JP2005252858A - Method of re-establishing path of ad hoc wireless network and wireless terminal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of re-establishing a path of an ah hoc wireless network for starting to establish another path while maintaining communication in an existing path if a defective link is detected on the existing path, and to provide a wireless terminal. <P>SOLUTION: The wireless terminal includes a means for monitoring a reception state of an adjacent link, a means for sending a path error message to an end terminal having a defective link with a reception state below a predetermined re-establishment threshold (Pth) as part of its path, a means for substitutively responding a path response message to a path request message having a registered path to its destination, a means for inhibiting the substitutive response of the path response message when the registered path contains the defective link, and a means for discarding the path request message received from the defective link. The method of re-establishing the path includes steps for the above means. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for establishing a communication path by executing an on-demand type routing protocol on an ad hoc wireless network and its wireless terminal, and particularly, there is a decrease in received power intensity in any wireless link of an existing path. When detected, the present invention relates to a route reestablishment method and a wireless terminal of an ad hoc wireless network that starts establishing another route while maintaining communication on the existing route.

  As a typical on-demand routing protocol in an ad hoc network, Non-Patent Document 1 discusses AODV (Ad hoc On-Demand Distance Vector). In AODV, unlike a conventional table-driven routing protocol, a communication path is established when communication is started. Specifically, the communication initiator sends a RREQ (Route Request) as a route request message by broadcast, and the communication partner that has received the RREQ returns a RREP (Route Reply) to the communication initiator by unicast, thereby communicating. A route is established.

  In addition, the wireless terminal that detects the disconnection of the adjacent link during communication transmits RERR (Route Error) to the communication initiator. The communication initiator who receives RERR reestablishes the communication path. As a method of detecting disconnection of a wireless link, Non-Patent Document 1 lists the following four methods.

  1. If ACK or CTS (Clear To Send) cannot be received even if data and RTS (Request To Send) are transmitted for the maximum number of retransmissions, it is considered that the link is broken.

  2. After the packet is transmitted to the adjacent node, it is monitored whether or not the adjacent node relays the packet, and if it is not relayed, it is regarded as a link disconnection.

  3. When each wireless terminal periodically transmits a hello packet by broadcast and cannot receive a hello packet of an adjacent node for a certain period of time, it is considered that the adjacent link with the adjacent terminal is disconnected.

4). When a RREQ or ICMP (Internet Control Message Protocol) Echo Request is transmitted to an adjacent node and the reply cannot be received, it is regarded as a link disconnection.
IETF RFC 3561 Ad hoc On-Demand Distance Vector (AODV) Routing

  In the current AODV, the reestablishment of the route is started only after the disconnection of the wireless link is detected, so that packet loss occurs. In the current TCP (Transmission Control Protocol), when packet discard occurs continuously, flow control that resumes the service from the lowest speed works, resulting in a decrease in throughput. In addition, when UDP (User Datagram Protocol) is adopted for communication, data loss occurs and the application is affected.

  The object of the present invention is to solve the above-described problems of the prior art, monitor each wireless link on an existing route, and detect a decrease in received power intensity on any wireless link. An object of the present invention is to provide an ad hoc wireless network route re-establishment method and a wireless terminal that start establishment of another route while maintaining communication.

  In order to achieve the above object, the present invention is characterized in that the following measures are taken in a wireless terminal that establishes a communication path by executing an on-demand routing protocol on an ad hoc wireless network. .

  (1) Means for monitoring the reception status of the adjacent link, means for sending a route error message to an end terminal having a bad link whose reception status is below the re-establishment threshold as part of the route, and the route to the destination are already registered Means for proxying a path response message to the path request message, means for prohibiting proxy response of the path response message when a registered path includes the fault link, and a path request message received from the fault link And a means for discarding.

  (2) In response to receiving the route error message, a means for transmitting a route request message in which a variable threshold is registered, and when a route response message is not returned to the route request message, the threshold is set more than the previous time. Means for retransmitting a route request message in which the lowered variable threshold is registered; means for extracting the variable threshold from the received route request message; and if the reception status of the route request message falls below the variable threshold, the route Means for discarding the request message.

