JP3943558B2 - Packet communication method and packet communication system. - Google Patents

Description

  The present invention relates to a packet communication method and a packet communication system for transmitting packets at a predetermined transmission rate. In particular, the present invention relates to “HSDPA (High speed), which is a packet communication technique for the purpose of increasing the peak transmission rate in the downlink direction, reducing the transmission delay, increasing the throughput, and improving the efficiency of radio resources. The present invention relates to a packet communication method and a packet communication system using a “downlink packet access” method.

  FIG. 1 shows a packet communication system using the HSDPA method. As shown in FIG. 1, the packet communication system includes a core network CN and a radio access network RAN including a plurality of radio control apparatuses RNC and radio base station apparatuses Node B.

  The radio access network RAN is connected to the mobile device UE via a radio interface. As shown in FIG. 1, the radio access network RAN transmits a downlink packet transmission transport channel “HS-DSCH (High speed-Downlink Shared Channel)” to the mobile device UE.

  Here, with reference to the flowchart shown in FIG. 2, a state in which the transmission rate of the downstream packet is changed in the conventional packet communication system will be described (for example, see Non-Patent Document 1 and Non-Patent Document 2).

  As shown in FIG. 2, in Step 601, RLC (Radio Link Control) is performed on the logical channel “DTCH (Dedicated Traffic Channel)” mapped to the HS-DSCH between the radio access network RAN and the mobile device UE. ) A connection is established. Here, the transmission rate of the downlink packet (HS-DSCH transmission rate or DTCH transmission rate) is “Tx1 (384 kbps or less)”, and the packet transmitted via the RLC connection (RLC-PDU: Radio Link). The size of “Control-Packet Data Unit” is assumed to be “336 bits”.

  In step 602, the radio access network RAN changes the transmission rate of the downlink packet when the data amount of the packet to be transmitted increases. For example, the transmission rate of the downstream packet is changed to “Tx2 (over 384 kbps)”.

  In step 603, when the transmission rate of the downstream packet is changed, a re-establishment of the RLC connection between the radio access network RAN and the mobile device UE occurs.

In step 604, after occurrence of the above-described RLC connection re-establishment, the size of the RLC-PDU is changed to “656 bits”. Such a change in RLC-PDU size takes transmission efficiency into consideration.
3rd Generation Partnership Project Technical Technical Group Radio Access Network, 25.321 V5.4.0 Medium Access Control (MAC) 3 3rd Generation Partnership Project Technical Technical Group Radio Access Network, 25.322 V5.4.0 Radio Link Control (RLC) Prototype 3

  However, in the conventional packet communication system, when the transmission rate of the downstream packet is changed, a re-establishment of the RLC connection occurs, and thus the packet stored in the transmission buffer is deleted, resulting in a decrease in throughput. There was a problem.

  The present invention has been made in view of the above points, and packet communication that can change the transmission rate of a downlink packet while preventing a decrease in throughput due to deletion of a packet accumulated in a transmission buffer. It is an object to provide a method and a packet communication system.

  A first feature of the present invention is a packet communication method for transmitting a packet at a predetermined transmission rate, and when changing the predetermined transmission rate, the packet communication method depends on the availability of a transmission buffer for storing the packet. The gist is to change the size of the packet.

  According to a second aspect of the present invention, there is provided a packet communication system that transmits packets at a predetermined transmission rate, and when the predetermined transmission rate is changed, the packet communication system responds to an empty state of a transmission buffer for storing the packets. The gist of the present invention is to provide a packet size management unit that changes the size of the packet.

  According to this invention, according to the empty state of the transmission buffer, for example, when the amount of data of the packet stored in the transmission buffer is large, transmission by R-connection of the RLC connection is performed without changing the size of the packet. Deletion of packets in the buffer can be prevented.

  In the second aspect of the present invention, the packet size management unit is configured such that the data amount of the packet stored in the transmission buffer is equal to or greater than a first data amount threshold, or the remaining amount of the transmission buffer is When it is equal to or smaller than the first buffer remaining amount threshold value, the packet size can be configured not to be changed.

  In the second feature of the present invention, the data amount of the packet stored in the transmission buffer is equal to or greater than a second data amount threshold, or the remaining amount of the transmission buffer is the second buffer remaining amount. When it is equal to or less than the amount threshold value, a transmission rate changing unit that changes the predetermined transmission rate to a higher transmission rate can be provided.

