US 6,154,461 AGrant
Seamless Roaming Among Multiple Networks
Issue Date:2000-11-28
•22 Claims
•9 Drawing Sheets
Abstract
The present invention relates to wireless communication systems involving multiple local area networks. A communication system according to the present invention includes a plurality of local area networks (LANs). Each of the LANs includes: a network backbone; and at least one access point coupled to the network backbone which, when a mobile terminal is registered to the access point, enables the mobile terminal to communicate wirelessly with a device on the network backbone via the at least one access point. When the mobile terminal is registered to at least one access point in one of the plurality of LANs the mobile terminal is assigned a first network address, and when the mobile terminal is registered to at least one access point in another of the plurality of LANs the mobile terminal is assigned a second network address in place of the first network address, the second network address being different from the first network address. The mobile communication system also includes a system backbone interconnecting the plurality of LANs for permitting communications between the plurality of LANs. Furthermore, the system includes a gateway controller, operatively coupled to one of the plurality of LANs, for serving as an intermediary for communications between the mobile terminal and a device on one of the system backbones in order that in the event the mobile terminal is assigned a different network address by virtue of registering with an access point in another of the LANs, the device is able to maintain communications with the mobile terminal without requiring knowledge of a change in the network address of the mobile terminal.
Metadata
Assignee
- Telxon Corporation
Inventors
- Emil A. Sturniolo
- Frank D. Ciotti, Jr.
- Krishna P. Seshadri
Application Information
Application Number:US 8561222
Filing Date:1997-05-14
Priority Date:1997-05-14
Art Unit:271
Classifications
IPC:
H04L 1246
Field of Search:
370455310;328;338;401;402;403;404;349;473432;550;556;561;575
Patent Drawings (9 sheets)
Description
Technical Field
The present invention relates generally to wireless mobile communication systems, and more particularly to mobile communication systems involving multiple local area networks (LANs).
Background of the Invention
In recent years, the use of wireless mobile communication systems has become increasingly popular. For example, wireless mobile terminals now serve to help automate and expedite processes in retail, manufacturing, warehousing and other industries. In a retail environment, wireless mobile terminals may take the form of a wireless bar code reading device for use in tracking inventory and checking prices. In the warehousing industry, the same mobile terminals may be used to keep accurate accounting of incoming and outgoing shipments. In health care, transportation and other industries, the mobile terminals may take the form of wireless pen based computers to aid with on-site document control procedures, etc. In order to provide for real time communication, the mobile terminals often include a radio which allows them to communicate with a host computer connected to a LAN, for example.
LANs typically allow for connecting of devices operating in a building or specified site. Devices physically connected to the LAN may include desk top computers, printers and host computers. If the LAN also supports wireless mobile terminals such as those mentioned above, the LAN will also have connected thereto one or more access points (sometimes referred to as base stations). Each access point is coupled to the LAN and includes at least one radio through which wireless communication with the mobile terminals can occur.
Each access point can communicate with mobile terminals operating within the cell coverage area of the access point. The cell coverage area is the area in which the access point can reliably communicate with a mobile terminal. Once the mobile terminal roams outside of the cell coverage area of the access point, the mobile terminal can no longer communicate with the LAN through that particular access point. In order to provide cell coverage throughout an entire building or site, a LAN typically includes multiple access points strategically located throughout the building or site. Thus, the combined cell coverage of the access points is sufficient to cover the entire building or site. Mobile terminals may then roam from one area to another within the LAN.
As a mobile terminal roams throughout a LAN, it is important that an end to end session established between the mobile terminal and a device coupled to the backbone be maintained as the mobile terminals move from one cell to another cell. Known techniques for providing such seamless roaming from one access point to another access point within a given LAN are described in U.S. Pat. No. 5,276,680, for example.
However, recent trends have shown a desirability for mobile terminals to be able to roam not only within a given LAN, but also among different LANs and/or wide area networks (WANs). Although there are known techniques for allowing mobile terminals to roam seamlessly from one access point to another within a given LAN, this does not include the ability for mobile terminals to roam seamlessly from LAN to LAN, or LAN to WAN, for example. According to current technology, when a mobile terminal wishes to roam from one LAN to another the mobile terminal typically must disassociate itself from one LAN and reassociate itself with another LAN. This break in communication makes it difficult for information originating from the former LAN to be forwarded to the mobile terminal in the new LAN. Such difficulty adds overhead such as time and complexity associated with establishing a new connection.
Further, regardless of whether a mobile terminal roams to different LANs or WANs, information may also be lost if a connection (also referred to as a session) between the mobile terminal and some device on the LAN terminates for whatever reason. Such termination of a session may occur, for example, due to the mobile terminal not responding to communication from the device on the LAN due to the mobile terminal having roamed out of coverage area or because the mobile terminal is in a power savings mode.
In view of the aforementioned shortcomings with conventional techniques, it will be appreciated that there is a strong need in the art for a wireless mobile communication system which provides for seamless roaming among different networks. In particular, there is a strong need in the art for a system which provides for seamless roaming between different LANs each forming part of a WAN.
Summary of the Invention
The communication system of the present invention introduces a gateway controller (hereinafter referred to simply as a "gateway") connected to at least one network such as a LAN or WAN. Each gateway functions as an intermediary for communications between mobile terminals registered to an access point within a network or otherwise coupled to the network and one or more other devices. By serving as an intermediary, the actual network addresses of the mobile terminals become transparent to the devices with which the mobile terminals are communicating. As a result, even if a mobile terminal roams from one LAN to another LAN and receives a new network address, communications between the mobile terminal and the other devices are not interrupted so as to provide for seamless roaming.
A primary difficulty in providing seamless roaming between different LANs and/or WANs had been the ability of the different networks to properly identify a mobile terminal as the same device. When the mobile terminal associates itself with a different network, a server on the network typically supplies the mobile terminal with a new network address (ID) from its list of available IDs. Since devices in the network with which the mobile terminal was previously communicating with ordinarily would not know the new network address of the mobile terminal, seamless roaming was difficult. With the gateway of the present invention, however, it is not necessary for the devices to know the new network address of the mobile terminal. The gateway routes the communications between the mobile terminals and the respective devices such that there is no need to first inform the devices of the new network address. Thus, by use of the gateway, seamless mobile terminal roaming is achieved.
According to one particular aspect of the invention, a communication system is provided, including: a plurality of local area networks (LANs), each of the LANs including: a network backbone; and at least one access point coupled to the network backbone which, when a mobile terminal is registered to the access point, enables the mobile terminal to communicate wirelessly with a device on the network backbone via the at least one access point; wherein when the mobile terminal is registered to at least one access point in one of the plurality of LANs the mobile terminal is assigned a first network address, and when the mobile terminal is registered to at least one access point in another of the plurality of LANs the mobile terminal is assigned a second network address in place of the first network address, the second network address being different from the first network address; a system backbone interconnecting the plurality of LANs for permitting communications between the plurality of LANs; and a gateway controller, operatively coupled to one of the plurality of LANs, for serving as an intermediary for communications between the mobile terminal and a device on one of the system backbones in order that in the event the mobile terminal is assigned a different network address by virtue of registering with an access point in another of the LANs, the device is able to maintain communications with the mobile terminal without requiring knowledge of a change in the network address of the mobile terminal.
In accordance with another aspect of the invention, a gateway controller for use in a mobile communication system including a plurality of local area networks (LANs), each of the LANs including a network backbone; and at least one access point coupled to the network backbone which, when a mobile terminal is registered to the access point, enables the mobile terminal to communicate wirelessly with a device on the network backbone via the at least one access point is provided, the gateway controller including: means for operatively coupling the gateway controller to the network backbone of a selected one of the plurality of LANs; a gateway address circuit for communicating with a mobile terminal registered with the access point of the selected LAN via the network backbone for establishing indica distinguishing the mobile terminal from among other mobile terminals; a communication circuit for receiving communications from the registered mobile terminal intended for the device and forwarding the received communications to the device together with at least part of the indicia as provided by the communication circuit, and for receiving communications, including the at least part of the indicia, from the device intended for the registered mobile terminal and forwarding the received communications to the registered mobile terminal based on the at least part of the indicia.
According to yet another aspect of the invention, a network communication system is provided, including: a plurality of local area networks (LANs), each of the LANs including: a network backbone; and at least one access point coupled to the network backbone which, when a mobile terminal is registered to the access point, enables the mobile terminal to communicate wirelessly with the network backbone via the at least one access point; a system backbone interconnecting the plurality of LANs for permitting communication between the plurality of LANs; and a gateway controller, operatively coupled to one of the plurality of LANs and able to communicate with devices on other of the plurality of LANs via the system backbone, the gateway controller serving as an intermediary for communications between the mobile terminal and a device on a first of the plurality of LANs; the gateway controller assigning a gateway address to the mobile terminal such that once the mobile terminal starts a session with the device coupled to the first of the plurality of network backbones, the mobile terminal may continuously maintain the session through the gateway even if the mobile terminal registers with an access point coupled to another of the plurality of network backbones.
To the accomplishment of the foregoing and related ends, the invention, then, comprises the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative embodiments of the invention. These embodiments are indicative, however, of but a few of the various ways in which the principles of the invention may be employed. Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings.
Brief Description of the Drawings
FIG. 1 is a block diagram of a wireless mobile communication system in accordance with the present invention;
FIG. 2 is a flowchart describing, in relevant part, the general operation of the mobile communication system in accordance with the present invention;
FIG. 3 is a schematic diagram showing a general format of an information packet in accordance with the present invention;
FIGS. 4a-4j are schematic illustrations representing an exchange of packets for establishing a virtual circuit, session and socket connection between a mobile terminal and another device on the network in accordance with the present invention;
FIGS. 4k-4o are schematic illustrations representing an exchange of data between a mobile terminal and another device before and after the mobile terminal moves from one LAN to another LAN;
FIG. 5a represents a virtual circuit table maintained in memory by each mobile terminal for keeping track of the various virtual circuits which have been established through a gateway with different devices in accordance with the present invention;
FIG. 5b represents a corresponding virtual circuit table maintained in memory by each gateway for keeping track of the various virtual circuits which have been established through the gateway between various mobile terminals and devices in accordance with the present invention;
FIG. 6 is a block diagram of a mobile terminal in accordance with the present invention;
FIG. 7 is a block diagram of an access point in accordance with the present invention; and
FIG. 8 is a block diagram of a gateway in accordance with the present invention.
Description of the Preferred Embodiment
The present invention will now be described with reference to the drawings wherein like reference numerals are used to refer to like elements throughout.
As is mentioned above, the present invention relates to wireless communication systems which include mobile terminals that can roam from cell to cell and from LAN to LAN. Such mobile terminals can be data terminals, telephones, pagers, etc. In the exemplary embodiment described hereinafter, each mobile device is a mobile data terminal (hereinafter "mobile terminal") used to communicate data such as inventory or the like within a communications system such as a cellular communication system. However, it is recognized that the invention contemplates other types of mobile terminals and is not intended to be limited to systems utilizing mobile data terminals. Other types of mobile terminals may be referred to in the industry as a mobile end system, mobile node, or mobile client, for example.
Referring now to FIG. 1, a communication system 20 is shown in accordance with the exemplary embodiment of the present invention. The communication system network 20 includes a plurality of LANs (e.g., LAN1-LAN3) each coupled together via a network backbone 26. Each LAN1-LAN3 itself forms a communication network. The LANs are interconnected according to generally known network principles by way of a system backbone 24, and specifically in the present embodiment by a WAN system backbone 24. It shall be appreciated, however, that the system backbone 24 need not be wireless in nature but rather hardwired such as those achieved by connecting to an intranet or internet, for example, which could also serve as the system backbone 24.
Each of the LANs (LAN1-LAN3) have generally the same configuration, hence only LAN1 will be described in detail. However, it will be appreciated that there may be variations in the respective LANs without departing from the scope of the invention. Referring initially to LAN1, the local area network comprises its own network backbone 26. The network backbone 26 may be a hardwired data communication path made of twisted pair cable, shielded coaxial cable or fiber optic cable, for example, or may be wireless in nature. Connected to the network backbone 26 are several access points 28, only one of which is shown (namely, access point AP1) for sake of illustration. Each access point 28 serves as a point through which wireless communications may occur with the network backbone 26. Additionally, in order to expand the effective communication range of the access points 28, one or more wireless access points (not shown) also may be included in LAN1.
Each access point 28 is capable of wirelessly communicating with other devices within its cell coverage via an antenna 32. As is known, depending on the type of antenna 32 selected and the output power of the respective access point 28 the cell coverage of the access point 28 may take any of several different forms and sizes. For example, FIG. 1 depicts the access point 28 as utilizing an omni-directional antenna 32 wherein a generally spherical cell area of coverage is obtained. However, a directed yagi-type antenna or other form of antenna could also be used as will be readily appreciated.
The LAN1 also includes one or more mobile terminals 36. For sake of example, only one mobile terminal 36 is shown although it will be appreciated that each LAN is likely to have several mobile terminals 36 associated therewith. Each mobile terminal 36 communicates with devices on the network backbone 26 of the LAN in which it is registered or, as described below, is capable of communicating with devices on the network backbone 26 of other LANs within the WAN. Within a given LAN (e.g., LAN1), the mobile terminal 36 may roam from one cell to another as covered by different access points 28. While roaming within a given LAN, the mobile terminal 36 is configured to associate itself with a new access point 28 in each new cell area according to conventional techniques. The mobile terminal 36 communicates with the network backbone via wireless communications through the access point 28.
According to the present invention, however, mobile terminals 36 also can seamlessly roam from one network to another network without a need to terminate and reestablish an end to end session between the mobile terminal 36 and a device coupled to one of the networks. For example, FIG. 1 illustrates in phantom the manner in which a mobile terminal 36 roams from LAN1 to LAN2. Specifically, the mobile terminal 36 originally is registered to an access point 28 (AP1) in LAN1. The mobile terminal 36 originally has a network identification or address which has been assigned to it by virtue of being registered within LAN1. However, when the mobile terminal 36 moves outside of the cell coverage of access point AP1 and into the cell coverage of an access point 28 (AP2) included in LAN2, the mobile terminal 36 newly registers with the access point AP2. As a result, the mobile terminal 36 receives a new network identification or address by virtue of becoming registered within LAN2.
Since the devices which the mobile terminal 36 had been communicating with in LAN1 would not know the new address assigned to the mobile terminal 36 upon moving to LAN2, the present invention provides a means for compensating for such lack of knowledge. Specifically, in the present embodiment each LAN also includes a gateway 40 which serves as an intermediary for communications between the mobile terminal 36 and other devices within the system 20. However, it will be appreciated that only one gateway 40 need be connected to one of the network backbones 26 to carry out the present invention. Mobile terminals registered with access points 28 on a network backbone 26 other then the network backbone 26 the gateway 40 is connected to would communicate with the gateway 40 via the system backbone 24 discussed above. As is described more fully below, for each mobile terminal 36, a virtual circuit is established between itself and the gateway 40. Although the network address of the mobile terminal 36 may change as a result of the mobile terminal 36 roaming from one LAN to another LAN, the relevant parameters of the corresponding virtual circuit remain the same. Hence, communications between the mobile terminal 36 and a given device are properly routed notwithstanding the change in the network address of the mobile terminal 36. In fact, in the preferred embodiment the devices with which the mobile terminal 36 is communicating remain unaware that the mobile terminal 36 has received a new network address. The manner in which such seamless roaming is carried out is described in more detail below in relation to FIGS. 2-5.
Also connected to the network backbone 26 of each LAN is a host computer 42 and a domain name server 44. The host computer 42 performs conventional host functions within the respective LAN. In addition, the host computer 42 serves as an interface connection to the system backbone 24 in a conventional manner. Of course, the gateway 40 or any other LAN device could alternatively serve as an interface connection to the system backbone 24. The domain name server 44 in each LAN performs the conventional function of providing a name to network address mapping for devices within each LAN. Furthermore, each LAN may include one or more other devices connected to the network backbone 26. Although not shown, such devices may include work terminals, printers, cash registers, etc.
Turning now to FIG. 2, the basic operating protocol for a mobile terminal 36 roaming between LANs is shown in accordance with the invention. For sake of example, it is assumed that the mobile terminal 36 initially powers up and registers within the cell area of an access point 28 (AP1) belonging to LAN1. Thereafter, the mobile terminal 36 will move to LAN2 as represented in FIG. 1 and register with access point AP2 in LAN2. It will be appreciated, however, that the same principles are applied when roaming between any two LANs.
Referring initially to step 50, the mobile terminal 36 is powered up and/or reset within the cell coverage of access point AP1. Next, in step 52 the mobile terminal 36 registers with the access point AP1 using any of several known conventional techniques, for example. By registering, the access point AP1 assumes responsibility for receiving wireless communications from the mobile terminal 36 and forwarding the communications onto the network backbone 26. Similarly, the access point AP1 assumes responsibility for receiving communications on the network backbone 26 which are destined for the mobile terminal 36. The access point AP1 then forwards such communications wirelessly to the mobile terminal 36.
Next, in step 54 the mobile terminal 36 obtains a network identification (ID)/address. Such network ID may be obtained via any of several known conventional techniques in which a unique network ID is assigned to each particular mobile terminal 36 within the LAN1. In some instances, the network ID and/or port ID may be statically preconfigured within the mobile terminal 36. In the exemplary embodiment, the mobile terminal 36 in step 54 obtains a network ID which includes a network address and port in accordance with conventional network protocol(s). The mobile terminal 36 also obtains the gateway 40 network ID and port ID in a similar fashion. Alternatively, the mobile terminal 36 may first obtain a link layer ID in accordance with the technique described in commonly assigned, co-pending U.S. patent application Ser. No. 08/778,405, filed Jan. 2, 1997 and entitled "Mobile Device ID Allocation System and Method" which in turn could be used to obtain a network ID. The disclosure of the '405 application is incorporated herein by reference.
Following step 54, the mobile terminal 36 in step 56 determines if any application program running on the mobile terminal 36 is currently attempting to communicate information to a device on the network backbone 26. If the mobile terminal 36 determines that no information currently needs to be transmitted, the mobile terminal goes to step 57 where it continues all of its other normal operations and returns again to step 56. If, however, the mobile terminal 36 does wish to communicate information to a device on the network, the mobile terminal 36 proceeds to step 58.
In step 58, the mobile terminal 36 determines if there is an existing session for the mobile terminal 36 to transmit the information it desires. As discussed in more detail below, the mobile terminal 36 may have already established a session with GATEWAY1 to communicate information to other devices throughout the communication system 20. If the mobile terminal 36 determines that a session is established for this information it desires to transmit then the mobile terminal 36 continues to step 60. If not, the mobile terminal 36 continues to step 62 where the mobile terminal determines if a virtual circuit has been established for transmitting the information.
Prior to being able to transmit the information to a device on the network, the mobile terminal 36 must, in step 60, determine if a socket end point is established (via GATEWAY1) to the device the mobile terminal 36 desires to communicate. Socket end points are frequently established and ended between a mobile terminal 36 and a device on the network and it may even be the case that more than one socket end point is established between a given mobile terminal 36 and a given device to accommodate the transfer of data between application programs running on each. Thus, in step 60, if a socket end point which is able to handle the transfer of current information from the mobile terminal 36 to the device is not established, the mobile terminal establishes such a socket end point. The socket end point is established based on an exchange of a series of packets between the mobile terminal 36 and GATEWAY1. This process is described below in connection with FIGS. 4g-4j. Once the socket is established, communications between the mobile terminal 36 and the device occur in step 67. The communications occur via GATEWAY1 serving as an intermediary. An example of such communication is described below in association with FIGS. 4k-4n. It is noted that in this example, the mobile terminal 36 initiated a connection oriented socket end point with the device it desired to communicate, however, connectionless oriented socket end point associations could also be established using conventionally known protocols such as UDP.
If in step 58, the mobile terminal 36 determines that there is not an existing session to transfer the current information to the device the mobile terminal 36 will have to establish such a session. However, prior to establishing such a session, the mobile terminal 36 in step 62 determines if a virtual circuit exists between a mobile terminal 36 and one or more other devices within the communication system 20. As will be described below, each virtual circuit in the preferred embodiment can include up to a predefined number of sessions. Each session, in turn, consists of up to a predefined number of sockets. The predefined number of session and sockets available are each typically of a very large magnitude (i.e. 2.sup.16) and therefore are often considered unlimited. If a virtual circuit already exists for transferring the current information as determined in step 62, the mobile terminal 36 goes to step 64 where it will establish a session within this virtual circuit prior to transferring the information to the device. If a virtual circuit does not exist, the mobile terminal 36 will have to first establish the virtual circuit before establishing the session as discussed below with respect to step 66.
Turning to step 64, a session is established in accordance with the present invention by exchanging a series of information packets between the mobile terminal 36 and GATEWAY1 as discussed below in relation to FIGS. 4c-4d and 5a-5b. If necessary address information for the particular device with which the mobile terminal wishes to communicate may be obtained using well known name resolution techniques. For example, the mobile terminal 36 may want to communicate with the host computer 42 (HOST1) in LAN1. As discussed below in connection with FIGS. 4e-4f, the mobile terminal 36 and GATEWAY1 exchange a series of packets which results in GATEWAY1 providing the mobile terminal 36 with the network address of the host computer HOST1. Once the session is established and the address of the particular device is determined, the mobile terminal continues to step 60 where a socket end is established.
If in step 62, the mobile terminal 36 determines that no virtual circuit exists for transferring the present information to the device, or if the mobile terminal 36 simply wishes to establish a new virtual circuit, the mobile terminal 36 goes to step 66. In step 66, a virtual circuit between the mobile terminal 36 and GATEWAY1 is established. As described below with respect to FIGS. 4a-45 and 5a-5b, the mobile terminal and GATEWAY1 exchange a series of information packets which establishes a virtual circuit entry in corresponding tables stored therein. The virtual circuit is used to identify a particular communication connection between the mobile terminal 36 and GATEWAY1 through which connections may be established with devices which the mobile terminal 36 wishes to communicate. Following the establishment of a virtual circuit in step 66, the mobile terminal continues to steps 64 and 60 where a session and socket are next established, respectively, within the virtual circuit.
Once a virtual circuit, session, and socket end point is established and the information is transmitted in step 67, the mobile terminal goes to step 68 to determine if any virtual circuits are to be terminated.
For example, the mobile terminal 36 may conclude that it no longer needs to communicate with the host computer HOST1 and wishes to terminate the connection. Alternatively, there may be a predefined time limit placed on the duration of each virtual circuit and thus all corresponding sessions. Accordingly, the GATEWAY1 may be responsible for serving as a timekeeper and determining when a virtual circuit is to terminate. The GATEWAY1 in such instance is responsible for informing the mobile terminal 36 that the virtual circuit is about to be terminated. If a virtual circuit is to end as determined in step 68, the system proceeds to step 70 in which the corresponding session and socket connection entries in the tables of the mobile terminal 36 and the GATEWAY1 are cleared as will be better understood in view of the discussion of FIGS. 5a-5b below.
If in step 68 the session has not ended, the system proceeds to step 72 in which the mobile terminal 36 determines it has moved to a new LAN (e.g., LAN2). The manner in which the mobile terminal 36 determines if it has moved to a new LAN can be based on known conventional techniques for determining entry to a new LAN. For example, such determination can be based on the known mobile internet protocol defined in Internet Engineering Task Force (IETF) Spec. R.F.C. 2002. Generally speaking, the mobile terminal 36 upon roaming from LAN1 to LAN2 will proceed beyond the cell coverage of AP1 in LAN1 and will not be able to register with any other access points 28 within LAN1. Hence, the mobile terminal 36 will conclude that it has roamed from the previous LAN (LAN1) to a new LAN (e.g., LAN2) with which it must newly register. It is noted that the steps of determining if a virtual circuit has ended (step 68) and the step of determining if the mobile terminal 36 roamed to a new LAN (step 72) may occur at any instant throughout the process described in FIG. 2 and is only shown at its current locations for discussion purposes only.
If the mobile terminal 36 concludes it has roamed to a new LAN, the mobile terminal 36 proceeds to step 74 in which it registers with an access point 28 (e.g, AP2) in the new LAN (e.g., LAN2) in the same manner as was done in step 52. Assuming the mobile terminal 36 has roamed within the cell coverage of the access point AP2, the mobile terminal 36 will thus be able to register with the access point AP2. Next, in step 76 the mobile terminal 36 obtains a new network ID pertaining to the new LAN2. Step 76 is similar to step 54 described above in that the mobile terminal 36 uses conventional techniques to obtain a unique network ID within its local network LAN2. There may or may not be communication between the different LANs 1-3 regarding the particular network IDs assigned to the mobile terminals 36 and the network IDs of the mobile terminals 36 are not fixed in the preferred embodiment. Thus, the new network ID of the mobile terminal 36 in step 76 may be different from the network ID assigned in step 54 in virtually every case.
Nevertheless, the virtual circuit, session, and socket connection information previously obtained via the GATEWAY1 is still valid despite the mobile terminal 36 receiving a new network address in step 76. Thus, packets delivered to the GATEWAY1 for routing to the mobile terminal 36 still may be routed to the mobile terminal 36 by the GATEWAY1 as discussed below in connection with FIG. 4o. Accordingly, the system returns to step 66 in which communications can be continued to be carried out seamlessly. If, on the other hand, the mobile terminal 36 does not roam to a new LAN as determined in step 72, the system returns directly to step 56. It is noted that under certain circumstances it may be the case that the mobile terminal 36 ends its session with a host computer or other device without the device knowing the session has ended and therefore communication destined for the mobile terminal 36 in such cases would not be forwarded on the GATEWAY1.
Turning now to FIG. 3, a standard packet format for information communicated in the system 20 is shown. The packet format shown in FIG. 3 includes a number of different fields, some or all of which may be present in a given packet at a given time. The packet consists primarily of a header portion 80 and a payload portion 82. The header portion 80 is included in all communications in the respective LANs. The payload portion 82 ordinarily is reserved for data being transferred between two or more devices communicating in a given LAN. According to the present invention, however, the payload portion 82 also is used to communicate information regarding the particular virtual circuit, session, socket, etc. As will be appreciated, this allows the present invention to be carried out in a manner which is transparent to most devices on the network with the exception of the gateway 40 and mobile terminals 36. Thus, the present invention can be incorporated into existing systems with only minor modifications.
As shown in FIG. 3, each packet includes a source address (SA) field which identifies the network address of the device transmitting the packet. In addition, each packet includes a destination address (DA) field which identifies the network address of the device to which the packet is being transmitted. Next, the packet includes a source port (SP) field and destination port (DP) field which identify the ports of the devices transmitting and receiving the packet, respectively. Within the payload portion 80, the packet may include a globally unique identification (GUID) field used for uniquely identifying a GUID associated with the mobile terminal 36 transmitting the packet. A virtual circuit identification (VCID) field is used for identifying a particular virtual circuit associated with the packet transmission. A flag (FLG) field is used to indicate a change in the network identification of the mobile terminal 36 as will be described below. Similarly, a session identification (SID) field and socket identification (SOID) field are used for identifying the particular session and socket, respectively, associated with the packet transmission as will be explained below.
A command (CMD) field is included in the packet for identifying particular functions to be carried out as will be described by way of example below. A data (DTA) field is used for containing data which is to be transmitted in accordance with the invention.
According to conventional communication network routing protocol, information packets ultimately are routed to the destination address and destination port identified in the DA and DP fields, respectively. With regard to packets which are transmitted from the mobile terminal 36, each access point 28 is configured to recognize a packet which is being transmitted from a mobile terminal 36 which is registered thereto. The access point 28 in turn receives the packet via its antenna 32 and retransmits its contents onto the network backbone 26 according to known convention. As far as packets which are destined for the mobile terminal 36, the access point 28 receives such a packet off the network backbone 26 and retransmits the information to the mobile terminal 36 via its antenna 32 according to known convention.
With the exception of the mobile terminals 36, the locations of all fixed devices on the respective LANs 1-3 and WAN 22 are essentially known based on conventional network routing protocol. In other words, provided a current network identification is known for a device, a packet will be delivered to the device via appropriate routers, etc. Thus, for example, the access point AP2 in LAN2 can transmit a packet to GATEWAY1 in LAN1 via the WAN backbone 24 according to conventional techniques. Hence, details regarding the communications between the fixed devices on the respective LANs will not be described in detail for sake of brevity.
Referring now to FIGS. 4a-4b, the manner in which a virtual circuit is established (FIG. 2, step 56) will be described. In the present example, the mobile terminal 36 initially registers to the access point AP1 in LAN1 as shown in FIG. 1. Next, as shown in FIG. 4a, the newly registered mobile terminal 36 generates and wirelessly transmits a packet 86 to the local gateway 40 (GATEWAY1). Using conventional techniques, the mobile terminal 36 retrieves its network ID and that of the gateway's 40 if such IDs are not already statically programmed into the mobile terminal 36. The SA field and SP field in packet 86 include the network address and port of the mobile terminal 36, respectively. The DA field and DP field include the network address and port of the GATEWAY1, respectively. The network address and port of the GATEWAY1 may be previously obtained by the mobile terminal 36 in a number of different manners. For example, each access point 28 may be programmed to provide the address and port for the default gateway 40 whenever a mobile terminal 36 newly registers. Alternatively, the network address and port for a gateway 40 may be statically configured within the mobile terminal 36.
The GUID field in the packet 86 is set to all zeros or some other predefined value to indicate that a GUID has not yet been assigned to the mobile terminal 36. Of course, in an alternative embodiment, the GUID may have been previously retrieved or preassigned by the mobile terminal 36. As is described below in relation to FIG. 4b, this prompts the GATEWAY1 to perform a function call to the LAN1 operating system requesting a GUID for the mobile terminal 36.
Referring briefly to FIG. 5a , shown is a virtual circuit table which is maintained in memory by the mobile terminal 36 for purposes of keeping track of the various virtual circuit connections. In the exemplary embodiment, the table consists of N rows with each row representing a possible virtual circuit (i.e., VC1 through VCN). N can be any preselected integer which represents the number of virtual circuits the mobile terminal 36 may have established at any given time. For each virtual circuit there is also a corresponding gateway 40 identification associated therewith (not shown) given that a mobile terminal could begin communicating via two or more gateways at any given time.
As shown in FIG. 5a, each virtual circuit entry (VC1 through VCN) has associated therewith L possible sessions (i.e., Session 1 through SessionL). L can be any preselected integer which represents the number of sessions in which the mobile terminal 36 can participate at any given time. Each session entry in the table has associated therewith a preselected number of possible sockets for representing socket end points in a given session. In the exemplary embodiment, each session includes two sockets (Socket1, Socket2), although a different number is possible. For each socket end point there is associated a device (i.e., HOST1) with which the mobile terminal 36 may communicate. As there may be many application programs running on the mobile terminal, there may also be several socket end points for the same device.
The mobile terminal virtual circuit table is empty initially and void of any valid columns or rows. As the mobile terminal 36 establishes new virtual circuits, sessions and sockets to establish communication links, entries to the table are inserted with corresponding information from the gateway 40 to indicate which virtual circuits, sessions and sockets are utilized. Thus, the virtual circuit table can dynamically grow in size.
When a particular virtual circuit, session and/or socket is not in use and/or is terminated, the mobile terminal 36 invalidates or deletes the corresponding entries in the virtual circuit table thereby possibly reducing it in size. Thus, the mobile terminal 36 may always look to the virtual circuit table to see which circuits, sessions and sockets are available and which are in use. It is noted that virtual circuit table could be configured to accept only a limited number of entries or that the virtual circuit table could be static in nature in alternative embodiments.
Turning briefly to FIG. 5b, a corresponding virtual circuit table which is stored in memory in each gateway 40 is shown. The table is structured in the same manner as the virtual circuit table described in FIG. 5a and may be static or dynamic in nature. The number of virtual circuits will typically be larger than those found in the mobile terminal 36. This is because each gateway 40 will likely be handling traffic for multiple mobile terminals 36. The number of sessions per virtual circuit and sockets per session preferably is the same as that for the mobile terminal 36. Hence, a given virtual circuit connection between the gateway 40 and the mobile terminal can provide for L sessions with two or more sockets per session, for example. Also, for each socket the table includes information pertaining to the particular mobile terminal as is discussed below.
Like the mobile terminal 36, the gateway 40 clears any entries which are not in use. Thus, the gateway 40 can look to its virtual circuit table at any time and determine which particular connections are in use and which are available. Although the present embodiment shows all entries related to the virtual circuit, sessions and sockets to be included in a respective single table such as those shown in FIG. 5a and 5b, it will be appreciated that separate tables could be maintained for each and indexed appropriately to provide association.
Referring then back to FIG. 4a, the VCID field in the packet 86 includes the identification of a mobile terminal virtual circuit which the mobile terminal 36 preselects for purposes of establishing a virtual circuit with the GATEWAY1. Specifically, the mobile terminal 36 is configured to look to its virtual circuit table (FIG. 5a ) and select a particular virtual circuit (e.g., VC1-VCN) which is presently available. The mobile terminal 36 selects one of the virtual circuits (nominally labeled MT VCID) and includes it the VCID field. This serves to inform the GATEWAY1 of the particular virtual circuit label the mobile terminal 36 is using to represent the connection which is to be established. Finally, the CMD field includes a predefined function call "VCKT.sub.-- START" intended to inform the GATEWAY1 that the mobile terminal 36 wishes to establish a virtual circuit.
The mobile terminal 36 then transmits the packet 86 wirelessly to the GATEWAY1 via the access point AP1. The GATEWAY1 receives the packet 86 and processes the packet as follows. The GATEWAY1 recognizes the VCKT.sub.-- START command and looks to its virtual circuit table (FIG. 5b) in order to select a particular virtual circuit (e.g., VC1-VCZ) which is presently available. The GATEWAY1 selects a particular virtual circuit (e.g., VC1) based on what is available (i.e., not in use). The GATEWAY1 then stores in its table in association with the selected virtual circuit entry the MT VCID obtained from the VCID field of the packet 86. Thus, the selected virtual circuit thereby becomes associated with the virtual circuit identified by MT VCID.
Moreover, the GATEWAY1 is configured to detect the presence of all zeros in the GUID field. In response, the GATEWAY1 performs a function call to the operating system of the LAN1 to obtain a GUID for the mobile terminal 36. The manner in which the operating system can provide such GUID is known in the art.
In response to the packet 86, the GATEWAY1 generates a packet 88 as shown in FIG. 4b. The purpose of the packet 88 is to inform the mobile terminal 36 that a virtual circuit has been established and to notify the mobile terminal 36 of the particular virtual circuit label being used to define the connection by the GATEWAY1. In addition, the packet 88 is used to inform the mobile terminal 36 of the particular GUID which is being assigned thereto. Thus, the SA and SP fields of the packet 88 correspond to the address and port of the GATEWAY1, respectively. The DA and DP fields of the packet 88 correspond to the address and port of the mobile terminal 36, respectively, as obtained from the SA and SP fields of packet 86. The GUID field contains the GUID for the mobile terminal 36 (MT GUID) as obtained from the operating system. The VCID field contains the virtual circuit selected by the GATEWAY1 (nominally labeled GW1 VCID). The CMD field contains the predefined command "VCKT.sub.-- STARTED" to indicate to the mobile terminal 36 that the virtual circuit has been started.
The GATEWAY1 then proceeds to transmit the packet 88 to the mobile terminal 36 via the access point AP1. The mobile terminal 36 receives the packet 88 and processes the packet 88 by storing in memory the MT GUID. In addition, the mobile terminal 36 stores in its virtual table entry for MT VCID the corresponding GW1 VCID as obtained from the VCID field of the packet 88.
Next, when the mobile terminal 36 is prepared to start a session (FIG. 2, step 64) the mobile terminal 36 generates a packet 90 to be sent to the GATEWAY1 as represented in FIG. 4c. The header portion of the packet 90 is identical to that of packet 86 (FIG. 4a). The VCID field includes the GW1 VCID assigned to the virtual circuit by the GATEWAY1 (as obtained from the virtual circuit table of the mobile terminal 36). In the SID field the mobile terminal 36 includes the identity of a session which the mobile terminal 36 selects for purposes of establishing the session. Specifically, the mobile terminal 36 again refers to its virtual circuit table (FIG. 5a) and selects a particular session (e.g., Session1) which is available within the previously selected virtual circuit (e.g., VC1). The mobile terminal 36 includes the session (nominally labeled MT SID) in the SID field of the packet 90. Finally, the mobile terminal 36 includes the predefined command "START.sub.-- SESSION" in the CMD field to notify the GATEWAY1 that the mobile terminal 36 wishes to start a session. The mobile terminal 36 then proceeds to transmit the packet 90 to the GATEWAY1.
The GATEWAY1 receives the packet 90. In response to the command START.sub.-- SESSION, the GATEWAY1 is configured to again look to its virtual circuit table (FIG. 5b ) for the virtual circuit corresponding to the GW1 VCID identified in the VCID field. Specifically, the GATEWAY1 selects a particular session which is available in conjunction with the GW1 VCID previously selected for purposes of generating the packet 88. The GATEWAY1 then proceeds to store in the table entry corresponding to the selected session the session identification (MT SID) selected by the mobile terminal 36 as provided in the SID field of the packet 90.
The GATEWAY1 then proceeds to generate a response packet 92 as shown in FIG. 4d. The purpose of the response packet 92 is to inform the mobile terminal 36 of the particular session label which the GATEWAY1 is assigning to the virtual circuit connection. Hence, the header portion is again standard and is identical to the header portion included in the packet 88. The VCID field includes the MT VCID for the virtual circuit as obtained from the virtual circuit table of the GATEWAY1 corresponding to the entry for GW1 VCID. The SID field includes the particular session (nominally labeled GW1 SID) selected by the GATEWAY1 in response to the packet 90. The CMD field includes a predefined command "SESSION.sub.-- STARTED" indicating to the mobile terminal 36 that the gateway has selected a corresponding session. The GATEWAY1 then proceeds to transmit the packet 92 to the mobile terminal 36.
The mobile terminal 36 receives the packet 92 and looks to the entry in its virtual circuit table corresponding to the MT VCID identified in the VCID field of the packet 92. The mobile terminal 36 then proceeds to store in its virtual circuit table the GW1 SID obtained from the SID field of the packet 92 in association with the particular session identified in the SID field of the packet 90. Thus, a virtual circuit and session are established between the mobile terminal 36 and the GATEWAY1 based on an exchange of the packets represented in FIGS. 4a-4d. The mobile terminal 36 and the GATEWAY1 each know the corresponding VCID and SID for the other device.
As referred to in step 64 of FIG. 2, the mobile terminal 36 will need to obtain network addressing information for the device on the network with which it desires to communicate in order to establish a socket connection with a particular device on the network. In the present example, it is assumed that the mobile terminal 36 wishes to communicate with the host computer HOST1 in the LAN1. The mobile terminal 36 is configured to first generate a packet 94 as shown in FIG. 4e for the purpose of requesting address information. The packet 94 is to be transmitted to the GATEWAY1 and hence has a header portion similar to that described above in connection with the packet 86. The VCID and SID fields include the GW1 VCID and GW1 SID information, respectively, corresponding to the particular virtual circuit and session the requested address information will relate to. The CMD field includes a predefined command "GET.sub.-- HOST.sub.-- BY.sub.-- NAME" or some other command identifying the particular device with which the mobile terminal 36 wishes to communicate. The DTA field of the packet 94 includes the particular name of the device (e.g., HOST1 NAME).
The packet 94 is transmitted to the GATEWAY1 which is configured to retrieve the device name from the DTA field and query the local name resolver such as DNS 44 for the corresponding network address. Next, the GATEWAY1 generates a response packet 96 as shown in FIG. 4f which is to be transmitted to the mobile terminal 36 with the appropriate header portion. The packet 96 includes the MT VCID and MT SID in the VCID and SID fields, respectively, as obtained from the virtual circuit table of the GATEWAY1, such identifications corresponding to the particular virtual circuit and session identified in the VCID and SID fields of the packet 94. The CMD field includes the predefined command GOT.sub.-- HOST.sub.-- BY.sub.-- NAME informing the mobile terminal of the purpose of the packet. The DTA field contains the actual network address(es) of the HOST1 as requested. The packet 96 is transmitted to the mobile terminal 36 which receives the packet and stores the network address.
Step 60 of FIG. 2 relates to establishing the actual socket connection between the mobile terminal 36 and the GATEWAY1. Such procedure begins with the mobile terminal 36 generating a packet 98 to be transmitted to the GATEWAY1 as shown in FIG. 4g. The packet 98 includes a header portion directing the packet to the GATEWAY1. In addition, the packet 98 includes the virtual circuit and session identifiers GW1 VCID and GW1 SID for the GATEWAY1 in the corresponding fields. Again, the mobile terminal 36 is able to obtain such information from the corresponding entries in its virtual circuit table (FIG. 5a). With respect to the SOID field, the mobile terminal 36 now looks to its virtual circuit table and selects an available socket corresponding to the previously selected virtual circuit and session. The mobile terminal 36 selects such a socket (nominally labeled MT SOID) and includes it in the SOID field of the packet 98. The CMD field includes a predefined "START.sub.-- SOCKET" command informing the GATEWAY1 that it is desired to allocate a socket endpoint.
The packet 98 is transmitted to the GATEWAY1 where it is processed as follows. Specifically, the GATEWAY1 selects an available socket corresponding to the information provided in the VCID and SID fields of the packet 98. The GATEWAY1 then stores in association with the selected socket the MT SOID provided in the SOID field of the packet 98. The GATEWAY1 then generates a response packet 100 to be transmitted to the mobile terminal 36 having the format shown in FIG. 4h. Following the standard header portion, the packet 100 includes the MT VCID and MT SID information in the VCID and SID fields similar to the packet 96. In the SOID field, the GATEWAY1 includes the particular socket (nominally labeled GW1 SOID) which was selected from its virtual circuit table (FIG. 5b ) in response to the packet 98. Finally, the CMD field includes a predefined command "SOCKET.sub.-- STARTED" indicating to the mobile terminal 36 that a socket has been established. The packet 100 is then transmitted to the mobile terminal 36.
The mobile terminal receives the packet 100 and proceeds to store the gateway socket information GW1 SOID in its virtual circuit table in association with the mobile terminal socket identified in the SOID field of the packet 98. Hence, after the exchange of the packets shown in FIGS. 4a-4h, the mobile terminal 36 and the GATEWAY1 have established a unique virtual circuit defined by a VCID, SID and SOID combination. The mobile terminal 36 and the GATEWAY1 each has stored in its virtual circuit table the VCID, SID and SOID combination both from the perspective of the mobile terminal 36 and the GATEWAY1.
Next, the mobile terminal 36 attempts to begin actual communications (FIG. 2, step 67) with the particular device (e.g., the HOST1). Initially, however, the mobile terminal 36 generates a packet 102 as shown in FIG. 4i. The packet 102 is addressed to the GATEWAY1 and serves the purpose of requesting that the GATEWAY1 obtain a conventional network connection with the HOST1. Specifically, the packet 102 has a standard header portion addressed to the GATEWAY1. The VCID, SID and SOID fields include the virtual circuit, session and socket information from the perspective of the GATEWAY1, i.e., GW1 VCID, GW1 SID and GW1 SOID, respectively. The CMD field includes the predefined CONNECT command notifying the GATEWAY1 of the desire to establish a connection between the gateway and the HOST1. The DTA field includes the actual network address of the HOST1 as obtained from packet 96 discussed above. It is noted that by this time the mobile terminal 36 has stored in the device entry of its virtual circuit table corresponding to the particular socket the identity of the particular device (e.g., the HOST1) and the gateway address and port corresponding to the GATEWAY1. This facilitates the mobile terminal 36 keeping track of such information when establishing virtual circuits with several such gateways 40 and devices in the network.
The packet 102 is transmitted to the GATEWAY1 which receives the packet. In response, the GATEWAY1 utilizes conventional network techniques to prepare and/or establish a connection between the GATEWAY1 and the HOST1 as identified in the DTA field of the packet 102. Thereafter, the GATEWAY1 generates a response packet 104 as shown in FIG. 4j. The packet 104 includes the standard header portion in order to be transmitted from the GATEWAY1 to the mobile terminal 36. In addition, the packet 104 includes the corresponding VCID, SID and SOID of the mobile terminal 36 in the appropriate fields. Finally, the CMD field includes a predefined command "CONNECT.sub.-- RESPONSE" intended to notify the mobile terminal 36 that the connection between the GATEWAY1 and the HOST1 is prepared and/or established.
It is noted that by this time the GATEWAY1 has stored in its mobile terminal entry of its virtual circuit table corresponding to the particular socket, the mobile terminal 36 address, port, and GUID. This facilitates the GATEWAY1 keeping track of which particular mobile terminal 36 is being handled by the respective virtual circuits. In addition, the mobile terminal entry of the virtual circuit table has stored therein the network address of the device (e.g, HOST1) with which the mobile terminal 36 is communicating via the particular virtual circuit connection. Finally, as is discussed below in relation to FIG. 41, the GATEWAY1 will also store in the mobile terminal entry of the table the particular port being used by the GATEWAY1 for communications with the HOST1 with respect to the specific socket connection.
The packet 104 is transmitted to the mobile terminal 36 and the mobile terminal 36 is now prepared to communicate with the HOST1 with the GATEWAY1 serving as an intermediary. For instance, FIG. 4k illustrates a packet 106 containing data which the mobile terminal 36 wishes to transmit to the HOST1. Rather than transmitting the data directly to the HOST1, the data stored in packet 106 is directed via the GATEWAY1 using the socket end points previously established for communications between the mobile terminal 36 and the HOST1. Namely, the header portion again includes the address and port of the GATEWAY1 in the DA and DP fields, respectively. The VCID, SID and SOID fields define the complete connection from the perspective of the GATEWAY1 as obtained from the corresponding entries in the virtual circuit table of the mobile terminal 36. The CMD field includes the predefined command "SEND.sub.-- DATA" informing the GATEWAY1 that the data is to be delivered to the corresponding device (i.e., the HOST1). The DTA field includes the actual data which is to be delivered to the HOST1.
The packet 106 is then transmitted to the GATEWAY1. The GATEWAY1 receives the packet 106 and in response to the SEND.sub.-- DATA command looks up the virtual circuit entry in its virtual circuit table corresponding to the information included in the VCID, SID and SOID fields of the packet 106. Based on this information the GATEWAY1 obtains the address information of the HOST1 from the corresponding mobile entry in its virtual circuit table. The GATEWAY1 then generates a packet 108 as shown in FIG. 4i to be sent to the HOST1. The SA field and SP field correspond to the address and port of the GATEWAY1. It is noted that the port utilized by the GATEWAY1 to communicate directly with the HOST1 (or other device) is selected by the GATEWAY1 so as to be unique to the corresponding socket of the virtual circuit. The DA field and DP field correspond to the address and port of the HOST1 as previously obtained and stored in the virtual circuit table. The DTA field contains the data included in the DTA field in the packet 106 from the mobile terminal 36. It is noted that the packet 108 follows a conventional format native to the end point with which the mobile terminal 36 is communicating.
FIG. 4m represents a packet 110 indicative of a communication sent back to the GATEWAY1 by the HOST1 in response to the packet 108. The DTA field of the packet 110 includes appropriate response data which ultimately is intended for the mobile terminal 36. Since the port identified in the DP field is selected to be unique to a given socket in the virtual circuit table of the GATEWAY1, the GATEWAY1 identifies such socket based on the information stored in the table as discussed above. From the unique gateway port, the GATEWAY1 is able to identify the VCID, SID and SOID of the mobile terminal 36 from the virtual circuit table. The GATEWAY1 then generates a packet 112 as shown in FIG. 4n which is to be transmitted back to the mobile terminal 36. The packet 112 includes the address and port of the mobile terminal 36 in the DA and DP fields, respectively, as obtained from the mobile entry of the virtual circuit table of the GATEWAY1. The DTA field includes the data from the DTA field received in the packet 110 from the HOST1.
Accordingly, communications between the mobile terminal 36 and the HOST1 can remain ongoing via an exchange of packets as represented in FIGS. 4k-4n. The GATEWAY1 simply determines where to direct a received packet based on the contents of its virtual circuit table.
Of course, there is the possibility that the mobile terminal 36 will roam to another LAN (e.g., LAN2) as outlined above. However, as will be apparent such roaming does not have an adverse affect on the virtual circuits formed via the GATEWAY1. Namely, referring back to FIG. 2 assume that the mobile terminal 36 does roam from LAN1 to LAN2. Such roaming is detected in step 72 and the mobile terminal 36 registers with a new access point (e.g., AP2) and obtains a new network identification (e.g., MT ADDRESS* and MT PORT*) (steps 74 and 76). However, the contents of the virtual circuit table (FIG. 5a ) of the mobile terminal 36 remain unchanged.
Hence, suppose the mobile terminal 36 wants to continue communicating with the HOST1 in LAN1. The mobile terminal 36 simply generates a packet 114 as shown in FIG. 4o. The source address SA and source port SP fields in the packet 114 will reflect the new network address of the mobile terminal 36 as a result of roaming to LAN2. However, the mobile terminal 36 continues to communicate with the HOST1 via the GATEWAY1 and the specific virtual circuit. Namely, the packet 114 includes the address and port of the GATEWAY1 in the DA and DP fields as shown. In addition, the packet 114, similar to the packet 106, includes the GW1 VCID, GW1 SID and GW1 SOID in the respective fields identifying the particular virtual circuit. The CMD field contains the same "SEND.sub.-- DATA" command as the packet 106, and the data which is to be transmitted to the HOST1 is included in the DTA field. In addition, though, the packet 114 includes the flag field FLG in which the flag is set to indicate to the GATEWAY1 that the address of the mobile terminal 36 has changed. The packet 114 is then sent to the GATEWAY1 via the access point AP2 and known routing techniques across the WAN 22.
The GATEWAY1 in turn receives the packet 114 and processes the packet in the same manner described above in relation to packet 106 (FIG. 4k) with the following exception. The GATEWAY1 detects from the FLG field that the address of the mobile terminal 36 has changed. In response, the GATEWAY1 updates its virtual circuit table (FIG. 5b) so as to now include the updated address of the mobile terminal 36 in the corresponding mobile entry. Such updated address is obtained via the SA field and SP field of the packet 114. Otherwise, the GATEWAY1 continues to act as an intermediary and forwards the data in the DTA field to the HOST1 in a packet in the exact same manner as described above in relation to packet 108 (FIG. 4i). In other words, the same procedures described above in relation to FIGS. 4k-4n are repeated. In this manner, the HOST1 is able to continue communicating with the mobile terminal 36, and vice versa, regardless of the fact that the network address of the mobile terminal 36 has changed. In situations where the mobile terminal 36 roams to another LAN but does not need to communicate with the HOST1 immediately, the mobile terminal 36 in the present embodiment is configured to send a gratuitous update packet to the GATEWAY1 in which the FLG field is set so that the GATEWAY1 can immediately update is tables and continue forwarding packets to the mobile terminal 36. Accordingly, seamless roaming is achieved.
FIG. 6 is a block diagram representing the basic structure of the mobile terminals 36 according to the exemplary embodiment. Each mobile terminal 36 includes a processor 170 which can be programmed to control and to operate the various components within the mobile terminal 36 in order to carry out the various functions described herein. The processor 170 is coupled to an operator input device 172 which allows an operator to input data to be communicated to the corresponding LAN such as inventory data, patient information, etc. This information may be sent to the host computer 42 which serves as a central data location, for example, or to a cash register connected to the network backbone 26, as another example, for providing price information. The input device 172 can include such items as a keypad, touch sensitive display, etc. The mobile terminal 36 also may include a bar code scanner 173 coupled to the processor 170 for providing another form of data input. A display 174 is also connected to and controlled by the processor 170 via a display driver circuit 175. The display 174 serves as a means for displaying information stored within the mobile terminal 36 and/or received over the network backbone 26 via an access point 28. The display 174 can be a flat panel liquid crystal display with alphanumeric capabilities, for example, or any other type of display as will be appreciated.
A memory 176 is included in each mobile terminal 36 for storing program code executed by the processor 170 for carrying out the functions described herein. The actual code for performing such functions could be easily programmed by a person having ordinary skill in the art of computer programming in any of a number of conventional programming languages based on the disclosure herein. Consequently, further detail as to the particular code has been omitted for sake of brevity. The memory 176 also serves as a storage medium for storing the above described virtual circuit table for the mobile terminal 36.
Each mobile terminal 36 also includes its own RF section 178 connected to the processor 170. The RF section 178 includes an RF receiver 182 which receives RF transmissions from an access point 28 and via an antenna 184 and demodulates the signal to obtain the digital information modulated therein. An example of a suitable RF receiver 182 for use in the mobile terminal 106 is the Model 025 Direct Sequence Spread Spectrum Radio Module, which is commercially available from Aironet Wireless Communications, Inc. of Akron, Ohio.
The RF section 178 also includes an RF transmitter 186. In the event the mobile terminal 106 is to transmit information to a LAN in response to an operator input at input device 172, for example, the processor 170 forms within the memory 176 the aforementioned information packets. The information packets are delivered to the RF transmitter 186 which transmits an RF signal with the information packet modulated thereon via the antenna 184 to the access point 28 with which the mobile terminal 36 is registered.
Referring now to FIG. 7, a block diagram representative of each access point 28 is shown. Each access point 28 is connected to the network backbone 26 via a connector 240 such as a DB-9 or RJ-45 connector. The connector 240 is connected to the network backbone 26 at one end and to a network adapter transceiver 252 included in the base station 108 at the other end. The network adapter transceiver 252 is configured according to conventional network adapter transceiver techniques to allow the access point 28 to communicate over the network backbone 26. The network adapter transceiver 252 is also connected to an internal bus 254 included within the access point 28. The access point 28 further includes a processor 256 connected to the bus 254 for controlling and carrying out the operations of the access point 28. The processor 256 may include any of a variety of different microprocessors, such as the Motorola 68360 (25 MHz) or Intel 80386 microprocessors.
The access point 28 also includes a memory 258 connected to the bus 254. The memory 258 stores program code executed by the processor 256 to control the other elements within the access point 28 to carry out the functions described herein. It will be readily apparent to a person having ordinary skill in the art of computer programming how to program the processor 256 and the other elements within the access point 28 to carry out the operations described herein using conventional programming techniques based on the flowcharts and descriptions provided herein. As a result, additional detail as to the specific program code has been omitted. Moreover, the memory 258 functions to store information tables maintained by the processor 256 including information such as a list of the mobile terminals 36 which are currently registered with the access point 28.
Also connected to the bus 254 is an RF section 260 included in the access point 28. The RF section 260 includes the aforementioned antenna 32 for receiving radio signals from and transmitting radio signals to mobile terminals 36 within the cell area of the access point 28. Information transmitted from a mobile terminal 36 is received via the antenna 32 and is processed by an RF receiver 262 which demodulates and decodes the signal and converts the information to a digital signal having the aforementioned packet format.
Thereafter, the processor 256 stores the packet in the memory 258 until such time as the base station 108 is able to transmit the information packet onto the network backbone 26 via the network adapter transceiver 252 and connector 240.
Information packets which are transmitted to the access point 28 via the network backbone 26 for transmission to a mobile terminal 36 are received by the network transceiver 252. The processor 256 controls an RF transmitter 264 included in the RF section 260, the RF transmitter 264 also being connected to the bus 254. The processor 256 causes the RF transmitter 264 to modulate an RF signal using spread spectrum techniques, for example, which in turn carries the information packet to the appropriate mobile terminal 36.
FIG. 8 represents a block diagram of a gateway 40 in accordance with the present invention. Each gateway 40 is connected to the network backbone 26 via a connector 340 such as a DB-9 or RJ-45 connector. The connector 340 is connected to the network backbone 26 at one end and to a network adapter transceiver 352 included in the gateway 40 at the other end. The network adapter transceiver 352 is configured according to conventional network adapter transceiver techniques to allow the gateway 40 to communicate over the network backbone 26. The network adapter transceiver 352 is also connected to an internal bus 354 included within the gateway 40. The gateway 40 further includes a processor 356 connected to the bus 354 for controlling and carrying out the operations of the gateway 40.
The gateway 40 also includes a memory 358 connected to the bus 354. The memory 358 stores program code executed by the processor 356 to control the other elements within the gateway 40 to carry out the functions described herein. It will be readily apparent to a person having ordinary skill in the art of computer programming how to program the processor 356 and the other elements within the gateway 40 to carry out the operations described herein using conventional programming techniques based on the flowcharts and descriptions provided herein. As a result, additional detail as to the specific program code has been omitted. Moreover, the memory 358 functions to store the aforementioned virtual circuit table (FIG. 5b) for the gateway 40.
Although the invention has been shown and described with respect to certain preferred embodiments, it is obvious that equivalents and modifications will occur to others skilled in the art upon the reading and understanding of the specification. For example, while the preferred embodiment utilizes three different layers for the virtual circuit (i.e., VCID, SID and SOID), it will be appreciated that some other number could also be used (e.g., 1, 2, 4, etc.).
Further, the present invention has been described with respect to wireless mobile devices utilizing RF to communicate with devices connected to the network backbones. However, the scope of the present invention also includes mobile devices which do not use RF to communicate but rather are physically connected and disconnected from each respective network backbone via a standard serial or parallel corn port or other wired network connection, for example.
Additionally, although the present invention was described with a network having discrete components such as the gateway 40, host 42, and DNS 44, it will be appreciated that all of these components could have been combined to form a single unit which can carry on the functionalities described herein.
The present invention includes all such equivalents and modifications, and is limited only by the scope of the following claims.
Claims
What is claimed is:
1. A communication system, comprising: a plurality of local area networks (LANs), each of the LANs including: a network backbone; and at least one access point coupled to the network backbone which, when a mobile terminal is registered to the access point, enables the mobile terminal to communicate wirelessly with a device coupled to the network backbone via the at least one access point; wherein when the mobile terminal is registered to at least one access point in one of the plurality of LANs the mobile terminal is assigned a first network address, and when the mobile terminal is registered to at least one access point in another of the plurality of LANs the mobile terminal is assigned a second network address in place of the first network address, the second network address being different from the first network address; a system backbone interconnecting the plurality of LANs for permitting communications between the plurality of LANs; a gateway controller, operatively coupled to one of the plurality of LANs, for serving as an intermediary for communications between the mobile terminal and a device on one of the system backbones in order that in the event the mobile terminal is assigned a different network address by virtue of registering with an access point in another of the LANs, the device is able to maintain communications with the mobile terminal without requiring knowledge of a change in the network address of the mobile terminal; and the gateway controller storing information relating to the current network address of the mobile terminal and the current network address of the device, wherein the gateway controller receives communications from the mobile terminal containing information intended for the device and forwards the information to the device, and the gateway controller receives communications from the device containing information intended for the mobile terminal and forwards the information to the mobile terminal.
2. The communication system of claim 1, wherein each of the plurality of LANs includes a gateway controller connected to the system backbone.
3. The communication system of claim 1, wherein the system backbone represents part of a wide area network (WAN).
4. The communication system of claim 1, wherein the mobile terminal comprises at least one of a data terminal, a telephone, and a pager.
5. A gateway controller for use in a communication system including a plurality of local area networks (LANs), each of the LANs including a network backbone; and at least one access point coupled to the network backbone which, when a mobile terminal is registered to the access point, enables the mobile terminal to communicate wirelessly with a device on the network backbone via the at least one access point, the gateway controller comprising: means for operatively coupling the gateway controller to the network backbone of a selected one of the plurality of LANs; a gateway address circuit for communicating with a mobile terminal registered with the access point of the selected LAN via the network backbone for establishing indica distinguishing the mobile terminal from among other mobile terminals; a communication circuit for receiving communications from the registered mobile terminal intended for the device and forwarding the received communications to the device together with at least part of the indicia as provided by the communication circuit, and for receiving communications, including the at least part of the indicia, from the device intended for the registered mobile terminal and forwarding the received communications to the registered mobile terminal based on the at least part of the indicia.
6. The gateway controller of claim 5, wherein the indicia represents a layer of addressing utilized in communications involving the gateway controller and the registered mobile terminal but which is not required in communications between other devices communicating on the network backbone.
7. The gateway controller of claim 6, wherein the layer of addressing permits the device wirelessly communicating with the mobile terminal to continue communicating with the registered mobile terminal even if another layer of addressing for the registered mobile terminal changes unbeknownst to the device.
8. The gateway controller of claim 5, wherein the indicia represents a plurality of layers of addressing utilized in communications involving the gateway controller and the registered mobile terminal but which are not required in communications between other devices communicating on the network backbone.
9. The gateway controller of claim 5, wherein the communication circuit includes a memory table in which the indicia for a plurality of mobile terminals are stored.
10. A network communication system, comprising: a plurality of local area networks (LANs), each of the LANs including: a network backbone; and at least one access point coupled to the network backbone which, when a mobile terminal is registered to the access point, enables the mobile terminal to communicate wirelessly with the network backbone via the at least one access point; a system backbone interconnecting the plurality of LANs for permitting communication between the plurality of LANs; a gateway controller, operatively coupled to one of the plurality of LANs and able to communicate with devices on other of the plurality of LANs via the system backbone, the gateway controller serving as an intermediary for communications between the mobile terminal and a device on a first of the plurality of LANs; the gateway controller assigning a gateway address to the mobile terminal such that once the mobile terminal starts a session with the device coupled to the first of the plurality of network backbones, the mobile terminal may continuously maintain the session through the gateway even if the mobile terminal registers with an access point coupled to another of the plurality of network backbones; and the gateway controller storing information in association with the gateway address relating to the current network address of the mobile terminal and the current network address of the device, wherein the gateway controller receives communications from the mobile terminal containing information intended for the device and forwards the information to the device, and the gateway controller receives communications from the device containing information intended for the mobile terminal and forwards the information to the mobile terminal.
11. The network communication system of claim 10, wherein each of the plurality of LANs includes a gateway controller connected to the system backbone.
12. The network communication system of claim 10, wherein the system backbone represents part of a wide area network (WAN).
13. The network communication system of claim 10, wherein the mobile terminal comprises at least one of a data terminal, a telephone, and a pager.
14. A mobile terminal for use in a communication system including a plurality of local area networks (LANs), each of the LANs including a network backbone and at least one access point coupled to the network backbone which, when the mobile terminal is registered to the access point, enables the mobile terminal to communicate wirelessly with a device coupled to the network backbone via the at least one access point, the mobile terminal comprising: mobile terminal address circuitry for establishing with a gateway controller coupled to one of the plurality of LANs via the network backbone indicia distinguishing the device from among other devices; and a communication circuit for transmitting communications destined for the device to the gateway controller together with at least part of the indicia, and for receiving communications transmitted by the device and destined for the mobile terminal from the gateway controller, the received communications having the at least part of the indicia included by the gateway controller.
15. The mobile terminal of claim 14, wherein the indicia represents a layer of addressing utilized in communications between the mobile terminal and gateway controller for identifying the device.
16. The mobile terminal of claim 15, wherein the layer of addressing permits the device communicating with the mobile terminal to continue communicating with the mobile terminal through the gateway even if another layer of addressing of the mobile terminal changes unbeknownst to the device.
17. The mobile terminal of claim 14, wherein the mobile terminal address circuitry includes a memory table in which the indicia for a plurality of devices are stored.
18. A mobile terminal for use in a wireless communication system including a plurality of local area networks (LANs), each of the LANs including a network backbone and at least one access point coupled to the network backbone, the mobile terminal including: a portable housing; means for assigning unique indicia to a plurality of devices in the wireless communication system with which the mobile terminal desires to communicate; and means for storing the unique indicia for the plurality of devices.
19. The mobile terminal of claim 18, further comprising a transceiver for wirelessly transmitting and receiving communications with at least one of the plurality of devices via a gateway controller coupled to the network backbone.
20. The mobile terminal of claim 19, wherein the communications received by the gateway controller from the one of the plurality of devices includes at least part of the unique indicia assigned to the one of the plurality of devices by the mobile terminal.
21. The mobile terminal of claim 20, wherein the unique indicia represents a layer of addressing utilized in communications between the mobile terminal and gateway controller.
22. The mobile terminal of claim 18, wherein the means for storing is a memory.
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