WO2009150027A1 - Mac protocol for cable data network - Google Patents
Mac protocol for cable data network Download PDFInfo
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- WO2009150027A1 WO2009150027A1 PCT/EP2009/056272 EP2009056272W WO2009150027A1 WO 2009150027 A1 WO2009150027 A1 WO 2009150027A1 EP 2009056272 W EP2009056272 W EP 2009056272W WO 2009150027 A1 WO2009150027 A1 WO 2009150027A1
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- Prior art keywords
- station
- frame
- access point
- data
- polling
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L12/00—Data switching networks
- H04L12/28—Data switching networks characterised by path configuration, e.g. LAN [Local Area Networks] or WAN [Wide Area Networks]
- H04L12/2801—Broadband local area networks
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L12/00—Data switching networks
- H04L12/28—Data switching networks characterised by path configuration, e.g. LAN [Local Area Networks] or WAN [Wide Area Networks]
- H04L12/2854—Wide area networks, e.g. public data networks
- H04L12/2856—Access arrangements, e.g. Internet access
- H04L12/2858—Access network architectures
- H04L12/2861—Point-to-multipoint connection from the data network to the subscribers
Definitions
- DIFS is a period of time for which a station waits after it has found the channel idle. That is, after a station finds the channel idle, it will wait for the DIFS and then send an RTS signal.
- the AP starts to transmit the Polling frame "Poll" downlink to the STA4 although the downlink data transmitted from the AP to the STA4 is null. This is different from the PCF mechanism in which the access point normally will poll a station only when it has downlink data frame to this station. Since the uplink data from the STA4 is null, after the CCA indicates an interval of SIFS, STA4 starts to transmit the uplink null frame "Null".
- the AP After the CCA indicates an interval of SIFS, the AP starts to transmit the data and Polling frame "D5+Poll" downlink to the STA5.
- the AP can maintain a "STA polling list". After an association was established between a STA and the AP, the STA is immediately added to the list. After the association was cancelled, the STA is immediately deleted from the list.
- DIFS DCF lnterframe Space
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- Engineering & Computer Science (AREA)
- Computer Networks & Wireless Communication (AREA)
- Signal Processing (AREA)
- Small-Scale Networks (AREA)
- Mobile Radio Communication Systems (AREA)
Abstract
The present invention provides a communication medium access control method for a cable data network comprising an access point and at least one station associated with the access point. The method comprises, at the level of the access point, the steps of: controlling the communication medium and polling the at least one associated station; and after polling all of the at least one associated station, sharing the communication medium with the at least one station according to a contention mechanism.
Description
MAC PROTOCOL FOR CABLE DATA NETWORK
FIELD OF THE INVENTION
The present invention generally relates to the network technology, and more particularly, to a MAC (Media Access Control) protocol for a cable data network.
BACKGROUND OF THE INVENTION
The present applicant has proposed to use a mature WiFi chipset with a frequency conversion circuit to realize an efficient and low-cost bi-directional data communication over the existing coaxial cable access network. Such a system is called an ADoC (Asymmetric Data over Coaxial Cable) system.
Figure 1 is an exemplary diagram showing the infrastructure of an ADoC network for access to the internet through an existing cable TV cable network. Here the term internet is used in a broad sense and refers to the wide area network, which could be the Internet or the operator's network with walled garden applications. At the server end of the system as shown by sign 100, during the downlink transmission (from the server end 100 to the client end 100'), a headend apparatus 10 is provided between the internet and the cable TV network. Said headend apparatus 10 comprises multiple access points 20 (AP1 ...APn). The access points 20 are used to transform the Ethernet network signal received via a switch 12 into an RF signal. The RF signals from the multiple access points 20 are combined with the cable TV signal by a splitter 30. Here the splitter 30 represents a set of power splitters and band splitters. The splitter 30 is connected to a cable 50. The access points 20 in the embodiment provide a data switching function over the DataLink Layer of the OSI (Open System Interconnect) Reference Model. As shown in Figure 1 , each client 40, for example client 2, at the remote client end 100' of the cable
TV network, is provided with a splitter 60 for separating the RF signal from the analog video signal of cable TV, and transmitting relevant signals to the modem 70 and the TV receiver 90 at client 2 respectively. Here, the splitter 60 can be implemented using power splitters and/or band pass filters. Finally, the data signal is demodulated by the modem 70 and sent to a PC 80 at client 2.
