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التعليقات (9)
Dial-up access is a form of Internet access through which the client uses a modem connected to a computer and a telephone line to dial into an Internet service provider's (ISP) node to establish a modem-to-modem link, which is then routed to the Internet.Despite the advent of widely available broadband Internet access in most parts of the Western world, many people worldwide still connect via dial-up simply because they do not have access to or cannot afford a high-speed Internet connection.Dial-up requires no additional infrastructure on top of the telephone network. As telephone points are available throughout the world, dial-up remains useful to travellers. Dial-up is usually the only choice available for most rural or remote areas where getting a broadband connection is impossible due to low population and demand. Sometimes dial-up access may also be an alternative to people who have limited budgets as it is offered for free by some, though broadband is now increasingly available at lower prices in countries such as the United States and Canada due to market competition.Dial-up requires time to establish a telephone connection and perform handshaking before data transfers can take place, potentially a source of frustration. In locales with telephone connection charges, each connection incurs an incremental cost. If calls are time-charged, the duration of the connection incurs costs.Dial-up access is a transient connection, because either the user or the ISP terminates the connection. Internet service providers will often set a limit on connection durations to prevent hogging of access, and will disconnect the user — requiring reconnection and the costs and delays associated with that.Modern dial-up modems typically have a maximum theoretical speed of 56 kbit/s (using the V.92 protocol), although in most cases only up to 53 kbit/s is possible due to overhead and FCC regulation. These speeds are currently considered the maximum possible; in many cases transfer speeds will be lower, averaging anywhere between 33-43 kbit/s. Factors such as phone line noise and conditions, as well as the quality of the modem itself, play a large part in determining connection speeds.Dial-up connections usually have high latency that can be as high as 200 ms or even more, which can make online gaming or videoconferencing difficult, if not impossible. Some games, such as Star Wars: Galaxies, The Sims Online and Guild Wars are capable of running on 56 K dial-up. Gamers with dial-up connections are often disconnected from game servers due to the "lag", or high latency, of the connection.What is often advertised as "high-speed dial-up Internet" or "accelerated dial-up" by service providers such as Earthlink and NetZero in the United States is a form of dial-up access that utilizes the newer modem standard v.92 to shortens the log-on (or handshake) process, and then once a connection has been established the provider will selectively compress, filter, and cache data being sent to the users home with the overall effect of increasing the speed of browsing most standard web pages (see also proxy server).The term high speed is misleading as these processes do not increase the overall throughput of the line, only making more efficient use of the bandwidth that is already there. Certain applications cannot be accelerated, such as SHTTP, streaming media, or file transfers. The compression of certain files such as pictures can have a negative affect on the browsing experience of the user, due to the lower quality that it imposes.
ياشيخه ربي يسعدك ويحميك
الف شكر
اقولك الباقي ولا خلاص تعبتك؟
داريه اني طماعه بس والله هالجامعه قلق يعني انا مالي دخل
طيب
باقي badbhon
wireless
satellite
ودي اعطيك الموقع اللي عندي بس اخاف يكفخوني المشرفات
لان الموقع اللي عندي انقلش ويتكلم عن هالاتصالات بس مااعرفت اطلعه
الف شكر
اقولك الباقي ولا خلاص تعبتك؟
داريه اني طماعه بس والله هالجامعه قلق يعني انا مالي دخل
طيب
باقي badbhon
wireless
satellite
ودي اعطيك الموقع اللي عندي بس اخاف يكفخوني المشرفات
لان الموقع اللي عندي انقلش ويتكلم عن هالاتصالات بس مااعرفت اطلعه
تفضلي الموضوع عن الويرلس
wireless
Wireless technology can provide many benefits to computing including faster response to queries,
reduced time spent on paperwork, increased online time for users, just-in-time and real time control,
tighter communications between clients and hosts. Wireless Computing is governed by two general
forces: Technology, which provides a set of basic building blocks and User Applications, which
determine a set of operations that must be carried out efficiently on demand. This paper summarizes
technological changes that are underway and describes their impact on wireless computing development
and implementation. It also describes the applications that influence the development and
implementation of wireless computing and shows what current systems offer.
1 Introduction
Wireless computing is the topic of much conversation today. The concept has been around for some
time now but has been mainly utilizing communication protocols that exist for voice based
communication. It is not intended to replace wired data communication but instead to be utilized in
areas that it would be otherwise impossible to communicate using wires. Only recently has the industry
been taking steps to formulate a standard that is more suitable to data transmission. Some the problems
to be overcome are:
(1) Data Integrity - relatively error free transmission,
(2) Speed - as close as possible to the speed of current wired networks,
(3) Protection - making sure that the data now airborne is encoded and cannot be tapped by
unwelcome receivers,
(4) Compatibility - ensuring that the many protocols that sure to be created subscribe to a standard
to allow inter-operability,
(5) Environmentally safe - strengths of electromagnetic radiation must be kept within normal levels.
In our study of the theories and implementation concerns of wireless computing, we found that it is
being treated in an object oriented fashion. Scientists and development crews, including the IEEE, are
doing their best to implement wireless connectivity without changing the existing computer hardware.
As a result, a lot of focus is on using existing computer hardware and software to convert data to a
format compatible with the new hardware which will be added to the computer using ports or PCMCIA
connections that already exist. This means that wireless communication will be transparent to the user
if and when wireless computing is utilized on a wide scale.
Wireless computing applications covers three broad areas of computing today. Replacement of normal
wired LAN's need to retain the speed and reliability found in wired LAN's. Creation of semipermanent
LAN's for quick and easy setup without the need for running wires. This would be necessary for events
such as earthquakes. The last category is that of mobile computing. With advent of PCMCIA cards,
notebook computers are being substituted for regular desktop machines with complete connectivity of
the desktop machine. However, you lose the connectivity when out of the office unless you have a
wireless means of communicating.
On the compatibility issue, the ability to mix wireless brands on a single network is not likely to come
soon. The IEEE Standards Committee is working on a wireless LAN standard -- 802.11, which is an
extension of the Ethernet protocol. Because the field of wireless communication is so broad, the IEEE
was not able to set a standard by the time private researchers were ready to test their theories hoping to
set the standard for others to follow.
2 Methods
There are a few methods of wireless communication being theorized and tested.
