KR20060134895A - Multimedia service method on wireless network - Google Patents

Abstract

The present invention provides a procedure for detecting a handoff at the network layer and an address reservation procedure, and a session update procedure using the reserved address before the wireless terminal reaches a cell switch threshold which is a time point at which the link layer handoff occurs. In order to conclude, the present invention provides a method for estimating movement of a link layer by using a signal strength when an MH is located between two adjacent access points AP1 and AP2, and (b) When the movement of the link layer is predicted in step (a), detecting a handoff at the network layer using the modified beacon frame, and (c) when the movement of the network layer is predicted in (b), Performing a pre-IP address reservation procedure to allocate a reserved IP address, and (d) handing off the MH after performing a pre-session update procedure using the reserved IP address assigned in step (c). And a step of performing. Therefore, there is an effect that can provide a high quality seamless multimedia service during handoff of the wireless terminal by reducing the interruption and delay time due to mobility in the real-time multimedia service.

Description

Multimedia service method over wireless network {MULTIMEDIA SERVICE METHOD ON WIRELESS NETWORK}

1 illustrates a signal state of a link layer used in a wireless terminal;

2 illustrates a beacon frame before modification and a beacon frame after modification;

3 is a flowchart illustrating a method for supporting mobility for a multimedia service using a wireless network according to the present invention;

4 is a block diagram illustrating a process of performing a procedure for detecting a handoff at a network layer in FIG. 3;

FIG. 5 is a block diagram illustrating a process of performing an address reservation procedure in FIG. 3;

FIG. 6 is a block diagram illustrating a process of performing a session update procedure using an MH reserved address in FIG. 3. FIG.

<Description of the code | symbol about the principal part of drawing>

301: MH 302, 304: gateway

303, 305: DHCP server 307: CH

The present invention relates to a multimedia service method on a wireless network, and more particularly, a procedure for detecting a handoff and an address reservation procedure at a network layer, and a session update using an address reserved by a wireless terminal (Mobile Host, MH). The procedure is completed before reaching the Cell Switch Threshold, which is the point at which the handoff of the link layer occurs, thereby reducing interruptions and delays due to mobility in real-time multimedia services, resulting in high-quality interruptions during handoff of wireless terminals. The present invention relates to a method for providing a multimedia service.

As is well known, there is an increasing demand for providing a real-time multimedia service in a wireless network environment according to the generalization of wireless terminals (MH). Mobile IP has been proposed to the IETF (Internet Engineering Task Force, 1996) to support mobility on wireless networks. Mobile IP does not change the IP address assigned to the wireless terminal even when the mobile terminal moves during communication, thereby ensuring mobility while maintaining the generated session without affecting the upper application.

Since Mobile IP uses the IP address permanently assigned to the wireless terminal and the IP address assigned from the visited network, the problem of address wasting and tunneling to match the IP address used in the visited network with the IP address given to the wireless terminal. I have a problem.

That is, the tunneling scheme of Mobile IP guarantees mobility, but it causes a packet delay problem called triangular routing and has a weakness in security. In addition, by using IP header including the address of the network visited in the existing IP packet for tunneling technique, it has a disadvantage of wasting resources and making it difficult to apply techniques for improving multimedia transmission quality. For this reason, it is difficult to provide a real-time multimedia service in Mobile IP.

On the other hand, the mobility support scheme at the application layer does not use tunneling schemes, so it can be supported by application modification without additional infrastructure, and there is no problem of depletion of IP addresses because it does not assign a permanent address. In addition, when a handoff occurs and the network changes, the wireless terminal using the mobility support scheme at the application layer receives a new IP address through Dynamic Host Configuration Protocol (DHCP). Create a new session with.

In addition, a real-time multimedia signaling protocol such as Session Initiation Protocol (SIP) based on Real-time Transport Protocol (RTP) is used as a mobility support method of the application layer.

In the case of SIP, mobility is ensured through SIP mid-call mobility, which supports the mobility of wireless terminals. When the wireless terminal moves to a new network, the wireless terminal is assigned a new IP address from a DHCP server and discards the existing session. At the same time, a new session is created with the other terminal with the new IP address. As described above, the time required for the wireless terminal to create a new session and communicate with the counterpart terminal from the time when the handoff occurs is called a handoff delay time.

