CPSC 471 Chapter 2 Exam Study Set

2.1-1 The client-server paradigm. Which of the characteristics below are associated with a client-server approach to structuring network applications (as opposed to a P2P approach)?

- There is a server with a well-known server IP address. - There is a server that is always on. - HTTP uses this application structure.

2.1-2 The peer-to-peer (P2P) paradigm. Which of the characteristics below are associated with a P2P approach to structuring network applications (as opposed to a client-server approach)?

- There is not a server that is always on. - A process requests service from those it contacts and will provide service to processes that contact it.

2.7-1 UDP Sockets. Which of the following characteristics below are associated with a UDP socket? Check one or more that apply.

- provides unreliable transfer of a groups of bytes ("a datagram"), from client to server - the application must explicitly specify the IP destination address and port number for each group of bytes written into a socket - data from different clients can be received on the same socket

2.2-06 A detailed look at an HTTP GET (2). Again, suppose a client is sending an HTTP GET request message to a web server, gaia.cs.umass.edu. The client-to-server HTTP GET message is the following (same as in previous problem):

United Kingdom English

2.6-2 Streaming video definitions. Match the definition/function of an element or approach in a networked streaming video system, with its name.

- A unit of video, each of which may be encoded at multiple different rates, stored in different files. = Chunk - A file containing the location and encoding rate of files corresponding to video segments in a video. = Manifest - An approach that allows a client to adapt the encoding rate of retrieved video to network congestion conditions. = DASH - A CDN approach that stores content in access networks, close to clients. = Enter deep

2.1-4 TCP service. When an application uses a TCP socket, what transport services are provided to the application by TCP? Check all that apply.

- Congestion control. The service will control senders so that the senders do not collectively send more data than links in the network can handle. - Loss-free data transfer. The service will reliably transfer all data to the receiver, recovering from packets dropped in the network due to router buffer overflow. - Flow Control. The provided service will ensure that the sender does not send so fast as to overflow receiver buffers.

2.4-07. DNS and HTTP Caching. We learned that in HTTP web browser caching, HTTP local web server caching, and in local DNS caching, that a user benefits (e.g., shorter delays over the case of no caching) from finding a local/nearby copy of a requested item. In which of the following forms of caching does a user benefit from its not only from its own recent requests (and cached replies) but also from recent requests made from other users?

- HTTP local web caching - Local DNS server caching

2.4-02 Why does the local DNS server perform caching? What is the value of caching in the local DNS name server? Check all that apply.

- DNS caching results in less load elsewhere in DNS, when the reply to a query is found in the local cache. - DNS caching provides for faster replies, if the reply to the query is found in the cache.

2.2-05 A detailed look at an HTTP GET (1). Suppose a client is sending an HTTP GET request message to a web server, gaia.cs.umass.edu. Suppose the client-to-server HTTP GET message is the following: What version of HTTP is the client using?

1.1

2.3-1 E-mail delays. How many RTTs are there from when a client first contacts an email server (by initiating a TCP session) to when the client can begin sending the email message itself - that is following all initial TCP or SMTP handshaking required? Recall the figure below from our class notes:

3

2.7-4 How many sockets? Suppose a Web server has five ongoing connections that use TCP receiver port 80, and assume there are no other TCP connections (open or being opened or closed) at that server. How many TCP sockets are in use at this server?

6

2.6-5. Netflix Streaming. Which of the following (one or more) statements are true about Netflix streaming (check all that are true) or video streaming services in general.

In Netflix, the client requests chunks of video, and each chunk may have a different encoding rate (video quality) and can be retrieved from a different server.

2.2-03 The HTTP GET. What is the purpose of the HTTP GET message?

The HTTP GET request message is used by a web client to request a web server to send the requested object from the server to the client.

2.2-13 Cookies. What is the purpose of a cookie value in the HTTP GET request?

The cookie value itself doesn't mean anything. It is just a value that was returned by a web server to this client during an earlier interaction.

