Multiplex communications – Communication over free space – Having a plurality of contiguous regions served by...
Reexamination Certificate
1999-06-16
2003-02-04
Ngo, Ricky (Department: 2664)
Multiplex communications
Communication over free space
Having a plurality of contiguous regions served by...
C370S330000, C370S352000, C370S401000, C370S475000, C455S433000, C455S436000
Reexamination Certificate
active
06515974
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a communication scheme for supporting data transfer to a visited site of a mobile terminal which moves across a private network operated by a private address system and an Internet operated by a global address system.
2. Description of the Background Art
A router device is used in connecting between LANs, and plays a role of transferring data packets (datagrams) from one LAN to the other LAN. Each data packet contains a description of its source and final destination network layer addresses (such as IP addresses in the case of IP, for example) in addition to communication data to be transferred, and the router device determines an output interface (port number) and a next transfer target node (a host that is either a router device or a communication terminal) of each data packet according to its address information.
Here, a routing by the router device will be described for an exemplary case of transmitting IP packets from a terminal A to a terminal B on a network.
An IP packet sent out from the terminal A is routed within the Internet according to an IP address written in its packet header, and transmitted up to a subnet to which the terminal B belongs. At that point, whenever a router device within the Internet is passed through, an IP forwarding processing in a sequence of: reception of a datalink layer packet→conversion into an IP packet→processing of an IP header information, etc. and an output target determination→conversion into a datalink layer packet→transmission of a datalink layer packet, is carried out with respect to an IP packet transmitted from the terminal A. Once it reaches to a router device of the final subnet, a logical address to physical address conversion is carried out by ARP (Address Resolution Protocol) (by obtaining a MAC address from an IP address, for example), and an IP packet is converted into a datalink layer packet by attaching a datalink layer header information such as MAC address, and this datalink layer packet is transmitted to the terminal B.
On the other hand, a technique for accommodating mobile terminals into the Internet-like network has been studied and developed. As one such mobile access technique, a scheme utilizing Mobile IP is known.
Mobile IP deals with the case where a user carrying a mobile terminal communicates while moving over the IP network across a plurality of subnets. In the case of communicating while moving over the IP network where the network address of the mobile terminal changes as the location of the terminal changes, there is a need to provide a scheme for managing a location of the terminal and transferring communication contents properly, and Mobile IP is a scheme that is proposed in order to fulfill that need. Mobile IP is a technique which makes the mobile terminal to appear to the other terminals as if it is connected at a location where it is normally expected to be located (a home address of a home network), regardless of a location at which the mobile terminal is connected on the network. Mobile IP has been promoted to RFC level by IETF in October, 1996.
In the following, the basic operation of Mobile IP will be described with reference to
FIG. 1
, which shows an exemplary network configuration in which a first network
100
-
1
and a second network
100
-
2
are connected through Internet
100
-
3
. Here, each of these networks is assumed to be operated using global addresses.
In Mobile IP, a network (home network)
100
-
1
to which a mobile terminal (mobile host: MH)
103
is normally connected has a router called home agent (HA)
105
located therein. The mobile terminal
103
is assigned with a home address at the home network, which is managed by the home agent
105
. Here, for the sake of explanation, it is assumed that the home address of the mobile terminal
103
is “10.2” and the address of its home agent
105
is “10.1”.
Next, suppose that the mobile terminal
103
moves and makes a connection at a visited site network
100
-
2
. The visited site network
100
-
2
has a router called foreign agent (FA)
106
located therein. After moving, the mobile terminal
103
receives packets destined to the own node via this foreign agent
106
. Here, for the sake of explanation, it is assumed that the IP address of the foreign agent
106
is “20.1”. In this case, the address “20.1” of the foreign agent
106
will be used as the current location address (called care-of address) of the mobile terminal
103
.
In order to notify the current location of the own node, the mobile terminal
103
notifies the IP address “20.1” of the current location from the visited site to the home agent
105
. Upon receiving this notification, the home agent
105
manages a correspondence between the home address “10.2” and the current location address “20.1” of the mobile terminal
103
.
Now, Mobile IP assumes that there exists a correspondent host who does not know that the mobile terminal
103
has moved. This correspondent host (CH)
109
that tries to communicate with the mobile terminal
103
does not know that the mobile terminal
103
has moved so that it transmits packets destined to the home address “10.2”. However, the mobile terminal
103
is currently absent from the home network. Hence, the home agent
105
which manages this mobile terminal
103
intercepts (receives as a proxy) a packet destined to the home address “10.2”, and transfers it by encapsulating it into an IP packet destined to the current location address “20.1” that is registered in advance. The foreign agent
106
that is located at the address “20.1” takes out this packet from the encapsulated packet that is transferred thereto, and delivers it to the visiting mobile terminal
103
at the datalink layer. By such a mechanism, the mobile terminal
103
can receive a packet that would have been received by the own node at its original home network
100
-
1
, even at its visited site.
In the opposite case where the mobile terminal
103
returns a packet to the correspondent host
109
from its current location, an IP packet is sent to the correspondent host
109
directly without going through the home agent
105
. At that point, the home address “10.2” is used as a source address to be attached to that packet, rather than the current location (care-of) address “20.1”. In this way, it appears as if the mobile terminal
103
is continually connected to its home network, from the correspondent host
109
, so that the influence of the moving can be eliminated entirely.
As described above, in Mobile IP, each node (correspondent host) on the network can access the mobile terminal
103
regardless of a location on the network at which the mobile terminal
103
is connected, by using the home address of the home network
103
.
Now, in the Mobile IP scheme, a protocol is designed by assuming only a case where the mobile terminal moves within a single address space. That is, it has been assumed that the current location registration message (which is also referred to as the mobility registration message) from the visited site can reach the home agent of the home network without failure.
However, nowadays, in the case where a large organization makes Internet connections, it is rather rare to have global IP addresses allocated to all the nodes within the organization because of the shortage of IP addresses, and usually private addresses (see RFC 1597) are used for operation within the organization and the address conversion to global addresses are carried out at a time of communications with the external.
Thus, in such a case, Mobile IP can be utilized only within a range where the mobile terminal moves within a single address space. In other words, there has been a problem that Mobile IP cannot support those services in which the mobile terminal is allowed to move across networks operated by mutually different address systems.
FIG. 2
shows an exemplary case where Mobile IP cannot be utilized, which is a network model in which a communication service
Inoue Atsushi
Kumaki Yoshinari
Foley & Lardner
Kabushiki Kaisha Toshiba
Ngo Ricky
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