WO2010008250A2

WO2010008250A2 - Apparatus for managing a flow control process and method thereof

Info

Publication number: WO2010008250A2
Application number: PCT/KR2009/003981
Authority: WO
Inventors: Ju Hyung Son; Seung Hyup Ryoo; Jae Joon Park
Original assignee: Lg Electronics Inc.
Priority date: 2008-07-18
Filing date: 2009-07-17
Publication date: 2010-01-21
Also published as: WO2010008250A3; WO2010008252A3; WO2010008252A2

Abstract

An apparatus for managing a flow control process and a method thereof are disclosed. A method of managing a flow control process in a device has first and second buffer information. The method includes determining whether to transmit a data message to the other device by checking the first buffer information, the first buffer information being related with an available buffer size of the other device, the other device being communicated with the device, transmitting the data message including second buffer information to the other device according to the determining step, the second buffer information being related with a buffer size, receiving third buffer information from the other device, the third buffer information being related to a buffer size of the other device, and updating the first buffer information to the third buffer information.

Description

APPARATUS FOR MANAGING A FLOW CONTROL PROCESS AND METHOD THEREOF

The present invention relates to an interface between elements contained in a device, and more particularly to a flow control process between elements contained in a device.

Recently, a Near Field Communication (NFC) concept as a substitute for wired communication or infrared communication has been introduced to the market. As a result, high-speed data communication can be achieved among a plurality of electronic appliances using a radio frequency instead of a physical cable. In addition, data communication is wirelessly achieved among a plurality of electronic devices, such that there is no need to connect a cable to any devices (for example, a digital camera, a printer, and the like). Based on the above-mentioned radio frequency (RF) communication, not only text data but also voice data can be communicated among a plurality of electronic devices.

Accordingly, the present invention is directed to an apparatus for managing a flow control process and a method thereof that substantially obviate one or more problems due to limitations and disadvantages of the related art.

Flow control is the mechanism by which the rates of data transmission between devices are managed. When one device transmits data to another device, which has different transmission speeds or data processing speeds, without flow control, data will be lost due to buffer overflow at the destination side.

The object of the present invention can be achieved by providing a method of managing a flow control process in a device having first and second buffer information, the method including determining whether to transmit a data message to the other device by checking the first buffer information, the first buffer information being related with an available buffer size of the other device, the other device being communicated with the device, transmitting the data message including second buffer information to the other device according to the determining step, the second buffer information being related with a buffer size, receiving third buffer information from the other device, the third buffer information being related to a buffer size of the other device, and updating the first buffer information to the third buffer information.

In another aspect of the present invention, there is provided an apparatus for managing a flow control process, the apparatus including a controller configured to control to determine whether to transmit a data message to other device by checking first buffer information, the first buffer information being related with an available buffer size of the other device, the other device being communicated with the device, configured to control to transmit the data message including second buffer information to the other device, the second buffer information being related with a buffer size, configured to control to receive third buffer information from the other device, the third buffer information being related to a buffer size of the other device, and configured to control to update the first buffer information to the third buffer information.

The present invention controls transmission or reception flow of data messages, commands, and events among elements contained in a device, such that it can guarantee stable and accurate data communication.

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constituted a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention.

In the drawings:

FIG. 1 is a block diagram illustrating a system according to the present invention.

FIG. 2 is a block diagram illustrating a controller contained in a system according to the present invention.

FIG. 3 is a flow chart of a command, an event, and a data message according to the present invention.

FIG. 4 is an open loop flow control process according to the present invention.

FIG. 5 is a query based flow control process according to the present invention.

FIG. 6 is a periodic flow control process according to the present invention.

FIG. 7 is an event based flow control process according to the present invention.

FIG. 8 illustrates formats of command and event related to a buffer size request according to the present invention.

FIG. 9 illustrates formats of parameters of "Total_Buffer_Size", "Current_Buffer_Size" and "Buffer_Size_Report_Period" contained in a command and event related to a buffer size request according to the present invention.

FIG. 10 is a flow control process executed under bidirectional transmission of a data message according to another embodiment of the present invention.

FIG. 11 is a flow control process executed under a unidirectional transmission of a data message according to another embodiment of the present invention.

FIG. 12 illustrates a format of a data message according to the present invention.

