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computer science
computer networking
Data Communications and Networking 5th edition Behrouz A. Forouzan - Solutions
In Figure 11.20, explain why we need only one address field. Explain why the address is set to the predefined value of (11111111)2.Figure 11.20 (11111111)2 (00000011)2 Flag Address Control Protocol 1 byte 1 byte Payload FCS Flag 2–4 bytes Variable 1 byte 1-2 bytes 1 byte
Compare the flag byte and the escape byte in PPP. Are they are the same? Explain.
Compare and contrast HDLC with PPP.
In PPP, we normally talk about user and system instead of sending and receiving nodes; explain the reason.
Compare Figure 11.6 and Figure 11.21. If both are FSMs, why are there no event/action pairs in the second?Figure 11.6Figure 11.21 Event 1 Note: Action 1. The colored Action 2. arrow shows the starting state. State I Event 2 State II Action 3. Event 3 Start Carrier detection failed Dead Carrier
In Figure 11.16, which frame type can be used for acknowledgment?Figure 11.16 User Flag Address Control FCS Flag I-frame information Flag Address Control FCS Flag S-frame Management information FCS Flag U-frame Flag Address Control
Assume the only computer in the residence uses PPP to communicate with the ISP. If the user sends 10 network-layer packets to ISP, how many frames are exchanged in each of the following cases:a. Using no authentication?b. Using PAP for authentication?c. Using CHAP for authentication?
Define piggybacking and its benefit.
Assume PPP is in the authentication phase, show payload exchanged between the nodes if PPP is usinga. PAPb. CHAP
Does the duplex communication in Figure 11.10 necessarily mean we need two separate media between the two nodes? Explain.Figure 11.10 Receiving node Sending node Frame ACK [CRC Network [CRC Network Data-link Data-link Logical link (duplex) Timer
Redraw Figure 11.21 with the system not using authentication.Figure 11.21 Carrier detection failed Start Dead Carrier detected Establish Carrier dropped Authentication needed Authentication failed Terminate Authenticate Authentication successful Network Done Network-layer configuration Data
In Figure 11.12, explain why we need a timer at the sending site, but none at the receiving site.Figure 11.12 Receiving node Network Sending node Network Data-link Data-link Packet Frame Legend Packet ACK Start the timer. Packet Stop the timer. Frame O Restart a time-out timer. Lost Frame (resent)
Assume PPP is in the established phase; show payload encapsulated in the frame.
In Figure 11.9, we show the packet path as a horizontal line, but the frame path as a diagonal line. Can you explain the reason?Figure 11.9 Sending node Receiving node Network Network Data-link Data-link Packet Frame Packet Packet Frame Packet Time Time Time Time
Redraw Figure 11.10 using piggybacking.Figure 11.10 Receiving node Frame Sending node ACK Network Network LCRC [CRC Data-link Data-link Logical link (duplex) Timer
Explain why there is no need for CRC in the Simple Protocol.
In the traditional Ethernet protocol (Chapter 13), the frames are sent with the CRC. If the frame is corrupted, the receiving node just discards it. Is this an example of a Simple Protocol or the Stop-and-Wait Protocol? Explain.
In Example 11.4 (Figure 11.13) how many frames are in transit at the same time?Figure 11.13 Sending node Receiving node Network Network Data-link Data-link Legend Packet Frame 0 Start the timer. Packet ACK 1 Stop the timer. Packet Frame 1 Restart a time-out timer. Lost Notes: Frame 1 (resent) A
In Figure 11.11, show what happens in each of the following cases:Figure 11.11a. The receiver is in the ready state and a packet comes from the network layer.b. The receiver is in the ready state and a corrupted frame arrives.c. The receiver is in the ready state and an acknowledgment arrives.
