U.S. patent application number 13/458443 was filed with the patent office on 2012-08-23 for media access control apparatus and method for guaranteeing quality of service in wireless lan.
This patent application is currently assigned to ELECTRONICS AND TELECOMMUNICATIONS RESEARCH INSTITUTE. Invention is credited to Dae Hwan HWANG, Ki Jong KOO.
Application Number | 20120213065 13/458443 |
Document ID | / |
Family ID | 34698506 |
Filed Date | 2012-08-23 |
United States Patent
Application |
20120213065 |
Kind Code |
A1 |
KOO; Ki Jong ; et
al. |
August 23, 2012 |
MEDIA ACCESS CONTROL APPARATUS AND METHOD FOR GUARANTEEING QUALITY
OF SERVICE IN WIRELESS LAN
Abstract
A media access control (MAC) apparatus and corresponding methods
for guaranteeing quality-of-service in a wireless local area
network (LAN) are presented. The MAC method includes extracting,
performing, determining, a first transmitting step, and a second
transmitting step. The extracting includes extracting a user
priority from a frame received from an upper layer and separately
storing a voice frame and a non-voice frame according to an access
category (AC). The performing includes independently performing
backoff operations for the voice frame and the non-voice frame. The
determining includes determining whether the backoff operations for
the voice frame and the non-voice frame have simultaneously ended.
The first transmitting includes transmitting the voice frame having
a higher priority first and performing the backoff operation for
the non-voice frame if the backoff operations have simultaneously
ended. The second transmitting includes transmitting a frame whose
backoff operation ends if the backoff operations have not
simultaneously ended.
Inventors: |
KOO; Ki Jong; (Daejeon-city,
KR) ; HWANG; Dae Hwan; (Daejeon-city, KR) |
Assignee: |
ELECTRONICS AND TELECOMMUNICATIONS
RESEARCH INSTITUTE
DAEJEON-CITY
KR
|
Family ID: |
34698506 |
Appl. No.: |
13/458443 |
Filed: |
April 27, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12423938 |
Apr 15, 2009 |
8199729 |
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13458443 |
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12349867 |
Jan 7, 2009 |
7616612 |
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12423938 |
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10917684 |
Aug 12, 2004 |
7489666 |
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12349867 |
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Current U.S.
Class: |
370/229 |
Current CPC
Class: |
H04W 28/14 20130101;
H04W 72/1242 20130101; H04W 84/12 20130101 |
Class at
Publication: |
370/229 |
International
Class: |
H04W 28/06 20090101
H04W028/06 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 26, 2003 |
KR |
10-2003-0097155 |
Claims
1. A media access control (MAC) method in a MAC apparatus
comprising: independently performing a backoff for a voice frame
and a non-voice frame; transmitting the voice frame with a higher
priority and invoking the backoff for the non-voice frame when the
backoff for the voice frame and the non-voice frame simultaneously
end; and transmitting a frame whose backoff ends first when the
backoff for the voice frame and the non-voice frame do not
simultaneously end.
2. The method of claim 1, further comprising: receiving a frame
from an upper layer comprising the voice frame and the non-voice
frame; detecting a busy channel; waiting during a distribution
inter-frame space (DIFS) time; and performing the backoff when the
channel is idle after the DIFS time lapses, wherein the backoff
operation is performed to obtain a channel access right.
3. The method of claim 1, wherein Arbitration inter-frame space
(AIFS) of the voice frame is shorter than the one of the non-voice
frame.
4. The method of claim 3, wherein ACK policy information is
included in a QoS control field of a header in the frame.
5. The method of claim 2, further comprising: transmitting the
frame without the backoff when the transmission queue is empty and
the channel is idle after the DIFS lapses.
6. The method of claim 1, further comprising: stopping the backoff
when the channel becomes busy during the backoff.
7. The method of claim 2, further comprising: performing backoff
from a last backoff count when the channel is continuously idle
during the DIFS time.
8. A media access control (MAC) apparatus comprising: a first
transmission queue configured to transmit a voice frame; a second
transmission queue configured to transmit a non-voice frame; and a
controller configured to independently perform a backoff for the
voice frame and the non-voice frame, transmit the voice frame with
a higher priority and invoking the backoff for the non-voice frame
when the backoff for the voice frame and the non-voice frame
simultaneously end, and transmit a frame whose backoff ends first
when the backoff for the voice frame and the non-voice frame do not
simultaneously end.
