02-03-2010, 05:19 PM
this is a short seminar of enabling voce over WLAN.
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Enabling Voice over WLAN
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31-03-2010, 12:43 PM
Providing Voice over WLAN
Author:
Mejhan Kodzhadzhiklioski
Introduction
The need for VoIP technology, which was presented by the network managers with practical solutions for combining voice and data over a network. Showed that VoIP can be very useful and much cheaper alternative to circuit-switched voice networks, and "promises" that can extend these benefits to the higher performance of teams of mobile workers in a company.
As a step to be able to continue to grow the business, mobile communications are considered as very important tool for the continuation of this growth. The success or failure of equipment may result depending on the ability or inability to access and distribute information through the company itself.
Using IP as a transport which is present everywhere can significantly increase the statistical benefit performance propusniot range, lower overall demand propusniot range, easier management and ability to quickly develop new applications. In a WLAN, data and voice share a common infrastructure . In contrast, other networks can use the use-it or lose-it models. In case the voice is not used in a given moment, all possible Bandwidth used by data and voice applications when they are active in them is guaranteed a Bandwidth . Therefore, the ability to converge voice and data wireless local networks could result in significant zashteduvanje and allows development of new applications that increase productivity and efficiency.
Stunning development of two leading technologies, wireless LAN and Voice over IP (VoIP), were unified to enable new applications, Voice over Wireless LANs (VoWLANs). Use of VoWLAN today can be found everywhere, particularly in the industrial section. It allows employees in the industry to be mobile at any time, in contrast to workers in offices and require specific applications for their devices. Adding VoWLAN can increase productivity and accountability for mobile employees on the workplace itself.
Allowing the WLAN requires WLAN infrastructure, which will be able to provide mobility for high-quality voice connections. AirFlow designed only WLAN solution that enables mobile users to roamiraat through the network without the need for AP-to-AP hand-off delays that are present in traditional WLAN. Instead of consumers needs to regroup and re-certifying as it moves through the network, with proportional delays in hundreds of milliseconds, AirFlow solution provides consumers must not always be regrouping and re-certifying as it moves through the network. The end result is a simple mobility, which limits the delays from 300 to 500 milliseconds with the AP-to-AP hand-offs with less than 20 milliseconds, enabling quality development of VoWLAN.
1.Kvalitet voice
Most network devices such as routers or komutatorite designed for efficient transmission, asynchronous data unpredictable. As a result, each packet may have different delays caused by zagushuvanjeto network. Kasnenjeto Although the package may affect propusnosta of the traffic, yet all this will influence the quality of end-users.
Rather it is as the voice traffic is izohroni, it requires time-division strimovite package for maintaining good audio quality. Unlike circuit-switched voice connections, paketiziraniot "voice transmission via a common voice and data networks offer no guarantee on time delivery of packages. Like the fact that all packages must be received given the same treatment for their completion, depending on the allowed Bandwidth. Therefore, when all types of packets that contain network resources must be implemented a method for priority voice to ensure that we will have sufficient time allocation and audio quality.
The challenge of providing good audio quality when taktiziraniot "vote increases by working in WLAN environments, where the wireless medium provides at least 1 Mbps divided by capacity. In this case, wireless telephones are "struggling" with other client devices for access point resources.
The quality of voice is traditionally measured by subjective opinion. Leading subjective quality metrics for voice e MOS (mean opinion score) as described in the ITU (International Telecommunications Union) recommended by R.800. ITU P.800 standard explains how people react - as a result can deliver - where sound is heard differently by various aspects of delays of packets or their loss.
However, significant advances have enabled the establishment of objective measurements of call quality. ITU recommended G.107 as defined in the E-model for measuring the quality of voice. Exit of E-model is the only result, called the R factor, which reports a kasnenjeto and factor weakening the equipment. Once R factor will be obtained, he may be in mapira ocenuvachki MOS. E-model is designed for measurement of VoIP in WLAN, providing powerful and recurrent way of access anywhere if the WLAN is able to provide satisfactory VoIP calls. E-model also shows two categories to reduce the effect of the digitization of voice signals to pass through the wireless medium, the effects caused by equipment and kasnenjeto. To provide quality voice these factors must be what can smaller.
1.1 Reduction kasnenjeto packages
Four components make up overall one-way delays between one who speaks in a moment, and one who listens in VoWLAN connection. In case you have two-way conversation these components will be different for each direction.
