JP2006005387A - Communication method, communication system, and communication apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a communication method capable of reflecting a share of a FEC overhead attached to transmission data on a permissible band in the case of applying the FEC (Forward Error Correction) technology to, e.g. a PON (Passive Optical Network) system. <P>SOLUTION: The communication method includes a band assignment step for assigning the permissible band to a plurality of communication apparatuses on the basis of a data band corresponding to data transmitted from the plurality of communication apparatuses sharing transmission bands and an additional band corresponding to the overhead attached to the transmission data. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a band control technique in a communication system in which a plurality of communication apparatuses share a band.

As a conventional access network for transmitting a multimedia service to each home, a PON (Passive Optical Network) system is known (see, for example, Patent Document 1). In this PON system, a plurality of subscriber side communication devices (ONU: Optical Network Unit) and a station side communication device (OLT: Optical Line Terminal) are connected via an optical fiber cable via a star coupler. It is economical because ONU shares a single OLT.
In this communication method using dynamic bandwidth allocation in the PON system, an ONU that intends to transmit data first declares the amount of transmission data stored in the buffer in accordance with an instruction from the OLT. The OLT that receives the report from each ONU calculates the permitted bandwidth based on the accumulated amount and notifies each ONU. Then, the ONU that has received the notification from the OLT transmits the data stored in the permitted bandwidth or less to the OLT.

International Publication Number WO99 / 38292 (page 4)

  In the conventional communication method disclosed in Patent Document 1, since the permitted bandwidth is calculated based on the amount of transmission data stored in the buffer, for example, the code error correction of the received signal is performed to extend the transmission distance by the optical fiber cable. When applying the FEC (Forward Error Correction) technique to be performed, there is a problem that the FEC overhead added to the transmission data cannot be reflected in the permitted band. For this reason, for example, there arises a problem that only a smaller number of frames than the number of frames expected in the permitted band can be transmitted from the ONU.

  The present invention has been made to solve the above-described problems. In the communication method, for example, when the FEC technology is applied to the PON system, the FEC overhead added to the transmission data can be reflected in the permitted band. The purpose is to.

  The communication method according to the present invention is based on a data band corresponding to data transmitted from a plurality of communication devices sharing a transmission band, and an additional band corresponding to overhead added to the transmitted data. A bandwidth allocation step of allocating a permitted bandwidth to the plurality of communication devices is provided.

  According to the present invention, in the communication method, dynamic bandwidth allocation can be performed by reflecting the overhead added to the transmitted data in the permitted bandwidth.

Embodiment 1 FIG.
In the communication method according to the first embodiment of the present invention, the communication request code transmitted from the ONU does not reflect the FEC overhead, but the OLT generates a communication permission code in consideration of the FEC overhead. Therefore, when the FEC technology is applied to the PON system, band allocation can be performed by reflecting the FEC overhead added to the transmission data in the permitted band.

  1 is a block diagram showing a network system in a communication method according to Embodiment 1 of the present invention. In the figure, 1 is a station side communication device (OLT: Optical Line Terminal), 2 is a subscriber side communication device (ONU: Optical Network Unit), 3 is an optical fiber cable, and 4 is a star coupler.

  FIG. 2 is a block diagram showing a station side communication apparatus in the communication method according to Embodiment 1 of the present invention. In the figure, 11 is a photoelectric conversion unit, 12 is a FEC (Forward Error Correction) processing unit, 13 is a communication request code extraction unit that extracts a communication request code from each ONU, and 14 is according to a request band from each ONU. A bandwidth allocation control unit as an additional bandwidth calculation unit that calculates the permitted bandwidth, 15 is a communication permission code generation unit that generates a communication permission code based on a calculation result (permitted bandwidth) of the bandwidth allocation control unit 14, and 16 is a communication permission code. Is a communication permission code insertion unit that inserts into the downlink signal. The communication request code extraction unit 13, the band allocation control unit 14, the communication permission code generation unit 15, and the communication permission code insertion unit 16 constitute a band allocation unit.