FIG. 13 illustrates a format of "Announce_Credit_Event" according to the present invention.

Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings.

The following detailed description includes specific details in order to provide a thorough understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced without such specific details. Prior to describing the present invention, it should be noted that most terms disclosed in the present invention correspond to general terms well known in the art, but some terms have been selected by the applicant as necessary and details thereof will hereinafter be disclosed in the following description of the present invention. Therefore, it is preferable that the terms defined by the applicant be understood on the basis of their meanings in the present invention.

Also, wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.

Embodiments of the present invention will hereinafter be described with reference to the annexed drawings in order to provide those skilled in the art with a thorough understanding of the present invention.

FIG. 1 is a block diagram illustrating an overall system according to the present invention.

For convenience of description and better understanding of the present invention, although the present invention uses a Near Field Communication (NFC) environment, which is a short-range wireless connectivity technology that enables simple and safe two-way interactions between electronic devices, as an exemplary communication environment, the scope or spirit of the present invention is not limited thereto and the present invention can be applied to other communication environments as necessary.

As shown in FIG. 1, an overall system for use in a Near Field Communication (NFC) environment may include an NFC device 10 and an external source 20.

The NFC device 10 may include a host 100 for controlling a controller 200 and Secure Elements (SEs) 301, 302 and 303, and the controller 200 for controlling communication between the NFC device 10 and the external source 20 under the NFC environment. The external source 20 communicates with the NFC device 10 through the controller 200 contained in the NFC device 10 under the NFC environment, and may include a reader for a transportation card or an access control system, a tag of a smart poster, etc.

FIG. 2 is a block diagram illustrating a controller 200 according to the present invention.

Referring to FIG. 2, the controller 200 may include an interface 201, a message manager 202, a buffer 203, a processor 204, and an antenna 205.

The interface 201 is defined as a logical and physical connection path among the host 100, the

SEs

301, 302 and 303, and the controller 200. Particularly, according to the embodiment of the present invention, the interface 201 may be used as a connection path between the host 100 and the controller 200 under the NFC environment, and may be defined as an NFC Host Controller Interface (NCI).

In the meantime, the interface 201 may be implemented in different ways according to whether one host 100 is connected to the controller 200 (i.e., a single-host architecture) or other constituent components including any secure element (SE) in addition to the host 100 are connected to the controller 200 (i.e., a multi-host architecture). Although the NCI scope does not change, the NCI needs to support additional features in a multi-host architecture, compared to the single-host architecture. Therefore, the required NCI functionality is different in a single-host or multi-host environment. While the interface 201 is included in the controller 200 in the exemplary embodiment of the present invention, it may be incorporated into the host 100 or into both the controller 200 and the host 100.

The interface 201 transmits signals received from the host 100 to individual constituent components of the controller 200, or sends signals processed by the constituent components to the host 100. In more detail, the interface 201 receives a command from the host 100, sends the command to the message manager 202, receives a response for the command from the message manager 202, and sends the response to the host 100. In the present invention, a concept including the command and the response is defined as a message. Specifically, the present invention will disclose a message flow in the scope of the NFC Host Controller Interface (NCI) used as the interface 201.

The message manager 202 receives a command from the interface 201 and generates a response message to the command. The response message may include an initial response indicating an acknowledgement message corresponding to the command originated from a host 100, and a subsequent response transmitted after the initial response such that it is used as one of a plurality of responses corresponding to the command. The controller 200 receives the command according to the embodiment of the present invention. In contrast, it is also obvious to those skilled in the art that the controller 200 generates a command and transmits the command to the host 100, and the host 100 generates a response to the command.

In addition, multiple responses corresponding to the command may be generated together with an identifier for identifying a transmission entity of such responses. The identifier generated from the message manager 202 may be equal to an identifier for identifying the command generated from the host 100.

Further, multiple responses corresponding to the command may be generated together with an identifier for identifying a transmission entity of such responses. The identifier generated from the message manager 202 may be equal to an identifier for identifying the command generated from the host 100.

Besides, upon receiving a get command and a set command from the host 100, the message manager 202 generates a get command response to the get command and a set command response to the set command. The get command response is generated in response to a get command including a parameter identifier for retrieving a parameter value of the controller 200, and the get command response has a retrieved value corresponding to the parameter. The set command response is generated in response to a set command including a parameter identifier for setting a parameter of the controller 200 to a target value.