1.1.1 Propagation Delay
Physical distance between two endpoints in a conversation determines the length of the propagation of signals between them. This delays is proportional to the speed of light, and that is the time required by the physical signal to pass through the copper, optical or wireless media. Because of the relative distances, propagacijata kasnenjeto in the WLAN does not matter how the string.
1.1.2 Packetization Delay
It takes time for the codes to convert analog signals into digital packets and vice versa. High-speed code as G.711 makes all this very quickly, about one milliseconds. For low-speed codes need more time for performing compression to reduce the size of the package. For example, codes in the family G.723 created 67.5 milliseconds delays for conversion from analog signals into digital packets. Therefore, the use of kompresirachki codes to reduce the overall VoWLAN traffic may increase kasnenjeto.
1.1.3 Jitter Buffer Delay
Jitter buffer is typically used by the recipient of the "settlement" of voice when we have variations in the arrival time of VoIP packets. Rather than directly converting the analog VoIP packets as incoming packets arrive is to be stored in the jitter buffer. Then the code used for converting them back from the buffer, so that packets always travel through the buffer before entering the code. Promenlivoto When the effect of delays in the network allows to reduce kasnenjeto of packets in the network, jitter buffer can be filled with too many packages. Conversely, when the network is going extra delays, the Code can continue to receive from the buffer, although at the same time new packets arrive. When delays occur too, reading from the buffer stops until they receive a new package and it's going to stop the conversation.The size of this buffer at the receiver is very important for VoWLAN systems. Buffer that stores a large number of packages may reduce the quality of voice creating great audio delays. However, with smaller buffer size would be kept small number of packages and it leads to loss of part of the conversation.
1.1.4 Transport Delay
Each network device (router, komutator etc..) Path between the "speakers" and "slushachot includes part inserted in transport delays. For some devices, such as hab, this is relatively constant delays. For other devices such as routers, the delays can grow over other traffic or zagushuvanjeto network. For WLAN transport delays is due to data installment. For 802.11b networks, transport of 1
Mbps e 11 times slower than the transport of 11Mbps. This is in addition to transport delays which is the result of arbitration CSMA and renewable mechanisms that are built into the 802.11 family of protocols. Hence, no QoS priority, the best service in 802.11 networks is insufficient to support voice opteretena network. Although transport delays is the largest and najpromenlivoto delays, it is a component that is najkompaktna the benefits of AirFlow technology. The large number of promises that all AirHubs VoWLAN handset-ROMs will always carry the greatest possible speed WLAN. This minimizes propusniot range used by other calls. In addition, most AirHubs allow greater range of handset-ROMs can be reduced, which causes a reduction in the number of devices in each domain CSMA. It also increases the performance of WLAN.
1.2 Weight loss equipment
Weakening of the voice signal in the wireless networks could happen in two ways. It can happen in codes when going A-to-D and D-to-A conversation and also because of the loss of packets in the network.
1.2.1 Codec Impairment
Slower codes reduce the quality of the audio signal much more than faster codes because they are compressed signal itself before sending.
1.2.2 Data Loss Impairment
Because sending VoIP packets to be conducted in real time, we lack the time for lodging packages. As a result, each packet loss reduces the quality of the audio signal.
There are two main reasons for coming to the loss of packages, CSMA too much traffic in the domain for which packets are rejected at zagushuvanje network or too variable delays, and packets are rejected because they arrive too late or too late in the jitter buffer by primachka . Mainly, there are two patterns of loss of packets. The simplest is the random loss of less common packages. Other template when it loses important package. In this case we have a greater weakening of the quality of the audio signal.
As a result, we have three ways to improve the quality of the voice on WLAN as:
¢ Reducing the total one-way delays in each direction. This can only be possible if the maximum transport speed WLAN for voice and data traffic.
¢ Reducing promenlivoto delays by reducing the number of customers for a CSMA domain. The best way to enable is to balance the number of users that have access to the 802.11 channels and reduce the level of output of all WLAN transmitter with minimal adjustments.
¢ Reducing the total paketska loss. Mechanisms controlling zagushuvanjeto in typical access points need to minimize the loss of packets. With the decision of AirFlow, each packet gets priority dispatch.This minimizes the chances of loss of packets while the voice packets receive higher priority.