  FIG. 3 is a block diagram showing a subscriber side communication apparatus in the communication method according to Embodiment 1 of the present invention. 21 is a photoelectric conversion unit, 22 is an FEC processing unit, 23 is a communication permission code extraction unit that extracts a received communication permission code, and 24 is a communication request that monitors the frame accumulation amount of the uplink buffer and generates a communication request code. A code generation unit, 25 is an upstream buffer, 26 is an upstream burst transmission that reads out an upstream signal from the upstream buffer 25 based on the communication start time and end time extracted by the communication permission code extraction unit 23 and outputs a control signal for transmission A control unit 27 is a switch unit that reads an upstream signal from a buffer and turns on / off transmission according to a control signal from the upstream burst transmission control unit 26. The communication request code extraction unit 23, the communication request code generation unit 24, the uplink buffer 25, the uplink burst transmission control unit 26, and the switch unit 27 constitute a bandwidth request unit.

Next, the operation will be described.
First, the ONU 2 stores an Ethernet (registered trademark) frame of user data input from the UNI (User Network Interface) side in the upstream buffer 25. The communication request code generation unit 24 generates a communication request code by monitoring the frame accumulation amount of the uplink buffer 25 and stores the communication request code in the uplink buffer 25. When the ONU 2 receives the communication permission code from the OLT 1, the communication permission code extraction unit 23 calculates the transmission start time and transmission end time of the upstream signal, and the upstream buffer of the upstream signal by the control signal from the upstream burst transmission control unit 26 The uplink signal transmission control is performed by controlling the reading and transmission from 25 by the switch unit 27. At the time of uplink signal transmission, the generated communication request code is also transmitted together with the frame of user data input from the UNI side. The FEC overhead that is a redundant byte for each frame is added to the upstream signal read from the upstream buffer 25 and output from the switch unit 27 by the FEC processing unit 22. After being converted to a signal, it is transmitted to OLT1.

On the other hand, on the OLT 1 side, the received optical signal is converted into an electrical signal by the photoelectric conversion unit 11, subjected to FEC processing by the FEC processing unit 12, and then sent to the communication request code extraction unit 13.
The communication request code extraction unit 13 extracts the communication request code of each ONU and notifies the bandwidth allocation control unit 14 of the requested bandwidth from each ONU. The bandwidth allocation control unit 14 calculates the permitted bandwidth for each ONU. At this time, an addition corresponding to the FEC overhead calculated according to the data bandwidth is added to the data bandwidth corresponding to the user data calculated for each ONU. The permitted bandwidth is calculated by adding the bandwidth. The communication permission code generation unit 15 generates a communication permission code for each ONU based on the permission band, and the communication permission code insertion unit 16 inserts the communication permission code into the downlink signal, and then the FEC processing unit 12 and the photoelectric conversion unit. It transmits to each ONU via the unit 11.

  As described above, in the communication method according to the first embodiment of the present invention, the FEC overhead is not reflected in the communication request code transmitted from the ONU, but the communication permission code with the FEC overhead added is used in the OLT. Therefore, when the FEC technology is applied to the PON system, it is possible to perform bandwidth allocation by reflecting the FEC overhead added to the transmission data in the permitted bandwidth. Thereby, it is possible to reduce the difference between the number of frames expected to be transmitted in the permitted band assigned by the OLT and the number of frames actually transmitted from the ONU, and to improve the data communication efficiency.

Embodiment 2. FIG.
In the communication method according to the second embodiment of the present invention, since a communication request code including the FEC overhead is transmitted from the ONU, the FEC added to the transmission data when the FEC technology is applied to the PON system. Bandwidth allocation can be performed by reflecting the overhead for the permitted bandwidth.

  4 is a block diagram showing a subscriber-side communication apparatus in a communication method according to Embodiment 2 of the present invention. In the figure, in addition to the configuration shown in FIG. 3, the ONU 2 a includes a communication request code extraction unit 200 that extracts a communication request code, and a request band change unit as an additional band calculation unit that changes a request band in the extracted communication request code 201, a delay circuit unit 202 that delays the main signal excluding the communication request code by a predetermined time, and a communication request code insertion unit 203 that inserts the changed communication request code into the main signal. The communication permission code extraction unit 23, the communication request code generation unit 24, the uplink buffer 25, the uplink burst transmission control unit 26, the switch unit 27, the communication request code extraction unit 200, the request band change unit 201, the delay circuit unit 202, and The communication request code insertion unit 203 constitutes a bandwidth request unit.

