JP2002135310A - Stream relay controller, stream relay control system, stream relay control method, and recording medium for recording the method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a stream relay control technology (device, system, method, and recording medium for recording the method) that collects distribution states of clients each and conducts quality management after efficiently conducting large-scale stream distribution. SOLUTION: The stream relay controller is provided with means (401, 201a) that receive a packet sent from a stream server, a means (202) that analyzes header information of the packet to identify whether or not the packet employs a stream control protocol, means (204, 205, 207, 208, 211, 212, 213, 402, 403) that informs a means (203) about packet information when the packet employs the stream control protocol, the means (203) that acquires state information and/or identifier of the stream server from the packet information, and a means (206) that generates an acknowledgement packet and transfers it to the stream server.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a stream relay control technique for efficiently realizing a large-scale stream distribution network. Stream relay control device that can collect and quality control
The present invention relates to a stream relay control system, a stream relay control method, and a recording medium on which the method is recorded.

[0002]

2. Description of the Related Art Conventionally, when performing stream distribution on the Internet, generally, a stream setting protocol for requesting and setting stream contents, a stream distribution protocol for distributing stream contents based on the settings, and a distribution. A stream control protocol for notifying the distribution status and distribution quality of the inside stream content packet and notifying the connection state between the server and the client is used.

[0003] The IETF (Internet Engineering Task Fo)
rce) includes RTSP (Rea
l Time Streaming Protocol: RFC2326), RTP (Real
-Time Transport Protocol: RFC1889) and RT
CP (RTP Control Protocol: RFC1889) is an example.

[0004] Also, when performing stream distribution using a protocol other than these, a protocol having substantially the above functions is used. Examples include Microsoft's MMS protocol, Real Network's RDT, and PNA protocol.

Since these protocols are basically protocols that are assumed to be exchanged one-to-one between a server and a client, the same stream contents can be transmitted to a very large number of clients. However, it was difficult to efficiently distribute the information. In addition, in the case of efficient distribution, it has not been possible to manage the state and distribution quality of the client receiving the stream content.

Here, a conventional stream distribution technique will be described with reference to FIGS. 8 and 9. FIG. FIG. 8 is a diagram illustrating a configuration example of a conventional stream distribution network. In this example, the stream server 100, the clients 300a to
300d, connection lines 400a to 400h, transfer device 50
0a to 500d. FIG. 9 is a diagram showing a sequence example of a stream control protocol exchanged between a stream server and a client.

[0007] In the case of broadcast-type stream distribution called live stream distribution, a client that requests reception receives a stream content distribution request from a stream server using a stream setting protocol. In this example, the clients 300a and 300b make a request for receiving the same live stream content to the stream server 100, and the stream server 100 that has received this request performs distribution setting according to the request. The stream content is distributed using the stream distribution protocol. During stream delivery,
The stream server and the client use a stream control protocol to check the distribution status of the stream contents.

As shown in the sequence example of FIG. 9, the stream server 100 transmits messages a and b to clients 300a and 300b, respectively. These messages a and b are sent to each client via a connection line or a transfer device. Each client measures, based on the transmitted message, information such as the reception status of the stream packet at the client, the discard rate and the number of discards, and the fluctuation of the packet, and transmits them to the stream server 100 as messages c and d. I do. By the sequence of these protocols, the stream server 100 can grasp distribution information to each client and confirm connectivity.

When the messages c and d from the client do not arrive at the stream server 100, distribution to the client may be stopped. Also, the distribution status information from the client may be used by the stream management server as statistical information of the stream distribution status.

When such a distribution method is adopted, the distribution request processing, the distribution control processing, and the stream content distribution processing are concentrated in the stream server 100. As a result, large-scale live stream distribution is performed. Was difficult.

[0011] To solve the above problem, there is a method of using a transfer technique called IP multicast as a method of reducing stream content distribution processing. This is to transfer stream content packets to be distributed using IP multicast.

In this case, the stream server transmits only one stream content packet regardless of the number of clients requesting reception. One stream content packet transmitted from the stream server is copied and transferred by the multicast-capable router or the multicast-capable switch according to the transfer path of the IP multicast, and transferred to the destination client. Thereby, stream content distribution processing in the stream server is reduced, and efficient one-to-many distribution can be performed.