2.7-5 socket connect(). What happens when a socket connect() procedure is called/invoked?

This procedure creates a new socket at the client, and connects that socket to the specified server.

2.2-11 What's in an HTTP reply? Which of the following pieces of information will appear in a server's application-level HTTP reply message? (Check all that apply.)

- A response phrase associated with a response code - A response code

2.2-02 HTTP cookies. What is an HTTP cookie used for?

A cookie is a code used by a server, carried on a client's HTTP request, to access information the server had earlier stored about an earlier interaction with this Web browser. [Think about the distinction between a browser and a person.]

2.4-03 What's in the DNS type A resource record? What information does the type "A" resource record hold in the DNS database? Check all that apply.

A hostname and an IP address.

2.2-14 HTTP GET (even more). Suppose a client is sending an HTTP GET message to a web server, gaia.cs.umass.edu. Suppose the client-to-server HTTP GET message is the following:

Yes, because this is a conditional GET.

2.7-3 Server reply (UDP). How does the networked application running on a server know the client IP address and the port number to reply to in response to a received datagram?

- The application code at the server determines client IP address and port # from the initial segment sent by client, and must explicitly specify these values when sending into a socket back to that client.

2.2-01 "HTTP is stateless." What do we mean when we say "HTTP is stateless"? In answering this question, assume that cookies are not used. Check all answers that apply.

An HTTP server does not remember anything about what happened during earlier steps in interacting with this HTTP client.

2.1-3 UDP service. When an application uses a UDP socket, what transport services are provided to the application by UDP? Check all that apply.

Best effort service. The service will make a best effort to deliver data to the destination but makes no guarantees that any particular segment of data will actually get there.

2.6-1 CDNs. What approach is taken by a CDN to stream content to hundreds of thousands of simultaneous users?

Store/serve multiple copies of videos at multiple geographically distributed sites.

2.2-12 If-Modified-Since. What is the purpose of the If-Modified-Since field in a HTTP GET request message?

To indicate to the server that the client has cached this object from a previous GET, and the time it was cached.

2.2-15 What happens after an HTTP reply? Suppose an HTTP server sends the following HTTP response message a client: HTTP/1.0 200 OK Date: Wed, 09 Sep 2020 23:46:21 +0000 Server: Apache/2.2.3 (CentOS) Last-Modified: Wed, 09 Sep 2020 23:51:41 +0000 ETag:17dc6-a5c-bf716880. Content-Length: 418 Connection: Close Content-type: image/html Will the web server close the TCP connection after sending this message?

Yes, because this is HTTP 1.0

2.2-08 A detailed look at an HTTP reply. Suppose now the server sends the following HTTP response message the client:

Yes, the server will close this connection because version 1.0 of HTTP is being used, and TCP connections do not stay open persistently.

2.6-3 What is DASH? In DASH (Dynamic, Adaptive Streaming over HTTP), a server divides a video file into chunks that ... (pick best completion from below)

... are stored, each encoded at multiple rates (video quality). The client plays the video chunk-by-chunk, with each chunk requested at encoding rate that fits the available bandwidth at the time.

2.2.16 Third party cookies. Which of the following properties are true of "third party" cookies.

- Are explicitly mentioned in new privacy laws such at the EU General Data Protection Regulation (GDPR). - Provide a mechanism for a website to track a browser's accesses to multiple other websites.

2.2-09 Why Web Caching? Which of the following are advantages of using a web cache? Select one or more answers.

- Caching uses less bandwidth coming into an institutional network where the client is located, if the cache is also located in that institutional network. - Caching generally provides for a faster page load time at the client, if the web cache is in the client's institutional network, because the page is loaded from the nearby cache rather than from the distant server.

2.2-10 HTTP/2 versus HTTP/1.1. Which of the following are changes between HTTP 1.1 and HTTP/2? Note: select one or more answers.