  Further, in the second feature of the present invention, the transmission rate changing unit is configured such that the data amount of the packet stored in the transmission buffer is not less than the second data amount threshold continuously for a certain period, Alternatively, the predetermined transmission rate can be changed to a higher transmission rate when the remaining amount of the transmission buffer is not more than the second buffer remaining amount threshold value for a certain period of time.

  As described above, according to the present invention, a packet communication method capable of changing the transmission rate of a downstream packet while preventing a decrease in throughput due to the deletion of the packet stored in the transmission buffer 11, and A packet communication system can be provided.

(Configuration of packet communication system according to the first embodiment of the present invention)
With reference to FIG. 3, the configuration of the radio access network RAN in the packet communication system according to the first embodiment of the present invention will be described.

  The radio access network RAN according to the present embodiment includes a transmission buffer 11, a transmission buffer management unit 12, a transmission rate management unit 13, a packet size management unit 14, and a transmission unit 15.

  The transmission buffer 11 stores packets (RLC-PDU) to be transmitted to the mobile device UE via the RLC connection. The transmission buffer 11 may be configured to store packets to be retransmitted in the mobile device UE via the RLC connection. Further, the transmission buffer 11 may be configured to delete packets that have been accumulated for a certain period since being accumulated, packets that have been retransmitted a predetermined number of times, and the like.

  The transmission buffer management unit 12 manages the free space in the transmission buffer 11. Specifically, the transmission buffer management unit 12 manages the data amount (bit number or packet number) of packets stored in the transmission buffer 11, the remaining amount (free capacity) of the transmission buffer 11, and the like. .

  The transmission rate management unit 13 manages the transmission rate of downlink packets for the mobile device UE.

  For example, as shown in FIG. 4, the transmission rate management unit 13 downloads the packet when the packet data amount x stored in the transmission buffer 11 is equal to or greater than the second data amount threshold Thd2 for a certain period. The transmission rate of the direction packet can be changed from a predetermined transmission rate Tx1 (for example, 384 kbps or less) to a higher transmission rate Tx2 (for example, more than 384 kbps).

  Further, the transmission rate management unit 13 transmits the packet transmission rate in the downlink direction when the average value of the data amount x of the packet stored in the transmission buffer 11 for a predetermined period is equal to or greater than the second data amount threshold Thd2. Can be changed from a predetermined transmission rate Tx1 to a higher transmission rate Tx2.

  As shown in FIG. 4, the transmission rate management unit 13 transmits the packet in the downlink direction when the remaining amount Br of the transmission buffer 11 is not more than the second buffer remaining amount threshold Thbr2 for a certain period. The speed can be changed from a predetermined transmission speed Tx1 to a higher transmission speed Tx2.

  In addition, the transmission rate management unit 13 determines the transmission rate of the downstream packet as the predetermined transmission when the average value of the remaining amount Br of the transmission buffer 11 during the predetermined period is equal to or less than the second buffer remaining amount threshold Thbr2. The speed Tx1 can be changed to a higher transmission speed Tx2.

  In this way, the transmission rate management unit 13 can change the transmission rate of the downlink packet to a higher transmission rate when the data amount of the packet to be transmitted increases.

  Also, the transmission rate management unit 13 increases the transmission rate of the downlink packet to a higher transmission rate when a predetermined condition is satisfied, such as when the state of the radio channel with the mobile station UE is improved. It may be configured to change.

  The packet size management unit 14 manages the size of a packet (that is, the size of the RLC-PDU) transmitted to the mobile device UE over the RLC connection.

  Further, the packet size management unit 14 is configured to generate a re-establishment of the RLC connection and change the size of the above-described packet when changing the transmission rate of the downstream packet.

  In principle, the packet size management unit 14 is configured to increase the size of the packet when the transmission rate of the downstream packet is changed from the predetermined transmission rate Tx1 to the high transmission rate Tx2. For example, in such a case, the packet size management unit 14 changes the above-described packet size from “336 bits” to “656 bits”.

  However, as shown in FIG. 4, even when the packet size management unit 14 changes the transmission rate of the downstream packet, the packet data amount x stored in the transmission buffer 11 is the first When the data amount threshold value Thd1 is equal to or greater than the threshold value, Re-establishment of the RLC connection is not generated, and the above-described packet size is not changed.

