JP2003274436A - Mobile node, mobile communication system, and communication control program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a mobile node, a mobile communication system and a communication control program capable of preventing a packet loss from causing during a hand-off period. <P>SOLUTION: A link layer of a mobile host 3 is connected to an access router 7 in a state I, since a default router is set to the access router 7, data packets (P1), (P2) reach the access router 7 and are routed to a communication opposite host 11. In states II and III, data packets (P3) to (P8) are not transmitted but buffered. When a mobile host 3 receives a router notice of an access router 9 to revise the default router from the access router 7 into the access router 9, the state is transited to a state IV, and the buffered data packets (P3) to (P8) are transmitted. The link layer of the mobile host 3 is connected to the access router 9, and since the default router is set to the access router 9, the data packets (P3) to (P8) reach the access router 9 to be routed to the communication opposite host 11. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a mobile node, a mobile communication system, and a communication control program.

[0002]

2. Description of the Related Art State transition at the time of handoff of a conventional mobile host when the mobile node is a mobile host will be described with reference to FIG. In FIG. 8, MH indicates a mobile host (Mobile Host), AR indicates an access router (Access Router), and CH indicates a communication partner host (Corresponding Host).

Here, it is assumed that the mobile host 101 communicates with the communication partner host 107 in the fixed network. As shown in FIG. 8, the state transition associated with the handoff of the mobile host 101 is divided into four.

State I: The link layer of the mobile host 101 is connected to the access router 103, and the default router (Default Router) is the access router 1.
It is set to 03.

State II: The link layer of the mobile host 101 switches the connection point from the access router 103 to the access router 105. The period during which the connection point is switched is called the link layer instantaneous interruption time. At this time, the default router is still the access router 103.

State III: The link layer of the mobile host 101 is connected to the access router 105. At this time, the default router is still the access router 103. In this state, the mobile host 101 is the access router 1
05 Router Advertisement (Router Advertisement)
ment) is received and the default router is changed from the access router 103 to the access router 105.

State IV: The router advertisement of the access router 105 is received, and the default router is set to the access router 10.
This is the state after changing from 3 to the access router 105. At this time, both the connection point of the link layer and the default router are the access router 105.

Table 1 summarizes the link layer connection points and the default routers in the above-mentioned states I to IV.

[Table 1]

Next, the state transition at the time of handoff of a conventional mobile router when the mobile node is a mobile router will be described with reference to FIG. In FIG. 9, SH is a fixed host (Stationary Host), MR is a mobile router (Mobile Router), AR is an access router (Access Router), and CH is a correspondent host (Corresponding Host).
t) is shown.

Here, it is assumed that the fixed host 109 in the mobile network communicates with the correspondent host 107. As shown in FIG. 9, the state transition associated with the handoff of the mobile router 111 is divided into four.

State I: The link layer of the mobile router 111 is connected to the access router 103, and the default router (Default Router) is the access router 1.
It is set to 03.

State II: The link layer of the mobile router 111 switches the connection point from the access router 103 to the access router 105. The period during which the connection point is switched is called the link layer instantaneous interruption time. At this time, the default router is still the access router 103.

State III: The link layer of the mobile router 111 is connected to the access router 105. At this time, the default router is still the access router 103. In this state, the mobile router 111 has the access router 1
05 Router Advertisement (Router Advertisement)
ment) is received and the default router is changed from the access router 103 to the access router 105.

State IV: The router advertisement of the access router 105 is received, and the default router is set to the access router 10.
This is the state after changing from 3 to the access router 105. At this time, both the connection point of the link layer and the default router are the access router 105.

Table 2 summarizes the link layer connection points and the default routers in the above-mentioned states I to IV.

[Table 2]

[0016]

However, it has been found that the above-mentioned conventional state transition at the time of handoff of the mobile node has the following problems.

First, a problem when the mobile node is a mobile host will be described. In the packet transmitted from the mobile host 101 to the correspondent host 107, if the connection point of the link layer and the default router match (state I and state IV), the access router set as the default router (access router 103 in state I). In the state IV, the packet is received by the access router 105) and routed to the communication partner host 107 in the fixed network. The mobile host continues to transmit packets addressed to the correspondent host during state II and state III.

