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Business Data Communications 6th Edition William Stallings - Solutions
What are some of the major uses of T-1 lines?
Why is the use of private T-1 lines attractive to companies?
In HDLC, flag fields delimit the frame at both ends with the unique pattern 01111110.A single flag may be used as the closing flag for one frame and the opening flag for the next. On both sides of the user–network interface, receivers are continuously hunting for the flag sequence to synchronize
It is clear that bit stuffing is needed for the Address, Data, and FCS fields of an HDLC frame. Is it needed for the Control field?
Because of the provision that a single flag can be used as both an ending and a starting flag, a single bit error can cause problems.a. Explain how a single bit error can merge two frames into one.b. Explain how a single bit error can split a single frame into two frames.
Suggest improvements to the bit stuffing algorithm to overcome the problems of single-bit errors described in the preceding problem.
Using the example bit string of Problem 17.1a, show the signal pattern on the line using NRZ-L coding. Does this suggest a side benefit of bit stuffing?
Consider that several physical links connect two stations.We would like to use a “multilink HDLC” that makes efficient use of these links by sending frames on a FIFO (first-in, first-out) basis on the next available link.What enhancements to HDLC are needed?
How do we achieve a data rate of 56 kbps in 23 channels using a DS-1 format?
To get some indication of the relative demands of voice and data traffic, consider the following:a. Calculate the number of bits used to send a 3-minute telephone call using standard PCM.b. How many pages of IRA text with an average of 65 characters a line and 55 lines a page corresponds to one
Recently a new scanner was announced that provided 1200 dpi resolution and over 1 billion colors.a. How much memory in bytes would it take to store a bit map of an 8 × 10 inch monochrome picture at 1200 dpi with a 10-bit gray scale?b. Suppose the colors are represented as a combination of three
To paraphrase Lincoln, all of the channel some of the time, some of the channel all of the time. Refer to Figure 17.5 and relate the preceding to the figure.
Consider the following fragment:legitimate code if data is Friday the 13th;crash_computer();legitimate code What type of malicious software is this?
Consider the following fragment in an authentication program:username = read_username();password = read_password();if username is “133t h4ck0r”return ALLOW_LOGIN;if username and password are valid return ALLOW_LOGIN else return DENY_LOGIN What type of malicious software is this?
How vulnerable do you think the typical computer site is?
What is the magnitude of the risk? That is, if security is compromised, what is the potential cost to the victim?
What policies and procedures can you suggest to counter the types of threats illustrated in this case study?
List and briefly define the key areas that comprise network management.
Define fault as it applies to network management.
List two ways in which a network management system may be characterized as integrated.
List and briefly define the key elements of SNMP.
What functions are provided by SNMP?
What lower-layer protocol encapsulates SNMP messages?
Describe two different interpretations of the term MIB.
What are the differences among SNMPv1, SNMPv2, and SNMPv3?
Because SNMP uses two different port numbers (UDP ports 161 and 162), a single system can easily run both a manager and an agent.What would happen if the same port number were used for both?
The original (version 1) specification of SNMP has the following definition of a new type:Gauge :: = [APPLICATION 2] IMPLICIT INTEGER (0..4294967295)The standard includes the following explanation of the semantics of this type:This application-wide type represents a non-negative integer, which may
One of the first steps in configuring a device to be managed is to give it an IP address.Why?
Many network administrators use the ping program as a primary management tool.a. Why would you ping a network device?b. Why would you ping yourself?
We have seen that SNMP uses UDP as its transport protocol.Why was UDP chosen over TCP?
Test the vulnerability of a machine at the following site: http://grc.com/default.htm.Follow the ShieldsUP! link for a series of free tests listed midway down the page.
The following code fragments show a sequence of virus instructions and a polymorphic version of the virus. Describe the effect produced by the metamorphic code. Original Code mov eax, 5 add eax, ebx call [eax] Metamorphic Code mov eax, 5 push ecx pop ecx add eax, ebx swap eax, ebx swap ebx, eax
What is the disadvantage of having the network management system operate at the application layer?
What are the characteristics of a virtual path?
Consider four different cellular systems that share the following characteristics. The frequency bands are 825 to 845 MHz for mobile unit transmission and 870 to 890 MHz for base station transmission. A duplex circuit consists of one 30-kHz channel in each direction.The systems are distinguished by
An analog cellular system has a total of 33 MHz of bandwidth and uses two 25-kHz simplex (one-way) channels to provide full duplex voice and control channels.a. What is the number of channels available per cell for a frequency reuse factor of(1) 4 cells, (2) 7 cells, and (3) 12 cells?b. Assume that
A cellular system uses FDMA with a spectrum allocation of 12.5 MHz in each direction, a guard band at the edge of the allocated spectrum of 10 kHz, and a channel bandwidth of 30 kHz.What is the number of available channels?
For a cellular system, FDMA spectral efficiency is defined aswhere Bc channel bandwidth Bw total bandwidth in one direction NT total number of voice channels in the covered area What is an upper bound on a na BCNT Bw
Global System for Mobile communications (GSM) is an international standard for digital cellular communication. Provide a basic overview of GSM, focusing on the three primary functional entities of a GSM network. Is the GSM strategy a superior or inferior alternative to CDMA? Support your answer.
Some concern has been expressed regarding potential health hazards related to cellular phone use. Discuss potential health risks related to cellular phone technology.What precautions can be taken to minimize potential dangers involved in cell phone use?
Differentiate between an analog and a digital electromagnetic signal.
What are three important characteristics of a periodic signal?
How many radians are there in a complete circle of 360 degrees?
What is the relationship between the wavelength and frequency of a sine wave?
Define fundamental frequency.
What is the relationship between a signal’s spectrum and its bandwidth?
