knowledge checks module 2

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

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A process requests service from those it contacts and will provide service to processes that contact it.

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.

HTTP uses this application structure.

There is a server with a well known server IP address.

There is a server that is always on

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)?

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There is a server with a well known server IP address.

HTTP uses this application structure.

There is a server that is always on.

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.

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.

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

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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.

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.

Real-time delivery. The service will guarantee that data will be delivered to the receiver within a specified time bound.

Flow Control. The provided service will ensure that the sender does not send so fast as to overflow receiver buffers.

Throughput guarantee. The socket can be configured to provide a minimum throughput guarantee between sender and receiver.

Congestion control.  The service will control senders so that the senders do not collectively send more data than links in the network can handle.

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.

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

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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.

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.

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.

Throughput guarantee. The socket can be configured to provide a minimum throughput guarantee between sender and receiver.

Real-time delivery. The service will guarantee that data will be delivered to the receiver within a specified time bound.

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.

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.

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.

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An HTTP client does not remember the identities of the servers with which  it has interacted.

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

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

The HTTP protocol is not licensed in any country.

We say this when an HTTP server is not operational.

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

What is an HTTP cookie used for?

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A cookie is a code used by a client to authenticate a person’s identity to an HTTP server.

A cookie is used to spoof client identity to an HTTP server.

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 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.]

Like dessert, cookies are used at the end of a transaction, to indicate the end of the transaction

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 is the purpose of the HTTP GET message?

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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 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 post an object on a web server

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.

What is the purpose of the conditional HTTP GET request message?

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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.

To allow a server to only send the requested object to the client if the client has never requested that object before.

To allow a server to only send the requested object to the client if the server is not overloaded.

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.

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:

GET /kurose_ross_sandbox/interactive/quotation2.htm HTTP/1.1
Host: gaia.cs.umass.edu
Accept: text/plain, text/html, text/xml, image/jpeg, image/gif, audio/mpeg, audio/mp4, video/wmv, video/mp4,
Accept-Language: en-us, en-gb;q=0.1, en;q=0.7, fr, fr-ch, da, de, fi
If-Modified-Since: Wed, 09 Sep 2020 16:06:01 -0700
User Agent: Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/535.11 (KHTML, like Gecko) Chrome/17.0.963.56 Safari/535.11

What version of HTTP is the client using?

1.1

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):

GET /kurose_ross_sandbox/interactive/quotation2.htm HTTP/1.1
Host: gaia.cs.umass.edu
Accept: text/plain, text/html, text/xml, image/jpeg, image/gif, audio/mpeg, audio/mp4, video/wmv, video/mp4,
Accept-Language: en-us, en-gb;q=0.1, en;q=0.7, fr, fr-ch, da, de, fi
If-Modified-Since: Wed, 09 Sep 2020 16:06:01 -0700
User Agent: Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/535.11 (KHTML, like Gecko) Chrome/17.0.963.56 Safari/535.11

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 are advantages of using a web cache? Select one or more answers.

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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.

Overall, caching requires  fewer  devices/hosts to satisfy a web request, thus saving on server/cache costs.

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 allows an origin server to more carefully track which clients are requesting and receiving which web objects.

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

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

HTTP/2 provides enhanced security by using transport layer security (TLS).

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 has many new HTTP methods and status codes.

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

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A response code

A sequence number

The name of the Web server (e.g., gaia.cs.umass.edu)

A response phrase associated with a response code

The server's IP address

A checksum

A response phrase associated with a response code

A response code

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

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

To inform the HTTP cache that it (the cache) should retrieve the full object from the server, and then cache it until the specified time.

To indicate to the server that the client wishes to receive this object, and the time until which it will cache the returned object in the browser's cache.

To indicate to the server that the server should replace this named object with the new version of the object attached to the GET, if the object has not been modified since the specified time

To allow the server to indicate to the client that it (the client) should cache this object.

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

What is the purpose of a cookie value in the HTTP GET request?

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The cookie value indicates whether the user wants to use HTTP/1, HTTP/1.1, or HTTP/2 for this GET request.

The cookie value encodes a default set of preferences that the user has previously specified for this web site.

The cookie value encodes the format of the reply preferred by the client in the response to this 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.

The cookie value is an encoding of a user email address associated with the 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.

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:

GET /kurose_ross_sandbox/interactive/quotation2.htm HTTP/1.1
Host: gaia.cs.umass.edu
Accept: text/plain, text/html, text/xml, image/jpeg, image/gif, audio/mpeg, audio/mp4, video/wmv, video/mp4,
Accept-Language: en-us, en-gb;q=0.1, en;q=0.7, fr, fr-ch, da, de, fi
If-Modified-Since: Wed, 09 Sep 2020 16:06:01 -0700
User Agent: Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/535.11 (KHTML, like Gecko) Chrome/17.0.963.56 Safari/535.11

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

Yes, because this is a conditional GET.

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

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

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Is able to use a persistent TCP connection to transfer multiple objects.

Has ASCII command/response interaction, status codes.