In states II and III, since the default router is the access router 103, the destination MAC (Media Access Controller) of these packets is
ol) address is the MAC address of the access router 103. However, since the link layer connection with the access router 103 is already broken, these packets do not reach the access router 103 and are not routed to the fixed network. As described above, in the state II or the state III, the packet transmitted from the mobile host 101 to the communication partner host 107 is
There is a problem that it does not reach 7, that is, packet loss occurs.

Next, the problem when the mobile node is a mobile router will be described. The packet sent from the fixed host 109 to the correspondent host 107 and routed by the mobile router 111 on the way is the default router only when the link layer connection point and the default router in the mobile router 111 match (state I and state IV). The packet is received by the access router (access router 103 in the state I, access router 105 in the state IV) set to No. 1 and routed to the communication partner host 107 in the fixed network. The IP layer of the mobile router 111 is in state II,
Even in the state III, the routing of the packet transmitted by the fixed host 109 and addressed to the correspondent host 107 is continued.

In states II and III, since the default router is the access router 103, the destination MAC address of these packets is the MAC address of the access router 103.
Address. However, the access router 103
Since the link layer connection with and has already been disconnected, these packets do not reach the access router 103 and are not routed to the fixed network. In this way, the packet transmitted from the fixed host 109 to the correspondent host 107 and routed by the mobile router 111 in the state II or the state III to the fixed network side is the correspondent host 1
There is a problem that it does not reach 07, that is, packet loss occurs.

Therefore, the present invention solves the above problems,
An object of the present invention is to provide a mobile node, a mobile communication system, and a communication control program capable of preventing packet loss during a handoff period.

[0022]

A mobile node according to the present invention is a mobile node that transmits a packet, buffers the packet during a handoff period, and buffers the packet when the handoff is completed. It is characterized by having a means for transmitting.

In the mobile node according to the present invention, the packet to be transmitted during the handoff period is buffered without being transmitted during the handoff period, and the buffered packet is transmitted when the handoff is completed. Will be sent. This can prevent packet loss during the handoff period.

Also, during the period for buffering packets by the above means, the link layer of the mobile node is not connected to any external link for switching the connection point, from the start of the link layer instantaneous interruption time, to the link concerned. It is preferable that it is a period until the access router providing the newly connected external link is changed to the default router after the end of the layer interruption time. With this configuration, the packet buffering period is set extremely appropriately, and packet loss can be reliably prevented.

Further, it is preferable that the means detects the start of the link layer instantaneous interruption time by a signal from an interface connected to an external link, and detects the change of the default router by a signal from the IP layer of the mobile node. With this configuration, it is possible to appropriately and easily detect the period for buffering the packet.

Further, the above-mentioned means uses the router advertisement (router a
It is preferable not to buffer the router solicitation for requesting the access router to transmit the dvertisement). Buffering all packets causes the following problems. In general, it is preferable that the mobile node that has switched the connection link receives the router advertisement as soon as possible in order to quickly know the default router on the newly connected link. Therefore, the mobile node can send a router solicitation to the access router using multicast addressed to all routers in the link immediately after the link connection point change is completed. However, if all the packets are buffered, the router solicitation does not reach the access router, and as a result, the mobile node receives the router advertisement in a delayed manner. Therefore, by not buffering the router solicitation, the router solicitation sent by the mobile node reaches the access router, and the mobile node can receive the router advertisement promptly.

On the other hand, the mobile communication system according to the present invention is
A mobile communication system comprising a mobile node transmitting a packet and a plurality of access routers providing an external link to the mobile node, wherein the mobile node buffers the packet during the handoff period, and the handoff is completed. It is characterized in that it has means for transmitting the buffered packet to the access router which provides the newly connected external link.

In the mobile communication system according to the present invention, in the mobile node, the packet to be transmitted during the handoff period is buffered without being transmitted during the handoff period, and is buffered when the handoff is completed. The ringed packet will be sent to the access router that provides the newly connected external link. This can prevent packet loss during the handoff period.