9. The apparatus of claim 8, wherein the controller is further
configured to receive a frame from an upper layer comprising the
voice frame and the non-voice frame, detect a busy channel, wait
during a distribution inter-frame space (DIFS) time, and perform
the backoff when the channel is idle after the DIFS time lapses,
wherein the backoff operation is performed to obtain a channel
access right.
10. The apparatus of claim 9, wherein the controller is further
configured to transmit the frame without the backoff when the
transmission queue is empty and the channel is idle after the DIFS
lapses.
11. The apparatus of claim 8, wherein the controller is further
configured to stop the backoff when the channel becomes busy during
the backoff.
12. The apparatus of claim 9, wherein the controller is further
configured to perform backoff from a last backoff count when the
channel is continuously idle during the DIFS time.
13. A media access control method in a MAC apparatus, comprising:
independently performing backoff in transmit queues; checking
whether the independent backoff simultaneously end in the transmit
queues; transmitting a frame having a higher priority and invoking
backoff operation for a frame having a lower priority when at least
two of the backoff simultaneously end; and transmitting a frame
whose backoff ends first when the backoff operations do not
simultaneously end.
14. The method of claim 13, wherein the frame comprises a header
having an acknowledgement (ACK) policy information field
representing whether a receiver should transmit an ACK
response.
15. The method of claim 14, wherein a QoS Control field of the
header includes the ACK policy information.
16. A media access control (MAC) apparatus, comprising: a frame
handler configured to classify frames into at least two groups
based on the user priority, and configured to store the frames in
at least two transmit queues corresponding to the groups; and a
controller configured to independently perform backoff operations
in the transmit queues, check whether or not the independent
backoff operations simultaneously end, transmit a frame having a
higher priority and invoking backoff operation for a frame having a
lower priority when at least two of the backoff operations
simultaneously end, and transmit a frame whose backoff operation
ends first when the backoff operations do not simultaneously
end.
17. The apparatus of claim 16, wherein the frame comprises a header
having an acknowledgement (ACK) policy information field
representing whether a receiver should transmit an ACK
response.
18. The apparatus of claim 17, wherein a QoS Control field of the
header includes the ACK policy information.
19. A computer program embodied on a non-transitory computer
readable medium, the computer program being configured to control a
processor to perform the method of claim 1.
20. A computer program embodied on a non-transitory computer
readable medium, the computer program being configured to control a
processor to perform the method of claim 13.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims priority under 35 U.S.C
119(a) to Korean Application No. 10-2003-0097155, filed on Dec. 26,
2003, in the Korean Intellectual Property Office, and claims the
benefit under 35 U.S.C. .sctn.119(e) of U.S. patent application
Ser. No. 10/917,684, filed on Aug. 12, 2004, now issued as U.S.
Pat. No. 7,489,666, U.S. patent application Ser. No. 12/349,867,
filed on Jan. 7, 2009, now issued as U.S. Pat. No. 7,616,612, and
U.S. patent application Ser. No. 12/423,938, filed on Apr. 15,
2009, which are incorporated herein by reference in their entirety
as set forth in full.
BACKGROUND
[0002] 1. Field
[0003] The present invention relates to a quality-of-service
technology for a communication system, and more particularly, to an
apparatus and method for guaranteeing quality-of-service in a
wireless local area network (LAN).
[0004] 2. Description of the Related Art
[0005] A voice-over-Internet protocol (VoIP) technology represents
an IP telecommunication technology used when a plurality of
facilities transfer voice information using an IP. In general, the
VoIP technology deals with not a conventional protocol based on
circuit as used for a public switched telephone network (PSTN) but
a protocol for sending voice information with a digital format in
discontinuous packets. Therefore, since packet transmission is
discontinuously achieved, it is difficult to guarantee
quality-of-service (QoS).
[0006] The QoS of voice information must be guaranteed for VoIP
services. Accordingly, an IEEE 802.11 wireless LAN media access
control (MAC) technology has recently been suggested as a new LAN
technology for guaranteeing the QoS.
[0007] However, the IEEE 802.11 MAC technology cannot support
frames to which discriminated user priorities are applied.
Basically, when a channel access right is granted, a distributed
coordination function (DCF) provides the same proportional channel
access right to all stations contending for channels in a basic
service set (BSS). However, the same proportional channel access
right is not preferable for stations having different user
priorities. Therefore, from the point of view of the QoS, the MAC
technology must discriminately deal with frames having different
priorities and provide a QoS field included in a frame header.
