Abstract:
Provided is a packet transfer method for ensuring continuity of packet delivery. The method includes: identifying whether a packet transfer apparatus is connected to a mobile host when requested by a location management apparatus to transfer a packet to the mobile host; reporting to the location management apparatus that the packet transfer apparatus is disconnected from the mobile host when it is identified that the packet transfer apparatus is disconnected from the mobile host; and storing the packet which has been requested for transfer to the mobile host. The packet transfer method can achieve lossless packet transmission by preventing a loss of important packets without the addition of a new common layer, despite intermittent disconnections in a mobile Internet environment.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
       [0001]    This application claims the benefit under 35 U.S.C. §119(a) of Korean Patent Application Nos. 10-2009-0125127, filed on Dec. 15, 2009, and 10-2010-0064521, filed on Jul. 5, 2010, the entire disclosures of which are incorporated herein by references for all purposes. 
       BACKGROUND 
       [0002]    1. Field 
         [0003]    The following description relates to a packet delivery method, and particularly, to a packet transfer method for ensuring continuity of ensuring packet delivery. 
         [0004]    2. Description of the Related Art 
         [0005]    With the development of wireless and mobile communication technologies, a wireless and mobile host method is expected to predominate in the future Internet environment by replacing a fixed host method. 
         [0006]    In a wireless environment, however, a host may be disconnected from the Internet for a relatively long time, for example, because the host enters a power-saving mode or due to network connection problems. 
         [0007]    The conventional Internet was designed assuming stable connectivity. Thus, when a host is disconnected from the Internet, it is fundamentally impossible to transmit a packet to the host. Therefore, there is a risk that data containing important information will not be delivered to the host. 
         [0008]    To solve this problem, technologies such as delay-tolerant networking (DTN) have been suggested. DTN is an approach that delivers messages in a store-and-forward manner in order to reduce a loss of transmission data in a situation where continuous end-to-end connectivity is not guaranteed. In the case of DTN, however, a host and each node of a network must have a bundle layer, which is a new common layer, between a transmission layer and an application layer. 
       SUMMARY 
       [0009]    The following description relates to a packet transfer method which can prevent packet loss without the addition of a new common layer, despite intermittent disconnections in Internet and future Internet environments. 
         [0010]    In one general aspect, there is provided a packet transfer method for ensuring continuity of packet delivery. The method includes: identifying whether a packet transfer apparatus is connected to a mobile host when requested by a location management apparatus to transfer a packet to the mobile host; reporting to the location management apparatus that the packet transfer apparatus is disconnected from the mobile host when it is identified that the packet transfer apparatus is disconnected from the mobile host; and storing the packet which has been requested for transfer to the mobile host. 
         [0011]    In another aspect, there is provided a packet transfer apparatus for ensuring continuity of packet delivery. The apparatus includes: a state identification unit identifying whether a packet transfer apparatus is connected to a mobile host when requested by a location management apparatus to transfer a packet to the mobile host; a state reporting unit reporting to the location management apparatus that the packet transfer apparatus is disconnected from the mobile host when it is identified that the packet transfer apparatus is disconnected from the mobile host; a packet storage unit storing packets which are to be transferred to mobile hosts; and a packet management unit storing the packet, which has been requested for transfer to the mobile host, in the packet storage unit. 
         [0012]    In another aspect, there is provided a method of managing the position of a mobile host to ensure continuity of packet delivery. The method includes: matching information about a mobile host with information about a packet transfer apparatus which is disconnected from the mobile host and storing the matched information when receiving from the packet transfer apparatus a message informing that the packet transfer apparatus is disconnected from the mobile host to which a packet must be transferred; and providing information about the packet transfer apparatus which is disconnected from the mobile host when reported by another packet transfer apparatus that the mobile host is connected to the another packet transfer apparatus. 
         [0013]    In another aspect, there is provided an apparatus for managing the position of a mobile host to ensure continuity of packet delivery. The apparatus includes: a position information storage unit configured to store information about the position of a mobile host and information about a packet transfer apparatus to which the mobile host belongs; a position information management unit configured to manage information stored in the position information storage unit and, when receiving from a packet transfer apparatus a message informing that the packet transfer apparatus is disconnected from a mobile host to which a packet must transferred, store information about the disconnection of the packet transfer apparatus from the mobile host in the position information storage unit; and a position information provision unit configured to extract the information about the packet transfer apparatus which is disconnected from the mobile host and provide the extracted information to another packet transfer apparatus when reported by the another packet transfer apparatus that the mobile host is connected to the another packet transfer apparatus. 
