KR20080105887A - Method for retransmitting multicast frame in wireless network - Google Patents

Abstract

A method for retransmitting a multi cast frame in a wireless network is provided to prevent the redundancy reception by preventing a legacy station not to support retransmission of a multicast frame from retransmitting and allowing the station supporting the retransmission to retransmit. Whether the retransmission of a previously transmitted first multicast frame is required is determined(S22). If the destination device of the first multicast frame includes a station supporting the retransmission when the retransmission of the first multicast frame is required, the second multicast frame is transmitted(S24).

Description

Method for retransmitting multicast frame in Wireless Network

1 is a diagram illustrating a wireless LAN as an example of a wireless network.

2 is a block diagram illustrating a normal transmission process of a multicast frame in a wireless network.

3A is a flowchart illustrating a retransmission method of a multicast frame in a wireless network according to a first embodiment of the present invention.

3B is a configuration diagram illustrating a data frame that is an example of a multicast frame.

4 is a flowchart illustrating a retransmission method of a multicast frame in a wireless network according to a second embodiment of the present invention.

5 is a flowchart illustrating a retransmission method of a multicast frame in a wireless network according to a third embodiment of the present invention.

6 is a flowchart illustrating a retransmission method of a multicast frame in a wireless network according to a fourth embodiment of the present invention.

** Description of the symbols of the main parts of the drawings **

100: wireless LAN system

110, 210: access point

120a, ..., 220b: Station

The present invention relates to a multicast frame retransmission method in a wireless network. More particularly, the multicast frame retransmission is required when the multicast frame is retransmitted after the multicast frame is transmitted in a WLAN. It is about how to.

In general, a representative example of a wireless network is a wireless LAN. Unlike a conventional wired LAN, the wireless LAN uses a wireless medium as a medium for data transmission, and does not require a cable connection used in a conventional wired LAN. Currently, the wireless LAN is attracting attention as an extension or alternative to the existing wired LAN by transmitting and receiving data using a radio resource for transmitting and receiving data.

The above-described wireless LAN is based on the IEEE 802.11 standard of the Institute of Electrical and Electronics Engineers (IEEE). Multicast is an MSDU that uses a multicast address as a destination address (DA) when applied to a medium access control service data unit (MSDU). In addition, multicast is an MPDU or control frame that uses a multicast address as a receiver address (RA) when applied to a medium access control protocol data unit (MPDU) or a control frame. Here, the multicast address refers to a MAC (Medium Access Control) address having a group bit set. MSDU refers to information transferred to a unit between MAC service access points. The MPDU is a unit of data exchanged between two parallel MAC layers using a service of a physical layer.

In general, data transmission in a WLAN uses a distributed coordination function (DCF), which is a basic medium access method of IEEE 802.11, and is based on a carrier sense multiple access with collision avoidance (CSMA / CA) protocol and a random backoff time. A medium is shared between terminals using a backoff time. All unicast frames are acknowledged through an acknowledgment (ACK) signal, and if there is no response within the ACK signal waiting time, retransmission is attempted and after all retransmissions (5 to 21 times) are attempted, the ACK is finished. If no signal is received, the unicast frame is discarded. This means transmission failure. However, broadcast frame and multicast frame transmission do not confirm the reception using the ACK signal. In other words, the MAC (Medium Access Control) of the IEEE 802.11 protocol basically supports a unicast frame retransmission method, but does not support retransmission of broadcast frames and multicast frames.

As a result, the transmission of the broadcast frame and the multicast frame has a high probability of transmission failure due to adjacent channel interference, multi-path padding, etc., and there is no retransmission. This means that the radio transmission of the multicast frame fails. This is a characteristic of wireless environment unlike wired. When transmitting multicast frame, it can hardly guarantee stable reception due to transmission failure and shows irregular quality of service according to channel status. Accordingly, there is a disadvantage in that wireless transmission of a multicast frame according to the conventional scheme is often failed and degrades quality of service.

An object of the present invention is to provide a method for retransmitting a multicast frame when the multicast frame is not transmitted properly after transmitting the multicast frame in order to increase the reliability of the reception of the multicast frame.

Another technical problem to be solved by the present invention is a new type of multicast frame that allows retransmission to only a station supporting retransmission without allowing retransmission to a legacy station that does not support retransmission of multicast frames. The present invention provides a method for retransmitting a.

