Currently, wireless convergence applications have attracted a lot of attention from companies. It can be imagined that enterprises will enter into a substantive application stage after related QoS and roaming standards are further improved.
Wireless convergence "strongly" concerned
As visionary companies phase out traditional PBXs and migrate to VoIP infrastructure, some of the more brave users are beginning to look for more freedom in voice implementations—VoWLAN.
The New York State court system is one of the users of VoWLAN. In some district courts in New York, dozens of WLAN IP phones were deployed for court officials and other personnel. These people use WLAN IP phones as complementary voice communication devices for standard shortwave radiotelephones. The court system's radiotelephone encountered transmission problems when its signal band collided with other radio frequencies used by the police and the emergency department. Many of these departments are located near the courts. In addition, the history of many court buildings is more than a century old, and granite, marble, and steel fixtures that block radio waves are used extensively. Because of FCC (Federal Communications Commission) regulations, the court cannot install radio repeaters that enhance radio information. At this time, the WLAN phone becomes a very good supplementary infrastructure.
If court personnel find themselves in an area where radio reception is not effective, they can switch to a WLAN phone to communicate. Since the WLAN is not licensed, the IT staff of the court system can install hundreds of WLAN access points in the city center and use WLAN coverage to enhance shortwave weak signal points.
With the evolution of campus-based VoWLAN deployments, users, vendors, and service providers are looking to integrate VoWLAN with cellular voice technology to create a voice service that users can freely roam between WLAN and public GSM wireless networks.
This kind of service has attracted the attention of enterprise users in particular. Proxim, a maker of Avaya, Motorola and WLAN equipment, has been collaborating on this technology for the past year. An advertising company in Atlanta uses the Avaya/Proxim/Motorola product portfolio to enable users to use a single device to meet the mobile voice needs of the office. The client manager owns a Motorola handset that is connected to the Avaya IP PBX through the WLAN infrastructure deployed in the company’s Atlanta office. When the user moves beyond the WLAN range, the phone triggers the office's infrastructure to switch. The call then switches to BellSouth's GSM service and connects to the user's mobile phone. This service is very suitable for customer-centric businesses.
Outside the United States, VoWLAN/cellular trials are being conducted at the National Center for Public Management Information Technology in Italy. The center also plans to test VoWLAN in Australia. In Australia, the trial of VoWLAN/GSM roaming service is expected to start this year.
Wireless convergence standards
Because VoIP on Wi-Fi tangles WLAN and IP telephony problems, it is very complicated. Currently, a variety of wireless standards for overcoming the limitations of voice and video applications over wireless networks are being developed. The following focuses on the current status of some of the key standards that enable quality of service, security, wireless resource management, and fast roaming.
802.11e
The 802.11e task group is adding QoS to the 802.11 wireless standard. The team has proposed two different types of QoS. Among them, prioritized QoS uses priority marking to put different types of transport streams into different queues. Some applications, such as voice, are prioritized rather than reserved or guaranteed bandwidth. This Wireless Multimedia Extension (WME) specification is the standard expected by the VoWLAN industry.
Parametric QoS effectively reserves a certain amount of bandwidth for a certain flow. This is very similar to the use of virtual circuits in TDM-based switching. Content providers need this Wireless Reservation Multimedia (WSM) standard for such applications as HDTV.
The 802.11e draft standard has passed the general review and is now being reviewed by selected experts. In order to meet the needs of VoWLAN, the temporary approval of the WME part of this standard is being carried out separately, and the finalization time of WME is expected to be in September.
802.11i
The 802.11i task force is using stronger, more voice-friendly security to enhance wireless technology. Although data security mechanisms are robust, they often introduce delays beyond the tolerance of voice: especially if they require re-authentication to log in to each new access point.
The 802.11i Task Force developed two new algorithms, TKIP and CCMP, to provide confidentiality, data integrity, and data source authentication. The task group also proposed an agreement for mutual authentication and key management. TKIP's security is not as strong as CCMP, but it can be achieved through firmware upgrades on existing hardware. The stronger CCMP algorithm is based on the US Government's Advanced Encryption Standard (AES), which requires it to implement new hardware.
802.11k
The 802.11k task group is developing radio resource management standards that make more efficient use of WLAN resources. Feedback from the client will enable the switch and access point to make better roaming decisions, thus providing faster and uninterrupted wireless service.
