Ch 2. test

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

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

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.

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.

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

-HTTP/2 allows objects in a persistent connection to be sent in a client-specified priority order. -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.

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

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.

A unit of video, each of which may be encoded at multiple different rates, stored in different files.

Chunk

Highest level of the DNS hierarchy, knows how to reach servers responsible for a given domain (e.g., *.com, *.edu).

DNS root servers

Provides authoritative hostname to IP mappings for organization's named hosts.

Authoritative DNS server

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

Pulls email to a mail client from a mail server.

IMAP

Replies to DNS query by local host, by contacting other DNS servers to answer the query.

Local DNS server

A file containing the location and encoding rate of files corresponding to video segments in a video.

Manifest

Pulls mail from one mail server to another mail server.

Neither SMTP nor IMAP does this.

Pushes email from a mail client to a mail server.

SMTP

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.

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.

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.

Suppose an HTTP server sends the following HTTP response message a client: Will the web server close the TCP connection after sending this message?

Yes, because this is HTTP 1.0

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): Does the client have a cached copy of the object being requested?

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

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

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

What information does the type "A" resource record hold in the DNS database? Check all that apply.

A hostname and an IP address.

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.

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.

Check all of the phrases below that state a 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.

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: Does the client have a cached copy of the object being requested?

Yes, because this is a conditional GET.

Suppose that the local DNS server caches all information coming in from all root, TLD, and authoritative DNS servers for 20 time units. (Thus, for example, when a root server returns the name and address of a TLD server for .com, the cache remembers that this is the TLD server to use to resolve a .com name). Assume also that the local cache is initially empty, that iterative DNS queries are always used, that DNS requests are just for name-to-IP-address translation, that 1 time unit is needed for each server-to-server or host-to-server (one way) request/response, and that there is only one authoritative name server (each) for any .edu or .com domain.

t=0, t=1, t=30

Which of the following are advantages of using a web cache? Sselect one or more answers.

-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. -Caching uses less bandwidth coming into an institutional network where the client is located, if the cache is also located in that institutional network.

Which of the following characteristics apply to both HTTP and SMTP? Note: check one or more of the characteristics below.

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

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

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.

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

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

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 -provides reliable, in-order byte-stream transfer (a "pipe"), from client to server -socket(AF_INET, SOCK_STREAM) creates this type of socket -a server can perform an accept() on this type of socket

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

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?

3

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

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.]

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.

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.

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.

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.

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.

Manifest file. What is the purpose of a manifest file in a streaming multimedia setting?

To let a client know where it can retrieve different video segments, encoded at different rates

Responsible for a domain (e.g., *.com, *.edu); knows how to contact authoritative name servers.

Top Level Domain (TLD) servers

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): What is the language in which the client would least prefer to get a response?

United Kingdom English

Suppose now the server sends the following HTTP response message the client: Will the web server close the TCP connection after sending this message?

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