Also, during the period of buffering packets by the above means, the link layer of the mobile node is not connected to any external link for switching the connection point, from the start of the link layer instantaneous interruption time, to the link concerned. It is preferable that it is a period until the access router providing the newly connected external link is changed to the default router after the end of the layer interruption time. With this configuration, the packet buffering period is set extremely appropriately, and packet loss can be reliably prevented.

Further, it is preferable that the means detects the start of the link layer instantaneous interruption time by a signal from an interface connected to an external link and detects the change of the default router by a signal from the IP layer of the mobile node. With this configuration, it is possible to appropriately and easily detect the period for buffering the packet.

Further, the above-mentioned means uses the router advertisement (router a
It is preferable not to buffer the router solicitation for requesting the access router to transmit the dvertisement). With this configuration, the router solicitation sent by the mobile node reaches the access router, and the mobile node can receive the router advertisement promptly.

Then, the communication control program according to the present invention causes the computer to buffer the packet during the handoff period in order to transmit the packet, and transmits the buffered packet when the handoff is completed. The feature is that it functions as a means.

In the communication control program according to the present invention, the computer functions as the above-mentioned means, whereby the packet to be transmitted during the handoff period is buffered without being transmitted during the handoff period, and the handoff period. The buffered packet will be sent when is completed. This can prevent packet loss during the handoff period.

Also, during the period for buffering packets by the above means, the link layer of the mobile node is not connected to any external link for switching the connection point, from the start of the link layer instantaneous interruption time, to the link concerned. It is preferable that it is a period until the access router providing the newly connected external link is changed to the default router after the end of the layer interruption time. With this configuration, the packet buffering period is set extremely appropriately, and packet loss can be reliably prevented.

Further, it is preferable that the above-mentioned means detects the start of the link layer instantaneous interruption time by a signal from the interface connected to the external link and the change of the default router by a signal from the IP layer of the mobile node. . With this configuration, it is possible to appropriately and easily detect the period for buffering the packet.

In addition, by the above means, the router notification (router
It is preferable not to buffer the router solicitation for requesting the access router to send the advertisement. With this configuration, the router solicitation sent by the mobile node reaches the access router, and the mobile node can receive the router advertisement promptly.

[0037]

BEST MODE FOR CARRYING OUT THE INVENTION A mobile node, a mobile communication system and a communication control program according to an embodiment of the present invention will be described with reference to the drawings. In the description, the same elements or elements having the same function will be denoted by the same reference symbols, without redundant description.

(First Embodiment) FIG. 1 is a diagram showing the configuration of a mobile communication system according to the first embodiment. In FIG. 1, MH is a mobile host,
HA is a home agent,
AR is an access router (Access Route)
r) and CH are communication partner hosts (Corresponde
nt Host) is shown.

As shown in FIG. 1, the mobile communication system 1 includes a mobile host 3, a home agent 5, a plurality of access routers 7 and 9, a correspondent host 11, and an IP network 13.

The mobile host 3 is a node that communicates with the correspondent host 11 while moving from link to link. The access routers 7 and 9 are routers that provide external links (wireless links) to which the mobile host 3 can connect.
The home agent 5 uses the IP mobility control method Mo
bileIPv6 (Internet Protocol)
It is a router that can transfer a packet addressed to the mobile host 3 to a link where the mobile host 3 is located (an external link provided by an access router or the like) using the L version 6). The correspondent host 11 is a node that communicates with the mobile host 3.

A node is a device for transmitting and receiving a packet compatible with IPv6, and a link is a communication path for transmitting a packet transmitted by a node to another node by a wired transmission method or a wireless transmission method. Links include home links and external links. The home link is a link to which the mobile host 3 belongs, and the external link is a link other than the home link. Mobile host 3
Is assigned a home address from the home link,
The care-of address is assigned from the external link.

FIG. 2 is a diagram showing the configuration of the mobile host 3. The mobile host 3 includes an application layer 31 including an application 31a, a TCP (Transmission).
onControl Protocol) and UDP
(User Datagram Protocol) 3
3a (hereinafter referred to as TCP / UDP) and a transport layer 33 including a buffer space 33b, IP (In
An IP layer 35 including a network protocol 35a, a link layer 37 including a link 37a and an interface 37b.

