DOCSIS®
Data Over Cable Service Interface Specification
*** see http://www.cablemodem.com/specifications/ for all DOCSIS specs
The CableLabs® Certified™ Cable Modem project, also known as DOCSIS® (Data Over Cable Service Interface Specification), defines interface requirements for cable modems involved in high-speed data distribution over cable television system networks. The certified cable modem project also provides cable modem equipment suppliers with a fast, market-oriented method for attaining cable industry acknowledgment of DOCSIS compliance and has resulted in high-speed modems being certified for retail sale. CableLabs is a membership organization of cable companies that service North and South America. One of its main goals is to promote interconnectivity among different hardware vendors.
The Excitement over DOCSIS 3.0
*** the vast majority of MSO's only offer DOCSIS 1.1, a few offer 2.0, but they are all talking about 3.0 !!!
Even though the industry is still mired in DOCSIS 1.1 (only a handful of MSO's offer DOCSIS 2.0) - today the buzz is all about DOCSIS 3.0, also called "channel bonding", or "wideband". The new protocol would likely require a silicon change (new hardware) at the modem and at the CMTS. It could offer an incredible downstream bandwidth of 200 Mbps per channel, and 100 Mbps per channel upstream. Today, DOCSIS 2.0 delivers up to 40 Mbps down/30 Mbps up. The 3.0 version would give operators enough bandwidth to offer a wide range of IP-based, entertainment-quality media services. Since the MSO's are offering v1.1 today, the strategy will likely involve a direct jump to 3.0, skipping DOCSIS 2.0 altogether. The faster pipe could also help cable operators stay a step ahead of DSL in the Internet data service speed race.
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DOCSIS 1.1 is the current version being used ! ! !
Before the customer can upgrade, the Cable Companies (MSO's) must first upgrade their infrastructure, and then the cable modem manufacturer's will begin selling the boxes.
Status of DOCSIS Versions
DOCSIS 1.0 (High Speed Internet Access)
DOCSIS 1.1 (Voice, Gaming, Streaming)
DOCSIS 2.0 (Capacity for Symmetric Services)
DOCSIS 3.0
DOCSIS Specs
DOCSIS 1.0
DOCSIS 1.1
DOCSIS 1.1 builds upon 1.0, but also includes the following features:
DOCSIS 2.0
DOCSIS 3.0
*** not released yet !!!
CableLabs commissions and oversees research of new technologies at the request of its members. In fact, the cable industry asked CableLabs to develop a set of standards so that CMTSs and cable modems could be used without the fear of incompatibility. For more information about CableLabs, you can check out the Web site at www.cablelabs.com .
The group's efforts to create a communication standard resulted in what is now known as Data Over Cable Service Interface Specification (DOCSIS). This standard communication specification is currently paving the way toward interoperability among cable modems and CMTSs. DOCSIS is currently at version 1.0, with version 1.1 being prepared for release sometime early next year.
The DOCSIS 2.0 specification promises to be more mature and pave the way for new technologies over the cable network. Quality of service (QoS) was one of the new features built into DOCSIS 1.1 and that has been refined in 2.0. Much like the QoS found in ATM, this lets the service providers guarantee a given amount of bandwidth to its customers. By slicing the bandwidth into smaller chunks, while not giving the full potential bandwidth of the cable, it allows more users to consistently get greater throughput.
CMTS (Cable Modem Termination Systems)
The CMTS is the unit that is purchased by and resides at the cable operator's facility, and acts as the connection between the cable network and the outside network. Cable modems are "certified" interoperable with each other while headend devices called Cable Modem Termination Systems (CMTSs) are qualified. CMTSs are termed "qualified" when they pass an interoperability test procedure similar to the modems. Here is a Certified List of CMTS's.
DOCSIS 3.0 and M-CMTS - Lightning-Speed Internet Access
IMPORTANT - DOCSIS 3.0 compliant modems are not commercially available yet. Even if the modems were available, they would be useless until the MSO's first upgrade their infrastructure !!! That will likely be a costly proposition, but well worth it.
Modular CMTS, or M-CMTS, is one of the latest initiatives within DOCSIS® 3.0 standardization to enable the development of a CMTS (cable modem termination system) where different elements can be implemented as separated physical entities.
Traditional CMTSs were built as a single monolithic entity. Inside a CMTS, you have various technologies - IP switching/routing, DOCSIS MAC (media access control), downstream QAM modulation and RF upconversion, and upstream QPSK/QAM demodulation. In the early development of the CMTS it was beneficial to have all of these technologies living in the same box to accelerate the development and deployment of the first systems. Nowadays, breaking these technologies apart allows operators to leverage economies of scale and share some components across multiple services.
One of the key goals of an M-CMTS is to enable higher data throughput for cable data subscribers. This is achieved by allowing multiple downstream data QAM channels to serve the same service group - commonly known as channel bonding or wideband DOCSIS.
VoD (Video on Demand) vs DOCSIS 3.0
VoD is a cable service that makes use of the same type of downstream QAM channel. DOCSIS 3.0 and the M-CMTS allow VOD Edge QAM channels, with minor modifications, to be alternatively employed as DOCSIS downstream data channels. Furthermore, sophisticated edge resource management will allow operators to flexibly and dynamically repurpose a VOD QAM channel to be a DOCSIS data channel, and vice versa. During the daytime, when VOD utilization is low, a VOD channel could be repurposed to be a data channel to provide, say, bandwidth capacity for commercial services. The widespread deployment of VOD Edge QAMs, and the subsequent rapid decline in per-QAM capital costs, is the catalyst which will enable the widespread and cost-effective deployment of wideband DOCSIS.
The M-CMTS main technical challenge - Timing ! ! !
A. DOCSIS has some sensitive timing requirements that regulate the flow of downstream and upstream data. When the upstream and downstream components are separated, extra care must be taken to ensure that these timing sensitivities are still respected.
DOCSIS 1.x and 2.0 make the assumption that a single downstream channel is associated with an upstream channel (although that downstream channel may be shared among many upstream channels). With just one channel, timing and synchronization is straightforward. However, with DOCSIS 3.0 multiple downstream channels can be associated with a single upstream channel.
The 4 Components of DOCSIS 3.0
M-CMTS offers exciting new opportunities that combine the best elements of video and the DOCSIS infrastructure technologies. This will enable more and better services over efficient and well managed cable plants. The following four Specifications will pave the way for multi-vendor M-CMTS component and solution offerings:
