The headend/control part of the linkage with an embedded cable modem, for use in situations where modems are nested inside devices such as a set-top boxes, or digital cable-ready TVs. A clunky term, to be sure, but not one that will likely ever see the light of day, in a consumer sense.
Hey. Could be worse: The inventors of DSG originally wanted to call it “DOCSIS Out-of-band Gateway,” or “DOG” for short. Sort of seems like an insult to dogs.)
DOCSIS is the subject of a 35-page CableLabs specification. If that sounds daunting, here’s a simplified way to imagine the workings of a DSG: Imagine a cable-ready HDTV that contains an embedded cable modem for purposes of two-way cable communications. (This could also be a digital video recorder, or a game console, or a portable video player — or anything else you can imagine as a cable-connected consumer device.)
Say this HDTV set is under the control of a customer who just initiated a video on demand session. The request is routed to the embedded cable modem, which passes it upstream, over the cable plant, to the headend. There, it goes where traffic from cable modems always goes: To the cable modem termination system. The CMTS looks at the incoming packets. “Aha,” it says. “You’re a session-set-up for a set top. Over there, please.”
It passes the VOD initialization request to the DSG, which talks back and forth with the set-top controller, which talks with the VOD controller, to set-up the session. The confirmation, and session details, move back to the embedded cable modem and HDTV in reverse order. Back at the couch, everything seems the same. Maybe the VOD title arrives a little faster, but faster in a way that isn’t obvious, except that it seems to work really well.
This pattern repeats for everything that needs to occur, or is planned to occur, between cable-connected devices and the servers and routers that handle information flows. Masterminding the flows is the DSG.
In a diagram, the DSG attaches to the CMTS on one side, and other background controllers (such as existing set-top controllers) on the other side. It’s partly a router, partly a proxy server, mostly an intermediary. Its primary role is to manage the business policies that describe how, and under what circumstances, different devices, with embedded cable modems, are allowed to connect.
Usage: DSG gurus are quick to point out that just because a device contains an embedded cable modem, that doesn’t mean “surf the Internet or send e-mail.” So far, DSG is strictly for the shuttling of command and control information.