(1) Radio: This is the method that makes use of standard radio waves in the 902 MHz to 928 MHz
frequency range. Although these frequencies are well used, methods have been developed to
ensure data integrity. Spread spectrum transmission of data is a method where the transmitter
will send information simultaneously out over many frequencies in the range increasing the
change that all data will eventually reach the receiver. Frequency hopping is an additional
measure that also enables data security. The 26 MHz range of frequencies is further divided in
to channels. The transmitter then sends out data hopping from one channel to the next in a
certain pattern known to the receiver. Within each channel, spread spectrum transmission can
be used to maintain interference avoidance. Some of this transmission manipulation can be
avoided by transmitting at a frequency that is less used. Some developers have tried
transmitting in the gigahertz range. The disadvantages here are: 1) Higher frequencies mean
shorter wavelengths and shorter wavelengths do not penetrate solid objects like walls and floors;
2) The same transmission strength employed by lower wavelength transmitters yields a shorter
range at higher frequencies. This means that transmission strength will need to be boosted
something hard to accomplish using portable tools and potentially dangerous to humans; 3)
Transmission frequencies of 3 GHz and higher are licensed by the Federal Communications
Commission. Developers in the range have the additional hassle of obtaining a license every
time an installation is done.
(2) Laser: Laser-based communication is the fastest way to communicate without wires.
Information travels at the speed of light. The drawbacks however far outweigh the speed
advantage and prevent this method from becoming the standard. The major drawback is that
communication is restricted to line of sight. Also, very thick fog or blizzard conditions will
diffuse the laser beam and causing interference and reducing data integrity.
(3) Infrared: This method is similar to Laser. High speed communications are easy to achieve
using this method. However, it suffers from the same problems that plague laser
communications. It requires line of sight transmission and can be disrupted by strong ambient
light. Infrared wireless computing exists more commonly in the form of peripheral connections
in a small area.
(4) Cellular connections although expensive to use now is the area of much development by private
companies. Cellular computing can be likened to the current wire-based internet network. Data
is packaged in to units, size of the unit is dependent on the actual hardware, and is sent to the
nearest participating cell. That cell then forwards the packet to the next cell and so forth until
the packet reaches its destination.
(5) Microwave: This method of communication has been utilized for quite some time now.
However this method has makes little provision for data aware transmission. It used extensively
in ****pe where wired transmission of any type including voice is poor. For data transmission,
a lot of technology is utilized in packaging the data into a form that is compatible to voice
communication. On the receiving end, the process is reversed. The advantage of this method
however is that communication can be accomplished using existing satellite connections making
worldwide connectivity possible.
3 Standards
The IEEE 802.11 committee has voted to create a minimum requirement for wireless computing
connections. In their consideration:
(1) Use the frequencies 2.4 to 2.5 GHz. This is in the low end of the high frequency spectrum and
is currently not licensed by the FCC.
(2) Use spread spectrum technology. Compared to the current bandwidth 26 MHz, 902 MHz to
928 MHz, the range 2.4 to 2.5 GHz yields a bandwidth of 100 MHZ. Spread spectrum
transmission now gives 385% percent increase in data reliability.
(3) Many more sub-channels can be formed in a bandwidth of 100 MHZ. This increases the
capability of frequency hopping which in turn yields greater data security.
(4) Utilize Gaussian Frequency Shift-Keying. Frequency shift-keying is a form of frequency
modulation in which binary signaling is accomplished by using two frequencies separated by
some Df Hz. The frequency duration is small compared with the carrier frequency, fc. A signal
received at frequency fc, would represent a digital low and signals received at frequency fc + Df,
would represent a digital high. Note that this does not interfere with spread spectrum or
frequency hopping capabilities since those function on frequencies separated by 1 MHz or more.
As part of setting a wireless standard some modifications of the standard set by the IEEE 802.3
committee have been adopted. The most significant of these is the modification to the carrier sense
multiple access / collision detection, or CSMA/CD, protocol used in wired networks today. This is a
method whereby any machine at any time, wishing to send a message on the net, will first send a token
out to ensure that a carrier exists (network ready). After establishing this, the message will be sent.
Because any machine may send at any time, collisions of information will occur. If any machine detects
a collision, it will send out a jamming signal to all the others. All machines will then wait on a random
interval timer after which they will try to send again.
For wireless networks however, since a machine is not in constant communication with the rest of the
LAN, detecting a collision and notifying all other machines on the net is impossible. A modification
in the way of the collision handling had to be made. A method known as collision avoidance is
employed to create the
CSMA/CA standard. In a
collision avoidance strategy, the
net estimates the average time
of collisions and send a
jamming signal at that time. A
wireless transceiver will not
only sense a carrier but will also
listen out for the jamming
signal. When all is clear it then send its message. This collision avoidance method has two drawbacks:
1) It cannot completely filter all collisions since it operates on estimated times of collisions; 2) and if
it did, it slows the network significantly by sending jamming signals whether or not a collision actually
occurs.
4 Physical Layer
Much of the focus of wireless computing development is centered on the physical and media access
control layers of a system. It is on this level of the LAN protocol of which wireless products like
modems and transceivers
On the physical layer issue, the 802.11 is focusing on the one proposed by Apple Computer
Corporation.
The Apple physical-layer protocol appears the most robust of any considered to date in 802.11. Apple's
system is a full-duplex, slow frequency-hopping protocol. By using a frequency-hop spread-spectrum
radio, the system fits with the spread-spectrum methods of virtually all 802.11 specifications.
Apple splits the data-transport protocol into two layers:
- The RF Adoption Layer is similar in some respects to cell-based data protocols, such as
Asynchronous Transfer Mode and IEEE 802.6 Switched Multimegabit Data Services; like ATM and
802.6, the RF Adoption Layer includes segmentation/reassembly functions and Protocol Data Unit
generation functions, and it also includes Forward Error Correction (FEC) generation and verification
functions which substantially increase packet integrity in wireless environments but adds FEC overhead.
- The RF Hopping Protocol Physical Layer consists of a transmission convergence sublayer including
header generation, RF framing, and RF hopping protocol functions and the physical- medium-dependent
sublayer, in which the actual characteristics of the RF channel are handled.
In the RF Adoption Layer, a Protocol Data Unit is split into three segments, and two error-correcting
data units are added. The RF Hopping segments, and two error-correcting data units are added. The RF
Hopping Physical Layer builds special Burst Protocol Data Units out of the data and FEC units and uses
carrier-sense methods borrowed from Ethernet to determine whether an RF Hop Group is clear for
transmission. Each hop group consists of five separate radio channels. The controller scans hop groups
via state-machine operation with four states: scan, receive, carrier-sense, and transmit. In early tests at
Apple, the hop system showed 80-microsecond hop times, 57-microsecond clock recovery, and a
5-microsecond lapse between the time an empty channel is sensed and transmission begins. Since each
cluster of wireless LANs can use different hop groups, multiple LANs could operate in the same area
without interference. One concern is whether the overhead for error correction for each packet, which
can be as much as 50% is too high to give the proposal a chance.
