Workin' the Net
if the lowest frequency in a channel is 1.22 MHz and the highest frequency is 1.25 MHz, what is the channel bandwidth?
1.25 MHz - 1.22 MHz = .03 MHz. This is the channels bandwidth
1. A) Distinguish between Step 1 and Step 2 in the routing process. B) if any row other than the default row matches an Ipv4 address, why will the router never choose the default row? C) which rows in figure 8-11 match 128.171.17.13 (Don't forget the default row.) show your calculations for rows that match D) which of these is the best match row? Justify your answer. E) What rows match 172.40.17.6? Show your calculations for rows that match F) which of these is the best match row? Justify your answer G) which rows match 172.30.12.47? Show your calculations for each match H) which of these is the best-match row? Justify your answer I) How would your previous answer change if the metric had been reliability?
10 ch. 8
1. A) Distinguish between step 2 and step 3 in routing B) what are router ports called? C) if the router selects row 13 as the best-match row, what interface will the router send the packet out? D) to what device? E) why is this router called the default router? (the answer is not in the text) F) if the router selects Row 2 as the best-match row for packet 172.30.33.6, what interface will the router send the packet out? G) To what device? (Don't say, "the local device")
11 ch. 8
11. A) The power level at 10 meters is 100 mW. At 20 meters, it is 5 mW. How many decibels has it lost? B) Compared to an omnidirectional antenna, a dish antenna quadruples radiated power. How much is this change in decibels? C) Compute the decibel value for a power ratio of 17:1? D) Of 1:33?
11. in ch. 7
1. A) Fill in the missing values in the table in decimal table. Approximate values for B) 8:1 C) 9:1 D) 110:1 E) 1:7 F) 1:90. Use terms like "a little higher than" or "a little lower than."
12 in ch. 7
1. An arriving packet has the destination Ipv4 address 128.171.180.13. Row 86 has the destination value 128.171.160.0. The row's mask is 255.255.224.0. Does this row match the destination Ipv4 address? Show your work. You can use the Windows Calculator if you have a Windows PC. In Windows Vista and earlier versions of Windows, choose scientific when you open the calculator. In the Windows 7 and Windows 10 calculator, choose programmer mode.
13 ch. 8
1. A) Write the following Ipv6 address in canonical form using RFC 5952: 2001:0ed2:056b:00d3:000c:abcd:0bcd:0fe0 B) Write the following Ipv6 address in canonical form using RFC 5952: 2001:0002:0000:0000:0000:abcd:0bcd:0fe0 C) Simplify the following Ipv6 address using RFC 5952: 2001:0000:0000:00fe:0000:0000:0000:cdef D) Simplify the following Ipv6 address using RFC 5952: 2001:0000:0000:00fe:0000:0000:ba5a:cdef E) What is the advantage of simplifying Ipv6 addresses according to strict rules? F) Which RFC is used to write Ipv6 addresses in canonical form?
21 ch. 8
Distinguish between 802.3 standards and 802.11 standards
802.3) IEEE 802.3 working group creates Ethernet standards 802.11) IEEE 802.11 working group creates the wireless LAN standards 802.3) Ethernet networks are single networks, so it uses standards at the physical layer and the data link layer 802.11) It is a set of physical layer specifications and media access control for implementing wireless LAN 802.3) This working group is constantly creating new and faster physical layer standards as electronics improve and is highly secured 802.11) 802.11 products are certified by Wi-Fi logo only when they confirm to certain standards of interoperability, but it is less secured
In the 2.4 GHz and 5 GHz service bands, what type of transmission method is required by regulators?
?????
what is a hertz?
A hertz is a measure of frequency that measures how many complete cycles a wave completes per second. One hertz is equal to one complete cycle per second.
1. A) You are considering a laptop computer that uses 802.11ay. Will your existing 802.11ac access point be able to communicate with the new device? B) What standard will they use in the communication if communication is possible? C) What principle does this communication exemplify?
A) The new device will be able to communicate with the older access point due to backward compatibility B) The standard that will be used for communication will be 802.11ac unless a new client device is purchased or an external 802.11ay device C) The principle of being able to communicate with previous standards is backwards compatibility
why does the access point connect to the corporate Ethernet LAN?
Access points allow hosts in a wireless LAN network to connect to a server that is not in the same wireless network
an FM radio station is called Moldy Oldies 101.1. Is this a channel or a service band?
An FM radio station called Moldy Oldies 101.1 is a channel not a service band
what two propagation problems become worse as frequency increases?
As frequency increases, signals experience more absorptive attenuation and dead zones
What other types of system do we call broadband?
Broadband has come to mean "fast", whether or not radio is used
what do we call a system whose channels are wide?
Channels with very wide bandwidth are called broadband channels
what causes dead zones?
Dead zones are caused when dense obstructions are in the direct line between the signal and receiver
how many channels are there in the FM band?
FM radio has around 20 channels
if the signal strength from an Omnidirectional radio source is 8mW at 30 meters, how strong will it be at 150 meters, ignoring absorptive attenuation?
