Low Latency DOCSIS - Technology Overview
draft-white-tsvwg-lld-00

Abstract

NOTE: This document is a reformatted version of [LLD-white-paper]. 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. 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 equipment 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.

Authors

Greg White
Karthik Sundaresan
Bob Briscoe

(Note: The e-mail addresses provided for the authors of this Internet-Draft may no longer be valid.)