Determination of acceptable sequence number ranges in a...

Details Determination of acceptable sequence number ranges in a... Determination of acceptable sequence number ranges in a...

2001-02-09

2004-07-20

Yao, Kwang Bin (Department: 2667)

Multiplex communications

Communication over free space

Having a plurality of contiguous regions served by...

C370S394000, C370S469000

Reexamination Certificate

active

06765885

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 method for determining acceptable sequence number ranges in a transmission time interval.
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 utilize a three-layer approach to communications. Please refer to FIG.
1
.
FIG. 1
is a block diagram of the three layers in 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
. The layer
3
interface
12
may also generate some layer
3
signaling messages
12
a
for the purpose of controlling layer
3
operations. 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. 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 is delivered 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
.
Of particular interest is the layer
2
interface, which acts as a buffer between the relatively high-end data transmission and reception requests of the layer
3
interfaces
12
and
22
, 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 simplified diagram of a transmission/reception process from a layer
2
perspective. The layer
2
interface
32
of a first station
30
receives a string of SDUs
34
from the 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
converts the string of SDUs
34
into a string of layer
2
PDUs
36
. The layer
2
PDUs
36
are sequentially ordered from 1 to 4, and are usually 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 second station
40
, with the second station
40
layer
2
interface
42
converting a received string of layer
2
PDUs
46
into a received string of layer
2
SDUs
44
, which are then passed up to a layer
3
interface
43
. There are two delivery modes: in-sequence delivery and out-of-sequence delivery. If the established connection between the first station
30
and the second station
40
is configured to be in the in-sequence delivery mode, the multi-layered protocol insists that the layer
2
interface
42
present the SDUs
44
to the layer
3
interface
43
in order. That is, the layer
2
interface
42
must present the layer
2
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
44
be delivered to the layer
3
interface
43
until all of the prior SDUs
44
have been delivered. However, if the established connection is configured to be in the out-of-sequence delivery mode, the layer
2
interface
42
can present the layer
2
SDUs
44
to the layer
3
interface
43
out of sequential order.
In line transmissions, such requirements are relatively easy to fulfill. In the noisy environment of wireless transmissions, however, the second station
40
often misses data. Additionally, under some transmission modes, the layer
2
interface
32
of the first station
30
may actually discard some of the layer
2
SDUs
34
or layer
2
PDUs
36
after a predetermined amount of time if the layer
2
SDUs
34
or PDUs
36
have not been transmitted. Some layer
2
PDUs in the received string of layer
2
PDUs
46
will therefore be missing, either due to deliberate discarding from the transmitting side, or from improper reception on the receiver side. Ensuring that the layer
3
SDUs
44
are presented in order, when the system is in the in-sequence delivery mode, can thus pose a significant challenge. Even in the out-of sequence delivery mode, a layer
2
SDU
44
cannot be presented until all of its composing layer
2
PDUs
46
have been correctly received. The format of the layer
2
PDUs
36
,
46
is thus carefully considered to help overcome these obstacles.
Generally speaking, there are two broad modes for transmitting and receiving data: acknowledged mode, and unacknowledged mode. For acknowledged mode data, the second station
40
sends a special acknowledging signal to the first station
30
to indicate successfully received layer
2
PDUs
46
. No such signaling is performed for unacknowledged mode data. For purposes of the present discussion, only the unacknowledged mode of data transmission and reception is considered. Please refer to
FIG. 3
in conjunction with FIG.
2
.
FIG. 3
is a block diagram of an unacknowledged mode data (UMD) PDU
50
, as defined by the 3GPP™ TS 25.322 specification. The UMD PDU
50
is used to transmit unacknowledged mode SDU data from the layer
3
interface
33
of the first station
30
, which is then received and reassembled by the second station
40
and presented to the layer
3
interface
43
as the layer
2
SDUs
44
. That is, layer
2
UMD PDUs
36
,
46
are used to carry the layer
2
SDUs
34
,
44
that originate from the layer
3
interfaces
33
,
43
. The UMD PDU
50
is divided into several fields, as defined by the layer
2
protocol. The first field
51
is a sequence number (SN) field, and is seven bits long. Successive UMD PDUs have successively higher sequence numbers, and in this way a receiver can properly reassembled UMD PDUs
46
to form the SDUs
44
. That is, if a UMD PDU
36
is transmitted with a sequence number value equal to 19, the next UMD PDU
36
would be transmitted with a sequence number value equal to 20, and so forth. The next field,
52
a
, is an extension bit, and when set indicates the presence of a following length indicator (LI). An LI may be either 7 bits long or 15 bits long, and is used to indicate the ending position of an SDU within the UMD PDU
50
. If a single SDU completely fills the data region
58
of the UMD PDU
50
, then the extension bit
52
a
would be zero, thereby indicating that no LI is present. In the example UMD PDU
50
, however, there are at least two SDUs ending in the PDU
50
:

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