Abstract:
A method for partially synchronizing a local database stored on a local computer and a remote database stored on a remote computer. The method includes forming a message including information related to a local update of the local database, selecting a path from one or more communication paths coupling the local computer to the remote computer to pass the message to the remote computer, and transmitting data including the message to the remote computer over the selected path. The method can include determining whether the local update to the local database should be sent to the remote computer. The method includes receiving the data at the remote computer, processing the message included in the received data, and providing the information related to the local update to a remote application executing on the remote computer. A remote database coupled to the remote application is then updated using the information related to the local update. Information related to an update of the remote can also be selectively sent to update the local database. Messages sent between a local computer and a remote computer can be passed through a networked server computer, coupled by wired or wireless data networks to both the local computer and the remote computer.

Description:
BACKGROUND 
     The invention relates to data access and synchronization from a remote computer. 
     Access to data is an important capability for users of computers that are physically remote from the computers holding the data. For example, a user of a mobile computer may need access to his electronic mail that is received and stored at a mail server computer on a local computer network at his home site. The user may also need to access and modify a calendar and address book, or access other database information that is maintained on an application or database server computer at his home site. In addition to using a remote computer, the user may at other times use a desktop computer that is directly connected to the local computer network at his home site to access and modify data that he previously accessed from the remote computer. 
     A remote computer may connect to an application or database server computer over one or more of a number of different communication paths. For example, the remote computer may connect to the server or to a gateway computer on a local network using a modem and a directly dialed telephone connection. Wireless access from the remote computer is also possible using a cellular telephone modem and a dialed telephone connection. Rather than establishing a telephone connection from the remote computer to the server or gateway computer, the remote computer may establish a telephone connection to an access point of a data network, such as the Internet. Communication between the remote computer and the server computer then passes through the telephone connection as well as through the data network. In addition, the remote computer may also communicate directly over a wireless data network, such as a cellular digital packet data (CDPD) network, or the ARDIS or RAM networks, which is coupled to the server computer or to the local network. 
     Communication paths between a remote computer and a server computer are typically significantly more limited than the communication path between a desktop computer and a server computer that are both directly coupled to a local computer network. Remote communication may be limited to data rates in the range of approximately 5-56 kb/s, while local network communication typically occurs at rates of 1-10 Mb/s or higher. In addition, latency of communication may be significant, several seconds in some wireless data networks, while typically being less than lOms in the local network. 
     Software on a remote computer and on a server computer can take several different approaches to making use of the communication paths described above. One approach is to provide the remote computer access to a local computer network as if the remote computer were physically connected to the network. Essentially the same application programs and communication protocols are then used on the remote computer to access the server computer as on the local desktop computer. For example, in the case of electronic mail, a remote client can access a mail server using client application programs that use application layer communication protocols such as POP, SMTP, IMAP, or MAPI, to retrieve and post mail messages. 
     Computers, such as remote computers and desktop computers, that access a server may keep local copies of data stored on the server. When these computers are able to communicate with the server, they exchange all updated information thereby resulting in their local data being fully synchronized with the server after such communication. 
     Another approach to remote data access is to provide a pair of applications, one for execution on the remote computer, and another to act as a proxy or agent application executing at the user&#39;s home site. The proxy application interacts with the server application over a high data rate communication path such as over a local computer network. The communication protocol between the remote application and the proxy application is typically tailored to the type of data, for example tailored for mail, and to the characteristics of the data channel being used. The remote application can be used to simply view and remotely manipulate data on the server computer, or may keep a synchronized copy of the data. 
     Yet another approach uses a network mail server coupled to the user&#39;s home site over a data network such as the Internet. A pair of applications, one executing at the remote computer and the other executing at the network server, are used to access mail messages stored on the network server over a wireless data network, such as the ARDIS network. For a mail message to be accessible from the remote computer, the message must have been explicitly addressed and sent to the network mail server by the sender, or automatically forwarded from a mail server at the user&#39;s home site. This automatic forwarding may depend on criteria such as the sender, other information in the message header, or information in the body of the message itself. 
     SUMMARY 
     In one aspect, in general, the invention is a method for partially synchronizing a local database stored on a local computer and a remote database stored on a remote computer. The method includes forming a message including information related to a local update of the local database, selecting a path from one or more communication paths coupling the local computer to the remote computer to pass the message to the remote computer, and transmitting data including the message to the remote computer over the selected path. The method can include determining whether the local update to the local database should be sent to the remote computer. The method includes receiving the data at the remote computer, processing the message included in the received data, and providing the information related to the local update to a remote application executing on the remote computer. The method also includes updating a remote database coupled to the remote application using the information related to the local update. 