1.3 taking propusniot range
Because of considerable size header package, the necessity of Bandwidth for VoIP is much larger than the data installments. With slower codes, such as G.729 useful data part is 8 kbps. However, this Bandwidth used is much greater. When sending in intervals of 30 ms, the size of the useful part is 30 bytes of datagram. In addition to all this header package includes additional 40 bytes for RTP header plus a 802.11 header. Accordingly, the total Bandwidth in one direction is higher than 25 kbps. To call in both directions you need Bandwidth of 50 kbps. With higher data installment of G.711 single call would have needed 160 kbps Bandwidth.
For a single access point to support 10 competitive VoIP calls using the G.711 code would require 1.6 Mbps Bandwidth without regeneration. The effect of reconstruction is needed to increase the number. It should be noted that with 10 clients who are "fighting" for a single 802.11b access point, the total bandwidth of the access point even higher data installments, the channel will be less than 1.6 Mbps, CSMA backoff algorithm for the protocol.
As a result, most access points and VoWLAN vendors recommend a maximum of 5 to 7 simultaneous calls for each access point, depending on the model. This number is based on 2Mbps operation and decreased to 50% if one of VoWLAN handset-s works at 1Mbps. Therefore it is necessary to estimate the number of VoWLAN handset-ROMs, and their expected size of calls for each access point to the maximum number of call. Higher data installments can only be maintained only by the scope of the standard AP. If VoWLAN handset-s work on the border of the RF coverage from the AP, they will automatically dropped the lowest possible rate and will need more Bandwidth. For example, VoWLAN applications may require 7% of the available Bandwidth for a call with 11 Mbps operations, which corresponds to 10% of the available Bandwidth for a call with 2 Mbps operation and 15% of the available Bandwidth for a call 1 Mbps operations.
There are four techniques that can be used to maintain the WLAN propusniot Range: compressed headers, silence suppression, frame packing, and call admission control.
With the kompresiranjeto hederite, the need for Bandwidth is reduced to half the slower codecs. Disadvantage is that the added delays, increases the transport delays.
Silence suppression saves propusniot the range of what makes a smaller payload. In most calls, we have moments when one speaker or both are in a state of silence. While it lasts, it is not necessary to send the whole package but much smaller packages, which say that we are in a state of silence. By enabling the two sides of the conversation, 50% of the payload field may be compressed.
Packaging of the preserving propusniot range by allowing more packets with audio information to be packed in one package, thus enabling the use of only one header for all the smaller packages. It increases kasnenjeto prepakuvanjeto for small packages and also far lost such a package it would mean the loss of many small packets simultaneously.
Finally, finally using the control dopuslivite calls provides too competitive not to discuss. Call manager software may limit the number of competing calls on a required number, to avoid overloading the access point.
Although all four techniques can increase VoWLAN performance, we need to get the final available WLAN capacity. It can be obtained only with non-preoptovaruvachki 802.11 channels. Packet antenna technology AirFlow Networks is one of the solutions.
In addition, it can reduce transport delays. By setting the wireless controllers closer to the border of the network can reduce the number of hopovi to be expired by the package, thereby improving performance.
1.4 VoWLAN Protocol Enhancements
Wireless Multimedia Extensions (WME) protocol is a subset of the 802.11 specification. It has improved the original 802.11 protocol family of specifications, designed to improve the user experience for voice communications. WME fills it all with the replacement of more deterministichki rasporeduvachki algorithms in place of best-effort CSMA algorithms used in the original specifications. With the introduction deterministichki of algorithms provides better support of QoS requirements in real-time applications like voice.
The popular private protocol to increase the quality of voice in VoWLAN systems was proposed by SpectraLink. This protocol introduces priorities for each package, and fast handoffs in WLAN access points to facilitate calls.
These protocols are easily preoptereteni on top of packet antenna technology. Wireless controller simply deploys traffic in real time in the AirHub the moment when the package is sent.
2nd Support for roaming
Traditional WLAN protocols require authentication data Summer to be suspended whenever the user roamira from one to another access point. The interruption may last from one quarter to one-half seconds, depending on network topology and location of the server for authentication.