If it is 8mW at 30 meters, it will be (150/30=5; 5*4=20; 8/20=0.4) 0.4mW at 150 meters
If you increase propagation distance by a factor of 100, how much will signal intensity change at the receiver?
If you increase propagation distance by 100, the signal will be 1/400th of its current power
if you want to transmit seven times as fast, how much wider must the channel be?
If you want to transmit 7X as fast, you need the bandwidth of the channel to be 7X as wide
In 802.3 Ethernet networks, can simple installation rules usually reduce propagation effects to nonissues?
In 802.3 Ethernet networks, simple installation rules CAN reduce propagation effects in wired transmission by respecting cord distance limits and taking other installation precautions because wired propagation is predictable
Why does it divide the channel into subcarriers?
In OFDM, the channel is divided into subcarriers so that if there is impairment in one or even a few subcarriers, all of the frame will usually still get through
at what range of frequencies do most wireless systems operate?
Most radio frequencies for wireless transceivers range between about 500 megahertz (MHz) and 10 gigahertz (GHz)
Does a signal travel at a single frequency, or does it spread over a range of frequencies?
Signals travel over a range of frequencies, this range is known as the bandwidth of the signal
does spread spectrum transmission increase transmission speed thanks to its wider channels?
Spread spectrum transmission does not increase transmission speed
is spread spectrum transmission done for security reasons in commercial WLANs?
Spread spectrum transmission is used solely to reduce propagation problems, not to provide security or higher transmission speed
what is the benefit of spread spectrum transmission for business communication?
Spread spectrum transmission uses a wider bandwidth which prevents multipath interference in channels
how many 20 MHz nonoverlapping channels does the 2.4 GHz band support? Why is this a problem?
The 2.4 GHz service band supports 3 nonoverlapping 20 MHz channels. This is a problem because if nearby access points can't be put on different channels, there will be co-channel interference
Why are companies moving rapidly into the 5 GHz band?
The 5 GHz service band supports more channels and there is less chance of co-channel interference
in what two service bands does 802.11 operate?
The 802.11 operates in the 2.4 GHz service band and the 5 GHz service band.
Distinguish among the frequency spectrum, service bands, and channels.
The frequency spectrum is the entire possible range of frequencies (from 0 Hz to infinity). Service bands are subranges that are dedicated to certain services (FM radio, emergency response, GPA, etc. Channels are subranges in service bands dedicated to different purposes, for example different FM radio stations
what is the actual difference between 802.11 and Wi-Fi?
The term Wi-Fi stems from the Wi-Fi alliance, which creates subsets of 802.11 standards with selected options. The 802.11 Working Group creates standards with many options.
what is a transceiver?
Transceivers are radio systems that both send and receive radio signals
In a Wi-Fi LAN, do two wireless hosts usually send frames directly to one another? Explain.
Two wireless hosts on a LAN network do not send frames directly to one another, they have to transmit the frame to an access point and then the access point retransmits that frame to the destination host
Do WLANs today use licensed or unlicensed service bands?
WLANs today (all 802.11 Wi-Fi networks) use unlicensed service bands
Wi-Fi operates in which frequency range?
Wi-Fi operates between 5.25 GHz and 5.725 GHz
Are wireless LAN standards governed by OSI or TCP/IP standards? Justify your answer.
Wireless LANs are governed by OSI standards since OSI dominates at the physical and data link layers
At what layers do wireless LANs operate?
Wireless LANs operate at the physical and data link layers
is wireless radio transmission usually described in terms of wavelength or frequency?
Wireless radio transmission is usually described in terms of frequency
Do we use the two terms interchangeably? (802.11 and Wi-Fi)
Yes, we use the terms Wi-Fi and 802.11 interchangeably
1. A) How many bits are there in an Ipv4 mask? B) What do the 1s in an Ipv4 network mask correspond to in Ipv4 addresses? C) What do the 1s in an Ipv4 subnet mask correspond to in Ipv4? Think carefully! D) When a network mask is applied to any Ipv4 address on the network, what is the result?
a) 32 bits b) In a network mask, the 1s correspond to the network part, the remaining parts are 0s c) In a subnet mask, the 1s correspond to both the network part and the subnet part d) ???????? (pg 262-263)
Compare the reated speeds of 802.11n and 802.11ac B) Compare the market status of 802.11n and 802.11ac C) If you need an access point providing 3 Gbps service, what choice do you have?
a) 802.11n products deliver speeds of 100 Mbps to 600 Mbps. 802.11ac products deliver speeds of 433 Mbps to 6.9 Gbps b) 802.11ac dominates sales today and will soon supplant 802.11n as the dominant Wi-Fi technology c) If you need an access point providing Gbps service, you can only choose 802.11ac
1. A) What initial authentication mode does 802.1i use? (This is a trick question) B) which initial authentication mode is used for message-by-message encryption, authentication, and message integrity? (another trick question)
a) 802.1i uses both Pre-shared key mode and 802.1X mode as authentication modes. Which one is used depends on the scenario b) Both PSK and 802.1X are used for message-by-message encryption, authentication, and message integrity
1. A) How long are sequence and acknowledgment numbers? B) How many flag fields do TCP headers have? C) if the ACK bit is set, what other field must have a value
a) ???? (pg. 282-283) b) TCP headers have nine single-bit flag fields c) If the ACK bit is set, the acknowledgment field must be filled in tot indicate which message is being acknowledged
