subject: Enterprise Vowlan Voip Application Difficulties [print this page] Dynamic enterprise VoIP rapid development of applications tend to diversification, VoIP with Wi-Fi integration and application of active vision has emerged, which is VoWLAN (Voice-Over-WLAN). Can be expected, VoWLAN will become more competitive voice transmission technology, by 2006 there will be 500 000 802.11 standards-based voice terminals into the market. However, enterprise applications VoWLAN, still faces some difficulties.
VoWLAN application form VoWLAN work in two ways. VoWLAN phone case is transferred to the terminal's call WLANAP, and then through the VoIP gateway to achieve with the existing circuit-switched PBX interoperability, achieved through the PBX and PS TN's Communicate ; The other is VoWLAN phone terminal through the IP PBX to connect directly with the AP, through IPPBX achieve interoperability with the PSTN. If the VoWLAN system connected directly with the VoIP phone provider, you can directly dial IP phone to the PSTN to achieve the floor.
VoWLAN terminal two forms, one is a Wi-Fi enabled wireless handheld IP Telephone People can be within WLAN coverage Mobile Call without having to be in the plane as in the past or desktop PC IP phones can play next. The other is the terminal form of soft, that the existing PDA And Notebook Install the phone software, start the software after the IP phone call. The advantage is with the soft end PDA and Notebook No need to use the hardware IP phones, the use of lower cost, now have PDA and notebook computer manufacturers to support pre-installed when playing soft VoWLAN terminal.
VoWLAN Enterprise Application considerations In the present circumstances, VoWLAN to be able to quickly get the application in the following aspects need to meet. VoWLAN or intend to use an existing WLAN plans to add VoIP functionality, they need to take into account the following factors.
1, VoWLAN communication quality of wireline voice communication quality must be comparable. Can reduce the communication cost in context, the necessary communication quality is a must, at least with the existing quality of wireline voice communication rather, otherwise the user will bring the communication barrier, thus affecting the normal work and Business Activities.
2, WLAN networks must have sufficient capacity bandwidth allocated to voice, so as to ensure call quality. Real-time voice communications on the higher, while the bandwidth occupied by the instant the call is relatively large, larger systems in telephone traffic, the WLAN will need to have enough bandwidth for the implementation of VoWLAN.
3, wireless coverage must be comprehensive and continuous enterprise-wide. Mobile and can roam wireless networks and the main features of VoWLAN, but if not completely cover voice quality will lead to decline and dropped calls, so to have to be the successful implementation of VoWLAN seamless coverage within the region.
4, the network should be Security Of. Wireless network security is one of the biggest problems, VoWLAN is also facing this problem, voice communications more informative, but also vulnerable to threats. Therefore increasingly important in today's information, the premise of successful application of one of the factors VoWLAN is to ensure that the network is secure.
Enterprise applications and solve the difficulties of VoWLAN
1, Quality Assurance Voice than data, more sensitive to network delay. When a user browsing the web, they can tolerate a few seconds to download using a web page. However, the use VoWLAN must ensure real-time communication and the downlink symmetry, so that users feel smooth. WLAN technology has some means of reducing speech delay, to ensure the communication quality.
For example, reduce the total in each direction on one-way delay, so long as to make WLAN voice and data are in the maximum rate for transmission can be achieved; reduce the time delay difference, reducing field of customers each CSMA Quantity can be achieved; reduce packet loss, even if packet loss, can retry 802.11 protocol mechanisms to reduce, AP's congestion control mechanisms to ensure voice packet loss must be at least, if each AP in the Launch Before the signal to ensure the priority of voice service, you can reduce the packet loss.
802.11 QoS mechanism to guarantee the lack of agreement. As a direct result of network congestion, the voice Service Will not be accorded priority interrupt calls will occur. Although the IEEE is committed to research related to 802.11e QoS quality assurance agreement, but it can be approved this year is uncertain. However, many private VoWLAN devices provide QoS or use some of the future 802.11e standard part. In fact, Wi-Fi Alliance recently approved the 802.11e standard part, the use of such equipment manufacturers devices can also receive QoS.
WLAN radio frequency conflicts and high utilization can greatly affect the call quality, and therefore the planning of WLAN should fully considered. In addition, the blind spot in the enterprise wireless LAN coverage is also very common, this can easily lead to the occurrence of dropped calls.
3, coverage and roaming AP roaming is a feature of the 802.11 protocol, which enable VoWLAN phone can automatically switch between different AP and mobile. This must be very fast switching time in order to achieve smooth handoff is not dropped. AP is usually the treatment quickly, but with the AP connected to cable transmission systems often have delays, and this delay is more than VoWLAN system limits.
VoWLAN system design time to particular attention. When users roam from one AP to another AP, the traditional WLAN authentication protocol will produce data flow interruption. Interruption, lasting from 0.25 to 0.5s, which depends on network topology and authentication Server Position. VoWLAN users often move frequently between the switch in the AP, the traditional authentication, mobile terminals may be heard when the call both momentary interruption. Therefore, the vast majority of VoWALN end solutions require a proprietary pre-accounting priority roaming algorithm to improve voice quality, and when the user moves within range of the AP to maximize the bandwidth switching.
AP's transmit power should meet the State Radio Management Committee of the transmission power requirement that the maximum transmit power should be
