Midterm 1 Flashcards
Describe the internet best service model.
The best-effort model is the internet’s best service model, which means that the internet service provider (ISP) will make its best effort to deliver data packets from one point to another, but does not guarantee delivery or prioritize one type of data over another. All data packets are treated equally, regardless of their type or priority. This model is based on the principle that the internet is a public network, and as such, it cannot guarantee the quality of service or reliability that would be possible with a dedicated private network.
Why is running over UDP an appropriate choice for the DNS application.
TCP services provides reliable transport, flow control, congestion control, and is connection-oriented. On the other hand, UDP provides unreliable data transfer, and does not provide flow control or congestion control. However, UDP allows for more versatile scalability, shorter delays, and easier rate control. The DNS being an application layer protocol uses a transport layer protocol. In specific, UDP is preferred over TCP. Although TCP is more reliable and DNS is supposed to be reliable, it utilizes UDP. This is because UDP is faster than TCP as TCP requires a 3-way handshake with is very ineffective for DNS. DNS requests often fit well in UDP segments as they are very small. Although UDP lacks reliability, it can be added on to the application layer.
What is the dynamic adaptive streaming over HTTP (DASH) protocol?
Dynamic Adaptive Streaming over HTTP is an adaptive streaming protocol. Essentially, it allows a video stream to switch between bit rates based on network performance. Enabling high quality streaming from conventional HTTP web servers. This allows a video to continue playing regardless of network performance and connectivity. With recent video traffic increase being a major consumer of internet bandwidth, there needed to be a solution. Something scalable and adaptable. DASH has both a server and client side. On the server side, it works by dividing a video into multiple chunks. Each chunk is then stored and encoded at different rates. On the client side, it periodically measures the server-to-client bandwidth. There is a level of intelligence at the client side, where it can determine when to request a chunk so that overflow doesn’t occur. It also knows what encoding rate to request at, such as higher quality when there is more bandwidth available. Lastly, it determines where to request a chunk.
For a P2P file-sharing application, do you agree with the statement, “There is no notion of client and server sides of a communication session”? Why or why not?
No. In P2P file-sharing applications, the peer that is receiving the file is typically the client and the peer that is sending the file is typically the server.
What information is used by a process running on one host to identify a process running on another host?
The IP address of the destination host and the port number of the socket in the destination process.
Consider an e-commerce site that wants to keep a purchase record for each of its
customers. Describe how this can be done with cookies.
When the user first visits the site, the server creates a unique identification number, creates an entry in its back-end database, and returns this identification number as a
cookie number. This cookie number is stored on the user’s host and is managed by the browser. During each subsequent visit (and purchase), the browser sends the cookie number back to the site. Thus the site knows when this user (more precisely,
this browser) is visiting the site.
Describe how Web caching can reduce the delay in receiving a requested object.
Web caching can bring the desired content “closer” to the user, possibly to the same LAN to which the user’s host is connected.
Will Web caching reduce the delay for all objects requested by a user or for only some of the objects?
Web caching can reduce the delay for all objects, even objects that are not cached, since caching reduces the traffic on links.
Suppose Alice, with a Web-based e-mail account (such as Hotmail or Gmail), sends a message to Bob, who accesses his mail from his mail server using POP3. Discuss how the message gets from Alice’s host to Bob’s host. Be sure to list the series of application-layer protocols that are used to move the message between the two hosts.
The message is first sent from Alice’s host to her mail server over HTTP. Alice’s mail server then sends the message to Bob’s mail server over SMTP. Bob then transfers the message from his mail server to his host over POP3.
What is an overlay network? Does it include routers?
The overlay network in a P2P file-sharing system consists of the nodes participating in the file-sharing system and the logical links between the nodes.
What are the edges in the overlay network?
There is a logical link (an “edge” in graph theory terms) from node A to node B if there is a semipermanent TCP connection between A and B. An overlay network does not include routers.
Besides network-related considerations such as delay, loss, and bandwidth performance, there are other important factors that go into designing a CDN server selection strategy. What
are they?
Other than network-related factors, there are some important factors to consider, such as load-balancing (clients should not be directed to overload clusters), diurnal effects,
variations across DNS servers within a network, limited availability of rarely accessed video, and the need to alleviate hot-spots that may arise due to popular video
content.
True or False. A user requests a Web page that consists of some text and three images. For this page,
the client will send one request message and receive four response messages.
False. When a user requests a web page that consists of text and images, the client will send one HTTP request message to the server. The server will respond with an HTTP response message that includes the HTML code for the text and the URLs for the three images.
The client will then send three separate HTTP requests for each image, and the server will respond with three separate HTTP response messages, each containing the image data.
Therefore, in total, the client will send one request message and receive four response messages: one for the HTML text and three for the images.
True or False. Two distinct Web pages (for example, www.mit.edu/research.html and
www.mit.edu/students.html ) can be sent over the same persistent connection.
True. Persistent connections allow multiple requests and responses to be sent over the same TCP connection. Once the initial TCP connection is established, subsequent HTTP requests and responses can be sent and received without the need to establish a new TCP connection for each request/response pair.
True or False. With nonpersistent connections between browser and origin server, it is possible for a
single TCP segment to carry two distinct HTTP request messages.
False. With nonpersistent connections between the browser and the origin server, each HTTP request and response pair is sent over a separate TCP connection. The connection is closed after the response is received, so the next request from the same client requires the establishment of a new TCP connection.
In this scenario, a single TCP segment can only carry a single HTTP request or response message, but not two distinct HTTP request messages. Each HTTP request message requires a separate TCP segment for its transmission, and there can only be one message in a segment.