- HTTP/2 allows a large object to be broken down into smaller pieces, and the transmission of those pieces to be interleaved with transmission other smaller objects, thus preventing a large object from forcing many smaller objects to wait their turn for transmission. - HTTP/2 allows objects in a persistent connection to be sent in a client-specified priority order.

2.3-4 Comparing and contrasting HTTP and SMTP (3). Which of the following characteristics apply to both HTTP and SMTP? Note: check one or more of the characteristics below.

- Has ASCII command/response interaction, status codes. - Is able to use a persistent TCP connection to transfer multiple objects.

2.3-3 Comparing and contrasting HTTP and SMTP (2). Which of the following characteristics apply to SMTP only (and do not apply to HTTP)? Note: check one or more of the characteristics below.

- Operates mostly as a "client push" protocol. - Uses server port 25. - Uses CRLF.CRLF to indicate end of message.

2.4-01 DNS functions. Match the function of a server to a given type of DNS server in the DNS server hierarchy.

- Provides authoritative hostname to IP mappings for organization's named hosts. = Authoritative DNS server - Replies to DNS query by local host, by contacting other DNS servers to answer the query. = Local DNS server - Responsible for a domain (e.g., *.com, *.edu); knows how to contact authoritative name servers. = Top Level Domain (TLD) servers - Highest level of the DNS hierarchy, knows how to reach servers responsible for a given domain (e.g., *.com, *.edu). = DNS root servers

2.3-5 Which e-mail protocol? Match the functionality of a protocol with the name of the email protocol (if any) that implements that functionality.

- Pushes email from a mail client to a mail server. = SMTP - Pulls mail from one mail server to another mail server. = Neither SMTP nor IMAP does this. - Pulls email to a mail client from a mail server. = IMAP -

2.4-04. The local DNS server. Check all of the phrases below that state at true property of a local DNS server.

- The local DNS server can decrease the name-to-IP-address resolution time experienced by a querying local host over the case when a DNS is resolved via querying into the DNS hierarchy. - The local DNS server record for a remote host is sometimes different from that of the authoritative server for that host.

2.3-2 Comparing and contrasting HTTP and SMTP. Which of the following characteristics apply to HTTP only (and do not apply to SMTP)? Note: check one or more of the characteristics below.

- Uses server port 80. - Uses a blank line (CRLF) to indicate end of request header. - Operates mostly as a "client pull" protocol.

2.7-2 TCP Sockets. Which of the following characteristics below are associated with a TCP socket? Check one or more that apply.

- when contacted, the server will create a new server-side socket to communicate with that client - a server can perform an accept() on this type of socket - provides reliable, in-order byte-stream transfer (a "pipe"), from client to server

2.2-07 A detailed Look at an HTTP GET (3). Again, suppose a client is sending an HTTP GET request message to a web server, gaia.cs.umass.edu. Suppose the client-to-server HTTP GET message is the following (same as in previous problem):

Yes, because this is a conditional GET, as evidenced by the If-Modified-Since field.

2.4-05. The DNS authoritative name server. What is the role of an authoritative name server in the DNS? (Check all that apply.)

It provides the definitive answer to the query with respect to a name in the authoritative name server's domain.

2.4-06. DNS local caches. We saw that a local DNS cache will respond immediately to a client when the local DNS has the name-to-address translation in its local cache. There are millions of such local DNS caches across the Internet. For a given Internet name, will the name-to-address translation pair stored in these local caches always be the same (i.e., are the contents of the local caches synchronized)?

No. The caches are not always synchronized. An entry in a local cache will eventually time out, and the local cache will again eventually go to the DNS hierarchy to get the name-to-address translation pair for this name. So if the name-to-address mapping changes in the DNS hierarchy, the new mapping will eventually (but not immediately) make its way into the local cache. Therefore, not all local caches may have the same value for name-to-address translation pair.

2.2-04 Conditional HTTP GET. What is the purpose of the conditional HTTP GET request message?

To allow a server to only send the requested object to the client if this object has changed since the server last sent this object to the client.