Support for roaming
Traditional WLAN protocols require authentication data Summer to be suspended whenever the user roamira from one to another access point. The interruption may last from one quarter to one-half seconds, depending on network topology and location of the server for authentication. Thereby reducing or not allowing users to roamiraat from one to another AP. However, VoWLAN users are much more mobile and therefore need more handoveri. Therefore, solutions are needed to solve this problem. Most solutions require private roaming algorithms to increase the quality of voice and to maximize propusniot handoveri range between access points. However, AirFlow technology supports fast and safe roamiranja users without previous authorization of VoWLAN users without a private protocol (improving the 802.11 specification).
Rare problems can occur due to use of wireless personal communications devices near sensitive equipment or industrial environment. Some wireless devices such as mobile phones and two-way radios can cause defects in their work due to electro-magnetic energy that emits from wireless devices. Because packet antenna technology AirFlow, VoWLAN devices can operate at significantly lower power than mobile phones and two-way radios. Usually mobile phones transmit a maximum authorized output of 3 W (Watts) from radio frekfenciskata power. Transferable celularni phones typically operate at a maximum power of 0.6 W (600 mW), although some units of work and higher, 1200 mW. Mobile phones usually fitted to control power to enable low transmisiona power to hold it longer battery life, but typically require full power when used indoors. For celularnata technology uses different frequencies for sending and receiving signals, celularnite phones send when there is constant conversation. Also you can send and when not able to talk without knowledge of the user to inform the network about their status and availability.
In contrast, VoWLAN phones based on packet antenna technology can reduce its effective power for sending packets to 10-15 mW, which corresponds to 1 / 50 of the radio output power of standard mobile phones. This technology increases the number of CSMA domains available for each channel. With the increasing number of domains decreases the average number of users for each domain.
Second, because AirHub are waiting for their turn with this technology to create a dynamic set of distributed rows of channels based on real-time location of users. Therefore, we have small queues in AirHubs which can be found in Ar-based networks under similar conditions. Well as rows are small, more calls can share the same waiting line with data packets without priority and without the opportunity for users to lose data.
Also very important part of a voice and mobility. VoWLAN users are generally more mobile than data users. Because VoWLAN users can roamiraat between access points more often, require less delay in handof between access points. Also they baraaat greater wireless coverage. In addition, if the client entered the wired network protocols such as Mobile IP or NAT must be used well to support the call. With AirFlow packet antenna technology, all voice traffic in WLAN is rutiran the wireless controller. This is enabled by using the VLAN configured in advance that they all tunelira enklapsulirani packets between each AirHub and wireless router.3rd Security
Voice over WLAN improves oporavuvanje plans after a disaster. After AirHubs will be powered directly from the network infrastructure, your WLAN can resume normal operations in the event of electrical failure of the network using the battery. Given the need for enhanced WLAN security, the 802.11 standard approved as the new 802.11i standard with increased security features and network devices. However, such security entertain hendoverite between access points. Thus, traditional solutions, the company that receives the network can choose between enhanced security and greater capacity of VoWLAN. Since AirFlow's Packet Antenna technology does not rely on handof 802.11, customers can roamiraat from one point to another with full 802.11i security which allows for less than 20 ms.
.
4th Development of VoWLAN
In the final step to secure VoWLAN is the configuration of access points themselves through their web browser, allowing private QoS protocols and rebutiranje each AP. AirFlow technology in nature supports multimedia applications such as voice, so private companies allows previous WLAN without re-configuration to add voice. The large number of AirHubs provides no effect to feel a drop AirHub, until neighboring AirHub not take all his traffic. This is important for applications which take place in real time, so that they can continue without interference.
Packet Antenna technology naizmenichnite channels can be used to provide traffic management. For example, this allows companies to rent two 802.11 channels (eg channel 1 and 6) for data traffic and another channel (eg channel 11) for voice. With this approach users of best-effort applications are separate from users with applications that take place in real time, as his voice.
Conclusion
Enabling voice communications in the same WLAN, which includes data traffic is something to which they rely most companies. Almost the entire industry, this innovative solution enables greater productivity for their own employees and increases the responsibility of the customer themselves. AirFlow packet antenna
The technology provides a unique combination of benefits that maximize performance and increase VoWLAN communication infrastructure that is decisive for success in today's business world.
read more
http://down.ciw.com.cn/ShowSoftDown.asp?...oftID=9661
Author:
Mejhan Kodzhadzhiklioski
Introduction
The need for VoIP technology, which was presented by the network managers with practical solutions for combining voice and data over a network. Showed that VoIP can be very useful and much cheaper alternative to circuit-switched voice networks, and "promises" that can extend these benefits to the higher performance of teams of mobile workers in a company.
