Reading...
Play button
Play button
Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
281 Cards in this Set
- Front
- Back
|
Define frequency spectrum...
|
all of the possible frequencies from 0 Hz to infinity
|
|
|
Define service bands...
|
divides the frequency spectrum, and dedicates these parts of the frequency spectrum to specific services
|
|
|
Define Channels...
|
the smaller frequency ranges which are portions of a service band
|
|
|
In radio, how can you send multiple signals without the signals interfering with one another?
|
a different signal can be sent in each channel because signals in different channels do not interfere with one another
|
|
|
Does a signal usually travel over a single frequency or over a range of frequencies?
|
single
|
|
|
What is channel bandwidth?
|
the difference between the highest and lowest frequency in a certain channel
|
|
|
If the lowest frequency in a channel is 1.22 MHz and and the highest is 1.25 MHz, what is the channels bandwidth?
|
.03 MHz
|
|
|
Why is a large channel bandwidth desirable?
|
because the maximum possible speed is directly proportional with bandwidth
|
|
|
What do we call a system whose channels have large bandwidth?
|
broadband channels
|
|
|
Write the Shannon Equation and list what each letter is in the equation?
|
C=B*[log2(1+s/n)]
C=maximum transmission speed B=bandwidth s=signal [s/n is a fraction not decimal] n=noise |
|
|
What information does C give you?
|
the maximum possible transmission speed in the channel (bps)
|
|
|
What happens to the maximum possible propagation speed in a channel if the bandwidth is tripled while the signal to noise ratio remains the same?
|
the maximum possible transmission speed also then triples
|
|
|
Given their relative bandwidths, about how many times as much data is sent per second in television than in AM radio?
|
AM radio bandwidth= 10 kHz
Television= 6 MHz --> 1 MHz=1,000 kHz, and since data would be directly proportional to bandwidth the ratio is 6000/10=600x |
|
|
In the Shannon Equation, should S/N be entered in a simple power ratio, in decibels, or either way?
|
in a simple power ratio (P2/P1)
|
|
|
What is the dividing line between narrowband and broadband speeds?
|
200 kBps
|
|
|
What is the Golden Zone in commercial mobile radio transmission?
|
high MHz to low GHz (approximately 800 MHz-6 GHz)
|
|
|
What is the clear line of sight limitation?
|
there cannot be any object between the sender or receiver (unobstructed direct path)
|
|
|
Do WLANs today use licensed or unlicensed bands?
|
unlicensed
|
|
|
What is the advantage of using unlicensed bands?
|
government approval does not have to be granted, access points can be shut off or moved as needed
|
|
|
What is the disadvantage of using unlicensed bands?
|
users of unlicensed bands must tolerate interference from other users
|
|
|
In what 2 unlicensed bands does 802.11 operate?
|
2.4 GHz and 5 GHz
|
|
|
How wide are 802.11 channels usually?
|
20 MHz wide
|
|
|
Which licensed band is defined the same way in most countries around the world?
|
2.4 GHz
|
|
|
Does the 2.4 GHz band or the 5 GHz band allow longer propagation distances for a given level of power?
|
2.4 GHz band because in the 5 GHz band the attenuates more
|
|
|
How many non overlapping channels does the 2.4 GHz band support?
|
3 (channels 1,6,11) without interference BUT 4 (20) MHz channels in the 83.5 MHz band
|
|
|
Why is the number of non overlapping channels that can be used important?
|
it tells you how many channels access points can use without experiencing mutual channel interference
|
|
|
How many non overlapping channels does the 5 GHz channel support?
|
11-24 non overlapping channels
|
|
|
In unlicensed bands what kind of transmission method is required by regulators?
|
spread spectrum transmission
|
|
|
What is the benefit of spread spectrum transmission for business communications?
|
using spread spectrum transmission reduces propagation problems- especially interference
|
|
|
Is spread spectrum transmission done for security reasons in commercial WLANs?
|
NO
|
|
|
In a normal radio operation, how does channel bandwidth usually relate to the bandwidth required to transmit a data stream of a given speed?
|
the channel bandwidth matches the bandwidth required for a given speed
|
|
|
How does this change in spread spectrum transmission?
|
in spread spectrum transmission bandwidth the channel bandwidth is much wider than what is needed, this is done to spread the signal over a range of frequencies which decreases the occurrence of interference
|
|
|
Describe FHSS...
|
uses only the bandwidth required by the signal, but hops frequently within the spread spectrum channel
|
|
|
What is FHSS's limitation?
|
useful for only relatively slow speeds (us to 2 Mbps)
|
|
|
For what WLAN standard is FHSS used?
|
no WLAN standards use FHSS but Bluetooth an alternative wireless technology uses FHSS
|
|
|
What spread spectrum transmission is used for 54 MBps 802.11g WLANs?
|
OFDM
|
|
|
Describe OFDM...
