Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
2001-04-02
2004-09-07
Dang, Khanh (Department: 2111)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C370S329000
Reexamination Certificate
active
06788944
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a wireless communications protocol. More specifically, the present invention discloses a data structure for a layer
2
protocol data unit (PDU).
2. Description of the Prior Art
The surge in public demand for wireless communication devices has placed pressure upon industry to develop increasingly sophisticated communications standards. The 3
rd
Generation Partnership Project (3GPP™) is an example of such a new communications protocol. Such standards may utilize a three-layer approach to communications. Please refer to FIG.
1
.
FIG. 1
is a block diagram of three layers in such a communications protocol. In a typical wireless environment, a first station
10
is in wireless communications with one or more second stations
20
. An application
13
on the first station
10
composes a message
11
and has it delivered to the second station
20
by handing the message
11
to a layer
3
interface
12
. Besides being used as a transmission and reception interface for the application
13
, the layer
3
interface
12
may also generate layer
3
signaling messages
12
a
for the purpose of controlling layer
3
operations between the first station
10
and the second station
20
. An example of such a layer
3
signaling message is a request for ciphering key changes, which are generated by the layer
3
interfaces
12
and
22
of both the first and the second stations, respectively. The layer
3
interface
12
delivers either the message
11
or the layer
3
signaling message
12
a
to a layer
2
interface
16
in the form of layer
2
service data units (SDUs)
14
. The layer
2
SDUs
14
may be of any length, and have an internal format that is dictated by the layer
3
interfaces
12
and
22
. The layer
2
interface
16
composes the SDUs
14
into one or more layer
2
protocol data units (PDUs)
18
. Each layer
2
PDU
18
is of a fixed length, and has an internal structure that is dictated by the layer
2
interfaces
16
and
26
. The layer
2
PDUs
18
are then passed on to a layer
1
interface
19
. The layer
1
interface
19
is the physical layer, transmitting data to the second station
20
. The transmitted data is received by the layer
1
interface
29
of the second station
20
and reconstructed into one or more PDUs
28
, which are passed up to the layer
2
interface
26
. The layer
2
interface
26
receives the PDUs
28
and builds up one or more layer
2
SDUs
24
. The layer
2
SDUs
24
are passed up to the layer
3
interface
22
. The layer
3
interface
22
, in turn, converts the layer
2
SDUs
24
back into either a message
21
, which should be identical to the original message
11
that was generated by the application
13
on the first station
10
, or a layer
3
signaling message
22
a
, which should be identical to the original signaling message
12
a
generated by the layer
3
interface
12
and which is then processed by the layer
3
interface
22
. The received message
21
is passed to an application
23
on the second station
20
.
Generally speaking, each layer in the transmitting first station
10
adds information to carry the message
11
and any appended data from the upper layers. For example, the layer
3
interface
12
packs the application message
11
into one or more layer
2
SDUs
14
. Each layer
2
SDU will not only include data from the message
11
, but will also include internal information that is required by the layer
3
interfaces
12
and
22
. The layer
2
interface
16
, in a similar manner, packs the layer
2
SDUs
14
into layer
2
PDUs
18
, each of which also has additional information required by the layer
2
interfaces
16
and
26
. On the receiving end at the second station
20
, each layer removes the added information particular to that layer, and passes the remainder up to the upper layer. Thus, the layer
2
interface
26
unpacks the layer
2
SDUs
24
from the received stream of layer
2
PDUs
28
, and passes only the layer
2
SDUs
24
up to the layer
3
interface
22
. Similarly, the layer
3
interface
22
unpacks the message
21
from the layer
2
SDUs
24
, passing only the complete message data
21
to the application
23
. As a note regarding terminology used throughout this disclosure, a PDU is a data unit that is used by a layer internally to transmit and receive information, whereas an SDU is a data unit that is passed up to, or received from, an upper layer. Thus, a layer
3
PDU is exactly the same as a layer
2
SDU. Similarly, a layer
2
PDU could also be termed a layer
1
SDU. For purposes of the following disclosure, the shortened term “SDU” is used to indicate layer
2
SDUs (that is, layer
3
PDUs), and the term “PDU” should be understood as layer
2
PDUs (i.e., layer
1
SDUs).
Of particular interest are the layer
2
interfaces
12
and
22
, which act as buffers between the relatively high-end data transmission and reception requests of the applications
13
and
23
, and the low-level requirements of the physical transmission and reception process at the layer
1
interfaces
19
and
29
. Please refer to FIG.
2
.
FIG. 2
is a diagram of a transmission/reception process from a layer
2
perspective. A layer
2
interface
32
of a transmitter
30
, which may be either a base station or a mobile unit, receives a string of layer
2
SDUs
34
from a layer
3
interface
33
. The layer
2
SDUs
34
are sequentially ordered from 1 to 5, and are of an unequal length. The layer
2
interface
32
packs the string of layer
2
SDUs
34
into a string of layer
2
PDUs
36
. The layer
2
PDUs
36
are sequentially ordered from 1 to 4, and are all of an equal length. The string of layer
2
PDUs
36
is then sent off to the layer
1
interface
31
for transmission. A reverse process occurs at the receiver end
40
, which may also be either a base station or a mobile unit, with a receiver layer
2
interface
42
unpacking a received string of layer
2
PDUs
46
into a received string of layer
2
SDUs
44
. Under certain transport modes, the multi-layered protocol insists that the receiver layer
2
interface
42
present the layer
2
SDUs to the layer
3
interface
43
in order. That is, the layer
2
interface
42
must present the SDUs
44
to the layer
3
interface
43
in the sequential order of the SDUs
44
, beginning with SDU
1
and ending with SDU
5
. The ordering of the SDUs
44
may not be scrambled, nor may a subsequent SDU be delivered to layer
3
until all of the prior SDUs have been delivered.
In line transmissions, such a requirement is relatively easy to fulfill. In the noisy environment of wireless transmissions, however, the receiver
40
, be it a base station or a mobile unit, often misses data. Some layer
2
PDUs in the received string of PDUs
46
will therefore be missing. Thus, ensuring that the layer
2
SDUs
44
are presented in order can pose a significant challenge. Wireless protocols are carefully designed to address such problems. Please refer to
FIG. 3
with reference to FIG.
1
.
FIG. 3
is a simplified block diagram of a layer
2
PDU
50
, as defined in the 3GPP™ TS 25.322 specification. In general, there are two types of PDUs: a control PDU or a data PDU. Control PDUs are used by the layer
2
interfaces
16
and
26
to control data transmission and reception protocols. This is somewhat analogous to the exchange of the signaling messages
12
a
and
22
a
of the layer
3
interfaces
12
and
22
. However, the layer
2
interfaces
16
and
26
do not interpret or recognize the layer
3
signaling messages
12
a
and
22
a
, whereas the layer
2
interfaces
16
and
26
do recognize layer
2
control PDUs, and do not hand layer
2
control PDUs up to the layer
3
interfaces
12
and
22
. Data PDUs are used to transmit data from the upper layers, i.e., the layer
3
interfaces
12
and
22
. Upon reception of data PDUs, the data contained therein is reassembled and presented to the upper layer
3
interface
12
or
22
AsusTek Computer Inc.
Dang Khanh
Hsu Winston
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