1 00:00:00,640 --> 00:00:07,840 In a later video, I'll show you a Wireshark capture, showing you what the traffic or frames look like 2 00:00:07,840 --> 00:00:10,110 when sent between two sites. 3 00:00:10,120 --> 00:00:17,230 But for the moment, the high level picture is as follows A PC in one local area network is sending 4 00:00:17,230 --> 00:00:23,020 traffic to a PC in another local area network when the traffic is sent across the land. 5 00:00:23,020 --> 00:00:28,810 And in this case we're using Ethernet, the IP packet is encapsulated in an Ethernet frame. 6 00:00:28,810 --> 00:00:32,860 So at a layer two, the encapsulation used is Ethernet. 7 00:00:32,860 --> 00:00:35,380 So as an example, it could be Ethernet too. 8 00:00:35,740 --> 00:00:42,460 When the frame arrives at the router, the router will strip the layer two headers and then send the 9 00:00:42,460 --> 00:00:45,790 frame across the WAN using, for example. 10 00:00:45,810 --> 00:00:46,840 Hdl-c. 11 00:00:47,230 --> 00:00:54,820 So if this .2. connection is configured with a layer two encapsulation of Hdl-c, the Ethernet headers 12 00:00:54,820 --> 00:01:04,060 are removed and the original IP packet that was sent by PC one is encapsulated in Hdl-c and is forwarded 13 00:01:04,060 --> 00:01:06,850 across the cereal link to router two. 14 00:01:07,180 --> 00:01:14,110 When router two receives the hdl-c frame, it strips the hdl-c headers and forwards the original IP 15 00:01:14,110 --> 00:01:20,380 packet sent by PC one onto the local area network using an Ethernet header. 16 00:01:20,530 --> 00:01:28,780 So the packet is encapsulated in Ethernet and an Ethernet frame is sent from router two to PC two using 17 00:01:28,780 --> 00:01:29,620 Ethernet. 18 00:01:29,920 --> 00:01:33,910 So we have Ethernet on the local area network on the left. 19 00:01:34,360 --> 00:01:38,980 The When encapsulation used is used between router one and router two. 20 00:01:38,980 --> 00:01:41,110 In this example, it's hdl-c. 21 00:01:41,110 --> 00:01:45,460 And then on land two, an ethernet encapsulation is used once again. 22 00:01:46,210 --> 00:01:52,390 The two layers that we're going to concentrate on in the OSA model for one technologies is the physical 23 00:01:52,390 --> 00:01:54,550 layer and the data link layer. 24 00:01:54,970 --> 00:02:02,200 At the physical layer, the physical presentation changes from what you've seen in an Ethernet environment. 25 00:02:02,200 --> 00:02:10,660 So rather than using RJ 45 Connectors and for instance Cat six cabling X 21 or V 35 cables would be 26 00:02:10,660 --> 00:02:11,410 used. 27 00:02:11,440 --> 00:02:18,130 So the physical characteristics of the one interface are different to the physical characteristics of 28 00:02:18,130 --> 00:02:20,380 Ethernet at layer two. 29 00:02:20,380 --> 00:02:25,870 Rather than using an Ethernet encapsulation, you would encounter encapsulation such as frame relay, 30 00:02:25,900 --> 00:02:30,130 PPTP, Hdl-c, ATM and MPLS. 31 00:02:30,430 --> 00:02:37,720 You may however today also encounter Ethernet when connections which are becoming more and more popular. 32 00:02:38,020 --> 00:02:43,690 But for the CCNA, when discussing a point to point one connection, we are going to be concentrating 33 00:02:43,690 --> 00:02:47,230 on a PPTP and Hdl-c encapsulation. 34 00:02:47,680 --> 00:02:52,120 So what kind of when devices would you typically see for point to point connections? 35 00:02:52,510 --> 00:02:57,850 Well, you'll typically find routers rather than switches connecting remote sites together. 36 00:02:58,330 --> 00:03:07,090 You'd also encounter a CSU, DSU or channel service unit data service unit, which allows you to connect 37 00:03:07,090 --> 00:03:13,300 to a leased line connection using, for example, an x 21 or v 35 cable. 38 00:03:13,450 --> 00:03:18,070 This converts the signals to the required format for when transmission.