The DOCSIS Set-top Gateway (DSG) specification defines the interface requirements on a DOCSIS CMTS and DOCSIS CM to support the configuration for transport of a class of service known as "Out-Of- Band (OOB) messaging" between a Set-top Controller (or application servers) and the customer premise equipment (CPE). In general, the CPE is intended to be a digital Set-top Device, but may include other CPE devices, such as Residential Gateways or other electronic equipment. Figure 1-1 provides the context for this specification in relation to the data over cable reference architecture and the other interface specifications in the family.

Traditionally, the physical transport of this Out-Of-Band messaging has been carried over dedicated channels, as specified by [ANSI/SCTE 55-1] and [ANSI/SCTE 55-2]. This specification defines the applicable communications standards and protocols needed to implement an Out-Of-Band messaging interface to the Set-top Device using DOCSIS as a transport. It applies to cable systems employing HFC and coaxial architectures. Specifically, the scope of this specification is to:

• Describe the communications protocols and standards to be employed
• Specify the data communication requirements and parameters that will be common to all units

The intent of this document is to specify open protocols, with a preference for existing, well-known and well-accepted standards. This interface specification is written to provide the minimal set of requirements for satisfactory communication between the Set-top Controller and the Set-top Device over the DOCSIS transport. "DOCSIS Set-top Gateway" (DSG) shall be the general term used to describe this interface.