SUMMARY
[0008] The present invention provides a media access control (MAC)
apparatus for guaranteeing quality-of-service (QoS) in a wireless
local area network (LAN), which can guarantee the QoS of VoIP
services with a relatively simple method in a wireless LAN
environment, and a method thereof.
[0009] According to an embodiment of the present invention, there
is provided a media access control (MAC) apparatus comprising: a
first transmission queue storing a voice transmission frame; a
second transmission queue storing a general transmission frame; a
frame handler extracting user priority information from a frame
input from an upper layer, mapping the frame to a relevant access
category (AC), and storing the frame in the first transmission
queue or the second transmission queue; a MAC controller
determining a backoff operation timing and a frame transmission
timing by checking a media status; a first arbitration inter-frame
space (AIFS) timer and a second AIFS timer, each reducing a
predetermined timer value set by the MAC controller by a
predetermined value unit; a first backoff block and a second
backoff block, each performing a separate backoff operation for
each AC using a predetermined backoff count value; a contention
resolution unit, which transmits the voice frame having a higher
user priority first and gives up transmission of the non-voice
frame when two ACs simultaneously end the backoff operations; a
frame detector, which determines whether or not to transmit ACK by
checking an ACK policy bit from a header of the received frame when
a frame is received from a physical layer; and a receive queue
storing the received frame and transmitting the frame to the upper
layer.
[0010] According to another embodiment of the present invention,
there is provided a media access control (MAC) method comprising:
extracting a user priority from a frame received from an upper
layer and separately storing a voice frame and a non-voice frame
according to an access category (AC); independently performing
backoff operations for the voice frame and the non-voice frame;
determining whether the backoff operations for the voice frame and
the non-voice frame have simultaneously ended; if the backoff
operations have simultaneously ended, transmitting the voice frame
having a higher priority first and performing the backoff operation
for the non-voice frame; and if the backoff operations have not
simultaneously ended, transmitting a frame whose backoff operation
ends.
[0011] According to another embodiment of the present invention,
there is provided a media access control (MAC) method comprising:
receiving a frame from a physical layer; decoding an ACK policy
from a header of the frame and determining whether or not to
perform an ACK response based on the decoded ACK policy; when the
ACK response must be performed, transmitting an ACK frame and
storing the received frame in a receive queue; and when a host is
ready, transmitting the frame to an upper layer regardless of a
priority.
[0012] Accordingly to yet another embodiment of the present
invention, there is provided a computer-usable medium having
computer readable instructions stored thereon for execution by a
processor in a wireless communication system to perform a media
access control (MAC) method comprising: extracting a user priority
from a frame received from an upper layer; mapping the frame to an
access category (AC) based on the user priority; storing a voice
frame exclusively in a first transmit queue, and storing a
non-voice frame in a second transmit queue according to the AC;
performing independently backoff operations in the first transmit
queue and the second transmit queue; checking whether or not the
independent backoff operations simultaneously end; transmitting the
voice frame having a higher priority and invoking backoff operation
for the non-voice frame when backoff operations simultaneously end;
and transmitting a frame whose backoff operation ends first when
backoff operations do not simultaneously end. The computer-usable
medium of this embodiment may optionally further comprising adding
a header having an acknowledgement (ACK) policy information to the
frame before transmitting the frame. An arbitration inter-frame
space (AIFS) of the voice frame can be longer than the one of the
non-voice frame. The ACK policy information can be included in a
QoS Control field of the header. Further, the ACK policy
information can be associated with whether or not a receiver should
transmit an ACK response. According to still yet another embodiment
of the present invention, there is provided a computer-usable
medium having computer readable instructions stored thereon for
execution by a processor in a wireless communication system to
perform a media access control method comprising: extracting a user
priority from frames received from an upper layer; classifying the
frames into at least two groups based on the user priority; storing
the frames respectively in at least two transmit queues
corresponding to the groups; performing independently backoff
operations in the transmit queues; checking whether or not the
independent backoff operations simultaneously end; transmitting a
frame having a higher priority and invoking a backoff operation for
a frame having a lower priority when at least two of the backoff
operations simultaneously end; and transmitting a frame whose
backoff operation ends first when the backoff operations do not
simultaneously end. This embodiment of the computer-usable medium
may also further comprise adding a header having an acknowledgement
(ACK) policy information to the frame before transmitting the
frame. Further the ACK policy information may also be included in a
QoS Control field of the header in which the ACK policy information
is associated with whether or not a receiver should transmit
ACK.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] The above and other features and advantages of the present
invention will become more apparent by describing in detail
exemplary embodiments thereof with reference to the attached
drawings in which:
[0014] FIG. 1 illustrates configurations of a header of a MAC frame
and a QoS control field included in the header of the MAC
frame;
[0015] FIG. 2 illustrates a procedure for performing an IEEE 802.11
DCF;
[0016] FIG. 3 is a block diagram of a MAC apparatus for supporting
QoS in a wireless LAN according to an exemplary embodiment of the
present invention; and
[0017] FIGS. 4 and 5 are flowcharts illustrating methods of
supporting QoS in a wireless LAN, which are performed in the MAC
apparatus shown in FIG. 3, according to exemplary embodiments of
the present invention.