In the mobile host 3, the data transmitted by the application 31a to another host is TCP / U.
It is transmitted from the interface 37b via the DP 33a, the IP 35a, and the link 37a. On the contrary, the data transmitted from another host is the interface 37b,
The application 31a is reached via the link 37a, the IP 35a, and the TCP / UDP 33a.

Buffer space 33b is for buffering packets during handoff. The TCP / UDP 33a buffers the packet in the buffer space 33b. During the period of buffering packets, the link layer 37 of the mobile host 3 is not connected to any external link due to the switching of the connection point from the start of the link layer 37 instantaneous interruption time to the link layer 37 instantaneous interruption time. Is a period until the access router providing the newly connected external link is changed to the default router after the end of. Here, the TCP / UDP 33a is
Link layer 37 Starts the momentary interruption time by interface 37b
Detected by the signal from the
It is detected by the signal from P35a.

When the connection point is switched from the access router 7 to the access router 9, the interface 37b receives the T
Issue a buffer command to the CP / UDP 33a. As a result, the TCP / UDP 33a detects the start of the instantaneous interruption time of the link layer 37. TCP receiving buffer command
The / UDP 33a uses the buffer space 33b to start buffering of the packet that should originally be passed to the IP 35a.

The IP 35a is a router advertisement (Router Advertisement) received from the access router 9.
ent), T when the default router is changed
Issue a buffer release command to the CP / UDP 33a. As a result, the TCP / UDP 33a detects the change of the default router. TC that received the buffer release command
The P / UDP 33a releases the buffering, and the packet buffered in the buffer space 33b is IP-routed.
Pass it to 35a. The packet passed to the IP 35a passes through the link 37a and the interface 3 as described above.
7b to the access router 9 (set as the default router) that provides the newly connected external link.

FIG. 3 is a sequence chart when the mobile host 3 communicating with the correspondent host 11 hands off from the access router 7 to the access router 9. A solid line arrow indicates a control packet for executing a handoff at the IP layer level using Mobile IPv6, and a dotted line arrow indicates that the mobile host 3 is the correspondent host 11
Indicates a data packet to be transmitted to State I in FIG.
-State IV corresponds to state I-state IV described in FIG.

In state I, the link layer 37 of the mobile host 3 is connected to the access router 7, and the default router is set to the access router 7,
The data packets (P1) and (P2) reach the access router 7 and are routed to the correspondent host 11. In the subsequent state II and state III, the data packets (P3) to (P8) are buffered without being transmitted.

The mobile host 3 receives the router advertisement from the access router 9 and sets the default router to the access router 7.
From the access router 9 to the state IV, buffered data packets (P3) to (P3)
8) is transmitted. Since the link layer 37 of the mobile host 3 is connected to the access router 9 and the default router is set to the access router 9, the data packets (P3) to (P8) reach the access router 9 and communicate. It is routed to the partner host 11. The data packets (P9) and (P10) also arrive at the access router 9 and are routed to the correspondent host 11.

When the mobile host 3 obtains the new care-of address used in the external link, the Binding U
The packet including the pdate option is transmitted to the home agent 5. Home Agent 5 is Bind
When receiving an ing Update packet, Bindi
ng (correspondence between the home address and the care-of address of the mobile host 3) is stored, and a Binding A
The packet including the acknowledgment option is transmitted to the mobile host 3.

In the first embodiment, for simplification, the mobile host 3 requests the router solicitation (Router Sol).
ICTation) is not sent. Of course, it can be applied to the mobile host 3 that transmits the router solicitation, but it is necessary to not buffer the router solicitation. Note that, as in the first embodiment, if the transport layer 33 buffers, the router solicitation is not buffered.

On the other hand, although it is possible to perform buffering at the IP layer 35, in this case, the IP layer 35 analyzes the packet below the IP header to determine whether or not the packet to be buffered is a router request. If it is a router solicitation, it must be excluded from the buffering targets. The analysis below the IP header of the packet specifically indicates the following operation. For each packet, the IP layer 35 checks the protocol number stored in the next header field in each IP header including the extension header. If the protocol number indicates 58 (icmp), the icmp that follows the IP header is checked. Check the field that indicates the type of. If the type number is 133 (router solicitation), it is determined that the packet is a router solicitation.