  Also, as shown in FIG. 4, the packet size management unit 14 determines that the remaining amount Br of the transmission buffer 11 is equal to or less than the first buffer remaining amount threshold Thbr1 even when changing the transmission rate of the downstream packet. In this case, the R-connection is not generated and the packet size is not changed.

  As described above, the packet size management unit 14 does not change the size of the packet when the data amount of the packet accumulated in the transmission buffer 11 is large (that is, when the free capacity of the transmission buffer 11 is small). It is possible to prevent the packet in the transmission buffer from being deleted by the Re-establishment of the RLC connection.

  The transmission unit 15 transmits a packet to the mobile device UE at the transmission rate instructed by the transmission rate management unit 13 and the RLC-PDU size instructed by the packet size management unit 14.

  Note that the transmission buffer 11, the transmission buffer management unit 12, the transmission rate management unit 13, the packet size management unit 14, and the transmission unit 15 are either the radio network controller RNC or the radio base station apparatus Node B constituting the radio access network RAN. It is sufficient if it is provided.

(Packet communication method according to this embodiment)
With reference to FIG. 5 and FIG. 6, an operation for changing the transmission rate of the downstream packet in the packet communication method according to the present embodiment will be described.

  As shown in FIG. 5, in step 301, an RLC connection is established between the radio access network RAN and the mobile device UE. Here, it is assumed that the transmission rate of the downlink packet is “Tx1 (384 kbps or less)” and the size of the RLC-PDU is “336 bits”.

  In step 302, the transmission rate management unit 13 of the radio access network RAN determines whether or not the data amount x of the packet stored in the transmission buffer 11 is equal to or greater than the second data amount threshold Thd2. If the data amount x is equal to or greater than the second data amount threshold Thd2, the flow proceeds to step 303. If the data amount x is not equal to or greater than the second data amount threshold Thd2, the flow repeats step 302.

  In step 303, the transmission rate management unit 13 changes the transmission rate of the downstream packet. That is, the transmission rate of the downstream packet is changed to “Tx2 (over 384 kbps)”.

  In step 304, the packet size management unit 14 of the radio access network RAN determines whether or not the data amount x of the packet stored in the transmission buffer 11 is equal to or greater than the first data amount threshold Thd1. If the data amount x is not equal to or greater than the first data amount threshold Thd1, the flow proceeds to step 305. If the data amount x is equal to or greater than the first data amount threshold Thd1, the flow repeats step 304.

  In step 305, Re-establishment of the RLC connection between the radio access network RAN and the mobile device UE occurs.

  In step 306, after the occurrence of the above-described RLC connection Re-establishment, the size of the RLC-PDU is changed to “656 bits”.

  Further, as shown in FIG. 6, the packet communication method according to the present embodiment changes the transmission rate of the downstream packet by changing steps 302 and 304 shown in FIG. 5 to steps 402 and 404. It may be configured.

  As shown in FIG. 6, in step 402, the transmission rate management unit 13 of the radio access network RAN determines whether or not the remaining amount Br of the transmission buffer 11 is equal to or less than a second buffer remaining amount threshold Thbr2. If the remaining amount Br of the transmission buffer 11 is less than or equal to the second buffer remaining amount threshold Thbr2, the flow proceeds to step 403, and if the remaining amount Br of the transmission buffer 11 is not less than or equal to the second remaining buffer amount threshold Thbr2, The flow repeats step 402.

  In Step 404, the packet size management unit 14 of the radio access network RAN determines whether or not the remaining amount Br of the transmission buffer 11 is equal to or less than the first buffer remaining amount threshold Thbr1. If the remaining amount Br of the transmission buffer 11 is not less than or equal to the first buffer remaining amount threshold Thbr1, the flow proceeds to step 405, and if the remaining amount Br of the transmission buffer 11 is less than or equal to the first buffer remaining amount threshold Thbr1, The flow repeats step 404.

  Next, with reference to FIG. 7 to FIG. 9, the operation of the radio access network RAN when changing the transmission rate of the downlink packet will be described from the viewpoint of the protocol architecture.

  First, the example of FIG. 7 will be described. In step 701, the RLC layer protocol function (RLC entity) of the radio access network RAN transmits the amount of RLC-PDU data to be transmitted (or retransmitted) to the mobile device UE via the RLC connection stored in the transmission buffer 11. Monitor x.

