第11章(6)教材配套课件

adj. 手提的，便携式的；轻便的
federated
adj. 联邦的；联合的；结成同盟的
arbitrary
adj. 任意的
Unit 11 Internet Communication
implementation smartphone in the reverse order IP packets digital-to-analog conversion voice stream open source voice codec portable devices
Unit 11 Internet Communication
Fig 11.1 VoIP
Unit 11 Internet Communication
Internet telephony refers to communications services — voice, fax, SMS, and/or voice-messaging applications— that are transported via the Internet, rather than the public switched telephone network (PSTN). The steps involved in originating a VoIP telephone call are signaling and media channel setup, digitization of the analog voice signal, encoding, packetization, and transmission as Internet Protocol (IP) packets over a packetswitched network.
宽带语音
SMS(Short Message Service)
短信通群法系统
PSTN(Public Switched Telephone Network )
公共交换电话网络
HD(High Definition)
高清
iLBC 一种专为包交换网络通信设计的编解码，优于目
前流行的G.729、G.723.1
Unit 11 Internet Communication
commonly refers to the communication protocols, technologies, methodologies, and transmission techniques involved in the delivery of voice communications and multimedia sessions over Internet Protocol (IP) networks, such as the Internet. Other terms commonly associated with VoIP(Fig 11.1) are IP telephony, Internet telephony, voice over broadband (VoBB), broadband telephony, IP communications, and broadband phone.
n. 实现；履行；安装启用 智能手机 相反的顺序 IP数据包 数模转换 语音流 开源语音编解码器 便携设备
Unit 11 Internet Communication
VoIP(Voice over Internet Protocol) 互联网协议语音
VoBB(Voice over BroadBand )
Unit 11 Internet Communication
Unit 11 Internet Communication
11.1 Text 11.2 Reading Materials
Unit 11 Internet Communication
11.1 Text
Internet Telephony & VoIP Voice over IP (VoIP, Voice over Internet Protocol)
Unit 11 Internet Communication
Early providers of voice over IP services offered business models (and technical solutions) that mirrored the architecture of the legacy telephone network. Second generation providers, such as Skype have built closed networks for private user bases, offering the benefit of free calls and convenience, while denying their users the ability to call out to other networks. This has severely limited the ability of users to mix-and-match third-party hardware and software. Third generation providers, such as Google Talk have adopted the concept of Federated VoIP which is a complete departure from the architecture of the legacy networks. These solutions typically allow arbitrary and dynamic interconnection between any two domains on the Internet whenever a user wishes to place a call.
Unit 11 Internet Communication
On the receiving side, similar steps (usually in the reverse order) such as reception of the IP packets, decoding of the packets and digital-to-analog conversion reproduce the original voice stream. Even though IP Telephony and VoIP are terms that are used interchangeably, they are actually different; IP telephony has to do with digital telephony systems that use IP protocols for voice communication, while VoIP is actually a subset of IP Telephony. VoIP is a technology used by IP telephony as a means of transporting phone calls.
11.1.1 Exercises
1. Put the Phrases into English
(1) 通信协议；
(2) 媒体信道；
(3) 数字化模拟语音信号； (4) 分组交换网络；
(5) 7) 封闭的网络。
Unit 11 Internet Communication
Unit 11 Internet Communication
VoIP systems employ session control protocols to control the set-up and tear-down of calls as well as audio codes which encode speech allowing transmission over an IP network as digital audio via an audio stream. The choice of codec varies between different implementations of VoIP depending on application requirements and network bandwidth; some implementations rely on narrowband and compressed speech, while others support high fidelity stereo codes. Some popular codes include u-law and a-law versions of G.711, G.722 which is a high-fidelity codec marketed as HD Voice by Polycom, a popular open source voice codec known as iLBC.
Unit 11 Internet Communication
Technical words and phrases
session
n. 对话
originate
vi. 发源；发生
subset
n. 子集
mirror
vt. 反射；反映
legacy
adj. 旧的，传统的
reverse
n. 背面；相反
portable
Unit 11 Internet Communication
3. Translation (1) The steps involved in originating a VoIP telephone call are signaling and media channel setup, digitization of the analog voice signal, encoding, packetization, and transmission as Internet Protocol (IP) packets over a packet-switched network. (2) Second generation providers, such as Skype have built closed networks for private user bases, offering the benefit of free calls and convenience, while denying their users the ability to call out to other networks.
2. Put the Phrases into Chinese (1) voice communications; (2) multimedia sessions; (3) a packet-switched network; (4) business models; (5) technical solutions; (6) third-party hardware; (7) dynamic interconnection; (8) compressed speech; (9) high fidelity stereo codecs.
Unit 11 Internet Communication
VoIP is available on many smart phones and Internet devices so that users of portable devices that are not phones, may place calls or send SMS text messages over 3G or Wi-Fi.