In the first embodiment, during the packet buffering period, the link layer 37 of the mobile host 3 is not connected to any external link due to the switching of the connection points. The period from the start of the time to the change of the access router providing the newly connected external link to the default router after the end of the instantaneous interruption time of the link layer 37 is described, but it is not limited to this. For example, the period for buffering packets may be set longer than the above period in consideration of the state of the wireless link.

As described above, in the first embodiment, while the packet cannot reach the access routers 7 and 9 from the mobile host 3 during the handoff period, the mobile host 3 performs the handoff. The packet to be transmitted is buffered during the period of, and the buffered packet is transmitted after the packet can reach the access routers 7 and 9 of the handoff destination. As a result, all packets that the mobile host 3 attempts to transmit during the handoff are routed to the correspondent host 11 via the access routers 7 and 9 of the handoff destination, and packet loss may occur during the handoff period. Can be prevented.

In the first embodiment, during the period in which the mobile host 3 buffers packets, the link layer 37 of the mobile host 3 is not connected to any external link in order to switch the connection point. The period is from the start of the momentary interruption time of the link layer 37 to the change of the access routers 7 and 9 that provide newly connected external links to the default routers after the termination of the momentary interruption time of the link layer 37. As a result, the period for buffering packets is set extremely appropriately, and packet loss can be reliably prevented.

In the first embodiment, TCP / UD
In P33a, the start of the instantaneous interruption time of the link layer 37 is detected by a signal from the interface 37b connecting to the external link, and the change of the default router is detected by a signal from the IP layer 35 of the mobile host 3. This makes it possible to appropriately and easily detect the period during which packets are buffered.

The mobile host 3 that sends the router solicitation
In the above, the following problems occur when all packets are buffered. Generally, the mobile host 3 preferably receives the router advertisement as soon as possible in order to know the default router as soon as possible. Therefore, the mobile host 3 can transmit the router solicitation to the access router by using the multicast addressed to all the routers in the link immediately after the change of the link connection point. However, if all the packets are buffered, the router solicitation does not reach the access routers 7 and 9, and as a result, the reception of the router advertisement of the mobile host 3 is delayed. Therefore, by not buffering the router solicitation, the router solicitation sent by the mobile host 3 reaches the access routers 7 and 9.
The mobile host 3 can receive the router advertisement promptly.

(Second Embodiment) FIG. 4 is a diagram showing the configuration of a mobile communication system according to the second embodiment. In FIG. 4, SH is a stationary host (Stationary Ho).
st), MR is a mobile router (Mobile Route)
r), HA is a home agent (HomeAgen)
t), AR is an access router (Access Rout)
er) and CH are correspondent hosts (Correspond
ent Host) is shown.

As shown in FIG. 4, the mobile communication system 51 includes a mobile router 53, a fixed host 55, a home agent 5, a plurality of access routers 7 and 9, a communication partner host 11, and an IP network 13.

The mobile router 53 moves from link to link with the mobile network 57 including the fixed host 55, and functions as a gateway router of the mobile network 57. The mobile router 53 uses the home address on the home link and the home address and the care-of address having the link prefix of each link on the external link. The fixed host 55 is a node whose connection relationship with the mobile router 53 does not change. The mobile network 57 may also include routers and mobile hosts. The home agent 5 provides a home link to the mobile router 53, and the access router provides an external link to the mobile router 53.

The mobile router 53 is the home agent 5
To the home address of the own node and the network prefix existing in the mobile network 57, and the binding of the care-of address acquired by the connection link, and the home agent 5 holds this binding. When the home agent 5 receives a packet addressed to the home address of the mobile router 53 or an address belonging to a network prefix in the mobile network 57, the home agent 5 creates an IP packet addressed to the care-of address that has been bound, and stores the IP packet in the payload section. The packet is stored and transferred to the mobile router 53. The mobile router 53, which has received the transfer packet, takes out the original packet from the payload portion and, if it is addressed to the host existing in the mobile network 57, routes it to the mobile network 57.

