WLAN Wireless network telephone system technology application

With the improvement of WiFi standard, 802.11 chip volume decreasing and function expanding, wireless area network voice (Vowlan) telephone system is also gradually improved. Dual-band mobile phones can use WLAN connections to provide reliable home voice services, while broadband telephony services are connected to laptops via WLAN. On the other hand, Internet telephony handsets, which are structured in WLANs, can easily support multiple handsets with a single WLAN base station, compared to traditional wireless telephones with low-cost advantages.

The 802.11 standard establishes the basic mechanism needed to provide a reliable, high-performance WiFi network telephone system. Notable examples are security (802.11I/WPA) and QoS (802.11e/wi-fi multimedia). In addition, the jumpstart for wireless, such as Atheros Open program code, makes it possible for all users to quickly set the configuration of WLAN phone handsets even when they cannot display English letters and numbers.

One of the items that has not been standardized in the WLAN telephony system is the polling method (polling methods). Therefore, in this paper, the existing two polling methods, respectively, discuss their different advantages and disadvantages, and particularly in mobile devices, the most critical factor-power consumption.

All methods to reduce power consumption must be as much as possible to allow the user device to use Low-power sleep mode, while 802.11 chips must be in sleep mode with the lowest electricity consumption to support this practice 802.11 chips must be supported by the lowest possible consumption of sleep mode. For example, Atheros's AR6000 Mobile Radio frequency single chip (Radio-on-a-chip mobile; ROCM) device to achieve a very low energy consumption of sleep mode, as well as automatic power-saving mode (Automatic Power-save Delivery; APSD) technology. ROCM also delivers excellent performance, enabling high-speed transmissions to shorten send/receive time, while embedded processors on the chip are self-contained drivers that can be allocated to handle regular network maintenance operations on host processors. Through the above approach and other power saving strategy, ROCM chip can improve the efficiency of WLAN operation, the effect can be as high as six times times the traditional WLAN chip, so can improve battery life. Now a new generation of 802.11 devices, which can implement a variety of VoIP applications, contains such chips. (Computer science)

Import voice into WLAN

While the 802.11 WLAN leverages high-performance components to provide reliable overall performance, the characteristics of this media still face considerable challenges in addressing voice traffic. Since WLAN uses a license-free spectrum, a large amount of interference from different external devices and other WLANs must be tolerated. In addition, as with other IP networks, WLANs do not support synchronous operations (synchronous operation). As a result, predictions cannot normally be made at the microsecond level. Since VoIP is a fixed digital rate (CBR) application that generates VoIP packets at fixed intervals (i.e. frames), the Csma competition method of WLAN obviously lacks the central synchronous timing (centralized synchronous timing).

This phenomenon contrasts with the standard telephony mechanisms that are implemented by mobile phone systems. The mobile phone system uses the authorized spectrum and carefully planned base station deployment to minimize radio interference. Mobile phone systems are synchronized from the phone to the backbone, so they can grasp the microsecond-level timing and never deviate, so they can predict the size of the capacity and the capacity to provide a single category of service design applications: Voice.

The features of these mobile phone systems make it easy to comply with the ITU-T recommended G.114 Standard, which specifies that endpoints should not be more than 150 microseconds behind the endpoint's latency budget. Because the overall architecture of the mobile phone system applies the time-pulse voice packets in a determined manner, there is no need to prioritize voice packets with a special quality of service (QoS) mechanism because of the need to ensure low latency. The mobile phone system uses existing slots, multiple workers and voice service management to join the data service.

In contrast to WLANs, voice services must be designed with the help of a feature intended for data. The WLAN can only use the endpoint for a portion of the endpoint latency budget of 150 microseconds, and if both ends use WLAN for dialogue, then the deferred budget is further reduced. In addition, if the voice packet must cross the Internet or a busy corporate network, the packet will not be able to avoid late arrivals and sometimes even inability to reach them. Late closures may arrive in droves.

These issues are familiar to people who use a legacy transcoding device for voice communication in an internetwork or a common WLAN. One of the ways to build high quality Vowlan is to change the WLAN to meet the needs of traditional encoders. In fact, the 802.11 mac can be changed to use synchronous, slot-like TDMA practices for both full time and time-sharing, and this approach can effectively address the problem of WLAN transmission, although such systems are often incompatible with existing WiFi devices and networks.

While a fully synchronized network is attractive, the lack of strict synchronization is the main strength of 802.11. Over the years, we have seen the advantages of such IP networks in the competition between Ethernet and ATM networks. When reliable, adaptable (good) access to a strict (perfect) sequential approach, a satisfactory approach is usually more diverse than popular.

Another reason to avoid using synchronization when designing Vowlan systems is that these systems do not operate in a closed environment. The main selling point of using WLAN to transmit voice is to allow dual-mode mobile phones and other voice devices to take advantage of existing WLAN infrastructures.

Next-generation decoder

One way to improve the existing 802.11 infrastructure is to leverage newer speech decoders developed for Internet applications. These decoders greatly simplify the design of Vowlan. Inefficient Internet telephony environment, enabling the development of decoder, can be very low speed to achieve good speech quality.

For example: The popular Skype network telephony system core ILBC decoder, can provide the equivalent of high-end ITU g.729 decoder features, the ITU decoder only 8kbps, to provide a payphone-like voice quality, and from the global IP sound ILBC decoder, The desired bit rate is slightly higher -13.3kbps. Global IP Sound says their encoder has better voice quality than the PSTN, and can tolerate up to 30% of the packet loss. The Network Engineering research team (Internet Engineering Task FORCE;IETF) has established standards for this decoder. The CableLabs is applied to the PacketCable AV Decoder specification of the multimedia terminal adapter and the media gate to be specified as the necessary decoder.