Test 1 - Problem/Question PowerSet
When a resident uses a dial-up or DLS service to connect to the Internet, what is the role of the telephone company?
The telephone company acts as an ISP. The connection from the resident tothe telephone company is a point-to-point access WAN that connects thepremises to the Internet. At the same time, the telephone company needs toprovide the necessary services such as e-mail.
Compare the telephone network and the Internet. What are the similarities? What are the differences?
The telephone network was originally designed for voice communication; the Internet was originally designed for data communication. The two networks are similar in the fact that both are made of interconnections of small networks. The telephone network, as we will see in future chapters, is mostly a circuit-switched network; the Internet is mostly a packet-switched network.
A signal has passed through three cascaded amplifiers, each with a 4 dB gain. What is the total gain? How much is the signal amplified?
The total gain is 3 × 4 = 12 dB. The signal is amplified by a factor 10^1.2 = 15.85.
In the ring topology in Figure 1.7, what happens if one of the stations is unplugged?
Theoretically, in a ring topology, unplugging one station, interrupts the ring. However, most ring networks use a mechanism that bypasses the station; the ring can continue its operation.
What is the bit rate for the signal in Figure 3.35?
There are 8 bits in 16 ns. Bit rate is 8 / (16 × 10^−9) = 0.5 × 10^−9 = 500 Mbps
We have two computers connected by an Ethernet hub at home. Is this a LAN or a WAN? Explain the reason.
This is a LAN. The Ethernet hub creates a LAN.
A signal has a wavelength of 1 μm in air. How far can the front of the wave travel during 1000 periods?
1 μm × 1000 = 1000 μm = 1 mm
Categorize the four basic topologies in terms of line configuration.
1. Mesh (every device connected by point to point) 2. Bus (multipoint connection where one cable links all devices using droplines and taps) 3. Star (each device connected by point to point to a central hub, not to each other) 4. Ring (each device connected by point to point with the two devices on either side; repeaters regenerate bits to pass data along)
For each of the following four networks, discuss the consequences if a connection fails. a. Five devices arranged in a mesh topology b. Five devices arranged in a star topology (not counting the hub) c. Five devices arranged in a bus topology d. Five devices arranged in a ring topology
1. Mesh topology: If one connection fails, the other connections will still be working. 2. Star topology: The other devices will still be able to send data through the hub; there will be no access to the device which has the failed connection to the hub. 3. Bus Topology: All transmission stops if the failure is in the bus. If the drop-line fails, only the corresponding device cannot operate. 4. Ring Topology: The failed connection may disable the whole network unless it is a dual ring or there is a by-pass mechanism.
For n devices in a network, what is the number of cable links required for a mesh, ring, bus, and star topology?
1. Mesh: n (n - 1) / 2 2. Star: n 3. Ring: n 4. Bus: n+1
Name the four basic network topologies, and cite an advantage of each type.
1. Mesh: secure 2. Bus: easy installation 3. Star: robust 4. Ring: easy fault isolation
If the bandwidth of the channel is 5 Kbps, how long does it take to send a frame of 100,000 bits out of this device?
100,000 bits / 5 Kbps = 20 s
Assume a system uses five protocol layers. If the application program creates a message of 100 bytes and each layer (including the fifth and the first) adds a header of 10 bytes to the data unit, what is the efficiency (the ratio of application layer bytes to the number of bytes transmitted) of the system?
100/(100+50) = 66.67%
A computer monitor has a resolution of 1200 by 1000 pixels. If each pixel uses 1024 colors, how many bits are needed to send the complete contents of a screen?
1200 × 1000 × 10 = 12,000,000 bits
A line has a signal-to-noise ratio of 1000 and a bandwidth of 4000 KHz. What is the maximum data rate supported by this line?
4,000 log2 (1 + 1,000) ≈ 40 Mbps
We measure the performance of a telephone line (4 KHz of bandwidth). When the signal is 10 V, the noise is 5 mV. What is the maximum data rate supported by this telephone line?
