Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
2001-07-09
2004-04-20
Urban, Edward F. (Department: 2685)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S438000, C455S440000, C455S442000, C370S331000
Reexamination Certificate
active
06725040
ABSTRACT:
BACKGROUND OF INVENTION
1. Field of the Invention
The present invention relates to a wireless communications network. In particular, the present invention discloses a method for performing lossless relocation of a serving radio network subsystem.
2. Description of the Prior Art
Please refer to FIG.
1
.
FIG. 1
is a block diagram of a wireless communications network
10
. The wireless communications network
10
comprises a plurality of radio network subsystems (RNSs)
20
in communications with a core network (CN)
30
. Each RNS
20
comprises one radio network controller (RNC)
22
that is in communications with a plurality of node Bs
24
. Each node B
24
is a transceiver, which is adapted to send and receive wireless signals. In particular, the wireless communications network
10
assigns a mobile unit
40
to a particular RNS
20
, which is then termed the serving RNS (SRNS)
20
s
of the mobile unit
40
. Data destined for the mobile unit
40
is sent by the CN
30
to the SRNS
20
s
. This data is in the form of service data units (SDUs)
28
that are held by the RNC
22
of the SRNS
20
s
pending transmittal by one of the Node Bs
24
. The RNC
22
selects a node B
24
that is best able to accurately transmit the SDUs
28
to the mobile unit
40
. Such a selection will depend, for example, upon the location of the mobile unit
40
within the domain of the SRNS
20
s
. The mobile unit
40
broadcasts SDUs
48
to the wireless communications network
10
, which are then picked up by the SRNS
20
s
and forwarded to the CN
30
. Occasionally, the mobile unit
40
may move close to the domain of another RNS
20
, which is termed a drift RNS (DRNS)
20
d
. A node B
24
of the DRNS
20
d
may pick up one or more of the SDUs
48
transmitted by the mobile unit
40
. The RNC
22
of the DRNS
20
d
forwards the received SDUs
48
to the SRNS
20
s
. The SRNS
20
s
then forwards these received SDUs
48
to the CN
30
. Consequently, all communications between the mobile unit
40
and the CN
30
must pass through the SRNS
20
s.
Please refer to
FIG. 2
in conjunction with FIG.
1
.
FIG. 2
is a block diagram of the RNC
22
of the SRNS
20
s
. Communications between the mobile unit
40
and the RNC
22
are effected through a multi-layered communications protocol that has a packet data convergence protocol (PDCP) layer
22
p
in communications with an upper layer
22
u
and a lower layer
22
L. The PDCP layer
22
p
receives a plurality of SDUs
28
from the upper layer
22
u
. Each SDU
28
includes a header
28
h
and data
28
d
. The primary purpose of the SDU
28
is to carry the data
28
d
to a destination indicated by the header
28
h
. The header
28
h
is analogous to an Internet protocol (IP) header. The header
28
h
may carry a lot of information that is redundant or repeated through the other SDU headers
28
h
in the other SDUs
28
. One purpose of the PDCP layer
22
p
is to compresses the headers
28
h
so as to maximize bandwidth. This compression is performed by way of a header compressor/decompressor
22
c
. The header compressor/decompressor accepts an SDU
28
and generates a PDCP protocol data unit (PDCP PDU)
29
. A PDCP PDU
29
includes a PDCP header
29
h
and data
29
d
. The data
29
d
includes compressed header data
29
x
that is generated by the header compressor/decompressor
22
c
according to the header
28
h
. Each PDCP PDU
29
s
is incrementally assigned a 16-bit sequence number (SN)
29
s
by the PDCP layer
22
p
. That is, each sequentially successive PDCP PDU
29
is assigned an incrementally higher SN
29
s
. For example, a first PDCP PDU
29
may be assigned an SN
29
s
of 62. A second PDCP PDU
29
immediately after the first PDCP PDU
29
would thus be assigned an SN
29
s
of 63, and so on. The SNs
29
s
are not actually a part of the PDCP PDUs
29
, but are internally maintained by the PDCP layer
22
p
. The PDCP PDUs
29
are then delivered to the lower layer
22
L for transmission. As there is a one-to-one correspondence between PDCP PDUs
29
and SDUs
28
, and as each PDCP PDU
29
has an assigned SN
29
s
, each corresponding SDU
28
also has an associated SN
29
s
. That is, the SNs
29
s
are associated with both the PDCP PDUs
29
and the corresponding SDUs
28
. Since bandwidth is to be maximized by the compression of the headers
28
h
, each PDCP PDU
29
should, ideally, be smaller in size than its corresponding SDU
28
. To ensure that this is indeed the case, the PDCP header
29
h
should be kept as small as possible. The type of header compression used for the header compressor/decompressor
22
c
will depend upon the format of the headers
28
h
. As an example, though, if the headers
28
h
are IP headers, then the compression performed could conform to the IP industry standard RFC 2507.