The safety of those operating new equipment now plays a larger role in determining the direction of
technological growth now more that ever. Factors under consideration are the effect of infrared and
strong electromagnetic radiation that would pervade the workplace on the workers. This limits the
strength of and communication device that would be used in accomplishing transmission.
For the Personal Computer. The adapters have a small attached antenna through which they send and
receive network traffic as radio signals. Some wireless products are small boxes that attach to your PC's
parallel port. In either case, the signals may travel from PC to PC, forming a wireless peer-to-peer
network, or they may travel to a network server equipped with both wireless and standard Ethernet
adapters, providing notebook users a portable connection to the corporate network. In either case,
wireless LANs can either replace or extend wired networks.
Standards are lacking. Wireless networking is still a technology looking for a standard, which is why
very few wireless products can work with one another. Each vendor uses a different protocol, radio
frequency, or signaling technology. If wired networks still operated like wireless, you would have to
use the same brand of network interface card throughout your network. Right now you are, for the most
part, tied to whichever brand of wireless LAN you pick. Most of the products in this comparison listed
their wireless protocol as Ethernet carrier sense multiple access/collision avoidance (CSMA/CA), a
variation of standard Ethernet. Unfortunately, each vendor has put its own spin on CSMA/CA, which
means even their protocols are incompatible.
5 Wireless services
As technology progresses toward smaller, lighter, faster, lower power hardware components, more
computers will become more and more mobile. For space concerns this paper will exclude any further
discussion of the hardware developments toward mobility except for devices directly related to wireless
connectivity such as modems.
A wireless computer is not connected via a wireline and thus has mobility and convenience. A wireless
LAN provides the convenience of eliminating the wires, yet is not necessarily mobile.
(What is mobility?)
Mobility is a characteristic where the wireless computer may connect, loose the physical
communication (possibly due to interference) and reconnect (possibly to another sub-network) and retain its virtual connections and continue to operate its applications. The
network protocols will be discussed later.
(Then, what is portable?)
Portable is defined that the wireless computer may connect, loose the connection and
then re-connect, as well. However, the mobile unit will have to restart if it is
reconnected to another sub-network, requiring that running processes be shut-down and
windows closed.
Mobility may be limited by the wireless service subscribed. Four basic service zones are described:
Global/National service zone: Ubiquitous radio coverage throughout a region, country or the
entire globe, low user densities, and minimal bandwidth
requirements. Typically satellite systems.
Mobile service zone: Radio coverage in urban, suburban and populated rural areas,
medium to high user densities, low to medium bandwidth
requirements (tens of Kbps), and high vehicular speed. Cellular
(AMPS) system is a good example.
Local/micro service zone: Radio coverage in densely populated urban areas, shopping
malls, and transportation centers. High enduser densities,
medium bandwidth requirements, hand-held portable terminals,
low-speed mobility.
Indoor/pica service zone: in-building radio coverage, low to high user densities, medium
to high bandwidth requirements (Mbps), very low mobility.
Prior to the cellular phone network, base station radio covering a single cell geographic area with a fixed
number of channels was the only service available.
The cellular phone service divides the service area into cells and assigns a subset of the available
channels to any given cell. This way the channels can be reused and interference from neighboring cells
is reduced. The system tracks the active mobile unit, delivers calls, and maintains connections as units
move between cells (Hand-off: a realtime transfer of a call between radio channels in different cells).
This system is called Advanced Mobile Phone Service (AMPS). Current cellular systems use analog
FM technology. However, implementation of digital radio technology is being deployed now. These
systems utilize Time Division Multiple Access (TDMA) or Code Division Multiple Access (CDMA)
to increase throughput up to ten times the previous analog system. Additionally, end users will access
a wider range of telecommunications as the implementation of integrated services digital network
(ISDN) principles are utilized. Personal Communication Services, similar to the current cellular system,
will soon be available from the larger telecommunication services, but with reduced price and wider
availability.
wireless
Wireless technology can provide many benefits to computing including faster response to queries,
reduced time spent on paperwork, increased online time for users, just-in-time and real time control,
tighter communications between clients and hosts. Wireless Computing is governed by two general
forces: Technology, which provides a set of basic building blocks and User Applications, which
determine a set of operations that must be carried out efficiently on demand. This paper summarizes
technological changes that are underway and describes their impact on wireless computing development
and implementation. It also describes the applications that influence the development and
implementation of wireless computing and shows what current systems offer.
1 Introduction
Wireless computing is the topic of much conversation today. The concept has been around for some
time now but has been mainly utilizing communication protocols that exist for voice based
communication. It is not intended to replace wired data communication but instead to be utilized in
areas that it would be otherwise impossible to communicate using wires. Only recently has the industry
been taking steps to formulate a standard that is more suitable to data transmission. Some the problems
to be overcome are:
(1) Data Integrity - relatively error free transmission,
(2) Speed - as close as possible to the speed of current wired networks,
(3) Protection - making sure that the data now airborne is encoded and cannot be tapped by
unwelcome receivers,
(4) Compatibility - ensuring that the many protocols that sure to be created subscribe to a standard
to allow inter-operability,
(5) Environmentally safe - strengths of electromagnetic radiation must be kept within normal levels.
In our study of the theories and implementation concerns of wireless computing, we found that it is
being treated in an object oriented fashion. Scientists and development crews, including the IEEE, are
doing their best to implement wireless connectivity without changing the existing computer hardware.
As a result, a lot of focus is on using existing computer hardware and software to convert data to a
format compatible with the new hardware which will be added to the computer using ports or PCMCIA
connections that already exist. This means that wireless communication will be transparent to the user
if and when wireless computing is utilized on a wide scale.
Wireless computing applications covers three broad areas of computing today. Replacement of normal
wired LAN's need to retain the speed and reliability found in wired LAN's. Creation of semipermanent
LAN's for quick and easy setup without the need for running wires. This would be necessary for events
such as earthquakes. The last category is that of mobile computing. With advent of PCMCIA cards,
notebook computers are being substituted for regular desktop machines with complete connectivity of
the desktop machine. However, you lose the connectivity when out of the office unless you have a
wireless means of communicating.
On the compatibility issue, the ability to mix wireless brands on a single network is not likely to come
soon. The IEEE Standards Committee is working on a wireless LAN standard -- 802.11, which is an
extension of the Ethernet protocol. Because the field of wireless communication is so broad, the IEEE
was not able to set a standard by the time private researchers were ready to test their theories hoping to
set the standard for others to follow.
2 Methods
There are a few methods of wireless communication being theorized and tested.
