WO1995003679A1

WO1995003679A1 - Method and apparatus for managing data transfer in a cellular communications system

Info

Publication number: WO1995003679A1
Application number: PCT/US1993/006805
Authority: WO
Inventors: Maureen Lambert; Rob Stevenson; Dave Folger
Original assignee: Nomadic Systems, Inc.
Priority date: 1993-07-20
Filing date: 1993-07-20
Publication date: 1995-02-02

Abstract

A method and apparatus for controlling the transmission of data sessions, comprising data locks, over a cellular communications system. The system is controlled by a processor and software at the cellular site, and additional software stored in a mobile user's computer. When a user of a cellular system wishes to transmit files or other data to or from a mobile computer, such as a laptop, which is connected to the cellular system, certain status data and priority codes are transmitted to the cellular system, which then determines whether the data transmission may begin. The user may intentionally select either a high or low priority, either to ensure immediate transmission, on the one band, or to delay transmission until a specified time of day, on the other. Once transmission has begun, the cellular system constantly monitors conditions, including crowding of the cellular channels, to determine whether the transmission of data should continue. If transmission of the data is found not to meet the predetermined criteria, then transmission is temporarily ceased. The cellular system and the mobile system both maintain a constantly updated record of the status of the transmission. Thus, if transmission is ceased either because of the criteria not being met or because of loss of signal, there is no need to retransmit the entire data session. When conditions again meet the predetermined criteria, transmission of the data is completed. The user may at any time either terminate the transmission or alter the priority code.

Description

Method and Apparatus for Managing Data Transfer in a Cellular Communications System

Background of the Invention As portable computers become ever more common, and users of portable computers produce documents and data at sites which are remote from their home offices, it has become increasingly important that such users be able to communicate with the home office systems with facility. A particular area of need is that of exchanging data and documents between a remote, mobile computer and the main system at a central office.

As of the past few years, cellular telephone systems have become widespread, and with the use of a modem, it is now possible to transfer data between a portable computer and a home system without directly accessing a land-based telephone system. A roaming employee may now establish communication with the home system virtually at will.

However, even as cellular communications systems become more available, the concentration of their use has become ever greater, such that in certain geographical regions, systems are saturated with actual and attempted calls. The overcrowding is especially aggravated at morning and evening commuting hours and near heavily populated metropolitan areas. This overcrowding causes a conflict both among the many voice calls and between the need to make voice calls and the need to exchange files between mobile computers and base computers, since all of these calls all utilize the same channels of the cellular communications system. When a caller is unable to establish a connection over the cellular network, he or she must try again at a later time, until a channel is freed up for use. Frequendy, though, the cellular user will not have another opportunity to call again. This is particularly problematic for a caller who wishes to transfer a file over the cellular system, since such an operation will, using presendy available resources, generally take considerable time and effort.

Compounding this problem is the fact that the amount of data, or the size of a file, which the user must send to the base system may be very large, and thus consume a considerable amount of air time on the cellular system. This both increases the overcrowding which is already prevalent at peak periods, and gives rise to the likelihood that the transfer of data will be interrupted, since unintended terminations of cellular calls are still rather common, especially as, for instance, an automobile driver passes out of a region with a sufficiently strong channel.

It is highly inconvenient, and often simply impracticable, for the travelling user to have to monitor the transmission of data, to ensure that it is uninterrupted and that the mobile modem terminates the call when the data transfer is complete. There is therefore a need for a system which ameliorates this overcrowding. It would be particularly useful to have a system which can determine priorities among voice and data calls, and manage these calls to minimize conflicts between them. While it is generally important to one who places a voice call that the connection be made quickly, however, the transfer of a file from a remote computer to a home system often will not be time critical in the short term. Thus, it has become important to distinguish between calls which are time critical and those which are not.

There is also a need for a system which can eliminate overcrowding of channels during peak times by managing the number of cellular calls being made which are of low priority.

In particular, a system is needed which manages data transfer calls over cellular networks in such a ashion that a user may place the desired call just once, and the system from then on will take control over the timing, monitoring and completion of the transfer. Such a system must be invisible to the user, except to the extent that the timing of the call is apparent; that is, the user must not be required to repeatedly attempt the call over the cellular system, monitor the transmission of files, or manually terminate the call.