  (3) When the variable threshold is lower than the re-establishment threshold, transmission of the path error message is prohibited for the adjacent link regardless of the reception state.

According to the present invention, the following effects are achieved.
(1) When a defective link whose reception state falls below the re-establishment threshold is detected on an existing route, another route that does not include the defective link is established while continuing communication using the existing route. Is switched from the existing route to the other route, it is possible to shift from the existing route to the new route without reducing the throughput.
(2) A variable threshold is registered in the route request message, and this variable threshold is lowered every time the route request message fails to be received and the route request message is retransmitted. Establishment is possible.
(3) If the variable threshold registered in the route request message is lower than the re-establishment threshold, even if the reception status of the radio link established satisfying the variable threshold falls below the re-establishment threshold Since an error message is not transmitted, when the route via the defective link is the best, communication via the route becomes possible.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a diagram schematically showing an example of a multi-hop wireless network to which the route update method of the present invention is applied. Here, a wireless terminal MS1 as a transmission source terminal is a wireless terminal MS2 as a relay terminal. A description will be given from a state in which the first route for communicating with the wireless terminal MS5 as the destination terminal is established via the MS3.

  All wireless terminals MS1 to MS5 are equipped with a reception power monitor as a system for determining the state of adjacent links terminated by themselves, and each wireless terminal periodically monitors the power of voice signals and data received from adjacent terminals. Then, the intensity of the received power is detected. When each wireless terminal periodically transmits a hello packet, the received power of the hello packet may be measured.

  Next, the first embodiment of the present invention will be described in detail with reference to the flowcharts of FIGS. 3 and 4 and the sequence flow of FIG. In the present embodiment, a case will be described as an example where the reception state of the adjacent link L2 common to the radio terminals MS2 and MS3 is lowered and another path that does not pass through the adjacent link L2 is reestablished.

  FIG. 3 is a flowchart showing the procedure of the adjacent link monitoring process periodically executed in each wireless terminal. In step S1, the received power intensity P of the adjacent link and the re-establishment threshold Pth registered in advance are obtained. To be compared. This re-establishment threshold value Pth is used as an index for determining whether or not the reception state of the adjacent link is lowered to a level that requires route re-establishment. When the reception state decreases in the adjacent link L2, both wireless terminals MS2 and MS3 determine that P <Pref, and the process proceeds to step S2. Thereafter, the same procedure is executed in each of the wireless terminals MS2 and MS3. Here, the description will be continued with attention paid to the operation of the wireless terminal MS2.

  In step S2, for example, a route error message (Route Error-X: RERR-X) in which the IP address is registered is generated as an identifier of an end terminal (source terminal and destination terminal) that is routed through the adjacent link L2. The If it is the wireless terminal MS2, RERR-X including the identifier of the destination terminal MS5 is generated. In step S3, as shown in an example in FIG. 6, the status of the entry corresponding to the destination “MS5” in the routing table is changed from “valid” in which the proxy response of the route reply message (Route Reply: RREP) is permitted. RREP proxy response is updated to “aux” which is prohibited. However, since data transmission / reception and relay are all permitted in “aux” as well as “valid”, data communication using the first route is continued even during re-establishment of the route.

  In step S4, the RERR-X is transmitted to the transmission source terminal MS1 by unicast. Also in other wireless terminals that relay this RERR-X, the status of the entry corresponding to the destination “MS5” in the routing table is updated from “valid” to “aux” as described above. If there are a plurality of other routes including the adjacent link L2 as in the second route shown in FIG. 2, the RERR-X is not transmitted separately to the end terminals of each route by unicast. In addition, simultaneous transmission may be performed by broadcasting.

  In step S5, as the identifiers of the radio terminals facing each other across the adjacent link L2, the MS3 identifier is registered in the blacklist if the radio terminal MS2, and the MS2 identifier is registered in the blacklist if the radio terminal MS3. From the source terminal MS1 that has received the RERR-X, a route request message (Route request: RREQ) for establishing a new route is broadcast. In this RREQ, the wireless terminal MS5 is registered as a destination.

  FIG. 4 is a flowchart showing a procedure of “RREQ reception processing” executed by each wireless terminal MS2, MS3, MS4 that has received the RREQ.

