Low Latency DOCSIS: Technology Overview
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© CableLabs 2019
Executive Summary
The evolution of the bandwidth capabilities—from kilobits per second to gigabits—across generations of DOCSIS cable broadband
technology has paved the way for the applications that today form our digital lives. Along with increased bandwidth, or “speed,” the
latency performance of DOCSIS technology has also improved in recent years. Although it often gets less attention, latency
performance contributes as much or more to the broadband experience and the feasibility of future applications as does speed. Now,
as we are looking toward a “10G” future with a 10 gigabit per second broadband platform, we need to make a similar quantum leap in
latency reduction—and that’s why we’re pioneering Low Latency DOCSIS technology.
Low Latency DOCSIS technology (LLD) is a specification developed by CableLabs in collaboration with DOCSIS vendors and cable
operators that tackles the two main causes of latency in the network: queuing delay and media acquisition delay. LLD introduces an
approach wherein data traffic from applications that aren't causing latency can take a different logical path through the DOCSIS network
without getting hung up behind data from applications that are causing latency, as is the case in today’s Internet architectures. This
mechanism doesn't interfere with the way applications share the total bandwidth of the connection, and it doesn't reduce one
application's latency at the expense of others. In addition, LLD improves the DOCSIS upstream media acquisition delay with a faster
request-grant loop and a new proactive scheduling mechanism. LLD makes the internet experience better for latency sensitive
applications without any negative impact on other applications.
The latest generation of DOCSIS that has been deployed in the field—DOCSIS 3.1—experiences typical latency performance of around
10 milliseconds (ms) on the Access Network link. However, under heavy load, the link can experience delay spikes of 100 ms or more.
LLD systems can deliver a consistent 1 ms delay on the DOCSIS network for traffic that isn’t causing latency, imperceptible for nearly
all applications. The experience will be more consistent with much smaller delay variation.
LLD can be deployed by field-upgrading DOCSIS 3.1 cable modem and cable modem termination system devices with new software.
The technology includes tools that enable automatic provisioning of these new services, and it also introduces new tools to report
statistics of latency performance to the operator.
Cable operators, DOCSIS equipment manufacturers, and application providers will all have to act in order to take advantage of LLD.
This white paper explains the technology and describes the role that each of these parties plays in making LLD a reality.
Introduction
Let's begin with bandwidth (or “speed”): the amount of data that can be delivered across a network connection over a period of time.
Sometimes bandwidth is very important to the broadband experience, particularly when an application is trying to send or receive large
amounts of data, such as watching videos on Netflix, downloading videos/music, syncing file-shares or email clients, uploading a video
to YouTube or Instagram, or downloading a new application or system update. Other times, bandwidth (or bandwidth alone) isn’t
enough, and latency has a big effect on the user experience.
Latency is the time that it takes for a short message (a packet, in networking terminology) to make it across the network from the
sender to the receiver and for a response to come back. Network latency is commonly measured as round-trip-time and is sometimes
referred to as "ping time." Applications that are more interactive or real-time, like web browsing, online gaming, and video
conferencing/chatting, perform the best when latency is kept low, and adding more bandwidth without addressing latency doesn’t make
things better.