As a user travels, the call on the cellular system may be handed off from one cell to another. In addition, a particular problem is presented when the user "roams", i.e. travels from one cellular system to another. Typically, a large metropolitan area will include two cellular systems, and each system includes dozens of cells; and the user does not control which of the systems or cells he or she is using at a given moment. Data transmission must automatically accommodate handoffs and roaming as the user moves about.

.Summary of the Invention The present invention presents solutions to these problems in a system which manages data transfer communications from the cell site of a cellular telephone system, in cooperation with each cellular telephone from or to which documents or other data should be transferred.

Both the cell site and the cellular telephone include control logic, which may entail general purpose or dedicated processors, which act together to identify non-voice data as such and to assign the communication of such data to or from a base computer system a priority status. In addition, voice data which is not time-critical, such a voice mail messages, may be assigned a similar priority status. In order to transfer data from the mobile computer to a base computer, the mobile computer transmits data concerning a desired data transmission via a modem to the cell site on the set-up channel (or control channel). The cell site's processor determines that the call is not a real-time voice call, and therefore assigns it a lower priority than a voice call would receive.

If a channel- is immediately available and the usage rate of the available cells is below some predetermined amount, the cell site completes the call, and transmission of the data may begin. If it is not, the cell site will wait until the usage rate or some other predefined criterion is met, and then instructs the mobile system to commence transmission.

If the usage rate goes up during the data transfer, or if the mobile user travels into an area where usage is high, the cell site will then terminate the call until the rate again drops, and then will reestablish the call between the remote system and the base system to complete the data transfer. These and other features of the present invention will more fully appear in the course of the following description. Brief Description of the Drawings

Figure 1 is a block diagram of a typical cellular communications system in conjunction with which the present invention may be used.

Figure 2 is a block diagram of a conventional cellular telephone incorporation apparatus for use with the present invention.

Figure 3 is a block diagram depicting channel allocation.

Figure 4 is a flow chart of a preferred implementation of the method of the invention.

Description of the Preferred Embodiments

A typical cellular telephone system is a communications network which includes a large number of cells, each of which has a dedicated cell site. Figure 1 is a block diagram illustrating such a system, having cell sites identified as A-G. Typically, there will be many more such sites, and they will occupy overlapping geographical regions to ensure smooth transition from one cell to the next as the user travels in the region covered by the cellular system.

A user of a remote station 10, i.e. a system including a potentially mobile computer such as a conventional portable or laptop computer 30 (see Figure 2) which is distant from the base system 20, will connect the computer 30 to a cellular telephone or modem 40. The telephone 40 either includes a modem integrally built into it, or if it is a more conventional cellular telephone, it must be connected to a modem for the transfer of data. Also integrally included is a control logic circuit 90, which may be implemented by the use any one of many standard processors. As will be seen in the course of the following discussion, given the teaching of the present invention it is a straightforward matter to program such a processor to carry out the invention.

The following discussion will be presented primarily in terms of a remote user initiating the transmission of a file or other data in a data session (which may be full duplex) between a mobile station and a base system. However, the teaching of this invention is equally applicable to transference of data from the base system 20 to the remote system 10. When a user wishes to transfer data to the base system 20, he or she places a call in a conventional fashion over the cellular system. In a typical cellular communications system, there will be a forward control channel (or access channel) 50 by which data is transmitted from the cell site to the remote system 10, and a reverse control channel (or paging channel) 60 which is transmitted from the remote system 10 to the cell site. See Figure 3. In some systems, these may be combined into a single control channel. In either case, the control channels carry only data information. There are also cell-site transmit channels 70 and mobile transmit channels 80, which comprise multiple voice channels, as shown in Figure 3.

There will typically actually be many available control channels (also known as set-up channels) available in a given cellular system. When a call is placed from the remote system 10, the system 10 selects the appropriate control channel, normally the one whose signal is strongest, and receives over that channel from the cell site (here, cell site A) the system information for the cellular system. This information includes status information for the voice channels 70 and 80, indicating whether any of these channels are idle, i.e. available. In normal (real-time voice) operation, as soon as an "idle" status is detected for a voice channel, the remote system 10 initiates the call specified by the user, via the reverse control channel 60, and the call will then be engaged over one of the pairs of channels 70 and 80.

In the present invention, data transfer information is also transmitted over the reverse control channel 60, relating to the desired transmission of data from the remote system 10 to the base system 20. This additional information includes: a code that the user wishes to send data information; the size of the file to be sent; and a priority code. The size-of-file code may be used to assign priorities based upon the length of files to be sent. Alternatively or in addition, a code may be sent indicating the estimated transfer time for completion of the session.