Another technical problem to be solved by the present invention is to provide a method for retransmitting a new type of multicast frame that can prevent a problem due to duplicate reception of the same multicast frame.

In a method for retransmitting a multicast frame according to an aspect of the present invention, a transmission device that has transmitted a first multicast frame determines whether retransmission of the first multicast frame is necessary, and requires retransmission of the first multicast frame. In a case where only a station (STA) supporting retransmission exists, the second multicast frame is transmitted.

According to another aspect of the present invention, there is provided a method for retransmitting a multicast frame, wherein the first multicast frame is transmitted by a transmitting device that has transmitted a first multicast frame including a sequence number field and a transmitter address (TA) field. It is determined whether retransmission of the frame is necessary, and when retransmission of the first multicast frame is required, the value of the sequence number field and the value of the transmitter address field are the same, and the second multicast frame is different from the type of the first multicast frame. Form a to transmit the second multicast frame.

According to still another aspect of the present invention, there is provided a method for retransmitting a multicast frame, in which a retransmission of the first multicast frame is performed by a transmitting device that has transmitted a first multicast frame having a first transmitter address (TA). Determine whether necessary, and when retransmission of the first multicast frame is required, the transmitting device forms a second multicast frame having a second transmitter address (TA) different from the first transmitter address; The second multicast frame is transmitted.

According to another aspect of the present invention, there is provided a method of retransmitting a multicast frame, wherein the first multicast frame is transmitted by a transmitting apparatus transmitting a first multicast frame having a first multicast group address as a receiver address (RA). Determine whether retransmission of the first multicast frame is necessary, and if the first multicast frame needs to be retransmitted, a second multicast frame having a second multicast group address different from the first multicast group address as a receiver address; Form and transmit the second multicast frame.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. Like numbers refer to like elements throughout the specification.

1 is a diagram illustrating a wireless LAN as an example of a wireless network. FIG. 1 relates to a wireless local access network (WLAN) according to the IEEE 802.11 standard, and the wireless LAN is only one example of a wireless network. Therefore, the present invention can be applied not only to a wireless LAN but also to a wireless network.

Referring to FIG. 1, the WLAN system 100 includes an access point (110, 210, Access Point; AP) and a station (120a, ..., 220b, Station; STA). The APs 110 and 210 are functional entities that have a radio station function and that provide access to distributed services via a wireless medium for an associated station. The AP (110, 210) is an example of a transmission device, a function for transmitting a multicast frame, a function for determining whether the multicast frame is properly transmitted and / or a new when the multicast frame is not properly transmitted It is responsible for forming and retransmitting multicast frames of type. The APs 110 and 210 may be called a centralized controller, a base station (BS), a node-B, or a site controller in addition to an access point. The stations 120a, ..., 220b are any device that includes a medium access control and a physical layer interface that conforms to the IEEE 802.11 standard for wireless media. The stations 120a, ..., 220b are responsible for receiving a multicast frame, and a legacy station that does not support retransmission cannot identify a multicast frame that is retransmitted and supports retransmission. The station may identify the multicast frame to be retransmitted. The stations 120a, ..., 220b may include, in addition to a wireless station, a wireless transmit / receive unit (WTRU), a user equipment (UE), a mobile station (MS), or a mobile subscriber unit (mobile). It may also be called a Subscriber Unit).

The WLAN system 100 is divided into two types depending on whether the APs 110 and 210 are included or not. That is, a form including the APs 110 and 210 is called an infrastructure basic service set (IBSS), and a form not including the APs 110 and 210 is called an ad-hoc network (not shown).

A service area provided by one AP 110 is referred to as a basic service area (BSA), and refers to a wireless terminal connected to the AP 110 including the AP 110 and referred to as a basic service set (BSS). . In this way, the wireless terminal is serviced by being connected to the AP 110 is referred to as SS (Station Service).

The SS also includes a service for exchanging stations between ad-hoc networks. As shown in FIG. 1, the service areas BSAs may overlap each other. Two or more APs 110 and 210 interoperate with each other so that stations 120a, 120b and 120c connected to one AP 110 communicate with stations 220a and 220b connected to another AP 210. Can be. In this case, the connection of the APs 110 and 210 is called a distribution system (DS), and a service provided through the DS is called a distribution system service (DSS).