|
Orthogonal Frequency Division Multiplexing. each broadband channel is divided into many smaller sub-channels, and parts of the frame are transmitted in each sub-carrier. (data is sent redundantly across the sub-carriers)
|
|
|
Describe the elements in a typical 802.11 LAN today?
|
each mobile host must have a wireless NIC(network interface card), a wireless access point and the rest of the wired LAN network
|
|
|
Why is wired LAN still needed if you have wireless LAN?
|
because Wireless LAN does not replace wired LAN rather it is an extension of the network, the wired LAN is required to connect to the server and/or router
|
|
|
Is a wireless access point a bridge or a router?
|
a bridge because it connects the wireless hosts to the wired network, Bridges (by definition) connect 2 different types of LANS
|
|
|
Why must the access point remove the arriving packet from the frame in which the packet arrives and place the packet in a different frame when it sends the packet back off?
|
the packet travels in a 802.11 frame over the wireless network where as the packet travels in the 802.3 frame over the wired network (data link layer frame format)
|
|
|
What is a handoff in 802.11?
|
in wireless LANS, a change in access points where a user moves to another location... "handed off if the sender is too far from the access point its intended for"
|
|
|
What is the relationship between handoffs and roaming in WLANs?
|
the ability to use handoffs is roaming
|
|
|
When there is an access point and several wireless hosts, why may only one transmit at a time?
|
because of MAC(media access control) which govern when hosts and access points may transmit to avoid collision
|
|
|
Describe CSMA/CA+ACK...
|
carrier sense multiple access with collision avoidance. this prevents a host from transmitting if it hears traffic
-if there is no traffic collision avoidance comes into play - if > critical value than then will transmit immediately if not then will wait |
|
|
Is CSMA/CA+ACK reliable?
|
YES, because when a host receives a frame from an access point it immediately sends an acknowledgment frame, a frame that is not acknowledged is retransmitted
|
|
|
Why is CSMA/CA+ACK inefficient?
|
because waiting before transmission and sending ACKs wastes valuable time
|
|
|
Distinguish between rated speed, aggregate throughput, and individual throughput?
|
rated speed: the official speed of a technology (usually misleading)
aggregate throughput: throughput shared by multiple users individual throughput: the actual speed a single user receives |
|
|
Why does transmission speed drop as a computer moves farther from an access point?
|
as a computer moves farther away from access points, both the computer and the access point will both switch to lower speed mode to reduce transmission errors
|
|
|
What are the rated speeds for 802.11, 802.11a, and 802.11b?
|
(2 Mbps, 54 Mbps, and 11 Mbps) respectively
|
|
|
In what band do 802.11, 802.11a, and 802.11b operate in?
|
2.4 GHz for 802.11 and 802.11b but 5 GHz band for the 802.11a
|
|
|
Why was 802.11a not popular when it first appeared?
|
because it was so expensive because of the higher rated speed and because it operated in the 5 GHz band
|
|
|
What was the first widely used 802.11 standard?
|
802.11
|
|
|
What was the main advantage of 802.11b over 802.11a?
|
because it operated in the 2.4 GHz band so equipment was relatively less expensive and because 802.11b used DSSS technology
|
|
|
What 802.11 standard has the largest market share today?
|
802.11g which operates in the 2.4 GHz unlicensed band, has a rated speed of 54 MBps, and uses OFDM (which now isn't that much more than DSSS)
|
|
|
How is 802.11g better than 802.11b?
|
802.11g is a seamless upgrade from 802.11b except the rated speed of 802.11g is 54 Mbps compared to 802.11b's 11 Mbps
|
|
|
Can you use 802.11b hosts with an 802.11g access point?
|
yes because they operate in the same 2.4 GHz band
|
|
|
Is there a speed penalty for using 802.11b hosts with an 802.11g access point?
|
no, if you have an 802.11g access point you can serve both 802.11g and b wireless hosts
|
|
|
What disadvantage does 802.11a have compared with 802.11g?
|
802.11g works in the 2.4 GHz band instead of the 5GHz band which 902.11a works in which is much cheaper and allows better propagation characteristics
|
|
|
Is 802.11a backward compatible with 802.11b or 802.11g?
|
neither, 802.11b and 802.11g are backward compatible with each other
|
|
|
What are the 2 benefits of MIMO?
|
1. increase throughput(transmission speed users actually get)
2. substantially increases propagation distances |
|
|
What will be 802.11n's rated speed?
|
100-300 Mbps
|
|
|
In what two ways does 802.11n increase throughput?
|
using more than 1 antenna and more than 1 radio signal throughput is increased
|
|
|
How does MIMO work?
|
multiple input/multiple output: sends two or more radio signals in the same channel between two or more different antennas on access points and wireless NICs
|
|
|
What is the risk in buying 802.11n equipment?
|
being locked into a single vendor, and financial risks of being out of date once the final standard is ratified
|
|
|
For what unlicensed radio band or bands will the 802.11n work?