FIG. 5 is a diagram showing the structure of the mobile router. IP including IP 71a and buffer space 71b
The link layer 73 includes a layer 71, a first link 73a, a second link 73b, a mobile network side interface 73c and a fixed network side interface 73d.

Mobile network side interface 73
The packet received from the interface c or the fixed network side interface 73d reaches the IP 71a via the first link 73a and the second link 73b, respectively. IP71
a refers to the routing table, determines whether the packet is to be sent to the fixed network side (default router) or the mobile network 57 side (fixed host 55), and depending on the determination result, sends the packet to the second link 73b or the second link 73b. Pass to 1 link 73a.

The buffer space 71b is for buffering packets during the handoff period. The IP 71a transfers the packet to the buffer space 71b.
Buffer to. During the packet buffering period, the second link 73b of the link layer 73 of the mobile router 53 and the fixed network side interface 73d are not connected to any external link in order to switch the connection point (second link 73b and fixed network side interface 73d) The access router 7, which provides a newly connected external link from the start of the momentary interruption time to the end of the momentary interruption time of the link layer (second link 73b and fixed network side interface 73d), This is the period until 9 is changed to the default router. Here, the IP 71a is a link layer (second link 73
b and fixed network side interface 73d) The start of the interruption time is fixed network side interface 7
It detects by the signal from 3d and detects the change of the default router by itself.

Fixed network side interface 73
When switching the connection point from access router 7 to access router 9, d issues a buffer command to IP 71a. As a result, the IP 71a detects the start of the momentary interruption time of the link layer (the second link 73b and the fixed network side interface 73d). The IP 71a that has received the buffer command uses the buffer space 71b and starts buffering of the packet that should originally be passed to the second link 73b.

When the IP 71a changes the default router by the router notification received from the access router 9, the IP 71a detects the change of the default router and cancels the buffering. Then, the IP 71a passes the packet buffered in the buffer space 71b to the second link 73b. As described above, the packet passed to the second link 73b is transmitted from the fixed network side interface 73d to the access router 9 (set as the default router) that provides the newly connected external link.

FIG. 6 is a sequence chart when the mobile router 53 communicating with the correspondent host 11 hands off from the access router 7 to the access router 9. A solid arrow indicates a control packet for executing handoff, and a dotted arrow indicates a data packet transmitted from the mobile router 53 to the correspondent host 11. State I to state IV in FIG. 6 correspond to state I to state IV described in FIG.

In the state I, the link layer 73 (the second link 73b and the fixed network side interface 73d) of the mobile router 53 is connected to the access router 7 and the default router is set to the access router 7. , Data packets (P1) and (P2)
Arrives at the access router 7 and is routed to the correspondent host 11. In the subsequent state II and state III, the data packets (P3) to (P8) are buffered without being transmitted.

When the mobile router 53 receives the router advertisement of the access router 9 and changes the default router from the access router 7 to the access router 9, the state transits to the state IV and the buffered data packets (P3) to
(P8) is transmitted. Link layer 73 of mobile router 53
Since the second link 73b and the fixed network side interface 73d are connected to the access router 9 and the default router is set to the access router 9, the data packets (P3) to (P8) are sent to the access router 9. When it arrives, it is routed to the correspondent host 11. Also, data packets (P9) and (P10)
Also reaches the access router 9 and is routed to the correspondent host 11.

When the mobile router 53 obtains the new care-of address used in the external link, the Binding
The packet including the Update option is transmitted to the home agent 5. Home Agent 5 is Bin
Bind when receiving a Ding Update packet
ing (correspondence between the home address and the care-of address of the mobile router 53) is stored, and a Binding is sent as a confirmation response.
The packet including the Acknowledgement option is transmitted to the mobile router 53.

In the second embodiment, for simplification, the mobile router 53 does not send the router solicitation. Of course, the mobile router 53 that sends the router solicitation
However, it is necessary not to buffer the router solicitation. When buffering at the IP layer 71, the IP layer 71 analyzes the packet below the IP header to determine whether or not the packet to be buffered is a router solicitation. It is necessary to exclude from buffering. The analysis below the IP header of the packet specifically indicates the following operation. The IP layer 71
When the protocol number stored in the next header field in each IP header including the extension header is checked and the protocol number indicates 58 (icmp), the field indicating the type of icmp following the IP header is checked. . If the type number is 133 (router solicitation), it is determined that the packet is a router solicitation.