Next, the operation will be described.
The ONU 2a generates a communication request code as in the first embodiment. Therefore, the request band stored in the communication request code generated by the communication request code generation unit 24 does not include the band for the FEC overhead.
In the ONU 2a according to Embodiment 2 of the present invention, the communication request code extraction unit 200 extracts the communication request code from the uplink signal. In the extracted communication request code, the request band changing unit 201 adds an additional band corresponding to the FEC overhead corresponding to the request band to the request band corresponding to the data band. The communication request code whose request band has been changed in this way is inserted into the main signal by the communication request code inserting unit 203 and then sent to the FEC processing unit 22.
On the other hand, the main signal from which the communication request code is removed is sent to the communication request code insertion unit 203 after the delay circuit unit 202 adds the same delay amount as the path through which the communication request code passes.

  As described above, since the communication request code that includes the FEC overhead is transmitted from the ONU, when the FEC technology is applied to the PON system, the transmission is performed without adding a function to the conventional bandwidth allocation control unit of the OLT. Bandwidth allocation can be performed by reflecting the FEC overhead added to the data in the permitted bandwidth. Thereby, it is possible to reduce the difference between the number of frames expected to be transmitted in the permitted band assigned by the OLT and the number of frames actually transmitted from the ONU, and to improve the data communication efficiency.

  Further, since the ONU 2a according to the second embodiment includes a delay circuit for main signals, the transmission order of transmission data is not changed even if the requested band change process is performed.

Embodiment 3 FIG.
The third embodiment of the present invention relates to a calculation method as an additional band calculation unit in the band allocation control unit 14 of the OLT 1 shown in FIG.
In the calculation method according to the first embodiment of the present invention, the OLT side adds an additional band corresponding to the data band as the ONU request band to the request band not including the FEC overhead. Although the transmission permission signal is transmitted to the ONU, as the third embodiment, the additional band may be added on the OLT side regardless of the data band as the requested band from the ONU. The same effect as in the first embodiment can be obtained.

Embodiment 4 FIG.
The fourth embodiment of the present invention relates to a calculation method as an additional band calculation unit in the band allocation control unit 14 of the OLT 1 shown in FIG.
In Embodiment 4 of the present invention, when performing bandwidth calculation, the maximum value of FEC overhead is calculated from the data bandwidth as the required bandwidth of each ONU, and the additional bandwidth corresponding to the maximum value of the FEC overhead is calculated from each ONU. In addition to the data bandwidth as the requested bandwidth, bandwidth allocation is calculated.

  GEPON (Gigabit Ethernet (registered trademark) Passive Optical Network) performs FEC for each frame of Ethernet (registered trademark). FIG. 5 shows an example of a frame to which FEC overhead is added in the GEPON system (see IEEE802.3ah / D3.1, pages 520 to 521). Field 401, field 405, field 406, and field 407 indicate FEC overhead. The Ethernet (registered trademark) frame portion indicated by the field 402, the field 403, and the field 404 is divided into blocks of 239 bytes, and (255, 239, 8) Reed Solomon encoder is used for FEC parity generation. When FEC parity generation is performed using this method, a 16-byte PARITY field 406 is added to each 239-byte block. Of the FEC overhead, the S_FEC field 401 is 5 bytes, and the T_FEC fields 405 and 407 are 6 to 7 bytes. In addition, when the frame length to which overhead is to be added is 239 bytes or less, the FEC overhead can be added as it is without performing padding processing to make the Ethernet (registered trademark) frame part 239 bytes. .

Here, the condition that the data amount of the FEC overhead becomes maximum is a case where the upstream buffer 25 of the ONU 2 is satisfied with a 72-byte Ethernet (registered trademark) frame that is the minimum value. Therefore, the value obtained by dividing the requested bandwidth (number of bytes) from a certain ONU by 72 bytes, multiplied by the FEC overhead length of 34 bytes, is added to the original requested bandwidth of the ONU, and this is the requested bandwidth from the ONU. By performing bandwidth allocation, a permission bandwidth may be given to each ONU, and the same effect as in the first embodiment can be obtained.
Furthermore, in this method, since the maximum value of the requested bandwidth is taken into account, it can be expected that the bandwidth allocation for ONU can be avoided compared to the bandwidth allocation without FEC. .