         [0014]    Other features and aspects will be apparent from the following detailed description, the drawings, and the claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  is a diagram illustrating the configuration of an exemplary Internet system; 
           [0016]      FIG. 2  is a diagram illustrating the configuration of an exemplary packet transfer apparatus; 
           [0017]      FIG. 3  is a diagram illustrating the configuration of an exemplary location management apparatus; 
           [0018]      FIG. 4  is a flowchart illustrating an exemplary packet transfer method for ensuring continuity of packet delivery; 
           [0019]      FIG. 5  is a flowchart illustrating an exemplary method of managing the position of a mobile host to ensure continuity of packet delivery; 
           [0020]      FIG. 6  is a diagram illustrating the configuration of an exemplary packet transfer system for ensuring continuity of packet delivery; 
           [0021]      FIG. 7  is a flowchart illustrating an exemplary packet transfer method used in a mobile Internet system to ensure continuity of packet delivery; 
           [0022]      FIG. 8  is a diagram illustrating the configuration of another exemplary packet transfer system for ensuring continuity of packet delivery; and 
           [0023]      FIG. 9  is a flowchart illustrating another exemplary packet transfer method used in a future Internet to ensure continuity of packet delivery. 
       
    
    
       [0024]    Throughout the drawings and the detailed description, unless otherwise described, the same drawing reference numerals will be understood to refer to the same elements, features, and structures. The relative size and depiction of these elements may be exaggerated for clarity, illustration, and convenience. 
       DETAILED DESCRIPTION 
       [0025]    The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings. These exemplary embodiments of the present invention will hereinafter be described more fully to convey the concept of the invention to those of ordinary skill in the art. 
         [0026]      FIG. 1  is a diagram illustrating the configuration of an exemplary Internet system. Referring to  FIG. 1 , the exemplary Internet system includes a location management apparatus  30  and first through fourth packet transfer apparatuses  40 - 1  through  40 - 4 , all of which are connected to each other through the Internet. 
         [0027]    The packet transfer apparatuses  40 - 1  through  40 - 4  may be edge routers. 
         [0028]    For example, a mobile host  10  may move from the first packet apparatus  40 - 1  to the fourth packet transfer apparatus  40 - 4  via the second and third packet transfer apparatuses  40 - 2  and  40 - 3 . In this case, it is assumed that the mobile host  10  cannot connect to the second and third packet transfer apparatuses  40 - 2  and  40 - 3  when passing through service areas of the second and third packet transfer apparatuses  40 - 2  and  40 - 3 . That is, the mobile host  10  may be disconnected from the second and third packet transfer apparatuses  40 - 2  and  40 - 3 , for example, due to an unstable communication environment or because the mobile host  10  enters a sleep mode to save power. Thus, when the mobile host  10  is located in the service area of the second or third packet transfer apparatus  40 - 2  or  40 - 3 , a transmitted packet may not be delivered to the mobile host  10 . That is, there is a risk that a packet containing important information will be lost without being delivered to the mobile host  10 . 
         [0029]    In the current exemplary embodiment, to deal with intermittent disconnections, the location management apparatus  30  must perform additional signaling and a database update. In the case of mobile IP, position information is managed in a soft state. 
         [0030]      FIG. 2  is a diagram illustrating the configuration of an exemplary packet transfer apparatus. Referring to  FIG. 2 , the exemplary packet transfer apparatus may be implemented as one of an access node, a foreign agent, and a router. As shown in  FIG. 2 , the exemplary packet transfer apparatus includes a packet storage unit  200 , a state identification unit  210 , a state reporting unit  220 , a packet management unit  230 , a package transfer unit  240 , a host management unit  250 , a packet request unit  260 , and a communication unit  270 . 
         [0031]    The packet storage unit  200  is implemented as a conventional memory device. For example, the packet storage unit  200  may be implemented as a buffer. In the current exemplary embodiment, the packet storage unit  200  stores a packet that is to be transferred to a mobile host which is disconnected from the exemplary packet transfer apparatus. The packet storage unit  200  temporarily stores the packet until the disconnected mobile host gets connected to another packet transfer apparatus in a stable manner. 
         [0032]    The state identification unit  210  identifies whether the exemplary packet transfer apparatus is connected to a mobile host when requested by a home agent or a host to transfer a packet to the mobile host. When the state identification unit  210  determines that the exemplary packet transfer apparatus is disconnected from the mobile host to which the packet must be transferred, the state reporting unit  220  reports this information to the location management apparatus. 