In Example 11.3 (Figure 11.12) how many frames are in transit at the same time?Figure 11.12 Receiving node Network Sending node Network Data-link Data-link Packet Frame Legend Packet ACK Start the timer. Packet Stop the timer. Frame O Restart a time-out timer. Lost Frame (resent) Packet Notes: A
In Figure 11.11, show what happens in each of the following cases:Figure 11.11a. The sender is at the ready state and an error-free ACK arrives.b. The sender is at the blocking state and a time-out occurs.c. The sender is at the ready state and a time-out occurs. Sending node Packet came from
In a bit-oriented protocol, should we first unstuff the extra bits and then remove the flags or reverse the process?
In Example 11.4 (Figure 11.13), assume the round trip time for a frame is 40 milliseconds. Explain what will happen if we set the time-out in each of the following cases.Figure 11.13a. 35 millisecondsb. 45 millisecondsc. 40 milliseconds Sending node Receiving node Data-link Network Network
In a byte-oriented protocol, should we first unstuff the extra bytes and then remove the flags or reverse the process?
Assume we change the Stop-and-Wait Protocol to include a NAK (negative feedback), which is used only when a corrupted frame arrives and is discarded. Redraw Figure 11.9 to show this change.Figure 11.9 Sending node Receiving node Network Network Data-link Data-link Packet Frame Packet Packet Frame
Compare and contrast byte-stuffing and bit-stuffing.
Unstuff the following frame payload: 00011111000001111101110100111011111000001111
Compare and contrast byte-oriented and bit-oriented protocols.
Bit-stuff the following frame payload: 00011111110011111010001111 111110000111
Assume a new character-oriented protocol is using the 16-bit Unicode as the character set. What should the size of the flag be in this protocol?
Unstuff the following frame payload in which E is the escape byte, F is the flag byte, and D is a data byte other than an escape or a flag character. D DEF E D DD DE E
Explain why flags are needed when we use variable-size frames.
Byte-stuff the following frame payload in which E is the escape byte, F is the flag byte, and D is a data byte other than an escape or a flag character. DEDDF D D E|ED F|D
Define framing and give the reason it is needed.
Figure 9.7 shows a system as either a host or a router. What would be the actual entity (host or router) of system A and B in each of the following cases:Figure 9.7a. If the link is the first one in the path?b. If the link is the middle one in the path?c. If the link is the last one in the path?d.
How many IP addresses and how many link-layer addresses should a router have when it is connected to five links?
Assume the network in Figure 9.7 does not support broadcasting. What do you suggest for sending the ARP request in this network?Figure 9.7 LAN System A System B N, L, N, L2 Request N3L3 N, L4 Request: Looking for link-layer address of a node with IP address N2 a. ARP request is broadcast LAN System
Why does a router normally have more than one interface?
In Figure 9.7, assume system B is not running the ARP program. What would happen?Figure 9.7 LAN System A System B N, L, N, L2 Request N3L3 N, L4 Request: Looking for link-layer address of a node with IP address N2 a. ARP request is broadcast LAN System A System B N2L2 ¡N, L, Reply N4 L4 N3L3
Why does a host or a router need to run the ARP program all of the time in the background?
In Figure 9.5, assume Link 2 is broken. How can Alice communicate with Bob?Figure 9.5 To another link N3 L3 Frame Alice L2 L, NNg Data N, L, RI N4 L4 N¡ L Link 1 Order of addresses N: IP address IP addresses: source-destination Legend L: Link-layer address Link-layer address:
In Figure 9.9, how does system A know what the link-layer address of system B is when it receives the ARP reply?Figure 9.9 System A System B N2 N1 L1 L2 (Not known by A) Ox0001 Ox04 Ox0800 Ох06 Ox0001 ARP request L1 N1 All Os| N2 Multicast frame From A to B A Data Destination Source. Ox0001
When we send a letter using the services provided by the post office, do we use an end-to-end address? Does the post office necessarily use an end-to-end address to deliver the mail? Explain.
In Figure 9.9, why is the destination hardware address of the frame from A to B a broadcast address?Figure 9.9 System A System B N2 N1 L1 L2 (Not known by A) Ox0001 Ox04 Ox0800 Ох06 Ox0001 ARP request L1 N1 All Os| N2 Multicast frame From A to B A Data Destination Source. Ox0001 Ox0800 B:
In the previous problem, assume Alice cannot find a direct flight from the Los Angeles to the Chicago. If she needs to change flights in Denver,a. Find the end-to-end addresses in this scenario.b. Find the link-layer addresses in this scenario.
In Figure 9.9, why is the destination hardware address all 0s in the ARP request message?Figure 9.9 System A System B N2 N1 L1 L2 (Not known by A) Ox0001 Ox04 Ox0800 Ох06 Ox0001 ARP request L1 N1 All Os| N2 Multicast frame From A to B A Data Destination Source. Ox0001 Ox0800 B: Broadcast address
Assume Alice is travelling from 2020 Main Street in Los Angeles to 1432 American Boulevard in Chicago. If she is travelling by air from Los Angeles Airport to Chicago Airport,a. find the end-to-end addresses in this scenario.b. find the link-layer addresses in this scenario.
Assume we have an isolated link (not connected to any other link) such as a private network in a company. Do we still need addresses in both the network layer and the data-link layer? Explain.
Is the current Internet using circuit-switching or packet-switching at the datalink layer? Explain.
What is the size of an ARP packet when the protocol is IPv4 and the hardware is Ethernet?
Explain why we may need a router in Figure 9.16. Bob Alice R Alice's site Bob's site
Is the size of the ARP packet fixed? Explain.
Explain why we do not need the router in Figure 9.15.
Can two hosts in two different networks have the same link-layer address? Explain.
Distinguish between a point-to-point link and a broadcast link.
Distinguish between communication at the network layer and communication at the data-link layer.
When we say that the transport layer multiplexes and demultiplexes applicationlayer messages, do we mean that a transport-layer protocol can combine several messages from the application layer in one packet? Explain.
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 thefuture, where should its position be in the suite? Redraw
Can you explain why we did not mention multiplexing/demultiplexing services for the application 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.
If there is a single path between the source host and the destination host, do we need a router between the two hosts?
What is the relationship between period and frequency?
What does the amplitude of a signal measure? What does the frequency of a signal measure? What does the phase of a signal measure?
Given the following periods, calculate the corresponding frequencies.a. 5 sb. 12 μsc. 220 ns
How can a composite signal be decomposed into its individual frequencies?
What is the phase shift for the following?a. A sine wave with the maximum amplitude at time zerob. A sine wave with maximum amplitude after 1/4 cyclec. A sine wave with zero amplitude after 3/4 cycle and increasing
Name three types of transmission impairment.
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.
Distinguish between baseband transmission and broadband transmission.
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.
Distinguish between a low-pass channel and a band-pass channel.
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?
What does the Nyquist theorem have to do with communications?
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.
What does the Shannon capacity have to do with communications?
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?
Why do optical signals used in fiber optic cables have a very short wave length?
What is the bit rate for the signal inFigure 3.35? 16 ns Time
Can we say whether a signal is periodic or nonperiodic by just looking at its frequency domain plot? How?
What is the frequency of the signal inFigure 3.36? 4 ms Time
What is the bandwidth of the composite signal shown inFigure 3.37? Frequency 180 5 5 5 5
Is the frequency domain plot of an alarm system discrete or continuous?
A periodic composite signal contains frequencies from 10 to 30 KHz, each with an amplitude of 10 V. Draw the frequency spectrum.
We send a voice signal from a microphone to a recorder. Is this baseband or broadband transmission?
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.
We send a digital signal from one station on a LAN to another station. Is this baseband or broadband transmission?
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?
We modulate several voice signals and send them through the air. Is this baseband or broadband transmission?
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?
The attenuation of a signal is −10 dB. What is the final signal power if it was originally 5 W?
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?
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?
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?
A file contains 2 million bytes. How long does it take to download this file using a 56-Kbps channel? 1-Mbps channel?
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?
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?
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?
What is the theoretical capacity of a channel in each of the following cases?a. Bandwidth: 20 KHz SNRdB = 40b. Bandwidth: 200 KHz SNRdB = 4c. Bandwidth: 1 MHz SNRdB = 20
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?
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?
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