CPSC 502 Test 1

Consider TDM-based circuit switching with 8000 frames per second and 32 time slots per frame. During each time slot 8 bits are sent. What is the shortest time possible (in seconds) to transmit a 1 Mbyte file over the given link?

3.9

How many values can 5 bits represent?

32

In a TCP connection, suppose that loss occurs whenever the window size of a connection hits W. Also suppose that the RTT is constant. Then the approximate average transmission rate is

.75 W*MSS/RTT

Computer A is sending a 100 kByte long file to Computer B via packet-switching over two consecutive 10 Mbps links of 1000 km length each.Assume that the signal propagation speed on both links is 2.5 x 108 m/s.Furthermore, assume that the maximum length of a packet is 1500 bytes and that Computer A fills each packet to the max, if possible. How long (in seconds) does it take Computer A to send out one packet of maximum length on the first link?

0.0012

Computer A is sending a 100 kByte long file to Computer B via packet-switching over two consecutive 10 Mbps links of 1000 km length each.Assume that the signal propagation speed on both links is 2.5 x 108 m/s.Furthermore, assume that the maximum length of a packet is 1500 bytes and that Computer A fills each packet to the max, if possible. If transmission starts at time t=0, at which time (in seconds) does the first bit arrive at the switch connecting link 1 and link 2?

0.004

Computer A is sending a 100 kByte long file to Computer B via packet-switching over two consecutive 10 Mbps links of 1000 km length each.Assume that the signal propagation speed on both links is 2.5 x 108 m/s.Furthermore, assume that the maximum length of a packet is 1500 bytes and that Computer A fills each packet to the max, if possible. If transmission starts at time t=0, how long (in seconds) does it take until Computer B has received the last bit of the complete file transfer?Assume that the switch between link 1 and 2 is a "store-and-forward" switch. Furthermore, assume that processing and queuing delays are negligible and no other stations are using the links.

0.0892

Consider the following scenario, in which Web browsers (lower) connect to a web server (above). There is also a local web cache in the browsers' access network. In this question, we will ignore browser caching (so make sure you understand the difference between a browser cache and a web cache). Assume that the total Round Trip Time propagation, queueing and object transmission delay between the browser and web server (and including TCP setup time) is 250 msec; if the object is retrieved from the local web cache, this delay is only 10 msec. Suppose that in step 1 in the figure above, a browser makes a request for an HTTP object, which is not found in the local cache. A very short time later another browser (on the right) makes a request for the same HTTP object. What is the time from when the browser issues the HTTP GET request (in step 2) until receives an HTTP reply containing the object?

10 msec

Computer A is sending a 100 kByte long file to Computer B via packet-switching over two consecutive 10 Mbps links of 1000 km length each.Assume that the signal propagation speed on both links is 2.5 x 108 m/s.Furthermore, assume that the maximum length of a packet is 1500 bytes and that Computer A fills each packet to the max, if possible. How many bytes will be contained in the last packet?

1000

Consider TDM-based circuit switching with 8000 frames per second and 32 time slots per frame. During each time slot 8 bits are sent. How long (in seconds) does it take to transmit a 1 Mbyte file over one circuit?

125

How many values can one bit represent?

2

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.)

2.5 RTT

Consider the following scenario, in which a Web browser (lower) connects to a web server (above). There is no web cache in this question (so make sure you understand the difference between a browser cache and a web cache). Assume that the total Round Trip Time (RTT) propagation and queueing delay between the browser and web server is 200 msec. Suppose that the browser makes an HTTP request to the server for an HTTP object, that the browser has a copy of that object in its cache, but that copy may or may not be up-to-date in its cache (and so the browser requests the object using the HTTP If-Modified-Since header field). Assume that the time taken to transmit an HTTP reply (by the sender into the TCP connection) that contains a requested object in the body of an HTTP reply is 50 msec, but that the time taken to transmit a HTTP reply with a "304 Not Modified" reply code without an included object is negligible (e.g., zero). You can assume that a TCP connection has already been set up, so do not include that delay in your answer below. What is the time from when the browser issues the initial HTTP GET request until it is able to display the requested object in the case that the browser does have the requested object in its browser cache?

200 msec

Consider TDM-based circuit switching with 8000 frames per second and 32 time slots per frame. During each time slot 8 bits are sent. What is the total transmission rate of the whole link in kbps?

2048

Computer A is sending a 100 kByte long file to Computer B via packet-switching over two consecutive 10 Mbps links of 1000 km length each.Assume that the signal propagation speed on both links is 2.5 x 108 m/s.Furthermore, assume that the maximum length of a packet is 1500 bytes and that Computer A fills each packet to the max, if possible. How "long" (in meters) is one bit on link 1?