DETAILED DESCRIPTION
[0018] Hereinafter, the present invention will now be described
more fully with reference to the accompanying drawings, in which
embodiments of the invention are shown.
[0019] FIG. 1 illustrates configurations of a header of a MAC frame
and a QoS control field included in the header of the MAC frame.
FIG. 2 illustrates a procedure for performing an IEEE 802.11
DCF.
[0020] An IEEE 802.11 MAC is based on a logic function called a
coordination function. The coordination function determines whether
a station transmits or receives a frame in a basic service set
(BSS). The coordination function is divided into two functions,
such as a distribution coordination function (DCF) based on a
contention method and a point coordination function (PCF) based on
a poll-response method, according to a method of obtaining a
channel access right. Today, most 802.11 apparatuses operate using
the DCF.
[0021] The 802.11 DCF operates with one transmission queue and is
located in a distributed MAC having a local evaluation function
with which a channel status can be evaluated in order to support a
carrier sense multiple access collision avoidance (CSMA/CA)
protocol.
[0022] Referring to FIG. 1, since a QoS control field is included
in a header of a MAC frame, one of a plurality of priority values
can be carried in the QoS control field. If a host or a router
sending traffic to a LAN grants an appropriate priority for an
individual packet to be transmitted, LAN devices, such as switches,
bridges, and hubs, appropriately deal with the packet.
[0023] Referring to FIG. 2, if a channel is busy when a frame
arrives in a transmission queue from an upper layer, after a MAC
apparatus waits until a medium is idle, the MAC apparatus waits
during a DCF inter-frame space (DIFS) time. If the channel is still
idle after the DIFS time lapses, the MAC apparatus performs a
backoff operation (transmission wait and try) to obtain a channel
access right using a random backoff counter.
[0024] If the medium is idle during every slot time, the MAC
apparatus decreases a random backoff count value, and if the count
value becomes 0, the MAC apparatus transmits the frame. If the
transmission queue is empty and the channel is idle for longer than
the DIFS time when a frame arrives in the transmission queue, the
MAC apparatus immediately transmits the frame without the backoff
operation. If the channel becomes busy during the backoff
operation, the MAC apparatus stops the backoff operation, and if
the channel is continuously idle during the DIFS time, the MAC
apparatus performs the backoff operation from the last backoff
count value again.
[0025] Each station maintains a contention window (CW), which uses
the random backoff count value. The backoff count value is a pseudo
random integer selected with an even probability in a range of [0,
CW]. The CW is initialized to CWmin and increases by CW=2(CW+1)-1
whenever transmission fails. This is a method for reducing a
collision proportion when a plurality of stations try to transmit.
The CW is set to at most CWmax, and after frame transmission
normally ends, the CW is initialized to CWmin. Also, even if a
frame waiting for transmission is not in the transmission queue, a
station, which has transmitted all data, waits during the DIFS
time, performs the backoff operation, and ends a transmission
process.
[0026] If a station successfully receives a frame, after a short
inter-frame space (SIFS) time lapses, the station indicates that it
has received the frame by immediately transmitting an ACK frame. If
a station does not receive the ACK frame after transmitting data,
the station performs retransmission after the random backoff
operation.