The user may deliberately select a priority which is lower or higher than that which would normally be assigned to the transmission. This will be especially useful when there is a different charge rate from the cellular service company for data transmissions vis-a-vis voice calls. Thus, if a data transmission is charged at a lower rate, the user may intentionally override the "data" status of the transmission by assigning it a priority normally used for voice calls; this would make the transmission immediate, and subject it to the higher rate.

Conversely, since cellular charges are generally lower at non-peak times, the user may give the desired transmission a priority code which will ensure that it will be sent at a low-rate period. The time for actually executing the data session may also be specified. The cell site A is managed by control logic, which may be implemented in a conventional microprocessor 100, and which includes software compatible with that stored in the computer 30 and control logic 90. In one embodiment, the processor 100 controls the operation of a standard cellular system transceiver 110, which is pan of the ceil site A. In the present invention, however, it is important to note that the actual control of the data session (i.e., transmission of the data) may be carried out either by the cell site or the remote system 10. The former approach has the advantage that the control of access to the cellular communications channels already resides in the cell site (as well as the switching office), so this centralizes the control function and ensures compliance with rules on data transmission access.

The latter approach has the advantage that new cellular equipment or remote system software can be upgraded as developments are made to it, simply by incorporating the new features in new products. In this case, the cell site will generally provide a certain minimum amount of information which is used by the remote system 10 in governing its own access to the cellular system for the purpose of data transmission.

However, the remote system 10 may also operate independently of the cell site, and contain all of the necessary software to implement the invention in certain embodiments. An example of this is in the management of the transmission of data at non-peak times of day. The necessary information and software may be reside in the remote system 10, which is thus self-governed in the transmission of data sessions. Other specific operations can be carried out in such a unilateral manner, in which cases the cell site need not be provided with the software of the invention.

As cellular telephones and modems become more sophisticated, it will even become possible to include the call management software of the invention in a processor contained within the telephone or modem itself, or even inside a pager which has data transmission capability.

Thus, although there are practical differences between these two approaches of where the actual control over the procedure resides, functionally they produce equivalent results of data session management. When the cell site receives the code that the mobile user is sending data, it determines whether the usage rate of its available channels is below a predetermined maximum. For instance, the cell site processor 100 (or, as noted above, the remote system's computer, such as computer 30 shown in Figure 2) may be programmed to disallow data transmission whenever the usage rate of the available channels exceeds 80%. This maintains a minimum level of available channels for the initiation of voice calls by other users.

The cell site processor 100 or remote computer 30 may also be programmed to allow data transmission only at certain non-peak hours of the day, excluding rush hours, lunchtime, and so on. Other criteria may be chosen, with the crucial factor being that the appropriate computer (30 or 100) must be given control over when and whether to allow the transmission of data. In any case, the priority code selected by the user is taken into account in completing the transmission. The remote computer 30, the cell site processor 100, and/or the processor 90 of the remote system includes a buffer memory for temporarily storing relatively small blocks of data to be transmitted at an appropriate time for the cellular system. In the present application, a "session" may be taken to means a group of data blocks which are to be transmitted together (and may also refer to the actual transmission of such data). Such blocks may be status or location data for the remote system, or short voice-mail type messages to be left at the base system, or other data for which the time of transmission is not crucial. Thus, a voice mail message may be identified as such by the remote user with a predetermined code, for which the user interface is preferably very simple, such as a button on the mobile telephone. When the cell site receives this code, it determines that a voice mail message is about to arrive, and therefore does not search for an idle voice channel; rather, it commences reception of the message immediately, and stores it in its local buffer. Then, when conditions are favorable, the message is sent on to the specified recipient telephone number.

Alternatively, either the control logic 90 or the processor 100 may detect the code and perform the buffering operation on the voice mail (or other) information its own buffer, and attempt to send it at a time which is specified by the remote user, or at which it detects an idle channel signal from the cell site. As with the file transfer discussed above, the transmission is preferably subject to a maximum usage rate criterion.