(1) Radio: This is the method that makes use of standard radio waves in the 902 MHz to 928 MHz
frequency range. Although these frequencies are well used, methods have been developed to
ensure data integrity. Spread spectrum transmission of data is a method where the transmitter
will send information simultaneously out over many frequencies in the range increasing the
change that all data will eventually reach the receiver. Frequency hopping is an additional
measure that also enables data security. The 26 MHz range of frequencies is further divided in
to channels. The transmitter then sends out data hopping from one channel to the next in a
certain pattern known to the receiver. Within each channel, spread spectrum transmission can
be used to maintain interference avoidance. Some of this transmission manipulation can be
avoided by transmitting at a frequency that is less used. Some developers have tried
transmitting in the gigahertz range. The disadvantages here are: 1) Higher frequencies mean
shorter wavelengths and shorter wavelengths do not penetrate solid objects like walls and floors;
2) The same transmission strength employed by lower wavelength transmitters yields a shorter
range at higher frequencies. This means that transmission strength will need to be boosted
something hard to accomplish using portable tools and potentially dangerous to humans; 3)
Transmission frequencies of 3 GHz and higher are licensed by the Federal Communications
Commission. Developers in the range have the additional hassle of obtaining a license every
time an installation is done.
(2) Laser: Laser-based communication is the fastest way to communicate without wires.
Information travels at the speed of light. The drawbacks however far outweigh the speed
advantage and prevent this method from becoming the standard. The major drawback is that
communication is restricted to line of sight. Also, very thick fog or blizzard conditions will
diffuse the laser beam and causing interference and reducing data integrity.
(3) Infrared: This method is similar to Laser. High speed communications are easy to achieve
using this method. However, it suffers from the same problems that plague laser
communications. It requires line of sight transmission and can be disrupted by strong ambient
light. Infrared wireless computing exists more commonly in the form of peripheral connections
in a small area.
(4) Cellular connections although expensive to use now is the area of much development by private
companies. Cellular computing can be likened to the current wire-based internet network. Data
is packaged in to units, size of the unit is dependent on the actual hardware, and is sent to the
nearest participating cell. That cell then forwards the packet to the next cell and so forth until
the packet reaches its destination.
(5) Microwave: This method of communication has been utilized for quite some time now.
However this method has makes little provision for data aware transmission. It used extensively
in ****pe where wired transmission of any type including voice is poor. For data transmission,
a lot of technology is utilized in packaging the data into a form that is compatible to voice
communication. On the receiving end, the process is reversed. The advantage of this method
however is that communication can be accomplished using existing satellite connections making
worldwide connectivity possible.
3 Standards
The IEEE 802.11 committee has voted to create a minimum requirement for wireless computing
connections. In their consideration:
(1) Use the frequencies 2.4 to 2.5 GHz. This is in the low end of the high frequency spectrum and
is currently not licensed by the FCC.
(2) Use spread spectrum technology. Compared to the current bandwidth 26 MHz, 902 MHz to
928 MHz, the range 2.4 to 2.5 GHz yields a bandwidth of 100 MHZ. Spread spectrum
transmission now gives 385% percent increase in data reliability.
(3) Many more sub-channels can be formed in a bandwidth of 100 MHZ. This increases the
capability of frequency hopping which in turn yields greater data security.
(4) Utilize Gaussian Frequency Shift-Keying. Frequency shift-keying is a form of frequency
modulation in which binary signaling is accomplished by using two frequencies separated by
some Df Hz. The frequency duration is small compared with the carrier frequency, fc. A signal
received at frequency fc, would represent a digital low and signals received at frequency fc + Df,
would represent a digital high. Note that this does not interfere with spread spectrum or
frequency hopping capabilities since those function on frequencies separated by 1 MHz or more.
As part of setting a wireless standard some modifications of the standard set by the IEEE 802.3
committee have been adopted. The most significant of these is the modification to the carrier sense
multiple access / collision detection, or CSMA/CD, protocol used in wired networks today. This is a
method whereby any machine at any time, wishing to send a message on the net, will first send a token
out to ensure that a carrier exists (network ready). After establishing this, the message will be sent.
Because any machine may send at any time, collisions of information will occur. If any machine detects
a collision, it will send out a jamming signal to all the others. All machines will then wait on a random
interval timer after which they will try to send again.
For wireless networks however, since a machine is not in constant communication with the rest of the
LAN, detecting a collision and notifying all other machines on the net is impossible. A modification
in the way of the collision handling had to be made. A method known as collision avoidance is
employed to create the
CSMA/CA standard. In a
collision avoidance strategy, the
net estimates the average time
of collisions and send a
jamming signal at that time. A
wireless transceiver will not
only sense a carrier but will also
listen out for the jamming
signal. When all is clear it then send its message. This collision avoidance method has two drawbacks:
1) It cannot completely filter all collisions since it operates on estimated times of collisions; 2) and if
it did, it slows the network significantly by sending jamming signals whether or not a collision actually
occurs.
4 Physical Layer
Much of the focus of wireless computing development is centered on the physical and media access
control layers of a system. It is on this level of the LAN protocol of which wireless products like
modems and transceivers
On the physical layer issue, the 802.11 is focusing on the one proposed by Apple Computer
Corporation.
The Apple physical-layer protocol appears the most robust of any considered to date in 802.11. Apple's
system is a full-duplex, slow frequency-hopping protocol. By using a frequency-hop spread-spectrum
radio, the system fits with the spread-spectrum methods of virtually all 802.11 specifications.
Apple splits the data-transport protocol into two layers:
- The RF Adoption Layer is similar in some respects to cell-based data protocols, such as
Asynchronous Transfer Mode and IEEE 802.6 Switched Multimegabit Data Services; like ATM and
802.6, the RF Adoption Layer includes segmentation/reassembly functions and Protocol Data Unit
generation functions, and it also includes Forward Error Correction (FEC) generation and verification
functions which substantially increase packet integrity in wireless environments but adds FEC overhead.
- The RF Hopping Protocol Physical Layer consists of a transmission convergence sublayer including
header generation, RF framing, and RF hopping protocol functions and the physical- medium-dependent
sublayer, in which the actual characteristics of the RF channel are handled.
In the RF Adoption Layer, a Protocol Data Unit is split into three segments, and two error-correcting
data units are added. The RF Hopping segments, and two error-correcting data units are added. The RF
Hopping Physical Layer builds special Burst Protocol Data Units out of the data and FEC units and uses
carrier-sense methods borrowed from Ethernet to determine whether an RF Hop Group is clear for
transmission. Each hop group consists of five separate radio channels. The controller scans hop groups
via state-machine operation with four states: scan, receive, carrier-sense, and transmit. In early tests at
Apple, the hop system showed 80-microsecond hop times, 57-microsecond clock recovery, and a
5-microsecond lapse between the time an empty channel is sensed and transmission begins. Since each
cluster of wireless LANs can use different hop groups, multiple LANs could operate in the same area
without interference. One concern is whether the overhead for error correction for each packet, which
can be as much as 50% is too high to give the proposal a chance.