However, when such a transfer technique is used, one-to-many distribution is performed, so that one-to-one state control / management using a stream control protocol becomes difficult. In particular, ATM (Asynchronous Transfer Mode)
When an IP multicast distribution is to be performed using a distribution network that performs a one-way p-mp distribution path as described above, a control protocol response message from a client cannot be transferred using the path, so that the message transfer is performed. It is necessary to prepare a separate path for this, and the route management becomes complicated. Also, although the stream server has sent only one stream packet,
When a plurality of control protocol messages arrive from a client, a state mismatch may occur.

[0014] In order to solve these problems, when using multicast for live stream distribution, a technique that does not use a stream control protocol may be adopted. In this case, the stream distribution status on the client cannot be grasped on the stream distribution side,
The collection / management of statistical information by the conventionally used stream management server could not be performed.

[0015]

As described above, in the conventional stream distribution technology, a large-scale live stream is used to perform distribution setting, distribution management, and stream distribution between a stream server and a client. When performing distribution, there is a problem in that the processing load on the stream server is concentrated, and further, the bandwidth of the connection line is wasted.

In order to solve such a problem and apply the IP multicast technology to reduce the stream distribution processing load on the server and to effectively use the bandwidth of the connection line, the application of the stream control protocol is not sufficient. It will be difficult. If a delivery mode that does not use the stream control protocol is used, another problem arises in that the delivery status to the client obtained by the protocol cannot be collected.

[0017] An object of the present invention is to solve the above-mentioned problems and stream stream control capable of efficiently performing large-scale stream delivery, collecting the delivery status of each client, and performing quality control. It is an object to provide an apparatus, a stream relay control system, a stream relay control method, and a recording medium on which the method is recorded.

[0018]

In order to achieve the above object, a stream relay control device of the present invention is: (a) a stream relay control device in a stream distribution network, which receives a packet sent from a stream server. Means (401, 201a), means (202) for analyzing header information of the packet and identifying that it is a stream control protocol,
Alternatively, means (204, 20) for transferring to a plurality of distribution destinations
5,207,208,211,212,213,40
(403) and means (20) for notifying the packet information when the packet is a stream control protocol.
2) and means for acquiring status information and / or an identifier of the stream server from the packet information (203)
And a means (206) for creating a response packet to the packet and transferring it to the stream server.

(B) In the stream relay control device of (a), a means (207) for rewriting server information and / or an identifier of the packet information sent from the stream server, It is characterized by having means for transferring to one or more distribution destinations.

(C) means (402, 403, 201b) for receiving a packet transmitted from a client or a device having a client function; analyzing header information of the packet; And a means for acquiring the packet information.

(D) In the stream relay control device of (c), a client or
Means (209) for storing stream control packet information sent from the device having the client function, and means (210) for responding to a request from the stream management server
It is characterized by having.

Further, the stream relay control system of the present invention is characterized by having (e) the stream relay control device of (a) and the stream relay control device of (c).

(F) It is characterized by having the stream relay control device of (b) and the stream relay control device of (d).

Also, the stream relay control method of the present invention is (g) a stream relay control method in a stream distribution network, wherein a step of receiving a packet transmitted from a stream server, analyzing the packet information, and Identifying the control protocol, transferring the packet to one or more destinations, and notifying the packet information to a stream control protocol processing unit (SCP); It is characterized by having a step of obtaining status information and / or an identifier of a server, and a step of creating a response packet to the packet and transferring the packet to a stream server.

(H) In the stream relay control method of the above (g), further, in the packet information sent from the stream server, the server status information and / or the identifier is rewritten to convert the packet into one or more packets. It is characterized by having a step of transferring to a distribution destination.

(I) A stream relay control method in a stream distribution network, comprising the steps of: receiving a packet transmitted from a client or a device having a client function; analyzing the packet information; And a step of acquiring the packet information.

In the recording medium of the present invention, (j) processing steps for realizing the stream relay control method according to any one of the above (g) to (i) are recorded as program codes. It is characterized by.

According to the present invention, by adopting the above configuration, the stream control protocol message sent from the stream server is appropriately distributed to the client receiving the stream content,
Since a response to the message can be sent to the stream server, server processing can be reduced, and large-scale stream distribution can be performed efficiently.