4,000 log2 (1 + 10 / 0.005) = 43,866 bps
The light of the sun takes approximately eight minutes to reach the earth. What is the distance between the sun and the earth?
480 s × 300,000 km/s = 144,000,000 km
Assume that the number of hosts connected to the Internet at year 2010 is five hundred million. If the number of hosts increases only 20 percent per year, what is the number of hosts in year 2020?
500m * (1+0.2)^10
A television broadcast is an example of _______ transmission. A) simplex B) half-duplex C) full-duplex D) automatic
A
Frequency of failure and network recovery time after a failure are measures of the _______ of a network. A) Reliability B) Performance C) Security D) Feasibility
A
In a ________ connection, three or more devices share a link. A) multipoint B) point-to-point C) (a) and (b) D) none of the above
A
Why are protocols needed?
A protocol defines what is communicated, in what way and when. This provides accurate and timely transfer of information between different devices on a network.
Explain the difference between an Internet draft and a proposed standard.
An Internet draft is a working document with no official status and a six-month lifetime.A proposed standard is a specification that is stable, well understood, and of sufficient interest to the Internet community. At this level, the specification is usually tested and implemented by several different groups.
What is an internet? What is the Internet?
An internet is an interconnection of networks. The Internet is the name of a specific worldwide network
Name three types of transmission impairment.
Attenuation, distortion, and noise
Which of the following data units is encapsulated in a frame? a. a user datagram b. a datagram c. a segment
B) datagram [although it is also made up of user datagram/segment, so you could consider it all 3]
An unauthorized user is a network _______ issue. A) Reliability B) Performance C) Security D) All the above
C
We have a channel with 4 KHz bandwidth. If we want to send data at 100 Kbps, what is the minimum SNRdB? What is the SNR?
C = B × (SNRdB /3) or SNRdB = (3 × C) /B SNRdB = 3 × 100 Kbps / 4 KHz = 75 SNR = 10^(SNRdB/10) = 10^7.5 ≈ 31,622,776
Assume six devices are arranged in a mesh topology. How many cables are needed? How many ports are needed for each device?
Cable links: n (n - 1) / 2 = (6 × 5) / 2 = 15 Number of ports: (n - 1) = 5 ports needed per device
When we use local telephones to talk to a friend, are we using a circuit-switched network or a packet-switched network?
Circuit switched
The presentation of data is becoming more and more important in today's Internet. Some people argue that the TCP/IP protocol suite needs to add a new layer to take care of the presentation of data. If this new layer is added in the future, where should its position be in the suite? Redraw Figure 2.4 to include this layer.
Directly under the application layer
How many point-to-point WANs are needed to connect n LANs if each LAN should be able to directly communicate with any other LAN?
Each LAN should be connected to (n − 1) LANs, which means that we will have n × (n − 1) connections. However, if each connection can be used in both directions, we need only [n × (n − 1)]/2 connections.
Which signal has a wider bandwidth, a sine wave with a frequency of 100 Hz or a sine wave with a frequency of 200 Hz?
Each signal is a simple signal in this case. The bandwidth of a simple signal is zero. So the bandwidth of both signals are the same.
Protocol layering can be found in many aspects of our lives such as air travelling. Imagine you make a round-trip to spend some time on vacation at a resort. You need to go through some processes at your city airport before flying. You also need to go through some processes when you arrive at the resort airport. Show the protocol layering for the round trip using some layers such as baggage checking/claiming, boarding/unboarding, takeoff/landing.
F this question
How can a composite signal be decomposed into its individual frequencies?
Fourier analysis; Fourier series gives the frequency domain of a periodic signal; Fourier analysis gives the frequency domain of a nonperiodic signal.
What is the relationship between period and frequency?
Frequency and period are the inverse of each other. T = 1/ f and f = 1/T.
List some application-layer protocols mentioned in this chapter.
Hypertext Transfer Protocol (HTTP) Simple Mail Transfer Protocol (SMTP) File Transfer Protocol (FTP) Terminal Network (TELNET) Domain Name System (DNS)
In the bus topology in Figure 1.6, what happens if one of the stations is unplugged?