As a step to be able to continue to grow the business, mobile communications are considered as very important tool for the continuation of this growth. The success or failure of equipment may result depending on the ability or inability to access and distribute information through the company itself.
Using IP as a transport which is present everywhere can significantly increase the statistical benefit performance propusniot range, lower overall demand propusniot range, easier management and ability to quickly develop new applications. In a WLAN, data and voice share a common infrastructure . In contrast, other networks can use the use-it or lose-it models. In case the voice is not used in a given moment, all possible Bandwidth used by data and voice applications when they are active in them is guaranteed a Bandwidth . Therefore, the ability to converge voice and data wireless local networks could result in significant zashteduvanje and allows development of new applications that increase productivity and efficiency.
Stunning development of two leading technologies, wireless LAN and Voice over IP (VoIP), were unified to enable new applications, Voice over Wireless LANs (VoWLANs). Use of VoWLAN today can be found everywhere, particularly in the industrial section. It allows employees in the industry to be mobile at any time, in contrast to workers in offices and require specific applications for their devices. Adding VoWLAN can increase productivity and accountability for mobile employees on the workplace itself.
Allowing the WLAN requires WLAN infrastructure, which will be able to provide mobility for high-quality voice connections. AirFlow designed only WLAN solution that enables mobile users to roamiraat through the network without the need for AP-to-AP hand-off delays that are present in traditional WLAN. Instead of consumers needs to regroup and re-certifying as it moves through the network, with proportional delays in hundreds of milliseconds, AirFlow solution provides consumers must not always be regrouping and re-certifying as it moves through the network. The end result is a simple mobility, which limits the delays from 300 to 500 milliseconds with the AP-to-AP hand-offs with less than 20 milliseconds, enabling quality development of VoWLAN.
1.Kvalitet voice
Most network devices such as routers or komutatorite designed for efficient transmission, asynchronous data unpredictable. As a result, each packet may have different delays caused by zagushuvanjeto network. Kasnenjeto Although the package may affect propusnosta of the traffic, yet all this will influence the quality of end-users.
Rather it is as the voice traffic is izohroni, it requires time-division strimovite package for maintaining good audio quality. Unlike circuit-switched voice connections, paketiziraniot "voice transmission via a common voice and data networks offer no guarantee on time delivery of packages. Like the fact that all packages must be received given the same treatment for their completion, depending on the allowed Bandwidth. Therefore, when all types of packets that contain network resources must be implemented a method for priority voice to ensure that we will have sufficient time allocation and audio quality.
The challenge of providing good audio quality when taktiziraniot "vote increases by working in WLAN environments, where the wireless medium provides at least 1 Mbps divided by capacity. In this case, wireless telephones are "struggling" with other client devices for access point resources.
The quality of voice is traditionally measured by subjective opinion. Leading subjective quality metrics for voice e MOS (mean opinion score) as described in the ITU (International Telecommunications Union) recommended by R.800. ITU P.800 standard explains how people react - as a result can deliver - where sound is heard differently by various aspects of delays of packets or their loss.
However, significant advances have enabled the establishment of objective measurements of call quality. ITU recommended G.107 as defined in the E-model for measuring the quality of voice. Exit of E-model is the only result, called the R factor, which reports a kasnenjeto and factor weakening the equipment. Once R factor will be obtained, he may be in mapira ocenuvachki MOS. E-model is designed for measurement of VoIP in WLAN, providing powerful and recurrent way of access anywhere if the WLAN is able to provide satisfactory VoIP calls. E-model also shows two categories to reduce the effect of the digitization of voice signals to pass through the wireless medium, the effects caused by equipment and kasnenjeto. To provide quality voice these factors must be what can smaller.
1.1 Reduction kasnenjeto packages
Four components make up overall one-way delays between one who speaks in a moment, and one who listens in VoWLAN connection. In case you have two-way conversation these components will be different for each direction.
