Abstract:
The present invention supports a generalized link-layer address extension for an information packet transmission on an IP mobility system. In the invention, a link-layer address for a node can be communicated in any information packet rather than confined to a specialized message format. The link-layer address can be used in link-layer routing protocols to simplify mobile IP hand-offs and routing, reducing overhead data traffic and allowing more efficient use of network resources.

Description:
TECHNICAL FIELD OF THE INVENTION 
   A modified address extension for use in a packet-based mobile communication system. 
   BACKGROUND OF THE INVENTION 
   Present-day Internet communications represent the synthesis of technical developments begun in the 1960s. During that time period, the Defense Department developed a communication system to support communication between different United States military computer networks, and later a similar system was used to support communication between different research computer networks at United States universities. 
   The Internet 
   The Internet, like so many other high tech developments, grew from research originally performed by the United States Department of Defense. In the 1960s, Defense Department officials wanted to connect different types of military computer networks. These different computer networks could not communicate with each other because they used different types of operating systems or networking protocols. 
   While the Defense Department officials wanted a system that would permit communication between these different computer networks, they realized that a centralized interface system would be vulnerable to missile attack and sabotage. To avoid this vulnerability, the Defense Department required that the interface system be decentralized with no vulnerable failure points. 
   The Defense Department developed an interface protocol for communication between these different network computers. A few years later, the National Science Foundation (NSF) wanted to connect different types of network computers located at research institutions across the country. The NSF adopted the Defense Department&#39;s interface protocol for communication between the research computer networks. Ultimately, this combination of research computer networks would form the foundation of today&#39;s Internet. 
   Internet Protocols 
   The Defense Department&#39;s interface protocol was called the Internet Protocol (IP) standard. The IP standard now supports communication between computers and networks on the Internet. The IP standard identifies the types of services to be provided to users and specifies the mechanisms needed to support these services. The IP standard also describes the upper and lower system interfaces, defines the services to be provided on these interfaces, and outlines the execution environment for services needed in this system. 
   A transmission protocol, called the Transmission Control Protocol (TCP), was developed to provide connection-oriented, end-to-end data transmission between packet-switched computer networks. The combination of TCP with IP (TCP/IP) forms a system or suite of protocols for data transfer and communication between computers on the Internet. The TCP/IP standard has become mandatory for use in all packet switching networks that connect or have the potential for utilizing connectivity across network or sub-network boundaries. 
   A computer operating on a network is assigned a unique physical address under the TCP/IP protocols. This is called an IP address. The IP address can include: (1) a network ID and number identifying a network, (2) a sub-network ID number identifying a substructure on the network, and (3) a host ID number identifying a particular computer on the sub-network. A header data field in the information packet will include source and destination addresses. The IP addressing scheme imposes a sensible addressing scheme that reflects the internal organization of the network or sub-network. All information packets transmitted over the Internet will have a set of IP header fields containing this IP address. 
   A router is located on a network and is used to regulate the transmission of information packets into and out of computer networks and within sub-networks. Routers are referred to by a number of names including Home Agent, Home Mobility Manager, Home Location Register, Foreign Agent, Serving Mobility Manager, Visited Location Register, and Visiting Serving Entity. A router interprets the logical address of an information packet and directs the information packet to its intended destination. Information packets addressed between computers on the sub-network do not pass through the router to the greater network, and as such, these sub-network information packets will not clutter the transmission lines of the greater network. If an information packet is addressed to a computer outside the sub-network, the router forwards the packet onto the greater network. 
   The TCP/IP network includes protocols that define how routers will determine the transmittal path for data through the network. Routing decisions are based upon information in the IP header and entries maintained in a routing table. A routing table possesses information for a router to determine whether to accept the communicated information packet on behalf of a destination computer or pass the information packet onto another router in the network or sub-network. The routing table&#39;s address data enables the router to accurately forward the information packets. 
   The routing table can be configured manually with routing table entries or with a dynamic routing protocol. In a dynamic routing protocol, routers update routing information with periodic information packet transmissions to other routers on the network. This is referred to as advertising. The dynamic routing protocol accommodates changing network topologies, such as the network architecture, network structure, layout of routers, and interconnection between hosts and routers. Internet Control Message Protocol (ICMP) information packets are used to update routing tables with this changing system topology. 
   The IP-Based Mobility System 
   The Internet protocols were originally developed with an assumption that Internet users would be connected to a single, fixed network. With the advent of portable computers and cellular wireless communication systems, the movement of Internet users within a network and across network boundaries has become common. Because of this highly mobile Internet usage, the implicit design assumption of the Internet protocols has been violated. 
   In an IP-based mobile communication system, the mobile communication device (e.g. cellular phone, pager, computer, etc.) is called a mobile node. Typically, a mobile node changes its point of attachment to a foreign network while maintaining connectivity to its home network. A mobile node may also change its point of attachment between sub-networks in its home network or foreign network. The mobile node will always be associated with its home network and sub-network for IP addressing purposes and will have information routed to it by routers located on the home and foreign network. 
   IP Mobility Protocols 
   During the formative years since the Internet was first established, Internet Protocol version 4 (IPv4) was recognized and adopted as the standard version of the Internet Protocol. With the advent of mobile IP and proliferation of computers and computer systems linked to the Internet, various limitations in the IPv4 standard and associated procedures have developed and emerged. In response, new standards are evolving and emerging. 
   The most pressing limitation in the IPv4 standard is the restriction on the number of possible IP addresses imposed by the 32-bit address field size. Newer standards increase the size of the available address space 400% to 128 bits, which vastly increases the number of available addresses. While the 32-bit address field provides 2 32  or approximately 4 billion IP address possibilities, a 128-bit field provides 2 128  IP address possibilities. 
   A number of benefits emerge from this vastly larger available address field. First, there is little chance of exhausting the number of IP addresses. Second, a large address field allows aggregation of many network-prefix routers into a single network-prefix router. Finally, the large address pool allows nodes to auto configure using simple mechanisms. 
   IP Mobility Care-of Addressing 
   In a mobile IP network, nodes will transmit notification and discovery information packets onto the network to advertise their presence on the network and solicit advertisements from other nodes. While on a foreign network, a mobile node will be assigned a care-of address that will be used to route information packets to the foreign network and the attached mobile node. An advertisement from a router on the foreign network will inform a mobile node that it is attached to a foreign network. The mobile node will typically obtain a care-of address from a router on the foreign network, which it will transmit to its home network in an information packet. 
   Information packets addressed to the mobile node on the home network will be encapsulated with the care-of address. This information packet will then be forwarded and routed to the mobile node on the foreign network by a router on the foreign network. 
   Mobile IP Extensions 
   Extensions have been defined in the EP protocol, and extensions can be used in similar protocols, to support transmission of variable amounts of data in an information packet. This includes address information for mobile nodes, routers, and networks. The extension mechanism in IP permits appropriate addressing and routing information to be carried by any information packet, without restriction to dedicated message types such as discovery, notification, control, and routing information packet formats. 
   The general extension format is found in  FIG. 1  in a Type-Length-Value format. As shown in  FIG. 1 , the Type data field (T)  1  occupies the first 8-bits (one octet) of the general extension. The value of this data field will designate the type of extension. The Length data field (L)  2  occupies the next 8-bits of the extension, and the value assigned is the length of the Value field (V)  3  in octets. The Value data field  3  occupies the remaining bits in the general extension as specified by the Type 1 and Length 2 data values. 
   Link Layer Address 
   There are seven protocol layers in computer systems. These layers include the physical, data link, network, transport, session, presentation, and application layers. Nodes attached to a sub-network or network have an actual physical location on that sub-network or network. The data link-layer is this physical communication link. Generally, all nodes on the same link-layer share the same router and can be referred to as neighboring nodes. When transmitting information packets across a network boundary, IP network-layer protocols are utilized. When transmitting data on the same network link, a link-layer protocol can be used. 
   A mobile node on its home network will be associated with a specific IP address. As a mobile node moves within its home network, its IP address will remain the same, but its link-layer connectivity will change. A link-layer address represents the link-layer connectivity, which is the actual physical connection between the mobile node and the network. This IP address association with a link-layer address is maintained in data tables on the network. 
   Routers on the network will maintain the link-layer address and IP address association for a mobile node on a data table, ensuring that information packets can be routed to a mobile node on the correct link-layer connection. This can also occur on a foreign network, where as a mobile node changes link-layer connectivity, routers update the link-layer address association for a mobile node in a data table. 
   At the link-layer protocol level, a frame, consisting of a small data link-layer address header plus a network-layer information packet, is moved from one computer to another computer on the link. To move an IP information packet from one node to the next node on a link, the link-layer address must be known to transmit the packet within a link-layer frame. To determine which link-layer address corresponds to a given IP address, an Address Resolution Protocol (ARP) must be performed. Alternatively, nodes can store a number of IP address/link-layer address mappings in a data table to determine a corresponding link-layer address. Specialized ARP and ICMP control and routing information packets are currently used to transmit link-layer addresses over a network so data tables can be updated. These specialized protocols have restrictions in their use on a network. 
   Having a simpler, more generic method of transmitting link-layer addresses in any information packet would be desirable and reduce overhead information message traffic. Moreover, an expanded address space over that available in IPv4 along with a link-layer address may be exploited to expand the application and utility of protocols at the link-layer level. 
   SUMMARY OF THE INVENTION 
   The invention is a Generalized Link-Layer Extension that can be included in the optional extension data fields of an information packet. This generalized extension of the present invention includes a type data field, a length data field, a sub-type data field, and a link-layer address data field. The link-layer address included in an information packet transmitted on a network with the extension indicates the physical connectivity of a node to the network. 
   The expanded 128-bit address field allows greatly increased link-layer address association. Expanded node-router associations are possible permitting wider application of link-layer protocols greatly simplifying hand-off procedures as a node changes connectivity. More advanced usage of link-layer protocols may evolve for communication between routers, correspondence nodes, mobile nodes, and neighbors across sub-network and network boundaries. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The objects and features of the invention will become more readily understood from the following detailed description and appended claims when read in conjunction with the accompanying drawings in which like numerals represent like elements and in which: 
       FIG. 1  is a general extension format; 
       FIG. 2  is a prior art schematic diagram of a mobile IP wireless communication network; 
       FIG. 3  is a general representation of the generalized link-layer address extension according to the invention; 
       FIG. 4  is a general representation of a cdma2000 link-layer address extension according to the invention; 
       FIG. 5  is a general representation of an Ethernet link-layer address extension according to the invention; and 
       FIG. 6  is a general representation of a global identifier link-layer address extension according to the invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 2  shows an embodiment for a mobile IP cellular communication network using the invention. Router  1  (R 1 )  60  is connected to a Base Station Controller  1  (BSC 1 )  40  by communication link  39 . Base Station Controller BSC  1   40  is connected to a transceiver  11  by communication link  9 . Transceiver  11  supports wireless communication in cell area  1  (C 1 )  10 . Base Station Controller BSC  1   40  is also connected to transceiver  16  by communication link  14 . Transceiver  16  supports wireless communication in cell area  2  (C 2 )  15 . 
   Router R 1   60  is connected to a second Base Station Controller  2  (BSC 2 )  45  by communication link  43 . Base Station Controller BSC  2   45  is connected to transceiver  21  by communication link  19 . Transceiver  21  supports communication in cell area  3  (C 3 )  20 . Base Station Controller BSC  2   45  is also connected to transceiver  26  by communication link  24 . Transceiver  26  supports communication in cell area  4  (C 4 )  25 . 
   A second router, Router  2  (R 2 )  65  is connected to a Base Station Controller  3  (BSC 3 )  50  by communication link  49 . The Base Station Controller BSC  3   50  is connected to transceiver  31  by communication link  29 . Transceiver  31  supports wireless communication in cell area  5  (C 5 )  30 . Base Station Controller BSC  3   50  is also connected to transceiver  36  by communication link  34 . Transceiver  36  supports wireless communication in cell area  6  (C 6 )  35 . 
   A Mobile Node (MN)  64  is located in cell area  3  (C 3 )  20 . The Mobile Node MN  64  can be a communication device, such as a cellular phone, or a router or other type of host. Wireless communication link  66  links transceiver  21  to Mobile Node MN  64 . Communication to and from Mobile Node MN  64  is controlled by Router R 1   60 . In  FIG. 2 , Mobile Node MN  64  is able to move from cell area  3  (C 3 )  20  to any adjoining cellular area—cell area  1  (C 1 )  10 , cell area  4  (C 4 )  25 , cell area  5  (C 5 )  30 , or cell area  6  (C 6 )  35 . Router R 1   60  is connected to coupling  70  by communication link  59 . Router R 2   65  is connected to coupling  70  by communication link  58 . Coupling  70  is a direct link between Router R 1   60  and Router R 2   65  on the same network. Correspondence Node (CN)  75  is connected to coupling  70  by communication link  76 , which is a direct, wired connection. 
   Nodes connected to the network have an assigned link-layer address representing the physical connection of the node to the network. Router R 1   60  and Router R 2   65  will have a fixed link-layer address. Mobile Node MN  64  will have a link-layer address assigned dependent upon its physical connectivity to transceiver  21 . This connection and link-layer assignment is made upon power-up in cell area  3  (C 3 )  20 . The IP address link-layer address association will be established and maintained in routing tables. As Mobile Node MN  64  moves across the cellular boundaries, its connectivity and link-layer address will change. 
     FIG. 2  shows two embodiments for movement of Mobile Node MN  64  to adjoining cell areas. The first is Mobile Node MN  64  moving from cell area  3  (C 3 )  20  to cell area  1   10 , shown as Mobile Node MN  64 ′. Although this movement results in no change to Mobile Node MN  64  router association, its link-layer connectivity, and thus its designated link-layer address for that connectivity, changes. This requires a hand-off procedure involving an exchange of ICMP and/or control and routing messages between the router and Mobile Node MN  64 ′ as well as an exchange of ARP messages on the network. The hand-off procedure will also update the various routing tables and other data tables maintaining the Mobile Node MN  64  IP-to-link-layer address association thereby ensuring the correct routing of information packets. 
     FIG. 2  also shows Mobile Node MN  64  moving from cell area  3  (C 3 )  20  to cell area  5  (C 5 )  30 , shown as Mobile Node MN  64 ″. This movement results in both a change in connectivity as well as a change in Mobile Node MN  64   s  router association from Router R 1   60  to Router R 2   65 . Hand-off procedures involve assignment of a care-of address by Router R 2   65  in an exchange of ICMP messages between MN  64 ″ and Router R 2   65 . 
   Additionally, ARP messages will be transmitted to change or establish link-layer address associations for the Mobile Node MN  64 ″ on the network, and Router R 1   60  will also need to be updated with the care-of address for Mobile Node MN  64 ″, which may include the link-layer address association. For both situations depicted by Mobile Node MN  64 ′ and Mobile Node MN  64 ″, the Correspondence Node CN  75  will need to continue communications. Correspondence Node CN  75  may maintain a data table with a link-layer address association for Mobile Node MN  64 . This link-layer address association for Mobile Node MN  64  will also be established and updated by either ICMP or ARP control and routing messages. 
   Coupling  70  can also represent other alternative embodiments besides a direct connection between Router R 1   60  and Router R 2   65 . Coupling  70  can also represent a communication link that includes another router on the same network. Coupling  70  can also represent a connection between two geographically separated sub-networks, interconnected by the Internet, with a server computer or router controlling movement of information packets between the remotely located routers, Router R 1   60  and Router R 2   65 . Another possible embodiment is Router R 1   60  and Router R 2   65  occupying separate networks, with coupling  70  including routers and server computers on the Internet. 
   The communication link  76  between coupling  70  and Correspondence Node CN  75  can also be a wireless connection on a cellular system with Correspondence Node CN  75  also moving across cell areas. Communication link  76  can also include an Internet connection through a separate sub-network or network. In each of these alternative embodiments, Correspondence Node CN  75  will have an associated link-layer connectivity and a designated link-layer address. 
   The essential depiction in  FIG. 2  is that Mobile Node MN  64  is switching its physical connectivity, and thus its link-layer address, as it moves across cell area boundaries. As Mobile Node MN  64  moves across cellular boundaries, there must be a mechanism for informing other nodes, including any neighboring nodes, routers, and correspondence nodes as well as Mobile Node MN  64 , of the new link-layer address and establishing and updating these link-layer address associations. Moreover, other nodes may have an associated link-layer address for their physical connectivity to a network, and this connectivity may also be subject to change, such as in the case of a mobile router. Currently, establishing and updating these link-layer address associations requires specialized information packets transmitted on a network. 
   The specialized information packets currently used to establish and update link-layer address associations are processed to incorporate the link-layer address associations on data tables. In  FIG. 2 , the Mobile Node MN  64 , Correspondence Node CN  75 , Router R 1   60 , and Router R 2   65  may maintain a data table associating each of the other nodes with a particular link-layer address. As Mobile Node MN  64  changes its connectivity, each of the nodes with a data table containing a link-layer address association for Mobile Node MN  64  needs to update the data table with the new link-layer address. 
   Other nodes may also need to establish or maintain a link-layer address association for Mobile Node MN  64 . If Correspondence Node CN  75  changes its link-layer connection, data tables in other nodes must also be updated or established. If Router R 1   60  and Router R 2   65  change their link-layer connection, data tables in nodes and server computers will also need to be updated or established. Updating and establishing the various link-layer associations on nodes and server computers requires significant message and data overhead on a network. Using a generalized link-layer extension in an information packet to communicate these changes would reduce this overhead. 
