facility where signals are first received, processed, formatted, and then distributed downstream to the cable network: the transportation and distribution network. The headend facility is usually unmanned, under security fencing, and is similar to a telephone company central office.
  • Transportation network: A transportation network links a remote antenna site to a headend or a remote headend to the distribution network. The transportation network can be microwave, coaxial supertrunk, or fiber-optic.
  • Distribution network: In a classic cable system called a tree-and-branch cable system, the distribution network consists of trunk and feeder cables. The trunk is the backbone that distributes signals throughout the community service area to the feeder and typically uses 0.750-inch (19-mm) diameter coaxial cable. The feeder branches flow from a trunk and reach all of the subscribers in the service area via coaxial cables. The feeder cable is usually a 0.50-inch (13-mm) diameter coaxial cable.
  • Subscriber drop: A subscriber drop connects the subscriber to the cable services. The subscriber drop is a connection between the feeder part of a distribution network and the subscriber terminal device (for example, TV set, videocassette recorder [VCR], High Definition TV set-top box, or cable modem). A subscriber drop consists of radio grade (RG) coaxial cabling (usually 59-series or 6-series coaxial cable), grounding and attachment hardware, passive devices, and a set-top box.
    • Content 2.2 Describing Cable Technology 2.2.4 Cable System Benefits The cable system architecture provides a cost-effective solution for densely populated areas by cascading a broadcast architecture to the users. The development of cable systems made new services possible. Cable systems support telephony and data services and analog and digital video services. With the advent of high-speed data, telephony, and similar services, larger cable operators adopted a common practice of keeping various equipment (for example, telephone switches and CMTS) in the same facility, integrating all types of services—telephony, data, and analog and digital video services. A high-speed cable data connection provides a cost-effective solution for accessing the Internet. Businesses that employ teleworkers can gain the following benefits from this widely available high-speed cable Internet access method: Cable provides teleworkers with secure high-speed remote access to the enterprise network with the same level of accessibility that workers in the office have and access to the Internet for e-mail communication and using corporate applications.
    Content 2.2 Describing Cable Technology 2.2.5 Sending Digital Signals over Radio Waves The electromagnetic spectrum encompasses a broad range of frequencies. Frequency is the rate at which current (or voltage) cycles occur; that is, the number of “waves” per second. Radio waves, generally called RF, constitute a portion of the electromagnetic spectrum roughly between approximately 1 kilohertz through 1 terahertz. When users tune a radio or TV set across the RF spectrum to find different radio stations or TV channels, they tune the radio or TV to different electromagnetic frequencies across that RF spectrum. The same principle applies to the cable system. The cable TV industry uses a portion of the RF electromagnetic spectrum. Within the cable, different frequencies carry TV channels and data. At the subscriber end, equipment such as TVs, VCRs, and High Definition TV set-top boxes tune to certain frequencies that allow the user to view the TV channel or, using a cable modem, to receive high-speed Internet access. A cable network is capable of transmitting signals on the cable in either direction at the same time. The following frequency scope is used: The downstream frequency range is divided into channels (6 MHz channels in North America and 7 to 8 MHz for Europe). The range of frequencies between the upstream and downstream frequency ranges is called a guard band. The guard band is required because of the cutoff characteristics of the high-pass and low-pass filtering. The filtering ensures that the signal does not spill into the adjacent spectrum. The cable industry defines the cable TV spectrum for the downstream path as follows: There is no frequency plan for the upstream path. The cable operator can monitor the frequency band of the upstream and place the upstream data signals into clean areas where there is no interference from noise and other signals. The area between 5 and 15 MHz is usually noisy and unusable. TV signals may also be transmitted over the air, and the channel assignments may not align with the over-the-cable assignments. Much of the RF spectrum is reserved for radio communications and therefore cannot be used for TV signals. In the over-the-air TV broadcast environment, a very-high frequency (VHF) range covering 30 to 300 MHz and an ultra-high frequency (UHF) range covering 300 to 3000 MHz are defined.
    Content 2.2 Describing Cable Technology 2.2.6 The Data-over-Cable Service Interface Specification: DOCSIS DOCSIS is an international standard developed by CableLabs, a nonprofit research and development consortium for cable-related technologies. CableLabs tests and certifies cable equipment vendor devices (cable modem [CM] and cable modem termination systems [CMTS]) and grants DOCSIS-certified or Qualified status. DOCSIS defines the communications and operation support interface requirements for a data-over-cable system and permits the addition of high-speed data transfer to an existing CATV system. Cable operators employ DOCSIS to provide Internet access over their existing HFC infrastructure. DOCSIS specifies the Open Systems Interconnection (OSI) Layers 1 and 2 requirements: DOCSIS currently uses two standards, and a third standard is under development: Note
    More information about DOCSIS is available at http://www.cablemodem.com/specifications. Plans for frequency allocation bands differ between U.S. and European cable systems. Therefore, Euro-DOCSIS was adapted for use in Europe. The main differences between DOCSIS and Euro-DOCSIS relate to