         [0033]    The packet management unit  230  stores the packet, which has been requested for transfer to the disconnected mobile host, in the packet storage unit  200 . When requested by another packet transfer apparatus to forward the stored packet, the packet management unit  230  extracts the packet from the packet storage unit  200 . 
         [0034]    The packet transfer unit  240  forwards the packet, which is extracted by the packet management unit  230  in response to the packet forward request, to the packet transfer apparatus which made the packet forward request. In addition, the packet transfer unit  240  receives a packet, which is destined for a mobile host currently connected to the exemplary packet transfer apparatus, from another packet transfer apparatus and transfers the received packet to the mobile host. 
         [0035]    When a new mobile host enters the service area of the exemplary packet transfer apparatus, the host management unit  250  reports the position information of the new mobile host to the location management apparatus. 
         [0036]    The packet request unit  260  receives from the location management apparatus a message informing about the existence of a packet that must be delivered to a mobile host and information about a packet transfer apparatus which stores the packet. Accordingly, the packet request unit  260  requests the packet transfer apparatus, which stores the packet, to forward the stored packet. 
         [0037]    The communication unit  270  includes a terminal communication unit  272  and a network communication unit  274 . In the current exemplary embodiment, the terminal communication unit  272  communicates with terminals located in a service area of the exemplary packet transfer apparatus, and the network communication unit  274  communicates with network apparatuses such as a location management apparatus and other packet transfer apparatuses. 
         [0038]      FIG. 3  is a diagram illustrating the configuration of an exemplary location management apparatus. Referring to  FIG. 3 , the location management apparatus may be implemented as a home agent. In the current exemplary embodiment, the location management apparatus includes a position information storage unit  300 , a position information management unit  310 , a position information provision unit  320 , and a communication unit  330 . 
         [0039]    The position information storage unit  300  stores the position information of a mobile host and information about a packet transfer apparatus to which the mobile host belongs. 
         [0040]    The communication unit  330  communicates with other packet transfer apparatuses through a network. 
         [0041]    The position information management unit  310  manages information stored in the position information storage unit  300 . In the current exemplary embodiment, when receiving from a packet transfer apparatus a message informing that the packet transfer apparatus is disconnected from a mobile host to which a packet must be transferred, the position information management unit  310  stores information about the disconnection of the packet transfer apparatus from the mobile host in the position information storage unit  300 . 
         [0042]    When reported by another packet transfer apparatus that the mobile host to which the packet must be transferred is connected to the another packet transfer apparatus, the position information provision unit  320  extracts information about the packet transfer apparatus which is disconnected from the mobile host and provides the extracted information to the another packet transfer apparatus which is connected to the mobile host. 
         [0043]    When reported by a packet transfer apparatus that the mobile host is connected to the packet transfer apparatus, the position information management unit  310  creates a database of the position information of the mobile host and stores the database in the position information storage unit  300 . In addition, when requested by the host to provide the position information of a mobile host, the position information management unit  310  provides the position information of the mobile host. 
         [0044]      FIG. 4  is a flowchart illustrating an exemplary packet transfer method for ensuring continuity of packet delivery. The exemplary packet transfer method is performed by a packet transfer apparatus such as a foreign agent or an access router. 
         [0045]    Referring to  FIGS. 2 and 4 , when requested by a host to transfer a packet ( 400 ), the state identification unit  210  identifies whether the packet transfer apparatus is connected to a mobile host to which the packet must be transferred ( 410 ). When it is identified that the packet transfer apparatus is connected to the mobile host ( 420 ), the packet transfer unit  240  transfers the packet to the mobile host ( 430 ). On the other hand, when it is identified that the packet transfer apparatus is not connected to the mobile host, the state reporting unit  220  reports this information to a location management apparatus ( 440 ). Then, the packet management unit  230  stores the packet, which has been requested for transfer to the mobile host, in the packet storage unit  200  ( 442 ). When requested by another packet transfer apparatus to forward the packet ( 444 ), the packet transfer unit  230  forwards the packet stored in the packet storage unit  200  to the another packet transfer apparatus which made the packet forward request ( 448 ). 
         [0046]    When receiving a connection request from a new mobile host ( 450 ), the host management unit  250  reports the access of the new mobile host to the location management apparatus ( 452 ). When receiving a message informing about the existence of a packet undelivered to the new mobile host and information about a packet transfer apparatus which stores the undelivered packet ( 454 ), the packet request unit  260  requests the packet transfer apparatus which stores the undelivered packet to forward the undelivered packet. Then, the packet transfer unit  240  receives the undelivered packet from the packet transfer apparatus which stores the undelivered packet and sends the received packet to the new mobile host ( 456 ). 