The buffer 203 stores a command generated from the host 100 and a response generated from the message manager 202, and transmits the command and the response to the processor 204. The buffer 203 may be used as a temporary storage unit while the controller 200 performs a given process. In addition, the buffer 203 may also be used to disperse the work load of the processor 204.

The processor 204 executes the command received from the buffer 203. The message manager 202 monitors the execution status of the processor 204, and generates the aforementioned initial response or subsequent response (i.e., an event) according to the execution status.

The antenna 205 is used as an interface between the controller 200 and the external source 20 for Near Field Communication (NFC), and is used for transmission and/or reception of a radio frequency (RF) signal.

According to the present invention, a data flow between a sender and a receiver may be classified into a command flow, an event flow, and a data message flow. Hereinafter, types of the above-mentioned data flows for use in the system will be described with reference to FIG. 3.

FIG. 3 shows flows of a command, events, and data messages between the host 100 and the controller 200 according to the present invention.

It is obvious to those skilled in the art that the sender may be the host 100 and the controller 200, and the receiver may also be the host 100 and the controller 200. For convenience of description and better understanding of the present invention, the following description assumes that an entity of the command is the host 100.

A command generated from the sender may command the receiver to carry out a specific action instructed by the command itself. The command may be answered with at least one event. Referring to an upper part of FIG. 3, when the host 100 transmits the command to the controller 200, the controller 200 transmits a first event (Event 1) and a second event (Event 2) as responses to the command. The first event (Event 1) indicates acknowledgement of reception of the command, and the second event (Event 2) is a final response indicating the completion of an operation for processing the command in the direction from the controller 200 to the host 100. After the first event (Event 1) has occurred, the second event (Event 2) is generated as one of a plurality of subsequent responses corresponding to the command. In FIG. 3, Event 1 may be implemented as mandatory and Event 2 may be implemented as optional, however, it may be possible implementing Event 1 as optional and Event 2 as mandatory. In other words, the first event (Event 1) and the second event (Event 2) may be implemented as mandatory or optional responses to the command. In this case, it is necessary to define the relationship between the command and the

Event

1 or 2 used as a response to this command. This relationship is referred to as a transaction.

The transaction is started with a command and is ended when this command is completed, and the concept of the transaction is applicable to commands and events having the parameter transaction identifier (TID). At least one event corresponding to the response of a command may have the same transaction identifier (TID) in connection with the command to which the event belongs.

The transaction identifier (TID) value may not be reused as long as the transaction is not complete. In other words, if the sender transmits a command, all events and commands associated with the transmitted command have the same transaction identifier value until the action based on the above-mentioned command is completed.

Referring to a lower part of FIG. 3, a data message can be sent from the host 100 to the controller 200 or vice versa. The sender (i.e., the host 100 of a data message) may not require an acknowledgement from the receiver (i.e., the controller 200).

The importance of a flow control provided when a command, events, and data messages are communicated between elements contained in the above-mentioned device, more specifically, between the host 100 and the controller 200, is the same as that of the above-mentioned description. Hereinafter, the embodiments of the flow control process will be given centering on the host 100 and the controller 200.

Flow control may be used in the direction from the host 100 to the controller 200 so as to control the buffer 203 in the controller 200. Flow control may also be required in the direction from the controller 200 to the host 100. That is, the flow control may be implemented not only in the host 100 but also in the controller 200.

For convenience of description, the following embodiment assumes that the host 100 is set to a sender and the controller 200 is set to a receiver. In contrast, it is obvious to those skilled in the art that the controller 200 may also be set to the sender and the host 100 may also be set to the receiver.

FIGS. 4 to 9 show flow control processes according to the present invention. Provided that a buffer size is recognized by a command related to the buffer size and an event related to this command, the embodiment shown in FIGS. 4 to 9 relates to a method for transmitting other commands, events, and data messages in consideration of the recognized buffer size.

Flow control processes shown in FIGS. 4 to 9 may be classified into an open loop flow control process and a closed loop flow control process according to whether or not information of a current buffer size is fed back from the receiver.

