WEBVTT 00:05.540 --> 00:09.800 So guys, next let us discuss socket message types. 00:09.950 --> 00:12.940 That is in socket based communication. 00:12.950 --> 00:19.610 The messages that are exchanged between the client and the server processes can be broadly classified 00:19.610 --> 00:21.200 into two types. 00:22.970 --> 00:28.580 The first type of messages are called connection, initiation request message. 00:28.970 --> 00:37.040 This message is used only by the client process, and this type of message is used by the client process 00:37.040 --> 00:42.170 to request the server process to establish a dedicated connection. 00:42.470 --> 00:49.100 So connection initiation request message is actually a request message that is generated by the client 00:49.100 --> 00:56.450 process and this message is sent by the client process to the server process, requesting the server 00:56.450 --> 01:02.660 process to accept and establish a dedicated connection with the client. 01:03.920 --> 01:10.590 Only after the connection between the client and the server process has been established, then only 01:10.590 --> 01:17.700 the client can send the second type of message, which is called service request message to the server. 01:18.000 --> 01:24.150 So you can see in this diagram we have a client process as well as the server process and it is the 01:24.150 --> 01:28.530 client process which wants to connect with the server process. 01:28.530 --> 01:35.400 So the very first thing that a client process needs to do is to send a connection, initiation request 01:35.400 --> 01:37.530 message to the server process. 01:37.740 --> 01:42.150 So CR stands for connection initiation request message. 01:43.940 --> 01:50.420 So connection initiation request message is actually a request to the server to accept and establish 01:50.420 --> 01:53.150 a dedicated connection with the client. 01:54.320 --> 02:01.250 So once the server accepts the connection initiation request from the client, the connection between 02:01.250 --> 02:06.260 the client and the server process is set to be established and complete. 02:07.300 --> 02:07.900 Right. 02:07.900 --> 02:13.720 So remember, connection initiation request messages are always generated by the client process and 02:13.720 --> 02:20.290 it is always targeted to the server process to which the client wants to carry out communication. 02:21.730 --> 02:26.230 The second type of message is actually called service request messages. 02:27.160 --> 02:34.930 These messages are generated by the client process and these are sent by the client process to the server 02:34.930 --> 02:37.510 once the connection is fully established. 02:37.780 --> 02:44.410 So remember, service request messages can only be sent by the client process only when the connection 02:44.410 --> 02:49.120 between the client process and the server process has been fully established. 02:51.130 --> 02:51.820 Right. 02:51.820 --> 02:58.270 So through these messages, that is service request messages, client requests, the server to provide 02:58.270 --> 02:59.290 a service. 02:59.320 --> 03:06.220 So here service is nothing but a functionality that is provided by the server process to the client. 03:07.360 --> 03:09.700 So you can see that in the step three. 03:09.700 --> 03:16.120 Once the connection is fully established between the client process and the server process in step three, 03:16.120 --> 03:21.790 the client process can now send service request message to the server process. 03:21.790 --> 03:28.690 Having received the service request message, the server can process the service request message and 03:28.690 --> 03:31.240 it can prepare some response. 03:32.540 --> 03:38.030 Once the server prepares the response, it sends the response message back to the client. 03:39.200 --> 03:46.220 So note that service request message is any data which is generated by the client process and is sent 03:46.220 --> 03:49.460 by the client to the server process for processing. 03:51.000 --> 03:53.940 So let us take a very simplest example. 03:53.940 --> 03:56.820 Suppose a client process generates two numbers. 03:56.820 --> 03:58.620 That is A and B. 03:59.910 --> 04:04.740 So both these numbers constitutes a service request message. 04:06.240 --> 04:08.610 Right and a client process. 04:08.610 --> 04:16.050 Let us assume that our client process cannot compute the multiplication of two numbers and it relies 04:16.050 --> 04:21.570 on the server process to actually multiply the two numbers and send back the result. 04:22.350 --> 04:29.100 So in this example, the multiplication service that is provided by the server process is actually a 04:29.100 --> 04:31.410 service that is provided to the client. 04:33.540 --> 04:40.200 So in this example, the service request message will actually be the pair of two integers which is 04:40.200 --> 04:43.440 generated by the client process and send to the server. 04:43.830 --> 04:50.520 Once the server receives this SRM, which is actually a set of two integers, the server process would 04:50.520 --> 04:56.460 perform the local computation on this message and it will compute the multiplication of two numbers. 04:58.390 --> 05:03.460 Once the server process performs the multiplication of two numbers and get the result. 05:03.490 --> 05:07.390 A server process can send back the response back to the client. 05:09.450 --> 05:16.260 So service request message is nothing, but it is any data which is generated by the client and need 05:16.260 --> 05:18.750 to be processed by the server process. 05:18.780 --> 05:26.430 The result of processing the SRM message is a response which is generated by the server process and 05:26.430 --> 05:28.170 directed to the client. 05:29.220 --> 05:33.540 So server identifies and process both the type of messages. 05:34.890 --> 05:40.860 Which type of messages, the connection, initiation, request message and service request message very 05:40.860 --> 05:41.760 differently. 05:41.970 --> 05:48.900 So you will understand this point when we will be actually discussing the code for implementing a socket 05:48.900 --> 05:53.280 based communication on the server side as well as on the client side. 05:54.690 --> 06:00.630 So the takeaway from this slide is that that the connection initiation request message is a message 06:00.630 --> 06:07.950 which is used to establish a connection with the server and service request message is any data which 06:07.950 --> 06:14.460 is sent by the client process to the server for processing and of course service request messages are 06:14.460 --> 06:15.810 sent only once. 06:15.810 --> 06:20.550 The connection between the client and server process has been fully established.