|
it will work in the 2.4 and 5 GHz bands
|
|
|
What are the two attractions of 5GHz 802.11n operation?
|
because in the 5GHz channels there can be multiple access points operating on different channels which wouldn't interfere allowing for faster transmission speeds
|
|
|
What is the advantage of dedicating channels to VoIp service?
|
keeping it relatively unpopulated allows VoIP users to get good service because it needs very fast and steady speed
|
|
|
What is the goal of the 802.11e standard?
|
this standard would allow managers to specify a very high level of quality of service with is crucial for VoIP as well as other multimedia applications
|
|
|
Describe how mesh networking would work in 802.11 WLANs?
|
wireless access points can organize themselves into a mesh, routing frames from one to another to deliver frames to the right wireless hosts
|
|
|
What two problems would 802.11 mesh networking designers (wireless) have to overcome?
|
1. maintaining the routing tables would be expensive if access points and routers enter and leave the mesh frequently
2. it will be difficult to avoid access points near the center from being overloaded |
|
|
What benefit will smart antennas bring?
|
having multiple antennas and changing the phase of waves, an access point can theoretically direct signals toward individual hosts instead of broadcasting the signal
|
|
|
Distinguish between war driver and drive by hackers?
|
war drivers: merely discover unprotected access points, only become drive by hackers if they break in
drive by hackers: sit outside corporate premises and read network traffic, can send malicious traffic into the network |
|
|
What is an evil twin access point?
|
an access point set up outside the walls of firm, intercepts authentication credentials, then able to decrypt messages encrypt them and send them along as if they weren't there
|
|
|
What is a rogue access point?
|
unauthorized access points set up by a department or an individual, have poor security making drive by hacking easier
|
|
|
When 802.11 was created, what security protocol did it offer?
|
WEP (wired equivalent privacy), everyone using an access point uses the same key
|
|
|
How long does it take to crack WEP today?
|
only about 10 minutes
|
|
|
Who created WPA?
|
wireless protected access was created by Wi-Fi Alliance
|
|
|
What is WPA's attraction compared with 802.11i?
|
802.11e security required more memory and processing power in wireless NICs and access points so older products would not be upgradeable
|
|
|
What is WPA's disadvantage with 802.11i?
|
WPA is a subset of 802.11i or (WPA2) so it does not have as extensive security
|
|
|
What should companies do if they have access points that are not upgradeable to WPA?
|
all equipment that cannot be upgraded to WPA should be discarded
|
|
|
What is the strongest protocol for 802.11 today?
|
802.11i or more commonly known as WPA2 (as called by the Wi-Fi alliance)
|
|
|
What encryption method does 802.11i use?
|
AES-CCMP
|
|
|
What is deterring companies from converting from WPA to 802.11i?
|
reconfiguring all of the access points and wireless hosts to 802.11i would be expensive
|
|
|
In what mode of 802.11i and WPA operation is a central authentication server used?
|
802.1x uses it for consistency and speed of change
|
|
|
What does the Wi-Fi alliance call 802.1X mode?
|
enterprise mode
|
|
|
Why does 802.1x not need security between the NAS and the computer in the Ethernet?
|
because it is difficult for another person to tap the wired access line between the computer and the switch, and there are easier ways to break into a network
|
|
|
Why does 802.1x need security between the NAS and the computer in the 802.11 wireless access?
|
because the transmissions between the wireless hosts and the point are easy to intercept and mimic
|
|
|
What standard governs authentication exchanges in 802.1X?
|
EAP (extensible authentication protocol)
|
|
|
Why are EAP extensions necessary in 802.11 networks using 802.11X?
|
to secure authentication between access points and the hosts to prevent hacking
|
|
|
What are 3 security extensions to EAP?
|
Protected EAP(PEAP)
EAP-TLS, EAP-TTLS |
|
|
Which EAP security extension is favored by Microsoft?
|
PEAP
|
|
|
How does PSK mode differ from 802.1X mode?
|
Pre-shared key mode (aka personal mode): the access points and hosts begin with a shared 64 bit key.. but after authentication the wireless access point gives each user a unique key to use while on the internet
|
|
|
What is a potential weakness of PSK mode?
|
if the organization implements a weak pre-shared key the key can be crack even faster than the WEP key
|
|
|
How long should pass phrases be with PSK?
|
20 or more characters long
|
|
|
How do VPNs enhance wireless security?
|
because it implements security all the way from the host to the receiver which is independent of the transmission path (add on layer)
|
|
|
How can VLANs enhance wireless security?
|
hosts in a VLAN can only communicate with other hosts on the same VLAN, only after hosts authenticate themselves to the corporate server are they allowed to enter the broader network
|
|
|
Describe the process by which access points are selected?
|
must be done carefully for good coverage and to minimize interference between access points
|
|
|
After access points are installed provisionally what must be done next?
