WEBVTT 00:04.980 --> 00:09.260 So guys, continuing with our implementation of Publisher subscriber example. 00:09.270 --> 00:14.700 So to begin with, we need a routing table data structures to begin with, right? 00:14.700 --> 00:17.570 Because we have chosen routing table as a data source. 00:17.580 --> 00:23.370 So we need a data structure which represents a routing table and we need a couple of APIs which can 00:23.370 --> 00:26.880 perform, create, delete or update operations on this routing table. 00:26.880 --> 00:31.230 So we need to define data structures, which represents a routing table. 00:31.230 --> 00:37.590 So you can see on the left hand side the keys of the routing table comprises of the destination as well 00:37.590 --> 00:39.510 as mask value, right? 00:39.600 --> 00:47.070 So mask value is any value between 0 to 32 and destination is any IP address, which can be 16 bytes 00:47.070 --> 00:47.640 long. 00:48.090 --> 00:52.320 So this data structure represents a key of a routing table entry. 00:52.470 --> 00:59.970 And this particular data structure that is entry represents one complete routing table entry, right? 00:59.970 --> 01:07.420 So a routing table entry has the keys and after that it has other data which is outgoing interface and 01:07.420 --> 01:08.230 Gateway. 01:08.410 --> 01:09.190 Right? 01:09.870 --> 01:14.060 And we were going to model this routing table as a doubly linked list. 01:14.070 --> 01:14.940 Right? 01:16.500 --> 01:21.540 So routing table is nothing, but it is a doubly linked list of routing table entries. 01:21.570 --> 01:27.950 It is for this reason that I have previous and next pointer within the routing table entry structure. 01:27.960 --> 01:28.740 Right. 01:29.100 --> 01:34.620 If you want some other alternative as an implementation of routing table, for example, you want to 01:34.620 --> 01:37.800 model routing table as an array, right? 01:37.950 --> 01:41.850 Array with some fixed number of entries, then you can do so. 01:41.850 --> 01:45.750 It really do not matter as long as this project is concerned. 01:46.710 --> 01:49.740 All you need is that you need a data source. 01:49.830 --> 01:55.070 And finally, we have a highest level data structure which actually represents a routing table. 01:55.080 --> 02:01.080 So routing table data structure simply carries a pointer, which points to the first entry of the routing 02:01.110 --> 02:01.680 table. 02:01.680 --> 02:03.990 That is the first entry, right? 02:04.580 --> 02:09.140 So you need to define all these data structures in the file attach. 02:09.140 --> 02:15.560 And after you have defined all these data structures in the file attach, we need to implement, create, 02:15.560 --> 02:19.240 read, update, delete operations on this routing table as well. 02:19.250 --> 02:20.030 Right. 02:20.330 --> 02:26.500 So let us look at the prototype of the APIs that would perform the Crud operations on this routing table. 02:26.510 --> 02:34.010 So you can see on the left hand side, following are the prototypes which would implement Crud operations 02:34.010 --> 02:35.390 on this routing table. 02:35.930 --> 02:38.750 Now to make things easier and faster. 02:38.750 --> 02:45.170 I have given you a raw file or underscore rorge and underscore raw. 02:45.860 --> 02:51.290 See these file exactly implements each of these APIs already. 02:51.320 --> 02:52.230 Right. 02:52.250 --> 02:59.990 So if you want to skip this dumb work of implementing a routing table as a data source, you can start 02:59.990 --> 03:05.370 the project by using underscore raw edge and underscore raw dot C file. 03:05.390 --> 03:11.500 You can rename these files to dot H and dot C in your project code. 03:11.510 --> 03:12.260 Right. 03:13.370 --> 03:18.700 Or it's up to you If you want to implement the routing table from absolute scratch, you can do so. 03:18.710 --> 03:24.230 But before using your own implementation of the routing table with the rest of the project, make sure 03:24.230 --> 03:27.890 that your implementation is bug free or otherwise. 03:27.890 --> 03:32.780 I would suggest use these raw files to start with this project. 03:32.780 --> 03:38.240 Right now, coming to the discussion on each of these prototypes of this API, you can see that the 03:38.240 --> 03:44.660 first API is used to actually add or update a particular entry in the routing table, right? 03:45.560 --> 03:49.520 Whereas the second API is used to delete an entry from the routing table. 03:49.520 --> 03:57.080 And for that all you need to specify is the key to find out uniquely an entry in the routing table which 03:57.080 --> 03:58.250 you want to delete. 03:58.280 --> 04:03.950 Similarly, you have implemented a lookup API to look up certain entry from the routing table. 04:04.100 --> 04:08.420 Of course, this API must return null if such an entry do not exist. 04:08.420 --> 04:09.080 Right. 04:09.080 --> 04:15.210 And then final is the API which you want to implement to dump the contents of the routing table. 04:15.210 --> 04:15.900 Right. 04:16.970 --> 04:22.520 Now in the next lecture video, let us start with our main function and see how we can going to build 04:22.520 --> 04:23.480 up this project.