The stream control protocol packet transmitted from the client or the device having the client function is analyzed by the stream relay control device to collect statistical information, and to respond to a collection request from the stream management server. Therefore, it is possible to perform a large-scale stream distribution using a point-to-multipoint transfer technique such as IP multicast after grasping the client distribution state using the stream control protocol.

Further, by using the recording medium of the present invention, the present invention can be widely distributed to the market.

[0031]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to the drawings. (First Embodiment) A stream relay control device having a function of processing a stream control protocol from a stream server and a stream relay control having a function of processing a stream control protocol from a client according to a first embodiment of the present invention. A stream relay control system composed of devices will be described with reference to FIG. 1 and FIG.

FIG. 1 is a diagram showing a configuration example of a stream distribution network service system according to the first embodiment of the present invention. In the first embodiment of the present invention, as shown in FIG.
0a-300d, connection lines 400a-400h, transfer device 500, means for analyzing the stream control protocol sent from the stream server, means for transferring the packet to one or more destinations, and the stream control protocol A stream relay control device 200a having means for creating a response packet to a packet and transferring it to a stream server, and a stream relay control device having means for analyzing a stream control protocol packet transmitted from a client or a device having a client function The feature is that it is composed of 200b and 200c.

Here, for example, the stream server 10
0, stream relay control device 200a, client 3
Although an example is shown in which the stream relay control device 00a and the stream relay control device 200b are directly connected via a connection line, this is merely an example, and there is no problem through a transfer device such as a router.

FIG. 2 is a diagram showing a main functional block configuration of the stream relay control device 200 according to the first embodiment of the present invention. As shown in FIG. 2, the stream relay control device 200 according to the first embodiment of the present invention includes line termination units 201a and 201b, a packet distribution unit 202, a control packet analysis unit 203, and a stream packet analysis unit 2
04, a route selection unit 205, a response packet generation unit 206,
It is characterized by comprising a packet rewrite processor 207, a read controller 208, a write processor 211, a common memory 212, a read processor 213, a packet buffer 214, and lines 401 to 403. The control packet analysis unit 203 and the response packet generation unit 206 constitute a stream control protocol processing unit SCP.

The flow of the stream control protocol packet processed by the present invention will be described with reference to the sequence diagram of FIG. 3, and the processing in the stream relay control device will be described in accordance with the block configuration of FIG. In this description, it is assumed that the setting has been completed by using the stream setting protocol for the stream content that the client has requested to receive, and that the stream distribution is being performed using the stream distribution protocol. I assume. FIG. 4 is a diagram showing an example of the content of a stream control protocol packet in the present description.

(Processing of Packet 10 in Stream Relay Control Device 200a) First, the stream server 100 sends out the stream control protocol packet 10.

In the stream relay control device 200a, the packet is received by the line 401, and the packet is terminated by the line terminating unit 201. Next, the packet distribution unit 202 analyzes the packet information. As a result, it identifies that the packet is a stream control protocol, and transfers the packet to the write processing unit 211.

The header information of the packet is used as information for determining whether or not the packet is a stream control protocol packet. For example,
It is known that when RTCP defined by IETF is used as a stream control packet, a port number that is one larger than the UDP port number used in RTP, which is a stream distribution protocol, is used. Therefore, in the packet distribution unit 202, the UDP
The port number may be analyzed to determine whether the value is the same.

After transferring the packet 10 to the write processor 211, the packet information is transferred to the control packet analyzer 2
03 and the stream packet analyzer 204.

Packet 1 transferred to write processing section 211
0 is stored in the common memory 212. At this time, based on the packet information notified to the stream packet analysis unit 204, a route is selected by the route selection unit 205 and stored in the packet buffer 214 corresponding to the destination according to the selection result. If there are a plurality of clients, they are copied and stored in a plurality of packet buffers 214.

Alternatively, pm of IP multicast or the like
When transmitting the packet 10 using the p distribution, the destination IP address is rewritten to the corresponding IP multicast address and the packet 10 is stored. In this example, p-mp distribution is used.

Next, according to the read time managed by the read control unit 208, the data is transferred from the read processing unit 213 to the line terminating unit 201 and transmitted via the line 402.

