Multiplex communications – Communication over free space – Combining or distributing information via time channels
Reexamination Certificate
1998-12-30
2002-09-17
Kizou, Hassan (Department: 2662)
Multiplex communications
Communication over free space
Combining or distributing information via time channels
C370S328000, C370S389000, C370S392000, C370S400000, C370S466000, C370S469000, C370S474000, C370S902000, C370S901000
Reexamination Certificate
active
06452920
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to data communications between a host and a mobile node, and in particular to data communications between the host and the mobile node that cross internetworks.
BACKGROUND OF THE INVENTION
The Internet Protocol (IP), the protocol that connects the networks of today's Internet, routes information or data packets to their destinations according to IP addresses. IP addresses are associated with a fixed network location much as a non-mobile phone number is associated with a physical jack in a wall. Thus, when a user of a computer attached to the Internet using the IP changes the computer's point of attachment to the Internet, his computing activities with respect to the Internet are disrupted. This is because each new point of attachment to the Internet is associated with a new network number, and hence, a new IP address. To resume Internet computing activities, the user must typically cause his computer to make a new Internet connection using the new IP address.
Highly portable wireless computing devices offering IP connectivity are becoming increasingly popular. Such devices include, for example, digital cell phones, personal digital assistants (PDA's), electronic pocket organizers, and even laptop computers equipped with interface mechanisms such as a wireless modem or a modem together with a cell phone. For a variety of reasons, a user on the move may have to change his computing device's point of attachment to the Internet. For example, the user's device may travel out of range of a wireless communication node through which the point of attachment was maintained and the link between the computing device and the Internet may be dropped, or long distance cell phone and/or roaming charges associated with maintaining the link may become prohibitive. Accordingly, the concept of mobile networking is becoming increasingly attractive. In mobile networking, computing activities are not disrupted when the user changes his computing device's point of attachment to the Internet. Instead, all the needed reconnection occurs automatically and non-interactively so that it can be transparent to the user.
Mobile IP (RFC 2002) is a standard proposed by a working group within the Internet Engineering Task Force, that was designed to solve the problem of making transparent mobility possible. Principles of Mobile IP are described, for example, in
Mobile Networking Through Mobile IP
, by Charles E. Perkins, copyright 1997 Institute of Electrical and Electronics Engineers, Inc., which is hereby incorporated by reference. Additional terms and principles relating to networking, including Point-to-Point Protocol (PPP) and Layer 2 Tunneling Protocol (L2TP) protocols, are variously described and defined in
Mobile Networking Terminology
, by Charles E. Perkins, copyright 1997 Institute of Electrical and Electronics Engineers, Inc.,
Nomadicity: How Mobility Will Affect the Protocol Stack
, by Charles E. Perkins, copyright 1997 Institute of Electrical and Electronics Engineers, Inc., and
Virtual Private Networking: An Overview
, copyright 1998 Microsoft Corporation, all of which are hereby incorporated by reference.
Mobile IP allows a mobile node (such as a user's wireless computing device) to receive data packets by using two IP addresses: a fixed “home” address and a “care-of” address.
The home address designates a home network for the mobile node, to which data for the mobile node can be sent. The home network can be, for example, an operator's network (like an Internet Service Provider, or ISP) or a corporate network.
The care-of address designates a different or “foreign” network to which the mobile node is attached, and to which data packets received by the home network for the mobile node can be forwarded for delivery to the mobile node.
Mobile IP requires the existence of a network node within the home network known as a “home agent”, and also a network node within the foreign network known as a “foreign agent”. The home agent is a router in the home network that performs the Mobile IP home agent functionality. The foreign agent is a router in the foreign network that performs the Mobile IP foreign agent functionality.
Whenever the mobile node moves, i.e., changes its point of attachment from one foreign network to another foreign network, it “registers” its new care-of address with its home agent. The home agent associates the home address of the mobile node with the current care-of address, and this information together with a lifetime for the registration (e.g., a time period during which the association will be considered valid) forms a “binding” for the mobile node. Thus, when the mobile node changes networks, it registers with the home agent and the home agent updates the binding to reflect the new care-of address.
In operation, the home agent receives all packets addressed to the home address and intended for the mobile node whenever the mobile node is not directly attached to its home network (and is therefore attached to the foreign network). These packets can be referred to as “terminating” packets. The home agent “tunnels” the terminating packets it has received to the foreign agent, which finally transfers them to the mobile node.
In general, tunneling is a method of using an internetwork infrastructure to transfer data from a first network to a second network over an intermediate network. The intermediate network can be of a type that is different from the type of the first and second networks. The data to be transferred (or “payload”) can be the frames (or packets) of another protocol. Instead of sending a frame as it is produced by the originating node, the tunneling protocol encapsulates the frame in an additional header. The additional header provides routing information so that the encapsulated payload can traverse the intermediate network. The encapsulated payloads are then routed between tunnel endpoints over the intermediate network or internetwork. The path through which the encapsulated packets travel through the internetwork or intermediate network is called a “tunnel”. Once the encapsulated payloads reach their destination on the internetwork, the payloads are unencapsulated and forwarded to their final destination in the second network. Tunneling includes the entire process of encapsulating, transferring, and unencapsulating.
To tunnel terminating packets between the home network and the foreign network in Mobile IP, the home agent modifies each terminating packet so that the care-of address appears as the destination IP address for the terminating packet. This modification can be understood as a packet transformation, or more specifically, as a “redirection”. In Mobile IP, the home agent redirects each terminating packet from the home network to the care-of address by constructing a new IP header that contains the mobile node's care-of address as the destination IP address. This new header then shields or encapsulates the original termination packet, including the original IP header, so that the mobile node's home address in the original IP header will have no effect on the encapsulated packet's routing until it arrives at the care-of address.
When the encapsulated terminating packet sent by the home agent is received at the care-of address, e.g., the foreign network to which the mobile node is connected, the foreign agent at the foreign network strips off the header containing the care-of address, thus unencapsulating the terminating packet, and forwards the terminating packet (bearing the home address in its header) to the mobile node. The home address ensures that the terminating packet will be processed properly by TCP or whatever higher level protocol logically receives it from the mobile node's IP (that is, layer-3) processing layer. The default encapsulation mechanism that must be supported by all mobility agents using Mobile IP is IP-within-IP as described above, which is a layer-3 tunnel.
In Mobile IP, as described above, a data packet in
Burns Doane Swecker & Mathis L.L.P.
Kizou Hassan
Logsdon Joe
Telefonaktiebolaget LM Ericsson
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