共查询到17条相似文献，搜索用时 106 毫秒
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前言
随着互联网的迅速发展,以IP技术为基础的新一代通信系统逐渐发展成熟,其中以VOIP技术为代表的通信技术已逐渐得到广泛的应用.SIP、H.323、MGCP等网络通信协议的开发为VOIP技术提供了技术保障,目前在国内正在大规模实施的NGN技术的核心即应用了VOIP技术. 相似文献
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介绍了VOIP的发展及特点,对基于H．323协议的VOIP系统构成进行了介绍,详细介绍了H．323协议标准和协议的体系结构。 相似文献
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随着IP网的迅速发展,人们除了在其上传输数据业务外,也开始传送语音等传统PSTN业务,VOIP随之产生。首先介绍了VOIP的原理,接着对其关键技术进行了分析,最后对其应用前景进行了探讨。 相似文献
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介绍了VOIP中的影响QOS的因素。然后讲了WLAN中VOIP的QOS存在的问题,对VOWLAN中的QOS目前研究状况进行了综述,并对进一步需要研究的问题进行了讨论。 相似文献
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介绍了基于网络上的VOIP电话的关键技术。要保证VOIP电话的语音质量,一是选用语音网关及适当的网守控制方式,二是提高IP网络的服务质量(QoS),使网络时延、时延抖动及包丢失率控制在一定限度以内。 相似文献
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在传统的语音通信业务中,被叫接听电话免费是各大提供商早就推行的一种服务,统称为回拨系统(Callback)。网络电话回拨系统(VOIP CALLBACK)就是运用接电话免费的特点让主叫方以非常低廉的资费获得较优质的语音通信服务的回拨系统。文章设计一款在智能手机平台上通过Wi Fi、GPRS数据传送呼叫信息形式的具备网络电话回拨功能的软终端和服务器系统,实现VOIP语音通信的低成本、低功耗和便携应用,为软交换的进一步研究应用抛砖引玉。 相似文献
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详细介绍了广播电视安全播出应急高度系统的主要技术、组成结构、系统功能。该系统通过分组语音(VOIP)技术利用现有资源,实现了工作模式的创新,为监管部门对广播电视安全播出应急保障任务提供了切实有效的技术手段。 相似文献
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为了提升VOIP的通话质量,提高回声抵消系统中双端通话检测的准确性,本文提出一种新的双门限双端通话检测算法。新算法首先利用小波阈值去噪算法对接收的各信号进行去噪处理;然后对去噪处理后的小波子带信号进行动态能量阈值比较,识别出静音帧、活跃帧和发声帧;再对活跃帧与静音帧进行基音周期比较,以判断活跃帧是处在近端发声阶段,还是回声路径的变化。仿真实验证明,新的双门限检测算法表现良好。 相似文献
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Jon-Arild JohannessenAuthor Vitae Bjørn OlsenAuthor Vitae 《International Journal of Information Management》2011,31(1):30-37
Although often downplayed and instrumental, there is evidence that communication in projects is essential in achieving value creation. Our main interest in this paper is on temporary continuity, a situation where the temporary becomes a permanent condition in social systems. The question that we have address is: What characterizes project communication in a situation with temporary continuity?We argue for the need to transform communication processes into communication capabilities. In a situation with temporary continuity, there is a need to connect to a large number of value-creating processes, and communicating capabilities need to be a part of a communication system, where the aim is to bind together value-creating processes and communication capabilities. We construct a viable system consisting of five sub-systems. To become a viable system, projects in the form of temporary continuity, must handle the potential conflict between a culture of performance and a culture of innovation. This involves developing social mechanisms for coordination and interaction, with a focus on developing communication capabilities, in parallel with focusing on all of the five value-creation processes. 相似文献
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To elucidate a higher rate of premature cardiovascular disease (CVD) in Asian Indian descendants (Roma) in Slovakia, we investigated frequency distribution, correlates and relationship of lipoprotein(a) [Lp(a)] to family CVD risk factors in Roma children and their Caucasian neighbors. The study sample consisted of 607 healthy children aged 7–18 years (55% Roma, 48% male) as part of the biracial (Roma–Caucasian) Slovak Lipid Community Study. Overall, frequency distribution data of Lp(a) were highly skewed to low concentrations, with markedly higher Lp(a) levels in Roma than in Caucasian children (median and range, mg/dL: 14.5; 0–159.2 vs 6.2; 0–112.3, P < 0.001), regardless of age and gender. Lp(a) was positively correlated with apo B (0.159, P = 0.004) in Roma, and LDL cholesterol (0.170, P = 0.005) in Caucasian children. In addition, daily income of the family was negatively related with Lp(a) in Roma (−0.134, P = 0.036) while positively in Caucasians (0.136, P = 0.047). For both race groups, no significant association was found between Lp(a) and age, body mass index, mean arterial pressure, smoking, and physical activity. Also, no significant relationships were examined between serum Lp(a) levels >30 mg/dL in children and family CVD risk factors, except for diabetes mellitus in parents of Caucasian origin (OR 4.46; 95%CI: 1.23–16.20). In a multivariate analysis, daily income, LDL cholesterol or apo B explained ~7% of the variance of Lp(a). This study suggests a significantly higher serum Lp(a) levels in Roma than in Caucasian children and a small effect, in general, of relevant CVD risk factors on the variation of Lp(a) levels in childhood. 相似文献