Network equipment will be able to determine who is using RF and what the quality of each RF connection is.
At present, 802.11k has just entered the “letter voting†stage, during which it will undergo general review. At present, it is not yet known when this standard will be completed.
802.11r
The recently established 802.11r task force will address the issue of fast roaming between access points. At the same time, some experts believe that the technology from 802.11i and 802.11k will guarantee switching within 50ms. They say that this speed (about 150ms for the human sensory process) is fast enough to make 802.11r redundant.
The protocol from 802.11k can mainly be used by the mobile station to find out where to move before losing the connection. The PMK caching technology from 802.11i makes it possible to establish secure connections quickly (20 ms to 30 ms). Together, these protocols enable fast, secure, and seamless switching of VoWLAN connections between access points.
The team is still in the process of defining its own framework and has not yet come up with draft standards.
Wireless QoS
For wireless convergence applications, the biggest difference is the more stringent QoS requirements for wireless networks. So we focus on the implementation of wireless QoS.
Currently, an upcoming upgrade software will improve the monitoring of wireless network call quality. When users feel that there is a problem with voice quality, they can trigger an automatic adjustment of the wireless network, or notify the management personnel to handle problems found in a certain location.
Forrester Research analysts said that with the increasing popularity of wireless convergence applications, and the requirement for more reliable and clear telephone calls, the current development of wireless network QoS has attracted the attention of almost all wireless mainstream vendors. Many vendors including 3Com, Broadcom, NETGEAR, Cisco/Linksys, Conexant, D-Link, HP, IBM, Intel, and NEC have certified their devices to comply with the Wireless Multimedia (WMM) specification.
WMM is an RFC subset of 802.11e. WMM was developed to facilitate the use of QoS that can interoperate between multi-vendor devices. This means that companies can now deploy wireless voice fairly decently. When the standard comes out, if they want to meet the standards, they can upgrade.
The biggest challenge for QoS is that WLAN is a shared medium, much like the Ethernet sharing technology before switching technology did not appear. WMM addresses how customer devices and access points communicate, what they need and what they can provide, but does not address how the device decides whether to accept an available connection. Once the telephone transmission is accepted by the access point, the algorithm determines when each device connected to an access point begins to transmit and the transmission stream with the highest priority is transmitted more frequently. These algorithms were developed to handle collisions and retransmissions on WLAN networks, but they can be adjusted to give voice higher priority than other applications.
WMM also needs the phone to tag voice packets so that access points and wireless switches can process prioritized incoming packets and assign them to the appropriate VLANs in the wired network that is connected to the access point. In order to ensure QoS and improve security, many users often establish separate VLANs for voice applications.
The wireless switch adds the highest priority tag to the outgoing voice packets to ensure that they do not stay in the access point waiting to send packets first. Once a VoWLAN user makes a call, they may move around, forcing the wireless network to switch calls between access points. So the roaming function is also crucial. Implementing a handover with QoS may require each access point to reserve some bandwidth to handle future call handovers. This bandwidth buffer is adjustable and is set by the network manager based on the degree of roaming of their users.
Roaming problem
As mentioned earlier, to make wireless convergence truly available, in addition to QoS, security, and other issues, mobility-related roaming features are also an important topic, and mobility is one of the most important selling points of wireless convergence.
The user needs to consider: how to deploy VoIP to avoid the specific details of issues such as dropped calls between access points and obstacles blocking calls in the building. Users often want the quality of the call in the WLAN to be the same as the call quality of the wired telephone.
To ensure roaming capabilities, you must first ensure that the access point can cover every location that the end user in the building may go to. Then, it must be ensured that enough overlapping access points are deployed to support the possible concurrency users' load and ensure perfect service for all.
Transmittance is also an important issue, as in the medical industry, changing the wall construction is a common practice, and because some of these walls are shielded to block x-rays, it also hinders the transmission of Wi-Fi. This requires the blind spot of the wireless network to be determined, and then the access point is reconfigured to bypass these blind spots.
The load balancing between access points is the key to efficiently allocating calls. The access point needs to allocate users evenly in the environment where the users are simultaneously in the coverage area of ​​multiple access points. Without this feature, the user equipment will compete for the access point with the strongest access signal.