|
an initial site survey must be done which would discover whether there are any dead spots or any other problems
|
|
|
Why is centralized access point desirable?
|
because by managing access points remotely from a central management console, labor costs therefore are kept under control
|
|
|
What are the two technologies for remote access point management?
|
1. smart access points: add intelligence to every access point so then the central management console can communicate directly with the access points
2. WLAN switches: many access points connect with each switch which have the "intelligence" |
|
|
What functions should remote access point management systems provide?
|
they should provide continuous monitoring at all access points
|
|
|
Contrast how 802.11 and Bluetooth are likely to be used in organizations?
|
blue tooth is created for PANs (intended to connect devices for a single person) rather than LANs. in a corporation blue tooth would be used to connect say a mouse with a computer
|
|
|
What is a PAN?
|
personal are network
|
|
|
Why are blue tooth application profiles attractive?
|
blue tooth does not use access points rather it connects device to device
|
|
|
What are the speeds of blue tooth transmission today?
|
3 Mbps
|
|
|
What is the normal maximum distance for blue tooth propagation?
|
100 meters but 30-50 meters is more realistic
|
|
|
What benefits do low speeds and short distances bring?
|
this allows for a long battery life because radio transmission power is low
|
|
|
What are the blue tooth application profiles?
|
application layer standards designed to allow devices to work together automatically with little or no user intervention
|
|
|
Compare the speeds of Blue tooth, UWB, and Zigbee?
|
Bluetooth: 3Mbps
UWB: ultra wide band 480 Mbps (3m) 110 Mbps (10m) Zigbee: 250 kbps |
|
|
What technology could replace universal bar codes on products?
|
RFID
|
|
|
What is the major requirement of software defined radio?
|
this will enable a wireless device to switch between 802.11, bluetooth, zigbee and other wireless standars by switching software programs instea of having the functionality built directly into the hardware
|
|
|
What is the name of the worldwide telecommunications network?
|
Public Switched Telephone Network (PSTN)
|
|
|
Does the PSTN handle only telephone traffic? (explain)
|
No the PSTN also handle video traffic
|
|
|
What are the 4 technical elements of the PSTN?
|
1. customer premises equipment
2. Access 3. Transport 4. Signaling |
|
|
What is customer premise equipment in PSTN?
|
equipment owned by the customer i.e. (at a business site) telephone handsets, wiring, and the PBX
|
|
|
What is the purpose of a PBX in PSTN?
|
the PBX acts as the internal telephone switch, it routes internal calls between handsets at the site and to the PSTN
|
|
|
What type of wiring does business telephony use for building wiring?
|
4 pair UTP
|
|
|
What is the most expensive part of the customer premises equipment to purchase and install (PSTN)?
|
the wiring
|
|
|
What is the local loop?
|
the collective group of access lines which connect customers to the central transport core
|
|
|
What is the function of the transport core?
|
transport means transmission- taking voice signals from one users access line and delivering them to another customers access line
|
|
|
What are the two elements of the transport core (PSTN)?
|
trunk lines and switches
|
|
|
What is changing more rapidly, the access system or the transport core (explain)?
|
the transport core, because it is much more expensive to update/change the access lines and updating the transport core could potentially save the company a lot of money
|
|
|
What is signaling (PSTN)?
|
the controlling of calling
|
|
|
In telephony, distinguish between transport and signaling?
|
in the PSTN transport is the transmission of voice communication. in contrast, signaling is the process of supervising voice communication sessions
|
|
|
What are the three tiers of carriers in the PSTN?
|
1. local carriers
2. long distance domestic (within a country) 3. international |
|
|
What are the connection points between carriers called in the PSTN?
|
points of presence (POPs)
|
|
|
What is circuit switching?
|
traditionally offered by telephone companies, in which the capacity for a phone conversation is reserved on every switch and trunk line, end to end between the two subscribers
|
|
|
Why does circuit switching make sense for voice communication?
|
because voice traffic is fairly constant, about 30% of capacity of each full duplex telephone circuit is actually used
|
|
|
What does it mean that data transmission is bursty?
|
in data transmission there are short high speed bursts followed by long silences (ie when you request a web page but then sit there reading it)
|
|
|
Why is burstiness bad in circuit switching?
|
reserved capacity, which is what circuit switching offers, is extremely wasteful, only 5% of capacity is actually used
|
|
|
What are the differences between dial up and leased line circuits?
|
Dial Up: separate circuit for each call, up to 33.6 kpbs for carrying data, only 1 voice call at a time
Leased Line: permanent circuit always on, 56 kpbs-giga bit speed, sevreal calls at a time due to multiplexing |
|
|
What is multiplexing, in the context of telephone calls in leased lines?
|
multiple voice circuits are mixed together on the same line
|
|
|
What method do leased lines use to ensure that every call never gets less than the fixed amount of capacity?