  In step S21, when reception of an RREQ addressed to a destination other than itself is detected, the process proceeds to step S22, whether or not the hop source of this RREQ is already registered in the blacklist, or the received power strength P of the RREQ is It is determined whether or not it is below the re-establishment threshold Pth. If the wireless terminal MS2 has received the RREQ from the transmitting terminal MS1 or the wireless terminal MS4 received from the wireless terminal MS2, the hop source is not already registered in the blacklist (or P <Pth is not satisfied), so step S23 Proceed to On the other hand, if the wireless terminal MS3 receives the RREQ from the transmission source terminal MS2 via the adjacent link L2, the hop source is already registered in the blacklist (or P <Pth), so the process goes to step S26. Go ahead and discard the RREQ. Therefore, relaying of the RREQ message via the adjacent link L2 is not performed.

  In step S23, it is determined whether or not the destination route information is already registered in its own routing table. If the route information is not registered, the process proceeds to step S27, and if already registered, the process proceeds to step S24. In step S24, the routing table is referred to, and the status of the entry corresponding to the RREQ destination “MS5” is determined. If the status is “valid”, since the proxy reply of RREP is permitted, the process proceeds to step S25, and the RREP is returned to the source terminal by unicast instead of the destination terminal, as in the prior art. On the other hand, in the case of the wireless terminal MS2, since the status of the entry corresponding to the destination “MS5” is “aux” and the proxy reply of RREP is prohibited, the process proceeds to step S27. As a result, even if the route reaching the destination “MS5” via the adjacent link L2 is already registered, it is possible to prevent the route from being re-established. In step S27, RREQ is broadcasted (relayed). In step S28, the routing table is updated.

  The destination terminal MS5 that has received the RREQ updates the routing table and returns RREP as in the prior art. Each wireless terminal that relays this RREP to the source terminal MS1 updates its routing table based on the RREP. As a result, as shown in FIG. 7, a third route or a fourth route that does not pass through the adjacent link L2 is established between the transmission source terminal MS1 and the destination terminal MS5. Data and audio signals are transmitted and received using the third route or the fourth route instead of the first route.

  Next, the operation of the second embodiment of the present invention will be described in detail with reference to the flowcharts of FIGS. 8 and 9 and the sequence flow of FIG. In this embodiment, as in the first embodiment, each wireless terminal monitors its own adjacent link, and when a bad link whose received power strength P is lower than the re-establishment threshold Pth is detected, the RERR-X is sent to each end terminal. Send.

  FIG. 8 is a flowchart showing the operation of the source terminal MS1 that has received the RERR-X from the radio terminal MS2. When RERR-X destined for itself is received in step S31, in step S32 the destination is wireless. RREQ set in terminal MS5 is generated. In step S33, an initial value “1” is set in the threshold switching variable i. In step S34, the first variable threshold Pth_1 (> Pth) associated with the current threshold switching variable i is registered in the RREQ as the variable threshold Pth_i. In step S35, the RREQ is transmitted by broadcast, and in step S36, it prepares for reception of an RREP returned in response to the RREQ.

  If the predetermined waiting time has timed out in step S37 without receiving RREP, the threshold value switching variable i is updated to “2” in step S38. In step S39, the threshold value switching variable i is compared with the upper limit value i_max. Since the threshold value switching variable i is initially lower than the upper limit value i_max, the process returns to step S34 and the second variable threshold value Pth_2 (Pth <Pth_2 <Pth_1) is set as the variable threshold value Pth_i. ) Registered RREQ is broadcast again. If RREP is not returned in response to this RREQ message, the threshold switching variable i is updated in the same manner as described above, and the RREQ registered with the third variable threshold Pth_3 (Pth <Pth_3 <Pth_2) is transmitted by broadcast. That is, in this embodiment, the RREQ in which the variable threshold Pth_i is registered is repeatedly broadcasted while gradually decreasing the variable threshold Pth_i within the range of Pth <Pth_i until the RREP in response thereto is received. The

  Thereafter, when reception of RREP is detected in step S36, the process proceeds to step S40. In step S40, the routing information in the routing table is updated based on the received RREP message.

