system
further comprises: control means in the mobile node arranged to
form a first logical link layer entity in response to connection
establishment and a second logical link layer entity in response to
a handover condition; signaling means in the mobile node for
detecting the handover condition and a handover completion; logical
link layer means in the mobile node arranged to renegotiate logical
link layer parameters with the second packet switched node after
the handover completion if the logical link layer parameters are
not suitable.
[0029] In one embodiment of the invention, the mobile node is a
mobile terminal, for example, a UMTS terminal, a GSM terminal, a
GPRS terminal, a WLAN terminal or a terminal within an arbitrary
cellular radio system.
[0030] In one embodiment of the invention, the mobile node is a
mobile computer, for example, a laptop computer, palmtop computer
or a personal digital assistant (PDA).
[0031] In one embodiment of the invention, the mobile communication
system is a General Packet Radio Service (GPRS), the first and
second packet switching nodes are Serving GPRS Support Nodes (SGSN)
and the logical link layer is GPRS Logical Link Control (LLC) and
the logical link parameter exchange is Logical Link Control (LLC)
exchange Identification (XID) negotiation. In one embodiment of the
invention the second packet switching node is a Base Station
Subsystem (BSS) node, for example, a base station controller or a
base station. In one embodiment of the invention, the first or the
second packet switching node is a node, which performs the
forwarding and switching of data packets at link layer. The
invention is not restricted to packet switching nodes that switch
packets at network layer level in the manner of e.g. IP routers. By
packets are meant herein throughout this disclosure data packets
pertaining to any protocol layer, for example, network layer
packets, link layer frames, Asynchronous Transfer Mode (ATM)
cells.
[0032] In one embodiment of the invention, the logical link
parameter exchange is performed in response to the detection of
handover condition at the first packet switching node.
[0033] In one embodiment of the invention, the first logical link
layer entity in the mobile node is removed after the detecting of
handover completion.
[0034] In one embodiment of the invention, the at least one
ciphering parameter is received from the first packet switching
node to the second packet switching node when the first packet
switching node requests handover preparation from the second packet
switching node. This means that the at least one ciphering
parameter is sent from the first packet switching to the second
packet switching in the message that requests handover
preparation.
[0035] In one embodiment of the invention, the logical link layer
information is received from the first packet switching node to the
second packet switching node when the first packet switching node
requests handover preparation from the second packet switching
node. This means that the logical link layer information is sent
from the first packet switching node to the second packet switching
in the message that requests handover preparation.
[0036] In one embodiment of the invention, the logical link
parameter exchange is performed in response to the condition where
the mobile node receives an LLC frame, which has a duplicate flag
set. The duplicate flag indicates the duplication of the LLC frame
for handover purposes. In one embodiment of the invention, the
duplicate flag is only accepted by the mobile node while handover
is being performed. Otherwise, the receiving of the flag results in
an error indication to the peer LLC-entity.
[0037] In one embodiment of the invention, the logical link layer
means in the mobile node and in the first and second packet
switching nodes are represented by one or many Logical Link Control
(LLC) entities, a Logical Link Management Entity (LLME) and a
multiplexing entity associated with them. On transmission the
multiplexing entity generates and inserts the FCS, performs a frame
ciphering function and provides SAPI-based logical link control
layer contention resolution between the various logical link
entities. The functions performed by multiplexing entity and LLME
are described in 3GPP specification 23.060.
[0038] In one embodiment of the invention, the control means in the
first and second packet switching node comprise the higher protocol
layer entities above the logical link layer. For example, in a SGSN
the control means may comprise the relay layer entities, the SNDCP
layer entities and the GTP layer entities.
[0039] In one embodiment of the invention, the control means in the
mobile node comprise the higher protocol layer entities pertaining
to the GPRS user plane.
[0040] In one embodiment of the invention, the signaling means in
the mobile node comprise the signaling protocols used to
communicate with the first and the second packet switching nodes.
In a GPRS mobile terminal the signaling means comprises the GPRS
control plane signaling protocol stack entities. In one embodiment
of the invention, the actual mobility management and radio control
related application logic are performed in control means or in
separate control means in association with signaling means. In this
embodiment the exchange of signaling messages is handled by
separate means reserved for the task.
[0041] In one embodiment of the invention, the signaling means in
the first and the second packet switching nodes comprise the
signaling protocols used to communicate with the mobile node. In a
SGSN the signaling means comprises the GPRS control plane signaling
protocol stack entities.