1.1.1 Propagation Delay
Physical distance between two endpoints in a conversation determines the length of the propagation of signals between them. This delays is proportional to the speed of light, and that is the time required by the physical signal to pass through the copper, optical or wireless media. Because of the relative distances, propagacijata kasnenjeto in the WLAN does not matter how the string.
1.1.2 Packetization Delay
It takes time for the codes to convert analog signals into digital packets and vice versa. High-speed code as G.711 makes all this very quickly, about one milliseconds. For low-speed codes need more time for performing compression to reduce the size of the package. For example, codes in the family G.723 created 67.5 milliseconds delays for conversion from analog signals into digital packets. Therefore, the use of kompresirachki codes to reduce the overall VoWLAN traffic may increase kasnenjeto.
1.1.3 Jitter Buffer Delay
Jitter buffer is typically used by the recipient of the "settlement" of voice when we have variations in the arrival time of VoIP packets. Rather than directly converting the analog VoIP packets as incoming packets arrive is to be stored in the jitter buffer. Then the code used for converting them back from the buffer, so that packets always travel through the buffer before entering the code. Promenlivoto When the effect of delays in the network allows to reduce kasnenjeto of packets in the network, jitter buffer can be filled with too many packages. Conversely, when the network is going extra delays, the Code can continue to receive from the buffer, although at the same time new packets arrive. When delays occur too, reading from the buffer stops until they receive a new package and it's going to stop the conversation.The size of this buffer at the receiver is very important for VoWLAN systems. Buffer that stores a large number of packages may reduce the quality of voice creating great audio delays. However, with smaller buffer size would be kept small number of packages and it leads to loss of part of the conversation.
1.1.4 Transport Delay
Each network device (router, komutator etc..) Path between the "speakers" and "slushachot includes part inserted in transport delays. For some devices, such as hab, this is relatively constant delays. For other devices such as routers, the delays can grow over other traffic or zagushuvanjeto network. For WLAN transport delays is due to data installment. For 802.11b networks, transport of 1
Mbps e 11 times slower than the transport of 11Mbps. This is in addition to transport delays which is the result of arbitration CSMA and renewable mechanisms that are built into the 802.11 family of protocols. Hence, no QoS priority, the best service in 802.11 networks is insufficient to support voice opteretena network. Although transport delays is the largest and najpromenlivoto delays, it is a component that is najkompaktna the benefits of AirFlow technology. The large number of promises that all AirHubs VoWLAN handset-ROMs will always carry the greatest possible speed WLAN. This minimizes propusniot range used by other calls. In addition, most AirHubs allow greater range of handset-ROMs can be reduced, which causes a reduction in the number of devices in each domain CSMA. It also increases the performance of WLAN.
1.2 Weight loss equipment
Weakening of the voice signal in the wireless networks could happen in two ways. It can happen in codes when going A-to-D and D-to-A conversation and also because of the loss of packets in the network.
1.2.1 Codec Impairment
Slower codes reduce the quality of the audio signal much more than faster codes because they are compressed signal itself before sending.
1.2.2 Data Loss Impairment
Because sending VoIP packets to be conducted in real time, we lack the time for lodging packages. As a result, each packet loss reduces the quality of the audio signal.
There are two main reasons for coming to the loss of packages, CSMA too much traffic in the domain for which packets are rejected at zagushuvanje network or too variable delays, and packets are rejected because they arrive too late or too late in the jitter buffer by primachka . Mainly, there are two patterns of loss of packets. The simplest is the random loss of less common packages. Other template when it loses important package. In this case we have a greater weakening of the quality of the audio signal.
As a result, we have three ways to improve the quality of the voice on WLAN as:
¢ Reducing the total one-way delays in each direction. This can only be possible if the maximum transport speed WLAN for voice and data traffic.
¢ Reducing promenlivoto delays by reducing the number of customers for a CSMA domain. The best way to enable is to balance the number of users that have access to the 802.11 channels and reduce the level of output of all WLAN transmitter with minimal adjustments.
¢ Reducing the total paketska loss. Mechanisms controlling zagushuvanjeto in typical access points need to minimize the loss of packets. With the decision of AirFlow, each packet gets priority dispatch.This minimizes the chances of loss of packets while the voice packets receive higher priority.