Now referring to Figure 4, the step-by-step procedure for carrying out data transmission using the present invention will be discussed. As indicated above, this example is in terms of a transmission from the remote system 10^' to the cell site, and thence to the switching office, the central office, and another user, such as at the base system or even another mobile system. However, it is equally applicable to data transmissions originating at a conventional base system and transmitting to a mobile system. The user first initiates the call, at box 210, to transmit the desired data or voice mail, assigning a priority code if desired. The remote system 10 automatically generates a default priority code if no override code is specified, and also generates the other necessary codes, including the size-of- file (or size-of-session) code and the code identifying the transmission as a data transmission.

If there are no data transmission codes included, or if the priority code has been assigned as being that of a voice call, then at box (i.e., decision diamond) 220 the cell site is immediately instructed to put the call through, subject to the normal limitations in a cellular system, such as availability and strength of channels. However, if the data codes are present, then the method of the invention proceeds to box 240.

The method then, at box 240, determines whether the usage conditions meet certain predetermined criteria. As mentioned above, these will include usage rate of the cells at the time of the attempted transmission, time-of-day limitations-if any-imposed by the assigned priority code, size-of- file restri ions, and so on.

If the predetermined criteria are not met, such as if the available channels are too crowded or if no channel is available, or if the priority code indicates that an off-peak transmission is desired, then the method branches to box 250. A this point, the user has the option of terminating the attempted transmission. For instance, if the user finds, after attempting to make the data transmission, that the call will not go through because of overcrowded channels, he or she may terminate the call and place it again with a voice-level priority code. However, in one embodiment the system may include an override to prevent data transmissions from being given top priority.

If the terminate option is selected, the method branches to box 350, and the call is terminated. As an alternative, the user may be given the option of changing the priority code without having to terminate and restart the transmission. This is done by displaying at the remote computer a message giving an options menu of how to proceed: whether to terminate the transmission, change the priority code, or proceed. In the last case, the method branches to box 250, which implements a "wait" period. The wait period may be either a predetermined length of time, after which the call is again attempted (at box 240); or the wait may continue until a predetermined time of day, determined by the priority code or the time-of-transmission code set by the remote user. Once the predetermined criteria considered in box 240 are met, the method proceeds to box 270 and places the call over the cellular network. Data is then transmitted, as at box 280, from the mobile system 10 to the cell site, and on to the switching office and central office.

During transmission of the data, which may be lengthy, the system of the invention periodically checks, at box 290, to ensure that the usage conditions continue to be met. Preferably, the frequency rate of this check is quite high, on the order of once every few seconds or greater. This is to respond to possible increases in voice traffic to the point that data transmissions encumbering the cellular network should be ceased. Thus, at such a point the method branches to box 300, where the user is again prompted to select options of terminating the call, reassigning its priority code, or proceeding. If the terminate option is selected, the method branches to box 350, and the call is terminated. If the priority is reassigned (not separately shown in the flow chart), the appropriate action is taken; i.e., if the priority code is decreased, then the call may cease until the usage level of the cellular channels decreases, or if the priority code is increased, then the data transmission may then be given the equivalent priority of voice calls for future actions. If the user does not choose to terminate the call, and does not reassign the priority code, then reception of data by the cell site processor 100 is automatically ceased, as at box 330. A wait period is then implemented, at box 340, which involves the same considerations as wait period 200. The system then checks again, at box 320, whether the usage conditions criteria are met; if not, the method returns to box 300, and performs this loop repeatedly until a "yes" condition is found at either box 300 or box 320, or until the priority code is altered by the user as discussed above.

Once the predetermined usage conditions criteria are again met, then the reception of data is recommenced, as at box 310. During reception, the method periodically checks, at box 290, to ensure that the conditions continue to be met.

As long as the conditions are met, the method will proceed from box 290 to box 300. The user has an effectively continuous option to terminate the transmission, which if exercised will cause the method to branch to the "terminate call" step at box 350. If this option is not exercised, data reception by the cellular site continues, as indicated at box 310, and the method loops to box 290.

The system of the invention constantly monitors the status of the transmitted data, and stores it locally at the cellular site, so that when reception is ceased at box 330, and then recommenced at box 310, the system may automatically pick up where it left off, without duplication of data transmission.

Often in the course of a cellular telephone call, unwanted noise and interruptions occur. Errors in the transmitted data may be taken care of by means of standard error-checking procedures commonly in use today. However, unexpected interruption of a data transmission must also be accommodated. The constant update on the status of the transmission, including identification and storage in memory at the cellular site (and retransmission to the base system) of all received data blocks, is important for this purpose. If the call is unexpectedly terminated, such as due to transmission conditions, then both the remote computer 30 and the cell site processor 100 will detect this, and both will have the necessary information on which data block to begin with when recommencing transmission of the data. The software implementing the present invention includes instructions for the mobile system 10 to retry the transmission of the data if such an interruption occurs. This removes the burden from the mobile user of manually resending the data.