         [0047]      FIG. 5  is a flowchart illustrating an exemplary method of managing the position of a mobile host to ensure continuity of ensure packet delivery. The exemplary method of managing the position of a mobile host may be performed by a home agent or a location management server. 
         [0048]    Referring to  FIGS. 3 and 5 , when requested by a host to provide the position information of a mobile host ( 500 ), the position information management unit  310  provides the position information of the mobile host ( 510 ). Before that, when a packet transfer apparatus detects the connection of a new mobile host thereto, the packet transfer apparatus reports registration of the new mobile host to a location management apparatus. Accordingly, the location management apparatus stores and manages information about the packet transfer apparatus to which the new mobile host is connected. 
         [0049]    When receiving from the packet transfer apparatus a message informing that the packet transfer apparatus cannot connect to a mobile host to which a packet must be transferred ( 520 ), the location management unit  310  stores information about the mobile host to which the packet must be transferred and information about the packet transfer apparatus which sent the message informing that the packet transfer apparatus cannot connect to the mobile host ( 530 ). 
         [0050]    Later, when receiving from another packet transfer apparatus a message reporting that the mobile host is connected to the another packet transfer apparatus ( 540 ), the position information provision unit  320  identifies whether there is a packet undelivered to the mobile host ( 550 ). When there is a packet undelivered to the mobile host, the position information provision unit  320  sends information about the packet transfer apparatus, which stores the packet, to the another packet transfer apparatus to which the mobile host is connected ( 560 ). 
         [0051]      FIG. 6  is a diagram illustrating the configuration of an exemplary packet transfer system for ensuring continuity of packet delivery. 
         [0052]    Referring to  FIG. 6 , the exemplary packet transfer system may be implemented as a mobile Internet system based on mobile IPv4. Here, a location management apparatus may be implemented as a home agent  32 , and each packet transfer apparatus may be implemented as a foreign agent  42 - 1 ,  42 - 2 ,  42 - 3 , or  42 - 4 . Each element of the packet transfer system operates in the same way as that described above with reference to  FIG. 1 , and thus a redundant description thereof is omitted. 
         [0053]      FIG. 7  is a flowchart illustrating an exemplary packet transfer method used in a mobile Internet system to ensure continuity of packet delivery. 
         [0054]    Referring to  FIG. 7 , a host  20  sends a packet to a home agent  32  of a home network to which a mobile host  10  belongs. Here, when the host  20  sends the packet to the home network of the mobile host  10 , the home agent  32  intercepts the packet destined for the mobile host  10  ( 700 ). Then, the intercepted packet is transferred to a first foreign agent  42 - 1  with which the position of the mobile host  10  has been registered ( 710 ). 
         [0055]    The first foreign agent  42 - 1  identifies that the mobile host  10  is not located in its service area and buffers the packet destined for the mobile host  10  ( 720 ). Then, the first foreign agent  42 - 1  sends to the home agent  32  a message informing that the mobile host  10  is not located in its service area ( 730 ). 
         [0056]    Based on the message received from the first foreign agent  42 - 1 , the home agent  32  records information indicating that the mobile host  10  is disconnected from the first foreign agent  42 - 1  in a position database of the mobile host  10  ( 740 ). 
         [0057]    The mobile host  10  may get reconnected to the Internet when arriving at a fourth foreign agent  42 - 4  via second and third foreign agents. Accordingly, the mobile host  10  sends a registration request message to the fourth foreign agent  42 - 4  in order to register its position with the home agent  32  ( 750 ). 
         [0058]    Then, the fourth foreign agent  42 - 4  sends the registration request message of the mobile host  10  to the home agent  32  ( 760 ). After registering the position of the mobile host  10 , the home agent  32  sends to the fourth foreign agent  42 - 4  a message informing that there is a packet to be transferred to the mobile host  10  and that the packet is buffered in the first foreign agent  42 - 1  ( 770 ). 
         [0059]    Based on the message received from the home agent  32 , the fourth foreign agent  42 - 4  requests the first foreign agent  42 - 1  to forward the packet ( 780 ). The first foreign agent  42 - 1  forwards the buffered packet to the mobile host  10  via the fourth foreign agent  42 - 4  ( 790 ). 
         [0060]      FIG. 8  is a diagram illustrating the configuration of another exemplary packet transfer system for ensuring continuity of packet delivery. 