In other words, since a procedure for creating a new session in SIP is performed in a wireless terminal and a counterpart terminal, it has an advantage of reducing delay time and minimizing packet loss. However, it takes several seconds to get a new IP address from a DHCP server and hundreds of milliseconds to renew a session. Also, the link layer handoff delay time and the time required to register a new address with the router are about 100 milliseconds. Thus, the total handoff delay in SIP takes several seconds.

Such handoff delay is not suitable for providing real-time multimedia services. In particular, audio services such as VoIP have a delay of more than 150 milliseconds, and the user feels disconnected during a call. In the case of video, if a delay of 1 second or longer occurs, video breakage or dropping of the screen may occur. It becomes impossible.

The proposed methods to solve the above problems have a big problem in distribution because they require the addition of a base station or a profound modification of an existing network protocol. In addition, there is still a problem that the total handoff delay is more than 1 second because only the delay time for updating the session is reduced and the time required for address assignment is not reduced.

Accordingly, an object of the present invention is to solve the above problems, and an object thereof is to provide a procedure for detecting a handoff at the network layer, an address reservation procedure, and a session update procedure using an address reserved by a wireless terminal. By finishing before reaching the Cell Switch Threshold, which is the time when the handoff occurs, the real-time multimedia service reduces interruption and delay time due to mobility, thereby providing high quality seamless multimedia service during handoff of the wireless terminal. The present invention provides a multimedia service method using a wireless network that can be provided.

In order to achieve the above object, according to the present invention, a multimedia service method using a wireless network includes (a) predicting movement of a link layer using signal strength when an MH is located between two adjacent access points (AP1 and AP2). Step (b) detecting a handoff at the network layer using a modified beacon frame when the movement of the link layer is predicted in step (a), and (c) step (b) If the network layer is predicted to move in the network layer, the step of assigning a reserved IP address by performing a pre-IP address reservation procedure and (d) performing a pre-session update procedure by using the reserved IP address allocated in step (c). And later performing a handoff of the MH.

DETAILED DESCRIPTION Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention.

1 is a diagram illustrating a signal state of a link layer used in a mobile terminal (MH) according to the present invention.

Referring to FIG. 1, the signal strength of a link layer received from an access point (AP) according to the position of the MH is shown in a graph, and the X axis of the graph has two access points (from one point to two CPT points). The location of the MH moving the point (Mobile Node Movement direction), and the Y axis of the graph represents the signal strength (SNR) (dB) of the link layer.

That is, when the MH communicating through access point 1 (AP1) moves to access point 2 (AP2), the signal of AP1 is weakened while the signal of AP2 is strong.

In other words, when the signal of AP1 falls below the Cell Prediction Threshold (CPT) via the Cell Search Threshold, the MH starts searching for a new access point. The cell prediction threshold (CPT) is a point where the signals of AP1 and AP2 are the same, and when this point is passed, the MH expects the access point to move to AP2. When the signal of AP1 falls below the Cell Switch Threshold, MH communicates through AP2, so MH prepares for handoff before the signal reaches the Cell Switch Threshold. The procedure must be completed.

Next, FIG. 2 shows a beacon frame before modification and a beacon frame after modification.

Referring to FIG. 2A, which shows a beacon frame before modification, the information contained in the frame includes information about a DA, which is a Media Access Control (MAC) address of 0 bits to 8 bits, and an access point of 8 bits to 16 bits. It consists of SA, MAC address, BSSID from 16bit to 24bit, and unused field from 24bit to 32bit. Before modifying the beacon frame, BOOTP (BOOTStrap Protocol) can find the IP address corresponding to the MAC address, but since most access points do not have an IP address, only information extracted from the beacon frame can be used for network layer information such as network prefix. Since we can't figure out, we can't detect the movement in the network layer using the extracted beacon frame.

Accordingly, referring to FIG. 2B, a modified beacon frame according to the present invention is shown. An address 4 area (a 24-bit to 32-bit area), which is a field not used to predict a network to move with this beacon frame, is shown. The gateway MAC address of the mobile network was modified. In other words, the address 4 area is not used when sending a beacon signal, and since it maintains a format for transmitting a MAC address, it does not affect the network component before modification. In addition, the gateway MAC address is useful information not only in the application layer protocol but also in the mobile layer IP and other protocols to ensure mobility.

Meanwhile, FIG. 3 is a diagram illustrating a detailed procedure for a method for supporting mobility of a multimedia service according to the present invention, wherein T0 to T5 represent time delays until a link layer handoff and a network layer handoff are terminated. will be.