  FIG. 9 is a flowchart showing a procedure of “RREQ reception processing” in each wireless terminal, and the same or equivalent processing is executed in steps denoted by the same reference numerals as those in FIG. 4 of the first embodiment.

  In the present embodiment, the variable threshold value Pth_i registered in the received RREQ is extracted in step S51, and compared with the received power intensity P of the RREQ in step S52. Since the wireless terminal MS2 determines that P <Pth_i for all the variable threshold values Pth_1, Pth_2, and Pth_3, the process proceeds to step S26 and all the RREQ messages are discarded. In the radio terminal MS4, for example, P <Pth_i is determined for the first and second variable threshold values Pth_1 and Pth_2, but P ≧ Pth_i is determined for the third variable threshold value Pth_3, so that the steps go through steps S23 and S24. In step S27, RREQ is broadcast.

  When this RREQ is received by the radio terminal MS5 and an RREP message is returned in response thereto, a new route that does not pass through the radio link L2 is established between the source terminal MS1 and the destination terminal MS5 .

  Next, the operation of the third exemplary embodiment of the present invention will be described in detail with reference to the flowchart of FIG. 11 and the sequence flow of FIG. Also in this embodiment, each wireless terminal monitors its adjacent link and transmits RERR-X when the received power strength P falls below the re-establishment threshold Pth, as in the above embodiments. Similarly to the second embodiment, the source terminal MS1 repeats the RREQ registered with the variable threshold value Pth_i while gradually decreasing the variable threshold value Pth_i until the RREP corresponding to the RREQ is received. However, in the present embodiment, unlike the second embodiment, the setting of the fourth variable threshold Pth_4 that is lower than the re-establishment threshold Pth is permitted.

  FIG. 11 is a flowchart showing a procedure of RREQ reception processing in the present embodiment, and the same or equivalent processing is executed in steps denoted by the same reference numerals as those in FIG. 9 of the second embodiment.

  In this embodiment, in each wireless terminal, the variable threshold value Pth_i registered in the received RREQ is extracted in step S51, and compared with the received power intensity P of the RREQ in step S52. Here, if the wireless terminal MS4 does not exist, the RREP is not replied to the RREQ registered with the third variable threshold Pth_3, so that the source terminal MS1 is the fourth lower than the re-establishment threshold Pth. RREQ registered with the variable threshold value Pth_4 is transmitted.

  In the wireless terminal MS3, only when the variable threshold Pth_i becomes the fourth variable threshold Pth_4, it is determined in step S52 that P ≧ up Pth_i, and the process proceeds to step S23. If it is determined in step S23 that the destination route information is not possessed, or if it is determined in step S24 that the status of the entry corresponding to the destination “MS5” in the routing table is not “valid”, the process proceeds to step S27. , RREQ is transmitted (relayed) by broadcast. In step S28, the route information is updated. In step S53, the current Pth_i (here, Pth_4) and Pth are compared. Here, since Pth_i <Pth is determined, the process proceeds to step S54. In step S54, transmission of RERR-X transmitted in step S4 is prohibited for the adjacent link L2.

  When the RREQ transmitted in step S27 is received by the radio terminal MS5 and a RREP message is returned in response thereto, the same path as the existing path is established between the source terminal MS1 and the destination terminal MS5. Will be. However, regarding the adjacent link L2, since the transmission of RERR-X is prohibited in step S54, the above process is not repeated.

  In the above-described embodiment, an ad hoc wireless network including only wireless terminals has been described as an example. However, the present invention is not limited to this, and as illustrated in FIG. The terminal may be a radio base station BS connected to an external network. In this case, the radio base station BS functions as the source terminal MS1 or the destination terminal MS5.

It is the figure which expressed typically an example of the multihop radio | wireless network to which the route update method of this invention is applied. It is the figure which expressed typically another example of the multihop radio | wireless network to which the route update method of this invention is applied. It is the flowchart which showed the procedure of the "adjacent link monitoring process" in 1st Embodiment of this invention. 5 is a flowchart showing a procedure of “RREQ reception processing” in the first embodiment of the present invention. It is a sequence flow of 1st Embodiment of this invention. It is the figure which showed an example of the routing table. It is the figure which showed an example of the re-established path | route. It is the flowchart which showed the procedure of "RERR-X reception process" in 2nd Embodiment of this invention. It is the flowchart which showed the procedure of "RREQ reception processing" in 2nd Embodiment of this invention. It is a sequence flow of 2nd Embodiment of this invention. It is the flowchart which showed the procedure of "RREQ reception processing" in 3rd Embodiment of this invention. It is a sequence flow of 3rd Embodiment of this invention. It is the figure which showed the network structure which concerns on 4th Embodiment of this invention.