Uses a blank line (CRLF) to indicate end of request header.

Uses server port 25.

Uses server port 80.

Operates mostly as a “client push” protocol.

Operates mostly as a “client pull” protocol.

Uses CRLF.CRLF to indicate end of message.

Operates mostly as a “client pull” protocol.

Uses server port 80.

Uses a blank line (CRLF) to indicate end of request header.

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

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Uses a blank line (CRLF) to indicate end of request header.

Operates mostly as a “client push” protocol.

Has ASCII command/response interaction, status codes.

Is able to use a persistent TCP connection to transfer multiple objects.

Uses server port 25.

Operates mostly as a “client pull” protocol.

Uses CRLF.CRLF to indicate end of message.

Uses server port 80.

Uses CRLF.CRLF to indicate end of message.

Operates mostly as a “client push” protocol.

Uses server port 25.

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

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Uses a blank line (CRLF) to indicate end of request header.

Is able to use a persistent TCP connection to transfer multiple objects.

Has ASCII command/response interaction, status codes.

Operates mostly as a “client pull” protocol.

Uses CRLF.CRLF to indicate end of message.

Operates mostly as a “client push” protocol.

Is able to use a persistent TCP connection to transfer multiple objects.

Has ASCII command/response interaction, status codes

what pushes email from a mail client to a mail server?

SMTP

neither

IMAP

SMTP

what pulls mail from one mail server to another mail server?

SMTP

neither

IMAP

Neither SMTP nor IMAP does this.

what pulls email to a mail client from a mail server?

SMTP

neither

IMAP

IMAP

what provides authoritative hostname to IP mappings for organization’s named hosts?

1. Authoritative DNS server

2. DNS root servers

3. Local DNS server

4. Top Level Domain (TLD) servers

1. Authoritative DNS server

what replies to DNS query by local host, by contacting other DNS servers to answer the query?

1. Authoritative DNS server

2. DNS root servers

3. Local DNS server

4. Top Level Domain (TLD) servers

1. Local DNS server

what is responsible for a domain (e.g., .com, .edu); knows how to contact authoritative name servers.

1. Authoritative DNS server

2. DNS root servers

3. Local DNS server

4. Top Level Domain (TLD) servers

1. Top Level Domain (TLD) servers

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

1. Authoritative DNS server

2. DNS root servers

3. Local DNS server

4. Top Level Domain (TLD) servers

1. DNS root servers

What is the value of caching in the local DNS name server? Check all that apply.

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DNS caching provides for faster replies, if the reply to the query is found in the cache.

DNS caching provides the ability to serve as authoritative name server for multiple organizations.

DNS caching provides prioritized access to the root servers, since the DNS request is from a local DNS cache.

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.

DNS caching results in less load elsewhere in DNS, when the reply to a query is found in the local cache.

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

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A hostname and an IP address.

An alias name and a true name for a server.

A name and the name of the SMTP server associated with that name.

A domain name and the name of the authoritative name server for that domain.

A hostname and an IP address.

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

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A hostname and an IP address.

An alias name and a true name for a server.

A name and the name of the SMTP server associated with that name.

A domain name and the name of the authoritative name server for that domain.

A hostname and an IP address.

Check all of the phrases below that state a true property of a local DNS server.

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The local DNS server record for a remote host is sometimes different from that of the authoritative server for that host.

The local DNS server holds hostname-to-IP translation records, but not other DNS records such as MX records.

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 is only contacted by a local host if that local host is unable to resolve a name via iterative or recursive queries 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.

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.

What is the role of an authoritative name server in the DNS? (Check all that apply)

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It provides a list of TLD servers that can be queried to find the IP address of the DNS server that can provide the definitive answer to this query.

It is a local (to the querying host) server that caches name-to-IP address translation pairs, so it can answer authoritatively and can do so quickly.

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

It provides the IP address of the DNS server that can provide the definitive answer to the query.

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

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

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To let a OTT (Over-the-top) video server know the video that the client wants to view.

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

Allows a video service to log the video and the server from which a client streams a video.

To allow a client to reserve bandwidth along a path from a server to that client, so the client can view a stream video without impairment.

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

What approach is taken by a CDN to stream content to hundreds of thousands of simultaneous users?

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Serve video from a single central “mega-server” with ultra-high-speed network connectivity, and high-speed storage.

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

Proactively push videos to a client device before they’re requested, using machine learning to predict requested videos.

Allow client devices to send requested content to each other, in order to offload the CDN infrastructure.

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

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

1. DASH

2. Manifest

3. Video frame

4. Enter deep

5. Chunk

chunk

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

1. DASH

2. Manifest

3. Video frame

4. Enter deep

5. Chunk

manifest

An approach that allows a client to adapt the encoding rate of retrieved video to network congestion conditions.

1. DASH

2. Manifest

3. Video frame

4. Enter deep

5. Chunk

DASH

A CDN approach that stores content in access networks, close to clients

1. DASH

2. Manifest

3. Video frame

4. Enter deep

5. Chunk

enter deep