In Fig.1 , for example, communication between an access point and a station may use a MAC protocol similar to the one established in the WiFi standard IEEE 802.11 , a standard in which two types of medium access mechanisms are defined: DCF (Distributed Coordination Function) and PCF (Point Coordination Function).
However, for the ADoC system, the DCF mechanism of the WLAN does not meet the requirements, while the PCF mechanism is too difficult to implement. Therefore, a MAC protocol suitable for the technical conditions of the ADoC system is needed.
SUMMARY OF THE INVENTION
In view of the above-described problems in IEEE802.1 1 MAC protocol, an embodiment of the present invention provides a MAC protocol for a cable data network. According to one aspect of the invention, there is provided a communication medium access control method for a cable data network comprising an access point and at least one station associated with the access point. The method comprises, at the level of the access point, the steps of: controlling the medium and polling the at least one associated station; and after polling all of the at least one associated station, sharing the medium with the at least one station according to a contention mechanism.
BRIEF DESCRIPTION OF DRAWINGS
These and other aspects, features and advantages of the present invention will become apparent from the following description in connection with the accompanying drawings in which:
Fig.1 is a schematic diagram for a system framework realizing a bi-directional data communication in a cable television access network;
Fig.2 is a schematic diagram for a forcible polling mechanism based on the CCA, SIFS, and PIFS in DCF according to an embodiment of the present invention;
Fig.3 is a schematic diagram for a CTS polling mechanism based on the SIFS and PIFS according to an embodiment of the present invention; and
Fig.4 is a schematic diagram for a CTS polling mechanism based on the NAV according to an embodiment of the present invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS In the following description, various aspects of an embodiment of the present invention will be described. For purposes of explanation, specific configurations and details are set forth in order to provide a thorough understanding. However, it will also be apparent to one skilled in the art that the present invention may be practiced without the specific details present herein.
As described above, IEEE 802.11 defines two types of medium access control mechanism, DCF and PCF. The DCF, which utilizes a carrier sense mechanism, is the most essential medium access control mechanism in a MAC layer and applicable to a distributed network. It transmits sporadic and random general packet data, and supports real time services of non-contention type and non-real time services of contention type. The PCF, which is based on the DCF operation mode, only supports non-real time
services of contention type and is applicable to a network with a central controller.
However, the above mentioned DCF and PCF mechanisms are both not applicable to cable data networks of bi-directional communication, for example, the ADoC system. 1. DCF mechanism
DCF is based on a CSMA/CA (Carrier Sense Multiple Access /Collision Avoidance) mechanism, and uses a RTS (Request To Send) /CTS (Clear To Send) message exchange mechanism as an auxiliary media access mode. The core of the DCF mechanism is to control the shared medium by a time delay mechanism to avoid collision as far as possible and enable each station (including the access point) to have an essentially fair occupancy of the shared medium.
The work flow of the CSMA/CA mechanism in DCF protocol is as follows: In case a station needs to transmit data in a wireless network, if no data transmission was detected in the channel, the station will wait for an additional period of time and have another detection. If there has been still no data transmission detected in the wireless network, then the station will start to transmit data. In case a station at the receiving end receives the whole data packet transmitted from the transmitting station, it will respond with an acknowledgement packet. If the acknowledgement packet is received by the transmitting station, then the process of data transmission is complete; if the transmitting end does not receive the acknowledgement packet, then either the transmitted data is not correctly received or the transmission of the ACK signal failed. No matter which one of the above cases occurs, the transmitting station will wait for a period of time and then retransmit the data packet.
Specifically, in the WLAN DCF mechanism, when a CCA (Clear Channel
Assessment) indicates that a channel is available, a station starts to occupy the channel to transmit data after a delay period of SIFS (Short lnterframe
Space) / PIFS (PCF lnterframe Space) or a period of DIFS (DCF lnterframe Space) / EIFS (Extended lnterframe Space) /+ BackoffTime.
CCA is a logical function defined in IEEE 802.1 1 within physical layers which determines the current state of use of a wireless medium and aids in contention avoidance.
SIFS is the small gap between the data frame and its acknowledgment which is used for the highest priority transmissions enabling stations with this type of information to access the channel first. Examples of information which will be transmitted after the SIFS has expired include ACK, RTS and CTS.