[0027] As described above, in the IEEE 802.11 MAC apparatus, if the
MAC apparatus includes only one transmission queue, since a
subsequent frame can be transmitted only after the transmission of
a preceding frame ends, when the transmission of the preceding
frame is delayed, it is difficult to guarantee QoS. This problem
can be solved with a plurality of queues. The IEEE 802.11e standard
recommends more than 4 classes of queues in a case of an access
point (AP) supporting a point-to-multipoint access. Also, the DCF
of the IEEE 802.11 MAC standard uses DIFS, CWmin, and CWmax, in
which priorities are not considered. Since the MAC standard
performs the backoff operation during a relatively long time for a
frame requiring QoS, it is difficult to guarantee the QoS.
[0028] Also, since the DCF of the IEEE 802.11 MAC standard ends a
frame transmission process only if an ACK response is received with
respect to all data and a management frame, the DCF is not suitable
for a frame requiring QoS in which transmission timing is more
important than transmission quality. This problem can be solved by
limiting the ACK response for a frame for which the QoS is
required.
[0029] Therefore, in an embodiment of the present invention, to
solve a QoS problem of a terminal supporting a VoIP service with
two classes of transmission queues, for real-time traffic such as
an access category 3 (AC-3), a queue for VoIP exclusive use is
used, an AIFS[3] parameter, a CWmin[3] parameter, and a CWmax[3]
parameter are used to guarantee a higher priority, and an ACK
response in response to a transmitted VoIP frame is not received.
For general traffic, to support priorities of all frames except the
VoIP frame, an AIFS[AC] parameter, a CWmin[AC] parameter, and a
CWmax[AC] parameter are used according to the AC, and an ACK
response may be received or not. A configuration of a MAC apparatus
having the features described above will now be described.
[0030] FIG. 3 is a block diagram of a MAC apparatus 100 for
supporting QoS in a wireless LAN according to an exemplary
embodiment of the present invention. The MAC apparatus 100 is an
IEEE 802.11 wireless LAN MAC apparatus 100 suitable for a terminal
supporting a VoIP service.
[0031] Referring to FIG. 3, the MAC apparatus 100 includes a frame
handler 101, first and second transmission queues 102 and 103, a
MAC controller 104, first and second arbitration inter-frame space
(AIFS) timers 105 and 106, first and second backoff blocks 107 and
108, a frame detector 109, a receive queue 110, and a collision
resolution unit 111. Here, the first transmission queue 102 is
composed of a voice frame transmission first-in-first-out (FIFO),
and the second transmission queue 103 is composed of a non-voice
frame transmission FIFO. The receive queue 110 is also composed of
a FIFO.
[0032] When a frame is received from an upper layer, the frame
handler 101 extracts user priority (UP) information from a traffic
ID (TID) included in a QoS control field (refer to FIG. 1) of a
frame header, and if the frame is a voice frame, the frame handler
101 maps the frame to AC[3], and if the frame is a non-voice frame,
the frame handler 101 maps the frame to AC[0]-AC[2]. Also, if the
frame is a voice frame, the frame handler 101 stores the frame in
the first transmission queue 102, which is the voice frame
exclusive transmission FIFO, and if the frame is a non-voice frame,
the frame handler 101 stores the frame in the second transmission
queue 103, which is the non-voice frame transmission FIFO.
[0033] If it is determined by the frame handler 101 that the AC is
3 and a voice frame transmission request is generated, the MAC
controller 104 checks a medium status and determines a backoff
operation timing and a frame transmission timing. Also, when the
frame transmission request is generated, if the medium is busy, the
MAC controller 104 waits until the medium is idle and sets the
first and second AIFS timers 105 and 106 to an SIFS+AIFS[3] slot
time according to the AC[3]. If the frame is a voice frame, a set
value of the first AIFS timer 105 is the same as a value of a
priority inter-frame space (PIFS).
[0034] Each of the timers 105 and 106 is a timer for reducing the
set value (SIFS+AIFS[3] slot time) in units of 1 .mu.s. If the
medium is still idle after the timer value becomes 0, the MAC
controller 104 commands a relevant backoff block to perform a
backoff operation on the frame. If two frames having different ACs
are in the first and second transmission queues 102 and 103,
respectively, and if separate frame transmission requests are
generated, the MAC controller 104 commands the first and second
backoff blocks 107 and 108 to independently perform backoff
operations on the two frames.
[0035] Each of the first and second backoff blocks 107 and 108 uses
a pseudo random integer evenly distributed in a range of [0, CW] as
a backoff count value. At this time, the CW is initialized with
CWmin[AC] and increases by CW=2(CW+1)-1 whenever frame transmission
fails. The CW has CWmax[AC] as a maximum value, and even if frame
transmission fails, the CW does not increase more than CWmax[AC].
