共查询到20条相似文献,搜索用时 109 毫秒
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PSTN/ISDN仿真子系统是下一代网络业务控制层中的一个重要子系统,本文在对它进行业务需求分析的基础上,主要对仿真系统的体系架构进行了介绍,并对目前的研究状况进行了分析。 相似文献
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可视电话从最初的基于PSTN网络的可视电话发展到基于ISDN网络的可视电话,再到今天基于IP互联网的可视电话,走过了20多年的历程。 相似文献
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可视电话的主要功能是点对点的视频通信,即支持彩色活动图像及语音的双向实时传输。从世界上诞生第一台可视电话到现在,可视电话经历了从沉寂到复苏的坎坷过程。在今天的多媒体通讯时代 可视电话又展现出了广阔的发展前景。一、可视电话的分类和发展状况可视电话产品主要有两种类型:一种是基于计算机的可视电话,另一种是一体化可视电话。而按照传输信道来分,以上两种类型又可分为在模拟电话网和在综合业务数字网ISDN上工作的可视电话。以个人电脑为核心的可视电话,是在计算机上安装摄像头、图像处理板和语音输入输出设备和可视电话应用软件,即可与基于PSTN的H.324标准,或基于ISDN的H.320标准的可视电话建立通信。如果图像压缩和解压的软件处理得当,图像的性能就比较好。除了以上两种网络环境的可视电话外,近一两年还出现了一种依托Internet的可视电话 用户只要支付上网费用,应用IP协议和标准实现实时的视频业务就可实现IP语音、可视图文、电子邮件等多种功能。但是,由于购买电脑或上网要花费比较高的费用操作又需要一定的电脑知识而且每次必须在开机状态下使用,所以,这种基于计算机的可视电话短期内还不宜大量投入生产。市场上比较多的还是... 相似文献
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基于H.264的可视电话软件开发 总被引:5,自引:2,他引:3
为了开发基于H.264标准的可视电话,采用高性能高速视频数字处理芯片(TMS320DM642)作视频编解码器,充分利用芯片的并行和流水处理功能,在单芯片上实现了视/音频编解码的并行实时处理,并达到可视电话实时通信要求. 相似文献
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会议电视第四讲桌面式会议电视与可视电话 总被引:4,自引:0,他引:4
本文首先分析了桌面会议电视是会议电视的一种发展趋势,接站介绍了几种桌面会议电视产品,然后介绍了几种LAN和Internet桌面会议电视,最后分析了PSTN多媒体可电话的编解码器的结构。 相似文献
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在PC机上实现GSTN网络电视电话终端 总被引:1,自引:0,他引:1
在概述了H.324建议并讨论了GSTN电视电话终端的几种实现方案后,介绍了H.324建议设计开发的基于PC机的GSTN电视电话终端原型。对其组成,特点和性能进行了详细论述,最后提出了进一步的研究方向并展望了这种电视电话终端的应用前景。 相似文献
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This paper proposes a new translation procedure which is based on a jumbogroup constitution for simultaneous multiplex transmission of telephone and videophone signals over a coaxial 60-MHz system and describes transmission characteristics of the C-60M system using the translation procedure. The translation procedure reduces group-delay distortion harmful to video transmission without changing telephone transmission capacity or without degrading telephone transmission characteristics. It is also capable of transmitting either 36 videophone signals with 1 MHz bandwidth or nine videophone signals with 4.3 MHz bandwidth. 相似文献
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K. Peppas F. Lazarakis D. I. Axiotis T. Al-Gizawi A. A. Alexandridis 《Wireless Networks》2009,15(7):859-873
In this paper we investigate the system level performance of an Orthogonal Frequency Division Multiplexing (OFDM) Wireless
LAN network enhanced through Multiple-Input Multiple-Output (MIMO) techniques and compare it to the performance of the conventional
Single-Input Single-Output (SISO) network. The MIMO scheme we apply is closed loop power allocation based on Singular Value
Decomposition (SVD). The above investigations are carried out by means of a software based simulation platform. In order to
characterize the system level performance accurately, a suitable link-to-system interface based on channel capacity has been
developed. The performance evaluation is achieved by monitoring the average system throughput and the percentage of satisfied
users. Extensive system level simulations have been carried out that prove the superiority of MIMO techniques especially for
heavy traffic load conditions. 相似文献
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详细介绍了PHILIPS公司新近推出的画中画芯片SAB9077H的结构、特点、功能和使用方法;随后给出了在1FH模式下的典型应用及在监控、保安系统、可视电话或电视会议中的应用实例。 相似文献
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Shin‐Jer Yang 《International Journal of Network Management》2001,11(2):91-101
This paper proposes an empirical approach to model the performance of Ethernet with QoS (Quality of Services) parameters. Hence, how to model the performance of Ethernet becomes a critical issue for the LAN implementation and operation. In the QoS approach, however, Ethernet network performance can be dynamically tuned by existing and enhanced operation parameters based on the current information status of the Ethernet LAN system. Consequently, Ethernet performance can be predicted and maintained through using the proposed methodology, and then to promote the system throughput. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
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Aki Silvennoinen Michael Hall Sven-Gustav Häggman 《Wireless Personal Communications》2007,41(4):487-505
The effect of terminal movement on the performance of the IEEE 802.11 g wireless LAN (WLAN) system is evaluated using a measurement
set-up including a radio channel simulator. The evaluation is based on laboratory measurements of WLAN PC cards in different
simulated radio environments. In the measurements, two different radio channel models are used; the exponential channel model
and the UMTS vehicular channel model. The measurement results indicate promising operation of IEEE 802.11 g WLAN systems as
such. However, the use of different packet sizes has a significant effect on the system behaviour. With large packets the
terminal is more likely to experience channel estimation errors than with small packets. This is due to the fact that the
IEEE 802.11 g receiver estimates the channel only once per frame, and uses this estimation over the entire frame. Based on
the measurement results we suggest a modification to the medium access control (MAC) layer operation that overcomes this problem:
the use of optimized fragmentation. 相似文献