Embodiment 5. FIG.
The fifth embodiment of the present invention relates to a calculation method as an additional band calculating unit in the required band changing unit 201 of the ONU 2a shown in FIG.
In the second embodiment of the present invention, the request band changing unit 201 of the ONU 2a sets this request band as a request band for the request band not including the FEC overhead in the communication request code generated by the communication request code generating unit 24 of the ONU 2a. In the fifth embodiment, the requested bandwidth changing unit 201 fixes the FEC overhead in a fixed manner regardless of the requested data bandwidth. A corresponding additional band may be added, and the same effect as in the second embodiment can be obtained.

Embodiment 6 FIG.
The sixth embodiment of the present invention relates to a calculation method as an additional band calculating unit in the required band changing unit 201 of the ONU 2a shown in FIG.
In the sixth embodiment of the present invention, the maximum value of FEC overhead is calculated from the data band as the requested band input to the requested band changing unit 201, and the additional band corresponding to the maximum value of the FEC overhead is calculated from the original request. In addition to the data bandwidth as the bandwidth, the request bandwidth is transmitted using the communication request code.

The condition for maximizing the amount of FEC overhead data is when the ONU upstream buffer is filled with a 72-byte frame, as described in the fourth embodiment. Therefore, similar to the calculation method described in the fourth embodiment, the request bandwidth is obtained by adding the value obtained by dividing the request bandwidth (number of bytes) by 72 bytes to the original request bandwidth by 34 bytes. By notifying with the request code, the same effect as in the fourth embodiment can be obtained.
Further, in the case of the sixth embodiment, it is not necessary to make a change for adding the additional band as shown in the fourth embodiment in the band allocation control unit 14 of the OLT 1 to the conventional configuration.

Embodiment 7 FIG.
In Embodiment 7 described above, in the ONU, the input frame is subjected to padding processing corresponding to the FEC overhead and written to the upstream buffer, so that the FEC overhead is reflected in the communication request code transmitted from the ONU. It is to make.

  6 is a block diagram showing a subscriber side communication apparatus in a communication method according to Embodiment 7 of the present invention. In the figure, in addition to the configuration shown in FIG. 3, a PAD insertion unit 204, an FCS (Frame Check Sequence) recalculation unit 205, a PAD deletion unit 206, and an FCS recalculation unit 207 are provided in the uplink signal path. is there. The uplink buffer 25, the PAD insertion unit 204, the FCS recalculation unit 205, the PAD deletion unit 206, and the FCS recalculation unit 207 constitute a required bandwidth calculation unit.

Next, the operation will be described.
In the ONU 2b, when an upstream frame is input from the UNI side, the PAD insertion unit 204 measures the frame length from the head of the input frame.
In the PAD insertion unit 204, when the input frame (field 402, field 403, field 404) is an even number byte in the frame having the same structure as that shown in FIG. 5, the S_FEC field 401 is 5 bytes and the T_FEC field. A PAD with a length obtained by adding a fixed overhead of 405 to 6 bytes and a T_FEC field 407 of 6 bytes and a variable overhead of a PARITY field 406 (number of bytes of input frame × 16 bytes / 239 bytes) depending on the frame length Add the field to the end of the input frame.
On the other hand, when the input frame is an odd number of bytes, the S_FEC field 401 is 5 bytes, the T_FEC field 405 is 7 bytes, the T_FEC field 407 is 6 bytes of fixed overhead, and the PARITY field 406 (input frame byte depending on the frame length). Add a PAD field with the length of the variable overhead (number x 16 bytes / 239 bytes) to the end of the input frame.
In addition, if the upper function has an input frame length check function and the frame length becomes longer as a result of padding processing and is discarded by the check function, the upper limit value of the PAD is limited to a length that will not be discarded. .
Next, the FCS recalculator 205 recalculates the FCS of the padded frame and sends it to the upstream buffer.

  When the ONU 2b receives the communication permission code from the OLT 1 and starts reading the frame from the uplink buffer 25, the read frame is inserted into the PAD field inserted by the PAD insertion unit 204 by the PAD deletion unit 206. Is deleted, and the FCS recalculation unit 207 recalculates the FCS. Thereafter, the FEC processing unit 22 adds the FEC overhead, and then transmits an upstream signal to the OLT 1.