|
time division multiplexing (TDM)
|
|
|
In TDM, distinguish between frames and slots?
|
frames (8,000 in a second) are divided into 24 slots
|
|
|
How are slots assigned in TDM?
|
each voice channel is assigned to a specific slot in each frame
|
|
|
Compare the 4-pair UTP wiring in corporate buildings and the UTP wiring in the residential local loop?
|
there are 3 types of wiring used, the most popular (because its already installed) is 1-pair voice grade UTP but 2-pair data grade UTP and optical fiber are also used
|
|
|
Distinguish between the UTP wiring in the residential local loop and the UTP wiring used for lower speed leased lines?
|
in residential settings one-pair voice grade is used (it has a much lower transmission quality than 4 pair UTP)
for the slowest leased lines 2 pair data grade lines are used |
|
|
What technology do the highest speed leased lines use?
|
faster than 2 Mbps optical fiber cord is used
|
|
|
What is provisioning when talking about telecommunications?
|
provision: install and set up (usually referring to wiring)
|
|
|
What is an end office switch?
|
where the access line (which runs from a company) runs to
|
|
|
Distinguish between analog and digital signals?
|
an analog signal rises and falls in intensity smoothly, with no clock cycles and no limited number of states as in digital signaling
|
|
|
What parts of the telephone system are largely digital today?
|
the PSTN transport core (this includes the switches and trunk lines) some businesses even have digitized their access lines
|
|
|
What parts of the telephone system are largely analog today?
|
on the local loop that connects residential customer to the nearest end office, the customers telephone sends and receives analog signals
|
|
|
What is the role of the codec in the end office switch?
|
the codec converts digital to analop signals and vice versa
|
|
|
When a customer signal arrive on the access line to the end office switch, does the codec perform ADC or DAC?
|
ADC or analog to digital conversion happens (also called coding)
|
|
|
Explain why bandpass filtering is done in ADC?
|
this is to limit voice bandwidth only to 4 Khz (most voice frequencies come either at or below 4Khz) and limiting it to only 4 KHz allows 5 times as many voice signals
|
|
|
Explain how the ADC generates 64 kpbs of data for voice calls when it uses PCM?
|
ADC samples the voice grade 8,000 times per second and their are 8 bits per samples = 64,000 bits per second ie 64 kpbs
|
|
|
Why do we need DACs?
|
Digital to Analog Conversion: are for converting transmissions from the digital telephone networks core to signals on the analog local loop
|
|
|
How do DACs work?
|
DAC reads each sample and it puts a signal on the local loop that has the intensity indicated for that sample
|
|
|
In cellular technology, what is a cell?
|
smaller geographical areas which divides a metropolitan are by cellular telephony
|
|
|
What is a cellsite in cellular telephony?
|
where the transceiver is in the middle of the cell, this is where mobile signals are received and send out
|
|
|
What are the two functions of the MTSO?
|
mobile telephone switching office: connects cellular customers to one another and to wired users and the MTSO also controls what happens at each of the cellsites
|
|
|
Why does cellular telephony use cells?
|
because of channel reuse: the number of channels permitted by regulators is limited and subscriber demand is heavy
|
|
|
If I use Channel 3 in a cell, can I reuse the same channel in adjacent cell with traditional cellular telephony?
|
no because there will be interference, in general the number of times you can reuse a channel is the total number of cells divided by 7
|
|
|
Can I reuse Channel 3 in adjacent cells if the cellular system uses CDMA technology?
|
code division multiple access: allows adjacent cells to transmit it adjacent cells without too much interference
|
|
|
Distinguish between handoffs and roaming in cellular telephony?
|
handoff: when a subscriber moves from one cellsite to another
roaming: if a subscriber leaves a metropolitan cellular system and goes to another city or country |
|
|
Distinguish between handoffs and roaming in cellular telephony and 802.11 wireless LANs?
|
in WLANs handoff and roaming mean the same thing
|
|
|
What is VoIP?
|
voice over internet protocol: is the transmission of telephone signals over IP routed networks (including the internet)
|
|
|
What is the promise of VoIP?
|
promises a reduction in cost because of the move from traditional circuit switching to more efficent packet switching
|
|
|
What two devices can be used by VoIP callers?
|
either a PC with multimedia hardware and VoIP software OR an IP telephone with Codec and TCP/IP functionality
|
|
|
What is the purpose of a media gateway?
|
this connects the VoIP system to the ordinary PSTN
|
|
|
Why is having a media gateway in a VoIP system important?
|
without this VoIP callers could only talk to one another
|
|
|
What are the two major protocols for VoIP signaling?
|
ISO H.323: 1st but very complex
Session Initiation Protocol: recently developed by the IETF |
|
|
Which of the two signaling protocols for VoIP signaling is growing rapidly?
|
SIP
|
|
|
Describe how SIP initiates a communication session?