     In a second aspect, in general, the invention is a method for providing a remote computer access to a local database. The method includes sending a message, including information related to a local update to the local database over a first data network to a networked computer, and receiving the message at the networked computer. A networked database hosted on the networked computer is then updated using the information related to the local update. The method also includes accessing and updating the networked database from a remote computer over a second data network, and sending a message that includes information related to the update of the networked database from the networked computer over the first data network. The message that includes the information related to the update of the networked database is received and the local database is updated using the information related to the update of the networked database. 
     In a third aspect, in general, the invention is a system that includes a local database, an agent for accessing information related to a local update of the local database and for forming a message including that information for transmission to a remote computer, and a message router for accepting the message from the agent, and for selecting a path from one or more communication paths coupling the message router and the remote computer to pass the message to the remote computer. The system also includes a local communication interface for accepting data including the message and transmitting the data to the remote computer over the selected path. 
     Aspects of the invention include one or more of the following features. 
     Information related to a remote update of the remote database is accepted from a remote application. A return path is selected from the one or more communication paths coupling the local computer to the remote computer to transmit the information related to the remote update to the local computer, and the information related to the remote update is transmitted to the message router over the selected return path. The local database is updated using the information related to the remote update. 
     Determining whether the local update to the local database should be sent to the remote computer includes accessing a local application coupled to the local database using a first application communication protocol, such as MAPI, and providing the information to the remote application uses a second application communication protocol, such as POP. 
     The local database and the remote database include electronic mail messages, or include personal calendar information. 
     Transmitting data to the remote computer over a selected path for a message includes transmitting the data to a networked server over a first data network, such as the Internet, storing the data in a networked database hosted on the networked server, providing the data from the networked database to the remote computer over a second communication network, such as a wireless data network. The message can be encrypted prior to transmission to the networked server and decrypted after receipt of the message at the remote computer. 
     An advantage of the invention is that a remote user has the capability to maintain and manipulate copies of data on his remote computer, without requiring that the data on the remote computer be fully synchronized with that on the server. Updates to the data on the remote computer can be selectively reflected on the server. Similarly, updates on the server computer can be selectively reflected on the remote computer. This approach of partial synchronization provides most of the benefits of complete synchronization with significantly reduced communication requirements compared to complete synchronization. Partial synchronization avoids unnecessary expense if the cost of the communication is based on usage, and also avoids unnecessary delays resulting from large backlogs of data to transmit. 
     Another advantage of the invention is that a remote user can use standard client application programs on the remote computer, rather than customized application programs, while realizing other advantages of this invention. 
     Yet another advantage of the invention is that effective use of communication channels is made by taking into account the communication characteristics, such as data rate and latency, as well as communication cost structures, such as per message, per byte, and per minute based charges. For example short messages over a channel with a high per message cost can be avoided. 
     In the case in which a network server is used in conjunction with an application or database server at the user&#39;s home site, this invention has the advantage that data is synchronized not only on the remote computer and the server computer, but also on the network server. In this case, the invention also has the additional advantage that additional data security for data stored on the network server can be provided using encryption of that date. 
     Other features and advantages of the invention will be apparent from the following description, and from the claims. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 a  is a remote computer coupled to a communication server computer through various telephone and data networks; 
     FIG. 1 b  is an application database server and a desktop computer coupled to a communication server computer over a local area network; 
     FIG. 2 a  is software modules on a remote computer and on a communication server computer; 
     FIG. 2 b  is software modules on an application and database server and on a desktop computer; 
     FIG. 3 is a network server coupled to a communication server over the Internet and to a remote computer over a wireless network; 
     FIG. 4 is a network server coupled to a communication server using http modules; and 
     FIG. 5 is a network server which forms part of a distributed communication interface. 