In a bus topology, no station is in the path of the signal. Unplugging a station has no effect on the operation of the rest of the network.
What is the difference between half-duplex and full-duplex transmission modes?
In half-duplex transmission, only one entity can send at a time; in a full-duplex transmission, both entities can send at the same time
When a party makes a local telephone call to another party, is this a point-to-point or multipoint connection? Explain the answer.
In this case, the communication is only between a caller and the callee. A dedicated line is established between them. The connection is point-to-point.
What is the total delay (latency) for a frame of size 5 million bits that is being sent on a link with 10 routers each having a queuing time of 2 μs and a processing time of 1 μs. The length of the link is 2000 Km. The speed of light inside the link is 2 × 108 m/s. The link has a bandwidth of 5 Mbps. Which component of the total delay is dominant? Which one is negligible?
Latency = processing time + queuing time + transmission time + propagation time Processing time = 10 × 1 μs = 10 μs = 0.000010 s Queuing time = 10 × 2 μs = 20 μs = 0.000020 s Transmission time = 5,000,000 / (5 Mbps) = 1 s Propagation time = (2000 Km) / (2 × 108 ) = 0.01 s Latency = 0.000010 + 0.000020 + 1 + 0.01 = 1.01000030 s The transmission time is dominant here because the packet size is huge.
Assume we have created a packet-switched internet. Using the TCP/IP protocol suite, we need to transfer a huge file. What are the advantage and disadvantage of sending large packets?
Less overhead & few packets, but greater risk of data loss and blockage
Using the internet in Figure 1.11 (Chapter 1) in the text, show the layers of the TCP/IP protocol suite and the flow of data when two hosts, one on the west coast and the other on the east coast, exchange messages.
Nah fam
In an internet, we change the LAN technology to a new one. Which layers in the TCP/IP protocol suite need to be changed?
Network Layer
Assume a private internet uses three different protocols at the data-link layer (L1, L2, and L3). Redraw Figure 2.10 with this assumption. Can we say that, in the data-link layer, we have demultiplexing at the source node and multiplexing at the destination node?
No because this would apply to the physical layer
Assume we want to connect two isolated hosts together to let each host communicate with the other. Do we need a link-layer switch between the two? Explain.
No you can use wireless
When we say that the transport layer multiplexes and demultiplexes application layer messages, do we mean that a transport-layer protocol can combine several messages from the application layer in one packet? Explain
No, multiplexing is for using multiple protocols at the same time not actual messages
In a LAN with a link-layer switch (Figure 1.8b), Host 1 wants to send a message to Host 3. Since communication is through the link-layer switch, does the switch need to have an address? Explain.
No. You do not need an ip address to transmit data to devices connected by a switch (layer 2); you only need the mac address. Switches accessed remotely through the network must have a layer 3 (ip) address.
What is the length of a bit in a channel with a propagation speed of 2 × 10^8 m/s if the channel bandwidth is a. 1 Mbps? b. 10 Mbps? c. 100 Mbps?
(bit length) = (propagation speed) × (bit duration) a. Bit length = (2 ×10^8 m) × [(1 / (1 Mbps)] = 200 m. This means a bit occupies 200 meters on a transmission medium. b. Bit length = (2 ×10^8 m) × [(1 / (10 Mbps)] = 20 m. This means a bit occupies 20 meters on a transmission medium. c. Bit length = (2 ×10^8 m) × [(1 / (100 Mbps)] = 2 m. This means a bit occupies 2 meters on a transmission medium.
The attenuation of a signal is −10 dB. What is the final signal power if it was originally 5 W?
-10 = 10 log10 (P2 / 5) → log10 (P2 / 5) = −1 → (P2 / 5) = 10−1 → P2 = 0.5 W
Explain the difference between a required RFC and a recommended RFC.
Required. An RFC is labeled required if it must be implemented by all Internet systems to achieve minimum conformance. For example, IP and ICMP (Chapter 19)are required protocols.An RFC labeled recommended is not required for minimum conformance; it is recommended because of its usefulness. For example, FTP(Chapter 26) and TELNET (Chapter 26) are recommended protocols.