If there are enough access points to guarantee coverage, the network manager must also ensure that when the person making the call enters or exits a different site, the device switches quickly. The switch must be less than 50 milliseconds, otherwise callers can't stand it, which means that careful network design is essential.
Outdoor roaming is a more potential market. Although roaming within a building can meet the needs of many users, corporate sales personnel can also benefit from wireless VoIP. Using VoIP radiotelephone or VoIP softphone software running on a wireless PC, users can save a large amount of telephone charges in public WLAN hotspots.
One of the key constraints currently exists is the number of public hotspots available, although their number is rapidly increasing. Even if there are enough hot spots, companies cannot control the design and management of public hotspot networks, so quality may suffer. In addition, if users want to keep in touch all day, they must carry two phones: one for Wi-Fi and the other for cellular networks.
VoWLAN deployment suggestions
How can enterprises ensure successful deployment of converged applications on WLANs? The basic sensitivity of VoIP to delay and jitter is very difficult to handle, so it is suitable for cable-connected packet switching environments. This situation becomes more challenging when using less predictable radio frequency media (WLAN). At the same time, the delay caused by switching between access points makes the problem more complicated.
It is very important and necessary to conduct on-site investigations in this case. One reason for this is because voice users use the network in locations where data users do not use the network, such as corridors or stairs. Similarly, voice site surveys will help users achieve higher coverage than is generally required in data-only WLANs, so that voice coverage will become seamless. At the same time, this coverage also ensures that load balancing can be more easily achieved between APs.
In the current environment, VoIP phones are mainly limited to 802.11b technology. Whether or not there will be many converged applications in 54 Mbps WLANs (802.11a and 802.11g) is difficult to say because the higher the transmission rate, the greater the required signal-to-noise ratio (SNR). The minimum SNR in an 802.11b network should be 25 dB.
In addition to careful on-site investigation, when deploying WLAN converged applications, the following points need attention:
Set the AP and IP phones to transmit at the same power level to prevent "one-way audio." If the AP is configured to transmit at different power levels, the phone is set to use the largest AP transmit power.
In an ideal RF environment, non-overlapping 802.11b coverage cells propose a minimum separation of 5 channels (ie, in the United States, neighboring coverage cells are to operate on channels 1, 6, and 11 and in Europe to operate on channels 2, 7, and 12). on).
It is recommended not to have more than one AP per coverage channel to avoid increased noise.
Editing and editing
Before "cool"
One can imagine a scenario where people flow in a Starbucks coffee shop on the ground floor of a commercial building. When you call after holding an “alternative†mobile phone, casually tell the person next to you that the call was free. of.
Personalization also saves money. It's not cool. Of course, the above scenario may be just a dream for you, because the WLAN voice is still a bit far away from us, we have to solve some key issues. However, this distance is not far away.
VoWLAN sounds like a cool word, and you realize that there is actually a two-level gap between "original" analog voice and VoWLAN. First, voice is digitized and packetized for transmission over local area networks. Now, at least part of the LAN's transmission process is wireless LAN.
There is no doubt that the Wi-Fi-based mobility provided by VoWLAN is indispensable for promoting its enterprise deployment and justifying the deployment. However, network managers who are just familiar with "ordinary" VoIP will certainly have a lot of questions about VoWLAN.
When VoIP was first proposed as a replacement for the PBX system, we were worried about a lot of things. Is there enough bandwidth? Can you guarantee voice quality? Is the call safe? The results show that we have no reason to worry. However, when voice is transmitted on today's Wi-Fi networks, these problems reappear and new problems arise.
Wi-Fi networks are slower (compared to Fast Ethernet) and they are shared. Therefore, performance degradation is possible, and service quality becomes more than just a theoretical consideration. The wireless broadcast nature makes session security a big problem.
The key technical problem is roaming. By definition, people using Wi-Fi phones may roam between access points while walking in a building. Roaming “gap†(acceptable for data applications) in seconds will offset all the benefits of using Wi-Fi because users will hang up.
At the same time that all these things happen, the very active 802.11 subcommittee is undoubtedly diligently meeting these challenges. Although many people have been unable to keep up with 802.11 with more and more letters, for the sake of wireless convergence tomorrow, what is this?
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