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ECE 3323 EXAM 2 QUESTIONS AND ANSWERS
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ECE 3323 EXAM 2 QUESTIONS AND ANSWERS
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ECE 3323 EXAM 2 QUESTIONS AND ANSWERS2.2-1 Simple HTTP GET request response time. Suppose an HTTP client makes a
request to the gaia.cs.umass.edu web server. The client has never before requested a
given base object, nor has it communicated recently with the gaia.cs.umass.edu server.
You can assume, however, that the client host knows the IP address of
gaia.cs.umass.edu.
How many round trip times (RTTs) are needed from when the client first makes the
request to when the base page is completely downloaded, assuming the time needed
by the server to transmit the base file into the server's link is equal to 1/2 RTT and that
the time needed to transmit the HTTP GET into the client's link is zero? (You should
take into account any TCP setup time required before the HTTP GET is actually sent by
the client, the time needed for the server to transmit the requested object, and any
propagation delays not accounted for in these amounts of time.) - Answers -2.5 RTT
1 RTT(TCP SETUP) + 1/2 RTT(SERVER TRANSMISSION) + 1RTT(PROPAGATION) =
2.5 RTT
Suppose also that after downloading the base file, the browser encounters a jpeg object
in the base html file that is stored on gaia.cs.umass.edu, and therefore makes another
GET request to gaia.cs.umass.edu for that referenced jpeg object.
How many round trip times (RTTs) are needed from when the client first makes the
request to when the base page and the jpeg file are completely downloaded, assuming
the time needed by the server to transmit the base file, or the jpeg file into the server's
link is (each) equal to 1/2 RTT and that the time needed to transmit the HTTP GET into
the client's link is zero? You should assume that persistent HTTP 1.1 is being used. -
Answers -4 RTTS
2.6-3 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.
Once a video starts streaming from a Netflix server to a client player, the video quality
remains constant throughout video playback.
Once a video starts streaming from a given Netflix server to a given client player, that
server will be the only server assigned to transmit that video to that client throughout the
viewing session for this video.
In many video streaming services, the client requests chunks of video from a server
using the HTTP protocol. - Answers -In many video streaming services, the client
requests chunks of video from a server using the HTTP protocol.
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)?
,HTTP uses this application structure.
There is not a server that is always on.
There is a server that is always on.
There is a server with a well known server IP address.
A process requests service from those it contacts and will provide service to processes
that contact i - Answers -HTTP uses this application structure.
There is a server that is always on.
There is a server with a well known server IP address.
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.
HTTP uses this application structure.
There is a server with a well known server IP address.
There is a server that is always on.
A process requests service from those it contacts and will provide service to processes
that contact it. - Answers -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.
2.1-3 UDP service. When an application uses a UDP socket, what transport services
are provided to the application by UDP? - Answers -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.
2.1-4 TCP service. When an application uses a TCP socket, what transport services are
provided to the application by TCP? - Answers -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.
Congestion control. The service will control senders so that the senders do not
collectively send more data than links in the network can handle.
2.2-1 "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.
We say this when an HTTP server is not operational.
The HTTP protocol is not licensed in any country.
An HTTP client does not remember anything about what happened during earlier steps
in interacting with any HTTP server.
, An HTTP client does not remember the identities of the servers with which it has
interacted. - Answers -An HTTP server does not remember anything about what
happened during earlier steps in interacting with this HTTP client.
2.2-2 HTTP cookies. What is an HTTP cookie used for?
A cookies 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 person.
[Think about the distinction between a browser and a person.]
A cookie is a code used by a client to authenticate a person's identity to an HTTP
server.
Like dessert, cookies are used at the end of a transaction, to indicate the end of the
transaction.
A cookie is used to spoof client identity to an HTTP server.
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.] - Answers -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.]
2.2-3 The HTTP GET. What is the purpose of the HTTP GET message?
The HTTP GET request message is sent by a web server to a web client to get the next
request from the web client.
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.
The HTTP GET request message is sent by a web server to a web client to get the
identity of the web client.
The HTTP GET request message is used by a web client to post an object on a web
server. - Answers -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.
2.2-4 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 the client is
authorized to received that object.
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.
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