Explanation of symbols

Pth: Reset threshold
Pth_i: Variable threshold

Claims (15)

In a wireless terminal that establishes a communication path by executing an on-demand routing protocol on an ad hoc wireless network,
Means for monitoring the reception status of adjacent links;
Means for transmitting a path error message to an end terminal having a bad link whose reception state is lower than a re-establishment threshold (Pth) as a part of the path;
And a means for establishing another detour route while maintaining the route including the defective link in response to receiving the route error message. Means for proxying the route response message to the route request message for which the route to the destination is already registered;
The wireless terminal of an ad hoc wireless network according to claim 1, further comprising means for prohibiting a proxy response of the route response message when the registered route includes the defective link.   The wireless terminal of an ad hoc wireless network according to claim 1 or 2, further comprising means for discarding a route request message received from the defective link. Means for transmitting a route request message in which a variable threshold (Pth_i) is registered in response to receiving the route error message;
Means for retransmitting a route request message in which a second threshold value, which is lower than the previous threshold value, is registered when a route response message is not returned to the route request message;
Means for extracting the variable threshold from the received route request message;
The wireless terminal of an ad hoc wireless network according to any one of claims 1 to 3, further comprising means for discarding the route request message when a reception state of the route request message falls below the variable threshold.   The wireless terminal of an ad hoc wireless network according to claim 4, wherein the variable threshold is higher than a re-establishment threshold.   The wireless terminal of the ad hoc wireless network according to claim 4, further comprising a variable threshold value lower than the re-establishment threshold value.   The radio of the ad hoc wireless network according to claim 6, wherein when the variable threshold is lower than the re-establishment threshold, transmission of the route error message is prohibited for the bad link regardless of its reception state. Terminal. In a method for re-establishing a communication path by executing an on-demand routing protocol on an ad hoc wireless network,
A procedure for each wireless terminal to monitor the reception status of adjacent links;
A procedure in which a wireless terminal whose reception state of an adjacent link is lower than a re-establishment threshold (Pth) transmits a route error message to an end terminal whose route is the defective link;
A route establishing method for an ad hoc wireless network, wherein the end terminal responds to the route error message and establishes another bypass route while maintaining the route including the defective link. A procedure in which the end terminal transmits a route request message in response to the route error message;
A wireless terminal that has received a route request message for which the route to the destination has already been registered, and a proxy response of the route response message,
When the route request message is received, even if the route to the destination is already registered, the proxy response of the route response message is prohibited when the registered route includes the defective link. The method for reestablishing a route of an ad hoc wireless network according to claim 8.   10. The route re-establishment method for an ad hoc wireless network according to claim 8, further comprising a procedure of discarding a route request message received from the defective link. In response to receiving the route error message, the end terminal transmits a route request message in which a variable threshold (Pth_i) is registered, and
A procedure in which the end terminal retransmits a route request message in which a variable threshold value lower than the previous time is registered when a route response message is not returned in response to the route request message;
A procedure by which the wireless terminal that has received the route request message extracts the variable threshold;
The ad hoc according to any one of claims 8 to 10, further comprising: a procedure in which the wireless terminal discards the route request message when a reception state of the route request message falls below the variable threshold. A method for re-establishing a route in a wireless network.   The method of claim 11, wherein the variable threshold is higher than a re-establishment threshold.   The method of claim 11, further comprising a variable threshold value lower than the reestablishment threshold value.   14. The route of the ad hoc wireless network according to claim 13, wherein when the variable threshold is lower than the re-establishment threshold, transmission of the route error message is prohibited for the bad link regardless of its reception state. How to re-establish.   The method for establishing a route of an ad hoc wireless network according to any one of claims 8 to 14, wherein at least one of the end terminals is a wireless base station connected to an external network.

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