How can telephone networks use communication facilities that limit the transmission of sound to a narrow bandwidth?
How does delay distortion place a limitation on the data rate for digital data?
What is noise?
What is white noise?
There are many cellular providers serving each geographic area, and each one may use a different technology.a. Who are the providers in your area and what are the multiple access technologies used?b. What are the technologies behind the cellular phones you or your family and friends use?
Under what circumstances would you use GEOS, LEOS, and MEOS, respectively?
Explain what GEOS, LEOS, and MEOS satellites are (including what the acronyms stand for). Compare the three types with respect to factors such as size and shape of orbits, signal power, frequency reuse, propagation delay, number of satellites for global coverage, and handoff frequency.
List and briefly explain the fields in an ATM cell.
List and briefly define the ATM service categories.
In every area of the country, the services available from carriers can vary. Determine the following for your area:a. What types of service are the most prevalent?b. What would be the cost of these services for 256 kbps? 512 kbps? 1 Mbps?c. In addition to the cost of the service, what other costs
List all 16 possible values of the GFC field and the interpretation of each value (some values are illegal).
One key design decision for ATM was whether to use fixed- or variable-length cells.Let us consider this decision from the point of view of efficiency.We can define transmission efficiency asa. Consider the use of fixed length packets. In this case the overhead consists of the header octets.Define L
Another key design decision for ATM is the size of the data field for fixed-size cells.Let us consider this decision from the point of view of efficiency and delay.a. Assume that an extended transmission takes place, so that all cells are completely filled. Derive an expression for the efficiency N
Consider the following applications. In each case indicate whether you would use X.25, frame relay, or ATM facilities. Assume that the facilities are available and “competitively”priced (i.e., determine, in each case, whether the functional characteristics of the service offering match well the
Consider compressed video transmission in an ATM network. Suppose standard ATM cells must be transmitted through 5 switches.The data rate is 43 Mbps.a. What is the transmission time for one cell through one switch?b. Each switch may be transmitting a cell from other traffic all of which we assume
A widely used set of standards employed in local ATM environments is called ATM LAN Emulation (LANE). Provide a basic overview of LANE and describe its place in an organization’s network strategy.
In order to support IP service over an ATM network, IP datagrams must first be segmented into a number of ATM cells before sending them over the ATM network.As ATM does not provide cell loss recovery, the loss of any of these cells will result in the loss of the entire IP packet. Given PC = cell
What geometric shape is used in cellular system design?
What is the principle of frequency reuse in the context of a cellular network?
List five ways of increasing the capacity of a cellular system.
Explain the paging function of a cellular system.
What is cellular handoff?
For a cellular system, describe the function of the following: control channels and traffic channels.
What is the wireless application protocol (WAP)?
Why does thermal noise place an upper bound on communication system performance?
Describe the phenomenon known as multipath.
What is differential encoding?
What function does a modem perform?
Are the modem and the codec functional inverses (i.e., could an inverted modem function as a codec, or vice versa)?
Indicate three major advantages of digital transmission over analog transmission.
How are binary values represented in amplitude shift keying, and what is the limitation of this approach?
Indicate the major categories into which modems may be classified based on their data rates.
What is NRZ-L? What is a major disadvantage of this data encoding approach?
Match the device or system with the correct type of signal and data. Device/System Modem transmissions Ethernet AM/FM radio PCM Data/Signal A. Digital data/digital encoding B. Digital data/analog encoding C. Analog data/digital encoding D. Analog data/analog encoding
How is the transmission of a single character differentiated from the transmission of the next character in asynchronous transmission?
What is a major disadvantage of asynchronous transmission?
Research current offerings for frame relay, ATM, and Ethernet MANs, and discuss the relative advantages of each.Haukeland University Hospital is one of the largest hospitals in Norway.The hospital offers almost every form of medical diagnosis and treatment. Haukeland University Hospital is the
What transition issues would you expect Haukeland to face in going from the frame relay WAN to the Ethernet WAN?Haukeland University Hospital is one of the largest hospitals in Norway.The hospital offers almost every form of medical diagnosis and treatment. Haukeland University Hospital is the
Define flow control.
Define error control.
List common ingredients for error control for a link control protocol.
What is the purpose of the flag field in HDLC?
What type of error detection is used in the HDLC frame check sequence field?
What is the difference between amplification and retransmission?
Define channel capacity.
What key factors affect channel capacity?
A signal has a fundamental frequency of 1000 Hz.What is its period?
Express the following in the simplest form you can: a. sin(2ft)+sin(2ft + ) b. sin 2ft+sin(2ft - )
Sound may be modeled as sinusoidal functions. Compare the relative frequency and wavelength of musical notes. Use 330 m/s as the speed of sound and the following frequencies for the musical scale. Note Frequency DE F 264 297 330 352 GA B C 396 440 495 528
If the solid curve in Figure 15.11 represents sin(2 t), what does the dotted curve represent?That is, the dotted curve can be written in the form A sin(2 ft ); what are A,f, and ?
Decompose the signal (1 + 0.1 cos 5t) cos 100t into a linear combination of sinusoidal functions, and find the amplitude, frequency, and phase of each component. Hint: Use the identity for cos a cos b.
Find the period of the function f(t) = (10 cos t)2.
Figure 15.4 shows the effect of eliminating higher-harmonic components of a square wave and retaining only a few lower harmonic components.What would the signal look like in the opposite case; that is, retaining all higher harmonics and eliminating a few lower harmonics?
Given the narrow (usable) audio bandwidth of a telephone transmission facility, a nominal SNR of 56dB (400,000), and a distortion level of a. What is the theoretical maximum channel capacity (Kbps) of traditional telephone lines (POTS)?b. What is the actual maximum channel capacity? 2.0 1.0 0 -1.0
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