    
    
     DESCRIPTION 
     Referring to FIGS. 1 a  and  1   b , a remote computer  110  is coupled to a communication server computer  180  through one or more paths through a communication network infrastructure made up of various telephone and data networks. Remote computer  110  is a lap-top, general-purpose computer, but could also be one of a variety of personal digital assistants (PDAs), or a special-purpose device such as an enhanced cellular telephone or paging receiver. Communication server computer  180  is a general purpose computer that is coupled to an application and database server  210  over a high-speed local computer network (local area network, LAN)  176 , communicating at rates of 1-10 kb/s or higher. Remote computer  110  communicates with server computer  180  over one or more of a variety of communication paths through the communication network infrastructure. These paths exhibit various communication characteristics. The communication paths include the following: 
     A bidirectional data stream over a dialed wired telephone connection from a wired modem  126  at the remote computer, over wired public switched telephone network (PSTN)  152  to wired modem  184  at the server computer. The data stream provides a data link for Internet Protocol (IP) data packets sent using the PPP protocol. The data rates on this path are typically limited to approximately 33 kb/s over standard telephone lines, although rates as high as 128 kb/s are possible over digital (ISDN) telephone lines. Cost of communication is not typically dependent on the amount of data sent, but may depend on the length of time connected. A modem  172  in a remote access server  170  coupled to a communication server  180  over LAN  176  may be used rather than using modem  184  in the communication server. 
     A bidirectional data stream over a dialed wired telephone connection from modem  126  at the remote computer, over PSTN  152 , to an Internet Point-of-Presence (POP)  158 . The Internet is then used for the remainder of the path, passing from POP  158  through Internet  160  to a gateway/router  174 , and then from gateway/router  174  over LAN  176  to server computer  180 . The cost of communication may depend on the length of time connected, due to a toll call being used, or due to charges from an Internet Service Provider that operates POP  158 . 
     The above two paths may use a wireless cellular modem  126  rather than wired modem  122  at remote computer  110 . The wireless telephone call passes through cellular telephone network  154  to PSTN  152  and either terminates at a wired modem  172 ,  184  at the user&#39;s site, or at Internet POP  158 . Current cellular modem data rates are limited to less than 15 kb/s over analog cellular telephone connections. A significant charge for connection time may be incurred from the cellular telephone service provider. 
     Rather than establishing a wireless telephone connection whenever communication between the remote computer and the user&#39;s site is needed, a wireless data interface  124 , such as a packet radio modem using the CDPD protocol, can be used to access a wireless data network  156 . Wireless data interface  124  provides a relatively low speed data channel. In the case of a CDPD modem, wireless network  156  is coupled to Internet  160 . The communication path to the user&#39;s site then passes through the Internet and gateway/router  174  to communication server computer  180 . Current data rates are limited to approximately 9 kb/s and a latency of up to several seconds. Cost of communication may be based on the total amount of data transferred. Other wireless data network connections are available using the ARDIS or RAM systems. In these systems, wireless data interface  124  is used at remote computer  110 , and a compatible wireless data interface  188  is used at communication server  180 . The cost of communication can be based on a combination of amount of data transferred as well as the number of messages sent. It can be expensive to send many short messages that do not contain much information. 
     Wireless data interface  124  can also be a two-way paging receiver. Communication rates are very limited using such systems. Communication from the remote computer using the pager is also very limited. Communication cost is also based on amount of data transferred and number of messages. 
     Remote computer  110  includes communication peripherals  120 , including one or more of wired modem  122 , wireless modem  126 , and wireless data interface  124  described above. The remote computer also includes a general purpose processor  112  coupled to communication peripherals  110 , for example over a communication bus. The processor is also coupled to working storage  114 , such as dynamic RAM, as well as permanent storage  116 , for example, a magnetic disk or an EPROM. User interface devices  118 , such as a graphical display, keyboard, and trackball, are also coupled to processor  112  and are used by a remote user to interact with application programs or to configure and maintain communication software on the remote computer. 
     At the user&#39;s home site, communication server computer  180  includes communication peripherals  182 , including a network interface  186  coupled to a LAN  176 , and may include one of wired modem  184  and wireless data interface  188  depending on the type of remote communication paths supported by the communication server. Communication server  180  has a general purpose processor  190 , working storage  192 , permanent storage  194 , and user interface devices  196 . The communication server may also have access to gateway/router  174  and remote access server  172  through network interface  186  and LAN  176 . Gateway/router  174  provides an interface to Internet  160 . Remote access server  170  provides access to wired modem  172  which may be shared with other computers on LAN  176 . 
     Referring to FIG. 1 b , also coupled to the LAN  176  is an application and database server computer  210 , which includes a processor  212 , working storage  214 , permanent storage  216  on which data is stored, and a network interface  218  coupled the processor to LAN  176 . 