  In step 702, when a predetermined condition is satisfied in the transmission buffer 11, the protocol function of the RLC layer, for example, the data amount x of the RLC-PDU in the transmission buffer 11 continues for a certain period, and the second data amount threshold Thd2 If it is above, or if the remaining amount Br of the transmission buffer 11 continues for a certain period and is equal to or less than the second buffer remaining amount threshold Thbr2, the transmission rate of the DTCH corresponding to the RLC connection is set to a predetermined transmission rate. The MAC layer protocol function (MAC entity) is instructed to change from Tx1 to a higher transmission rate Tx2.

  In step 703, the MAC layer protocol function changes the HS-DSCH transmission rate mapped to the DTCH from a predetermined transmission rate Tx1 to a higher transmission rate in response to an instruction from the RLC layer protocol function. The protocol function of the physical layer is instructed to change to Tx2.

  In response to an instruction from the MAC layer protocol function, the physical layer protocol function changes the transmission rate of the physical channel mapped to the HS-DSCH from a predetermined transmission rate Tx1 to a higher transmission rate Tx2. .

  In step 704, when the RLC layer protocol function instructs the MAC layer protocol function to change the transmission rate of the DTCH, the RLC layer protocol function displays the measurement result of the data amount x of the RLC-PDU in the transmission buffer 11 as the upper layer. Notify the layer protocol function.

  In step 705, the upper layer protocol function determines whether or not the data amount x of the RLC-PDU in the transmission buffer 11 is greater than or equal to the first data amount threshold Thd1, or whether the remaining amount Br of the transmission buffer 11 is the first. It is determined whether or not it is equal to or less than one buffer remaining amount threshold Thbr1.

  When the data amount x of the RLC-PDU in the transmission buffer 11 is not greater than or equal to the first data amount threshold Thd1, or when the remaining amount Br of the transmission buffer 11 is not less than or equal to the first buffer remaining amount threshold Thbr1, The function notifies the RLC layer protocol function of a Re-establish request that instructs to change the size of the RLC-PDU.

  On the other hand, when the data amount x of the RLC-PDU in the transmission buffer 11 is equal to or greater than the first data amount threshold Thd1, or when the remaining amount Br of the transmission buffer 11 is equal to or less than the first buffer remaining amount threshold Thbr1, The protocol function of the upper layer does not notify the Re-establish request to the protocol function of the RLC layer.

  In step 706, the RLC layer protocol function performs a Re-establish process in response to the Re-establish request from the higher layer protocol function.

  Specifically, the protocol function of the RLC layer sets a new RLC connection with the protocol function of the RLC layer in the mobile station UE after discarding all RLC-PDUs in the transmission buffer 11.

  Note that the size of the RLC-PDU transmitted on the newly set RCL connection has been changed to the size indicated by the Re-establish request, and usually the RLC-PDU transmitted on the previous RCL connection. Larger than the size of.

  Second, the example of FIG. 8 will be described. In step 801, the protocol function of the RLC layer of the radio access network RAN monitors the data amount x of RLC-PDU to be transmitted (or retransmitted) to the mobile device UE via the RLC connection stored in the transmission buffer 11. .

  In step 802, the protocol function of the RLC layer notifies the upper layer of the measurement result of the data amount x of the RLC-PDU in the transmission buffer 11 at a predetermined cycle.

  In step 803, the upper layer protocol function determines whether or not to change the transmission rate and size of the RLC-PDU transmitted on the RLC connection according to the measurement result from the RLC layer protocol function.

  When a predetermined condition is satisfied in the transmission buffer 11, the upper layer protocol function notifies the RLC layer protocol function of a Re-establish request that instructs to change the transmission rate and size of the RLC-PDU. .

  For example, the data amount x of the RLC-PDU in the transmission buffer 11 is continuously equal to or greater than the second data amount threshold Thd2 for a certain period, and the data amount x of the RLC-PDU in the transmission buffer 11 is the first When the data amount is less than the data amount threshold Thd1, the upper layer protocol function notifies the RLC layer protocol function of a Re-establish request.