Each of the first and second backoff blocks 107 and 108 starts a
backoff operation using a backoff count value selected by the
method described above, decreases a random backoff count value in
every slot time in which the medium is idle while performing the
backoff operation, and informs the MAC controller 104 of the end of
the backoff operation if the random backoff count value becomes
0.
[0036] If the MAC controller 104 is informed of the end of the
backoff operation, the MAC controller 104 transmits a frame of the
AC for which the backoff operation is performed to a physical
layer. At this time, if two ACs simultaneously end the backoff
operations, the collision resolution unit 111 transmits a voice
frame having a higher UP first and gives up transmission of other
non-voice frames. The collision resolution unit 111 commands the
second backoff block 108 to perform the backoff operation again
using an increased CW value for the other non-voice frame.
[0037] Also, when a transmission request is generated, if the
medium is in a waiting status during the AFIS[AC] or performing the
backoff operation, the MAC controller 104 waits until the medium is
idle. When the medium is idle, the MAC controller 104 sets one of
the first and second AIFS timers 105 and 106 to an AIFS timer value
according to an AC value and waits until the AIFS timer value
becomes 0. If the medium is still idle after the AFIS[AC] time
lapses, the MAC controller 104 starts a backoff operation by
selecting one of the first and second backoff blocks 107 and 108.
If the medium is idle during every slot time while performing the
backoff operation, the MAC controller 104 decreases a random
backoff count value. If the random backoff count value becomes 0,
the MAC controller 104 transmits a frame.
[0038] Also, when a transmission request is generated, if the
medium is idle for a longer time than the AFIS [AC] time, the MAC
controller 104 immediately transmits a frame.
[0039] When a frame is received from the physical layer, the frame
detector 109 determines whether or not to transmit an ACK frame by
checking an ACK policy bit (refer to FIG. 1) included in the QoS
control field of the frame header.
[0040] Also, if the received frame is a beacon frame transmitted
from the AP, the frame detector 109 extracts parameters related to
the QoS (For example, AIFS[AC], CWmin[AC], and CWmax[AC]) and
updates existing values.
[0041] The receive queue 110 is composed of one FIFO, stores a
frame, and transmits a relevant frame to the upper layer whatever
UPs of received frames are.
[0042] FIGS. 4 and 5 are flowcharts illustrating methods of
supporting QoS in a wireless LAN, which are performed in the MAC
apparatus 100 shown in FIG. 3, according to exemplary embodiments
of the present invention. FIG. 4 illustrates a processing method of
the MAC apparatus 100, that is performed in response to a frame
received from an upper layer, and FIG. 5 illustrates a processing
method of the MAC apparatus 100, that is performed in response to a
frame received from a physical layer.
[0043] First, referring to FIG. 4, the MAC apparatus 100 determines
a user priority (UP) of a frame input from an upper layer and maps
the frame to an access category (AC) in step 1000. The MAC
apparatus 100 determines whether the input frame is a voice frame
in step 1010.
[0044] If the input frame is a voice frame corresponding to an
AC[3] in step 1010, the MAC apparatus 100 stores the frame in the
first transmission queue 102, which is a voice exclusive FIFO, in
step 1020. If the input frame is a non-voice frame corresponding to
one of AC[0]-AC[2] in step 1010, the MAC apparatus 100 stores the
frame in the second transmission queue 103, which is a general
FIFO, in step 1030.
[0045] After the voice frame is stored in the first transmission
queue 102 in step 1020, it is determined whether a backoff
operation has ended in step 1040, and if the backoff operation has
not ended in step 1040, the MAC apparatus 100 performs the backoff
operation of the voice frame using CWmin[3], CWmax[3], and AIFS[3]
in step 1050. It is determined whether a backoff operation has
ended again in step 1040, and if the backoff operation has ended,
the MAC apparatus 100 performs step 1080.
[0046] On the other hand, after the non-voice frame is stored in
the second transmission queue 103 in step 1030, it is determined
whether a backoff operation has ended in step 1060, and if the
backoff operation has not ended in step 1060, the MAC apparatus 100
performs the backoff operation of the non-voice frame using
CWmin[AC], CWmax[AC], and AIFS[AC] according to the AC in step
1070. It is determined whether a backoff operation has ended again
in step 1060, and if the backoff operation has ended, the MAC
apparatus 100 performs step 1080.