     Also coupled to LAN  176  is a desktop computer  220  which may be used by the user when he is at his home site. The user can access application and database server  210  from two different computers, remote computer  110  and desktop computer  220 . The desktop computer includes a processor  222 , working and permanent storage  224 ,  226 , network interface  228  and user interface devices  230 . 
     Referring to FIG. 2 a , remote modules  310  include instructions and data hosted on remote computer  110  and communication server modules  330  include instructions and data hosted on communication server computer  180 . Referring again to FIG. 1 a , the remote modules are stored in working and permanent storage  114 ,  116  and are executed by processor  112  on remote computer  110 . Similarly, the communication server modules are stored in working and permanent storage  192 ,  194  and executed by processor  190  on communication server computer  180 . Drivers and communication services  320  in remote modules  310  shown in FIG. 2 a  are coupled to drivers and communication services  348  in communication server modules  330  along a communication path  310 . Referring again to FIG. 1 a , communication path  310  passes through communication peripherals  120  on remote computer  110 , through one or more of telephone and data networks  152 ,  154 ,  156 ,  160 , and through communication peripherals  182  on communication server computer  180 . Referring to FIGS. 2 a and  2   b , communication server modules  330  are coupled over communication path  370  (passing through LAN  176 ) to application server modules  360 , hosted on application and database server computer  180  (shown in FIG. 1 b ). Application server modules  360  are also coupled over communication path  372  (passing through LAN  176 ) to desktop modules  380 , hosted on desktop computer  220  (shown in FIG. 1 b ). 
     Referring again to FIG. 2 a , remote modules  310  and communication server modules  330  provide a mechanism for applications on the remote computer to communicate over a telephone or data network with corresponding agent modules on the communication server. In particular, a standard application and database  312  communicates with the communication server via an application hook module  314 . The application hook module provides a standard interface to application  312 , for example using industry standard MAPI or POP protocols, and sends messages to and receives messages from a corresponding agent module  332  at the communication server. Custom application and database  316  can also interchange messages with a corresponding agent module  332  at the communication server without requiring the services of an application hook module using an interface that may be particular to transaction layer  318 . An agent module  332  at the server computer communicates with standard and custom applications on remote computers, and couples those remote applications to a corresponding server application  362  (shown in FIG. 2 b ) executing on an application and database server computer  210  (shown in FIG. 1 b ). Desktop software and data modules  380  are hosted on a desktop computer  220 , and include a desktop application  383  which also communicates with server application  362 . In general, agent module  332  and desktop application  382  communicate with server application  362  using the same or similar protocols in order to access and manipulate data in database  364 . In particular, for an electronic mail application such as Microsoft Exchange server, agent module  332  and desktop application  382  communicate with server application  362  using the MAPI communication protocol. 
     Communication between an application hook  314  or a custom application  316  on a remote computer and an agent module on the communication server is message based. Communication logically flows between an application hook  314  or a custom application  316  and an agent module  332  along a logical communication path  306 . Logical communication path  306 , including the support for addressing, acknowledgments, and data link control, is provided by transaction layer  318  and driver and communication services  320  on the remote computer, message router  334 , communication interfaces  340  and drivers and communication services  348  on the communication server, and communication path  310  corresponding to the peripheral devices and network connections between the remote computer and the communication server computer. 
     Transaction layer  318  on the remote computer provides four basic services to an application hook or a custom application. The first two services allow an application hook or a custom application to register and unregister itself. An application registers itself by providing a symbolic name (i.e., a character string). The transaction layer can then route messages received from the communication server that are addressed to the application with that registered name. The other two basic services are used to send and to receive messages. A message sent by an application hook or a custom application includes a data portion that does not to be interpreted by the transaction layer, and a portion that identifies a communication server and an agent on that server using symbolic names. Transaction layer  318  includes configuration data  317  that is maintained by the remote user using a graphical user interface (GUI)  319 . This configuration data provides information necessary for transaction layer  318  to determine which communication path from the remote computer to the communication server computer should be used for any message received from an application or application hook. In particular one function of the transaction layer is to map the symbolic name for the communication server into a network address, such as a telephone number, an IP address, or an ARDIS address, needed for delivery of the data in the message. 
     If transaction layer  318  is configured to send a message over a wireless data network, the transaction layer accesses lower-level communication services associated with that network. For example, if a cellular CDPD network is to be used, transaction layer  318  calls UDP related routines in UDP/IP/CDPD interface  324 . If the message is larger than can be handled by a single UDP message (datagram) due, for example, to constraints imposed by the network, the transaction layer sends the message in a sequence of UDP datagrams. 