In addition, an area in which the DSS can be provided is called an extended service area (ESA), and an extended service is performed by adding all the stations 120a,... 220b and APs 110, 210 that receive the DSS in the ESA. It is called an Extended Service Set (ESS). In a wireless LAN, one or more APs 110 and 210 are connected to each other so that networks are classified by ESSID.

2 is a block diagram illustrating a normal transmission process of a multicast frame in a wireless network. Herein, the MC frame means a multicast frame.

Referring to FIG. 2, when the multicast frame is normally transmitted in the WLAN, the first MC frame is transmitted, and then through the DIFS (Distributed Inter Frame Space), no acknowledgment (ACK) signal is received. After the off algorithm, the 2MC frame is transmitted.

3A is a flowchart illustrating a retransmission method of a multicast frame in a wireless network according to a first embodiment of the present invention, and FIG. 3B is a block diagram illustrating a data frame that is an example of a multicast frame.

Referring to FIG. 3A, first, a transmitter device transmits a first multicast frame (S11). Here, the first multicast frame is a message that a transmission device, for example, the AP intends to transmit to a destination device, an example of which is a data frame 300 shown in FIG. 3B.

The data frame 300 may include a frame control field, a persistence / ID field, an address field, a sequence control field, a quality of service (QoS) control field, a frame body field, and / or a frame check. Sequence) field.

The frame control field contains the version and type of the protocol as part of the MAC header. The frame control field serves to control the frame. The persistent / ID field is 16 bits long as part of the MAC header, and its range varies depending on the frame type. The address field is composed of four address fields as part of the MAC header. The address field indicates a BSSID, a source address (SA), a destination address (DA), a transmitter address (TA), and / or a receiver address (RA). Used. The sequence control field has a length of 16 bits as a part of the MAC header and consists of a fragment number and a sequence number. The QoS control field has a length of 16 bits as part of the MAC header and controls QoS. Since the frame type of the data frame 300 depends on the QoS control field, the data frame 300 is often referred to as a QoS data frame. The frame body field is a variable length field that contains specific information of each frame type. The length of the frame bodyfield starts at least 0 octets. The FCS field is a 32-bit length field including a 32-bit cyclic redundancy check (CRC). The FCS field is calculated over both the MAC header and the frame bodyfield. Thus, the FCS field is called a calculated field.

Subsequently, referring to FIG. 3A, it is determined whether retransmission of the first multicast frame transmitted in S11 is necessary (S12).

There may be a case of retransmitting the first multicast frame. For example, if the first multicast frame is not transmitted due to a collision, retransmission is required. Here, there is no limitation on a method of determining whether the first multicast frame collides. For example, the following methods may be used.

First, after transmitting the first multicast frame, the channel state is determined through physical carrier sense. If the channel is not idle, it may be determined that the multicast frame has collided. However, not all multicast frames may be detected to have collided. In this case, the physical carrier sense is provided by a physical layer (PHY) as one of the carrier sensing methods.

Second, after transmitting the first multicast frame, if there is no channel access during the Extended Interframe Space (EIFS) or more, it may be considered that a collision has occurred. However, it cannot be assumed that all the multicast frames have collided. The EIFS is used under a DCF (Distributed Coordination Function) when the PHY informs that the MAC frame has not been transmitted with the correct FCS (Frame Check Sequence) value.

Subsequently, referring to FIG. 3A, if it is determined that retransmission of the first multicast frame is necessary, it is determined whether only a station (STA) supporting retransmission is included in the BSS (S13).

If the destination device of the first multicast frame includes only a station supporting retransmission, the second multicast frame is transmitted (S14). The type of the second multicast frame may be the same as or different from the type of the first multicast frame. However, even if the type of the second multicast frame is different from the type of the first multicast frame, the frame body will be the same.

If there is only a legacy station that does not support retransmission, the second multicast frame is not transmitted. In addition, even if a legacy station that does not support retransmission and a station that supports retransmission coexist, the second multicast frame is not transmitted. If the second multicast frame is the same as the first multicast frame, if the second multicast frame is transmitted, the legacy station receives the second multicast frame and delivers it to an application layer. Supporting unwanted services can cause problems. If the second multicast frame is different from the first multicast frame, there is no problem because the legacy station cannot identify the second multicast frame and will not accept it.

