DOCSIS 3.1 Speeds
DOCSIS, which stands for Data Over Cable Interface Specification, is the international standard regulating the use of coaxial cable lines and modems providing data transmission and internet services at high speeds over specified frequencies.
Since the release of DOCSIS 1.0 in 1998, the standard has undergone multiple iterations, each representing a significant increase in speed, performance, or both. The current standard, DOCSIS 3.1, has utilized orthogonal frequency division multiplexing (OFDM), forward error correction (FEC) and other advancements to achieve speeds previously attainable only through fiber optic technology.
The DOCSIS Standard
In 1994, the Institute of Electronic and Electrical Engineering (IEEE) formed a working group of industry experts to develop an international cable modem standard. When the long-awaited specification still had not been delivered more than two years later, cable operators joined forces to form the Multimedia Cable Network System Partners Ltd. (MCNS) and began drafting a new standard of their own. The eventual result was DOCSIS 1.0.
CableLabs began their certification program for DOCSIS equipment in 1998, ensuring interoperability between different vendors’ devices. This has continued through the years over multiple iterations, leading up to DOCSIS 3.1 and 3.1 Full Duplex. The International Telecommunications Union (ITU) has ratified multiple DOCSIS versions as international DOCSIS standards, although discrete annexes of the standards are sometimes required to accommodate differing frequency and bandwidth allocation outside of the United States, such as “EuroDOCSIS”. Certification is often performed by other organizations within the county or region of origin.
DOCSIS Speed Improves
While the proliferation of cable television may have been the driving force that led to a common standard for coaxial cable connections, the eventual result was a remarkably fast mode of internet data transmission that continues to keep pace with the insatiable appetite for bandwidth.
The earliest DOCSIS internet connections achieved speeds surpassing anything that had preceded them, but the innovative premise of internet transmission through coaxial television cable was perhaps ground breaking enough in the early adoption stages. When DOCSIS 1.1. arrived in 1999, the focus was not on enhancing the speed of DOCSIS but improving quality of service (QoS) through privacy improvements and traffic prioritization. Still utilizing a single channel, DOCSIS download speeds clocked in at 40 Mbps, while DOCSIS upload speeds of 10 Mbps were the norm.
Obtaining the improvement in upload speeds that symmetrical applications like peer-to-peer file sharing and VoIP required was a challenging proposition for new millennium developers. DOCSIS 2.0, released in 2002, made use of wider bandwidth to bump DOCSIS upload speeds up to 30 Mbps, but download speeds remained unchanged from DOCSIS 1.1.
The advent of streaming and other data-intensive innovations made additional DOCSIS speed and capacity enhancement imperative. Since replacing or redesigning existing coax lines was not a viable option, more traffic had to be crowded into the same geometric space, all the while traveling exponentially faster. Accomplishing this on our automotive highways would doubtless be a recipe for gridlock or worse. DOCSIS 3.0 was the innovation that rose to this formidable challenge.
DOCSIS 3.0 Max Speeds
There is no doubt fiber has inherent advantages over coax cable when it comes to bandwidth and speed. With an ultra-thin profile, low power consumption over long distances and light-speed delivery, fiber optic cable deployments including fiber-to-the-home (FTTH) have significantly raised the bar for speed and reliability. A cogent improvement was required to prevent DOCSIS from being left behind, and DOCSIS 3.0 delivered this by providing maximum DOCSIS download speeds exceeding 1 Gbps, while DOCSIS 3.0 upload speeds climbed to 200 Mbps or more. The breakthrough technology that made this leap in DOCSIS speeds possible was channel bonding.
“Bonding”, in this context, means sending segments of data simultaneously through multiple channels, then recombining the data at the destination, providing more efficient utilization of the available bandwidth. To the modem, the bonded channels are discrete pieces of one larger channel, even though they are physically separate and not necessarily adjacent. This advancement allowed cable modems to combine multiple quadrature amplitude modulation (QAM) channels into groups, for both the receiving and sending of data.
Each additional channel doubles the data carrying capacity in that direction. For example, what was a 40 Mbps upstream/30 Mbps downstream DOCSIS 2.0 configuration could be multiplied by up to 32x in the downstream and 8x in the upstream using DOCSIS 3.0, producing a maximum total speed of around 1.2 Gbps upstream/240 Mbps downstream.