1. A) What has been holding back the adoption of Ipv6?
a) ?????(pg. 276) Organizations resisting the expensive transition from Ipv4 to Ipv6 has been holding Ipv6 back
1. A) What is a typical speed, distance, and power consumption for Bluetooth LE slaves? B) what are Bluetooth LE advertising messages? C) How do Bluetooth LE beacons differ from basic advertisement messages? D) in general, how do Bluetooth LE profiles differ from Classic Bluetooth profiles? (you will have to think about this one a little)
a) ???????? (pg. 247) b) Bluetooth LE beacons differ from basic advertising messages because masters can read the information in beacons without establishing a connections c) ??????? (pg. 247) Classic Bluetooth profiles center around one-to-one connections with other devices with Bluetooth compatibilities such as printers or input devices. Bluetooth LE profiles center around different uses such as navigational uses, sport uses, medical uses, etc.
1. A) Distinguish between application message fragmentation and packet fragmentation. B) Under what circumstances would the identification, flags, and fragment offset fields be used in IP? C) Why did we not study them in detail? D) Does Ipv6 allow packet fragmentation?
a) ???????? (pg. 274) TCP fragments application messages and sends them in individual packets. Internet Protocol deals with packet fragmentation, however, Ipv4 and Ipv6 do not fragment packets. b) ?????? (pg. 274) c) We didn't study these fields in Ipv4 and Ipv6 because they are "about as useful as the human appendix" d) Ipv6 does not allow for packet fragmentation
1. A) Why are routing tables more complex than Ethernet switching tables? Give a detailed answer.
a) ????????? (pg. 264)In Ethernet switching, there is only a single possible path between any two hosts across the network. Switches only have one possible port to send the frame back out. Routers on the other hand have many possible alternative routes between endpoints because they have many interfaces.
1. A) What is a FIN segment? B) Distinguish between four-way closes and abrupt resets. C) Why is a reset segment not acknowledged? D) What other type of segment is not acknowledged?
a) A FIN segment is a formal segment that initiates the ending of a connection b) Four-way closes have a FIN segment that initiates the ending of a connection. This FIN segment is acknowledged with an ACK segment. An abrupt reset sends an RST segment, and nothing follows after, the connection is ended immediately c) The reset segment is not acknowledged because it is usually sent when a problem is encountered during a connection, it is similar to if someone were to hang up on you on the phone, you wouldn't acknowledge this because the person on the other line wouldn't hear the acknowledgement anyways d) Pure acknowledgements are also not acknowledged
1. A) What problem is caused by the way that Ipv4 handles options?
a) A lack of required order means that each router must look at every option to see if it applies. This is time consuming.
1. A) who creates a rogue access point? B) Why can they defeat 802.11i security? C) Do employees who set up rogue access points have malicious motives?
a) A rogue access point is one that is unsecure and can easily be bypassed by a drive-by-hacker b) If a drive-by-hacker bypasses a rogue access point, they have access to a firm's internal network c) An employee who sets up a rogue access point does not usually have malicious intent. It's usually because they don't have good Wi-Fi and want to set up their own access point
1. A) Which two layers standardize Ethernet and Wi-Fi operation? B) Which two layers standardize most of the Internet's operation? C) What do IP, TCP, and UDP govern? D) What do TCP/IP supervisory protocols govern?
a) Ethernet and Wi-Fi operation are governed by Layer 1 and Layer 2 standards b) Most of the Internet is governed by Layer 3 and Layer 4 standards c) TCP, IP, and UDP govern the internet and transport layers d) Supervisory standards govern how routers and hosts on the Internet work beyond the delivery of packets
1. A) Why is handling options the way that Ipv4 does undesirable? B) Why is the approach of using optional extension headers desirable? C) What is often the only extension header that routers must consider? D) How does the last extension header before a UDP datagram indicate that the UDP datagram comes next? E) If you see 0 in the Next Header Field of a header, what will follow this header? F) Why are the terms payload and data field not synonymous?
a) Few Ipv4 packets have options, but each router must check each packet for options, and this can cost significant time, especially because many options are only relevant to the destination host b) Each extension header has a well-defined purpose. The only extension header that routers have to deal with is the Next Header Field which saves time that Ipv4 wasted c) The only extension header that routers must consider is the Next Header Field, which specifies that next extension header d) The last extension header before the UDP datagram have a Next Header Field value that corresponds to the UDP datagram e) If you see 0 in the Next Header Field, the hop-by-hop options will come next f) Data field is the content message being delivered. Payload includes everything beyond the main packet header, so it includes both extension headers and the data field
A) Why would it be nice if Wi-Fi offered a basic printing profile? B) What Bluetooth profile would you use for a game joystick, based on information in the text
a) If Wi-Fi offered a basic printing profile, you would be able to print from any BPP compliant printer without having to install a printer driver b) A game joystick is an input device, so you would use the human interface device (HID) profile
1. A) What does a router do if it receives a packet with a TTL value of 2? B) What does the next router do? C) What does the Protocol Field value tell the destination host? D) what will the destination internet process do if it sees 17 in the Data Field?
a) If the destination address does not belong to that router then it will decrease the TRTL value by 1 (to 1) b) The next router to receive this packet will discard the packet if it does not belong at that router because the TTL value will be 0 after decreasing it by 1 again c) The protocol field reveals the contents of the data field d) If the value of the data field is 17, the internet process will pass the contents of the data field to UDP because UDP has a protocol value of 17
1. A) Why does the Wi-Fi Alliance release compatibility testing profiles in waves instead of combining the entire standard's features initially? B) When someone says that an access point is a Wave 1 802.11ac device, what improvements do you expect to receive with a Wave 2 802.11ac device?
a) Including all of the features that come with a later wave of a certain standard would be very expensive or sometimes impossible to include in the initial creation of the standard. b) When someone says that an access point is a Wave 1 802.11ac device, this means that the product is probably limited to 80 MHz channels and up to three MIMO spatial streams. With a Wave 2 device, there would instead be 160 MHz channels and a fourth antenna to give four MIMO spatial streams. This will bump the data stream from 1.3 Gbps to about 2.6 Gbps
1. A) What is the main problem with Ipv4 that Ipv6 was created to solve? B) How does Ipv6 solve this problem
a) Ipv4's main problem was the lack of number of addresses available (4.3 * 10^9) b) Ipv6 solves this problem by adding way more potential addresses (3.4 * 10^38)
1. A) Why are Ipv6 addresses simplified? B) Why must simplification rules be followed precisely? C) are simplified Ipv6 addresses written in uppercase or lowercase letters? D) are simplified Ipv6 addresses written with decimal or hexadecimal symbols? E) How many symbols are there in a field? F) how many bits are there in a field? G) How are fields separated? H) How many fields are there in an Ipv6 address?
a) Ipv6 addresses are simplified because it is not natural for the human eye to register patterns in a series of 128 1s and 0s b) Simplification rules must be followed precisely in order for the computer to understand exactly what the Ipv6 addresses is c) Simplified Ipv6 addresses are written in lowercase letters d) Simplified Ipv6 addresses are written in hexadecimal symbols e) There are 4 symbols in a field f) There are 16 bits in a field (each letter or 0 represents 4 bits) g) Fields are separated by a colon (:) h) There are 8 fields in an Ipv6 address
How is the access point used in Wi-Fi Direct?
a) No access point is involved in Wi-Fi Direct
1. A) Do public hot spots protect your transmissions? B) What type of attack did Ms. Davies use? C) how long did it take her to hack the connection, including reading the tutorial? D) How can a drive-by hacker defeat a site's border firewall?
a) Public hot spots do not protect your transmissions b) Ms. Davies used a man-in-the-middle attack c) It took Ms. Davies 10 minutes and 54 seconds to hack the connection d) If a drive-by-hacker connects to an unsecure access point, then the hacker can communicate with any hosts within the site without going through the border firewall
1. A) what is roaming in 802.11?
a) Roaming is when a device enters and leaves the ranges of multiple access points in the same network
1. A) How might a security administrator use SNMP Set commands to access points? B) How does centralized management provide for the detection of rogue access points? C) Comment on the cost of central access point management
a) SNMP Set commands can be used to adjust access points in the network to mitigate problems. With SNMP Set commands, an administrator can increase power, decrease power, switch channels, or make other changes to access points b) SNMP Trap commands indicate abnormal error rates, the detection of rogue access points, or disassociate messages that break connections c) While Central Access Points Management is expensive, the net savings from it in the long run can be significant which makes it a smart investment
1. A) Why can a TCP handle long ap[plication messages? B) Why can UDP not handle long application messages? C) What is the maximum application message size when UDP is used at the transport layer?
a) TCP can handle long application messages because it has the ability to fragment long messages. b) UDP cannot handle long application messages because it does not have the ability to fragment long messages. c) The maximum application message size when UDP is used at the transport layer is 216 bits or 65,536 octets
1. A) What cryptographic protections does 802.11i provide? B) How is this protection limited? C) Distinguish between link security and end-to-end security. D) What does the Wi-Fi- Alliance call 802.11i? E) When offered the choice when you are configuring a wireless access point, which WLAN security standard should you choose?
a) The cryptographic protections provided by 802.11i include initial authentication plus message-by-message confidentiality, integrity, and authentication b) ?????? pg 226 c) Link security is protection between the wireless clint and the wireless access point. End-to-end security is protection from the wireless client all the way to the server on the wired LAN d) The Wi-Fi Alliance calls 802.11i the WPA2 e) When offered the choice for configuring a wireless access point, you should use 802.11i/WPA2
1. A) What is the main promise of 802.11ax over 802.11ac? B) Why is the 60 GHz unlicensed band attractive? C) What problems does it pose for Wi-Fi? D) How is 802.11ay likely to be better than 802.11ad?