The safety of those operating new equipment now plays a larger role in determining the direction of
technological growth now more that ever. Factors under consideration are the effect of infrared and
strong electromagnetic radiation that would pervade the workplace on the workers. This limits the
strength of and communication device that would be used in accomplishing transmission.
For the Personal Computer. The adapters have a small attached antenna through which they send and
receive network traffic as radio signals. Some wireless products are small boxes that attach to your PC's
parallel port. In either case, the signals may travel from PC to PC, forming a wireless peer-to-peer
network, or they may travel to a network server equipped with both wireless and standard Ethernet
adapters, providing notebook users a portable connection to the corporate network. In either case,
wireless LANs can either replace or extend wired networks.
Standards are lacking. Wireless networking is still a technology looking for a standard, which is why
very few wireless products can work with one another. Each vendor uses a different protocol, radio
frequency, or signaling technology. If wired networks still operated like wireless, you would have to
use the same brand of network interface card throughout your network. Right now you are, for the most
part, tied to whichever brand of wireless LAN you pick. Most of the products in this comparison listed
their wireless protocol as Ethernet carrier sense multiple access/collision avoidance (CSMA/CA), a
variation of standard Ethernet. Unfortunately, each vendor has put its own spin on CSMA/CA, which
means even their protocols are incompatible.
5 Wireless services
As technology progresses toward smaller, lighter, faster, lower power hardware components, more
computers will become more and more mobile. For space concerns this paper will exclude any further
discussion of the hardware developments toward mobility except for devices directly related to wireless
connectivity such as modems.
A wireless computer is not connected via a wireline and thus has mobility and convenience. A wireless
LAN provides the convenience of eliminating the wires, yet is not necessarily mobile.
(What is mobility?)
Mobility is a characteristic where the wireless computer may connect, loose the physical
communication (possibly due to interference) and reconnect (possibly to another sub-network) and retain its virtual connections and continue to operate its applications. The
network protocols will be discussed later.
(Then, what is portable?)
Portable is defined that the wireless computer may connect, loose the connection and
then re-connect, as well. However, the mobile unit will have to restart if it is
reconnected to another sub-network, requiring that running processes be shut-down and
windows closed.
Mobility may be limited by the wireless service subscribed. Four basic service zones are described:
Global/National service zone: Ubiquitous radio coverage throughout a region, country or the
entire globe, low user densities, and minimal bandwidth
requirements. Typically satellite systems.
Mobile service zone: Radio coverage in urban, suburban and populated rural areas,
medium to high user densities, low to medium bandwidth
requirements (tens of Kbps), and high vehicular speed. Cellular
(AMPS) system is a good example.
Local/micro service zone: Radio coverage in densely populated urban areas, shopping
malls, and transportation centers. High enduser densities,
medium bandwidth requirements, hand-held portable terminals,
low-speed mobility.
Indoor/pica service zone: in-building radio coverage, low to high user densities, medium
to high bandwidth requirements (Mbps), very low mobility.
Prior to the cellular phone network, base station radio covering a single cell geographic area with a fixed
number of channels was the only service available.
The cellular phone service divides the service area into cells and assigns a subset of the available
channels to any given cell. This way the channels can be reused and interference from neighboring cells
is reduced. The system tracks the active mobile unit, delivers calls, and maintains connections as units
move between cells (Hand-off: a realtime transfer of a call between radio channels in different cells).
This system is called Advanced Mobile Phone Service (AMPS). Current cellular systems use analog
FM technology. However, implementation of digital radio technology is being deployed now. These
systems utilize Time Division Multiple Access (TDMA) or Code Division Multiple Access (CDMA)
to increase throughput up to ten times the previous analog system. Additionally, end users will access
a wider range of telecommunications as the implementation of integrated services digital network
(ISDN) principles are utilized. Personal Communication Services, similar to the current cellular system,
will soon be available from the larger telecommunication services, but with reduced price and wider
availability.
يسلمو كثير كثير
طيب باقي عن satellite
bhodbon ترا اسبلينق هالكلمه مااظنه صح
طيب باقي عن satellite
bhodbon ترا اسبلينق هالكلمه مااظنه صح
BHO DEMON
BROWSER HELPER OBJECT
A Browser Helper Object (BHO) is a DLL module designed as a plugin for Microsoft's Internet Explorer web browser to provide added functionality. BHOs were introduced in October 1997 with the release of version 4 of Internet Explorer. Most BHOs are loaded once by each new instance of Internet Explorer. However, in the case of the Windows File Explorer, a new instance is launched for each Window.
Some modules enable the display of different file formats not ordinarily interpretable by the browser. The Adobe Acrobat plugin that allows Internet Explorer users to read PDF files within their browser is a BHO.
Other modules add toolbars to Internet Explorer, such as the Alexa Toolbar that provides a list of web sites related to the one you are currently browsing, or the Google Toolbar that adds a toolbar with a Google search box to the browser user interface.
The BHO API exposes hooks that allow the BHO to access the Document Object Model (DOM) of the current page and to control navigation. Because BHOs have unrestricted access to the Internet Explorer event model, some forms of malware have also been created as BHOs. For example, the Download.ject exploit installed a BHO that would activate upon detecting a secure HTTP connection to a financial institution, record the user's keystrokes (intending to capture passwords) and transmit the information to a website used by Russian computer criminals. Other BHOs such as the MyWay Searchbar track users browsing patterns and pass the information they record to third parties.
In response to the problems associated with BHOs and similar extensions to Internet Explorer, Microsoft added an Add-on Manager to Internet Explorer with the release of Service Pack 2 for Windows XP. This displays a list of all installed BHOs, Browser Extensions and ActiveX controls, and allows the user to enable or disable them at will.
For users that are not using Windows XP, there are free tools (such as BHODemon) that list installed BHOs and allow the user to disable malicious extensions.
Many BHOs actually install toolbars in Internet Explorer. It is therefore possible that a PC contains BHOs that the owner doesn't know about. The security risk here is that the BHO doesn't need any kind of permission to install malicious components and thus spywares may be spread without the user's knowledge.
Since it's relatively easy to write BHOs, many badly written BHOs will harm the computer and compromise its security, and even sometimes destroy valuable data or corrupt system files.
BROWSER HELPER OBJECT
A Browser Helper Object (BHO) is a DLL module designed as a plugin for Microsoft's Internet Explorer web browser to provide added functionality. BHOs were introduced in October 1997 with the release of version 4 of Internet Explorer. Most BHOs are loaded once by each new instance of Internet Explorer. However, in the case of the Windows File Explorer, a new instance is launched for each Window.
Some modules enable the display of different file formats not ordinarily interpretable by the browser. The Adobe Acrobat plugin that allows Internet Explorer users to read PDF files within their browser is a BHO.
Other modules add toolbars to Internet Explorer, such as the Alexa Toolbar that provides a list of web sites related to the one you are currently browsing, or the Google Toolbar that adds a toolbar with a Google search box to the browser user interface.
The BHO API exposes hooks that allow the BHO to access the Document Object Model (DOM) of the current page and to control navigation. Because BHOs have unrestricted access to the Internet Explorer event model, some forms of malware have also been created as BHOs. For example, the Download.ject exploit installed a BHO that would activate upon detecting a secure HTTP connection to a financial institution, record the user's keystrokes (intending to capture passwords) and transmit the information to a website used by Russian computer criminals. Other BHOs such as the MyWay Searchbar track users browsing patterns and pass the information they record to third parties.
In response to the problems associated with BHOs and similar extensions to Internet Explorer, Microsoft added an Add-on Manager to Internet Explorer with the release of Service Pack 2 for Windows XP. This displays a list of all installed BHOs, Browser Extensions and ActiveX controls, and allows the user to enable or disable them at will.
For users that are not using Windows XP, there are free tools (such as BHODemon) that list installed BHOs and allow the user to disable malicious extensions.
Many BHOs actually install toolbars in Internet Explorer. It is therefore possible that a PC contains BHOs that the owner doesn't know about. The security risk here is that the BHO doesn't need any kind of permission to install malicious components and thus spywares may be spread without the user's knowledge.
Since it's relatively easy to write BHOs, many badly written BHOs will harm the computer and compromise its security, and even sometimes destroy valuable data or corrupt system files.
satellite
A satellite is any object that orbits another object (which is known as its primary). Satellites can be manmade or may be naturally occurring such as moons, comets, asteroids, planets, stars, and even galaxies.
All masses that are part of our solar system, including the Earth and Sun, are satellites of either a planet, the Sun, or the galactic center of the Milky Way.
It is not always a simple matter to decide which is the "satellite" in a pair of bodies. Because all objects with mass are affected by gravity, the motion of the primary object is also affected by the satellite. If two objects are sufficiently similar in mass, they are generally referred to as a binary system rather than a primary object and satellite; an extreme example is the 'double asteroid' 90 Antiope. The general criterion for an object to be a satellite is that the center of mass (known as the Barycenter) of the two objects is inside the primary object. Another, perhaps better known, example is the dwarf planet Pluto and its companion, Charon. While many consider Charon to be a satellite of Pluto, this can be debated, as their masses are similar to the point where their barycenter is not within either object. Accordingly, some consider Pluto and Charon to be the two members of a double planet system.
What seems the first fictional depiction of an artificial satellite launched into Earth orbit seems to be in Jules Verne's The Begum's Millions (1879). In this book, however, this is a completely unintentional result of the book's villain building an enormous artillery piece in order to destroy his enemies, and imparting to the shell a greater velocity than intended.
In 1903 Konstantin Tsiolkovsky (1857–1935) published (The Exploration of Cosmic Space by Means of Reaction Devices), which was arguably the first academic treatise on rocketry. He calculated the escape velocity from Earth into orbit at 8 km/second and that a multi-stage rocket fueled by liquid oxygen and liquid hydrogen would be required. During his lifetime he published over 500 works on space travel and related subjects, including science fiction novels. Among his works are designs for rockets with steering thrusters, multi-stage boosters, space stations, airlocks for exiting a spaceship into the vacuum of space, and closed cycle biological systems to provide food and oxygen for space colonies. He also delved into theories of heavier-than-air flying machines, independently working through many of the same calculations that the Wright brothers were performing at about the same time.
In 1928 Herman Poto nik (1898–1929) published his sole book, Das Problem der Befahrung des Weltraums - der Raketen-motor (The Problem of Space Travel - The Rocket Motor), a plan for a breakthrough into space and a permanent human presence there. He conceived of a space station in detail and calculated its geostationary orbit. He described the use of orbiting spacecraft for detailed peaceful and military observation of the ground and described how the special conditions of space could be useful for scientific experiments. The book described geostationary satellites (first put forward by Tsiolkovsky) and discussed communication between them and the ground using radio, but fell short of the idea of using satellites for mass broadcasting and as telecommunications relays.
In 1945 the English science fiction writer Arthur C. Clarke (b. 1917) conceived of the possibility for mass artificial communication satellites in his Wireless World article.
Clarke examined the logistics of satellite launch, possible orbits and other aspects of the creation of a network of world-circling satellites, pointing to the benefits of high-speed global communications. He also suggested that three geostationary satellites would provide coverage over the entire planet.
The first artificial satellite was Sputnik 1 launched by Soviet Union on 4 October 1957.
In May, 1946, Project RAND released the Preliminary Design of an Experimental World-Circling Spaceship, which stated, "A satellite vehicle with appropriate instrumentation can be expected to be one of the most potent scientific tools of the Twentieth Century. The achievement of a satellite craft would produce repercussions comparable to the explosion of the atomic bomb…"
The space age began in 1946, as scientists began using captured German V-2 rockets to make measurements in the upper atmosphere.
Before this period, scientists used balloons that went up to 30 km and radio waves to study the ionosphere. From 1946 to 1952, upper-atmosphere research was conducted using V-2s and Aerobee rockets. This allowed measurements of atmospheric pressure, density, and temperature up to 200 km. (see also: magnetosphere, Van Allen radiation belt)
The United States had been considering launching orbital satellites since 1945 under the Bureau of Aeronautics of the United States Navy. The Air Force's Project RAND eventually released the above report, but did not believe that the satellite was a potential military weapon; rather they considered it to be a tool for science, politics, and propaganda. In 1954, the Secretary of Defence stated, "I know of no American satellite program."
Following pressure by the American Rocket Society, the National Science Foundation, and the International Geophysical Year, military interest picked up and in early 1955 the Air Force and Navy were working on Project Orbiter, which involved using a Jupiter C rocket to launch a small satellite called Explorer 1 on January 31, 1958.
On July 29, 1955, the White House announced that the U.S. intended to launch satellites by the spring of 1958. This became known as Project Vanguard. On July 31, the Soviets announced that they intended to launch a satellite by the fall of 1957. On October 4, 1957 Sputnik 1 was launched into orbit, which triggered the Space Race between the two already adversarial nations.
