何謂 cable modem ?

纜線數據機
(Cable Modem 或稱 C.M.) ，是利用有線電視雙向同軸網路提供網際網路相關應用服務的技術，上行頻率介於5至50MHz，下行頻率佔用一個或以上的電視訊道頻寬(6MHz)。

A cable modem
is a type of network bridge and modem that provides bi-directional data communication via radio frequency channels on a HFC and RFoG infrastructure. Cable modems are primarily used to deliver broadband Internet access in the form of cable Internet, taking advantage of the high bandwidth of a HFC and RFoG network. They are commonly deployed in Australia, Europe, Asia and Americas.

Cable modems and VoIP

With the advent of Voice over Internet Protocol (VoIP) telephony, cable modems have been extended to provide telephone service. Some companies which offer cable TV service also offer VoIP phone, allowing customers who purchase cable TV to eliminate their plain old telephone service (POTS). Because many telephone companies do not offer naked DSL (DSL service without POTS line service), VoIP use is higher amongst cable modem users. Any high-speed Internet service subscriber can use VoIP telephony by subscribing to a third-party service (e.g., Vonage, Skype), the problem is that doing so, you need to turn on your computer to use the telephone, while cable modems have a port to connect the phone directly, without using a computer. However, there are also stand-alone VoiP systems available that connect directly to a broadband router (wired or wireless).

Many cable operators offer their own VoIP service, based on PacketCable. PacketCable allows multiple system operators (MSOs) to offer both high-speed Internet and VoIP through the same cable transmission system. PacketCable service has a significant technical advantage over third-party providers in that voice packets are given guaranteed quality of service across their entire transmission path, so call quality can be assured.

When using cable operator VoIP, a combined customer premises equipment device known as an embedded multimedia terminal adapter (E-MTA) will often be used. An E-MTA is a cable modem and a VoIP adapter (MTA, multimedia terminal adapter) bundled into a single device.

出自:
http://zh.wikipedia.org/zh-tw/Cable_modem
http://en.wikipedia.org/wiki/Cable_modem