[0042] In one embodiment of the invention, the sending of logical
link layer frames or any other messages between the mobile node and
the packet switching nodes is performed via a radio access network
so that the frames and messages are forwarded by one or many
intermediate network elements such as base station controllers,
radio network controllers and base transceiver stations. In one
embodiment of the invention, the first and the second packet
switching nodes are directly connected to base transceiver stations
and manage the radio network control procedures directly.
[0043] The benefits of the invention are associated with improved
quality of service. With the invention it is now possible to
provide a continuous packet stream to a mobile station during
handover.
[0044] Other objects and features of the present invention will
become apparent from the following detailed description considered
in conjunction with the accompanying drawings. It is to be
understood, however, that the drawings are designed solely for
purposes of illustration and not as a definition of the limits of
the invention, for which reference should be made to the appended
claims. It should be further understood that the drawings are not
necessarily drawn to scale and that, unless otherwise indicated,
they are merely intended to conceptually illustrate the structures
and procedures described herein.
BRIEF DESCRIPTION OF THE DRAWINGS
[0045] The accompanying drawings, which are included to provide a
further understanding of the invention and constitute a part of
this specification, illustrate embodiments of the invention and
together with the description help to explain the principles of the
invention. In the drawings:
[0046] FIG. 1 is a block diagram illustrating the prior art
architecture and the protocol stacks in a General Packet Radio
Service (GPRS) system in association with the GSM/EDGE Radio Access
Network (GERAN);
[0047] FIG. 2 is a block diagram illustrating General Packet Radio
Service (GPRS) network architecture and problems in prior art
associated with duplicated packet forwarding;
[0048] FIG. 3 is a signaling diagram illustrating signaling during
a packet switched handover in prior art;
[0049] FIG. 4 is a signaling diagram illustrating the delay
associated with a solution, which merely forwards packets from a
source node to a target node during handover processing;
[0050] FIG. 5 is a signaling diagram depicting one embodiment of
packet switched handover method utilizing state transfer, according
to the invention;
[0051] FIG. 6a is a block diagram depicting one embodiment of
packet switched handover method utilizing frame forwarding via
Serving GPRS Support Node (SGSN), according to the invention;
[0052] FIG. 6b is a block diagram depicting one embodiment of
packet switched handover method utilizing frame forwarding directly
to target Base Station Subsystem, according to the invention;
[0053] FIG. 7 is a signaling diagram depicting one embodiment of
packet switched handover method utilizing logical link parameter
reset, according to the invention;
[0054] FIG. 8 is a block diagram depicting one embodiment of packet
switched handover method utilizing duplicate logical link control
entities, according to the invention;
[0055] FIG. 9 is a signaling diagram depicting one embodiment of
packet switched handover method utilizing a duplicate frame
indicator, according to the invention;
[0056] FIG. 10 is a flow chart depicting one embodiment of packet
switched handover method utilizing context transfer, according to
the invention;
[0057] FIG. 11 is a flow chart depicting one embodiment of packet
switched handover method utilizing frame forwarding, according to
the invention;
[0058] FIG. 12 is a flow chart depicting one embodiment of packet
switched handover method utilizing logical link reset, according to
the invention;
[0059] FIG. 13 is a flow chart depicting one embodiment of packet
switched handover method utilizing duplicate logical link control
entities, according to the invention;
[0060] FIG. 14 is a flow chart depicting one embodiment of packet
switched handover method utilizing a duplicate frame indicator,
according to the invention;
[0061] FIG. 15 illustrates a Serving GPRS Support Node (SGSN) in
one embodiment of the invention; and
[0062] FIG. 16 illustrates a mobile node in one embodiment of the
invention.
DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS
[0063] Reference will now be made in detail to the embodiments of
the present invention, examples of which are illustrated in the
accompanying drawings.
[0064] FIG. 10 is a flow chart depicting one embodiment of packet
switched handover, which utilizes state transfer using a signaling
illustrated in FIG. 5. The signaling is performed in GPRS system
architecture, which is illustrated in FIG. 2. At step 1000 it is
checked if handover occurs. In case there is handover MS 100 sends
radio quality measurement information pertaining to neighboring
cells to source BSS 262 using message 301. Based on the measurement
information source BSS 262 determines that handover is required.