That is, referring to FIG. 3, T0 is a handoff delay time at the link layer, T1 is a time required to detect movement at the network layer, and T2 is a procedure for detecting handoff at the network layer. Is the time required for MH to be assigned a new address when moving the network, and T3 registers the assigned IP address with the router of the visited network and makes other settings. T4 is a procedure of performing a session update procedure using a reserved address by the MH, and is a time required to update a session by notifying a correspondent host (Correspondent Host, CH) of a newly allocated address. T5 represents the time taken to deliver the actual packet. Here, the T2 procedure of performing the procedure of detecting handoff at the network layer, the process of performing the address reservation procedure, and the T4 procedure of performing the session update procedure using the MH reserved address before handoff. By minimizing the handoff delay time by performing on, the actual handoff delay time is T0, T1, T3, T5.

Next, a process of detecting handoff at the network layer according to the present invention will be described with reference to FIGS. 3 and 4.

First, referring to FIG. 3, when the MH 301 detects a movement in the link layer, the MAC address received from the AP of the mobile network, for example, the gateway in the address 4 region in the beacon frame after modification of FIG. 2B. Extract the MAC address.

Subsequently, the MH 301 uses BOOTP (BOOTStrap Protocol), a protocol for sending a request to an external network using UDP broadcasting as a protocol for finding an IP address that matches a MAC address in order to detect movement in the network layer. It sends the BOOTP request message to the external network that finds the IP address corresponding to the extracted gateway MAC address, which uses a request message format such as DHCP and UDP port, and shares the DHCP server 303 and 305. do. Therefore, the MH 301 broadcasts the MAC address of the gateway to DHCP servers 303 and 305 of the perimeter network using BOOTP. Here, in the existing network, the UDP broadcasting is transmitted only within the same network and the router blocks the transmission to the external network. When the DHCP relay agent is used, the BOOTP request message can be delivered to the adjacent DHCP servers 303 and 305.

DHCP server 303, 305 receives the BOOTP request message from MH 301, and then sends the IP address to the MH 301 using a BOOTP reply message when it finds an IP address that matches the MAC address of the gateway. .

After obtaining the IP address of the gateway, the MH 301 extracts the network prefix of the mobile network and predicts the movement of the network layer. If the handoff of the network layer is predicted, the procedure for pre-address reservation is performed. If the handoff of the network layer is not expected, the pre-address reservation procedure and the session update procedure are terminated and the link layer handoff is performed. .

In more detail, FIG. 4 is a block diagram illustrating a procedure of performing a procedure for detecting handoff at the network layer in FIG. 3. When the MH 301 detects a movement in the link layer, the block diagram is moved. A MAC address received from the AP of the network, for example, the gateway MAC address of address 4 in the beacon frame after the modification of FIG. 2B is extracted.

Subsequently, the MH 301 finds an IP address corresponding to the extracted gateway MAC address using BOOTP (BOOTStrap Protocol), and then sends a BOOTP request message together with the gateway 302 and 304 MAC addresses using a UDP broadcast address. For example, the process is transmitted to the DHCP server (DHCP_1) 303 and the DHCP server (DHCP_2) 305 as shown in Step 1 of FIG. 4. Here, since BOOTP uses a UDP port such as DHCP, the DHCP server 303 or 305 processes the BOOTP request message.

DHCP server 303, 305 extracts the MAC address included in the BOOTP request message, performs a comparison with the MAC address of the gateway A, B (302, 304) of the network including the DHCP server (303, 305), Only when it matches, the IP addresses of gateways A and B 302 and 304 are sent to the MH 301 as an example using a BOOTP reply message, and if not, a DHCP relay agent is used. The BOOTP reply message is transmitted to the MH 301 through the DHCP server 303 or 305 of the peripheral network. Here, since the DHCP relay agent serves to deliver the BOOTP reply message, the address information of the MH 301 included in the BOOTP reply message is not changed, so that the DHCP server 303 or 305 of the external network does not change the BOOTP reply. The message may be sent to the MH 301. That is, the DHCP server 303 or 305 of the external network receives a BOOTP reply message and then transmits an IP address corresponding to the MAC address registered in its address table to the MH 301 using a BOOTP reply message.

After receiving the gateway 304 IP address from the DHCP server (DHCP_2) 305 of the mobile network, the MH 301 compares the gateway IP address with the address of the network to which it belongs and compares the handoff at the network layer. The MH 301 performs an address reservation procedure and a session update procedure when it is predicted to occur and when a handoff is detected at the network layer. If no handoff occurs, the previous advance address reservation and session update procedures are terminated and the link layer handoff procedure is performed.