The control packet analysis unit 203 analyzes the packet transferred from the packet distribution unit 202 and, as shown in FIG. 4, because it is a Sender Report message, the stream control sent from the stream server. Identify the packet. Further, the sender identifier is analyzed to extract that the source of the packet is the stream server 100.

Next, the result of the analysis is notified to the response packet generator 206, and the response packet generator 205 generates the response packet 11 to the server 100. In this example, Receiveiv is an identifier indicating that the packet is a response packet.
er Report, 200a as sender identifier, Sender Repo
rt (SR) 10 as the sender identifier according to the analysis result
0, the discard rate 0 as the distribution status information,
To be stored. Next, the data is stored in the common memory 212 via the packet rewrite processing unit 207. At that time, the server 10
Packet buffer 21 corresponding to the destination to be transferred to 0
4 is stored. Next, the data is transmitted to the line according to the read time managed by the read control unit 208.

(Processing of Packet 10 in Stream Relay Control Device 200b) The packet 10 transmitted from the stream relay control device 200a arrives at the stream relay control device 200b via the transfer device 500.

In the stream relay control device 200b, the packet is sent to the stream relay control device 200a via the write processing unit 211 in the same manner as the processing of the packet 10 in the stream relay control device 200a.
It is stored in the common memory 212. In this example, when transferring to a plurality of clients, IP multicast is not used.
To use IP unicast, a plurality of copies are made and stored in the packet buffer 214 corresponding to the corresponding destination,
The data is transmitted to the line according to the read time managed by the read processing unit 208.

In the stream relay control device 200b,
Since it is not directly connected to the stream server 100 but via the stream relay control device 200a, the analysis of the packet 10 and the response packet generation processing are not performed.

(Packet 1 at stream server 100)
Process 1) The packet 11 transmitted from the stream relay control device 200a arrives at the stream server 100 via the line 400a.

The stream server 100 analyzes the packet 11 and recognizes that the packet is a response packet to the packet 10 transmitted by the stream server 100, and maintains the connectivity to the stream relay control device 200a. It recognizes that the stream content being distributed is distributed without loss to the stream relay control device 200a. Thereby, the stream distribution of the stream content is continuously performed.

(Processing of Packet 10 at Client)
The packet 10 transmitted from the stream relay control device 200b reaches the clients 300a and 300b via the lines 400e and 400g.

The client 300a analyzes the packet 10 and sends the packet to the Sender Report.
, And creates a response packet 12 for the packet.

In this example, it is indicated that the packet is a response packet.
Receiver Report, 300a as sender identifier, Sende
r 100 is stored in the response packet 12 as the Report (SR) sender identifier according to the analysis result, and the discard rate 0.01 as the distribution status information. Next, the response packet 12 is transmitted to the stream relay control device 200b via the line 400e.

Similarly, the client 300h generates a response packet 13 and sends the response packet 13 to the stream relay control device 200b via the line 400f.

(Processing of Packets 12 and 13 in Stream Relay Control Device 200b) Clients 300a and 30
Packets 12 and 13 transmitted from the line 400b are
e, 400g, the stream relay control device 200
Arrives at b.

In the stream relay control device 200b, as a result of the packet analysis process in the packet distribution unit 202, after notifying the control packet analysis unit 203 of the packet information, the analysis process of the packets 12 and 13 is performed. Is a response packet to the packet 10 transmitted by the stream relay control device 200b, and recognizes that both the clients 300a and 300b have connectivity.

Note that packet 1
If the response packets 11 and 12 for 0 have not arrived, it is determined that the connectivity with the client that is supposed to send the packet that has not arrived has been interrupted, and the distribution of stream contents is stopped or the stream session is disconnected. Can be performed from the stream relay control device side. After analyzing the packets 12 and 13, there is no need to transfer the packets to the upstream stream relay control device, and the packets 12 and 13 may be discarded by the stream relay control device 200 b.

According to the first embodiment described above, a one-to-one relationship between a stream server and a stream relay control device, or between a client or a device having a client function and a stream relay control device, using a stream control protocol. After confirming the connectivity, it is possible to efficiently realize one-to-many large-scale stream distribution. In particular, as a distribution network between stream relay control devices,
It becomes possible to use one-way p-mp distribution of ATM. Further, since there is no need to transfer stream control protocol packets between the stream relay control devices, it is not necessary to reduce unnecessary packet processing and secure a path for packet transfer.