The determination is performed using an algorithm that is executed
in a Base Station Controller (BSC) within the source BSS 262. At
time to source BSS 262 determines that handover is to be performed
to a new cell, which is in the area of a new SGSN, which is SGSN
204. Source BSS 262 sends a PS Handover Required message 302 to old
SGSN 202. The message comprises, for instance, the source cell, the
target cell, TLLI, cause and a transparent container. SGSN 202
determines based on the target cell if the handover is an intra- or
inter-SGSN handover. SGSN 202 determines the identity of the new
SGSN and sends a Prepare PS Handover Request message 303 to SGSN
204.
[0065] At step 1002 the state pertaining to the logical link is
obtained by the LLC-entity in SGSN 204. This is achieved so that
Prepare PS Handover Request message carries LLC state information
element 500. LLC state information element 500 comprises
information that is used to synchronize LLC-entities in SGSN 202
and SGSN 204. Information element 500 comprises at least the
session key K.sub.c, the IOV values for both modes of operation,
both LFN values and the four OC values. SGSN 204 stores information
element 500 until SGSN 202 forwards packets to it. The handover
signaling between network elements continues as explained in
association with FIG. 3.
[0066] At step 1004 when a first forwarded packet is received from
SGSN 202, an LLC entity is initialized in SGSN 204. During
initialization SGSN 204 uses information element 500. By having
information element 500 and the LLC state information in it, it is
possible for SGSN 204 to construct an LLC-entity, which is an exact
replica of the LLC-entity in SGSN 202 from MS 100 point of view.
Thereupon, MS 100 is able to receive LLC frames from both
LLC-entities without noticing a difference. In one embodiment of
the invention the LLC-entity in SGSN 204 is initialized and started
already after SGSN 204 has received message 303 and no packets to
be forwarded have yet been received by SGSN 204. At step 1006 SGSN
204 starts forwarding packets received via SGSN 202 using the
LLC-entity constructed and initialized at step 1006.
[0067] FIG. 11 is a flow chart depicting one embodiment of packet
switched handover, which utilizes frame forwarding in a system as
illustrated in FIG. 6a or 6b. At step 1100 SGSN 202 waits for a
message from source BSS 262 indicating that handover is required.
In one embodiment of the invention the handover indication may also
be received from MS 100. When the message is received method
continues in step 1102. At step 1102 SGSN 202 waits for an event
where SGSN 202 receives a packet 610 from GGSN 200, which is the
first user plane packet after the start of handover. At this event
a first LLC frame 614 that carries data from packet 610 is to be
sent by SGSN 202. When the event occurs packet 610 is received by
an SNDCP entity 600 in SGSN 202 via the GTP and relay layers as
illustrated in FIG. 1.
[0068] Packet 610 is received to SGSN 202 via tunnel 240. The SNDCP
entity 600 performs packet segmentation for packet 610 and other
SNDCP level tasks and issues a request to an LLC-entity 252 to send
first LLC-frame 614. The request is issued in the form of an LLC
Service Data Unit (SDU). At step 1104 LLC-entity 252 prepares an
LLC-PDU using the information contained in LLC-SDU and the
LLC-entity 252 state variables. At step 1106 LLC-entity 252 sends
the prepared LLC-PDU in a first LLC-frame 614 to source BSS 262 and
BSC 212 therein.
[0069] At step 1108 LLC-entity 252 passes the LLC-PDU in a second
LLC-frame 616 to a frame forwarding entity 604 in association with
SNDCP entity 600. It should be noted that second LLC-frame 616 is a
duplicate of LLC-frame 614. Frame forwarding entity 604 sends the
second LLC-frame 616 to SGSN 204 using a connection 241, which
tunnels LLC-frames prepared by LLC-entity 252 to SGSN 204.
Connection 241 is, for example, a GTP tunnel established between
SGSN 202 and SGSN 204 for the transparent forwarding of LLC-frames.
The second LLC-frame 616 is received by LLC-entity 606 in SGSN 204.
LLC-entity 606 is configured to receive LLC-frames via connection
241 and forward them transparently towards target BSS 264. The
transparent forwarding means in this case that the LLC-entity does
not alter the LLC-frame fields indicating LLC-entity 252 state. In
one embodiment of the invention, relay LLC PDU formed from
LLC-frame 616 is not relayed through SNDCP protocol entity in SGSN
204. In another embodiment of the invention the LLC PDU from
LLC-frame 616 is relayed through protocol entity chain
GTP-SNDCP-LLC-BSSGP in order to be sent to target BSS 264.
[0070] In one embodiment of the invention illustrated in FIG. 6b
SGSN 202 passes second LLC-frame 616 directly to target BSS 264.