  In addition, the remaining amount Br of the transmission buffer 11 is continuously equal to or less than the second buffer remaining amount threshold Thbr2 for a certain period, and the remaining amount Br of the transmitting buffer 11 is not less than or equal to the first buffer remaining amount threshold Thbr1. In addition, the upper layer protocol function notifies the RLC layer protocol function of a Re-establish request.

  In other cases, the upper layer protocol function does not notify the RLC layer protocol function of the Re-establish request.

  In step 804, in response to the Re-establish request from the upper layer protocol function, the RLC layer protocol function changes the DTCH transmission rate corresponding to the RLC connection from a predetermined transmission rate Tx1 to a higher transmission rate. Instructs the protocol function of the MAC layer to change to (transmission rate instructed in the Re-establish request) Tx2.

  In step 805, in response to an instruction from the protocol function of the RLC layer, the protocol function of the MAC layer changes the transmission speed of the HS-DSCH mapped to the DTCH from a predetermined transmission speed Tx1 to a higher transmission speed. The protocol function of the physical layer is instructed to change to Tx2.

  In response to an instruction from the MAC layer protocol function, the physical layer protocol function changes the transmission rate of the physical channel mapped to the HS-DSCH from a predetermined transmission rate Tx1 to a higher transmission rate Tx2. .

  In step 806, the protocol function of the RLC layer performs a re-establish process in response to the re-establish request from the protocol function of the step upper layer, as in step 706 described above.

  Third, the example of FIG. 9 will be described. In step 901, the protocol function of the RLC layer of the radio access network RAN monitors the data amount x of RLC-PDU to be transmitted (or retransmitted) to the mobile device UE via the RLC connection stored in the transmission buffer 11. .

  Here, the protocol function of the RLC layer determines whether or not the transmission rate and size of the RLC-PDU transmitted over the RLC connection should be changed according to the measurement result of the data amount x of the RLC-PDU in the transmission buffer 11. to decide.

  When a predetermined condition is satisfied in the transmission buffer 11, the RLC layer protocol function instructs the MAC layer protocol function to change the transmission rate of the RLC-PDU in step 902.

  For example, when the data amount x of the RLC-PDU in the transmission buffer 11 is continuously greater than or equal to the second data amount threshold Thd2 for a certain period, or the remaining amount Br of the transmission buffer 11 continues for a certain period. When the second buffer remaining amount threshold Thbr2 or less, the protocol function of the RLC layer changes the transmission rate of the DTCH corresponding to the RLC connection from the predetermined transmission rate Tx1 to a higher transmission rate Tx2. Next, it instructs the protocol function of the MAC layer.

  In step 903, in response to an instruction from the protocol function of the RLC layer, the protocol function of the MAC layer changes the transmission speed of the HS-DSCH mapped to the DTCH from a predetermined transmission speed Tx1 to a higher transmission speed. The protocol function of the physical layer is instructed to change to Tx2.

  In response to an instruction from the MAC layer protocol function, the physical layer protocol function changes the transmission rate of the physical channel mapped to the HS-DSCH from a predetermined transmission rate Tx1 to a higher transmission rate Tx2. .

  In step 904, when the protocol function of the RLC layer instructs the MAC layer protocol function to change the transmission rate of the DTCH, the data amount x of the RLC-PDU in the transmission buffer 11 is the first data amount. It is determined whether or not the threshold value Thd1 is equal to or greater than the threshold value Thd1, or whether or not the remaining amount Br of the transmission buffer 11 is equal to or less than the first buffer remaining amount threshold value Thbr1.

  When the data amount x of the RLC-PDU in the transmission buffer 11 is not greater than or equal to the first data amount threshold Thd1, or when the remaining amount Br of the transmission buffer 11 is not less than or equal to the first buffer remaining amount threshold Thbr1, the protocol of the RLC layer The function performs a re-establish process as in step 706 described above.

  On the other hand, when the data amount x of the RLC-PDU in the transmission buffer 11 is equal to or greater than the first data amount threshold Thd1, or when the remaining amount Br of the transmission buffer 11 is equal to or less than the first buffer remaining amount threshold Thbr1, The protocol function of the RLC layer does not perform the above-described Re-establish process.

(Operation and effect of packet communication system and packet communication method according to this embodiment)
According to the packet communication system and the packet communication method according to the present embodiment, for example, when the data amount x of the packet stored in the transmission buffer 11 is large according to the empty state of the transmission buffer 11 (that is, the transmission buffer 11). In the case where the free space Br is small, it is possible to prevent the packet in the transmission buffer from being deleted by the re-establishment of the RLC connection by not changing the size of the packet.