A signal with 200 milliwatts power passes through 10 devices, each with an average noise of 2 microwatts. What is the SNR? What is the SNRdB?
SNR = (200 mW) / (10 × 2 × μW) = 10,000 SNRdB = 10 log10 SNR = 40
If the peak voltage value of a signal is 20 times the peak voltage value of the noise, what is the SNR? What is the SNRdB?
SNR= (signal power)/(noise power). However, power is proportional to the square of voltage. SNR = [(signal voltage)^2 ] / [(noise voltage)^2 ] = [(signal voltage) / (noise voltage)]^2 = 202 = 400 SNRdB = 10 log10 SNR ≈ 26.02
What is the bandwidth of a signal that can be decomposed into five sine waves with frequencies at 0, 20, 50, 100, and 200 Hz? All peak amplitudes are the same. Draw the bandwidth.
See Figure 3.1
Explain the difference between the duties of the IETF and IRTF.
The IETF is responsible for identifying operational problems and recommending solutions; the IRTF focuses on long-term research topics.
What does the amplitude of a signal measure? What does the frequency of a signal measure? What does the phase of a signal measure?
The amplitude of a signal measures the value of the signal at any point. The frequency of a signal refers to the number of periods in one second. The phase describes the position of the waveform relative to time zero.
Can you explain why we did not mention multiplexing/demultiplexing services for the application layer?
The application layer is the top layer in the suite; it does not provide services to any layer, which means multiplexing/demultiplexing does not exist for this layer.
What is the bandwidth of the composite signal shown in Figure 3.37?
The bandwidth is 5 × 5 = 25 Hz.
A file contains 2 million bytes. How long does it take to download this file using a 56-Kbps channel? 1-Mbps channel?
The file contains 2,000,000 × 8 = 16,000,000 bits. With a 56-Kbps channel, it takes 16,000,000/56,000 = 289 s. With a 1-Mbps channel, it takes 16 s.
What is the first principle we discussed in this chapter for protocol layering that needs to be followed to make the communication bidirectional?
The first principle dictates that if we want bidirectional communication, we need to make each layer so that it is able to perform two opposite tasks, one in each direction.
If a port number is 16 bits (2 bytes), what is the minimum header size at the transport layer of the TCP/IP protocol suite?
The minimum header size will be (2*16 bits) 32 bits to contain the sending and receiving port address.
In Figure 2.10, when the IP protocol decapsulates the transport-layer packet, how does it know to which upper-layer protocol (UDP or TCP) the packet should be delivered?
The protocol header is used to demultiplex
A nonperiodic composite signal contains frequencies from 10 to 30 KHz. The peak amplitude is 10 V for the lowest and the highest signals and is 30 V for the 20-KHz signal. Assuming that the amplitudes change gradually from the minimum to the maximum, draw the frequency spectrum.
The signal is nonperiodic, so the frequency domain is made of a continuous spectrum of frequencies as shown in Figure 3.4.
A periodic composite signal contains frequencies from 10 to 30 KHz, each with an amplitude of 10 V. Draw the frequency spectrum.
The signal is periodic, so the frequency domain is made of discrete frequencies. as shown in Figure 3.3.
What is the frequency of the signal in Figure 3.36?
The signal makes 8 cycles in 4 ms. The frequency is 8 /(4 ms) = 2 KHz
What is the maximum number of characters or symbols that can be represented by Unicode?
Unicode uses 32 bits to represent a symbol or a character. We can define 2^32 different symbols or characters.
A TV channel has a bandwidth of 6 MHz. If we send a digital signal using one channel, what are the data rates if we use one harmonic, three harmonics, and five harmonics?
Using the first harmonic, data rate = 2 × 6 MHz = 12 Mbps Using three harmonics, data rate = (2 × 6 MHz) /3 = 4 Mbps Using five harmonics, data rate = (2 × 6 MHz) /5 = 2.4 Mbps
A periodic composite signal with a bandwidth of 2000 Hz is composed of two sine waves. The first one has a frequency of 100 Hz with a maximum amplitude of 20 V; the second one has a maximum amplitude of 5 V. Draw the bandwidth.