Similarly, PDCP PDUs
27
received from the lower layer
22
L (i.e., originating from the mobile unit
40
) are fed into the header compressor/decompressor
22
c
to generate the corresponding SDUs
48
. The SDUs
48
so generated are then delivered to the upper layer
22
u
. Each PDCP PDU
27
has a 16-bit SN
27
s
assigned to the PDCP PDU
27
by the PDCP layer
22
p
, in a manner that is analogous to the SNs
29
s
. These SNs
27
s
are also associated with the corresponding SDUs
48
.
As the mobile unit
40
moves closer towards the domain of the DRNS
20
d
, more and more SDUs
48
are received and forwarded by the DRNS
20
d
. Eventually, a decision is made by the wireless network
10
to place the mobile unit
40
under the DRNS
20
d
, and a transfer process is enacted. This process is termed a SRNS relocation procedure, and should be lossless. Lossless means that no SDUs
28
,
48
are lost during the relocation procedure. Please refer to
FIG. 3
in conjunction with
FIGS. 1 and 2
.
FIG. 3
is a block diagram of the mobile unit
40
undergoing a lossless SRNS relocation procedure. The DRNS
20
d
becomes a target RNS (TRNS)
20
t
. After completion of the relocation procedure, the TRNS
20
t
will serve as the new SRNS
20
s
for the mobile unit
40
. In order for the TRNS
20
t
to properly take up its job as the new SRNS
20
s
for the mobile unit
40
, the current SRNS
20
s
must forward key information to the TRNS
20
t
. Please refer to
FIG. 4
in conjunction with
FIGS. 2 and 3
.
FIG. 4
is a message sequence chart for the prior art lossless SRNS relocation procedure. The SRNS
20
s
sends forwarding information
50
to the TRNS
20
t
. This forwarding information includes a downlink sending sequence number (DL Send_SN)
52
, an uplink receiving sequence number (UL Receive_SN)
54
, and all unconfirmed SDUs
28
. The multi-layered communications protocol used by both the SRNS
20
s
and the mobile unit
40
enables the mobile unit
40
to confirm those PDCP PDUs
29
transmitted by the SRNS
20
s
that are successfully received by the mobile unit
40
. Any PDCP PDUs
29
not explicitly confirmed as received by the mobile unit
40
are termed unconfirmed PDCP PDUs
29
. As there is a one-to-one correspondence between SDUs
28
and PDCP PDUs
29
, an unconfirmed PDCP PDU
29
means that there is a corresponding unconfirmed SDU
28
. These unconfirmed SDUs
28
are forwarded by the SRNS
20
s
to the TRNS
20
t
. The DL Send_SN
52
is the value of the SN
29
s
associated with the sequentially earliest unconfirmed PDCP PDU
29
. As the SNs
29
s
are not explicitly carried in the SDUs
28
, this enables the TRNS
20
t
to properly associate an SN
29
s
for the corresponding PDCP PDU
29
of each forwarded SDU
28
. The UL Receive_SN
54
is the value of the SN
27
s
associated with the PDCP PDU
27
that the SRNS
20
s
next expects to receive from the mobile unit
40
. This enables the TRNS
20
t
to properly associate an SN
27
s
for each subsequently received PDCP PDU
27
from the mobile unit
40
. The TRNS
20
t
sends the UL Receive SN
54
to the mobile unit
40
. From this, the mobile unit
40
can determine which packets
48
to begin sending to the TRNS
20
s
under its guise as the new SR
AsusTek Computer Inc.
Hsu Winston
Le Duy K
Urban Edward F.
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