|
the calling VoIP sends a SIP invite to its IP proxy server this gives the IP address of the receiver the callers SIP proxy server than send the invite to the receivers proxy server
|
|
|
What is the purpose of a VoIP codec?
|
codecs are needed to convert analog voice signals into digital voice data streams
|
|
|
Some codecs compress voice more. What do they give up in doing so for VoIP?
|
lose voice quality
|
|
|
Does a VoIP transport packet use UDP or TCP?
|
UDP because TCP would provide greater reliability it takes too long for voice conversations
|
|
|
What two problems in UDP does RTP fix for VoIP?
|
RTP adds a sequence number to ensure packets are delivered in order, and contains a time stamp which tells the receiver how the octets should be played relatively
|
|
|
List the headers and messages in a VoIP transport packet, beginning with the first packet header to arrive at the receiver?
|
Codec Byte Stream, RTP header, UDP header, IP header...
|
|
|
If a company already has a multisite PBX network installed for site-to-site voice service, what must it add for site-to-site VoIP?
|
it has to add a VoIP module to each PBX
|
|
|
Do many carriers offer VoIP services to business customers?
|
yes, carriers are beginning to offer VoIP services directly to firms
|
|
|
Can a company save more money with long distance VoIP or within the companys' site?
|
its more financially feasible to use VoIP with long distance as opposed to within the site
|
|
|
What is the main advantage of VoIP within sites?
|
it opens up the ability to create applications that integrate voice and data
|
|
|
What carriers provide VoIP services?
|
both traditional telephone carriers and "new entrants" such as cable companies offer VoIP services
|
|
|
What two concerns do corporate telecommunications staffs have about VoIP?
|
VoIP networks are likely to bring lower QoS and and significantly lower availability
|
|
|
What is the "last mile"?
|
the access line to a residential home
|
|
|
What type of access line do telephone companies already have installed to most customer premises?
|
1 pair voice grade UTP
|
|
|
What transmission medium do cable companies primarily use?
|
(coaxial cable) trunk lines are ran from the head end past homes and thinner drop cables are ran from these to the homes
|
|
|
What was the traditional division of market dominance between telephone companies and cable television companies?
|
traditionally the cable company and the phone company were not seen as competitors because they offered completely different services
|
|
|
What does a telephone modem do?
|
they receive digital signals from a computer, convert the digital signals into analog signals, and transmit the analog signals over the subscribers access line
|
|
|
Why is the telephone companies use of existing access lines important to ADSL service?
|
because it meant that the telephone company did not have to install entirely new wiring
|
|
|
In ADSL service what does the DSLAM do?
|
(at the end office switch) passes the data signals to a data network
|
|
|
Do the telephone modems tie up your telephone line when you use them to carry data? Do ADSL modems?
|
yes, no
|
|
|
In DSL what must be plugged into each telephone outlet?
|
a splitter which seperates voice and data signals
|
|
|
Why is residential DSL service called ADSL service?
|
(asymmetrical digital subscriber line) because the speed provided is different in each direction, download speed is higher than its upload speed
|
|
|
Distinguish between 2G and 3G cellular service for data transmission?
|
3G can move data faster, this changed data transmission speed from a lousy 10 kbps to 2-3 Mbps(potential)
|
|
|
What may limit 3G cellulars acceptance?
|
their cost
|
|
|
Do WiMax carriers primarily use licensed or unlicensed bands?
|
WiMax carriers can operate in both type of bands because it is primarily based on the IEEE 802.16 standard
|
|
|
What four advanced technologies does WiMax use?
|
Scalable OFDM, MIMO, adaptive antennas systems (AAS), and cellular organizations
|
|
|
How does WiMax ensure that each customer gets its fair share of transmission speed?
|
by using TDM in downstream links. TDM guarentees a time slot in each frame for each subscriber
|
|
|
What is the biggest problem for satellite access service?
|
it has relatively low speed and high costs
|
|
|
What do companies call the "triple play"?
|
offering telephone service, data access, and television in an integrated package
|
|
|
What aspect of the triple play requires a huge increase in bandwidth?
|
video
|
|
|
What technology will bring speeds of 100 Mbps or more to subscribers?
|
FTTH fiber to the home
|
|
|
What is the backhaul issue and why is it important?
|
the entire carrier backbone plant has to be able to handle the much higher speeds that customer premises guarentee
|
|
|
Is the U.S. the leader in broadband speeds?
|
we are behind many countries especially Japan and South Korea
|
|
|
What is the advantage of being a leader in broadband service?
|
also the leader in next generation applications to utilize the speed
|
|
|
How are telephony and WAN related?
|
wide area network technology is built on top of the already existing PSTN technology
|
|
|
What are the three main purposes for WANs?
|
1. to provide remote access to employees or customers at home or traveling
2. to link two or more sites within the same organization 3. provide corporate access to the internet |
|
|
What are carriers and why must they be used?
|
a transmission service company
|
|
|
How are prices and costs related in carrier WAN services?
|
because of carriers there is little relationship between the price and the cost
|
|
|
Does a company have more service options with LANs or WANs?
|
LANs
|
|
|
Are service options and prices similar around the world?
|
no pricing and service options vary widely around the world
|
|
|
Compare WAN and LAN transmission speeds... why are they different?
|
long distance communication is much more expensive per bit transmitted so companies content themselves with slower speeds (256 kbps and 50 Mbps) as compared with LANs 100 Mbps
|
|
|
Distinguish between the technologies of leased line voice networks and leased line data networks?
|
data networking using leased lines is based on the same technology used for leased line telephone networks. the main difference is that data networks use routers at each site rather than PBXs
|
|
|
What is the advantage of a full mesh leased line network?
|
this type of network is very reliable because if one site or leased line fails communication is unimpeded
|
|
|
What is the disadvantage of a full mesh leased line network?
|
it is highly expensive
|
|
|
What is the advantage of a pure hub and spoke leased line network?
|
this type of network is very inexpensive
|
|
|
What is the disadvantage of a pure hub and spoke leased line network?
|
unreliability
|
|
|
Do most leased line networks use a full mesh or a full hub and spoke topology?
|
neither, most corporations use a mixture of the two
|
|
|
A company has 3 sites (A,B,C). They form a geographical triangle. A and B need 100 Mbps of transmission capacity between them. B and C need 200 Mbps capacity between them. A and C need 300 Mbps between them. Create a hub and spoke network with A as the hub. What links will there be and how fast will they have to be?
|
there would be two connections 1 being 200 Mbps and the other being 300 Mbps
|
|
|
Below what speed are there different leased line standards in different parts of the world?
|
below 50 Mbps
|
|
|
At what speeds do the slowest leased lines run?
|
56 kbps (North America)... 64 kbps European
|
|
|
What is the exact speed of a T1line?
|
in the US it operates at 1.544 Mbps and 2.048 Mbps
|
|
|
Why are fractional T1 speeds and E1 speeds desirable?
|
provide intermediate speeds at intermediate prices
|
|
|
List common fractional T1 speeds...
|
128 kbps, 256 kbps, 384 kbps , 512 kbps or 786 kbps
|
|
|
What are the most widely used leased lines?
|
T1/E1 and fractional T1/E1
|
|
|
What leased line standards are used above 50 Mbps
|
SONET and SDH
|
|
|
What device must a company have to connect a router to a leased line?
|
CSU/DSU
|
|
|
What is the function of the CSU?
|
is designed to protect the telephone network by keeping the subscriber from sending improper signals, such as signals with voltages which are too high
|
|
|
What is the function of the DSU?
|
formats the data in a way the leased line requires
|
|
|
How do the lowest speed leased lines and DSL lines differ in terms of transmission media?
|
leased lines transmit over 2-pair data grade UTP while DSL transmits over 1 pair voice grade UTP
|
|
|
Describe HDSL and HDSL2 in terms of speed?
|
HDSL: downstream and upstream throughput=786 kbps
HDSL2: 1.544 Mbps |
|
|
Describe SHDSL in terms of speed?
|
384kbps-2.3 Mbps (downstream and upstream)
|
|
|
Which DSL service usually offer QoS guarantees?
|
all DSL services
|
|
|
Describe the physical components of PSDN technology?
|
the user needs only a leased line from a site to the PSDNs nearest access point called the point of presence
|
|
|
Do companies need leased lines if they are using PSDN?
|
yes
|
|
|
Compare leased line costs for leased line networks and PSDNs?
|
for PSDNs the overall cost would be less because there are less leased lines needed
|
|
|
Which is usually less expensive overall- leased line data networks or PSDN transmission?
|
PSDN transmission
|
|
|
What happens at eh PSDN transport core?
|
the transport core has internal switches and trunk lines which the customer does not have to be concerned with
|
|
|
Why do PSDNs tend to cost less than leased line networks?
|
it is cheaper to manage the traffic of many firms than of one firm that is why it is cheaper to use PSDN
|
|
|
For what is OAM&P an abbreviation for?
|
operation, administration, maintenance and provisioning
|
|
|
What is provisioning?
|
the supplying of service to a new customer
|
|
|
What things do SLAs guarantee?
|
QoS guarantees for throughput, availability, latency, error rate and other service conditions
|
|
|
Why would an SLA agreement guarantee maximum latency as opposed to minimum?
|
its a "no more than" policy
ex. no more than25 milliseconds 99.999 percent of the time |
|
|
Why are virtual circuits used?
|
to determine the best possible path for transmission before the transmission begins
|
|
|
With virtual circuits, on what does a switch base its forwarding decision when a frame arrives?
|
according to the virtual circuit number in the frames header
|
|
|
Do PSDN frames have destination addresses or virtual circuit numbers int their header?