We know the lowest frequency, 100. We know the bandwidth is 2000. The highest frequency must be 100 + 2000 = 2100 Hz. See Figure 3.2.
A color image uses 16 bits to represent a pixel. What is the maximum number of different colors that can be represented?
With 16 bits, we can represent up to 2^16 different colors.
Assume that a private internet requires that the messages at the application layer be encrypted and decrypted for security purposes. If we need to add some information about the encryption/decryption process (such as the algorithms used in the process), does it mean that we are adding one layer to the TCP/IP protocol suite? Redraw the TCP/IP layers (Figure 2.4 part b) if you think so.
Yeet
Assume that an application-layer protocol is written to use the services of UDP. Can the application-layer protocol uses the services of TCP without change?
Yes using multiplexing
If there is a single path between the source host and the destination host, do we need a router between the two hosts?
Yes, for necessary TCP/IP protocol changes
A device is sending out data at the rate of 1000 bps. a. How long does it take to send out 10 bits? b. How long does it take to send out a single character (8 bits)? c. How long does it take to send a file of 100,000 characters?
a. (10 / 1000) s = 0.01 s b. (8 / 1000) s = 0. 008 s = 8 ms c. ((100,000 × 8) / 1000) s = 800 s
What is the phase shift for the following? a. A sine wave with the maximum amplitude at time zero b. A sine wave with maximum amplitude after 1/4 cycle c. A sine wave with zero amplitude after 3/4 cycle and increasing
a. 90 degrees (π/2 radian) b. 0 degrees (0 radian) c. 90 degrees (π/2 radian)
What are the types of addresses (identifiers) used in each of the following layers? a. application layer b. network layer c. data-link layer
a. Application layer: site name or email (specific address). b. Network layer: logical address (IP address). c. Data-link layer: link-layer address (source and destination like MAC).
What is the theoretical capacity of a channel in each of the following cases? a. Bandwidth: 20 KHz SNRdB = 40 b. Bandwidth: 200 KHz SNRdB = 4 c. Bandwidth: 1 MHz SNRdB = 20
a. C = B × (SNRdB /3) = 20 KHz × (40 /3) = 267 Kbps b. C = B × (SNRdB /3) = 200 KHz × (4 /3) = 267 Kbps c. C = B × (SNRdB /3) = 1 MHz × (20 /3) = 6.67 Mbps
Match the following to one or more layers of the TCP/IP protocol suite: a. route determination b. connection to transmission media c. providing services for the end user
a. Data Link / Network b. Physical c. Application
Performance is inversely related to delay. When we use the Internet, which of the following applications are more sensitive to delay? a. Sending an e-mail b. Copying a file c. Surfing the Internet
a. E-mail is not an interactive application. Even if it is delivered immediately, it may stay in the mail-box of the receiver for a while. It is not sensitive to delay. b. We normally do not expect a file to be copied immediately. It is not very sensitive to delay. c. Surfing the Internet is the an application very sensitive to delay. We except to get access to the site we are searching.
Answer the following questions about Figure 2.2 when the communication is from Maria to Ann: a. What is the service provided by layer 1 to layer 2 at Maria's site? b. What is the service provided by layer 1 to layer 2 at Ann's site?
a. Layer 1 packs layer 2's info and applies dst address b. Layer 1 recognizes the sender's address and unpacks ciphertext
Answer the following questions about Figure 2.2 when the communication is from Maria to Ann: a. What is the service provided by layer 2 to layer 3 at Maria's site? b. What is the service provided by layer 2 to layer 3 at Ann's site?
a. Layer 2 encrypts the data from layer 3 b. Layer 2 decrypts data and passes it to layer 3
How many bits can fit on a link with a 2 ms delay if the bandwidth of the link is a. 1 Mbps? b. 10 Mbps? c. 100 Mbps?