The largest artificial satellite currently orbiting the Earth is the International Space Station.
Types
Anti-Satellite weapons, sometimes called "Killer satellites" are satellites designed to destroy "enemy" satellites, other orbital weapons and targets. Some are armed with kinetic rounds, while others use energy and/or particle weapons to destroy satellites, ICBMs, MIRVs. Both the U.S. and the USSR had these satellites. Links discussing "Killer satellites", ASATS (Anti-Satellite satellite) include USSR Tests ASAT weapon and ASAT Test. See also IMINT
Astronomical satellites are satellites used for observation of distant planets, galaxies, and other outer space objects.
Biosatellites are satellites designed to carry living organisms, generally for scientific experimentation.
Communications satellites are an artificial satellite stationed in space for the purposes of telecommunications. Modern communications satellites typically use geosynchronous orbits, Molniya orbits or low Earth orbits.
Miniaturized satellites are satellites of unusually low weights and small sizes. New classifications are used to categorize these satellites: minisatellite (500–200 kg), microsatellite (below 200 kg), nanosatellite (below 10 kg).
Navigation satellites are satellites which use radio time signals transmitted to enable mobile receivers on the ground to determine their exact location. The relatively clear line of sight between the satellites and receivers on the ground, combined with ever-improving electronics, allows satellite navigation systems to measure location to accuracies on the order of a few metres in real time.
Reconnaissance satellites are Earth observation satellite or communications satellite deployed for military or intelligence applications. Little is known about the full power of these satellites, as governments who operate them usually keep information pertaining to their reconnaissance satellites classified.
Earth observation satellites are satellites intended for non-military uses such as environmental monitoring, meteorology, map making etc. (See especially Earth Observing System.)
Solar power satellites are proposed satellites built in high Earth orbit that use microwave power transmission to beam solar power to very large antenna on Earth where it can be used in place of conventional power sources.
Space stations are man-made structures that are designed for human beings to live on in outer space. A space station is distinguished from other manned spacecraft by its lack of major propulsion or landing facilities — instead, other vehicles are used as transport to and from the station. Space stations are designed for medium-term living in orbit, for periods of weeks, months, or even years.
Weather satellites are satellites that primarily are used to monitor Earth's weather and climate.
Orbit types
Low Polar Orbit
Geostationary Orbit
Centric Classifications
Galacto-centric Orbit - An orbit about the center of a galaxy. Earth's sun follows this type of orbit about the galactic center of the Milky Way.
Heliocentric Orbit - An orbit around the Sun. In our Solar System, all planets, comets, and asteroids are in such orbits, as are many artificial satellites and pieces of space debris. Moons by contrast are not in a heliocentric orbit but rather orbit their parent planet.
Geocentric Orbit - An orbit around the planet Earth, such as the Moon or artificial satellites. Currently there are approximately 2465 artificial satellites orbiting the Earth.
Areocentric Orbit - An orbit around the planet Mars, such as moons or artificial satellites.
A satellite is any object that orbits another object (which is known as its primary). Satellites can be manmade or may be naturally occurring such as moons, comets, asteroids, planets, stars, and even galaxies.
All masses that are part of our solar system, including the Earth and Sun, are satellites of either a planet, the Sun, or the galactic center of the Milky Way.
It is not always a simple matter to decide which is the "satellite" in a pair of bodies. Because all objects with mass are affected by gravity, the motion of the primary object is also affected by the satellite. If two objects are sufficiently similar in mass, they are generally referred to as a binary system rather than a primary object and satellite; an extreme example is the 'double asteroid' 90 Antiope. The general criterion for an object to be a satellite is that the center of mass (known as the Barycenter) of the two objects is inside the primary object. Another, perhaps better known, example is the dwarf planet Pluto and its companion, Charon. While many consider Charon to be a satellite of Pluto, this can be debated, as their masses are similar to the point where their barycenter is not within either object. Accordingly, some consider Pluto and Charon to be the two members of a double planet system.
What seems the first fictional depiction of an artificial satellite launched into Earth orbit seems to be in Jules Verne's The Begum's Millions (1879). In this book, however, this is a completely unintentional result of the book's villain building an enormous artillery piece in order to destroy his enemies, and imparting to the shell a greater velocity than intended.
In 1903 Konstantin Tsiolkovsky (1857–1935) published (The Exploration of Cosmic Space by Means of Reaction Devices), which was arguably the first academic treatise on rocketry. He calculated the escape velocity from Earth into orbit at 8 km/second and that a multi-stage rocket fueled by liquid oxygen and liquid hydrogen would be required. During his lifetime he published over 500 works on space travel and related subjects, including science fiction novels. Among his works are designs for rockets with steering thrusters, multi-stage boosters, space stations, airlocks for exiting a spaceship into the vacuum of space, and closed cycle biological systems to provide food and oxygen for space colonies. He also delved into theories of heavier-than-air flying machines, independently working through many of the same calculations that the Wright brothers were performing at about the same time.
In 1928 Herman Poto nik (1898–1929) published his sole book, Das Problem der Befahrung des Weltraums - der Raketen-motor (The Problem of Space Travel - The Rocket Motor), a plan for a breakthrough into space and a permanent human presence there. He conceived of a space station in detail and calculated its geostationary orbit. He described the use of orbiting spacecraft for detailed peaceful and military observation of the ground and described how the special conditions of space could be useful for scientific experiments. The book described geostationary satellites (first put forward by Tsiolkovsky) and discussed communication between them and the ground using radio, but fell short of the idea of using satellites for mass broadcasting and as telecommunications relays.
In 1945 the English science fiction writer Arthur C. Clarke (b. 1917) conceived of the possibility for mass artificial communication satellites in his Wireless World article.
Clarke examined the logistics of satellite launch, possible orbits and other aspects of the creation of a network of world-circling satellites, pointing to the benefits of high-speed global communications. He also suggested that three geostationary satellites would provide coverage over the entire planet.
The first artificial satellite was Sputnik 1 launched by Soviet Union on 4 October 1957.
In May, 1946, Project RAND released the Preliminary Design of an Experimental World-Circling Spaceship, which stated, "A satellite vehicle with appropriate instrumentation can be expected to be one of the most potent scientific tools of the Twentieth Century. The achievement of a satellite craft would produce repercussions comparable to the explosion of the atomic bomb…"
The space age began in 1946, as scientists began using captured German V-2 rockets to make measurements in the upper atmosphere.