In addition, the closed loop flow control process may be referred to as a query based flow control process, a periodic flow control process, an event based flow control process, or the like according to the presence or absence of periodicity of an event value fed back from the receiver. The above-mentioned classification and denomination are disclosed only for illustrative purposes, and the scope or spirit of the present invention is not limited thereto.

FIG. 4 shows an open loop flow control process according to the present invention.

Referring to FIG. 4, if the host 100 transmits a command related to a request of a total buffer size to the controller 200 at step S10, the controller 200 transmits an event related to the total buffer size to the host 100 by replying to the command at step S15. Speed or the like of the command, each event, and each data message transmitted to the controller 200 may be controlled on the basis of the received total buffer size. In FIG. 4, the size of the buffer 203 contained in the controller 200 can be confirmed by only one request of the total buffer size, and a transmission speed (or a transfer rate) of the command, event, or data message can be adjusted on the basis of the confirmed buffer size, so that the burden of signal processing in the host 100 and the controller 200 according to a flow control process can be minimized.

FIG. 5 shows a query based flow control process according to the present invention.

Referring to FIG. 5, if the host 100 transmits a command related to a request of a buffer size that is currently available for the controller 200 to the controller 200 at step S20, the controller 200 transmits an event related to the currently-available buffer size to the host 100 by replying to the command at step S25. The host 100 may control the speed or the like of the command, event, and data message transferred to the controller 200 on the basis of the received current buffer size.

FIG. 6 shows a periodic flow control process according to the present invention.

The periodic flow control process of FIG. 6 is different from the query based flow control process of FIG. 5 because the periodic flow control process transmits an event related to the current buffer size to the host 100 at intervals of a predetermined period of time defined by the host. On the other hand, in the periodic flow control process, although a current time reaches a transmission time of the event related to the current buffer size according to the period defined by the host 100, the event related to the current buffer size may not be transferred to the host 100 under the condition that there is no change in buffer size.

FIG. 7 shows an event based flow control process according to the present invention.

Referring to FIG. 7, when the host 100 transmits a command related to a request of a current buffer size to the controller 200, a buffer-size related event is generated whenever a buffer size is changed in response to the command, such that the generated event can be transmitted to the host 100 whenever the buffer size is changed. The host 100 may control the speed of the command, event, and data message transferred to the controller 200 on the basis of the received buffer size. In this embodiment, the host 100 can acquire the latest buffer size information of the controller 200.

FIG. 8 shows a format of command and event related to a buffer size request according to the present invention.

Although the embodiment of FIG. 8 defines a command related to a total buffer size request as "NCI_Read_Total_Buffer_Size_CMD" and defines a command related to a current buffer size request as "NCI_Read_Current_Buffer_Size_CMD" for convenience of description, the scope or spirit of the present invention is not limited thereto.

"NCI_Read_Total_Buffer_Size_CMD" may include parameters about a Source Address (SA), a Destination Address (DA), and a Transaction ID (TID) as the command related to the total buffer size request of the open loop flow control process. The response event related to such parameters is "NCI_Read_Total_Buffer_Size_EVENT" and may include parameters of a Source Address (SA), a Destination Address (DA), a Transaction ID (TID), and a total buffer size (Total_Buffer_Size).

"NCI_Read_Current_Buffer_Size_CMD" is a command related to a current buffer size request of the closed loop flow control process shown in FIGS. 5 to 7, and may include parameters of a Source Address (SA), a Destination Address (DA), a Transaction ID (TID) and a buffer size report period (Buffer_Size_Report_Period). A response event related to "NCI_Read_Current_Buffer_Size_CMD" is "NCI_Read_Current_Buffer_Size_EVENT" and may include parameters of a Source Address (SA), a Destination Address (DA), a Transaction ID (TID), and a current buffer size (Current_Buffer_Size).

The parameter of the transaction ID (TID) is the same as described above. The transaction ID (TID) originated from one command has the same value until the command is completed. Therefore, in FIG. 8, the transaction ID (TID) value of the above command "NCI_Read_Total_Buffer_Size_CMD" is determined to be equal to that of the event "NCI_Read_Total_Buffer_Size_EVENT".

Detailed descriptions of parameters of "Total_Buffer_Size", "Current_Buffer_Size" and "Buffer_Size_Report_Period" will be given below with reference to FIG. 9.