1.3 taking propusniot range
Because of considerable size header package, the necessity of Bandwidth for VoIP is much larger than the data installments. With slower codes, such as G.729 useful data part is 8 kbps. However, this Bandwidth used is much greater. When sending in intervals of 30 ms, the size of the useful part is 30 bytes of datagram. In addition to all this header package includes additional 40 bytes for RTP header plus a 802.11 header. Accordingly, the total Bandwidth in one direction is higher than 25 kbps. To call in both directions you need Bandwidth of 50 kbps. With higher data installment of G.711 single call would have needed 160 kbps Bandwidth.
For a single access point to support 10 competitive VoIP calls using the G.711 code would require 1.6 Mbps Bandwidth without regeneration. The effect of reconstruction is needed to increase the number. It should be noted that with 10 clients who are "fighting" for a single 802.11b access point, the total bandwidth of the access point even higher data installments, the channel will be less than 1.6 Mbps, CSMA backoff algorithm for the protocol.
As a result, most access points and VoWLAN vendors recommend a maximum of 5 to 7 simultaneous calls for each access point, depending on the model. This number is based on 2Mbps operation and decreased to 50% if one of VoWLAN handset-s works at 1Mbps. Therefore it is necessary to estimate the number of VoWLAN handset-ROMs, and their expected size of calls for each access point to the maximum number of call. Higher data installments can only be maintained only by the scope of the standard AP. If VoWLAN handset-s work on the border of the RF coverage from the AP, they will automatically dropped the lowest possible rate and will need more Bandwidth. For example, VoWLAN applications may require 7% of the available Bandwidth for a call with 11 Mbps operations, which corresponds to 10% of the available Bandwidth for a call with 2 Mbps operation and 15% of the available Bandwidth for a call 1 Mbps operations.
There are four techniques that can be used to maintain the WLAN propusniot Range: compressed headers, silence suppression, frame packing, and call admission control.
With the kompresiranjeto hederite, the need for Bandwidth is reduced to half the slower codecs. Disadvantage is that the added delays, increases the transport delays.
Silence suppression saves propusniot the range of what makes a smaller payload. In most calls, we have moments when one speaker or both are in a state of silence. While it lasts, it is not necessary to send the whole package but much smaller packages, which say that we are in a state of silence. By enabling the two sides of the conversation, 50% of the payload field may be compressed.
Packaging of the preserving propusniot range by allowing more packets with audio information to be packed in one package, thus enabling the use of only one header for all the smaller packages. It increases kasnenjeto prepakuvanjeto for small packages and also far lost such a package it would mean the loss of many small packets simultaneously.
Finally, finally using the control dopuslivite calls provides too competitive not to discuss. Call manager software may limit the number of competing calls on a required number, to avoid overloading the access point.
Although all four techniques can increase VoWLAN performance, we need to get the final available WLAN capacity. It can be obtained only with non-preoptovaruvachki 802.11 channels. Packet antenna technology AirFlow Networks is one of the solutions.
In addition, it can reduce transport delays. By setting the wireless controllers closer to the border of the network can reduce the number of hopovi to be expired by the package, thereby improving performance.
1.4 VoWLAN Protocol Enhancements
Wireless Multimedia Extensions (WME) protocol is a subset of the 802.11 specification. It has improved the original 802.11 protocol family of specifications, designed to improve the user experience for voice communications. WME fills it all with the replacement of more deterministichki rasporeduvachki algorithms in place of best-effort CSMA algorithms used in the original specifications. With the introduction deterministichki of algorithms provides better support of QoS requirements in real-time applications like voice.
The popular private protocol to increase the quality of voice in VoWLAN systems was proposed by SpectraLink. This protocol introduces priorities for each package, and fast handoffs in WLAN access points to facilitate calls.
These protocols are easily preoptereteni on top of packet antenna technology. Wireless controller simply deploys traffic in real time in the AirHub the moment when the package is sent.
2nd Support for roaming
Traditional WLAN protocols require authentication data Summer to be suspended whenever the user roamira from one to another access point. The interruption may last from one quarter to one-half seconds, depending on network topology and location of the server for authentication.
Support for roaming
Traditional WLAN protocols require authentication data Summer to be suspended whenever the user roamira from one to another access point. The interruption may last from one quarter to one-half seconds, depending on network topology and location of the server for authentication. Thereby reducing or not allowing users to roamiraat from one to another AP. However, VoWLAN users are much more mobile and therefore need more handoveri. Therefore, solutions are needed to solve this problem. Most solutions require private roaming algorithms to increase the quality of voice and to maximize propusniot handoveri range between access points. However, AirFlow technology supports fast and safe roamiranja users without previous authorization of VoWLAN users without a private protocol (improving the 802.11 specification).