  As described above, when padding processing is performed on an input frame, a frame to which a PAD field is added is written in the upstream buffer 25. Since the ONU 2b monitors the upstream buffer 25 and generates a communication request code, the generated communication request code has a request band reflecting the FEC overhead. Therefore, when FEC technology is applied to the PON system, bandwidth allocation is performed by reflecting the FEC overhead added to the transmission data in the permitted bandwidth without adding functions to the conventional bandwidth allocation control unit of OLT. Can do. Thereby, it is possible to reduce the difference between the number of frames expected to be transmitted in the permitted band assigned by the OLT and the number of frames actually transmitted from the ONU, and to improve the data communication efficiency.

Embodiment 8 FIG.
In the seventh embodiment, the input frame is padded in the ONU, but in the eighth embodiment, the dummy frame corresponding to the overhead for each frame is generated and written in the upstream buffer in the ONU. Thus, the FEC overhead is reflected in the communication request code transmitted from the ONU.
FIG. 7 is a block diagram showing a subscriber side communication apparatus in a communication method according to Embodiment 8 of the present invention. In the figure, in addition to the configuration shown in FIG. 3, a dummy frame generation unit 208 and a dummy frame discarding unit 209 are provided in the uplink signal path. The upstream buffer 25, the dummy frame generation unit 208, and the dummy frame discard unit 209 constitute a required bandwidth calculation unit.

Next, the operation will be described.
In the ONU 2c, when an upstream frame is input from the UNI side, the dummy frame generation unit 208 sequentially measures the frame length from the head of the input frame.
In the frame having the same structure as that shown in FIG. 5, when the input frame (field 402, field 403, field 404) is an even number of bytes, the S_FEC field 401 is 5 bytes and the T_FEC field 405 is 6 bytes. The T_FEC field 407 is a length obtained by adding a fixed overhead of 6 bytes and a variable overhead of a PARITY field 406 (number of bytes of input frame × 16 bytes / 239 bytes) depending on the frame length.
On the other hand, when the input frame is an odd number of bytes, the S_FEC field 401 is 5 bytes, the T_FEC field 405 is 7 bytes, the T_FEC field 407 is 6 bytes of fixed overhead, and the PARITY field 406 (input frame byte depending on the frame length). The length is the sum of the variable overhead (number x 16 bytes / 239 bytes).
The dummy frame generation unit 208 inserts a 64 byte dummy frame and stores it in the upstream buffer 25 every time the FEC overhead for the input frame length reaches 64 bytes.

  When the ONU 2c receives a communication permission code from the OLT 1 and starts reading a frame from the upstream buffer 25, the read frame is a dummy frame inserted by the dummy frame generation unit 208 by the dummy frame discarding unit 209. Is deleted. Thereafter, the FEC processing unit 22 adds the FEC overhead, and then transmits an upstream signal to the OLT 1.

  As described above, when a dummy frame corresponding to the input frame length from UNI is inserted, it is written into the upstream buffer 25. Since the ONU 2c monitors the upstream buffer 25 and generates a communication request code, the generated communication request code has a request band reflecting the FEC overhead. Therefore, when FEC technology is applied to the PON system, bandwidth allocation is performed by reflecting the FEC overhead added to the transmission data in the permitted bandwidth without adding functions to the conventional bandwidth allocation control unit of OLT. Can do. Thereby, it is possible to reduce the difference between the number of frames expected to be transmitted in the permitted band assigned by the OLT and the number of frames actually transmitted from the ONU, and to improve the data communication efficiency.

  As described above, in the first to eighth embodiments of the present invention, the overhead added to the transmission data is the FEC overhead. However, what is added to the transmission data is not limited to this. Absent.

  In the first to eighth embodiments of the present invention, Ethernet (registered trademark) frames are used. However, the frame format is not limited to this, and any frame compatible with packet communication may be used.

  In the first to eighth embodiments of the present invention, the case where the present invention is applied to the PON system is shown. Needless to say, the application system is not limited to this, and a plurality of communication devices share a transmission band. As long as bandwidth control is performed, the present invention can be applied to any system such as optical or electrical wired communication or wireless communication.