DIFS is a period of time for which a station waits after it has found the channel idle. That is, after a station finds the channel idle, it will wait for the DIFS and then send an RTS signal.
PIFS has a higher priority than DIFS. When the channel has been idle for a period greater than the PIFS, stations operating in contention free mode may have immediate access to the medium. As such, PIFS has a shorter duration than DIFS. Unlike SIFS, PIFS and DIFS, the EIFS has a variable value and is only used when there has been an error in frame transmission.
The CSMA/CA mechanism used in a WLAN system has a problem of hidden stations, namely, a transmitting station can not detect that another station is transmitting data at the same time. This problem will result in a collision at a receiving station, and therefore the CCA fails between those stations that are hidden from each other. Also, under the CSMA/CA mechanism, the online number of stations is limited.
Therefore, a RTS/CTS mechanism is incorporated into the DCF to solve or relieve the problem of hidden stations. The above mentioned RTS/CTS mechanism is as follows:
In case the transmitting station needs to transmit data, it will firstly detect whether the channel is idle or not. If the channel is idle, the transmitting station will transmit a RTS signal which includes information such as the address of the transmitting station, the address of the receiving station, the duration during which the next batch of data will be continuously transmitted. After a receiving station receives the RST signal, it will respond with a CTS packet. Then after the transmitting station receives the CTS packet, it will immediately start to send a data packet. After the receiving station receives the data packet, it will use the value of CRC (Cyclic Redundancy Check) in the packet to check whether the data in the packet is correct or not. If the check shows a correct result, the receiving station will respond with an acknowledgement packet to inform the transmitting station that the data packet has been received correctly. If the transmitting station does not receive an acknowledgement packet from the receiving station, it will consider that the data packet was lost during the transmission and retransmit the data packet.
An ADoC system operates in a tree-type or star-type structure of coaxial cable of cable television network, where the problem of hidden stations is more serious than that of a WLAN system.
In case the number of online stations is relatively large, the problem of hidden stations of the CSMA/CA mechanism will lead to an efficiency drop and deteriorated channel utilization rate of the ADoC system, or even result in an interruption of communication for some stations. For a headend receiver, the stronger a signal is, the higher its priority is. In such case the stations may be caused to be in a state of inequality since a RTS with a strong signal may
overwhelm a weak signal (for example, RTS, short packet without RTS, and the like).
2. PCF mechanism
According to a fundamental principle of the PCF mechanism, a Point Coordinator is used to poll stations to centrally control access to a channel.
Generally a device called access point will serve as the Point Coordinator.
The PCF can be used to support realtime services of non-contention type. The PCF mechanism divides the channel access time into super frames each of which includes one CFP (Contention Free Period) and one CP (Contention Period). The CFP period uses a poll mechanism to transmit realtime services, and the CP period uses the standard DCF contention mechanism to transmit non-realtime services.
A station that needs to transmit data firstly sends an Association Request frame to an access point and indicates in a CF-Pollable subfield of a function performance field of the frame that it needs to join in a polling list of the access point. After the access point receives the Association Request frame, it will list the station into the polling list in which all the associated stations are arranged in an ascending order of AID (Association ID). The AID is a 16bit identifier assigned to a station by the access point. After transmitting a Beacon frame which indicates the beginning of a CFP period, the access point will transmit a Poll frame or a Data frame to a station in the poll list in turn. If no response from the station in a time interval of PIFS, which indicates that the station has no data to transmit, the access point will continues to transmit a Poll frame to the next station. There is a particular case in the above-described polling process. If during one CFP period, not all stations in the polling list are polled, then during the next CFP period, the polling will start from the first station that is not polled in the last CFP period. If all stations in the polling list were polled before one
CFP period is end up, the access point would randomly select a station to continue to transmit a Poll frame.