Rare problems can occur due to use of wireless personal communications devices near sensitive equipment or industrial environment. Some wireless devices such as mobile phones and two-way radios can cause defects in their work due to electro-magnetic energy that emits from wireless devices. Because packet antenna technology AirFlow, VoWLAN devices can operate at significantly lower power than mobile phones and two-way radios. Usually mobile phones transmit a maximum authorized output of 3 W (Watts) from radio frekfenciskata power. Transferable celularni phones typically operate at a maximum power of 0.6 W (600 mW), although some units of work and higher, 1200 mW. Mobile phones usually fitted to control power to enable low transmisiona power to hold it longer battery life, but typically require full power when used indoors. For celularnata technology uses different frequencies for sending and receiving signals, celularnite phones send when there is constant conversation. Also you can send and when not able to talk without knowledge of the user to inform the network about their status and availability.
In contrast, VoWLAN phones based on packet antenna technology can reduce its effective power for sending packets to 10-15 mW, which corresponds to 1 / 50 of the radio output power of standard mobile phones. This technology increases the number of CSMA domains available for each channel. With the increasing number of domains decreases the average number of users for each domain.
Second, because AirHub are waiting for their turn with this technology to create a dynamic set of distributed rows of channels based on real-time location of users. Therefore, we have small queues in AirHubs which can be found in Ar-based networks under similar conditions. Well as rows are small, more calls can share the same waiting line with data packets without priority and without the opportunity for users to lose data.
Also very important part of a voice and mobility. VoWLAN users are generally more mobile than data users. Because VoWLAN users can roamiraat between access points more often, require less delay in handof between access points. Also they baraaat greater wireless coverage. In addition, if the client entered the wired network protocols such as Mobile IP or NAT must be used well to support the call. With AirFlow packet antenna technology, all voice traffic in WLAN is rutiran the wireless controller. This is enabled by using the VLAN configured in advance that they all tunelira enklapsulirani packets between each AirHub and wireless router.3rd Security
Voice over WLAN improves oporavuvanje plans after a disaster. After AirHubs will be powered directly from the network infrastructure, your WLAN can resume normal operations in the event of electrical failure of the network using the battery. Given the need for enhanced WLAN security, the 802.11 standard approved as the new 802.11i standard with increased security features and network devices. However, such security entertain hendoverite between access points. Thus, traditional solutions, the company that receives the network can choose between enhanced security and greater capacity of VoWLAN. Since AirFlow's Packet Antenna technology does not rely on handof 802.11, customers can roamiraat from one point to another with full 802.11i security which allows for less than 20 ms.
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4th Development of VoWLAN
In the final step to secure VoWLAN is the configuration of access points themselves through their web browser, allowing private QoS protocols and rebutiranje each AP. AirFlow technology in nature supports multimedia applications such as voice, so private companies allows previous WLAN without re-configuration to add voice. The large number of AirHubs provides no effect to feel a drop AirHub, until neighboring AirHub not take all his traffic. This is important for applications which take place in real time, so that they can continue without interference.
Packet Antenna technology naizmenichnite channels can be used to provide traffic management. For example, this allows companies to rent two 802.11 channels (eg channel 1 and 6) for data traffic and another channel (eg channel 11) for voice. With this approach users of best-effort applications are separate from users with applications that take place in real time, as his voice.
Conclusion
Enabling voice communications in the same WLAN, which includes data traffic is something to which they rely most companies. Almost the entire industry, this innovative solution enables greater productivity for their own employees and increases the responsibility of the customer themselves. AirFlow packet antenna
The technology provides a unique combination of benefits that maximize performance and increase VoWLAN communication infrastructure that is decisive for success in today's business world.
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http://down.ciw.com.cn/ShowSoftDown.asp?...oftID=9661
07-12-2011, 03:03 PM
Can I have the report and the power point presentation of "Voice over Wireless lan"?
thx..
thx..
08-12-2011, 09:46 AM
to get information about the topic" Enabling Voice over WLAN"refer the page link bellow
http://studentbank.in/report-enabling-vo...1#pid59571
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