In the second embodiment, during the packet buffering period, the second link 73b of the link layer 73 of the mobile router 53 and the fixed network side interface 73d are not connected to any external link in order to switch the connection point. Link layer (second link 73b and fixed network side interface 73) not connected to
d) From the start of the instantaneous interruption time, the link layer (second link 7)
3b and fixed network side interface 73d)
Although it is a period until the access routers 7 and 9 that provide newly connected external links are changed to default routers after the momentary interruption time ends, the present invention is not limited to this. For example, the period for buffering packets may be set longer than the above period in consideration of the state of the wireless link.

As described above, in the second embodiment, while the packet cannot be reached from the mobile router 53 to any of the access routers 7 and 9 during the handoff period, the mobile router 53 is handed off. Buffer the packets that should be sent during the period of
The buffered packet is transmitted after the packet reaches the access routers 7 and 9 at the handoff destination. As a result, all packets that the mobile router 53 attempts to route to the fixed network side during handoff are handed off to the access routers 7 and 9.
The communication partner host 11 is routed through the packet, and packet loss can be prevented during the handoff period.

In the second embodiment, during the period in which the mobile router 53 buffers packets, the second link 73b of the link layer 73 of the mobile router 53 and the fixed network side interface 73d are used for switching the connection points. From the start of the interruption time of the link layer (second link 73b and fixed network side interface 73d) that is not connected to any external link, the concerned link layer (second link 73b and fixed network side interface 73d) interruption time It is a period until the access routers 7 and 9 which provide the newly connected external links are changed to the default routers after the end of. As a result, the period for buffering packets is set extremely appropriately, and packet loss can be reliably prevented.

In the second embodiment, the IP 71a detects the start of the link layer (second link 73b and fixed network side interface 73d) instantaneous interruption time by a signal from the fixed network side interface 73d connecting to the external link. However, it detects the change of the default router. This makes it possible to appropriately and easily detect the period during which packets are buffered.

The mobile router 5 that sends the router solicitation
In 3, the mobile router 53 preferably does not buffer router solicitations. As a result, the router solicitation transmitted by the mobile router 53 reaches the access routers 7 and 9, and the mobile router 53 can receive the router notification promptly.

Finally, the communication control program according to the embodiment of the present invention will be described. The communication control program is
To send a packet, the computer functions as a means of buffering the packet during the handoff and sending the buffered packet when the handoff is complete. The communication control program is recorded in a computer-readable storage medium, for example. Here, the recording medium refers to a magnetic device, an optical device, or
By causing a changed state of energy such as electricity, the description content of the program can be transmitted to the reading device in the form of a signal corresponding thereto. Examples of such a recording medium include a magnetic disk, an optical disk, and a CD-RO.
M, a memory built in the computer, and the like.

The recording medium 81, as shown in FIG.
A program area 83 for recording a program is provided. In this program area, the communication control program 85
Is recorded. The communication control program is a main module 85a that controls the process, and a packet buffering control module that buffers packets during the handoff period of the mobile node and transmits the buffered packets when the handoff is completed. 85b and.

The computer functions as the mobile host 3 in the first embodiment or the mobile router 53 in the second embodiment by executing the communication control program described above. As a result, the packet that should be transmitted during the handoff period is buffered without being transmitted during the handoff period, and the buffered packet is transmitted when the handoff is completed. It is possible to prevent packet loss from occurring during the period.

[0080]

As described above in detail, according to the present invention, it is possible to provide a mobile node, a mobile communication system, and a communication control program capable of preventing packet loss during a handoff period. You can

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a mobile communication system according to a first embodiment.

FIG. 2 is a diagram showing a configuration of a mobile host.

FIG. 3 is a sequence chart when a mobile host communicating with a communication partner host hands off.

FIG. 4 is a diagram showing a configuration of a mobile communication system according to a second embodiment.

FIG. 5 is a diagram showing a configuration of a mobile router.

FIG. 6 is a sequence chart when a mobile router communicating with a correspondent host hands off.

