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CODE DIVISION MULTIPLE ACCESS FOR DETERMINISTIC ETHERNET APPLICATIONS

IP.com Disclosure Number: IPCOM000239475D
Publication Date: 2014-Nov-11
Document File: 8 page(s) / 172K

Publishing Venue

The IP.com Prior Art Database

Abstract

Presented herein is method to determine zero-jitter regular scheduling for Deterministic Ethernet time sensitive traffic that does not enforce constraints on flows, but instead, relies on Code Division Multiple Access (CDMA) encoding of the Ethernet payload.

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CODE DIVISION MULTIPLE ACCESS FOR DETERMINISTIC ETHERNET APPLICATIONS

  AUTHORS: Salvatore Valenza

 Domenico Ficara Roberto Muccifora Leo Caldarola

Davide Cuda

CISCO SYSTEMS, INC.

ABSTRACT

    Presented herein is method to determine zero-jitter regular scheduling for Deterministic Ethernet time sensitive traffic that does not enforce constraints on flows, but instead, relies on Code Division Multiple Access (CDMA) encoding of the Ethernet payload.

DETAILED DESCRIPTION

    In the context of industrial automation, Deterministic Ethernet has gained attention as a way to adopt widely used Ethernet technology for time critical and sensitive tasks such as those that take place in factory plants and vehicles. Deterministic Ethernet may exhibit packet loss and deterministic reduced jitter for time sensitive traffic. This is accomplished through careful ad-hoc scheduling of streams that is mostly done off-line and often enforces some constraints on streams.

    Deterministic Ethernet (DE) applications are intrinsically jitter sensitive, e.g., industrial automation with sensors and Programmable Logic Controllers (PLCs) may expect to receive data at a predefined point in time. This is usually a very hard constraint to meet, especially when fragmentation of data and multiple paths for forwarding data comes into the picture. An innovative technique is presented herein to provide zero jitter traffic.

Copyright 2014 Cisco Systems, Inc.

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    Since this field is growing, and has recently seen a number of different companies proposing their own solution, the scheduling algorithm for Deterministic Ethernet is usually specific to each company and is not publically disclosed. This solution proposes to adopt a Deterministic Binary Scheduler (DBS).

    A related approach proposes a scheduler that solves most of the problems of DBS for all rates with optimal minimum jitter, based upon Information Theory findings.

    However, in all pure time-slot scheduling systems, because of the discrete nature of slots, there will always be a minimum amount of jitter, e.g., if flows A and B have periods of 4 and 3, respectfully, they are bound to collide at a certain slot, as shown in Figure 1).

Time 0 1 2 3 4 5 6 7 8

A A A

B B B

Figure 1. Collision case for periodic flows

    In this example, outcome scheduling, as shown in Figure 2, will definitely provide some jitter as the third packet of flow B is moved to slot 7, although it was due for slot 8.

Time 0 1 2 3 4 5 6 7 8 Scheduling A B A B B A

Figure 2. Scheduling for flows of fig.1,

Jitter occurs for flow B in slot 7

    In order to remove the jitter, CDMA techniques may be used. A brief overview is provided below.

Copyright 2014 Cisco Systems, Inc.

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CDMA Techniques Generally

    CDMA allows multiple users to transmit at the same time on the same physical medium. This is done using a combination of a stream of bits to be transmitted with orthogonal codes called chip codes. The chip codes are a pseudo-random periodic sequenc...