Configuration diagram showing a network system in a communication method according to Embodiment 1 of the present invention The block diagram which shows the station side communication apparatus in the communication method by Embodiment 1 of this invention 1 is a configuration diagram showing a subscriber-side communication device in a communication method according to Embodiment 1 of the present invention. The block diagram which shows the subscriber side communication apparatus in the communication method by Embodiment 2 of this invention The figure which shows the frame structure in the communication method by Embodiment 4 of this invention The block diagram which shows the subscriber side communication apparatus in the communication method by Embodiment 7 of this invention The block diagram which shows the subscriber side communication apparatus in the communication method by Embodiment 8 of this invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Station side communication apparatus 2 Subscriber side communication apparatus 13 Communication request code extraction part 14 Band allocation control part 15 Communication permission code generation part 16 Communication permission code insertion part 23 Communication permission code extraction part 24 Communication request code generation part 25 Up buffer 26 Upstream burst transmission control unit 27 Switch unit 200 Communication request code extraction unit 201 Request band change unit 202 Delay circuit unit 203 Communication request code insertion unit 204 PAD insertion unit 205 FCS recalculation unit 206 PAD deletion unit 207 FCS recalculation unit 208 Dummy frame Generation unit 209 Dummy frame discard unit

Claims (15)

  Based on a data band corresponding to data transmitted from a plurality of communication apparatuses sharing a transmission band and an additional band corresponding to overhead added to the transmitted data, a permitted band for the plurality of communication apparatuses. A communication method comprising the step of allocating bandwidth. A bandwidth requesting step for requesting a requested bandwidth from the plurality of communication devices based on the data bandwidth,
The communication method according to claim 1, wherein the bandwidth allocation step allocates a permitted bandwidth to the plurality of communication devices based on the requested bandwidth requested in the bandwidth requesting step and the additional bandwidth. Based on a data band corresponding to data transmitted from a plurality of communication apparatuses sharing a transmission band and an additional band corresponding to overhead added to the transmitted data, a request band from the plurality of communication apparatuses A bandwidth request process for requesting,
A communication method comprising a bandwidth allocation step of allocating a permitted bandwidth to the plurality of communication devices based on the requested bandwidth requested in the bandwidth requesting step.   The communication method according to claim 1, wherein the overhead is a FEC (Forward Error Correction) overhead.   The communication method according to claim 1, further comprising an additional band calculation step of calculating the additional band regardless of the data band.   The communication method according to claim 1, further comprising an additional band calculating step of calculating the additional band based on the data band.   4. The communication method according to claim 3, further comprising a required bandwidth calculation step of calculating the required bandwidth by adding dummy data corresponding to the overhead to the transmitted data and writing it to a buffer.   Based on a data band corresponding to data transmitted from a plurality of communication apparatuses sharing a transmission band and an additional band corresponding to overhead added to the transmitted data, a permitted band for the plurality of communication apparatuses. A communication system comprising a bandwidth allocation unit for allocating. A bandwidth request unit that requests a requested bandwidth from the plurality of communication devices based on the data bandwidth,
9. The communication system according to claim 8, wherein the bandwidth allocation unit allocates a permitted bandwidth to the plurality of communication devices based on the requested bandwidth requested by the bandwidth request unit and the additional bandwidth. Based on a data band corresponding to data transmitted from a plurality of communication apparatuses sharing a transmission band and an additional band corresponding to overhead added to the transmitted data, a request band from the plurality of communication apparatuses A bandwidth request unit that requests
A communication system comprising: a bandwidth allocation unit that allocates a permitted bandwidth to the plurality of communication devices based on a requested bandwidth requested by the bandwidth request unit.   11. The communication system according to claim 8, wherein the overhead is a FEC (Forward Error Correction) overhead.   The communication method according to claim 8, further comprising an additional band calculation unit that calculates the additional band regardless of the data band.   The communication method according to claim 8, further comprising an additional band calculation unit that calculates the additional band based on the data band.   11. The communication system according to claim 10, further comprising: a request band calculation unit that calculates the request band by adding dummy data corresponding to the overhead to the transmitted data and writing the data in a buffer.   A bandwidth allocation unit that allocates a permitted bandwidth to a plurality of communication devices that share a transmission bandwidth, and a data bandwidth corresponding to transmitted data and an additional bandwidth corresponding to overhead added to the transmitted data A communication apparatus comprising a bandwidth request unit that requests a requested bandwidth based on the request.

Images