When the CFP period is end up, the access point will transmit an End frame to indicate the end of a CFP period and the beginning of a CP period. The standard WLAN PCF mechanism is complex. Some definitions of
PCF are also meaningless within a coaxial cable data network, for example: (1 ) declaration of a CF-Pollable subfield of a capacity information field of a request frame associated with a station; (2) members of a CF parameter set included in a Beacon frame; (3) the minimum service set of a polling list established for ensuring that multiple pollable stations controlled by multiple PC in multiple BSSs (Basic Service Set) can cooperate with each other; (4) NAV (Network Allocation Vector) which needs to be updated by each station according to the associated Beacon frame and which should include a NAV time length in other beacon frames of "the same channel" or "the overlapping channel". In addition, the PCF mechanism is an optional mechanism in the IEEE 802.1 1 standard, so few IC manufacturers provide products that support the WLAN PCF mechanism.
As described above, given that the DCF mechanism of a WLAN system can not meet the requirements of an ADoC network while the PCF mechanism is difficult to implement, the present invention provides a medium access control method for a cable data network. According to the present embodiment, a simplified polling mechanism is proposed to replace the RTS/CTS mechanism of the DCF to forcibly control the channel with data frames as defined in DCT (for example, through SIFS, PIFS or NAV) by an access point and further poll the associated stations. The access point will poll all the associated stations regardless of whether it has downlink data packet to be transmitted to these stations. According to the present embodiment, the problem of hidden stations of the DCF mechanism and the above-described
inherent defects of the PCF mechanism can be overcome. Furthermore, the embodiment also reserves the DCF mechanism to have a DCF time window which enables new stations to realize operations such as association register.
According to the present embodiment, after a Beacon frame was transmitted, an access point will forcibly control the channel through one or some of the SIFS, PIFS, DIFS and NAV and poll the stations to perform data communication (including unicast, multicast and broadcast data) with the stations until all the associated stations are polled. Normally, the forcible polling will be finished a short time (several milliseconds in practice) before the end of a Beacon duration. It is known to a person skilled in the art that a
Beacon frame is a kind of management frame which carries control information to be used by stations to locate an access point. Normally the
Beacon frame can be transmitted by the access point for polling purposes.
The access point will periodically transmit Beacon frames, and the time between two consecutive Beacon frames is called a Beacon duration.
After all the associated stations are polled, the access point will release the channel to the system and return to the DCF state, where the access point contends for the channel, for example, through the DIFS, EIFS and
BackoffTime in the same manner as the stations in the network to enable new stations to carry out association.
1. SIFS polling
In this embodiment, according to the DCF mechanism, after a Beacon frame is transmitted, an access point will use the CCA, SIFS and PIFS to control the channel and use various data frames defined in IEEE802.1 1 to forcibly poll each station.
Fig.2 shows an exemplary flow chart of forcible polling based on the CCA, SIFS and PIFS according to the embodiment.
Firstly, abbreviations used for the embodiment of Figure 2 are listed and described as follows:
SIFS: Short lnterframe Space
PIFS: PCF lnterframe Space DIFS: DCF lnterframe Space
AP: access point
STA: station
Dbm: Broadcast/Multicast data
Un+ACK: uplink frame of a station (IEEE802.1 1 DATA Frame, subtype: 0001 : n=positive integer)
Dn+Poll: downlink frame of an access point (IEEE802.11 DATA Frame, subtype: 0010: n=positive integer)
Dn+ACK+Poll: downlink frame of an access point (IEEE802.1 1 DATA Frame, subtype: 001 1 : n=positive integer) Null: uplink null frame of a station (IEEE802.1 1 DATA Frame, subtype:
0100)
ACK: uplink acknowledgement frame of a station (IEEE802.1 1 DATA Frame, subtype: 0101 )
Poll: downlink polling frame of an access point (IEEE802.11 DATA Frame, subtype: 01 10)
ACK+Poll: downlink frame of an access point (IEEE802.1 1 DATA Frame, subtype: 01 1 1 )
As shown in Fig.2, after a Beacon frame is transmitted, when the CCA indicates an interval of SIFS, an AP starts to transmit the Broadcast/Multicast data "Dbm". This is different from the PCF mechanism where the access point will start the polling process but not transmit data frames at the beginning of a
CFP.
After the CCA indicates an interval of SIFS/PIFS, the AP starts to transmit the data and Polling frame "D1 +PoII" downlink to the STA1.
As shown in Fig.2, next, after the CCA indicates an interval of SIFS, the
AP starts to transmit the uplink data and acknowledgement frame "U1 +ACK"; After the CCA indicates an interval of SIFS, the AP starts to transmit the data, acknowledgement and Polling frame "D2+ACK+PoH" downlink to the
STA 1 and STA2.