FIG. 9 shows formats of parameters of "Total_Buffer_Size", "Current_Buffer_Size" and "Buffer_Size_Report_Period" contained in a command and event related to a buffer size request according to the present invention.

Referring to FIG. 9, "Total_buffer_size" indicates a maximum buffer size of the controller 200. "Current_Buffer_Size" indicates a currently available buffer size. "Buffer_Size_Report_Period" may indicate a characteristic of an event transmitted from the controller 200. If "Buffer_Size_Report_Period" is set to "0x01" the event based flow control process of FIG. 7 is carried out. If "Buffer_Size_Report_Period" is set to "0xFF", the query based flow control process of FIG. 5 is carried out. If "Buffer_Size_Report_Period" is set to "0x02 ~ 0xFE", the periodic based flow control process of FIG. 6 is carried out. In this case, the period of the event transferred from the controller 200 may have the value of 0x02 ~ 0xFE [ms]. On the other hand, if the host 100 does not want to receive the event related to the buffer size from the controller 200, the host 100 sets the parameter of "Buffer_Size_Report_Period" contained in "NCI_Read_Current_Buffer_Size_CMD" to "0x00" and transmits a command, such that the controller 200 may no longer transmit the event related to the buffer size.

FIGS. 10 to 14 show flow control processes according to another embodiment of the present invention. The embodiment shown in FIGS. 10 to 14 relates to a method for transmitting other commands, events, and data messages and at the same time providing information of a buffer. For the convenience of description and better understanding of the present invention, the following description will be given centering on transmission of data messages. However, it is obvious to those skilled in the art that the inventive concept of the present invention is also equally applicable to the command and the event.

FIG. 10 is a flow control process executed under bidirectional transmission of a data message according to another embodiment of the present invention. Although information about the buffer is referred to as "Remote_Buf_Avail" in the following embodiment, it will be apparent to those skilled in the art the scope or spirit of the present invention is not limited thereto. "Remote_Buf_Avail" may have a value defined as at least one of "Available Number of Buffer" and "available Size of Buffer". For convenience of description, it is assumed that "Remote_Buf_Avail" has a value corresponding to "available Number of Buffer" and a data message corresponds to the size of one buffer.

Referring to FIG. 10, in order to transmit a data message from the host 100 to the controller 200, the value of "Remote_Buf_Avail" contained in the host 100 is checked at step S100. If "Remote_Buf_Avail" has a value greater than zero "0", i.e., if the number of available buffers is one or more, the number of available buffers is reduced by one, and a corresponding data message is transmitted at step S110. In contrast, if "Remote_Buf_Avail" has a value of zero "0", it is impossible to transmit the data message to the controller 200. If transmission of the data message transferred from the host 100 to the controller 200 is confirmed in the host 100, the host 100 increases the value of "Remote_Buf_Avail" by one at step S120. On the other hand, the data message received from the controller 200 includes information about the buffer 203 of the controller 200 at step S130. A detailed description thereof will be given below with reference to FIGS. 12 to 14. The value of "Remote_Buf_Avail" contained in the host 100 may be replaced with the buffer information (i.e., the number of available buffers) contained in the data message by the host 100 at step S140. As a result, the host 100 can update the information about the buffer 203 of the controller 200.

FIG. 11 is a flow control process executed under unidirectional transmission of a data message according to another embodiment of the present invention.

Compared with the embodiment of FIG. 10, the embodiment of FIG. 11 is different from that of FIG. 10 because the host 100 receives no data message from the controller 200. Therefore, in order to acquire the latest buffer information from the controller 200, the host 100 defines "Announce_Credit_Event". A detailed format of "Announce_Credit_Event" will be given below with reference to FIG. 13. "Announce_Credit_Event" may include buffer-associated information contained in the data message, for example, information about the number of available buffers. As a result, the value of "Remote_Buf_Avail" contained in the host 100 may be replaced with the buffer-associated information.

FIG. 12 is a format of a data message according to the present invention.

Referring to FIG. 12, the size of a buffer may be specified through the parameter of "Credit_Avail" and may also be specified as either an actual data value associated with a buffer size or the number of buffers. In addition, "Data Payload" may include information of data to be actually transmitted. Further, a data message header may include a message type which includes at least one command, event and data message, a Packet Boundary Flag (PBF) which is used to indicate the segmentation and reassembly information of a message, and a connection identifier which is used to identify the connection to which this data belongs.

