Set-Top Lexicon: What Is A Back Channel?

by Jane Clarke, Feb 17, 2011, 2:30 PM

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CIMM's Set-Top Box Data Lexicon is a compilation of terms and definitions associated with Set-Top Box data and its measurement. This Word-A-Week column highlights a term and definition from the CIMM Lexicon. It is our hope that this will help in creating a common language for Set-Top Box data usage and help expedite the roll-out of the data for its many industry applications.

Continuing on last week's discussion of Return Path Data, which is a more accurate term for what we tend to call Set-Top Box data, we now take a look at the term "Back Channel" also known as Back Path or Back Haul.

It is the existence of the Back Channel that enables us to receive the data from its various source points. But the mere existence of a Back Channel is not a guarantee of receiving a full range of data gathered on the box. Some Back Channels, lacking bandwidth, do not have enough capacity to return a full range of data. In addition, Satellite companies receive the back channel data from phone lines which can vary by household.

Back Channel

See also Back Haul and Back Path

CIMM DEFINITION : 1. A return path connection that can be used by a Set-Top Box to communicate with the cable headend; Can be used to communicate to cable headend or the service provider. It applies to asymmetric data connections and is the slower of the two data paths in the connection.

2 : "A communication channel that can be used by a Set-Top Box to communicate with the cable headend or other devices. Also known as Back Haul. A term used to describe the technology which provides the infrastructure for electronic traffic traveling from the subscriber to the platform company." (Source: Nielsen)

3 : "Term commonly used to describe the action of sending data back to a host server over a phone wire or cable pipe." (Source: itvt.com/glossary)

NOTE- Available bandwidth on the return path is severely limited within the existing digital cable environment, and exceeding bandwidth limits can be catastrophic -i.e., STB reboots, network downtime. Motorola systems are limited to a raw bitrate of 256 Kbps per node (i.e., 500 to 1500 STBs), much of which is consumed by the system itself, VOD session management, IPG interaction, interactive application processing, etc., Also, communication on this return path is limited to User Datagram Protocol (UDP), which does not guarantee delivery of information from STB to the back-end, and generates additional bandwidth usage by applications to confirm delivery and resend lost data. Cisco systems provide slightly more return path bandwidth and support Transmission Control Protocol (TCP) which guarantees delivery of data, but typically reserve more return path bandwidth for system and resident application (e.g., SARA) use. Collecting STB measurement data with low Latency is a complex task, especially for census data. Load on the back channel is an issue in downloading STB data. (Source: FourthWall Media

Please refer to the CIMM Lexicon online at http://www.cimm-us.org/lexicon.htm for additional information on these and other terms.

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