     At the communication server computer, drivers and communication services  348  receive the message and buffer it until one of communication interfaces  340  requests data. 
     One of communication interfaces  340  then requests data from drivers and communication services  348 , accepts the data, and reconstructs a message, for example, combining multiple data packets if necessary to form a single message. The message, including the name of the addressed agent, is then available to message router  334 . 
     Message router  334  provides a communication interface to agent modules  332 . Agent modules register themselves by name, in a similar manner as application hooks and custom applications register themselves with the transaction layer on the remote computer. When an agent module  332  requests data from message router  334 , the message router determines whether any messages for that agent are currently queued to be delivered and provides any such messages to the agent. 
     An application hook  314  or custom application  316  on the remote computer has three options related to acknowledgment of messages sent to an agent  332 . The first choice is that no acknowledgment is provided. The application receives no indication if a message is lost or delayed. The second choice is that once the message is reconstructed by one of the communication interfaces  340  at the communication server, an acknowledgment is sent back to the sending application hook or custom application. The third choice is for the sending application or application hook to receive an acknowledgment when message router  334  provides the message to the destination agent module. 
     The acknowledgment messages sent back to the remote computer may have different levels of urgency. For example, a confirmation that a request for a stock trade has been received by an agent module may require quick acknowledgment, possibly in the order of seconds, while acknowledging the transfer of messages containing an updated address in an address book may be much less urgent. Most typically, application hooks and custom applications are designed so that acknowledgments of successful transmission of messages is not needed, relying instead on application layer protocols above the message transport over logical communication path  306  to deal with communication errors and delays. 
     Messages from an agent module at the communication server to an application hook or custom application on the remote computer are sent in a similar fashion. The agent provides a message addressed to a particular application and remote computer to message router  334 . The message router includes configuration data  336  that is maintained by a user using GUI  338 . The configuration data includes information that is used by the message router to determine over which communication path to transmit the message to the remote computer. The message router then passes the message to one of the communication interfaces  340  based on the communication path chosen. Configuration data  334  also includes information needed by the communication interface translating the symbolic name of a remote computer to an address suitable for delivery of the message over the communication network used for the selected communication path. 
     The chosen communication interface accepts the message and then either passes the message immediately to the appropriate modules in driver and communication services  348 , or buffers the message for later transmission if the remote computer cannot be accessed at that time. 
     In order to optimize communication over a particular type of communication path, a communication interface, for example, wireless data network interface  346 , may buffer several messages before transmission. This allows the communication interface to aggregate the messages into a larger data packet for transmission over the communication path. This may be desirable to reduce communication cost on a path where there is a per-message cost. In order that a message not be delayed too long using such an aggregation mechanism, the agent module may specify a time limit by which time a message needs to be sent to the remote computer. 
     A communication interface may also be configured to prevent transmission of excessively long messages. For example, there may be a size limit for messages for transmission over a slow or expensive communication path. 
     Referring to FIG. 2 a , and as described above, application hook  314  and custom application  316  make use of the communication mechanism for transmission of messages over logical communication path  306 . Delivery of messages is not necessarily instantaneous and may be significantly delayed. Delivery is not necessarily reliable, application hooks and custom applications may choose not to require end-to-end acknowledgments. The application hook or custom application may rely on application layer protocols for error handling. 
     Referring to FIGS. 2 a  and  2   b , agent module  332  couples the application hook or custom application to server application  362 . Agent module  332  communicates over communication path  370  to application server modules  360 . Agent module  332  communicates with server application  362  using an appropriate application layer communication protocol. Agent module  332  may include library routines which provide a software interface within the agent module and provides support for the application layer protocol, and communicates using drivers and communication services  348  with the server application. An example of use of such a library mechanism is an agent module which uses a dynamically linked library (DLL) implementing a MAPI interface for communicating with a Microsoft Exchange server application. 
     In the case of electronic mail, agent module  332  is a mail agent. The mail agent performs one or more of the following functions. Periodically, the mail agent queries server application  362  to determine whether new mail has been received for a particular remote user. The server application maintains a database  364 , in this case a database of mail messages. If the server application determines that unread mail is stored in database  364 , this unread mail is provided to the mail agent. The mail agent determines whether the received mail should be forwarded to the remote computer. This decision may be based on a variety of factors, including the sender or other information in the message header, the length of the message, or information related to attachments to the message. Having decided to forward a message to a remote computer, the mail agent constructs a message including the mail message and addressed by name to the remote computer and the remote mail application, and then provides the message to message router  334 . 