This is achieved so that a connection 241b is formed between SGSN
202 and target BSS 264. This is achieved so that at step 1108 is
omitted from the method. Instead, at step 1110 LLC-entity 252
passes the LLC-PDU in a second LLC-frame 616 to a frame forwarding
entity 604b in association with SNDCP entity 600. Frame forwarding
entity 604b sends the second LLC-frame 616 to target BSS 264 using
connection 241b. Target BSS 264 is configured to receive LLC-frame
616 and other duplicate LLC-frames for handover and to prepare them
for transmission to MS 100.
[0071] FIG. 12 is a flow chart depicting one embodiment of packet
switched handover, which utilizes logical link reset achieved using
a signaling illustrated in FIG. 7. The signaling is performed in
GPRS system architecture, which is illustrated in FIG. 2. At step
1200 it is checked if handover occurs. In case there is handover MS
100 sends radio quality measurement information pertaining to
neighboring cells to source BSS 262 using message 301. Based on the
measurement information source BSS 262 determines that handover is
required. The determination is performed using an algorithm that is
executed in a Base Station Controller (BSC) within the source BSS
262. At time to source BSS 262 determines that handover is to be
performed to a new cell, which is in the area of a new SGSN, which
is SGSN 204. Source BSS 262 sends a PS Handover Required message
302 to SGSN 202. The message comprises, for instance, the source
cell, the target cell, TLLI, cause and a transparent container.
SGSN 202 determines based on the target cell if the handover is an
intra- or inter-SGSN handover. SGSN 202 determines the identity of
a new SGSN, which in this case is SGSN 204, and sends a Prepare PS
Handover Request message 303 to SGSN 204.
[0072] At step 1202 cipher parameters pertaining to the logical
link are obtained by the LLC-entity in SGSN 204. This is achieved
so that Prepare PS Handover Request message carries cipher
parameter information element 700. Information element 700
comprises, for example, the session key K.sub.c and any other
parameters not re-negotiated at during XID-reset procedure. At step
1204 SGSN 202 starts XID-reset procedure so that LLC-entity 252 in
SGSN 202 sends an XID command message 701 to MS 100 via source BSS
262. XID command message 701 includes information on LLC parameters
such as, for example, LLC version number, IOV values,
retransmission timeout, maximum number of retransmissions, maximum
information field lengths in the two acknowledgement modes, frame
buffer sizes in uplink and downlink direction, window sizes in
uplink and downlink directions and layer-3 parameters. XID command
message 701 proposes LLC parameter values that correspond to
initial LLC values set when a new SGSN initializes its LLC-entity.
At the receipt of XID command message 701, MS 100 sets LLC
parameters to the values proposed and issues XID response message
702 acknowledging the proposed parameter values. In one embodiment
of the invention MS 100 is configured to accept the parameters
proposed by SGSN 202 automatically when it is aware that a handover
process is pending. In one embodiment of the invention MS 100
accepts a downlink PDU automatically from SGSN 204 if it is flagged
accordingly and if it is received during handover.
[0073] At step 1206 SGSN 204 starts receiving packets forwarded
from SGSN 202. In FIG. 7 such packets are carried in packet stream
308. SGSN 204 initializes its LLC-entity 254 to have initial LLC
parameter values. The initial values correspond to the
LLC-parameter values negotiated between SGSN 202 and MS 100 during
XID-reset procedure at step 1204. Thereupon, SGSN 204 starts
sending the forwarded packets towards MS 100. Afterwards, SGSN 204
and MS 100 may negotiate more optimal LLC parameters. Typically the
re-negotiation of LLC parameters is performed after routing area
update.
[0074] FIG. 13 is a flow chart depicting one embodiment of packet
switched handover, which utilizes illustrated in FIG. 8. At step
1300 MS 800 has only one LLC-entity, which is first LLC-entity 802.
First LLC-entity 802 is the peer entity for LLC-entity 252 in SGSN
202. There is an LLC connection 842 between LLC-entities 252 and
802. LLC connection 842 carries a packet stream originating from
GGSN 200 to MS 800. MS 800 waits for a condition where handover is
required. This is determined based on, for example, a handover
command received from BSS 262. When the condition is detected the
method continues in step 1302. At step 1302 MS 100 constructs a
second LLC-entity 804, which exists simultaneously with first
LLC-entity 802 at least during handover. Second LLC-entity 804 is
the peer entity for LLC-entity 254 in SGSN 204. At step 1304 MS 800
initializes second LLC-entity 804. The LLC parameters are
initialized to values compatible with the values to which SGSN 204
initializes the LLC parameters while it initializes LLC-entity 254
at step 1306. At step 1306 SGSN 204 receives packets forwarded from
SGSN 202 via a tunneling connection 241. Tunneling connection 241
is, for example, a GTP tunnel. SGSN 204 sends the forwarded packets
towards MS 800 using LLC connection 844, which it sets up between
LLC-entities 254 and 804. At step 1308 MS 800 checks if handover is
finished. If handover is not finished method continues at step
1308.
