Abstract:
A method and system for delivering data packets from a network node to a mobile node, wherein a unidirectional interface to the mobile node is detected and a binding update indicating a care-of-address being an address of said detected unidirectional interface is transmitted to the network node. In response to this binding update request, data packets are delivered via the unidirectional interface. Thus, the performance of communication can be increased considerably by using a high bandwidth unidirectional broadcast network to deliver downlink data.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to a method and system for delivering data packets from a network node of a packet data network, such as an IP network, to a mobile node, e.g. a mobile terminal device.  
         BACKGROUND OF THE INVENTION  
         [0002]    Mobility support for Internet devices is quite important, since mobile computing is getting more widespread. It is expected that the number of mobile computers will increase dramatically. Furthermore, there are already first products of cellular phones offering IP (Internet Protocol) services based on WAP (Wireless Application Protocol) or GPRS (General Packet Radio Services), and their number will increase rapidly. Cellular devices of the 3 rd  generation will be packet switched devices instead of circuit switched devices. Therefore, IP services on 3 rd  generation cellular devices will be an integral part in the future.  
           [0003]    Today, several problems have to be faced making roaming with mobile Internet devices difficult. The problems start if somebody disconnects his mobile device from the Internet in order to connect it elsewhere. Normally, he would not be able to continue communication until he configures the system with a new IP address, the correct net mask and a new default router.  
           [0004]    This problem is based on the routing mechanisms which are used in the Internet. IP addresses define a kind of topological relation between the linked computers. Today&#39;s versions of Internet protocols assume implicitly that a node has always the same point of attachment to the Internet. Additionally, the node&#39;s IP address identifies the link on which the node resides. If a node moves without changing its IP address, there is no information in its network address about the new point of attachment to the Internet.  
           [0005]    To support mobile devices, which dynamically change their access points to the Internet, the Internet Engineering Task Force (IETF) currently standardizes a protocol supporting mobile Internet devices, called Mobile IP. There are two variations of Mobile IP, namely Mobile IPv4, based on IPv4 (Internet Protocol version 4), and Mobile IPv6, based on IPv6 (Internet Protocol version 6). The latter one is described in David W. Johnson and Charles Perkins, Mobility Support in IPv6, Internet Draft, 2000. Further information on the IPv6 can be obtained from IETF specification RFC 2460, 1998.  
           [0006]    Mobile IPv6 allows an IPv6 host to leave its home subnet while transparently maintaining all of its present connections and remaining reachable to the rest of the Internet. This is realized in Mobile IPv6 by identifying each node by its static home address, regardless of its current point of attachment to the Internet. While a mobile node is away from home it sends information about its current location to a home agent on its home link. The home agent intercepts packets addressed to the mobile node and tunnels them to the mobile node&#39;s present location. This mechanism is completely transparent for all layers above IP, e.g. for TCP (Transmit Control Protocol), UDP (User Datagram Protocol) and of course for all applications. Therefore, domain name server (DNS) entries for a mobile node refer to its home address and don&#39;t change if the mobile node changes its Internet access point. In fact, Mobile IPv6 influences the routing of packets but is independent of the routing protocol itself.  
           [0007]    The solution given by Mobile IPv6 consists of creating a so-called care-of-address whenever a node changes its point of attachment to the web. The care-of-address is an IP address associated with a mobile node while visiting a foreign link. The subnet prefix of this IP address is a foreign subnet prefix. Among the multiple care-of-addresses that a mobile node may have at a time (e.g. with different subnet prefixes), the one registered with the mobile nodes home agent is called its “primary” care-of-address. A care-of-address can be derived from the receipt of router advertisements in a so-called “stateless address auto-configuration” as described in S. Thomson and T. Narten, “IPv6 Stateless Address Auto-Configuration”, IETF specification RFC 2462, 1998, or can be assigned by a DHCP (Dynamic Host Configuration Protocol) server in a so-called “stateful address auto-configuration”. Mobile nodes are always identified by their (static) home address regardless of their current point of attachment to the Internet. While away from home each mobile node has an additional (temporary) address which identifies its current location. Thus, basically messages that arrive at the original home address are redirected or tunneled to the care-of-address.  
           [0008]    Mobile IPv6 requires the exchange of additional information. All new messages used in Mobile IPv6 are defined as IPv6 destination options. These options are used in IPv6 to carry additional information that needs to be examined only by a packet destination node. In particular, a binding update option is used by a mobile node to inform its home agent or any other correspondent node about its current care-of-address. A binding acknowledgement option is used to acknowledge the receipt of a binding update, if an acknowledgement was requested. Furthermore, a binding request option is used by any node to request a mobile node to send a binding update with the current care-of-address. Finally, a home address option is used in a packet sent by a mobile node to inform the receiver of this packet about the mobile node&#39;s home address. If a packet with the home address option is authenticated then the home address option must also be covered by this authentication.  