25

Consider the following scenario, in which a Web browser (lower) connects to a web server (above). There is no web cache in this question (so make sure you understand the difference between a browser cache and a web cache). Assume that the total Round Trip Time (RTT) propagation and queueing delay between the browser and web server is 200 msec. Suppose that the browser makes an HTTP request to the server for an HTTP object, that the browser has a copy of that object in its cache, but that copy may or may not be up-to-date in its cache (and so the browser requests the object using the HTTP If-Modified-Since header field). Assume that the time taken to transmit an HTTP reply (by the sender into the TCP connection) that contains a requested object in the body of an HTTP reply is 50 msec, but that the time taken to transmit a HTTP reply with a "304 Not Modified" reply code without an included object is negligible (e.g., zero). You can assume that a TCP connection has already been set up, so do not include that delay in your answer below. What is the time from when the browser issues the initial HTTP GET request until it is able to display the requested object in the case that the browser does not have the requested object in its browser cache?

250 Msec

2^32 is roughly ...

4 billion

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. 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. (You should take into account any TCP setup time required before an 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.)

4RTT

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. 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 HTTP 1.0, which only supports non-persistent connections, is being used. (You should take into account any TCP setup time required before an 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.)

5 RTT

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. Suppose also that after downloading the base file, the browser encounters five (5) jpeg objects in the base html file that are stored on gaia.cs.umass.edu, and therefore makes four more GET requests to gaia.cs.umass.edu for those referenced jpeg objects. How many round trip times (RTTs) are needed from when the client first makes the request to when the base page and the jpeg files are completely downloaded, assuming the time needed by the server to transmit the base file, or any of the jpeg files 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 with pipelining is being used. (You should take into account any TCP setup time required before an 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.)

6 RTT

Consider TDM-based circuit switching with 8000 frames per second and 32 time slots per frame. During each time slot 8 bits are sent. What is the bit rate of one circuit in kbps?

64

What are the names of all the OSI layers?

7) Application Layer. Message 6) Presentation Layer. 5) Session Layer. 4) Transport Layer. Segment 3) Network Layer. Datagram 2) Data Link Layer. Frame 1) Physical Layer. Bits

How many bits are one byte?

8

Consider TDM-based circuit switching with 8000 frames per second and 32 time slots per frame. During each time slot 8 bits are sent. Assuming it is possible to combine several circuits, how many circuits does it take to keep the transmission time of a 1 Mbyte file below 15 seconds?

9

Ed has been hired by a private company to connect two remote sites with a Wide Area Network (WAN). Each of these sites has more than 200 users, and they all need to constantly transfer files across the WAN. One of the sites has a customer database that is accessed by both sites at all hours of the day. Access to the database and other information is time sensitive and constant. The company estimates that their aggregate bandwidth needs to be approximately 40 Mpbs. Management says that they need to guarantee access to this information and that money is not a factor in the WAN implementation. Which WAN technology should Ed recommend for this scenario?

A T-3 dedicated leased line

Ralph is an employee of a company that offers the option to telecommute from home. As a telecommuting employee, he needs to connect to the company network to access client information, transfer files, and send email through a Virtual Private Network (VPN) connection. Ralph is investigating the different Wide Area Network (WAN) services available for the remote connection before he implements one. His home is over 30 years old; the existing telephone wiring was not run through conduit, and the wiring seems to be deteriorating. Ralph has cable television (CATV) service, and his home is also approximately 20,000 feet from the nearest telephone central office. He wants to implement the fastest remote connection service possible, but cost is a factor in the decision. Which WAN technology should Ralph implement?

A broadband CATV connection

Check all of the services below that are provided by the UDP protocol.

A message abstraction, that preserves boundaries between message data sent in different socket send calls at the sender.

If you want to allow both voice and data traffic to be transmitted across the same Digital Subscriber Line (DSL) connection, what type of device is required at the customer site?

A splitter

What do we mean when we say "HTTP is stateless"? In answering this question, assume that cookies are not used.

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.

To which of the following Internet connection types does a specification called DOCSIS apply?

Cable broadband

Which of the following are advantages of using a web cache?

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.

Why does DSL (Digital Subscriber Line) technology support faster data transmissions than a standard Public Switched Telephone Network (PSTN) modem connection?

DSL uses a higher frequency range.

What does the network layer do?

Delivery of datagrams from a source host to a destination host (typically). Decides the physical path the data will take

What are the two main factors that affect DSL (Digital Subscriber Line) transmission rates?

