The technologies that make it possible for some packets to get preferential treatment over other packets. Services that run over broadband have different “nutritional” needs; QoS recognizes that not all packets are created equal. It enables broadband service providers to differentiate their broadband services, maybe by goosing available speeds, or by assuring that technologically “needy” services, such as voice or video, run smoothly. In short, QoS is what makes managed broadband networks work better than the public Internet.
Conversationally, its spoken either as its constituent letters, or as a word: “Kwoss.”
The quality additions can be applied in speed — you need more speed to view a streamed clip — or in transit timeliness. The latter matters especially to isochronous services, like phone. Without QoS, voice calls over the IP data path run the risk of sounding awkward — where one or both callers feels the need to follow each uttered phrase with “over,” or where callers start to sound like the teacher in Charlie Brown.
Technically, at least as it relates to the cable industry, QoS is rooted in the DOCSIS 1.1 cable modem specification. Essentially, 1.1 describes a way to “stripe” packets that flow to and from a cable modem. The striping is done with “service identifiers” (SIDs, pronounced “sihds”). There are 16 of them in DOCSIS 1.1. How they’re applied depends on the strategic roadmap of varying service providers, and what qualitative, competitive differences they want to offer.
Prior to DOCSIS 1.1, cable modem technology followed a best-effort practice: Available bandwidth was shared by the number of simultaneously-used modems connected, per 500-home HFC node. Nobody could take priority over each other for more bandwidth. To keep heavy users from being bandwidth hogs, cable providers capped everyone at maximum downstream/upstream rates, usually 1-2 Mbps/384 kbps. (This was before the “speed wars” between cable and DSL.)
Note that the qualitative and quantitative improvements that can be put into motion with QoS are not contained to broadband speeds. Consider, for instance, Customer Bob, who happens to buy a cell phone with built-in WiFi capabilities. Let’s say Bob isn’t particularly enthused with the cellular service he gets inside his house. However, Bob also happens to have a WiFi network, and a cable modem, in his house.
In the growing discussions between cable and wireless providers, one obvious use of cable’s QoS is to jointly solve Bob’s problem: When he’s in his house, he’s talking on the WiFi part of his cell phone. The cable modem, behind the WiFi antenna, hands his speak-bits off to his cellular carrier. When Bob climbs into his car and backs out of the driveway, the call reverts to cellular mode.
The technology behind making that scenario work, behind the scenes, is QoS. It “protects” Bob’s speak-bits, so that they get to where they’re going (the person he’s talking to) without incident.
Couldn’t the cellular carrier just bypass the cable operator, and do the WiFi connection to Bob without the knowledge of the broadband connection?
Yes. The notion of “bypass” started with companies like Vonage adding voice services, undetectably, over cable modem passageways. Yet it can be extended to practically anything the imagination can cook up. But, without QoS, “bypass” services will only be as sturdy as the weakest link in their delivery chain — which means they have an “end-and-end” connection, not an “end-to-end” link.