a. Number of bits = bandwidth × delay = 1 Mbps × 2 ms = 2000 bits b. Number of bits = bandwidth × delay = 10 Mbps × 2 ms = 20,000 bits c. Number of bits = bandwidth × delay = 100 Mbps × 2 ms = 200,000 bits
Given the frequencies listed below, calculate the corresponding periods. a. 24 Hz b. 8 MHz c. 140 KHz
a. T = 1 / f = 1 / (24 Hz) = 0.0417 s = 41.7 × 10^-3 s = 41.7 ms b. T = 1 / f = 1 / (8 MHz) = 0.000000125 = 0.125 × 10^-6 s = 0.125 μs c. T = 1 / f = 1 / (140 KHz) = 0.00000714 s = 7.14 × 10^-6 s = 7.14 μs
We need to upgrade a channel to a higher bandwidth. Answer the following questions: a. How is the rate improved if we double the bandwidth? b. How is the rate improved if we double the SNR?
a. The data rate is doubled (C2 = 2 × C1). b. When the SNR is doubled, the data rate increases slightly. We can say that, approximately, (C2 = C1 + 1).
Match the following to one or more layers of the TCP/IP protocol suite: a. creating user datagrams b. responsibility for handling frames between adjacent nodes c. transforming bits to electromagnetic signals
a. Transport b. Data Link c. Physial
A host communicates with another host using the TCP/IP protocol suite. What is the unit of data sent or received at each of the following layers? a. application layer b. network layer c. data-link layer
a. application layer : messages b. network layer: datagrams or packets c. data-link layer: frames
What is the bit rate for each of the following signals? a. A signal in which 1 bit lasts 0.001 s b. A signal in which 1 bit lasts 2 ms c. A signal in which 10 bits last 20 μs
a. bit rate = 1/ (bit duration) = 1 / (0.001 s) = 1000 bps = 1 Kbps b. bit rate = 1/ (bit duration) = 1 / (2 ms) = 500 bps c. bit rate = 1/(bit duration) = 1 / (20 μs/10) = 1 / (2 μs) = 500 Kbps
Given the following periods, calculate the corresponding frequencies. a. 5 s b. 12 μs c. 220 ns
a. f = 1 / T = 1 / (5 s) = 0.2 Hz b. f = 1 / T = 1 / (12 μs) =83333 Hz = 83.333 × 103 Hz = 83.333 KHz c. f = 1 / T = 1 / (220 ns) = 4550000 Hz = 4.55× 106 Hz = 4.55 MHz
A router connects three links (networks). How many of each of the following layers can the router be involved with? a. physical layer b. data-link layer c. network layer
a. physical layer: 3 b. data-link layer: 3 c. network layer: 1
Which of the following data units has an application-layer message plus the header from layer 4? a. a frame b. a user datagram c. a bit
b) user diagram
Which of the following data units is decapsulated from a user datagram? a. a datagram b. a segment c. a message
c) message
A signal travels from point A to point B. At point A, the signal power is 100 W. At point B, the power is 90 W. What is the attenuation in decibels?
dB = 10 log10 (90 / 100) = -0.46 dB
Which layers of the TCP/IP protocol suite are involved in a link-layer switch?
data-link and physical
What are the advantages of a multipoint connection over a point-to-point one?
ease of installation and low cost
What is the first principle we discussed in this chapter for protocol layering that needs to be followed to make the communication bidirectional?
it is able to perform two opposite tasks, one in each direction
In the TCP/IP protocol suite, what are the identical objects at the sender and the receiver sites when we think about the logical connection at the application layer?
messages
What are the three criteria necessary for an effective and efficient network?
performance, reliability, and security
What are the two types of line configuration?
point to point and multipoint
Identify the five components of a data communications system
sender, receiver, transmission medium, message, and protocol
What are some of the factors that determine whether a communication system is a LAN or WAN?
size, distances (covered by the network), structure, and ownership
What is the transmission time of a packet sent by a station if the length of the packet is 1 million bytes and the bandwidth of the channel is 200 Kbps?
transmission time = (packet length)/(bandwidth) (8,000,000 bits) / (200,000 bps) = 40 s