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Q: Imagine that you have trained your St. Bernard, Bernie, to carry a box of three 8mm tapes instead of a flask of brandy. (When your disk fills up, you
Q: An alternative to a LAN is simply a big timesharing system with terminals for all users. Give two advantages of a client-server system using a LAN.
Q: The performance of a client-server system is influenced by two network factors: the bandwidth of the network (how many bits/sec it can transport) and
Q: Besides bandwidth and latency, what other parameter is needed to give a good characterization of the quality of service offered by a network used for
Q: A factor in the delay of a store-and-forward packet-switching system is how long it takes to store and forward a packet through a switch. If
Q: A client-server system uses a satellite network, with the satellite at a height of 40,000 km. What is the best-case delay in response to a request?
Q: In the future, when everyone has a home terminal connected to a computer network, instant public referendums on important pending legislation will
Q: A collection of five routers is to be connected in a point-to-point subnet. Between each pair of routers, the designers may put a high-speed line, a
Q: A group of 2n - 1 router is interconnected in a centralized binary tree, with a router at each tree node. Router i communicate with router j by
Q: A disadvantage of a broadcast subnet is the capacity wasted when multiple hosts attempt to access the channel at the same time. As a simplistic
Q: What are two reasons for using layered protocols?
Q: The president of the Specialty Paint Corp. gets the idea to work with a local beer brewer to produce an invisible beer can (as an anti-litter
Q: What is the principal difference between connectionless communication and connection-oriented communication?
Q: Two networks each provide reliable connection-oriented service. One of them offers a reliable byte stream and the other offers a reliable message
Q: What does ''negotiation'' mean when discussing network protocols? Give an example.
Q: In Fig. 1-19, a service is shown. Are any other services implicit in this figure? If so where? If not, why not?
Q: In some networks, the data link layer handles transmission errors by requesting damaged frame to be retransmitted. If the probability of a frame's
Q: Which of the OSI layers handles each of the following? (a) Dividing the transmitted bit stream into frames. (b) Determining which route through the
Q: If the unit exchanged at the data link level is called a frame and the unit exchanged at the network level is called a packet, do frames encapsulate
Q: A system has an n-layer protocol hierarchy. Applications generate messages of length M bytes. At each of the layers, an h-byte header is added. What
Q: List two ways in which the OSI reference model and the TCP/IP reference model are the same. Now list two ways in which they differ.
Q: What is the main difference between TCP and UDP?
Q: The subnet of Fig. 1-25(b) was designed to withstand a nuclear war. How many bombs would it take to partition the nodes into two disconnected sets?
Q: The Internet is roughly doubling in size every 18 months. Although no one really knows for sure, one estimate put the number of hosts on it at 100
Q: When a file is transferred between two computers, two acknowledgement strategies are possible. In the first one, the file is chopped up into packets,
Q: Why does ATM use small, fixed-length cells?
Q: How long was a bit on the original 802.3 standard in meters? Use a transmission speed of 10 Mbps and assume the propagation speed in coax is 2/3 the
Q: An image is 1024 x 768 pixels with 3 bytes/pixel. Assume the image is uncompressed. How long does it take to transmit it over a 56-kbps modem
Q: Ethernet and wireless networks have some similarities and some differences. One property of Ethernet is that only one frame at a time can be
Q: Wireless networks are easy to install, which makes them inexpensive since installation costs usually far overshadow equipment costs. Nevertheless,
Q: List two advantages and two disadvantages of having international standards for network protocol?
Q: When a system has a permanent part and a removable part (such as a CD-ROM drive and the CD-ROM), it is important that the system be standardized, so
Q: Compute the Fourier coefficients for the function f (t) = t (< t < 1).
Q: A noiseless 4-kHz channel is sampled every 1 msec. What is the maximum data rate?
Q: Television channels are 6 MHz wide. How many bits/sec can be sent if four-level digital signals are used? Assume a noiseless channel.
Q: If a binary signal is sent over a 3-kHz channel whose signal-to-noise ratio is 20 dB, what is the maximum achievable data rate?