(Second Embodiment) A stream relay control device 200 having a function of processing a stream control protocol from a stream server according to a second embodiment is described with respect to a stream relay control device 200 according to an embodiment of the present invention. A stream relay control system including a stream control protocol processing function from a client, a stream relay control device having an information storage function, and a stream management server will be described with reference to FIGS. Note that the description of the part that performs the same processing as that of the above-described first embodiment may be omitted.

FIG. 5 is a diagram showing a configuration example of a stream distribution network service system according to the second embodiment of the present invention. In the second embodiment of the present invention, FIG.
In addition to the configuration described above, a stream management server 600 having a function of managing the distribution status and the like to a client, and a connection line 400i for connecting to a stream relay control device
The feature is that it is constituted by ~ 400k. Here, the stream management server and the stream relay control device are connected, but a configuration in which the stream server and the stream management server are connected to manage the distribution status of the stream server may be used.

FIG. 6 is a diagram showing a main functional block configuration of a stream relay control device 200 according to the second embodiment of the present invention. The stream relay control device according to the second embodiment of the present invention has an information storage storing a statistical information table 209a in addition to the configuration of the stream relay control device according to the first embodiment shown in FIG. Part 20
9. It has a management server response generation unit 210.

Regarding the flow of the stream control protocol packet processed by the second embodiment of the present invention, the processing of the packets 12 and 13 in the stream relay control device 200b, which is the difference from the first embodiment, is described. explain.

(Processing of Packets 12 and 13 in Stream Relay Control Device 22b) Clients 300a and 300
b, packets 12 and 13 transmitted from line 400
e, 400f, the stream relay control device 200
Arrives at b.

The stream relay control device 200b analyzes the packets 12 and 13 and recognizes that the packet is a response packet to the packet 10 sent out by the stream relay control device 200b. It recognizes that both have connectivity.

Next, the connection status and distribution quality status of each client are stored in the statistical information table 209a of the information storage unit 209 via the control packet analysis unit 203.

FIG. 7 is a diagram showing a configuration example of the statistical information table 209a according to the second embodiment of the present invention.
FIG. 11 is a specific example of a statistical information table 209a that manages which content is received at what quality (here, discard rate) for each client managed by a client number. In this example, the client with the client number “300a” is assigned the content number “Cont.
ent A ”is received at a discard rate of 0.01, the content of content number“ Content B ”is received at a discard rate of 0, and the client number“ 300b ”is received.
Is an example in which the client No. 1 receives the content of the content number “Content A” at the discard rate 0.

Thereafter, in response to a statistical information collection / management request from the stream management server 600, the management server response generation unit 210 generates a response packet based on the statistical information table 209a stored in the information storage unit 209. Then, the response packet is stored in the packet buffer 214 of the common memory 212 via the packet rewrite processing unit 207, and transmitted to the stream management server 600.

According to the second embodiment described above,
After efficiently performing large-scale stream distribution, using the statistics of the stream reception status from the client,
The stream management server 600 can perform statistical processing / state management.

In the description of the first and second embodiments, the case where the discard rate is collected as information on the stream reception status from the client has been described. However, the present invention is not limited to the discard rate. Needless to say, information such as the information may be collected.

Each process for realizing the above-described stream relay control method according to the present invention is converted into a program code, recorded on a computer-readable recording medium such as a CD-ROM, FD, or HD and distributed to the market. Thereby, the stream relay control method of the present invention can be widely spread.

[0070]

According to the present invention, a stream relay control apparatus and a stream relay control system capable of efficiently performing large-scale stream distribution and collecting and managing the distribution status of each client. The present invention can be widely spread by distributing a recording medium on which the stream relay control method is recorded to the market.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration example of a stream distribution network service system according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a main functional block configuration of a stream relay control device according to the first embodiment of the present invention.

FIG. 3 is a sequence diagram showing a flow of processing of a stream control protocol packet.

FIG. 4 is a diagram showing an example of the content of a stream control protocol packet according to the present description.