     At the remote computer, a standard application  312  is used to access electronic mail. A corresponding application hook  314  has previously registered itself with transaction layer  318  with the name of the remote mail application. This application hook receives the message sent by the mail agent, extracts the mail message and provides the mail message to the standard mail application by writing the mail message in a shared directory of a file system on the permanent storage of the remote computer. Other methods of communication between the application hook and the standard application may also be used, depending on the standard interface supported by the application. 
     The user of the remote computer interacts with the mail application, reading the newly received message. Having read the mail message, the mail application marks the mail message as “read” so that it is not presented to the user again as a newly received message. In order that the same mail message is not presented as newly received when the user accesses database  364  from desktop computer  220  at a later time, the application hook sends a message to the mail agent with instructions to mark that mail message as read. The mail agent then communicates with server application  362  and the message stored in database  364  is marked as read. Similarly, if the remote user files the mail message in a folder or directory, or deletes it altogether, instructions to reflect those changes are sent to the mail agent. It may also be possible for the user to explicitly manipulate the local copy of the mail database without reflecting the changes in the database on the application server computer. For example, the user may delete messages on the remote computer to recover limited storage space, without having those mail messages deleted on the application server. Also, messages that are read on the remote computer may not be marked as read on the application server, for example, if the remote user wants to have them presented as unread when he accesses the mail database from the desktop computer at a later time. 
     Note that the remote mail application maintains a database as if it is totally synchronized with the mail database on the application server. However, due to factors including the mail agent selectively forwarding messages, a user choosing not to reflect changes such as deleting and marking messages as read, and the delay and unreliability of message delivery, the databases may be only partially synchronized. 
     A user may access an application server from a desktop application  382  prior to messages sent from the mail agent being delivered to the remote computer. For example, newly arrived mail messages may have been sent by the mail agent through the message router and may be queued for transmission in the wireless data network interface. If the user now reads those mail messages from the desktop computer, the mail agent determines that delivery of previously sent messages is no longer necessary and sends a “flush” message through the message router. The message router passes this flush message to the communication interface where the mail message can be erased if it has not yet been sent. 
     In the case of electronic mail, the application hook or custom application and the mail agent communicate using an application layer protocol that is not specific to any particular mail system. In this way, a mail client for one type of mail system, for example Microsoft Exchange, can communicate with a mail application server for another mail system, for example Lotus CC:Mail. 
     In addition to electronic mail, similar cooperating application hook and agent modules support data access and partial synchronization of personal information databases, for example containing a personal calendar and address book. In addition, custom applications may provide access to a database, such as an inventory database for a mobile inventory control application. 
     Referring to FIG. 3, a second configuration involves a network mail server  420  coupled to a communication server  430  over Internet  452  and coupled to a remote computer  410  over a wireless network  450 . In an arrangement similar to that of the previously described configurations, an agent module  432  executes on communication server  430  and interacts with a server application  442  that maintains a database  444  on an application server  440 . The communication server and the application server are situated at the user&#39;s home site, while the network mail server is geographically separated from the communication and application servers, as well as from the remote computer. 
     Network mail server  420  is configured to receive electronic mail for registered users of that server, to maintain that mail in network mail database  422 , and to post mail through the Internet on behalf of the registered users. The mail is sent and received by Internet mail interface  426  using the SMTP application layer protocol. When incoming mail is received by the network mail server, it is stored in network mail database  422 . A remote user accesses the stored mail from a remote computer  410  using remote application and wireless interface  412  executing on the remote computer. The remote computer and the network communication server are coupled by a wireless network  450 , for example an ARDIS packet radio network. A wireless interface  424  on the network mail server provides the remote computer access to the network mail database through the wireless network. In this configuration, the remote application either does not maintain its own local copy of mail, or its local copy is synchronized with the copy in network database  422 . One mode of making use of the network mail server is to forward mail received at application server  440  to network mail server  420  for access by a remote user. 
     Rather than forwarding mail from the application server  440  to network mail server  420 , agent module  432  is used to maintain partial synchronization between network mail database  422  and database  444  on the application server. After a mail message for a user is received and stored in database  444 , agent module  432  determines whether that message should be sent to the user at a remote computer. If it should be sent, agent module  432  sends a message to network mail server  420  so that the mail message can be stored in network database  422  where it is accessible to the user from remote computer  410 . 