Q: What signal-to-noise ratio is needed to put a T1 carrier on a 50-kHz line?
Q: What is the difference between a passive star and an active repeater in a fiber network?
Q: How much bandwidth is there in 0.1 micron of spectrum at a wavelength of 1 micron?
Q: It is desired to send a sequence of computer screen images over an optical fiber. The screen is 480 x 640 pixels, each pixel being 24 bits. There are
Q: Is the Nyquist theorem true for optical fiber or only for copper wire?
Q: In Fig. 2-6 the left hand band is narrower than the others. Why?
Q: Radio antennas often work best when the diameter of the antenna is equal to the wavelength of the radio wave. Reasonable antennas range from 1 cm to
Q: Multi path fading is maximized when the two beams arrive 180 degrees out of phase. How much of a path difference is required to maximize the fading
Q: A laser beam 1 mm wide is aimed at a detector 1 mm wide 100 m away on the roof of a building. How much of an angular diversion (in degrees) does the
Q: The 66 low-orbit satellites in the Iridium project are divided into six necklaces around the earth. At the altitude they are using, the period is 90
Q: Consider a satellite at the altitude of geostationary satellites but whose orbital plane is inclined to the equatorial plane by an angle. To a
Q: How many end office codes were there pre-1984, when each end office was named by its three-digit area code and the first three digits of the local
Q: Using only the data given in the text, what is the maximum number of telephones that the existing U.S. system can support without changing the
Q: A simple telephone system consists of two end offices and a single toll office to which each end office is connected by a 1-MHz full-duplex trunk.
Q: A regional telephone company has 10 million subscribers. Each of their telephones is connected to a central office by a copper twisted pair. The
Q: Is an oil pipeline a simplex system, a half-duplex system, a full-duplex system, or none of the above?
Q: The cost of a fast microprocessor has dropped to the point where it is now possible to put one in each modem. How does that affect the handling of
Q: A modem constellation diagram similar to Fig. 2-25 has data points at the following coordinates: (1, 1), (1, -1), (-1, 1), and (-1, -1). How many bps
Q: A modem constellation diagram similar to Fig. 2-25 has data points at (0, 1) and (0, 2). Does the modem use phase modulation or amplitude modulation?
Q: In a constellation diagram, all the points lie on a circle centered on the origin. What kind of modulation is being used?
Q: How many frequencies does a full-duplex QAM-64 modem use?
Q: An ADSL system using DMT allocates 3/4 of the available data channels to the downstream link. It uses QAM-64 modulation on each channel. What is the
Q: In the four-sector LMDS example of Fig. 2-30, each sector has its own 36-Mbps channel. According to queuing theory, if the channel is 50% loaded, the
Q: Ten signals, each requiring 4000 Hz, are multiplexed on to a single channel using FDM. How much minimum bandwidth is required for the multiplexed
Q: Why has the PCM sampling time been set at 125 µsec?
Q: What is the percent overhead on a T1 carrier; that is, what percent of the 1.544 Mbps are not delivered to the end user?
Q: Compare the maximum data rate of a noiseless 4-kHz channel using (a) Analog encoding (e.g., QPSK) with 2 bits per sample. (b) The T1 PCM system.
Q: If a T1 carrier system slips and loses track of where it is, it tries to resynchronize using the 1st bit in each frame. How many frames will have to
Q: What is the difference, if any, between the demodulator part of a modem and the coder part of a codec? (After all, both convert analog signals to
Q: A signal is transmitted digitally over a 4-kHz noiseless channel with one sample every 125 µsec. How many bits per second are actually sent for each
Q: A pure sine wave of amplitude A is encoded using delta modulation, with x samples/sec. An output of +1 corresponds to a signal change of +A/8, and an
Q: SONET clocks have a drift rate of about 1 part in 109. How long does it take for the drift to equal the width of 1 bit? What are the implications of
Q: In Fig. 2-37, the user data rate for OC-3 is stated to be 148.608 Mbps. Show how this number can be derived from the SONET OC-3 parameters.
Q: To accommodate lower data rates than STS-1, SONET has a system of virtual tributaries (VT). A VT is a partial payload that can be inserted into an
Q: What is the essential difference between message switching and packet switching?
Q: What is the available user bandwidth in an OC-12c connection?
Q: Three packet-switching networks each contain n nodes. The first network has a star topology with a central switch, the second is a (bidirectional)
Q: Compare the delay in sending an x-bit message over a k-hop path in a circuit-switched network and in a (lightly loaded) packet-switched network. The
Q: Suppose that x bits of user data are to be transmitted over a k-hop path in a packet-switched network as a series of packets, each containing p data
Q: In a typical mobile phone system with hexagonal cells, it is forbidden to reuse a frequency band in an adjacent cell. If 840 frequencies are
Q: The actual layout of cells is seldom as regular that as shown in Fig. 2-41. Even the shapes of individual cells are typically irregular. Give a
Q: Make a rough estimate of the number of PCS micro cells 100 m in diameter it would take to cover San Francisco (120 square km).
Q: Sometimes when a mobile user crosses the boundary from one cell to another, the current call is abruptly terminated, even though all transmitters and
Q: D-AMPS has appreciably worse speech quality than GSM. Is this due to the requirement that D-AMPS be backward compatible with AMPS, whereas GSM had no
Q: Calculate the maximum number of users that D-AMPS can support simultaneously within a single cell. Do the same calculation for GSM. Explain the
Q: Suppose that A, B, and C are simultaneously transmitting 0 bits, using a CDMA system with the chip sequences of Fig. 2-45(b). What is the resulting
Q: In the discussion about orthogonality of CDMA chip sequences, it was stated that if S•T = 0 then is also 0. Prove this.
Q: Consider a different way of looking at the orthogonality property of CDMA chip sequences. Each bit in a pair of sequences can match or not match.
Q: A CDMA receiver gets the following chips: (-1 +1 -3 +1 -1 -3 +1 +1). Assuming the chip sequences defined in Fig. 2-45(b), which stations transmitted,
Q: At the low end, the telephone system is star shaped, with all the local loops in a neighborhood converging on an end office. In contrast, cable
Q: A cable TV system has 100 commercial channels, all of them alternating programs with advertising. Is this more like TDM or like FDM?
Q: A cable company decides to provide Internet access over cable in a neighborhood consisting of 5000 houses. The company uses a coaxial cable and
Q: Using the spectral allocation shown in Fig. 2-48 and the information given in the text, how many Mbps does a cable system allocate to upstream and
Q: How fast can a cable user receive data if the network is otherwise idle?
Q: An upper-layer packet is split into 10 frames, each of which has an 80 percent chance of arriving undamaged. If no error control is done by the data
Q: The following character encoding is used in a data link protocol: A: 01000111; B: 11100011; FLAG: 01111110; ESC: 11100000 Show the bit sequence
Q: The following data fragment occurs in the middle of a data stream for which the byte-stuffing algorithm described in the text is used: A B ESC C ESC
Q: One of your classmates, Scrooge, has pointed out that it is wasteful to end each frame with a flag byte and then begin the next one with a second
Q: A bit string, 0111101111101111110, needs to be transmitted at the data link layer. What is the string actually transmitted after bit stuffing?
Q: When bit stuffing is used, is it possible for the loss, insertion, or modification of a single bit to cause an error not detected by the checksum? If
Q: Can you think of any circumstances under which an open-loop protocol, (e.g., a Hamming code) might be preferable to the feedback-type protocols
Q: To provide more reliability than a single parity bit can give, an error-detecting coding scheme uses one parity bit for checking all the odd-numbered
Q: Sixteen-bit messages are transmitted using a Hamming code. How many check bits are needed to ensure that the receiver can detect and correct single
Q: An 8-bit byte with binary value 10101111 is to be encoded using an even-parity Hamming code. What is the binary value after encoding?
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