         [0061]    Referring to  FIG. 8 , the exemplary packet transfer system may also be implemented as a further Internet system. Here, a location management apparatus may be implemented as a location management server  35 , and each packet transfer apparatus may be implemented as an access router  45 - 1 ,  45 - 2 ,  45 - 3 , or  45 - 4 . 
         [0062]    The location management server  35  manages the position information of a mobile host  10  on the Internet so as to transfer a packet to the mobile host  10 . 
         [0063]    To send a packet to the mobile host  10 , a host  20  asks the location management server  35  about the position of the mobile host  10 . When identifying the position of the mobile host  10 , the host  20  sends the packet to the mobile host  10  based on the identified position of the mobile host  10 . 
         [0064]    For example, the mobile host  10  connected to the first access router  45 - 1  may move from the first access router  45 - 1  to the fourth access router  45 - 4  via the second and third access routers  45 - 2  and  45 - 3 . In this case, it is assumed that the mobile host  10  cannot connect to the second and third access routers  45 - 2  and  45 - 3 . That is, the mobile host  10  may be disconnected from the second and third access routers  45 - 2  and  45 - 3 , for example, due to an unstable communication environment or because the mobile host  10  enters a sleep mode to save power. Thus, when the mobile host  10  is located in a service area of the second or third access router  45 - 2  or  45 - 3 , if the host  20  transmits a packet to the mobile host  10 , the mobile host  10  cannot receive the packet. 
         [0065]    In order to solve this problem, the location management server  35  and the first through fourth access routers  45 - 1  through  45 - 4  should perform buffering and additional signaling to ensure that the mobile host  10  can receive packets after being reconnected to the Internet, despite unstable network connectivity. Specifically, when the mobile host  10  is not connected to an access router, that is, when the mobile host  10  is located in the service area of the second or third access router  45 - 2  and  45 - 3 , a packet requested for transfer to the mobile host  10  is buffered in the first access router  45 - 1  which was previously connected to the mobile host  10 . 
         [0066]    Then, when the mobile host  10  is connected to the fourth access router  45 - 4  in a stable manner, the packet buffered in the first access router  45 - 1  can be delivered to the mobile host  10  without a loss. 
         [0067]      FIG. 9  is a flowchart illustrating another exemplary packet transfer method used in a future Internet to ensure continuity of packet delivery. 
         [0068]    Referring to  FIG. 9 , a host  20  asks a location management server  35  about the position of a mobile host  10  to send a packet to the mobile host  10  ( 900 ). Accordingly, the location management server  35  provides a finally registered position of the mobile host  10 , e.g., information about a first access router  45 - 1  to the host  20  ( 910 ). Then, the host  20  sends the packet to the first access router  45 - 1  ( 920 ). The first access router  45 - 1  identifies that the mobile host  10  is not connected thereto and buffers the packet ( 930 ). Then, the first access router  45 - 1  sends to the location management server  35  a message informing that the mobile host  10  is not connected to the first access router  45 - 1  ( 940 ). 
         [0069]    The location management server  35  records information indicating that the mobile host  10  is disconnected from the first access router  45 - 1  in a position database of the mobile host  10  ( 950 ). 
         [0070]    The mobile host  10  may get connected to the fourth access router  45 - 4  in a stable manner when arriving at the fourth access router  45 - 4  via service areas of second and third access routers without being connected to the second and third access routers. When the mobile host  10  is connected to the fourth access router  45 - 4 , the fourth access router  45 - 4  provides the position information of the mobile host  10  to the location management server  35  ( 960  and  970 ). 
         [0071]    The location management server  35  notifies the fourth foreign agent  42 - 4  of the fact that there is a packet to be transferred to the mobile host  10  and that the packet is buffered in the first access router  45 - 1  ( 980 ). 
         [0072]    Accordingly, the fourth access router  45 - 4  requests the first access router  45 - 1  to forward the packet ( 990 ). 
         [0073]    In response to the packet forward request from the access router  45 - 4 , the first access router  45 - 1  identifies the packet buffered for transfer to the mobile host  10  and forwards the buffered packet to the fourth access router  45 - 4  ( 995 ). 
         [0074]    A packet delivery method and a location management method described above can be written as a computer program. The program can be stored in a computer-readable storage medium and can be read and executed by a computer. Examples of the computer-readable storage medium include magnetic recording media and optical recording media. 
         [0075]    While this invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. The exemplary embodiments should be considered in descriptive sense only and not for purposes of limitation. Therefore, the scope of the invention is defined not by the detailed description of the invention but by the appended claims, and all differences within the scope will be construed as being included in the present invention.