[0075] When the handover is finished LLC connection 842 between
LLC-entities 252 and 802 is no longer used to carry LLC-frames. In
one embodiment of the invention at step 1310 MS 800 checks if LLC
parameters pertaining to LLC connection 844 are suitable taking
into consideration, for example, the radio conditions at the cell
served by BTS 224. MS 800 may also readjust the parameters
depending on available memory and the data rate on LLC connection
844. In one embodiment of the invention LLC parameters at
LLC-entity 254 are initialized first to moderate values, which are
made suitable for most mobile stations under different radio
conditions. Mobile stations may have also varying memory sizes and
software versions. For example, information field lengths, frame
buffer and window sizes may be first set to values lower than would
otherwise be negotiated between peering LLC-entities. If MS 800
determines that LLC parameters are not suitable, it readjusts them
to different values at step 1312. The parameters are to be
readjusted, for example, using an XID reset procedure involving the
exchanging of XID command and XID response between LLC-entities 804
and 254. If parameter values are suitable no readjusting is
needed.
[0076] In one embodiment of the invention, MS 800 removes the first
LLC-entity, which was used prior to handover, after the handover is
complete. At step 1314 MS 800 performs the procedures necessary for
removing LLC-entity 802, which is no longer used. MS 800 may also
remove LLC-entity 802 directly after step 1308 before checking
whether the LLC parameters are suitable. The removing of LLC-entity
comprises, for example, the releasing of memory reserved for the
use of LLC-entity 802 and LLC connection 842 in MS 800. Similarly,
information pertaining to LLC-entity 802 and LLC connection 842 may
be removed from memory tables maintained in MS 800.
[0077] FIG. 14 is a flow chart depicting one embodiment of packet
switched handover method, which utilizes a duplicate frame
indicator conveyed and processed using a signaling illustrated in
FIG. 9. The signaling is performed in GPRS system architecture,
which is illustrated in FIG. 2. At step 1400 it is checked if
handover occurs. In case handover occurs MS 100 sends radio quality
measurement information pertaining to neighboring cells to source
BSS 262 using message 301. Based on the measurement information
source BSS 262 determines that handover is required. The
determination is performed using an algorithm that is executed in a
Base Station Controller (BSC) within the source BSS 262. At time to
source BSS 262 determines that handover is to be performed to a new
cell, which is in the area of a new SGSN, which is SGSN 204. Source
BSS 262 sends a PS Handover Required message 302 to SGSN 202. The
message comprises, for instance, the source cell, the target cell,
TLLI, cause and a transparent container. SGSN 202 determines based
on the target cell if the handover is an intra- or inter-SGSN
handover. SGSN 202 determines the identity of a new SGSN, which in
this case is SGSN 204, and sends a Prepare PS Handover Request
message 303 to SGSN 204.
[0078] At step 1402 cipher parameters pertaining to the logical
link are obtained by the LLC-entity in SGSN 204. This is achieved
so that Prepare PS Handover Request message carries cipher
parameter information element 900. Information element 700
comprises, for example, the session key K.sub.c and any other
parameters not re-negotiated at during a XID-reset procedure.
[0079] At step 1404 SGSN 204 waits for packets forwarded from SGSN
202 to it. When such a packet is received in message 308, the
method continues at step 1406. At step 1406 an SNDCP entity in SGSN
204 indicates to LLC-entity in SGSN 204 while requesting the
sending of an LLC-SDU that the LLC-SDU is a first LLC-SDU
comprising data from packets forwarded from SGSN 202 to SGSN 204.