Before this period, scientists used balloons that went up to 30 km and radio waves to study the ionosphere. From 1946 to 1952, upper-atmosphere research was conducted using V-2s and Aerobee rockets. This allowed measurements of atmospheric pressure, density, and temperature up to 200 km. (see also: magnetosphere, Van Allen radiation belt)
The United States had been considering launching orbital satellites since 1945 under the Bureau of Aeronautics of the United States Navy. The Air Force's Project RAND eventually released the above report, but did not believe that the satellite was a potential military weapon; rather they considered it to be a tool for science, politics, and propaganda. In 1954, the Secretary of Defence stated, "I know of no American satellite program."
Following pressure by the American Rocket Society, the National Science Foundation, and the International Geophysical Year, military interest picked up and in early 1955 the Air Force and Navy were working on Project Orbiter, which involved using a Jupiter C rocket to launch a small satellite called Explorer 1 on January 31, 1958.
On July 29, 1955, the White House announced that the U.S. intended to launch satellites by the spring of 1958. This became known as Project Vanguard. On July 31, the Soviets announced that they intended to launch a satellite by the fall of 1957. On October 4, 1957 Sputnik 1 was launched into orbit, which triggered the Space Race between the two already adversarial nations.
The largest artificial satellite currently orbiting the Earth is the International Space Station.
Types
Anti-Satellite weapons, sometimes called "Killer satellites" are satellites designed to destroy "enemy" satellites, other orbital weapons and targets. Some are armed with kinetic rounds, while others use energy and/or particle weapons to destroy satellites, ICBMs, MIRVs. Both the U.S. and the USSR had these satellites. Links discussing "Killer satellites", ASATS (Anti-Satellite satellite) include USSR Tests ASAT weapon and ASAT Test. See also IMINT
Astronomical satellites are satellites used for observation of distant planets, galaxies, and other outer space objects.
Biosatellites are satellites designed to carry living organisms, generally for scientific experimentation.
Communications satellites are an artificial satellite stationed in space for the purposes of telecommunications. Modern communications satellites typically use geosynchronous orbits, Molniya orbits or low Earth orbits.
Miniaturized satellites are satellites of unusually low weights and small sizes. New classifications are used to categorize these satellites: minisatellite (500–200 kg), microsatellite (below 200 kg), nanosatellite (below 10 kg).
Navigation satellites are satellites which use radio time signals transmitted to enable mobile receivers on the ground to determine their exact location. The relatively clear line of sight between the satellites and receivers on the ground, combined with ever-improving electronics, allows satellite navigation systems to measure location to accuracies on the order of a few metres in real time.
Reconnaissance satellites are Earth observation satellite or communications satellite deployed for military or intelligence applications. Little is known about the full power of these satellites, as governments who operate them usually keep information pertaining to their reconnaissance satellites classified.
Earth observation satellites are satellites intended for non-military uses such as environmental monitoring, meteorology, map making etc. (See especially Earth Observing System.)
Solar power satellites are proposed satellites built in high Earth orbit that use microwave power transmission to beam solar power to very large antenna on Earth where it can be used in place of conventional power sources.
Space stations are man-made structures that are designed for human beings to live on in outer space. A space station is distinguished from other manned spacecraft by its lack of major propulsion or landing facilities — instead, other vehicles are used as transport to and from the station. Space stations are designed for medium-term living in orbit, for periods of weeks, months, or even years.
Weather satellites are satellites that primarily are used to monitor Earth's weather and climate.
Orbit types
Low Polar Orbit
Geostationary Orbit
Centric Classifications
Galacto-centric Orbit - An orbit about the center of a galaxy. Earth's sun follows this type of orbit about the galactic center of the Milky Way.
Heliocentric Orbit - An orbit around the Sun. In our Solar System, all planets, comets, and asteroids are in such orbits, as are many artificial satellites and pieces of space debris. Moons by contrast are not in a heliocentric orbit but rather orbit their parent planet.
Geocentric Orbit - An orbit around the planet Earth, such as the Moon or artificial satellites. Currently there are approximately 2465 artificial satellites orbiting the Earth.
Areocentric Orbit - An orbit around the planet Mars, such as moons or artificial satellites.
اموه
ربي يسعدك
طيب اكتشفت كمان شغله
شي عن cable modem servic
وربي اخر شي خلاص.. ماعاد اطلب شي غير اللهم ابغى المصدر
تعرفين بحث ولازم اكتب بالنهايه من وين جبته
ربي يسعدك
طيب اكتشفت كمان شغله
شي عن cable modem servic
وربي اخر شي خلاص.. ماعاد اطلب شي غير اللهم ابغى المصدر
تعرفين بحث ولازم اكتب بالنهايه من وين جبته
عبارات إنجليزيه معانيها تختلف عن الترجمه الحرفيه لها→
I will write to you about the DSL okay
DSL is a technology that uses a standard copper two-wire pair (or line) to transmit high speed (high frequency) Internet connectivity to areas that will support the service.
DSL can obtain speeds as high as 6.0Mbps. The speed your location can receive depends on your address, line quality and the distance to your local phone company's central office. A Central Office (CO) is the main switching station for the phone lines in your area. It is the office where the ILEC (your telephone company) connects the phone circuits, and makes the routes between local and long distance.
Each DSL has different distinguishing attributes that affect quality and price.
• Line-share — "Traditional" Asymmetric DSL (ADSL)
Available up to 15,000 feet from a CO. Typically the download speed is faster than the upload speed. While ADSL can generally be installed up to 15,000 feet, this general rule does not guarantee that we will be able to install the circuit or that the circuit will perform at a reasonable level (see Terms of Service for more detail).
Speed, quality and availability is determined by both distance to CO and copper quality. Speeds expressed with ADSL packages are the maximum speeds your line may achieve. Although we will do everything within our power to provide you with the best possible service, due to the nature of the technology, ADSL services do not come with a service level guarantee (see Terms of Service for more detail). Since many businesses require a guaranteed service level agreement (SLA), ADSL is not available for business locations. Symmetric DSL (SDSL) is recommended for all eligible businesses.
• OneLink™ — Dedicated Line DSL
OneLink™ DSL does not require phone service, but does require a phone line at the location for the DSL to run through. It requires a technician visit to connect the phone jack that will be used for DSL inside the premises with the local loop outside the premises.
OneLink DSL is also known as Naked DSL, Dedicated Line DSL or 2nd Line DSL. OneLink DSL is ideal for people who use cellular phones as their primary voice lines or want to replace their conventional phone service with feature-rich, cost-effective Voice over IP (VoIP) service.
For Home/Home Office customers, OneLink DSL is typically delivered as an ADSL product, though the same technology can also be used to deliver business-level SDSL (Symmetric DSL) service.