4 is a flowchart illustrating a retransmission method of a multicast frame in a wireless network according to a second embodiment of the present invention. Here, the present embodiment is the same except that the second multicast frame of the first embodiment of FIG. 3A is changed to a new type of multicast frame, and will be briefly described below based on differences.

Referring to FIG. 4, first, a transmission device transmits a first multicast frame including a sequence number field and a transmitter address (TA) field (S21). Reference is made in detail to the form of the multicast frame in FIG. 3B.

Subsequently, it is determined whether retransmission of the transmitted first multicast frame is necessary (S22). There may be a case of retransmitting the first multicast frame. For example, if the first multicast frame is not transmitted due to a collision, retransmission is required. Here, the method of determining whether the first multicast frame collides is not limited. For example, several methods may be used. These methods are already mentioned.

If it is determined that retransmission of the first multicast frame is necessary, the value of the sequence number field and the value of the transmitter address field are the same and form a second multicast frame different from the type of the first multicast frame. (S23). The sequence number indicates a sequence number of a MAC Service Data Unit (MSDU) or a MAC Management Protocol Data Unit (MMPDU). The transmitter address refers to an address of the side transmitting the second multicast frame when transmitting the second multicast frame.

The second multicast frame is transmitted (S24). Here, legacy stations that do not support retransmission discard the new type of second multicast frame. This is because the legacy station cannot identify the new type of second multicast frame. When identifying a new type of second multicast frame, a sequence number and a TA value are stored in a cache, and if the cache has the same information, it is regarded as a duplicate multicast frame. If only a station supporting retransmission exists, the second multicast frame is received.

5 is a flowchart illustrating a retransmission method of a multicast frame in a wireless network according to a third embodiment of the present invention. Here, the present embodiment is the same except that the second multicast frame of the first embodiment of FIG. 3A is changed to a new type of multicast frame, and will be briefly described below based on differences.

Referring to FIG. 5, a transmitting device first transmits a first multicast frame having an address of a first transmitter (S31). Reference is made in detail to the form of the multicast frame in FIG. 3B.

It is determined whether retransmission of the first multicast frame is necessary (S32). There may be a case of retransmitting the first multicast frame. For example, if the first multicast frame is not transmitted due to a collision, retransmission is required. Here, the method of determining whether the first multicast frame collides is not limited. For example, several methods may be used. These methods are already mentioned.

If it is determined that retransmission of the first multicast frame is necessary, the transmitting device forms a second multicast frame having a second transmitter address (TA) different from the first transmitter address (S33). ). Here, the first transmitter address refers to an address of the side transmitting the first multicast frame when the first multicast frame is transmitted, and the second transmitter address refers to the second multicast when the second multicast frame is transmitted. Refers to the address of the sender of the frame. The first transmitter address is an actual MAC (Media Access Control) address of the transmitter, that is, a BSSID, and the second transmitter address is a virtual MAC address of the transmitter, that is, a virtual BSSID. The BSSID refers to a unique ID of a basic service set (BSS).

Subsequently, the second multicast frame is transmitted (S34). Here, legacy stations that do not support retransmission discard the second multicast frame. This is because the second transmitter address of the second multicast frame is not the first transmitter address of the transmitter associated with the legacy station. If it is recognized that the second transmitter address of the second multicast frame corresponds to a known virtual BSSID, the second multicast frame is regarded as a retransmitted second multicast frame and detected as a duplicate by a cache. If only a station supporting retransmission exists, the second multicast frame is received.

6 is a flowchart illustrating a retransmission method of a multicast frame in a wireless network according to a fourth embodiment of the present invention. Here, the present embodiment is the same except that the second multicast frame of the first embodiment of FIG. 3A is changed to a new type of multicast frame, and will be briefly described below based on differences.

Referring to FIG. 6, first, a transmission device transmits a first multicast frame having a first multicast group address as a receiver address (RA) (S41). Reference is made in detail to the form of the multicast frame in FIG. 3B.

