A Data Communication Historical Series
By Bob Pollard
Internet Connection Media high-lites (ca 2003):
The standard high speed Internet connection through a 56Kbps MODEM on a telephone line, used by many individuals for years, is being replaced by higher speed services. Such as; DSL (Digital Subscriber Line), ADSL (Asymmetric Digital Subscriber Line), HDSL (High-bit-rate Digital Subscriber Line) and VDSL (Very High bit-rate Digital Subscriber Line), and in addition, Cable connections, all offering a much higher transmission speed.
Examples of the various connection media is provided below:
56.6kbps MODEM; a plug-in unit contained in the Computer main housing (Main Frame)
DSL (Digital Subscriber Line) MODEM Typical Interface Connection:
PSTN: (Public Switched Telephone Company)
DSLAM: (DSL Access Multiplexer)
Low Pass Filter: Normally required to separate the telephone frequency (band) from the high speed digital signal. The filter is inserted in the line at the telephone or fax machine connection to avoid interference from the high frequency signal.
The DSLAM (DSL Access Multiplexer) at the access provider is the equipment that makes DSL function. A DSLAM takes connections from many users and aggregates them onto a single, high-capacity connection to the Internet. The DSLAM units are generally flexible and able to support multiple types of DSL, as well as provide additional functions such as routing and dynamic IP address assignment for users
The Telephone Company can provide the ISP (Internet Service Provider) functions or the ISP functions can be provided by a separate entity.
A Cable MODEM can be either an internal or external computer unit. The external connection to the computer is normally through an USB (Universal Serial Bus) or an Ethernet connection.
A benefit of the cable MODEM for Internet access is that, unlike ADSL, its performance isn’t affected by the distance from the central cable office. A digital CATV system is designed to provide digital signals at a particular quality to a user’s household regardless of the distance. On the upstream side, the burst modulator in a cable MODEM is programmed with the distance from the head-end, and provides the proper signal strength for accurate transmission.
All computer network devices have a MAC (Media Access Control), but in the case of a cable MODEM the tasks are more complex than those of a normal Network Interface (NIC) card. For this reason, in many cases, some of the MAC functions will be assigned to a central processing unit (CPU); either the CPU in the cable MODEM or the CPU of the user's system.
A Cable MODEM can be either an internal or external computer unit. The external connection to the computer is normally through an USB (Universal Serial Bus) or an Ethernet connection. In some cases, the cable MODEM can be part of a cable box, requiring that only a keyboard and mouse be connected for Internet access. If the cable system has upgraded to digital cable, the new cable box the cable company provides will be capable of connecting to the Internet, whether or not Internet access is through the CATV connection.
HOME and Cable Company example: