Abstract:
Systems and methods of enabling a user host device to communicate on a network. In an embodiment, a system receives a request packet from a user host device. The request packet, such as an ARP request packet, may include a target IP address that corresponds to a static IP address that is different from any IP address associated with the system. In response to receiving the request packet, the system may send a response packet, such as an ARP response packet, with a sender address that corresponds to the static IP address, and with a sender hardware address that corresponds to a hardware address of the system.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 12/240,427, filed Sep. 29, 2008; which is a continuation of U.S. patent application Ser. No. 11/097,925, filed Apr. 1, 2005, now U.S. Pat. No. 7,554,995; which is a continuation of U.S. patent application Ser. No. 09/684,937, filed Oct. 6, 2000, now U.S. Pat. No. 7,088,727; which is a continuation-in-part of U.S. patent application Ser. No. 09/041,534, filed Mar. 12, 1998, now U.S. Pat. No. 6,130,892; which is a continuation-in-part of U.S. patent application Ser. No. 08/816,174, filed Mar. 12, 1997, now abandoned. All of the aforementioned applications are hereby incorporated by reference as if set forth herein in their entireties. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED R&amp;D 
     The U.S. government may have rights in this invention as provided for by the terms of Contract No. DAAH01-97-C-R179 awarded by DARPA. 
    
    
     BACKGROUND 
     The present invention is generally related to the art of network communications. 
     User digital communication addresses such as internet or IP addresses are conventionally associated with a fixed physical location, similar to a user&#39;s business telephone line. However, portable communication devices such as laptop computers are becoming increasingly popular, and it is common for a user to access the internet from locations as diverse as hotel rooms and airplanes. 
     Digital communication networks are set up to route communications addressed to a communication or network address to an associated destination computer at an established physical location. Thus, if a laptop computer is moved to a remote location, communications to and from the laptop computer may not reach the new physical location. 
     For a computer (host) to communicate across a network (e.g., the internet), software protocols (e.g., Transport Control Protocol/Internet Protocol (TCP/IP)) must be loaded into the host. A host computer sends information (i.e., packets of data) to another destination computer via devices on the network (routers) which receive the packets and send the packets to the network or segment of the destination host. 
     The destination host will route replies back using a similar process. Each host computer and router must therefore be configured to send the packets of data to an appropriate router to reach the intended destination. However, a router will receive the packets only if the host computers specifically send (address) the packets to that router at the link layer of the communication protocol. If a host is configured incorrectly (bad address or address of a router not on the local network), then the host computer and router will be unable to communicate, i.e., the router will not listen to the host or will “drop” packets. 
     With the advent of mobile computers (laptops) and the desire to plug them into various networks to gain access to the resources on the network and internet, a mobile computer must be reconfigured for each network. Traditionally this new configuration can be done either (i) manually in software on the mobile computer (usually causing the mobile computer to be restarted to load the new configuration), or (ii) with a new set of protocols which must be utilized on the mobile computer to obtain the configuration information from a device on the network to which the computer is being connected. When new services (protocols) are created to add functionality to the host computers, these new protocols may need to be updated in the host computers or routers, depending upon the type of new functionality being added. 
     SUMMARY 
     In accordance with the present invention, a “Nomadic” router or translator enables a laptop computer or other terminal which is configured to be connected to a local home network to be connected to any location on the internet or other digital data communication system. The nomadic router automatically and transparently reconfigures packets sent to/from the terminal for its new location by processing outgoing and incoming data. 
     The nomadic router includes a processor which appears as the home network to the terminal, and appears as the terminal to the communication system. The terminal has a terminal address, the nomadic router has a router address, and the terminal transmits outgoing data to the system including the terminal address as a source address. Whether or not the message is addressed to the nomadic router at the link layer, the processor intercepts the message and translates the outgoing data by replacing the permanent address with the router address as the source address. Incoming data intended for the terminal from the system includes the translator address as a destination address, and the processor translates the incoming data by replacing the translator address with the permanent address as the destination address. 
     The terminal can be directly connected to a point on a local network, and the nomadic router connected to another point on the network. The nomadic router can be employed to implement numerous applications including nomadic e-mail, network file synchronization, database synchronization, instant networking, a nomadic internet, mobile virtual private networking, and trade show routing, and can also be utilized as a fixed nomadic router in hotels, or multi-dwelling units, or multiple tenant units, for example. 
     The nomadic router can be implemented as software and/or hardware. The nomadic router establishes location and device transparency for a digital communication terminal such as a laptop computer. The terminal can be connected to any of a variety of networks and locations which can employ a variety of communication interface devices. 
     The nomadic router automatically converts the actual location address to a unique communication address for the user such as an internet address, such that the terminal performs communications originating from the communication address regardless of the physical location of the terminal. 
     The nomadic router includes software and services which can be packaged in a personal portable device to support a rich set of computing and communications capabilities and services to accommodate the mobility of nomads (users) in a transparent, integrated, and convenient form. This is accomplished by providing device transparency and location transparency to the user. 
     There is a vast array of communication device alternatives such as Ethernet, Wireless LAN, and dialup modem among which the user switches when in the office, moving around the office, or on the road (such as at a hotel, airport, or home). The device transparency in the nomadic router provides seamless switching among those devices (easily, transparently, intelligently, and without session loss). The location transparency support in the nomadic router prevents users from having to reconfigure (e.g., IP and gateway address) their network device (laptop) each time they move to a new network or subnetwork. 
     The nomadic router provides a separation of location and identity by providing a permanent IP address to the network device (host). The nomadic router provides independence between the location, communication device, and the host operating system. There are no new standards which need to be adopted by the networking community. All specialized processing is stored internally to the nomadic router with standard interfaces to the host device and various communication devices. 
     The nomadic router supports the migration to Network Computers by providing identity and security services for the user. The nomadic router also supports multiple parallel communication paths across the communications network for soft handoff, increased throughput, and fault tolerance by supporting multiple communication substrates. 
     A portable router for enabling a data communication terminal to be location and device transparent according to the present invention, comprises: a first module for storing a digital communication address of a user; a second module for detecting a data communication network location to which the terminal is connected; a third module for detecting communication devices that are connected to the terminal; a fourth module for establishing data communication between the terminal and the network such that the communication address of the location from the second module is automatically converted to the communication address of the user from the first module; and a fifth module for automatically selecting a communication device which was detected by the third module for use by the fourth module. 
     The nomadic router utilizes a unique process embodied in a self-contained apparatus which manipulates the packets of data being sent between the host computers and routers. This process provides an intelligent active universal translation of the content of the packets being transmitted between the host computer and nomadic router. The translation allows the host computer to communicate with the nomadic router, which intercepts packets from the host, even when the host computer is not configured to communicate with the nomadic router. 
     This is achieved by the nomadic router pretending to be the router for which the host is configured, and by the nomadic router pretending to be the host with which the router expects to communicate. Therefore, the nomadic router supports the mobility of computers in that it enables these computers to plug into the network at different locations (location independence) without having to install, configure, or utilize any net protocols on the mobile computer. 
     The mobile computer continues to operate without being aware of the change in location or configuration of the new network, and the nomadic router translates the data allowing the host to think that it is communicating with its home router. By putting this process in a self-contained apparatus, the deployment of new protocols can be performed independently of the host computer and its operating system (host independent). 
     All specialized processing and translation is stored internally in the nomadic router with standard interfaces to the host device and various communication devices. Thus, no new standards need be adopted. By removing the complexity of supporting different network environments out of the mobile computer and into this self-contained apparatus, the nomadic router allows the host computer to maintain a minimal set of software protocols and functionality (e.g., the minimum functionality typically installed in network computers) to communicate across the network. 
     The nomadic router translation ability also enables the use of alternate communication paths (device independence) without the host computer being aware of any new communication device that utilizes an alternate communication path. The translation of the packets is done not just at the physical, link, or network layer of the protocol stack but at the transport and application layers as well. This allows the network card, protocol stack, and application running on the host computer to be independent of the network environment and configuration. 
     As an example of the communication device independence, the translation allows soft handoff, increased throughput, and fault tolerance by supporting multiple communication substrates. In addition, the nomadic router translation ability provides a flexible process for deploying enhanced nomadic and mobile computing software and services such as filtering of packets and determining which packets should be allowed to be transmitted between the mobile computer and the nomadic router or local area network (Internal Firewall). 
     The router apparatus can be: (i) carried with the mobile user (e.g., using an external box); (ii) attached to the mobile computer (e.g., PCMCIA card); (iii) installed inside the mobile computer (e.g., a chip in the laptop); (iv) or installed into the remote network infrastructure to provide network access for any mobile computer (e.g., a box which plugs into the remote or foreign local area network translating packets being sent between the host and its router, or a chip which is installed in routers on the remote network). The nomadic router can also be provided in the form of software which is loaded into and run in the mobile computer or another computer or router on a network. 
     These and other features and advantages of the present invention will be apparent to those skilled in the art from the following detailed description, taken together with the accompanying drawings, in which like reference numerals refer to like parts. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram illustrating one implementation of a nomadic router positioned between the host computing device and various communication devices using standard interfaces; 
         FIG. 2  is a diagram illustrating a basic nomadic router architecture, which is referred to as the hardware implementation architecture; 
         FIG. 3  is a flowchart illustrating a configuration overview of the basic steps performed when a host device is attached to the present nomadic router and when a network interface is attached to the router; 
         FIG. 4  is a flowchart illustrating automatic adaptation to the host device when the first data packet from the host is sent to a home network router or when an activation interrupt or signal is received; 
         FIG. 5  is a flowchart illustrating a process initializing and checking the various communication device interfaces for initialization, activation, etc.; 
         FIG. 6  is a diagram illustrating a basic nomadic router architecture when implemented as software in the host device; 
         FIGS. 7A to 7G  are diagrams illustrating protocol stack implementations for various network devices, with the translation function performed for all layers of the protocol stack in the nomadic router; 
         FIG. 8  is a flowchart illustrating a proxy ARP packet interception and host reconfiguration process; 
         FIGS. 9A and 9B  provide a flowchart illustrating a translation process which takes place in the host computer and nomadic router at various levels in the protocol stack; 
         FIG. 10  is a diagram illustrating the architecture of the nomadic router implemented as a hardware device including a microcontroller and a non-volatile memory for storing algorithms implementing the translation function; 
         FIG. 11  is a diagram illustrating the architecture of the nomadic router apparatus implemented as an Application Specific Integrated Circuit (ASIC) chip; 
         FIGS. 12A to 12E  are diagrams illustrating host and network interface modes in which the nomadic router is able to operate; 
         FIG. 13  is a simplified perspective view illustrating the nomadic router as implemented in a self-contained box which connects onto a local area network via a network interface port and has multiple ports to connect to host computers; 
         FIG. 14  is a simplified perspective view illustrating the nomadic router apparatus as implemented on a PCMCIA Type II card where the nomadic router plugs into the host computer&#39;s type II slot and the communication card device, of Type II, plugs directly into the nomadic router so both may be powered and stored in the portable host computer; and 
         FIG. 15  is a simplified perspective view illustrating the nomadic router as implemented on a PCMCIA Type II cared where the nomadic router plugs into the host computer via a type II interface slot and where the communication card device, Type II, plugs into the nomadic router type II card. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  illustrates a “nomadic” translator or router  10  embodying the present invention as being connected between a host device or computer  12  and a communications device  14 . Host device  12  is a laptop computer or other fixed or mobile digital data communication terminal which is sufficiently portable or mobile that it can be carried from one location to another. A laptop computer, for example, can be used in any convenient location such as an airplane, customer&#39;s office, home, etc. 
     Communications device  14  can be part of any type of communication system to which host computer  12  can be connected. Such communication systems include, but are not limited to, local networks, wide area networks, dial-up and direct internet communications, etc. In a typical application, the communications device will connect the host computer to a local network which itself is connected to the internet. Thus, host device  12  is able to communicate with an unlimited number of networks and nodes which are themselves interconnected with routers, switches, bridges, etc. in any known manner. 
     Router  10  includes a terminal interface  10   a  which normally is used to connect router  10  to host device  12 , and a system interface  10   b  which connects router  10  to communications device  14 . Router  10  generally includes a processor consisting of hardware and/or software which implements the required functionality. Router  10  is further configured to operate in an alternate mode in which host device  12  is connected directly to a network, and router  10  is also connected to a point in the network via system interface  10   b . In this case, terminal interface  10   a  is unused. 
     Although device  10  is described herein as being a router, it will be understood that router  10  is not a conventional router in that it includes the capability for providing interconnectability between networks. Instead, router  10  is essentially a translator which enables host device  12  to be automatically and transparently connected to any communications device  14 , and process incoming and outgoing data for device  12 . 
     Host device  12  may be provided with a permanent internet address which conveniently need not be changed in accordance with the present invention. Device  12  is initially configured to communicate with a particular gateway or other home device at its base location. The gateway has a link layer address which device  12  attempts to locate when it is connected to any communication system. Without the functionality of nomadic router  10 , host device  12  would not be able to operate at a remote location because it would not find its gateway. 
     It will be understood that the term “home” does not relate to a residence, but is the network, gateway or other communication device or system to which the terminal is normally connected and which corresponds to the home internet or IP address. 
       FIG. 1  further illustrates a top protocol layer  16  representing host computer device  12  which generates and consumes data that is transferred through communications device  14 . Interface  16  is below the IP layer, and above the link layer in the typical OSI/ISO model. In the middle is a layer  18 , which represents router  10 , whose function is to adaptively configure and utilize the underlying communications device and provide router support. A lower layer  20  is a physical communication which carries out the communication (potentially wire-lined internet based, ad-hoc or wireless) as made available and determined for use by the nomadic router or user. Between router layer  18  and layers  16  and  20  are interfaces  22  and  24  which router  10  identifies and configures dynamically. 
     The present invention operates with host computers, routers, and other network devices through well-defined standard interfaces such as specified by the IETF (Internet Engineering Task Force) and IEEE standardization committees. These standards specify the packet format, content, and physical communication characteristics. As shown in  FIG. 7A , host computers have to be configured at various layers of the protocol stack depending on the communication capabilities and configurations of the current network. 
     Hubs, as shown in  FIG. 7B , provide a well defined interface to connect host computers and network devices by transmitting packets across multiple physical connections. Hubs do not provide any manipulation or translation of the content of the packets being transmitted. 
     Bridges or switches, as shown in  FIG. 7C , provide an intelligent filtering mechanism by which packets are transmitted across multiple physical connections based upon the physical connection the device is connected to, according to the link layer addressing (Media Access Control Address). Bridges and switches do not manipulate the content of the packet and do not provide any higher layer protocol functionality. 
     Routers, as shown in  FIG. 7D , accept packets based upon the destination address at the network layer in the packet. However, the host computer must explicitly address the packet to the router at the link layer. The router will then retransmit the packet across the correct physical connection based upon how it is configured. No modification or translation of the packet is performed at any higher layer of the protocol stack than the network layer. 
     Firewalls, as shown in  FIG. 7E , filter packets at the network and transport layers to allow only certain packets to be retransmitted on the other physical connection. Firewalls do not manipulate the content of the packet, only forward it on to the next hop in the network if it passes the transport (port) or network (IP address) filter. 
     Proxies and gateways, as shown in  FIG. 7F , only receive packets explicitly addressed to them by host computers. They only manipulate packets at the application level. The present nomadic router  10 , as shown in  FIG. 7G , manipulates and content of the packets at the link, network, transport, and application layers of the protocol stack to provide a translation between the host computer configuration and the configuration of the remote or foreign network to which the host computer is currently attached. 
     Unlike all other devices shown in  FIGS. 7A to 7F , router  10  automatically intercepts and translates packets without the other devices being aware of router  10  or being configured to use it, i.e., without packets being addressed to router  10 . The translation algorithms in router  10  which provide this location independence are provided completely internal to router  10 . Thus, no new standards need to be developed, accepted, or implemented in host computers  12  or routers  26  to deploy new network services when using the nomadic router. 
     Whenever a new or different communication device (which includes the link and physical layers) is utilized in a host computer  12 , the host computer&#39;s network layer must be aware of this new communication device. Since router  10  has its own network interface to the communication device, alternate communication devices can be utilized in router  10  which the host computer  12  can utilize but does not have to be configured to use. 
     Permanent Addressing not Location Based 
     Today we communicate with individuals in terms of the location of their communications instruments (for instance, their computer&#39;s IP address or their fax machine&#39;s phone number). To support mobility and changing communication environments and devices, it is necessary to create an environment where people communicate with other people, and not specifically with the devices they use. To transparently support mobility and adaptivity in a wireless, potentially ad-hoc, communication internetwork, a common virtual network must be provided by an intelligent device or agent which supports the various computing hosts and communication devices. 
     Nomadic router  10  provides the mapping between the location based IP address used in the internet today and the permanent user based address housed in the host CPU in device  12 . This is illustrated in  FIG. 2  as “IP Mapping.” This mapping is done without support or knowledge of such mapping by the host CPU or user. 
     The internet RFC 2002 Mobile IP protocol specifies the mapping between permanent and temporary IP addresses. The unique aspect of the nomadic router is that the Mobile IP protocols are not necessarily running in, or supported by, the host CPU but rather are internal to the nomadic router. The host configuration information, such as IP number, is discovered or determined as illustrated in  FIG. 4  and stored in nomadic router  10  as illustrated in  FIG. 2  as “Host Info.” This configuration process is overviewed in  FIG. 3 . 
     Optional Off-Loaded Processing 
     As illustrated in  FIG. 2 , nomadic router  10  can provide off-load communication processing for the host CPU by being physically separate from host device  12 . The adaptation, selection, and transportation of information across the network is performed by nomadic router  10 . This allows the host terminal or device  12  to utilize the network without having to directly support the network protocols. By having the nomadic router be responsible for adapting to the current network substrate, the host CPU can maintain a higher performance because the routing, adaptation, packetization, etc. algorithms, or packet processing, are performed by router  10 . 
     The nomadic router can also queue, transmit, and receive data independent of whether the host device  12  is available or even attached. CPU  1  built into nomadic router  10  may provide all necessary computing routines to be a fully functional network co-processor independent of the host CPU. This will allow increased battery life for the user because the nomadic router does not have numerous user I/O devices as does the host device  12 . 
     Location Independence 
     The instant network nomadic router provides the ability to provide ubiquitous and reliable support in a location independent fashion. This removes any burden on the user for device reconfiguration (e.g., IP address configuration, gateway or next hop router address, netmask, link level parameters, and security permissions) or data transmission. 
     The problem with existing protocol stacks is that communicating devices have to be reconfigured every time the communication environment changes. TCP/IP requires a new network node and gateway number. Appletalk will automatically choose an unused node number and discover the network number, but all open communications are lost and services have to be restarted to begin using the new information. 
     This occurs, for example, when a PowerBook is plugged into a network, put to sleep, and then powered up in a different network. All network services are restarted upon wakeup, and network applications get confused if they are not restarted. The nomadic router solves this problem by providing temporary as well as permanent network and node numbers similar to that provided by Mobile IP. However, the nomadic router will also work with other protocol stacks (e.g., AppleTalk). 
     Mobile IP provides location independence at the network level and not at the link level. All link level parameters, which are device specific, will be automatically configured as illustrated in  FIG. 5  when a new communications (network interface) device is attached to the nomadic router. The nomadic router completely eliminates the need for manual configuration by adaptively supporting device independence. 
     Multiple Substrates (Device Independence) 
     Another innovative feature of the nomadic router is the support for simultaneous use of multiple communication substrates. This is illustrated in  FIG. 2  as “Device Selection.” Users should be able to utilize two or more communication substrates, either to increase throughput or to provide soft-handoff capability. This functionality is not supported in today&#39;s typical protocol stacks (e.g., TCP/IP or AppleTalk). 
     For example, via the “network” control panel, the user can select between communications substrates such as EtherTalk, LocalTalk, Wireless, ARA, etc., but cannot remotely login across EtherTalk while trying to print via LocalTalk. Routers are typically able to bridge together various communication substrates, but merging the LocalTalk and EtherTalk networks together is often not desirable for many reasons, including performance and security. 
     A problem with existing routers is that they require manual configuration and exist external to the node. To overcome this, the nomadic router can support automatic configuration and full router functionality internally. This allows a mobile or nomadic node to adapt to various communication and network devices dynamically, such as when the user plugs in a PCMCIA card or attaches a communications device to the serial port. 
     Once the nomadic router becomes aware of the available communication devices and activates them, the transport of data across the multiple communication substrates can take place. The unique algorithm and protocol in the nomadic router which chooses the most appropriate device to use, is shown in  FIG. 2  and  FIG. 5  as part of the “nomadic router Device Checker” through the “nomadic router Device Selection” across each interface. 
     There are numerous factors that can affect the selection of utilizing one or more devices. Such factors typically include available bandwidth, cost to initiate and maintain connection, power requirements and availability, and user&#39;s preference. 
     Another feature of the nomadic router is the support for alternate or simultaneous use of various communication substrates. This is performed as part of step  5  in  FIG. 6  when the source address is that of the communication substrate on which the nomadic router is going to send the packet. Host computers will now indirectly be able to utilize two or more communication substrates, either to increase throughput or to provide soft-handoff capability. 
     This functionality is not supported in typical protocol stacks (e.g. TCP/IP or AppleTalk). Once the nomadic router becomes aware of the available communication devices and activates them, the transport of data across the multiple communication substrates can take place. The unique algorithm and protocol in the nomadic router which chooses the most appropriate device to use is part of the “nomadic router Device Checker” through the “nomadic router Device Selection” across each interface. 
     There are numerous factors that can affect the selection of utilizing one or more devices. Such factors typically include available bandwidth, cost to initiate and maintain connection, power requirements and availability, and user&#39;s preference. 
     Hardware Specification 
     The nomadic router can run completely in software without any special hardware as shown in  FIG. 6 , or without a CPU separate from the main host, or packaged in the form of a hardware device as shown in  FIG. 2 . The nomadic router can also be provided as a digital storage medium which stores the software program that implements the functionality of the router&#39;s translation processing. Examples of digital storage media include optical media (e.g. CD-ROM), magnetic media (e.g. floppy disks), non-volatile or read-only memories, or any combination thereof. The program is loaded into and run on mobile terminal  12 , or alternatively into any other computer or router which is connected to a network. 
     One potential implementation of the nomadic router device uses Embedded PC Technology. As an example, the rugged PC/104 standard modules have a form-factor of 3.550″ by 3.775″ and typically 0.6″ per module and weigh approximately 7 oz. per module. The PC/104 module&#39;s utilization of a self-stacking bus with minimum component count and power consumption (typically 1-2 Watts per module) eliminates the need for a backplane or card cage. 
     The nomadic router can run on a 16 bit bus with an 80486 processor, for example. The standard network access devices can support burst rates up to 10 Mbps with typical user data throughput around 1-2 Mbps. The user bandwidth is less depending on the available wireless communication device. For example, Proxim&#39;s 2 Mbps wireless LAN typically covers 500 yards with user data throughput around 500 Kbps. As illustrated in  FIG. 1 , nomadic router  10  typically includes three modules; a processor  10 , host device or terminal interface  10   a , and communication device or system interface  10   b.    
     Another potential hardware implementation is with the CARDIO S-MOS System technology. This CPU board is basically the same size as a PCMCIA credit card adapter. It is 3.55×3.775×0.6 inches. The power requirements are +5V DC ±10% with an operating temperature of 0 to 70° C., a storage temperature of −40 to 85° C., and relative humidity of 10% to 85% non-condensing. 
     The CARDIO is the most compact PC/104 compatible system available which meets the one-stack mechanical and electrical PC/104 Rev. 2.2 specifications. Power fail indicator, battery backup, and automatic switchover are also possible. 
     The nomadic router can also be implemented on a small portable device such as a PCMCIA card or partially on a PCMCIA card. In the case of a full implementation on a PCMCIA card, the host CPU and power supply are used to execute the Nomadic Routing and other protocols, algorithms, operating system, and application services. A hybrid implementation with some components as part of a PCMCIA card and others as part of other hardware implementation can also be used. 
     Apparatus Components 
     By performing packet translation in a self-contained apparatus, processing done on the packets in the nomadic router does not affect the host computer. All specific translation of the packets to match the network&#39;s configuration and available services is done internally to the nomadic router. The nomadic router can queue, transmit, and receive data independent of whether the host computer is available or even attached. The algorithms and microcontroller built into the nomadic router provides all necessary computing routines to be a fully functional network co-processor independent of the host computer. 
     By allowing the nomadic router to process packets independently of the host computer, the host computer can be powered down or asleep while processing is taking place, providing an increase in battery life for the mobile host computer. 
     The nomadic router can be configured with various components in several different ways. In  FIG. 10 , the nomadic router contains a processor or microcontroller  11  to translate the packets stored in packet buffers in random access memory. The translation functions are stored in non-volatile memory  13  with the Real Time Operating System (RTOS) and configuration information relative to the types of translation that need to be performed. 
     Upon startup (boot) of the nomadic router, the RTOS and translation algorithms are loaded from non-volatile memory into RAM where they are executed. There may be zero, one, or more host interfaces in which host computers are connected. There are one or more network interfaces. If no host interface is available, the nomadic router receives packets via the host computer from the network interface. 
     In  FIG. 11 , nomadic router  10  is implemented as an Application Specific Integrated Circuit (ASIC) or Field Programmable Gate Array (FPGA)  15 . These chips embed the algorithms for packet translation. The chip can include storage for non-volatile memory  17  which stores the configuration information such as when manually configured for the current network. The chip  15  can also include random access memory to buffer packets for translation in the nomadic router before being sent off to the host or network interface. 
     Apparatus Packaging 
     As described above, the nomadic router can be packaged in several different hardware configurations. The nomadic router can be embedded in the host computer, or a network device, such as a switch or router. It can also be implemented as a PCMCIA card which plugs into the host computer, or as a self-contained external box. 
     Each nomadic router can have from one to many interfaces. If router  10  is put into the network infrastructure, it does not have to be carried around with the mobile user. As shown in  FIG. 12   a , nomadic router  10  is attached to a Local Area Network (LAN) of the network infrastructure (which constitutes the communications device  14 ) through system interface  10   b . LAN  14  is connected through a conventional router  26  to the internet  28 . In this case, host computer interface  10   a  of nomadic router  10  is not needed since packets from host computer  12  are received through LAN  14 . 
     To provide a secure interface between host computer  12  and network  14  to prevent host computers from being able to watch (sniff) packets on network  14 , nomadic router  10  can have one interface to host computer  12  (terminal interface  10   a ) and a second interface ( 10   b ) to network  14  as shown in  FIG. 12B . Nomadic router  10  can provide filtering of packets received and retransmitted between the various interfaces thus providing a firewall type of security device which operates internally on the network. 
     To support multiple host computers  12   a  . . .  12   n  with a single nomadic router  10 , nomadic router  10  may have multiple host interfaces  10   a   1  . . .  10   a   n  as shown in  FIG. 12C  and in  FIG. 13 , and a network or system interface  10   b.    
     If the nomadic router is carried around by the mobile user, it can take the form of a PCMCIA card. In  FIG. 12D , nomadic router  10  is implemented as a PCMCIA card. The processing and translation capability is stored inside the card and the interface to host computer  12  is through a PCMCIA BUS interface or communication card  30 . 
     The nomadic router may also be used as an interface between a local area network  14  and a router  26  as illustrated in  FIG. 12E . Local area network  14  may be a mobile or portable network with router  26  being fixed at a particular location with a physical connection to the internet. Such an arrangement may be used for a customer demonstration or trade show, for example, where the local area network  14  is established among computers previously configured to communicate with each other but not with the foreign network having router  26 . 
     As shown in  FIG. 14 , the PCMCIA card can fit in a type III slot where there is a connector on nomadic router  10  which accepts communication card  30  (a type II PCMCIA card). In this mode, the nomadic router does not require internal communication device specific components. 
     Nomadic router  10  can also take the form of a type II PCMCIA card. In this form, the communication device or card  30  plugs into the opposite end of nomadic router card  10  as illustrated in  FIG. 15 . 
     Translation Operation of the Nomadic Router 
     Initialization and Self Configuration 
     The nomadic router initialization and self configuration process provides the means by which the nomadic router is able to learn about the host computer and network so it knows what translation is necessary. 
     Host Learning 
     Depending on the particular application, the nomadic router may have to learn the configuration of the host computer, the remote/foreign network, or both. For example, when utilized as a fixed nomadic router in a hotel or multiple dwelling unit, the nomadic router will have already learned (or been manually configured for) the remote/foreign network. The nomadic router need only determine the settings of mobile hosts which are subsequently connected to the network. Similarly, when the nomadic router is implemented as a PCMCIA card which travels with the mobile host, the nomadic router need only learn the settings of the foreign/remote network (since the host settings were previously learned or manually configured). In some applications, the nomadic router learns both the network and host configurations as previously described. 
     Nomadic router  10  is able to learn the host computer  12  configuration by looking at the content of the packets sent from host computer  12 . Rather than host computer  12  sending packets directly to router  26  or other network device (which is what it is initially configured to do), nomadic router  10  is able to redirect all outbound packets from the host computer  12  to itself. This redirection can be accomplished in several ways as described below. 
     1. Proxy ARP Packet Interception and Host Reconfiguration 
     Whenever a host computer  12  has an IP packet to send to router  26  or other network device, host computer  12  uses the Address Resolution Protocol (ARP) to obtain the link layer Media Access Control address (MAC address). As illustrated in  FIG. 8 , when host computer  12  broadcasts an ARP request for the MAC address of a destination node, nomadic router  10  intercepts this ARP request broadcast and responds with its own MAC address (rather than that of the destination node). 
     When host computer  12  receives the ARP reply from nomadic router  10  (which contains the MAC address of nomadic router  10 ), host computer  12  caches this MAC address and sends all packets destined for the configured router or network device to the MAC address of nomadic router  10 . Host computer  12  will think that the MAC address is that of its originally configured IP network device. However, nomadic router  10  is only pretending (proxying) to be the device (its home gateway) that host computer  12  expects to find. 
     Nomadic router  10  is also able to reconfigure and intercept return packets from a router or other network device using the same process. 
     2. Promiscuous Mode Packet Interception 
     Since the MAC address is cached in host computer  12  for a short period of time, host computer  12  will not send out a new ARP request to obtain the MAC address again unless a timeout period occurs or the cache is cleared, such as when computer  12  is restarted. 
     When a conventional network device receives or hears a packet with a MAC address which does not match its own, it will ignore or drop the packet. Since it is possible to rapidly switch from one network environment to another using a portable computer, nomadic router  10  must be able to intercept packets even when the MAC address is not that of the nomadic router&#39;s home gateway or device. 
     This is accomplished by placing the nomadic router&#39;s network connection in promiscuous mode. In this mode, the network connection on the nomadic router accepts all packets being transmitted on the communication link, not just ones being broadcast or addressed specifically to it. 
     3. Dynamic Host Configuration Protocol (DHCP) Service 
     Nomadic router  10  may also provide other network services to host computer  12 . For example, host computer  12  may be able to utilize the DHCP service to obtain configuration information rather than being manually configured. However, a host computer utilizing the DHCP service requires that a DHCP server be installed on the network segment to which it is currently attached. If host computer  12  is configured to use this service but a DHCP server is not available on the remote/foreign network, nomadic router  10  will intercept the DHCP requests and respond with configuration information for host computer  12  to use. 
     Network Learning 
     The nomadic router is able to learn about the network environment it is currently attached using several different methods as described below. 
     1. Dynamic Host Configuration Protocol (DHCP) 
     When the nomadic router is connected to a different network, it will broadcast a DHCP request to obtain configuration information for that network. If no DHCP service is available on the network, the nomadic router will use another method to learn about the network configuration. 
     2. Router Information Packets 
     For example, routers on the network will periodically broadcast router information packets which are used to build routing tables and allow routers to adapt to changes in the network. Nomadic router  10  will listen on the network for these router information packets. When a router information packet is received, the nomadic router will extract the configuration information from each packet and store the information for use in translating packets from the mobile host. 
     3. Passive Learning 
     By placing the nomadic router&#39;s network connection in promiscuous mode, the nomadic router receives all packets (not just ones addressed to the nomadic router). The nomadic router examines all packets received on the network interface to discover the network configuration. The nomadic router is also able to determine the IP addresses used on the current network and which machines are routers (by the final destination address not being the next hop address). 
     Using this method, nomadic router  10  is passively able to learn how the network is configured and will elect to use an unused IP address. If that IP address does become used by another network device, the nomadic router will switch over to another unused IP address. 
     4. Manual Configuration 
     The network configuration information can also be manually configured in nomadic router  10  as described above. This information can be set using an embedded web server, Simple Network Management Protocol (SNMP) tools, an application running on one of the computers in the network, or other suitable means. When manual configuration is used to set the network configuration, nomadic router  10  will still automatically learn the host information and provide all the translation capabilities so the host computers do not have to be aware of the correct network information of the LAN to which they are currently connected. 
     Packet Translation 
     After learning the network and/or host computer configuration(s), the nomadic router has the necessary information to translate packets transmitted/received by the host computer. The nomadic router&#39;s packet translation function provides a mapping between location and service dependent configurations used by host computer  12  and that used by network  14  to which it is currently attached. For outbound traffic from host computer  12  to network  14 , the translation function changes the content of the packet such as the source address, checksum, and application specific parameters, causing all packets sent out to network  14  to be directed back to nomadic router  10  rather than to host computer  12 . 
     Inbound traffic from network  14  arriving at nomadic router  10  (which is really for host computer  12 ), is passed through the translation function so host computer  12  thinks that the replies were sent directly to it. Host computer  12  will be completely unaware of all the translation being performed by nomadic router  10 . 
     The translation functions works as illustrated in  FIGS. 9   a  and  9   b . In these figures, the operations performed in the OSI/ISO model application, transport, network, link, and physical layers are illustrated in rows opposite the layer designations. The operations performed by host computer  12 , nomadic router  10  and network  14  are illustrated in columns below the device designations. 
     Host computer  12  will generate network packets using the current configuration stored in host computer  12  using the standard protocol stack as shown in step  1 . This configuration information is either manually configured in host computer  12  or obtained using DHCP (from the network or the nomadic router). 
     As shown in step  2 , when host computer  12  attaches the link level destination address (automatically obtained using the Proxy ARP packet interception routine described earlier), host computer  12  will send the packet to the network address of its standard router or home gateway device using the link level address of the nomadic router  10 . 
     In step  3 , the packet is transmitted across the standard physical connection between host computer  12  and nomadic router  10 . As shown in step  4 , nomadic router  10  will receive the packet at the link level either because the Proxy ARP function reconfigured the host computer&#39;s MAC address, or because nomadic router  10  has the network link level in promiscuous mode which causes it to receive the packet even if addressed to a different MAC address. 
     Once the packet is passed to the network layer, shown in step  5 , the nomadic router translation function will modify the content of the packet to change the source address to match that of the nomadic router&#39;s address instead of the host computer&#39;s address. It will also translate other location dependent information such as the name of the local Domain Name Service (DNS) server. When translating the DNS packet, it will change the source address to that of the nomadic router&#39;s address and the destination address to that of a local DNS server. 
     Once the network layer translation is complete, the packet can be translated at the application and transport layers. The application layer is translated next, as shown in step  6 , because the transport layer required a pseudo-network layer header which includes the course and destination addresses and the content from the application layer. 
     At the application layer translation, any addresses which describe the source address of the host computer, such as with FTP, are translated to be that of the nomadic router&#39;s address. Any application layer destination addresses, such as a local proxy server, are translated to match that of the server running on the current network. 
     Once this application layer translation is complete, the transport layer, as shown in step  7 , can complete the checksum and any port number manipulation. The port number is manipulated if more than one host computer  12  is attached to nomadic router  10 . Each request sent by any one of the host computers  12  include a specific port that is translated to match an available inbound port on the nomadic router  10 . 
     The port number assigned for use with each host computer  12  is stored in a table in nomadic router  10  and is utilized with the reply packet to route the reply to the corresponding host computer as describer later. Finally, the outgoing packet is transmitted over network  14  in step  8 . 
     When a reply packet is transmitted over network  14 , as shown in step  9 , nomadic router  10  will receive the packet. In step  10 , nomadic router  10  will perform the reverse network layer translation to set the destination address to that of host computer  12  rather than the nomadic router&#39;s address, and any source address to the source address replaced by nomadic router  10  in step  5 . 
     Once network translation is complete, the packet is translated at the application layer, as shown in step  1 , to change the destination address to that of host computer  12  and the source address to the original destination address stored from step  6 . In step  12 , any port manipulation performed in step  7  is changed to the original setting and a new checksum is computed. Finally, as shown in step  13 , the packet is sent to host computer  12  which then processes the packet normally. 
     Options of the Nomadic Router 
     There are numerous options and applications of the nomadic router. These applications include, but are not limited to, Nomadic E-mail, Remote Network File Synchronization, Nomadic Database Synchronization, Instant Network Nomadic Routing, Nomadic Intranets, and Trade Show Data Exchange. Each of these are described in more detail below. 
     Nomadic E-Mail 
     The Nomadic E-mail application provides a synchronized yet distributed means for updates, reconciliation, and replicas to propagate through the internet. Nomadic routers are located on various networks of the internet and are equipped with nomadic E-mail support to provide synchronization, etc. Each nomadic router enabled for nomadic E-mail can utilize protocols such as IMAP to provide support for mobile users without the host device having to support it (similar to the POP3 protocol standard in internet E-mail clients). 
     Remote Network File Synchronizer 
     The Remote Network File Synchronization option of the nomadic router provides copies of user files that are stored/cached at various locations (e.g., hotel, office, home) on other nomadic routers equipped for remote network file synchronization. Copies of updated files are automatically synchronized and distributed among all peer locations. Local updates can be made while the host is disconnected from the nomadic router and from the network. 
     Nomadic Database Synchronizer 
     The Nomadic Database Synchronizer houses the user&#39;s (synchronized) master databases (e.g., contacts, addresses, phone numbers). The nomadic router of the database synchronizer does not need to be used on the network because it will interface directly with various host devices such as laptops, desktops, personal digital assistants, handheld personal computers, pagers, etc. via various standard ports. 
     Instant Network Nomadic Router 
     The objective of the instant network nomadic router is to enable rapid deployment of a communication network in any environment with little or no fixed infrastructure. The host and communication devices do not have to directly support the rapid deployment functionality. 
     The instant network nomadic router distributedly and intelligently establishes a wireless (or wired) communication link between the host device and the desired communication system while performing configuration, security, multihop routing, and network level data transmission over various communication devices. The nomadic router performs all the necessary network creating and processing automatically to remove configuration and system support from the host system or user. The instant network nomadic router utilizes proprietary and existing/emerging wireless communication systems, and multihop routing protocols. 
     Many communication infrastructures are varied and fragmented, which is likely to be exacerbated as more technologies are introduced. For example, high performance LANs, wireless services, cellular telephony, satellite, and ubiquitous paging networks, all provide varying degrees of coverage, cost, and bandwidth/delay characteristics. 
     Conditions may range from no connectivity at all because of lack of service, to partial and/or intermittent connectivity as devices are plugged and unplugged from a system. Likewise, damage to communications infrastructures (deliberately or by accident), lossy communication as a system moves through various service areas or difficult domains, and times when multiple network devices (communication substrates) can be used at the same time complicate connectivity. The instant network nomadic router will dynamically adapt the communication internetwork (dynamically creating one if necessary) to provide survivable communication in a mobile chaotic environment without the need for centralized control or fixed infrastructures. 
     The rapidly deployable nomadic router is a device associated with each user host device (e.g., PDA or laptop computer). It transparently provides the following capabilities for host computer systems using various wireless communication devices for physical and link layer access: dynamic wireless network creation; initialization into existing wireless networks; automatic configuration; network and subnetwork level data transmission; and multihop routing functionality. 
     The nomadic router can detect another device by polling the interface, providing an interrupt signal, or through specialized signaling. This in turn activates the nomadic router to provide translation for the device (if necessary) and establish a communication link to an appropriate corresponding interface and wireless subnetwork. The nomadic router operates at a level between the host device generating data and the physical communication transmission device as illustrated in  FIG. 1 . 
     Nomadic Intranet 
     The Nomadic Intranet application provides all network and server type services for users to dynamically create an adhoc network. This is similar to the instant network nomadic router except the nomadic intranet is a single device with multiple ports into which laptop/devices can be plugged. The instant network nomadic router is distributed to each host device. The nomadic intranet not only provides adhoc networking but can also provide services such as temporary file storage, protocol conversion, act as a print server, and provide other services described as part of the Basic nomadic router. 
     Trade Show Nomadic Router 
     The Trade Show nomadic router applications not only provide the basic nomadic router functionality for an exhibitor&#39;s computer that is brought to the show, but also provides lead capture and/or information distribution. Lead capture can be provided by interfacing with a badge reader to read attendees&#39; information. This information is then captured by the nomadic router and made available in the exhibitor&#39;s lead database. 
     The nomadic router can also provide a mechanism for distributing information to the attendees&#39; personalized web pages or sent via e-mail directly across the internet. The exhibit&#39;s computer is able to control the information flow with the nomadic router by running software, such as a web browser, which talks with the service/control software stored in the nomadic router. The standard web browser can control display and capture of lead information, collection of qualification information, and selection of information to be distributed back to the attendee. 
     Fixed Nomadic Router 
     As briefly described above, the fixed nomadic router applications provide the same basic functionality and architecture as the portable nomadic router with the nomadic router stored in one location. The fixed nomadic router acts as a surrogate or “Home Agent” for the user when he/she is away on travel. When the user wishes to register or utilize their host device elsewhere in the network, the portable nomadic router will register with the fixed nomadic router where it is temporarily attached to the network so information can be forwarded to the user&#39;s new location. The fixed nomadic router can also be used to house the master copy of the user&#39;s E-mail for the nomadic E-mail service, or files for the nomadic file synchronizer. 
     Mobile Virtual Private Network 
     The nomadic router provides the mapping between the location-based IP address used in the internet today and the permanent user-based address housed in the host CPU. This mapping is done without support or knowledge of such mapping by the host CPU or user. The Internet RFC 2002 Mobile IP protocol specifies the mapping between permanent and temporary IP addresses. The unique aspect of the nomadic router is that the Mobile IP protocols are not necessarily running in, or supported by, the host CPU, but rather are internal to the nomadic router. 
     By implementing this protocol as part of the translation function in the nomadic router, the nomadic router can encapsulate packets from the host computer and transmit them back to the fixed nomadic router which are sent out (un-encapsulated) on the native (home) network. Replies from the home network are received by the fixed nomadic router and are encapsulated and sent back to the nomadic router. When packets are transmitted between the nomadic router and fixed nomadic router, the packets are encrypted and sent using the Internet Tunneling Protocol. 
     Since the (mobile) nomadic router provides location independence and the fixed nomadic router forwards all packets from a corresponding host to the host computer via the nomadic router, any changes in the location, failure of a network link, or attachment point of the mobile host computer does not cause any open session to be lost. This session loss prevention is possible since the fixed nomadic router pretends to be the mobile host computer, and the nomadic router pretends to be the home network. The fixed nomadic router and nomadic router translation functions hide the link and network loss from the transport and application session. 
     While embodiments of the invention have been illustrated and described, it is not intended that these embodiments illustrate and describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention. It is understood that the present invention is broadly applicable to the field of electronic data communications using computers and other devices.