Next, a process of performing an address reservation procedure according to the present invention will be described with reference to FIGS. 3 and 5.

First, referring to FIG. 3, the MH 301 transmits an IP address allocation request (DHCP discovery) message to the DHCP server 305 to obtain an IP address. Here, in order to transmit an IP address assignment request message to the DHCP server 305 of the mobile network, the MH 301 sends a request message to a broadcasting address corresponding to the network address of the mobile network. For example, when the network address of the mobile network is 192.168.0, the MH 301 transmits an IP address assignment request message to the 192.168.0.255 address.

Subsequently, when the DHCP server 305 receives the IP address assignment request message from the MH 301, the DHCP server 305 performs address overlap detection and DAD (Duplicated Address Detection), and then uses the DHCP offer message to the MH 301. Send the address.

The MH 301 receives a new IP address from the DHCP server 305 and then transmits a DHCP request message to the DHCP server 305 of the network to use the IP address. Then, the DHCP server 305 receives the DHCP request message from the MH 301 and then ends the address assignment procedure by sending a DHCP ACK message to the MH 301.

In more detail, FIG. 5 is a block diagram illustrating a process of performing an address reservation procedure in FIG. 3. When the MH 301 detects a handoff at a network layer, an address reservation procedure to be used in a mobile network is performed. Perform

That is, the address reservation procedure starts by transmitting a DHCP discovery message for receiving an address assignment to a DHCP server (DHCP_2) 305 of a network to which the MH 301 moves, for example, as shown in Step 1 of FIG. 5. Send DHCP Discovery messages to the broadcast address of the network to be moved for transmission. In other words, DHCP Discovery messages should be transmitted to the broadcasting address of the mobile network using the IP address of the mobile network obtained in the process of FIG. 4. For example, if 192.168.0.1 is acquired as the router IP address of the mobile network in the process of FIG. 4, the broadcasting address of the mobile network is 192.168.0.255, and the MH 301 uses the address to send DHCP Discovery messages to the DHCP server ( 305).

Subsequently, since the DHCP server 305 includes the current IP address of the MH 301 in the DHCP Discovery message, the DHCP server 305 can assign an IP address to the MH 301 as it can respond to a DHCP request from an external network. For example, the DHCP offer message is transmitted as in Step 2 of FIG. 5.

When the MH 301 receives the DHCP offer message from the DHCP server 305, the MH 301 transmits the DHCP request message to the DHCP server 305 to which the address is assigned, as shown in step 3 of FIG. 5.

For example, if the DHCP server 305 transmits a DHCP ACK message to the MH 301 as shown in Step 4 of FIG. 5, the pre-address reservation procedure is completed.

Next, a process of performing a session update procedure using the reserved address according to the present invention will be described with reference to FIGS. 3 and 6.

First, referring to FIG. 3, the MH 301 performs a pre-session update procedure T4. That is, when the MH 301 obtains the IP address of the network to be moved, a new session is created using the CH 307 and the reserved IP address. After a new session is created, CH 307 uses bicasting to send the same data to the old and new sessions.

In more detail, FIG. 6 is a block diagram illustrating a process of performing a session update procedure using the reserved address by the MH 301 in FIG. 3, and the MH 301 uses the reserved address. Perform the session update procedure. The session update procedure maintains the currently created session before the handoff occurs and, by using the SIP Re-Invite procedure, creates a new session to the reserved address and transmits it to the CH 307, for example, as in Step 1 of FIG. 6. do.

Subsequently, when the CH 307 transmits an OK message to the MH 301 as an example, as shown in Step 2 of FIG. 6, the two terminals transmit the generated data. CH 307 performs by-casting that simultaneously transmits the same data through the session created by the current IP address and the IP address of the network to be moved, and the by-casting is performed until the end of the handoff of the MH 301. . When the handoff of the MH 301 ends, the MH 301 sends a session termination message to the CH 307 to terminate the session created with the previous IP address.

In conclusion, as shown in FIG. 3, T2 and T4 are preliminary procedures performed before the handoff of the link layer occurs, and the cell switch threshold at which the AP1 signal of FIG. 1 occurs when the handoff of the link layer occurs. Must be completed before the threshold is reached. As shown in FIG. 3, when T4 is completed, the MH 301 performs an actual handoff procedure. That is, T0, T1, T3, and T5 of FIG. 3 are performed, and the MH 301 communicates with the CH 307 through the access point of the moved network.