It is determined whether retransmission of the first multicast frame is necessary (S42). There may be a case of retransmitting the first multicast frame. For example, if the first multicast frame is not transmitted due to a collision, retransmission is required. Here, the method of determining whether the first multicast frame collides is not limited. For example, several methods may be used. These methods are already mentioned.

If it is determined that retransmission of the first multicast frame is necessary, the transmitting device forms a second multicast frame having a second multicast group address different from the first multicast group address as a receiver address (S43). . In this case, the second multicast group address is a MAC address that performs 1: 1 mapping with the first multicast group address. Here, the first multicast group address refers to an address of the side receiving the first multicast frame when transmitting the first multicast frame. The second multicast group address refers to an address of the side receiving the second multicast frame when transmitting the second multicast frame.

Subsequently, the second multicast frame is transmitted (S44). Here, the legacy station that does not support retransmission discards the second multicast frame because it has not subscribed to the second multicast group address. If only a station supporting retransmission exists, the second multicast frame is received.

As mentioned above, although preferred embodiments of the present invention have been described in detail, those of ordinary skill in the art to which the present invention pertains should realize the present invention without departing from the spirit and scope of the present invention as defined in the appended claims. It will be appreciated that various modifications or changes can be made. Accordingly, modifications to future embodiments of the present invention will not depart from the technology of the present invention.

As described above, in the present invention, when retransmission of a multicast frame is required, a station supporting retransmission will receive the multicast frame again, and a station supporting the retransmission already received will perform retransmission of the multicast frame. This helps prevent duplicate reception. If a legacy station that does not support retransmission has already received a transmission, it will not be able to identify a new type of multicast frame and will discard the retransmitted multicast frame. Since the multicast frame is discarded because the cast frame cannot be identified, duplicate reception can be prevented.

Claims (11)

In a method for retransmitting a multicast frame in a wireless network, Determining whether retransmission of the previously transmitted first multicast frame is necessary; And When it is determined that retransmission of the first multicast frame is necessary and the destination device of the first multicast frame includes only a station (STA) that supports retransmission, the second multicast frame Retransmission method of the multicast frame comprising the step of transmitting. The method of claim 1, When it is determined that retransmission of the first multicast frame is necessary, and the target device of the first multicast frame includes one or more legacy stations that do not support retransmission, the second multicast frame Retransmission method of a multicast frame, characterized in that not to transmit. The method of claim 1, The type of the second multicast frame is the same as the type of the first multicast frame or different from the type of the first multicast frame. In a method for retransmitting a multicast frame in a wireless network, Determining whether retransmission of a first multicast frame including a previously transmitted sequence number field and a transmitter address (TA) field is required; When it is determined that retransmission of the first multicast frame is necessary, the value of the sequence number field and the value of the transmitter address field are the same and form a second multicast frame different from the type of the first multicast frame. step; And Transmitting the second multicast frame. The method of claim 4, wherein The second multicast frame may not identify a legacy station that does not support retransmission, and may identify a station that supports retransmission. In a method for retransmitting a multicast frame in a wireless network, Determining, by a transmitting device that has transmitted a first multicast frame having a first transmitter address (TA), whether retransmission of the first multicast frame is necessary; When it is determined that retransmission of the first multicast frame is necessary, the transmitting device forms a second multicast frame having a second transmitter address (TA) different from the first transmitter address. step; And Transmitting the second multicast frame. The method of claim 6, And the second multicast frame can not identify a legacy station that does not support retransmission and can identify a station that supports retransmission. The method of claim 6, And the first transmitter address is an actual MAC (Medium Access Control) address of the transmitting device, and the second transmitter address is a virtual MAC address of the transmitting device. In a method for retransmitting a multicast frame in a wireless network, Determining, by a transmitting device that has transmitted a first multicast frame having a first multicast group address as a receiver address (RA), whether retransmission of the first multicast frame is necessary; If it is determined that retransmission of the first multicast frame is necessary, the transmitting device forms a second multicast frame having a second multicast group address different from the first multicast group address as a receiver address; ; And Transmitting the second multicast frame. The method of claim 9, And the second multicast frame can not identify a legacy station that does not support retransmission and can identify a station that supports retransmission. The method of claim 9, Wherein the first multicast group address is a MAC address of a first multicast frame and the second multicast group address is a MAC address that performs 1: 1 mapping with the first multicast group address. How to retransmit frames.

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