Distance to the nearest central office, Line reflection, Line conditions

Nmap is often used to:

Do port scans over a range of ports at a target host.

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 a server with a well known server IP address. There is a server that is always on.

What does a DNS root servers do?

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

Over a TCP connection, suppose host A sends two segments to host B, host B sends an acknowledgement for each segment, the first acknowledgement is lost, but the second acknowledgement arrives before the timer for the first segment expires.

Host A will retransmit neither segments

Consider the latency model for static congestion windows. If the server receives an acknowledgement for the first data segment in the first window before the server completes the transmission of the first window, then the latency for an object of size O is:

Latency = 2 RTT + O/R

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

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. Congestion control. The service will control senders so that the senders do not collectively send more data than links in the network can handle. Flow Control. The provided service will ensure that the sender does not send so fast as to overflow receiver buffers.

What does the application layer do?

Protocols that are part of a distributed network application. It is the layer which interacts with the user to provide access to services and data that is sent/received over a network.

What is IMAP?

Pulls email to a mail client from a mail server.

What is SMTP?

Pushes email from a mail client to a mail server.

Which DSL (Digital Subscriber Line) technology can adjust its transmission speed based on line conditions?

RADSL

What is meant by transport-layer demultiplexing?

Receiving a transport-layer segment from the network layer, extracting the payload (data) and delivering the data to the correct socket.

Check all of the services below that are provided by the TCP protocol.

Reliable data delivery. In-order data delivery A congestion control service to ensure that multiple senders do not overload network links. A flow-control service that ensures that a sender will not send at such a high rate so as to overflow receiving host buffers. A byte stream abstraction, that does not preserve boundaries between message data sent in different socket send calls at the sender.

What does a Local DNS server server do?

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

What does a Top Level Domain (TLD) servers do?

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

Which of the following broadband WAN services provides equal amounts of upstream and downstream bandwidth?

SDSL

Which of the following is the U.S. standard for synchronous data transmissions that defines data rates designated by optical carrier levels, such as OC-3, OC-12, OC-48, and OC-192?

SONET

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.

What is meant by transport-layer multiplexing?

Taking data from one socket (one of possibly many sockets), encapsulating a data chuck with header information - thereby creating a transport layer segment - and eventually passing this segment to the network layer.

Which of the definitions below describe what is meant by the term "encapsulation"?

Taking data from the layer above, adding header fields appropriate for this layer, and then placing the data in the payload field of the "packet" for that layer.

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.

Consider the latency model for dynamic congestion windows. Which of the following components contribute to latency?

round trip time, RTT. the transmission time of the object, O/R. the sum of all the stalled times.

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 does the data link layer do?

Transfer of data between neighboring network devices. defines formatting and movement of data at the lowest level, between hardware devices in the same network

What does the transport layer do?

Transfer of data between one process and another process (typically on different hosts) Transmits data using transmission protocols including TCP and UDP

Where is transport-layer functionality primarily implemented?

Transport layer functions are implemented primarily at the hosts at the "edge" of the network.

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/1.1Host: gaia.cs.umass.eduAccept: 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, fiIf-Modified-Since: Wed, 09 Sep 2020 16:06:01 -0700User 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.

What does the Presentation layer do?

deals with formatting of data and encryption.

What does the session layer do?

maintains connections and is responsible for controlling ports and sessions

UDP has which of the following characteristics:

none of the above

How many units are a "Giga"?

one billion

What does a Authoritative DNS server do?

pPovides authoritative hostname to IP mappings for organization's named hosts

Which of the following parameters influence(s) the time that it takes a computer to send out a data packet? (Mark all that apply.)

packet length, propagation speed of the signal

When a UDP segment arrives to a host, in order to direct the segment to the appropriate socket, the OS uses

the destination port number

When a TCP segment arrives to a host, the socket to which the segment is directed depends on?

the destination port number. the source port number. the source IP address of the datagram that encapsulated the segment.

Consider the latency model for dynamic congestion windows. The value P is equal to

the number of times the server stalls

What does the physical layer do?

transmits the raw bit stream over a physical medium

Pipelining requires which of the following

transmitting many packets before receiving acknowledgements. unique sequence numbers for each in-transit packet. sender-side buffering of unacknowledged packets.

TCP applies fast retransmit to a segment when

when it receives three ACKs for an earlier segment

The stop-and-wait protocol is highly inefficient when

when there is a large distance between source and destination and the transmission rate is high

With SYN cookies, when a server receives a SYN segment, it returns a SYNACK with:

with an initial sequence number that is a hash of the IP addresses and port numbers in the SYN segment (as well as of other things).