Accordingly, the present invention provides a procedure for detecting a handoff at the network layer, an address reservation procedure (T2), and a session update procedure (T4) using the reserved address at the wireless terminal, which is a point in time when handoff occurs at the link layer. By finishing before reaching the cell switch threshold, it is possible to provide high quality seamless multimedia service during handoff of the wireless terminal by reducing interruption and delay time due to mobility in the real-time multimedia service.

In addition, since the present invention is disclosed as a right within the spirit and claims of the present invention, the present invention may include any modification, use and / or adaptation using general principles, and the present invention as a matter deviating from the description of the present specification. It includes everything that falls within the scope of known or customary practice in the art to which it belongs and falls within the scope of the appended claims.

As described above, the present invention provides a cell switch threshold at which a handoff of a link layer occurs in a procedure for detecting a handoff and an address reservation procedure at a network layer, and a session update procedure using a reserved address at a wireless terminal. By finishing before reaching, it is possible to provide high quality seamless multimedia service during handoff of the wireless terminal by reducing interruption and delay time due to mobility in the real-time multimedia service.

Claims (7)

A method of providing a multimedia service to a wireless terminal (MH) using a DHCP server in a wireless network, (a) predicting the movement of the link layer by using the signal strength when the MH is located between two adjacent access points AP1 and AP2; (b) detecting a handoff at the network layer using a modified beacon frame when the movement of the link layer is predicted in step (a); (c) assigning a reserved IP address by performing a pre-IP address reservation procedure when the movement of the network layer is predicted in step (b); (d) performing an MH handoff after performing a pre-session update procedure using the reserved IP address allocated in step (c) Multimedia service method on a wireless network comprising a. The method of claim 1, The handoff detection method in the network layer in the step (b), (b1) extracting the gateway MAC address from the modified beacon frame provided by the MH from the AP of the mobile network; (b2) searching for an IP address corresponding to the extracted gateway MAC address using BOOTP (BOOTStrap Protocol) after the gateway MAC address is extracted in step (b1); (b3) the MH sending a BOOTP request message to the DHCP server using a UDP broadcast address together with a gateway MAC address corresponding to the IP address found in step (b2); (b4) The DHCP server uses the BOOTP reply message to extract the MAC address included in the BOOTP request message and compares it with the gateway MAC address of the network including the DHCP server. Transmitting to the MH by (b5) after receiving the gateway IP address from the DHCP server of the mobile network in the MH, comparing the current IP address with the gateway IP address and predicting whether a handoff occurs at the network layer; Multimedia service method over a wireless network, characterized in that it further comprises. The method of claim 2, If it does not match in step (b4) using a DHCP relay agent multimedia service method on a wireless network, characterized in that to send a BOOTP reply message to the MH through a DHCP server of a neighboring neighbor network. The method of claim 2, Step (b5) is, And comparing the prefix of the gateway IP address of the mobile network with the prefix of the address of the network to which the mobile network belongs, and ending the pre-address reservation procedure if the same is the same. The method of claim 1, In the step (c), the advance IP address reservation procedure, (c1) transmitting a DHCP discovery message for receiving an address assignment to a DHCP server of a network to which the MH moves; (c2) transmitting, by the DHCP server, a DHCP offer message for allocating an IP address to the MH in response to a DHCP discovery message; (c3) the MH transmitting a DHCP request message to a DHCP server in response to a DHCP offer message; (c4) completing the pre-address reservation procedure by transmitting a DHCP ACK message to the MH in response to a DHCP request message from the DHCP server; Multimedia service method over a wireless network, characterized in that it further comprises. The method of claim 1, In the step (d) the pre-session update procedure, (d1) When the MH obtains the IP address of the mobile network, the SIP Re-Invite procedure is performed while maintaining the currently created session before the handoff occurs using the reserved host address (Correspondent Host, CH) and the reserved IP address. Creating a new session with the reserved address and transmitting it to the CH; (d2) CH sends OK message to MH after a new session is created by step (d1); (d3) CH performing bicasting simultaneously transmitting the same data through sessions created by the current IP address and the IP address of the network to be moved until the end of the MH handoff. Multimedia service method over a wireless network, characterized in that it further comprises. The method of claim 1, When the handoff of the MH is finished in the step (d), the MH sends a session termination message to the CH to terminate the session created with the previous IP address. Multimedia service method over a wireless network, characterized in that it further comprises.

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