1 is an overall configuration diagram of a packet communication system including a radio access network. It is a flowchart figure which shows the operation | movement which changes the transmission rate and size of a packet in the radio | wireless access network which concerns on a prior art. It is a functional block diagram of the radio access network concerning one embodiment of the present invention. It is a figure for demonstrating the transmission buffer in the radio | wireless access network which concerns on one Embodiment of this invention. It is a flowchart figure which shows the operation | movement which changes the transmission rate and size of a packet in the radio | wireless access network which concerns on one Embodiment of this invention. It is a flowchart figure which shows the operation | movement which changes the transmission rate and size of a packet in the radio | wireless access network which concerns on one Embodiment of this invention. It is a sequence diagram which shows an example of the operation | movement which changes the transmission rate and size of a packet seen from protocol architecture in the radio | wireless access network which concerns on one Embodiment of this invention. It is a sequence diagram which shows an example of the operation | movement which changes the transmission rate and size of a packet seen from protocol architecture in the radio | wireless access network which concerns on one Embodiment of this invention. It is a sequence diagram which shows an example of the operation | movement which changes the transmission rate and size of a packet seen from protocol architecture in the radio | wireless access network which concerns on one Embodiment of this invention.

Explanation of symbols

CN ... core network RAN ... radio access network RNC ... radio control device Node B ... radio base station device UE ... mobile station 11 ... transmission buffer 12 ... transmission buffer management unit 13 ... transmission rate management unit 14 ... packet size management unit 15 ... transmission Part

Claims (6)

A packet communication method for transmitting a packet at a predetermined transmission rate,
A step of changing the size of the packet according to the availability of a transmission buffer for storing the packet when changing the predetermined transmission rate ;
In the step of changing the size of the packet, the data amount of the packet stored in the transmission buffer is greater than or equal to a first data amount threshold value, or the remaining amount of the transmission buffer is the first buffer remaining amount A packet communication method characterized by not changing the size of the packet when it is equal to or less than a threshold value .   The data amount of the packet stored in the transmission buffer is equal to or greater than a second data amount threshold value smaller than the first data amount threshold value, or the remaining amount of the transmission buffer is equal to the first data amount threshold value. 2. The packet communication method according to claim 1, further comprising a step of changing the predetermined transmission rate to a higher transmission rate when it is equal to or smaller than a second buffer remaining amount threshold value that is smaller than the buffer remaining amount threshold value. .   In the step of changing the transmission rate, the data amount of the packet stored in the transmission buffer is continuously greater than or equal to the second data amount threshold for a certain period, or the remaining amount of the transmission buffer is 3. The packet communication method according to claim 2, wherein the predetermined transmission rate is changed to a higher transmission rate when the predetermined buffer rate is not more than the second buffer remaining amount threshold value continuously for a certain period of time.   A packet communication system for transmitting packets at a predetermined transmission rate,
  A packet size management unit that changes the size of the packet according to the availability of a transmission buffer for storing the packet when changing the predetermined transmission rate;
  The packet size management unit is configured such that the data amount of the packet stored in the transmission buffer is equal to or greater than a first data amount threshold value, or the remaining amount of the transmission buffer is equal to or less than a first buffer remaining amount threshold value. In some cases, the packet communication system does not change the size of the packet.   The data amount of the packet stored in the transmission buffer is equal to or greater than a second data amount threshold value that is smaller than the first data amount threshold value, or the remaining amount of the transmission buffer is equal to the first data amount threshold value. 5. The transmission speed changing unit according to claim 4, further comprising: a transmission speed changing unit that changes the predetermined transmission speed to a higher transmission speed when the second buffer remaining capacity threshold is less than or equal to a second buffer remaining capacity threshold that is smaller than the buffer remaining capacity threshold. Packet communication system.   The transmission rate changing unit is configured such that the data amount of the packet stored in the transmission buffer is continuously equal to or greater than the second data amount threshold for a certain period, or the remaining amount of the transmission buffer is constant. The packet communication system according to claim 5, wherein the predetermined transmission rate is changed to a higher transmission rate when the period is continuously equal to or less than the second buffer remaining amount threshold.

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