a) The main promise of 802.11 is to increase density (the number of hosts per access point). The 802.11ax standard promises to serve four times as many hosts per access point than 802.11ac. b) ????? (maybe that it has 14 GHz of total bandwidth) c) The 60 GHz band is in a range of frequency that has high absorptive attenuation d) 802.11ad does not offer MIMO or other advances. 802.11ad provides 7 Gbps of speed. On the other hand, 802.11ay should bump speed to 20 or 30 Gbps and be able to travel much farther distances. 802.11ay will also have MU-MIMO which can direct energy with beamforming
1. A) What is the main version of the Internet Protocol in use today? B) Which field can be used to specify quality of service? C) How can the ECN Field be used?
a) The main version of internet protocol used today is the Internet Protocol Version 4 (Ipv4) b) The Differentiated Services Control Point Field can be used for priority or other quality of service purposes c) The Explicit Congestion Notification (ECN) Field can be used to reduce the transmission frequency between a pair of hosts to cope with congestion in the transmission system between them.
A) If you triple channel bandwidth in a service band, what happens to the number of channels in a service band?
a) The number of channels decreases by a factor of 3X
1. A) How do the Version Number Fields in Ipv4 and Ipv6 differ? B) What is the general purpose of the Diffserv subfield? C) of the Flow Label Field? D) in Ipv6, how can the receiver tell the length of the packet? E) Does the Payload Length Field include the lengths of any extension headers in the packet? F) How is the Hop Limit Fields used? G) Does Ipv6 have a header checksum field? H) what is the consequence of this?
a) The version number value in Ipv4 is 0100 (four). The version number value for Ipv6 is 0110 (six) b) The Differentiated Services (diffserv) subfield specifies whether a particular packet should be given either best-effort service, high-priority low-latency service, or some other type of service c) The Flow Label Field indicates that the packet is a member of a particular flow. The router has rules that apply to every packet in the flow d) In Ipv6, the receiver can tell the length of the packet by looking at the Payload Length Field, which gives the length of everything beyond the 40-octet main packet header e) The Payload Length Field includes both extension headers and the data field f) The Hop Limit Field is similar to the Ipv4 Time to Live field. It has a value that is decremented by 1 for each router hop it does. Once the value hits zero, the packet is discarded g) Ipv6 does not have a header checksum field h) Ipv6 does not have a header checksum field because it was proven to be irrelevant and an extra cost. Originally, Ipv4 had this field to check for packet errors because it was believed that errors in packets affected the internet in a negative way. This was proven to not be true to the header checksum field was done away with in Ipv6
1. A) How does MIMO use spatial streams to increase transmission speed? B) What is the main benefit of MIMO? C) what is its other benefit?
a) With multiple spatial streams, access points and hosts can transmit multiple message in the same channel without interference. The messages are slightly delayed and they are able to be separated. Multiple messages at once allows for greater transmission speed. b) The main benefit of MIMO is increasing transmission speed c) The other benefit of MIMO is increasing transmission range which also reduces equipment costs because less is required
A) What kind of network is Zigbee used for? B) Compare the roles of Zigbee controllers, Zigbee end devices, and Zigbee routers. In what radio bands does Zigbee operate? C) What other ad hoc networking protocol is widely used? D) In what radio band or bands does it operate?
a) Zigbee is used for ad-hoc wireless networks b) Zigbee controllers are what coordinate the network. It is also the gateway to the internet. Zigbee end devices are IoT devices such as light switches, light bulbs, door locks, and televisions. Zigbee routers allow Zigbee networks to expand larger distances than what a Zigbee controller would permit alone c) Z-wave is another ad-hoc network used frequently d) Zigbee operates in the 2.4 GHz unlicensed band and the 800/900 MHz unlicensed band. Z-Wave only operates in the 800/900 MHz unlicensed band.
B) What characteristics do all access points in a corporate network share?
b) ?????
B) Describe the steps that occur when the server transmits a packet back to the wireless client.
b) When the server replies, the wireless access point receives the 802.3 frame, removes the packet from the Ethernet frame, and forwards the packet to the wireless host in a Wi-Fi frame
C) Over what transmission system do access points communicate with each other to accomplish roaming?
c) Access points communicate over a distribution system to accomplish roaming. All access points in this distribution system have the same SSID
D) Distinguish between a BSS, an ESS, and an SSID.
d) BSS - Basic service set. A BSS is an access point and its wireless host ESS - Extended service set. A ESS is a group of BSSs with the same SSID that connects via a distribution system. SSID - Service set ID. A SSID identifies an access point
if you quadruple propagation distance, how much will signal intensity change at the receiver?
If you quadruple propagation distance (*4), signal intensity will be (4*4 = 16) 1/16th of its current strength
if you triple channel bandwidth, what happens to the number of channels in a service band? (The answer is not directly in the text).