[0047] It is determined whether the backoff operations of the voice
frame and the non-voice frame have simultaneously ended in step
1080. If a single backoff operation ends in step 1080, the MAC
apparatus 100 transmits the frame whose backoff operation ends
regardless of priority in step 1090, and when the frame
transmission ends, the MAC apparatus 100 switches to a receive mode
in step 1110.
[0048] If it is determined that the backoff operations has
simultaneously ended in step 1080, the MAC apparatus 100 performs
internal collision management to which the priority is applied in
step 1120. That is, the MAC apparatus 100 transmits the voice frame
first by applying the priority to the internal collision management
in step 1100 and allows the backoff operation to be performed by
increasing a backoff count in step 1070. When the frame
transmission ends, the MAC apparatus 100 switches to the receive
mode in step 1110.
[0049] The processing method of the MAC apparatus 100 in response
to a frame received from a physical layer will now be described
with reference to FIG. 5.
[0050] Referring to FIG. 5, the MAC apparatus 100 receives a frame
from a physical layer in step 1200. The MAC apparatus 100 decodes
an ACK policy from a header of the received frame and determines
whether an ACK response is performed using the ACK policy in step
1210. If the ACK response must be performed as a result determined
in step 1210, the MAC apparatus 100 transmits the ACK response in
step 1220 and stores the received frame in the receive queue 110 in
step 1230. When a host is ready, the MAC apparatus 100 transmits
the frame to the upper layer regardless of priority in step
1240.
[0051] As described above, in a MAC apparatus and method for
guaranteeing QoS in a wireless LAN according to embodiments of the
present invention, for a real-time traffic VoIP such as an AC-3, a
VoIP exclusive queue is used (refer to the reference number 102 of
FIG. 3), and a back operation is performed using AIFS[3], CWmin[3],
and CWmax[3] parameters corresponding to the AC-3 to guarantee a
higher priority. For simultaneously generatable non-real-time
traffic, a backoff operation is performed using AIFS[AC],
CWmin[AC], and CWmax[AC] parameters according to the AC to support
all priorities except the VoIP traffic. Also, when the back
operations are simultaneously ended by the two transmission
requests that are simultaneously generated, QoS is guaranteed by
transmitting the VoIP traffic having a higher priority first.
[0052] The invention can also be embodied as computer readable
codes on a computer readable recording medium. The computer
readable recording medium is any data storage device that can store
data which can be thereafter read by a computer system. Examples of
the computer readable recording medium include read-only memory
(ROM), random-access memory (RAM), CD-ROMs, magnetic tapes, floppy
disks, optical data storage devices, and carrier waves (such as
data transmission through the Internet). The computer readable
recording medium can also be distributed over network coupled
computer systems so that the computer readable code is stored and
executed in a distributed fashion. Accordingly, it is envisioned
that the computer-readable medium may include any known
computer-readable media such as an electrical connection having one
or more wires, a portable computer diskette, a hard disk, a random
access memory (RAM), a read-only memory (ROM), an erasable
programmable read-only memory (EPROM or Flash memory), an optical
fiber, a portable compact disc read-only memory (CD-ROM), an
optical storage device, a transmission media such as those
supporting the Internet or an intranet, or a magnetic storage
device. It is also envisioned that the computer-readable medium
could even be paper or another suitable medium upon which a program
is printed, in that the printed program can be electronically
captured, via, say for example, optical scanning of the paper or
other medium, then subsequently compiled, interpreted, or otherwise
processed in a suitable manner, if necessary, and then subsequently
being stored in a computer memory. Accordingly, the
computer-readable medium may be any medium that can contain, store,
communicate, propagate, or transport the program for use by or in
connection with the instruction execution system, apparatus, or
device.
[0053] As described above, according to a MAC configuring method
for guaranteeing QoS in a wireless LAN according to an embodiment
of the present invention, a wireless LAN MAC, in which functions
are simplified while guaranteeing QoS of a VoIP service, can be
provided. Therefore, it becomes easy to manufacture commercial chip
with low costs, and a terminal supporting a wireless VoIP service
with a low price can be mass-produced.
[0054] While the present invention has been particularly shown and
described with reference to exemplary embodiments thereof, it will
be understood by those of ordinary skill in the art that various
changes in form and details may be made therein without departing
from the spirit and scope of the present invention as defined by
the following claims.
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