Chapter 5 mini case: Network and Transport Layers Eating lunch at your desk You are at work, eating your lunch while sitting at your desk. Your company laptop is connected to the internet over the company's WI-FI. You want to read an article about the latest DDOS attack from the Arstechnica.com website, one of your favorite news sources. You have typed in the URL of the website and clicked on the article you want to read. The website has responded by sending the requested article to your computer. So far, the physical layer of your computer has received packets as wireless Wi-Fi signals, and passed them on to the data link layer. The data link layer has passed the packets to the Network Layer, and then on to the Transport Layer. 1. When you typed the URL into your browser, how did your packets get the destination IP address they needed? Select an answer and fully describe the process. a. The computer already knew it from its IP address table, and supplied it to the Transport layer b. The browser issues a DNS request and passes it to the TCP layer, which creates a UDP datagram and passes it to the Network layer, which eventually is resolved by a DNS server The Ethernet Layer initiated the DNS request, which eventually was resolved by a DNS server d. The Transport layer initiated the DNS request, which eventually was resolved by a DNS server 2. There are several applications running on your laptop. Many of these applications have packets arriving from the internet (Spotify, email, GoToMeeting, Text Messaging). How does the Transport layer know that the packets arriving from the Arstechnica.com web site should be passed to the web browser? Select an answer and fully describe the process a. The packets arrive at the TCP layer with the name of the destination application b. The IP of the laptop identifies the destination application, so the data link layer knew where to send them Browser packets are distinctive, so the TCP layer knew where they should be sent d. Portaddresses (one for outgoing, another one for incoming for popular applications are standardized so incoming packets would be formed with the standard browser port address 3. Refer to figure 5-13 on page 137 of the textbook. Your company is Autonomous System and your computer is connected to a Wi-Fi access point that is directly connected to Router 2. You want to send a message to someone that works for the company that runs Autonomous System A, and that person's computer is directly connected to Router 1. If the first hop is from your laptop to the Wi-Fi access point, and all routers along the way are working perfectly, how many hops will your message have on the trip from your laptop to its destination? a 6 hops b. 8 hops c 9hops d. 10 hops 4. The web article that you have requested is actually a large PDF file, broken into smaller segments for the transmission by the sender. The Network layer has stripped off the IP addresses from each packet and delivered them to the Transport bayer. In what form will the Transport layer deliver the PDF file to the browser? a. Packets are delivered to the browser as they arrive b. The PDF file is delivered to the browser only after all the frames/packets have arrived and the TCP has assembled them into a complete message. The PDF file was transmitted as one large packet so no assembly was required before delivery to the browser. d. The PDF file is assembled by the TCP and converted to a bit-mapped image before delivery to the browser