     Referring to FIG. 4, communication server  430  includes a message router  460  and a hyper-text transport protocol (http) client interface  462  on the communication path joining agent module  432  and network mail server  420 . Internet interface  426  on the network mail server includes an http server interface  466 , a transaction layer  468 , and a custom interface application  470 . 
     If the remote user accesses mail stored in network mail database  422  and updates the database, for example, by marking messages as read, deleting messages, or by filing messages in folders, custom interface application  470  send a message to agent module  432  with instructions to update database  444 . Similarly, if the user posts a message, that message is sent by custom interface application  470  to agent module  432  and then to server application  442  from where the message is transmitted to the intended recipient. Custom interface application  470  and agent module  432  communicate along a logical communication path  472  using a message passing technique such as that described in the previous configuration. In particular, messages sent between custom interface application  470  and agent module  432  have the identical form as messages sent between an application hook  314  and an agent module  332  shown in FIG. 2 a . Furthermore, agent module  432  is not necessarily aware that it is communicating with network mail server  420  rather than with an application hook  314  on a remote computer. The agent module addresses messages symbolically and provides them to message router  460 . Custom interface application  470  addresses messages symbolically and provides them to transaction layer  468  for delivery to agent module  432 . 
     In certain installations, a gateway/router on the path between communication server  430  and the Internet  452  may include a gateway filter  464  that limits communication, for example, limiting communication to selected communication ports or to communication using selected application protocols for security reasons. In the configuration shown in FIG. 4, gateway filter  464  allows communication using the hyper-text transport protocol (http) passing messages formatted according to the hyper-text markup language (HTML). In order to pass messages between message router  460  and transaction layer  468  without filtering, http client interface  462  embeds outgoing messages in HTML format communication using a tunneling approach. Http server interface  466  extracts the message from the HTML data stream and provides it to transaction layer  468 . Messages from transaction layer  468  to message router  460  are provided in HTML format responses to requests from http client interface  462  to http server interface  466 , for example in a polling arrangement in which the client interface periodically requests messages from the server interface. 
     Referring to FIG. 5, a third configuration also makes use of network mail server  420  for accessing and synchronizing data between remote computer  410  and the application server  440 . Agent  432  is coupled to application server  440  as in the previous configurations. In order to send a message to the remote computer, agent  432  passes a message to a network server interface  474  that passes the message to a communication server interface  476  on network mail server  420 . Network server interface  474  include a message router and an http client interface, and communication server interface  476  includes a http server interface, a transaction layer, and a custom interface application, as in the previously described configuration. Communication server interface  476  stores received messages in network mail database  422  for later retrieval from the remote computer. When remote computer  410  and network mail server  420  are in contact over wireless network  450 , messages destined for the remote computer that are stored in the network mail database are passed through remote computer interface  478 , wireless network  450 , and wireless interface  414 , and provided to transaction layer  413 . Transaction layer  413  communicates with a remote application  412  which accepts the message. The remote application may be the combination of an application hook and a standard application, or a custom application as in the previous configurations. Messages from transaction layer  413  to agent  432  are similarly buffered in network mail database  422 . In this way, remote application  412  and agent  432  are coupled by a logical communication path  480 . The combination of network server interface  474 , communication server interface  476 , network mail database  422 , and remote computer interface  478  logically forms a distributed communication interface  482  for communicating between an agent and a remote computer over a wireless network. In this way, neither agent  432  nor transaction layer  413  are necessarily aware that messages are buffered on a network mail server  420  rather than being sent directly between communication server  430  and remote computer  410 . 
     In this third configuration, messages stored in network mail database  422  can be encrypted to provide additional security. In particular, the message content may be encrypted and decrypted in network server interface  474  and wireless interface  414 . The network mail server does not require access to the content of messages sent by agent  432  or remote application  412 . 
     Also in the third application, remote computer interface  478  may be identical to wireless interface  424  in the second configuration. That is, the network mail server may not be aware of the nature of the remote application and wireless interface executing on the remote computer. In this way, the network mail server can concurrently support the communication approaches described in the second and third configurations described above. 
     It is to be understood that while the invention has been described in conjunction with the detailed description thereof, the foregoing description is intended to illustrate and not limit the scope of the invention, which is defined by the scope of the appended claims. Other aspects, advantages, and modifications are within the scope of the following claims.