This short course will introduce you to the principal concepts of TV broadcast and internet broadband over Cable, the underlying technology, and the delivery mechanism to the consumer’s home.

The Headend:

The headend acts as a central hub where TV signals are received, processed, and distributed to millions of households. It consists of various components and technologies, that collectively ensure a seamless TV broadcast experience and internet connection.

Headend Components:

The main components of the headend are:

• Receivers: The headend receives TV signals, by Satellite or over the internet (IP Streams), integrating them into the cable broadcast lineup.
• Encoder: This device digitizes the received video and audio content, compresses it by using codecs like MPEG, and prepares it for transmission over the cable network.
• Multiplexer: The multiplexer combines multiple channels into a single transport stream, maintaining synchronization and optimizing bandwidth utilization.
• Conditional Access System (CAS): CAS ensures that only authorized subscribers can access specific TV channels or pay-per-view content, preventing unauthorized access.
• Modulator: The modulator translates the digital compressed signal into analog format for transmission over the cable network.
• Optical Transmitter: In some cases, fiber optic cables are used for long-distance distribution, and optical transmitters convert the electrical signals into optical signals for efficient transmission.
• Upstream Receiver: It receives and processes signals transmitted from the consumers’ premises via the cable modems, allowing interactive features and internet access.

The DOCSIS Technology:

Digital Over Cable Service Interface Specification, or in short – the DOCSIS technology, enables the transmission of high-speed internet and cable TV services over a coaxial cable. DOCSIS serves as an industry standard that ensures compatibility and interoperability between all headend components, set top boxes, cable modems, and other developments by cable operators and different vendors.

One key feature of DOCSIS is that it enables bi-directional data flow, so not only the reception of TV signals (one way) but also a return path (two way) for interactive features, such as video on demand and internet access.

The CMTS

CMTS stands for Cable Modem Termination System. The CMTS facilitates communication between cable modems in the customer premise and the headend.

The CMTS acts as a hub that receives and sends data between the cable network and the internet. It converts the RF signals transmitted over coaxial cables into IP, so it can be understood by the internet infrastructure. Additionally, it manages the allocation and control of bandwidth, ensuring a fair distribution of network resources among multiple cable modems.

Some of the key functions of a CMTS are:

• Downstream communication: The CMTS receives digital data from our network and converts it into a format that can be transmitted to the cable modems.
• Upstream communication: It receives data from cable modems, aggregates it, and transmits it back to our network.
• Address assignment: The CMTS assigns unique IP addresses to each connected cable modem, allowing them to be identified and communicate with the internet.
• Quality of Service (QoS) management: The CMTS ensures that bandwidth is allocated appropriately to maintain service quality for all connected cable modems, giving priority to certain types of traffic like voice or video.
• Security: CMTS devices enforce security measures to protect the cable network from unauthorized access and potential attacks.

Delivery to the Consumer:

a. Cable TV through Set-Top Box (STB): Television signals received at the headend are transmitted to the consumer’s home through coaxial cables. At the consumer’s end, a set-top box decodes the signal, allowing users to browse through the channel lineup, access interactive features, and control their TV viewing experience through a user-friendly interface.

b. Broadband Internet via Cable Modem: Simultaneously, the same coaxial cable also carries high-speed internet services to the consumer’s home. Cable modems act as the bridge between the cable network and the user’s devices, enabling fast internet connectivity.

Glossary:

• CPE – Customer Premise Equipment, usually refers to either STB’s or CM’s 
• Set top box: (or STB) a type of CPE that connects to a television and receives digital signals from the headend to display the channels and content on the TV.
• Cable modem: A cable modem (or CM) is a CPE that connects a home network to the internet via the existing coaxial infrastructure. 
• Transport Stream: a digital data stream used for transmitting video, audio, and other information to subscribers. Transport streams are typically multiplexed, meaning that multiple audio and video streams are combined into a single stream for transmission, which allows for efficient use of bandwidth and enables the delivery of multiple channels to subscribers.
• Channel lineup: a list of available channels offered to subscribers.
• Encoder: a device used in a cable headend to convert audio and video signals into a compressed digital format.
• Multiplexer: A multiplexer is a device that combines multiple audio and video signals into a single stream for efficient transmission over a cable network.
• CAS (Conditional Access System): A CAS is a headend system used to encrypt and secure content. It controls access to specific channels and ensures that only authorized subscribers can view them.
• Return path: the return path refers to the portion of the cable network that carries signals from subscribers back to the headend. It allows for two-way communication, such as viewers interacting with interactive TV features or sending data to the operator.