           [0009]    Due to the asymmetric nature of communications in the IP networks, the use of uni-directional links provides a way to improve network performance and capacity. Unidirectional links might be used to deliver downlink data, but the problem is that this option is not supported natively in IP networks.  
         SUMMARY OF THE INVENTION  
         [0010]    It is therefore an object of the present invention to provide a method and system for delivering data packets to a mobile node by using uni-directional links, by means of which the resource utilization and/or performance of communication can be increased.  
           [0011]    This object is achieved by a method of delivering data packets from a network node of a packet data network to a mobile node, said method comprising the steps of:  
           [0012]    detecting a unidirectional interface to said mobile node;  
           [0013]    transmitting to said network node a binding update indicating a care-of-address, said care-of-address being an address of said detected unidirectional interface;  
           [0014]    and  
           [0015]    delivering said data packets from said network node to said mobile node via said unidirectional interface in response to said binding update.  
           [0016]    Furthermore, the above object is achieved by a system for delivering data packets from a network node of a packet data network to a mobile node, wherein said mobile node is arranged to detect a unidirectional interface, and to transmit to said network node a binding update indicating a care-of-address, said care-of-address being an address of said detected unidirectional interface; and wherein said network node is arranged to deliver said data packets via said unidirectional interface in response to said binding update.  
           [0017]    Additionally, the above object is achieved by a mobile node for receiving data packets from a packet data network, wherein said mobile node is arranged to detect a unidirectional interface to said mobile node, and to transmit to said network node a binding update indicating a care-of-address, said care-of-address being an address of said detected unidirectional interface.  
           [0018]    Accordingly, unidirectional channels can be used to boost the performance of uni-cast communications, such as deliveries of downlink data in IP networks. Thereby, the performance of communications and the resource utilization can be increased considerably by using a high bandwidth unidirectional link to deliver the downlink data.  
           [0019]    Another care-of-address associated with said mobile node while visiting a foreign link may be registered, said other care-of-address being an address of a bi-directional interface to said mobile node. Preferably, the other care-of-address is configured as a primary care-of-address registered with the home agent of said mobile node. Thus, the multi-homing feature already supported in the Mobile IPv6 protocol can be used for implementing the present dual care-of-address scheme.  
           [0020]    The detecting step may be based on a router advertisement, that may contain predetermined information to inform about the unidirectionality of the link.  
           [0021]    A message indicating that the mobile node is unreachable may be sent if problems occur during the delivering step, wherein said binding by said care-of-address may be deleted in response to said message, and the data packets may be delivered via the home agent of the mobile node. Thereby, the bi-directional link via the other care-of-address can be used if there are any problems in the unidirectional channel.  
           [0022]    Furthermore, a new binding update request may be transmitted in order to change the other care-of-address. The mobile node may thus change the care-of-address used in the connection whenever it decides so by sending a new binding update request with the home address or a different care-of-address.  
           [0023]    An access list indicating allowed users of the unidirectional interface may be maintained at the packet data network, e.g. at a unidirectional access router. Then, an authenticated binding update procedure can be used to open a communication channel between the mobile node and the unidirectional access router providing the unidirectional interface. Thereby, the mobile node can authorize itself by sending a binding update to the unidirectional access router, which address may be resolved from router advertisements.  
           [0024]    Preferably, an information about network parameters of the unidirectional interface may be obtained from a lower protocol layer. The information may comprise an information about free bandwidth, costs and/or reliability of the connection via the unidirectional interface.  
           [0025]    Furthermore, an information about a binding deletion in the network node may be obtained from the data packets received by the mobile node.  
           [0026]    A predetermined information may be added to a router advertisement to inform the mobile node about the unidirectionality and/or specific parameters of the unidirectional interface. In this case, the specific parameter may comprise a congestion situation, wherein a congestion flag may be added to the router advertisement. This congestion flag may be set when the free bandwidth has dropped below a predetermined threshold. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0027]    In the following, the present invention will be described in greater detail on the basis of preferred embodiments with reference to the accompanying drawings in which:  
         [0028]    [0028]FIG. 1 shows a network architecture in which the present invention can be applied;  
         [0029]    [0029]FIG. 2 shows a signaling diagram indicating the delivery of downlink data according to the preferred embodiment of the present invention;  
         [0030]    [0030]FIG. 3 shows a mobile node configured as a multi-homed node with two network interfaces; and  
         [0031]    [0031]FIGS. 4A and 4B show data flows using a primary packet route between a mobile node and a correspondent node, and using a primary packet route with a secondary care-of-address, respectively. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0032]    The preferred embodiment will now be described on the basis of a Mobile IPv6 architecture as shown in FIG. 1.  
         [0033]    According to FIG. 1, the mobile IPv6 architecture includes three specific network elements, a mobile node  10  which can change its point of attachment from one link to another, while still being reachable via its home address, a home agent  30  which is a router on the mobile nodes home link with which the mobile node  10  has registered its current care-of-address, and a correspondent node  20  which is a network node with which the mobile node  10  is communicating. The correspondent node  20  may be either a mobile node or a stationary node. While the mobile node  10  is away from its home location, the home agent  30  intercepts packets on the home link destined to the mobile nodes home address, encapsulates them, and tunnels them to the mobile node&#39;s registered care-of-address. Among the multiple care-of-addresses which the mobile node  10  may have at a time (e.g., with different subnet prefixes), the one registered with the mobile nodes home agent  30  is called its “primary” care-of-address. The home link corresponds to the link on which the mobile nodes home subnet prefix is defined. Standard IP routing mechanisms will deliver packets destined for the mobile nodes home address to its home link. A foreign link is any link other than the mobile nodes home link. The home subnet prefix corresponds to the IP subnet prefix corresponding to the mobile nodes home address.  
         [0034]    The mobile node  10 , the home agent  30 , and the correspondent node  20  are connected to a packet data network, e.g. an IP network  40  such as the Internet. A movement of the mobile node  10  corresponds to any change in the mobile nodes point of attachment to the IP network  40  such that it is no longer connected to the same link as it was previously. If the mobile node  10  is not currently attached to its home link, the mobile node  10  is said to be “away from home”.  
         [0035]    When the mobile node  10  moves away from its home network, it sends a binding update (BU) to its home agent  30 . The BU is used to associate the identity (home address) of the mobile node  10  to its current location (care-of-address), i.e. to configure a care-of-address at the home agent  30 . After receiving of the BU, the home agent  30  sends a binding acknowledgement (BA) to the mobile node  10 . Then, a binding is created for the mobile node  10  in the home agent  30 . If the home agent  30  wants to communicate with the mobile node  10 , it sends an IP packet with the care-of-address as destination address and places the home address, i.e. the address to which the connection is initiated, to the routing header. After receiving the packet, the mobile node  10  moves the home address from the routing header to the IP packet destination address. If the correspondent node  20  sends an IP packet to the mobile node  10 , the home agent  30  intercepts the packet and then tunnels (IP tunnel) it to the mobile node  10 . After having received the tunneled packet, the mobile node  10  sends a BU to the correspondent node  20  and after that the IP packets are routed directly from the correspondent node  20  to the mobile node  10  as with the home agent  30  above.  
         [0036]    In the Mobile IPv6 protocol, a multi-homed node is considered as a host with several physical and/or logical interfaces to the IP network, of which it can use one or more for communication at a time. Used interfaces can be chosen e.g. according to the free bandwidth, reliability and/or cost. Multi-homing is implemented by supporting multiple care-of-addresses, wherein one of the care-of-addresses should be chosen as a primary care-of-address associated to the home address of the home agent  30 .  
         [0037]    Unidirectional channels, e.g. unidirectional broadcast channels, can be used to boost the performance of a unicast communication, such as the delivery of downlink data. According to the preferred embodiment, the mobile node  10  is arranged to detect an operational unidirectional interface so as to configure a new care-of-address for this unidirectional interface, e.g. by sending a BU to the home agent  30  and/or a correspondent node  20 . The new care-of-address can now be used for communication, but of course only in the downlink direction, i.e. the mobile node  10  can only receive packets with the new care-of-address of the unidirectional interface.  
         [0038]    In a case where the mobile node  10  has both uni- and bi-directional interfaces available, a signaling procedure as indicated in FIG. 2 can be used to provide an increased performance for downlink data delivery. According to FIG. 2, the mobile node  10  sends its home registration to the home agent  30  with its primary care-of-address CoA 1  which is the care-of-address of a bi-directional interface IF 1  shown in FIG. 3. According to FIG. 3, the mobile node  10  may also receive data from the IP network  40  via a unidirectional interface IF 2 .  
         [0039]    [0039]FIG. 4A shows the initial situation in which a mobile node  10  is registered to its home agent  30  with its primary care-of-address CoA 1 . Packets sent to the mobile node  10  by the correspondent node  20  are tunneled by the home agent  30  to the mobile node  10  via the bi-directional interface IF 1 , as indicated by the arrow in FIG. 4A.  