The transmission is ultimately terminated when the end of the data stream or voice mail message is reached. This is accomplished by automatically inseπing a "terminate" code at the end of each data session, so that the call from the mobile user's cellular modem is automatically ended when the data have been transmitted. In this way, the mobile user does not have to monitor the transmission, and need not be concerned that connect charges will be incurred once transmission is complete.

Each of the cell sites B-G shown in Figure 1 is essentially identical to cell site A as depicted in the block diagram of Figure 2. When a mobile user travels from one cell to another, as is typical for automobile- or boat-based systems, then a handoff from one cell to the next takes place, controlled by the switching office. Thus, if the user moves from cell A to cell B, as shown in dotted fashion for the remote system 10, the switching office hands off the call to cell site B. The handoff procedure is carried out in a manner which is conventional in cellular communications systems.

Cell site B must now manage the transmission of the data session which had heretofore been managed by cell site A. Thus, in an embodiment where the cell site has the primary responsibility for managing data block transmission, cell site B must include a processor and the software implementing the invention, fully duplicating the functionality of cell site A. In the embodiment discussed above wherein the processor 30 has the primary responsibility for managing transmission of the data blocks, less is required of the cell sites; only the minimal information of cellular channels usage and the like is required, while the crucial information of status of the data session's transmission resides in the processor 30. The same is true if the control logic 90 is the managing processor.

The current status of the data transmission, as well as the status information for the data session (size of file, priority code, etc.) are transmitted to cell site B at the time of handoff. If the cell site processor 100 is the managing processor, this is most effectively done by providing the switching office with software for its own processor (not separately shown) which acts in conjunction with the conventional cell transfer procedures, adding the functions of also transmitting to cell B the data session information and transmission status information. This creates a seamless handoff of the mobile user's data transmission as the user moves among the available cells.

In a preferred embodiment of the system, the remote system 10 also maintains a fully redundant set of the information relating to the status of the data transmission. This is used for error checking as the user move from cell to cell.

Utilizing the remote processor 30 as the managing processor has the advantage that any information regarding the temporary status of transmission of a data session is stored in the system originating the transfer and in which the data blocks reside, rather than at the central location of the cell site-which might involve too cumbersome a storage problem (for many thousands of file transfers in a cellular communications region), and additionally presents the problem of how long to store such status data before disposing of it.

It will frequendy be the case the a mobile user wishes to transfer files to two different recipients, such as to two colleagues who are in different offices. If the system attempts to place a call to a base station the first of these offices and receives a busy signal, it will then terminate that attempt, and try instead to reach the other office. These attempts will be repeated until one of the calls is successfully placed. If the successful call is interrupted for any of the reasons noted above, the system 10, or fails for some reason, the system 10 is instructed to attempt the call that has not yet been made, pending success of the incomplete call. In this way, one or more files may be queued, and then transferred to two different locations in a multiplexed or time-interleaved fashion.

Use of the above apparatus and method thus allows for fully automatic transmission of data between mobile users and their base systems. Each of the above procedures is utilized, regardless of the origin or destination of the data transmission call. The involvement of the user is thus unnecessary once the call is placed, and yet there is no interference with voice calls on the cellular system.

Other specific methods and apparatus for implementing the present invention may be made without departing from the scope of the invention.

Claims

ClaimsWhat is claimed is:

1. An method for transmission of a first data session from a first communications station to a second communications station via one of a plurality of communications channels managed by a control processor, including the steps of: (1) sending status information relating to said data to the control processor, said data including an identification of the amount of said data to be transmitted and a priority code;

(2) determining whether usage conditions of the communications channels and the status information meet predetermined criteria for allowing data transmission;

(3) if step 2 is affirmative, then commencing transmission of the first data session to the second station.

2. The method of claim 1 , wherein step 2 includes determining whether a usage rate of the communications channels is below a predetermined level.

3. The method of claim 1, wherein step 2 includes determining whether the priority code matches a minimum predetermined priority code level for allowing data transmission.