FIG. 5 is a diagram illustrating a configuration example of a stream distribution network service system according to a second embodiment of the present invention.

FIG. 6 is a diagram showing a main functional block configuration of a stream relay control device according to a second embodiment of the present invention.

FIG. 7 is a diagram illustrating a configuration example of a statistical information table according to a second embodiment of the present invention.

FIG. 8 is a diagram illustrating a configuration example of a conventional stream distribution network.

FIG. 9 is a diagram showing a sequence example of a stream control protocol exchanged between a stream server and a client in FIG.

[Explanation of symbols]

10: packet, 11, 12, 13: response packet, 100: stream server, 200 (200a, 200b, 200c): stream relay control device, 201 (201a, 201b): line termination unit, 202: packet distribution unit, 203: control packet analysis unit, 204: stream packet analysis unit, 205: route selection unit, 206: response packet generation unit, 207: packet rewrite processing unit, 208: read control unit, 209: information storage unit, 209a: statistical information Table, 210: management server response generator, 211: write processor, 212: common memory, 213: read processor, 214: packet buffer, 300 (300a, 300b, 300c, 300d):
Client 400 (400a, 400b, 400c, 400d, 4
00e, 400f, 400g, 400h, 400i, 4
00j, 400k): connection line, 401, 402, 403: line, 500 (500a, 500b, 500c, 500d):
Transfer device, 600: stream management server, SCP: stream control protocol processing unit, a, b, c, d: message.

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Shinya Hanano 2-3-1 Otemachi, Chiyoda-ku, Tokyo Inside Nippon Telegraph and Telephone Corporation (72) Inventor Kiyoshi Yanagimoto 2-3-3, Otemachi, Chiyoda-ku, Tokyo No. 1 Nippon Telegraph and Telephone Corporation F term (reference) 5B089 GA31 GB02 JA33 JB15 KA13 5K030 GA11 HA08 JT03 KA03 KA05 KA13 KX13 KX28 LD05

Claims (10)

[Claims] 1. A stream relay control device in a stream distribution network, comprising: means for receiving a packet transmitted from a stream server; means for analyzing header information of the packet and identifying the packet as a stream control protocol. Means for transferring the packet to one or more destinations, means for notifying the packet information when the packet is a stream control protocol, and status information and / or an identifier of the stream server from the packet information. A stream relay control device, comprising: means for acquiring; and means for creating a response packet to the packet and transferring the packet to a stream server. 2. The stream relay control device according to claim 1, wherein, of the packet information sent from the stream server, means for rewriting server information and / or an identifier, and transferring the packet to one or more distribution destinations A stream relay control device comprising a transfer unit. 3. A stream relay control device in a stream distribution network, comprising: means for receiving a packet transmitted from a client or a device having a client function; analyzing header information of the packet; A stream relay device comprising: means for identifying a control protocol; and means for acquiring the packet information. 4. The stream relay control device according to claim 3, wherein the means for storing stream control packet information transmitted from the client or a device having a client function, and a means for responding to a request from the stream management server. A stream relay device comprising: 5. A stream relay control system comprising the stream relay control device according to claim 1 and the stream relay control device according to claim 3. 6. A stream relay control system, comprising: the stream relay control device according to claim 2; the stream relay control device according to claim 4; and a stream management server. 7. A stream relay control method in a stream distribution network, comprising: a step of receiving a packet transmitted from a stream server; a step of analyzing the packet information to identify a stream control protocol; Notifying the stream control protocol processing unit of the packet information after transferring the packet to one or a plurality of distribution destinations; obtaining the stream server state information and / or identifier from the packet information; A stream relay control method, comprising: creating a response packet to a packet and transferring the packet to a stream server. 8. The stream relay control method according to claim 7, wherein, of the packet information sent from the stream server, server status information and / or an identifier is rewritten and the packet is transferred to one or more distribution destinations. A stream relay control method. 9. A stream relay control method in a stream distribution network, comprising: a step of receiving a packet transmitted from a client or a device having a client function; analyzing the packet information to be a stream control protocol. And a step of acquiring the packet information. 10. A computer-readable recording medium in which processing steps for realizing the stream relay control method according to claim 7 are recorded as program codes.