The LLC-PDU is therefore a duplicate of another LLC-PDU sent from
SGSN 202. LLC-entity in SGSN 204 sets a duplicate for handover flag
in the header of the LLC-PDU to be sent. The flag may be carried
in, for example, in one of the reserved bits in LLC address field
or in one of the UI control field bits. Therefore, no extra bits
are needed in LLC-PDU header. LLC parameters are set to default
handover values. The default values may be standardized so that
optimization is maximized or normal default values are used. When
MS 100 receives the LLC-PDU in an LLC frame, it detects that the
duplicate for handover bit is set. At step 1408 MS performs
implicit XID-reset for the LLC-entity in it. In implicit XID-reset
the MS 100 sets automatically the LLC parameters to values, which
are compatible with values set by LLC-entity in SGSN 204 when it is
first created and initialized. Implicit XID-reset is required in MS
100 before it is able to process any LLC frames from SGSN 204. For
example, this is due to the differing ciphering parameters, for
example overflow count, which have not been received at step
1402.
[0080] FIG. 15 illustrates a Serving GPRS Support Node (SGSN) in
one embodiment of the invention. SGSN 1500 comprises a signaling
entity 1504, which communicates with a logical link layer entity
1506. Signaling entity 1504 performs GPRS control plane signaling.
Logical link layer entity 1506 carries both control plane and user
plane messages as specified in 3GPP 23.060 pertaining to LLC. In
the embodiment of the invention disclosed in association with the
description of FIGS. 6 and 11 logical link layer entity 1506 is
responsible for forming logical link layer Protocol Data Units
(PDU) and sending the logical link layer Protocol Data Units (PDU)
to new SGSN. In one embodiment of the invention the sending of the
logical link layer PDUs to new SGSN is achieved so that logical
link layer entity 1506 passes the PDUs to control entity 1502,
which sends them via, for example, a GTP entity 1510 to the new
SGSN. In one embodiment of the invention signaling entity 1504 is
responsible for detecting handover conditions, requesting handover
preparation from other SGSNs, receiving handover preparation
requests from other SGSNs, sending logical link layer state
information, ciphering parameters and other information to other
SGSNs. In one embodiment of the invention, the actual mobility
management and radio related application procedures associated with
signaling messages received to signaling entity 1504 are performed
by control entity 1502 or by a separate control entity within
signaling entity 1504. In one embodiment of the invention control
entity 1502 is responsible, for example, for setting the state in
logical link layer entity 1506 based on logical link layer
information received from another SGSN and sending logical link
layer frames to mobile node during handover. The actual sending of
logical link layer frames is performed via lower protocol layers
1508. The arrows in FIG. 15 illustrate directions of information
flows between the entities within SGSN 1500.
[0081] FIG. 16 illustrates a mobile node in one embodiment of the
invention. In FIG. 16 mobile node is more specifically a GPRS
mobile terminal. Mobile node 1600 comprises a signaling entity
1604, which communicates with a logical link layer entity 1606.
Logical link layer entity 1606 carries both control plane and user
plane messages as specified in 3GPP 23.060. In one embodiment of
the invention signaling entity 1604 is responsible for receiving
signaling messages from the base station subsystem and detects
handover conditions and handover completion based on received
signaling messages. Logical link layer entity 1606 performs the
Logical Link Control (LLC) protocol related tasks. In the
embodiment of the invention disclosed in association with the
description of FIG. 12 logical link layer entity 1606 is arranged
to renegotiate logical link layer parameters with new SGSN after
the handover completion. Mobile station 1600 comprises also a
control entity 1602, which performs higher protocol layer related
tasks and overall coordination of communication. In one embodiment
of the invention control entity 1602 is arranged to form a first
logical link layer entity during connection establishment procedure
and a second logical link layer entity in response to a handover
condition. The arrows in FIG. 15 illustrate directions of
information flows between the entities within mobile node 1600.
[0082] It is obvious to a person skilled in the art that with the
advancement of technology, the basic idea of the invention may be
implemented in various ways. The invention and its embodiments are
thus not limited to the examples described above; instead they may
vary within the scope of the claims.
[0083] Thus, while there have shown and described and pointed out
fundamental novel features of the invention as applied to a
preferred embodiment thereof, it will be understood that various
omissions and substitutions and changes in the form and details of
the devices illustrated, and in their operation, may be made by
those skilled in the art without departing from the spirit of the
invention. For example, it is expressly intended that all
combinations of those elements and/or method steps which perform
substantially the same function in substantially the same way to
achieve the same results are within the scope of the invention.
Moreover, it should be recognized that structures and/or elements
and/or method steps shown and/or described in connection with any
disclosed form or embodiment of the invention may be incorporated
in any other disclosed or described or suggested form or embodiment
as a general matter of design choice. It is the intention,
therefore, to be limited only as indicated by the scope of the
claims appended hereto.
* * * * *