DOCSIS 3.1 Max Speeds
If high speed internet service was a race, fiber optics would certainly find itself in the pole position. Utilizing new innovations such as wavelength division multiplexing (WDM) and spatial division multiplexing (SDM), transmission speeds over fiber exceeding 9.6 Tbps have been recorded in tests. This is nearly one thousand times greater than DOCSIS 3.1 max speeds. Given the physical limitations of traditional cable, this gap in performance can never be fully bridged. DOCSIS 3.1 has differentiated itself in other important ways to remain viable.
In terms of deployment costs, DOCSIS 3.1 allows the “last mile” between node and subscriber to retain its coax infrastructure, even while the cable feeding these interfaces is increasingly supplanted by fiber. This last mile is where most of the digging, plowing, installing and connecting takes place for pure FTTH installations, so the monetary implications of the DOCSIS 3.1 option are significant.
DOCSIS 3.1 is fully backward compatible with DOCSIS 3.0, meaning users can keep their existing modems rather than making wholesale equipment changes. This backward compatibility has allowed a gradual and seamless transition between DOCSIS iterations. With improvements in error correction also incorporated in DOCSIS 3.1, higher orders of modulation, including 4096 QAM and scaling up to 16384 QAM, are now supported.
- DOCSIS 3.1 Downloads
DOCSIS download speeds have continued to meet the needs of users consistently, and the 10-fold improvement over DOCSIS 3.0 has increased this specification to an impressive 10 Gbps. This has largely been accomplished through the introduction of orthogonal frequency domain multiplexing (OFDM), an advanced modulation technique designed to squeeze even more signals into a finite space by minimizing the space required between them.
- DOCSIS 3.1 Upload Speeds
DOCSIS 3.1 upload speeds can reach 2 Gbps. This has enabled seemingly instant transmission of large files, videos, and other content that previously took hours to upload. With new applications like virtual reality and gaming once again driving the demand for symmetric data delivery, Full Duplex DOCSIS 3.1 has been created to provide 10 Gbps speeds for both upload and download directions. This means simultaneous 10 Gbps transmission in both directions, utilizing the same spectrum.
- DOCSIS 3.1 Upstream
Given the current focus on upstream performance, it is imperative to take advantage of each opportunity to optimize DOCSIS 3.1 upstream transmission quality. Pre-equalization of cable modem termination system return ports is one way to achieve this. Another important consideration is the upstream modulation profile. By paying attention to the modulation error rate, the actual volume of information contained in the modulated signal can be quantified and optimized.
DOCSIS 3.1 Latency
Since transmission speeds have outpaced most users’ requirements in recent years, noticeable delays in web page uploads, communication responses, and other performance issues are now more latency-dependent than was the case in the early days of DOCSIS. Many web pages require numerous round trips to fully load, so even latency in the 500 millisecond (ms) range can be easily perceptible in the aggregate.
DOCSIS 3.1 technology has improved upon packet-queueing algorithms, leading to a significant improvement in overall packet latency. This is particularly important for applications like online gaming that are more sensitive to perceptible system lag. Active Queue Management has been incorporated into DOSCIS 3.1, whereby the transmission control protocol (TCP) is monitored to optimize traffic flow and buffer levels. Low Latency DOCSIS (LLD) technology can reduce latency to as little as 1 ms.
The benefits of DOCSIS cannot be fully realized unless the correct provisioning steps have been implemented to set up and optimize the network for DOCSIS 3.1. For example, although subscribers may utilize a wide variety of modems and devices, provisioning strategies that integrate firmware management will ensure the latest updates required for optimal performance are intelligently deployed.
Validating DOCSIS configuration files is another provisioning function that is essential for error reduction and efficient device registration. New devices entering an existing provisioning platform should automatically be detected and the DOCSIS version identified. In this way, the correct services can be assigned to the user. Privacy and security are additional QoS concerns that can be addressed through DOCSIS provisioning. Services that scan device leases regularly are one approach that is used to detect and block illegitimate users, preventing unwanted network intrusions.
DOCSIS 3.1 has kept the DOCSIS platform in the high-speed internet conversation through creative physical layer utilization, innovative modulation processes and advanced provisioning protocols. As the five generations of DOCSIS over twenty years have proven, further speed and quality enhancements are always possible. DOCSIS 3.1 speeds have already entered the Terabit zone, but this may very well be only the beginning.