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Mehul Jariwala S. Suvarna G. Kiran Kumar Alpa Amin A. C. Udas 《Indian journal of clinical biochemistry : IJCB》2014,29(2):181-188
A study of iron, zinc, copper and selenium concentration levels was carried out in three compartments namely, maternal serum (MS), colostrums and cord blood serum (CS) of healthy Indian mothers (n = 42) who delivered healthy normal neonates without any congenital anomalies at Bhabha Atomic Research Centre hospital, Mumbai. Fe, Zn, Cu in maternal serum, cord blood and colostrums were estimated by flame atomic absorption spectrometry while Se was determined by graphite furnace absorption spectrometry. It was seen that there was a significant difference in the level of trace elements in the three compartments. The average levels of Fe in the three compartments were 1,132 ± 519, 2,312 ± 789 and 1,183 ± 602 μg/L while Zn was 514 ± 149, 819 ± 224 and 7,148 ± 2,316 μg/L respectively. Mean Cu values were 1,614 ± 295, 301 ± 77 and 392 ± 174 μg/L respectively while Se values were 70 ± 15, 36 ± 10 and 23 ± 8 μg/L respectively. The results indicated a positive correlation of Fe and Zn concentrations in MS versus CS which were (r = 0.386), (r = 0.572) respectively and Fe levels in MS and colostrums (r = 0.235). A few inter element correlations were found within compartments. Zn and Se showed a negative correlation in both MS (r = −0.489) and colostrums (r = −0.258) while a positive inter correlation of Fe and Zn was seen in MS (r = 0.44) and in CS (r = 0.54). This study gave us an overview of the serum and colostrum values of mother and neonates in Indian population, data of which are scarce. 相似文献
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Five hundred million tweets are posted daily, making Twitter a major social media platform from which topical information on events can be extracted. These events are represented by three main dimensions: time, location and entity-related information. The focus of this paper is location, which is an essential dimension for geo-spatial applications, either when helping rescue operations during a disaster or when used for contextual recommendations. While the first type of application needs high recall, the second is more precision-oriented. This paper studies the recall/precision trade-off, combining different methods to extract locations. In the context of short posts, applying tools that have been developed for natural language is not sufficient given the nature of tweets which are generally too short to be linguistically correct. Also bearing in mind the high number of posts that need to be handled, we hypothesize that predicting whether a post contains a location or not could make the location extractors more focused and thus more effective. We introduce a model to predict whether a tweet contains a location or not and show that location prediction is a useful pre-processing step for location extraction. We define a number of new tweet features and we conduct an intensive evaluation. Our findings are that (1) combining existing location extraction tools is effective for precision-oriented or recall-oriented results, (2) enriching tweet representation is effective for predicting whether a tweet contains a location or not, (3) words appearing in a geography gazetteer and the occurrence of a preposition just before a proper noun are the two most important features for predicting the occurrence of a location in tweets, and (4) the accuracy of location extraction improves when it is possible to predict that there is a location in a tweet. 相似文献