FIG. 7 is a diagram showing a configuration of a storage medium.

FIG. 8 is a sequence chart showing a state transition at the time of handoff of a conventional mobile host.

FIG. 9 is a sequence chart showing a state transition at the time of handoff of a conventional mobile router.

[Explanation of symbols]

1, 51 ... Mobile communication system, 3 ... Mobile host, 5 ... Home agent, 7, 9 ... Access router, 11 ... Communication host, 13 ... IP network, 31 ... Application layer, 33 ... Transport layer, 33b, 71
b ... buffer space, 35 ... IP layer, 37 ... link layer, 37b ... interface, 53 ... mobile router, 5
5 ... Fixed host, 71 ... IP layer, 73 ... Link layer, 73
d ... Fixed network side interface, 81 ... Recording medium, 85 ... Communication control program, 85b ... Packet buffering control module, 101 ... Mobile host, 1
03, 105 ... Access router, 107 ... Communication host, 109 ... Fixed host, 111 ... Mobile router.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Ichiro Okajima             2-11-1, Nagatacho, Chiyoda-ku, Tokyo Stock             Ceremony company NTT Docomo (72) Inventor Narumi Umeda             2-11-1, Nagatacho, Chiyoda-ku, Tokyo Stock             Ceremony company NTT Docomo F term (reference) 5K030 HA08 HC01 HD03 HD06 JT09                       KA03                 5K067 AA23 BB21 CC08 DD51 EE02                       EE10 EE16 FF02 HH23 JJ35                       JJ39 KK15

Claims (12)

[Claims] 1. A mobile node for transmitting a packet, comprising means for buffering the packet during a handoff and transmitting the buffered packet when the handoff is completed. The mobile node to do. 2. The period during which the packet is buffered by the means, from the start of a link layer interruption time when the link layer of the mobile node is not connected to any external link for switching the connection point, The mobile node according to claim 1, wherein the mobile node is a period until the access router that provides the newly connected external link is changed to the default router after the end of the link layer interruption time. 3. The means detects the start of the link layer interruption time by a signal from an interface connecting to an external link, and detects the change of the default router by a signal from the IP layer of the mobile node. The mobile node according to claim 2, characterized in that 4. The means is a router advertisement.
mobile node according to any one of claims 1 to 3, characterized in that it does not buffer a router solicitation for requesting the access router to transmit a tisement). 5. A mobile communication system comprising a mobile node transmitting a packet and a plurality of access routers providing external links to the mobile node, wherein the mobile node transmits the packet during a handoff period. A mobile communication system comprising means for buffering and transmitting the buffered packet to an access router which provides a newly connected external link when the handoff is completed. 6. The period for buffering the packet by the means, from the start of a link layer interruption time when the link layer of the mobile node is not connected to any external link for switching the connection point, The mobile communication system according to claim 5, wherein it is a period until the access router that provides the newly connected external link is changed to a default router after the end of the link layer interruption time. 7. The means detects the start of the link layer interruption time by a signal from an interface connecting to an external link, and detects the change of the default router by a signal from the IP layer of the mobile node. The mobile communication system according to claim 6, wherein the mobile communication system is a mobile communication system. 8. The means is a router advertisement (router adver).
The mobile communication system according to any one of claims 5 to 7, wherein a router solicitation for requesting the access router to transmit the communication is not buffered. 9. To transmit a packet, the computer functions as a means for buffering the packet during a handoff and transmitting the buffered packet when the handoff is complete. Communication control program. 10. The period during which the packet is buffered by the means, from the start of a link layer interruption time when the link layer of the mobile node is not connected to any external link for switching the connection point, The communication control program according to claim 9, wherein the communication control program is a period until the access router that provides a newly connected external link is changed to a default router after the end of the link layer interruption time. 11. The means causes the start of the link layer instantaneous interruption time to be detected by a signal from an interface connecting to an external link, and the change of the default router to be detected by a signal from the IP layer of the mobile node. The communication control program according to claim 10. 12. A router advertisement (router a
The communication control program according to any one of claims 9 to 11, wherein a router solicitation for requesting the access router to transmit a dvertisement) is not buffered.