|
virtual circuit numbers
|
|
|
What is the name of the frame relay circuit number?
|
Data Link Control Identifier (DLCI)
|
|
|
How long is the DLCI usually?
|
10 bits long
|
|
|
How many virtual circuits does this number of bits allow?
|
512, 2 to the 10th power
|
|
|
List the technical components in the Frame Relay network?
|
access devices, access lines, ports at POPs
|
|
|
Briefly explain the purpose of each of the technical components of the Frame Relay network?
|
Access Devices: converts between internal and frame relay
Access Lines: the physical connection POP: contains the switch that contains multiple ports of different speeds |
|
|
Which usually is the most expensive component in the Frame Relay pricing?
|
port speed
|
|
|
What is managed relay Frame Relay service?
|
offered by vendors which include the Frame Relay service plus some (managed day to day traffic, fix problems, and manage corporate devices)
|
|
|
Compare Frame Relay and ATM speed ranges?
|
Frame relay operates at 56 kbps while ATM operates from 1 Mbps up to several Gigabits per second
|
|
|
Are frame relay and ATM competitors?
|
no because most carriers provide both
|
|
|
How long are ATM headers and payloads?
|
5 octets header
|
|
|
Why does ATM use short frames?
|
short length minimizes latency
|
|
|
Compare what ATM has to offer to voice and data service?
|
ATM supports Qos for voice but not for data because data gets what ever is left over
|
|
|
Why does ATM have strong management tools?
|
because ATM was created originally to become the transport mechanism for the worldwide PSTN
|
|
|
Why is ATM's sophistication beneficial?
|
because it already has a set of management protocols established
|
|
|
Why may ATM usage grow in the future?
|
as corporate demands for WAN speeds increase the need for ATM over frame relay will develop
|
|
|
What is metropolitan area ethernet?
|
MAN: spans to a single urban area including subburbs
|
|
|
Distinguish between e-line and e-lan service?
|
e-line: provide point to point connections such as leased lines do
e-Lan: link multiple sites simultaneously |
|
|
Why is metro Ethernet attractive?
|
low cost, high speeds, familiar technology, rapid provisioning
|
|
|
Why are companies hesitant to create large metro Ethernet MANs?
|
because metro Ethernet has not completely developed the QoS and traffic management tools needed to offer true carrier class service
|
|
|
In terms of ease of use, why is IP WAN transmission attractive compared with Layer 2 WAN service?
|
because frame relay and other WAN protocols usually are relatively unfamiliar to corporate networks
|
|
|
What are the two ways that companies can get IP WAN service?
|
1. simply use the internet
2. IP carrier network |
|
|
Which of these approaches generally is used only for intra company site to site communication?
|
IP carrier network
|
|
|
What is the big attraction for data transmission?
|
IP carrier network because of security and qos can be provided
|
|
|
Are IP carrier networks more expensive or less expensive than transmission over the Internet?
|
more expensive
|
|
|
Which alternative can offer QoS SLAs?
|
IP carrier networks
|
|
|
What security protections do IP carrier networks offer?
|
VPNs
|
|
|
Distinguish between route based VPNs and cryptographic VPNs?
|
route based VPN: provides security by hiding information from potential hackers
cryptographic VPN: this provides cryptographic security for transmission |
|
|
In a case of an IP carrier network, what is a VPN?
|
a virtual private network (cryptographic)
|
|
|
What are the two types of VPN connections that companies can create for themselves for transmission over the Internet?
|
remote access VPNs and site to site VPNs
|
|
|
What is remote access VPN?
|
connects the remote user to a corporate site
|
|
|
What is site to site VPN?
|
these VPNs connect all conversations between sites
|
|
|
At what layer does IPsec operate?
|
at the internet layer or the 3rd layer
|
|
|
What layers do Ipsec tunnel mode?
|
the IPsec connection extends only between the the IPsec gateways at the two sites not within the sites
vs transport mode |
|
|
What is the main disadvantage of tunnel mode?
|
simpler security
|
|
|
How is SSL/TLS limited and why is it attractive?
|
SSL/TLS only protects applications which are SSL/TLS aware, provides a secure connection at the transport layer
|
|
|
Without an SSL/TLS gateway under what circumstances is the SSL/TLS likely to be used?
|
for remote web access
|
|
|
When a SSL/TLS gateway is used, how many SSL/TLS connections does the client have?
|
this authenticates the user to access any sites they are allowed to access
|
|
|
What is webification?
|
involves converting screen images from these nonweb applications into webpages that browsers can read, this is what SSL/TLS gateway vendors can do
|
|
|
What is the advantage of webification?
|
expanded the ability of remote access users to use non web applications
|
|
|
Which VPN tends to require the installation of software on many client PCs?
|
IPsec VPN (transport mode)
|
|
|
Which of the technologies that we saw in this should we considered legacy technologies?
|
Frame Relay technology
|