     FIG. 3  shows the format for the Generalized Link-Layer Address Extension (GLLA) of the invention, which follows the general format for an extension shown in  FIG. 1 . The first 8-bit data field is the Type field (T)  210 , which the assigned value will designate the extension as a GLLA. The Length field (L)  220  is the next 8-bit data field, and the value will equal the length of the link-layer address, in octets, plus the 8-bit (one octet) Sub-Type field  230 . The next 8-bit data field is the Sub-Type field (ST)  230 , and this field will identify the sub-type of the link-layer address extension. The final data field is the link-layer address extension data field (LLA)  240 , and this data field is variable in length. 
   A number of link-layer address protocols or standards are utilized, and these need to be identified in the extension. Three specific sub-type embodiments for link-layer addresses are 1) the cdma2000 extension 2) the Ethernet extension, and 3) the Global Identifier extension.  FIG. 4  shows the embodiment for the cdma2000 Link-Layer Address Extension Sub-Type. The T  310  field designates the extension as a GLLA. The L  320  will have a value equal to the length of the International Mobile Station Identifier (IMSI) field plus one-octet. The ST  330  field will have an assigned value designating the GLLA sub-type as a cdma2000 Link-Layer Address Extension. The extension will contain an IMSI address field  340 . This field will be in the form of &lt;IMSI&gt;:&lt;Connection ID&gt;. The &lt;IMSI&gt; field contains an ASCII-based representation of the IMSI. The “:” is ASCII 0x3a, and the &lt;Connection ID&gt; is the ASCII representation of a small, decimal number used for distinguishing different link-layer connections from the same device. 
     FIG. 5  shows the embodiment for an Ethernet Link-Layer Address Extension sub-type GLLA. The T  410  occupies the first 8-bit field and designates the extension type as a GLLA. The L  420  8-bit field will have the length of the extension in octets plus one, which will be 7 (56 bits). The ST  430  8-bit field will identify the GLLA as an Ethernet Link-Layer Address Extension. The final address extension field  440  will contain the Ethernet Media Access Control (MAC) address  440 , which is 48 bits long. 
     FIG. 6  shows the embodiment for a Global Identifier Link-Layer Address extension sub-type GLLA. The T  510  occupies the first 8-bit field and designates the extension type as a GLLA. The next 8-bit field L  520  has a value of 9. The ST  530  is 8-bits long and designates the sub-type as a Global Identifier (EUI-64) Address extension. The final data field  540  will contain an IEEE 64-bit Global Identifier (GID) (EUI-64) Address extension, which is 64 bits in length. 
   Looking at  FIG. 2 , the link-layer address association for Mobile Node MN  64 ′ can be updated on Mobile Node MN  64 ′, Router R 1   60 , and Correspondence Node CN  75  without using any specialized information packets. The generalized link-layer address extension can be contained in an information packet transmitting data to or from any node as part of an ongoing communication session. The same information packet can be processed by Mobile Node MN  64 ′, Router R 1   60 , and Correspondence Node CN  75  to update a data table with a link-layer address. Router R 1   60  can add the extension to an information packet to communicate the link-layer address change to Mobile Node MN  64 ′, Correspondence Node CN  75 , or some other node or server computer. 
   A specialized information packet, such as a notification message or routing message, can also be transmitted to update any nodes or server computers of the link-layer address change using the extension. Upon initial power-up these specialized information packets can also be used to register the Mobile Node MN  64  with Router R 1   60  and any other node or server computers and establish data tables on these nodes, or server computers, with a link-layer address association for the Mobile Node MN  64 , which can be later updated with any information packet containing the GLLA extension. 
   For MN  64 ″ on  FIG. 2 , as the Mobile Node MN  64  moves across the cell area boundary to Mobile Node MN  64 ″, link-layer address associations can be updated or established on a data table on a node using the GLLA extension in any information packet in the same manner utilized by Mobile Node MN  64 ′. Any transmitted information packet received by a node or server computer communicating with Mobile Node MN  64 ″ or Router R 2   65  can contain the extension and be processed to update a data table. Although specialized information packets may be utilized to update or establish a link-layer address association for the Mobile Node MN  64  at locations shown as Mobile Node MN  64 , Mobile Node MN  64 ′, and Mobile Node MN  64 ″, the ability to use the extension in any type of information packet will permit and encourage further development and exploitation of link-layer addressing and routing protocols. Message traffic involving discovery, notification, control, or routing messages will be reduced freeing up network resources. 
   While the invention has been particularly shown and described with respect to preferred embodiments, it will be readily understood that minor changes in the details of the invention may be made without departing from the spirit of the invention.