FIG. 13 is a format of "Announce_Credit_Event" according to the present invention. "Announce_Credit_Event" of FIG. 13 is an independent event unconcerned with the command, and is different from the event corresponding to the response to the command of FIG. 3 in terms of a transaction identifier (Transaction ID) and the like.

Referring to FIG. 13, the size of a buffer may be specified through the parameter of "Credit_Avail" and may also be specified as either an actual data value associated with a buffer size or the number of buffers. On the other hand, in order to transmit the data message, a connection open stage for transmitting the data message must be firstly carried out between the host 100 and the controller 200. For example, if the connection open command is transferred from the host 100 to the controller 200, the controller 200 may perform assignment of a corresponding connection identifier as a connection open event. The data message transmission can be carried out after the connection identifier has been assigned. The connection ID (ConnID) of FIG. 13 indicates that the event is associated with the connection ID associated with data message transmission. In other words, it can be recognized that the flow control of FIG. 13 is based on a connection associated with the above-mentioned connection ID. "Command/Event Header" may include a message type, a Message Concatenation Field (MCF) which is used to indicate support for the concatenation between commands or events, a Packet Boundary Flag (PBF) field which is used to indicate the segmentation and reassembly information of a message, a Group Identifier (GID) field which is used to indicate the group of different Commands and Events, and an Optical Identifier (OID) field which is used to identify a command.

While the exemplary embodiments of the present invention have been described above in the context of the controller 200 being a command receiver, they are also applicable to the case where the controller 200 generates a command and transmits the command with parameters to the host 100.

While the present invention has been described and illustrated herein with reference to the preferred embodiments thereof, it will be apparent to those skilled in the art that various modifications and variations can be made therein without departing from the spirit and scope of the invention. Thus, it is intended that the present invention covers the modifications and variations of this invention that come within the scope of the appended claims and their equivalents.

Various embodiments have been described in the best mode for carrying out the invention.

As apparent from the above description, the present invention controls transmission or reception flow of data messages, commands, and events among elements contained in a device, such that it can guarantee stable and accurate data communication.

Claims

A method of managing a flow control process in a device having first and second buffer information, the method comprising:

determining whether to transmit a data message to the other device by checking the first buffer information, the first buffer information being related with an available buffer size of the other device, the other device being communicated with the device;

transmitting the data message including second buffer information to the other device according to the determining step, the second buffer information being related with a buffer size;

receiving third buffer information from the other device, the third buffer information being related to a buffer size of the other device; and

updating the first buffer information to the third buffer information.
The method of claim 1, wherein the third buffer information is included in a data message, the data message being transmitted from the other device.
The method of claim 1, wherein the third buffer information is included in an event, the event being transmitted from the other device.
The method of claim 1, further comprising:

adjusting the first buffer information when to transmit the data message to the other device.
The method of claim 3, wherein in the adjusting step, decreasing the available buffer size of the other device if the data message transmits to the other device.
The method of claim 3, wherein in the adjusting step, increasing the available buffer size of the other device if the transmitting step is accomplished.
An apparatus for managing a flow control process, the apparatus comprising:

a controller configured to control to determine whether to transmit a data message to other device by checking first buffer information, the first buffer information being related with an available buffer size of the other device, the other device being communicated with the device, configured to control to transmit the data message including second buffer information to the other device, the second buffer information being related with a buffer size, configured to control to receive third buffer information from the other device, the third buffer information being related to a buffer size of the other device, and configured to control to update the first buffer information to the third buffer information.
The apparatus of claim 7, wherein the third buffer information is included in a data message, the data message being transmitted from the other device.
The apparatus of claim 7, wherein the third buffer information is included in an event, the event being transmitted from the other device.
The apparatus of claim 7, wherein the controller is further configured to adjust the first buffer information when to transmit the data message to the other device.
The apparatus of claim 10, wherein the controller is configured to control to decrease the available buffer size of the other device if the data message transmits to the other device.
The apparatus of claim 10, wherein the controller is configured to control to increase the available buffer size of the other device if the data message transmission is accomplished.