If you triple the channel bandwidth, the number of channels will increase by a factor of 3
1. A) In figure 8-11, how will a router test whether Row 3 matches the Ipv4 address 60.168.6.7? Show the calculations in the format given in Figure 8-12 B) is the row a match? C) why is the last row called the default row? D) why must a router look at all rows in a routing table? E) which rows in Figure 8-11 match 172.30.17.6 (Don't forget the default row) Show you calculations for rows that match F) which rows match 60.168.7.32? Show you calculations for rows that match G) which rows in Figure 8-11 match 128.171.17.13 (Show you calculations for rows that match)
9 ch. 8
in 802.11 Wi-Fi networks, can simple installation rules usually reduce propagation effects to nonissues?
In 802.11 Wi-Fi networks, simple installation rules CANNOT reduce propagation effects in wireless transmission because radio signals are unpredictable and can be effected by obstacles in the signals path
Contrast inverse square law attenuation and absorptive attenuation.
Inverse square law attenuation is when the distance of a signal is increased, the strength of the signal is decreased by a factor that is 4 times the change in distance. Absorptive attenuation, in contrast, is the decrease in strength of a signal from obstructions in the environment such as rain, hills, dense walls, etc.
in radio, how can you send multiple signals without the signals interfering with one another?
Multiple signals can be sent without interfering with each other in radio because the signals are in different channels and therefore different ranges of the frequency spectrum
Why is large channel bandwidth desirable?
Large channel bandwidth is desirable because it carries data very quickly compared to small bandwidth
distinguish between omnidirectional and dish antennas in terms of operation. under what circumstances would you use an omnidirectional antenna? under what circumstances would you use a dish antenna? what type of antenna normally is used in WLANS? Why?
Omnidirectional) Transmits and receives signals from all directions Dish) Transmits and receives signals in one particular direction Omnidirectional) Optimal for short distances such as on a wireless LAN or cellular telephone network Dish) Optimal for long distance travel even though it requires the same amount of energy as Omnidirectional transmission. Can also pick up weaker signals than Omni can.
what is the most serious propagation problem in WLANs?
The most serious propagation problem is multipath interference which is when multiple signals collide and cancel each other out.
are the set of frequencies used for police communication in a city channels or a service band? Explain.
The set of frequencies used for police communication are in their own service bands. Within this service band there are different channels
What spread spectrum transmission method dominates today?
The spread spectrum transmission method that dominates today is orthogonal Frequency Division Multiplexing (OFDM)
1. A) For what use scenario was 802.11i PSK mode created? B) For what use scenario was 802.11i's 802.1X mode created? C) Does the choice of initial authentication mode change how other phases of 802.11i work?
a) 802.11i PSK was created for residential use or businesses with only a single access point b) 802.1X was created for commercial use or enterprises with many access points c) No, these modes are only for initial connection with a server and client. The ongoing message-to-message protection is completely separate
1. A) What is a PAN? (Do not just spell out the abbreviation) B) Compare the relative benefits of the two types of Classic Bluetooth C) Why would you not want to use high-speed Bluetooth all the time? D) What is the benefit of Bluetooth Low Energy? E) What type of battery do very small Bluetooth LE devices require, and why is this important? F) why do small IoT devices only implement Bluetooth LE?
a) A PAN is a personal area network which is a small group of devices in a communication bubble around a person's body or a single desk. It is essentially a cable replacement technology b) The two types of classic Bluetooth are: Enhanced Data Rate Bluetooth and High-Speed Bluetooth. Enhanced Data Rate offers good performance at modest power and High-Speed offers brief high-speed transfers at modest power c) You would not want to use high-speed Bluetooth all the time because it drains battery life rapidly d) While Bluetooth Low Energy is low-speed, it is very low cost for its infrequent communication abilities e) Small Bluetooth LE devices require small coin batteries. These batteries are not rechargeable and should last a very long time. In order to last a long time, the power usage should be low and infrequent, which Bluetooth LE offers. f) Small IoT devices only implement Bluetooth LE because they usually only have a coin battery. Using traditional Bluetooth would quickly decrease the life span of the battery so Bluetooth LE helps sustain battery life as long as possible
1. A) Connecting different networks is the main job of what type of router? B) what type of router connects different subnets
a) A border routers main job is to connect different networks b) An internal routers main job is to connect different subnets
1. A) In a routing table, what does a row represents? B) Do Ethernet switches have a row for each individual Ethernet address? C) Do routers have a row for each individual Ipv4 address? D) What is the advantage of the answer to the previous subparts of this question?
a) A row represents a range of Ipv4 addresses b) Ethernet switches have a row for each individual Ethernet address c) Routers do not have a row for each individual Ipv4 address. A row represents a group of Ipv4 addresses d) With each row representing a group of Ipv4 addresses, this means that a router needs many fewer rows than an Ethernet switch would need for the same number of addresses
1. A) What kind of physical device is an evil twin access point? B) what does the evil twin do after initial association when the victim client transmits? C) distinguish between evil twin access points and rogue access points (the answer is not explicitly in the text) D) how are VPNs able to defeat evil twin attacks? Explain in detail E) How can you tell if your client computer has succumbed to an evil twin attack? why is this important?
a) An evil twin is actually a laptop with software that mimics an access point b) When the host transmits a frame, the host first encrypts their message with key Client-ET. The evil twin receives this message, decrypts it, and can read the messages clearly. c) Evil twin access points are outside hackers that use software to mimic an access point in order to eavesdrop on clients within a network. Evil twins are an example of a man-in-the-middle attack. Rogue access points are weak access points within a network that are easily hack-able because they have poor security. d) VPNs add an extra layer of encryption which make it extremely difficult for evil twins to intercept transmission. e) ????????? pg. 233-235 (you cant tell if you've succumbed to an evil twin attack)
1. A) What is beamforming? B) What benefits can it bring? C) Distinguish between MIMO and multiuser MIMO (MU-MIMO)
a) Beamforming is the use of multiple antennas to focus a signal in a particular direction rapidly (towards a host). b) Beamforming allows signals to be stronger. This in turn allows radios to operate at lower power and send signals farther. Beamforming also allows multiuser MIMO which eliminates the time a device may have to wait before transmitting because the access point is communicating with multiple devices simultaneously c) ??????? pg 207 of textbook
1. A) what does it mean that Bluetooth uses one-to-one operation? B) Is this still true if a master communicates with four slaves simultaneously? C) Can a Bluetooth master have multiple slaves? D) Can a Bluetooth slave have two masters? E) Can a Bluetooth device be both a master and a slave simultaneously
a) Bluetooth always uses point-to-point communication between a pair of devices b) While a master can have up to seven slaves simultaneously, each connection is still a one-to-one connection c) A Bluetooth master can have up to seven slaves d) A Bluetooth slave can have up to seven masters e) A Bluetooth device can be both a master and slave simultaneously
1. A) What does CS mean? B) How is carrier sensing used in multiple access? C) Why is CA desirable? D) Does a frame's receiver transmit an ACK immediately or after a random delay? E) Is CSMA/CA+ACK reliable or unreliable? F) Why was 802.11 made reliable? G) is CSMA/CA+ACK efficient
a) CS stands for carrier sense. This means that this media access control listens to traffic in the network and only allows one transmission to happen at a time to avoid collisions between signals b) Answered in a) c) Collision avoidance is desirable because without it, signals would cancel each other out and never reach the receiver d) ACKs are transmitted immediately transmitted when a message is sent to the receiver e) CSMA/CA+ACK is reliable f) ???????? g) CSMA/CA+ACK is not efficient because the delays that assure one signal is transmitted waste valuable time
1. A) A mask has eight 1s, followed by 0s. Express this mask in dotted decimal notation. B) Express this mask in prefix notation. C) In prefix notation, a mask is /16. Express this mask in dotted decimal notation. D) Express the mask /18 in dotted decimal notation. (you will need a calculator for this.)
a) Dotted decimal notation: 255.0.0.0 b) Prefix notation: /8 c) Dotted decimal notation: 255.255.0.0 d) Dotted decimal notation: 255.255.192.0
1. A) Describe the process by which access point locations are determined B) when must firms do site surveys to give users good service?
a) First, access point service strength is determined so that an appropriate radius can match the building. Next, site surveys are conducted to see where dead spots and other issues are. Access points are placed in order to provide good service to all areas of the building and so access point interference is minimized b) Site surveys should be conducted frequently. As objects such as desks or furniture within a building change, new dead spots and places of poor service can be created. Site surveys will assure these areas are accounted for and access points can be put in new locations
A) Why is a short transmission range not a protection against eavesdroppers? B) Describe the state of cryptographic security for new transmission standards. C) Why is device theft or loss a serious risk?
a) Hackers can have antennas that can travel very far and pick up signals from short range devices such as near field communication devices b) Many new transmission standards do not have cryptological security (NFCs) c) Device theft or loss is a serious risk because many devices are only secured by a short PIN. If people break this PIN and access the device, not only can they access that individual's private data but they can also access corporate sensitive information.
1. A) What should a router do if it receives several packets going to the same destination Ipv4 address? B) How would decision caching speed the routing decision for packets after the first one? C) Why is decision caching dangerous?
a) If a router receives several packets going to the same destination Ipv4 address it should use either standard routing (go through the 3-step process to see which row in the routing table is the best match and send the packet through that interface) or decision caching (skipping the 3 steps) b) Decision caching would speed the routing decision process because if the destination address is the same, the router does not have to go through the 3-step process repeatedly because it knows where to send the packet already c) Decision caching is dangerous because a cached decision that is used for too long will result in non-optimal routing of even routes that will not work and that will effectively send packets into a black hole
1. All wireless hosts and the access point that serves them transmit on the same channel. A) what problem does this cause? B) How does media access control (MAC) address this problem? C) does media access control apply to wireless hosts, access points, or both? D) Can a wireless access point and one of the wireless clients in its BSS transmit simultaneously?
a) If the signals transmit at the same time, their signals will collide and become unreadable b) MAC governs when hosts and access points may transmit so that collisions are avoided c) MAC applies to both wireless hosts and access points d) Only one device can transmit at a time. Wireless access points and wireless clients cannot transmit simultaneously
1. A) What are interfaces? B) Explain the network adage "Switch where you can; route where you must."
a) Interfaces are what provide connectivity to the router. They have a parallel function to ports on switches b) The adage "switch where you can; route where you must" is phrased this way because when routers receive packets, the process of this packet coming in is much more complex than frames coming in to switches.
A) Why is low speed and short distance good in the Internet of Things? B) Is there a single dominant IoT communication standard?
a) Low speed and short distance is ideal for IoT because fast and far communication drains battery life. This is especially true for devices that use coin batteries which are supposed to last for months or even years b) There are many IoT communications standards, however not a dominant one. For IoT devices with coin batteries, standards that require the least amount of energy are suitable.
1. A) Contrast the use scenarios for initial authentication in PSK mode and 802.1X mode B) which initial authentication mode or modes of 802.11i authentication use(s) a central authentication server? C) What does the Wi-Fi Alliance call this 802.1i initial authentication mode D) in 802.1X operation, what device acts as the authenticator in Wi-Fi? E) In 802.1X, which is the verifier?
a) PSK is used in the residential use scenario or in small businesses with only one access point. In PSK mode, the user just needs to know the pre-shared key for authentication. 802.1X mode (or enterprise mode) is only used in enterprises with many access points. In this mode, the client server (or supplicant) must request access with its credentials and be granted access from the authentication server through the access point. b) 802.1X or enterprise mode uses a central authentication server c) 802.1X is also called enterprise mode d) In 802.1X, the access point acts as the authenticator in Wi-Fi e) In 802.1X, the central authentication server is the verifier because it compares the supplicant credentials to the authentication database
1. A) Describe RTS/CTS B) Is CSMA/CA+ACK required or optional? C) is RTS/CTS required or optional? D) which is more efficient, RTS/CTS or CSMA/CA+ACK? E) When does it make sense to use RTS/CTS?
a) RTS/CTS is an optional protocol that prevents multiple hosts from transmitting messages at the same time. In this protocol, the host that wishes to transmit sends a Request-to-Send message (RTS) to an access point. The access point then broadcasts a Clear-to-Send message (CTS) that allows the requesting host to transmit. All other hosts must wait until the receiving host has transmitted in order for further transmitting to proceed. b) CSMA/CA+ACK is required c) RTS/CTS is optional d) CSMA/CA+ACK is more efficient e) It makes sense to use RTS/CTS when two wireless clients can both hear an access point but cannot hear each other. RTS/CTS prevents these two clients form transmitting at the same time
1. A) For what use scenario was 802.11i PSK mode created B) What must a user know to authenticate his or her device to the access point? C) In what ways is the pairwise session key the user receives after authentication different from the PSK? D) What three operational security threats must PSK users consider? E) Why is this risk probably acceptable for the PSK use scenario? (The answer is not in the text) F) How long must passphrases be to generate strong pre-shared keys?
a) The 802.11i PSK mode was created for residential use or businesses with one access point b) In order the authenticate a device to the access point, the user must know the passcode/passphrase c) The pairwise session key is only good for a single communication session. Each time a new session is started a new pairwise session key will be used d) Three operational security threats that PSK users must be aware of are: 1) sharing the authentication code with others outside of the company. 2) not changing the passcode after someone has left the company. 3) creating a weak passcode that can easily be broken e) This risk is probably acceptable because the PSK mode is meant for residential use or small businesses with only one access point. This means that there are only a couple people using the access point and the chances of someone sharing the passcode are slim compared to a large corporation with many people. f) To generate a strong pre-shared key, the passphrase should be at least 20 characters long
1. A) Why must an access point remove an arriving packet from the frame and place the packet in a different frame when it sends the packet back out?
a) The packet must be put into an 802.11 frame. 802.11 frames are much more complex than 802.3 Ethernet frames. Much of this complexity is needed to counter wireless propagation problems
1. A) What are the three parts of an IPv4 address? B) How long is each part? C) What is the total length of an Ipv4 address? D) in the Ipv4 address, 10.11.13.13, what is the network part? E) if you see an Ipv4 address, what do you know for certain
a) The three parts of Ipv4 addresses are: Network parts, subnet parts, and host parts b) Each part has a variable length, not a set length c) The total length of Ipv4 addresses is 32 bits d) In the example Ipv4 address 10.11.13.13, you can't tell what the network part is because each part has a variable length e) If you see an Ipv4 address, the only thing you know for certain is that it is 32 bits long
A) When two devices communicate using NFC, how close must they be? B) How does near field communication differ from normal radio communication? C) Passive RFID chips have no batteries. How can they transmit when queried? D) What is the state of NFC standards?
a) When two devices communicate using NFC, they must be just a few inches away from each other b) Near field does not propagate away from the antenna. Instead it pulses outward a short distance and then is reabsorbed into the antenna c) Since they do not have batteries, RFID circuits use the power of the near field to modulate the near field to send information d) NFC standards are not concrete yet because it is a rapidly changing market
1. A) You are using an access point with a rated speed of 4 Gbps. Why will experience much less speed. B) What will happen to your speed as you move away from the access point?
a) You will experience much less speed because aggregate throughput is always less than the rated throughput due to number of devices on the network and distance from the access point b) As you move away from the access point, aggregate throughput will also go down