         [0040]    When the mobile node  10  detects the operational unidirectional interface IF 2 , it can configure a second care-of-address CoA 2  for this interface. The detection may be based on a router advertisement (RA) received from a unidirectional access router (UAR)  50  via the unidirectional interface IF 2  (cf. broken arrow in FIG. 2). It is assumed that the detection has led to the result that the received router advertisement indicates an operational unidirectional interface. Hence, the mobile node  10  can now receive data packets with a new care-of-address CoA 2  of the unidirectional interface IF 2 . In case of a subsequent downlink delivery of packet data, packets initially sent to the mobile node  10  by the correspondent node  20  are tunneled by the home agent  30  to the mobile node  10  via the bi-directional interface IF 1 , as indicated by the double-lined arrows in FIG. 2. When the mobile node  10  receives tunneled packets, it may send a BU with its primary care-of-address CoA 1  to the correspondent node  20  and after that the packets are routed directly from the correspondent node  20  to the mobile node  10  via the bi-directional interface IF 1 . However, when the mobile node  10  configures the new care-of-address CoA 2  by sending a BU with its secondary care-of-address CoA 2  of the unidirectional interface to the correspondent node  20 , packets coming from the correspondent node  20  are routed directly to the mobile node  10  via the unidirectional interface IF 2 , as indicated by the dot-dashed arrows in FIG. 2, while the packets going from the mobile node  10  to the correspondent node  20  are routed through the bi-directional interface IF 1 .  
         [0041]    [0041]FIG. 4B shows the above situation, where the mobile node  10  is configured as a multi-homed node which sends uplink data via the bi-directional interface IF 1  and which receives downlink data via the unidirectional interface IF 2  based on its secondary care-of-address CoA 2 . Thus, an improved performance of the downlink data delivery can be achieved.  
         [0042]    If problems occur in the unidirectional channel, the IP network  40  may send a destination unreachable message to the correspondent node  20 , and the correspondent binding of the mobile node  10  will be deleted. Then, the correspondent node  20  sends packets via the home agent  30  using the primary care-of-address CoA 1 . In this case, the mobile node  10  again receives packets tunneled through the bi-directional channel and may send a new BU with one of its care-of-addresses to the correspondent node  20 . The mobile node  10  may also change the care-of-address used in the connection whenever it decides so by sending a new BU with a different care-of-address.  
         [0043]    Moreover, the mobile node  10  may itself detect failures, e.g. a drop of the unidirectional link, and may act in a suitable manner, e.g. as explained above.  
         [0044]    As regards the above preferred embodiment, it is to be noted that the detection of the unidirectional interface IF 2  and the configuration of the corresponding secondary care-of-address CoA 2  may as well be performed when the mobile node  10  is located at its home link. In this case, the care-of-address CoA 2  relating to the unidirectional interface IF 2  is configured at the correspondent node  20  without using the primary care-of-address CoA 1 . Thus, in this case, the initial binding update signaling in FIG. 2 is not required and the downlink data is not transmitted via the home agent  30 .  
         [0045]    The usage of the unidirectional interface IF  2  can be restricted by the UAR  50 . To achieve this, the UAR  50  can maintain an access list at the edge of the unidirectional network. Since the UAR  50  is already known by its router advertisements, the mobile node  10  can authorize itself by sending a BU to the UAR  50 . If the mobile node  10  receives an accepted binding acknowledgement (BA) from the UAR  50  via the unidirectional interface IF 2 , the unidirectional link can be considered to be functional and authorized to use. This authenticated BU may also be used to open a communication channel from the UAR  50  to the mobile node  10 , i.e. to handle the AAA (Authorization, Authentication and Accounting) issues of the unidirectional network easier.  
         [0046]    The home registration by the mobile node  10  always has to be performed with the primary care-of-address CoA 1  of the bi-directional interface or network. The reason for this is to ensure reachability of the mobile node  10  and the fact that normally there is not much traffic between the home agent  30  and the mobile node  10 . Only the first packets are tunneled by the home agent  30  in every connection with the correspondent node  20 , and all other traffic between the home agent  30  and the mobile node  10  is considered to be quite insignificant.  
         [0047]    The selection algorithm for the care-of-address may be implementation-specific. For example, it may derive information about the free bandwidth, the cost and/or the reliability of the connection from lower protocol layers. At IP level, the algorithm may use the information about the binding deletion in the correspondent node  20  before the lifetime has elapsed, which can be concluded from the received tunneled packets before the entry&#39;s lifetime in the binding update list has not elapsed. The IP network  40  may use a congestion information, e.g. a specific congestion flag C as a new flag in the advertisement, to inform mobile nodes about a congestion in the unidirectional network. This congestion flag C may be set e.g. when the free bandwidth is below a predefined threshold value, e.g. 64 kb. Additionally, information about the functionality of the IP network  40  and any other applicable information may be used in the router advertisements.  
         [0048]    It is noted, that the present invention is not restricted to the specific preferred embodiment described above, but can be used in any packet data network having bi-directional and unidirectional interfaces or networks. The preferred embodiment may thus vary within the scope of the attached claims.