In Fig.2, after the CCA indicates an interval of SIFS, the STA2 starts to transmit the uplink data and acknowledgement frame "U2+ACK". As shown in Fig.2, after the CCA indicates an interval of SIFS, since the downlink data transmitted from the AP to the STA3 is null, the AP starts to transmit the acknowledgement and Polling frame "ACK+PoH" downlink to the STA2 and STA3.
Next, due to no acknowledgement from the STA3 in the case shown in Fig.2, after the CCA indicates an interval of PIFS, the AP starts to transmit the Polling frame "Poll" downlink to the STA4 although the downlink data transmitted from the AP to the STA4 is null. This is different from the PCF mechanism in which the access point normally will poll a station only when it has downlink data frame to this station. Since the uplink data from the STA4 is null, after the CCA indicates an interval of SIFS, STA4 starts to transmit the uplink null frame "Null".
After the CCA indicates an interval of SIFS, the AP starts to transmit the data and Polling frame "D5+Poll" downlink to the STA5.
The uplink data from the STA5 is null, and after the CCA indicates an interval of SIFS, the STA5 starts to transmit the uplink acknowledgement frame "ACK".
Thereafter, the AP controls the channel through the SIFS and PIFS to forcibly poll all the associated STAs according to the above-mentioned mechanism. Exhaustive illustrations are omitted herein.
Finally, as shown in Figure 2, at a time shortly before one Beacon duration ends up, the AP finishes the forcible polling. In one case, if at this time a STAn has no uplink data, then the AP responds with an "ACK" or a "Null" to finish the forcible polling and enter into the DCF state. In another case, if the STAn has uplink data, the AP will respond with an "ACK" and then finishes the forcible polling and enter into the DCF state. In this embodiment, the counter value of forcible polling time of the AP may be a value close to one or several Beacon durations. As shown in Figure 2, the forcible polling is finished within one Beacon duration. Preferably in this case, the period of the DCF state is smaller than 5 percent of the Beacon duration. Under the DCF mechanism, the AP contends for a channel through the
DIFS, EIFS and BackoffTime in the same manner as the STAs in the network, thus enabling new STAs to perform operations such as association register.
In the SIFS polling mechanism, the AP can maintain a "STA polling list". After an association was established between a STA and the AP, the STA is immediately added to the list. After the association was cancelled, the STA is immediately deleted from the list.
A channel access control method based on the CCA, SIFS and PIFS polling mechanism has been illustrated with a specific example above. It is obvious that the above-described steps are exemplary, with an object to illustrate the invention principles. Those skilled in the art will appreciate that each step and its sequence in the above-mentioned process is not limitative but exemplary.
It can be understood from the above description that, although this embodiment also employs a polling manner, the difference between the method employing a simply polling mechanism of the invention and the method employing the PCF mechanism is that there is only one BSS in the invention, so that it is not necessary to consider problems such as coexistence of multiple BSSs. According to the invention, various data frames defined for the PCF are simply used to realize the forcible poll.
2. CTS polling
According to one respect of this embodiment, based on the DCF mechanism, a station can correctly process CTS including its own MAC address under a condition that it does not send a RTS.
According to another respect of this embodiment, after transmitting a Beacon frame, an access point will continuously control a channel through the CCA, SIFS and PIFS until the time several milliseconds before one Beacon duration end up. If the access point does not receive any response from a station that should make a response (the station does not receive data packet or CTS, or no data packet is available to transmit, or it is shut down, etc.), after an interval of PIFS (or SIFS+aSlotTime), the access point will transmit the next frame. Fig.3 is a schematic diagram of the CTS polling based on the SIFS and
PIFS according to an embodiment of the invention.
Firstly, abbreviations used for the embodiment of Figure 3 are listed and described as follows:
SIFS: Short lnterframe Space PIFS: PCF lnterframe Space
DIFS: DCF lnterframe Space
AP: access point
STA: station
Dbm: Broadcast/Multicast data
Un: uplink data frame of the station (IEEE802.1 1 DATA Frame, subtype: 0000: n=positive integer)
Dn: downlink data frame of the access point (IEEE802.1 1 DATA Frame, subtype: 0000: n=positive integer)
ACK: uplink control frame of the station (IEEE802.1 1 Control Frame, subtype: 1 101 )
CTS: downlink control frame of the access point (IEEE802.1 1 Control Frame, subtype: 1 100) As shown in Fig.3, after transmitting a Beacon frame, when the CCA indicates an interval of SIFS, an AP starts to transmit the broadcast/multicast data "Dbm".