4. The method of claim 1, further including, after step 3, the steps of:

(4) determining whether the usage conditions and status information continue to meet the predetermined criteria;

(5) if step 4 is affirmative, then continuing transmission of the first data session to the second station; and

(6) if step 4 is negative, then ceasing transmission of the first data session to the second station.

5. The method of claim 4, including, before step 6 and if step 4 is negative, the steps of:

(7) storing status data relating to the current status of transmission of the first data session;

(8) waiting a predetermined wait period;

(9) repeating step 4;

(10) reiterating steps 7 through 9 until step 4 results in an affirmative determination, and then recommencing transmission of the first data session at step 5.

6. The method of claim 1, including the steps ofc

(11) monitoring input to the system to determine whether a terminate code has been received; and

(12) when a terminate code is received, terminating the transmission of the first data session.

7. The method of claim 6, wherein the terminate code is input by a user at the first station.

8. The method of claim 6, wherein the terminate code comprises a portion of the first data session, indicating that the transmission thereof is complete.

9. The method of claim 1, wherein the usage conditions include a predetermined maximum level of usage of the communications channels before allowing data transmission as in step 2.

10. The method of claim 1, wherein, if step 2 is negative, then prompting a user of the method with an option to alter the priority code.

11. The method of claim 1, wherein the priority code relates to a predetermined hierarchy or priority between voice calls and data transmission.

12. The method of claim 1, wherein the priority code relates to a time of day for completing transmission of the data.

13. The method of claim 4, wherein the method is for sending a plurality of data sessions to a plurality of communications stations, in a time- interleaved fashion, and further including, after step 6, the steps of:

(13) determining whether a second data session is queued for transmission to a third communications station;

(14) if step 13 is affirmative, then, while transmission of the first data session to the second communications station is ceased, proceeding with steps 1 through 6 for the second data session; and

(15) if the transmission of the second data session is ceased, then returning to reiterate steps 1 through 6 for the first data session.

14. An apparatus for the transmission of a first data session from a first communications station to a second communications station via one of a plurality of communications channels managed by a control system, including: a processor for controlling the transmission of said first data session; means coupled to said processor for storing said first data session and for storing first status information relating to said data session; means coupled to said processor and controlled thereby for initiating transmission of said first data session to said second communications station via a first said communications channel; means coupled to said processor for determining whether a first predetermined transmission criterion is met by said first status information; means coupled to said processor for ceasing said transmission if said criterion is not met.

15. The apparatus of claim 14, wherein said storing means is also for storing second status information, relating to status of transmission of said first data session.

16. The apparatus of claim 15, further including: means coupled to said processor for recommencing said transmission of said first data session at a point where said transmission was ceased, utilizing said second status information.

17. The apparatus of claim 14, wherein: said first status information includes a data transmission priority code indicating an attempt to transmit data; and said transmission criterion includes a priority code hierarchy including said data transmission code and a voice transmission code, wherein said data transmission code is has a lower priority than said voice transmission code.

18. The apparatus of claim 17, wherein said transmission criterion includes an instruction for said processor to implement data transmissions only when a level of use of said communications channels for voice transmissions falls below a predetermined usage rate.

19. The apparatus of claim 17, wherein said transmission criterion includes an instruction for said processor to implement data transmissions only at a predetermined time.

20. The apparatus of claim 19, wherein said predetermined time is a non-peak usage time.

21. The apparatus of claim 19, wherein said predetermined time is a specific time of day.

22. The apparatus of claim 14, further including means coupled to said processor for reattempting said transmission until said predetermined criterion is met.

23. The apparatus of claim 22, wherein said apparatus is for transmitting a plurality of data sessions to a plurality of communications stations, and wherein: said storing means is also for storing a second data session and third status information relating to said second data session; said initiating means is also for initiating transmission of said second data session to said third communications station; and said means for determining whether said first predetermined transmission criterion is met by said first status information is also for determining whether said first predetermined transmission criterion is met by said second status information; and wherein the apparatus further includes: means coupled to said processor for determining whether said second data session is queued for transmission to said third communications station; and means coupled to said processor for commencing transmission of said second data session upon cessation of said transmission of said first data session, and for commencing transmission of said first data session upon cessation of said transmission of said second data session, for completing transmission of both said first and second data sessions in a time-interleaved fashion.

24. The apparatus of claim 23, wherein said predetermined transmission criterion comprises a criterion for determining whether said transmission of either of said first and second data sessions has been successfully initiated.