After the CCA indicates an interval of SIFS/PIFS, the AP starts to transmit the data frame "D1 " downlink to the STA1. As shown in Fig.3, after the CCA indicates an interval of SIFS, the STA1 starts to transmit the uplink acknowledgement frame "ACK".
After the CCA indicates an interval of SIFS, the AP starts to transmit the CTS frame "CTS" downlink to the STA1.
After the CCA indicates an interval of SIFS, the STA1 starts to transmit the uplink data frame "U1 ".
After the CCA indicates an interval of SIFS, the AP starts to transmit the acknowledgement frame "ACK" downlink to the STA1.
After the CCA indicates an interval of SIFS, the AP starts to transmit the data frame "D2" downlink to the STA2. As shown in Fig.3, in this embodiment, the downlink data frame "D2" to the STA2 is lost during transmission. Then after the CCA indicates an interval of PIFS, the AP starts to retransmit the data frame "D2" downlink to the STA2.
Then the downlink data frame "D2" to the STA2 is lost again. After the CCA indicates an interval of PIFS, the AP starts to retransmit the data frame "D2" downlink to the STA2.
After the CCA indicates an interval of SIFS, the STA2 starts to transmit the uplink acknowledgement frame "ACK", which shows that the retransmission is successful.
After the CCA indicates an interval of SIFS, the AP starts to transmit the CTS frame "CTS" downlink to the STA2.
If there is no response from the STA2, after the CCA indicates an interval of PIFS, the AP starts to transmit the data frame "D3" downlink to the STA3.
After the CCA indicates an interval of SIFS, STA3 starts to transmit the uplink acknowledgement frame "ACK".
Thereafter, the AP controls the channel through the SIFS and PIFS and forcibly polls all STAs according to the above-mentioned mechanism. Exhaustive illustrations are omitted herein.
Finally, after the CCA indicates an interval of SIFS/PIFS, the AP will transmit the CTS frame "CTStoSelf". The AP will finish the forcible polling and enter into the DCF state.
Fig.4 is a schematic diagram of the CTS polling based on a NAV according to an embodiment of the invention.
Firstly, abbreviations used for the embodiment of Figure 4 are listed and described as follows:
SIFS: Short lnterframe Space
PIFS: PCF lnterframe Space DIFS: DCF lnterframe Space
XIFS: one of SIFS, PIFS, DIFS
AP: access point
STA: station
Dbm: Broadcast/Multicast data
Un: uplink data frame of the station (IEEE802.1 1 DATA Frame, subtype: 0000: n=positive integer)
Dn: downlink data frame of the access point (IEEE802.1 1 DATA Frame, subtype: 0000: n=positive integer)
ACK: uplink control frame of the station (IEEE802.1 1 Control Frame, subtype: 1 101 )
CTS: downlink control frame of the access point (IEEE802.1 1 Control Frame, subtype: 1 100) As shown in Fig.4, a NAV included in a Beacon frame is transmitted to each station, or an access point transmits the NAV to each station by a CTS frame "CTStoSelf".
After transmitting the Beacon frame (that is, after transmitting the CTStoSelf), when the CCA indicates an interval of XIFS, the AP starts to transmit the broadcast/multicast data "Dbm".
After the CCA indicates an interval of XIFS, the AP starts to transmit the downlink data frame "D1 " to the STA1.
After the CCA indicates an interval of SIFS, the STA1 starts to transmit the uplink acknowledgement frame "ACK". After the CCA indicates an interval of XIFS, the AP starts to transmit the downlink CTS frame "CTS" to the STA1.
After the CCA indicates an interval of SIFS, the STA1 starts to transmit the uplink data frame "U1 ".
After the CCA indicates an interval of SIFS, the AP starts to transmit the downlink acknowledgement frame "ACK" to the STA1.
After the CCA indicates an interval of XIFS, the AP starts to transmit the downlink data frame "D2" to the STA2.
As shown in Fig.4, in this embodiment, the downlink data frame "U2" to the STA2 is lost. Then after the CCA indicates an interval of XIFS, the AP starts to retransmit the downlink data frame "D2" to the STA2.
If the downlink data frame "D2" to the STA2 is lost again, then after the CCA indicates an interval of XIFS, the AP starts to retransmit the downlink data frame "D2" to the STA2.
After the CCA indicates an interval of SIFS, the STA2 starts to transmit the uplink acknowledgement frame "ACK", which shows that the retransmission is successful. After the CCA indicates an interval of XIFS, the AP starts to transmit the downlink CTS frame "CTS" to the STA2.
As shown in Fig.4, in this embodiment, there is no response from the STA2. Then after the CCA indicates an interval of XIFS, the AP starts to transmit the downlink data frame "D3" to the STA After the CCA indicates an interval of SIFS, the STA3 starts to transmit the uplink acknowledgement frame "ACK".
Thereafter, the AP controls the channel through the SIFS and PIFS, and forcibly polls all STAs according to the above-mentioned mechanism. Exhaustive illustrations are omitted herein. Finally, after the CCA indicates an interval of SIFS/PIFS, the AP will transmit the "CTS frame" (CTStoSelf) to finish the forcible polling and enter into the DCF state.
In the above mentioned embodiment, the NAV transmitted by a CTS is virtual and greater than the time maxPPDUTime+2*SIFS+ACK, which allow a station to transmit a biggest data packet in the condition that the system operates at the lowest rate. For example, this time can be 3 seconds. When the STA can recognize the "Data+CTS" frame, NAV = APdataPPDUTime +
STAmaxPPDUTime + 2*SIFS+ACK. In the above equations, PPDU is the acronym of Presentation Protocol Data Unit.
According to the function of an IC, the SIFS, PIFS, DIFS and XIFS in Fig.4 can be combined as described in Fig.3.
Although the embodiments of the invention have been illustrated by taking the ADoc system as an example, the invention is not limited to this. Those skilled in the art will appreciate that the invention is also applicable to other MAC layer protocols of cable data network.
Claims
1. A communication medium access control method for a cable data network comprising an access point and at least one station associated with the access point, characterized in that the method comprises, at the level of the access point, the steps of: controlling the communication medium and polling the at least one associated station; and after polling all of the at least one associated station, sharing the communication medium with the at least one station according to a contention mechanism.
2. The method according to claim 1 , wherein the contention mechanism is based on the Distributed Coordination Function (DCF) protocol.
3. The method according to claim 1 , wherein the period of contention is smaller than 5 percent of a communication cycle which is defined as the period of polling plus the period of contention.
4. The method according to claim 1 , wherein the access point maintains a station polling list for recording the at least one associated station.
5. The method according to claim 1 , wherein the data communication includes unicast, multicast and broadcast.
6. The method according to claim 2, wherein the access point logical functions and control frames as defined in Distributed Coordination Function (DCF) to control the medium and poll the at least one station.
7. The method according to claim 6, wherein a Clear To Send (CTS) frame is used to poll the at least one associated station.
8. The method according to claim 7, wherein the Clear To Send (CTS) frame is transmitted to an associated station regardless of whether the associated station transmits a Request To Send (RTS) frame to the access point
9. The method according to claim 8, wherein the Network Allocation
Vector (NAV) transferred by the Clear To Send (CTS) frame is greater than the time for the at least one station to transfer a biggest data packet under the condition that the network operates at the lowest rate.
10. The method according to claim 8, wherein the Clear To Send (CTS) frame comprises the MAC address of the associated station to which the frame is transmitted.
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| EP08290478 | 2008-05-26 | ||
| EP08290478.0 | 2008-05-26 |
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| WO2009150027A1 true WO2009150027A1 (en) | 2009-12-17 |
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| PCT/EP2009/056272 WO2009150027A1 (en) | 2008-05-26 | 2009-05-25 | Mac protocol for cable data network |
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| WO (1) | WO2009150027A1 (en) |
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| US10736145B2 (en) | 2014-12-30 | 2020-08-04 | Lg Electronics Inc. | Method and device for performing uplink transmission after receiving trigger frame in wireless LAN system |
| WO2017034081A1 (en) * | 2015-08-21 | 2017-03-02 | 엘지전자(주) | Data transmission method and device in wireless communication system |
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