GPON Framing Structure:Uplink Frame

GPON Framing Structure

Uplink Frame Structure

Well, after this “GPON Framing Structure:Downlink Frame”–the basic introduction about GPON downlink frame structure, hope our readers have a certain interesting in GPON frame structure.

Like a twins,there is not only DownStream but also UpStream. Now warmly introducing to the another blog chapter: uplink frame structure.

Introduction

A PON’s upstream channel behaves in a model of point to point communication. Here, each ONT transmits content to the OLT at 1310nm. It is therefore necessary to use arbitration transmission channel models by use of TDMA (Time Division Multiple Access) for each ONT send the information in different times. This control is done from the OLT. At the same time, all users are synchronized through a process known as “Ranging.” 

US(UpStream) GPON format

As shown in the picture below, there are 4 different US overhead types:

  PLOu: Physical Layer Overhead upstream

        –  always sent by ONU when taking over from another ONU
        –  contains preamble and delimiter (lengths set by OLT in PLOAMd)

           BIP (1B), ONU-ID (1B), and Indication of real-time status (1B)

  PLOAMu: PLOAM upstream (13B) – messaging with PLOAMd

  PLSu: Power Levelling Sequence upstream (120B)

        –  used during power-set and power-change to help set ONU power so that OLT sees similar power from all ONUs

  DBRu: Dynamic Bandwidth Report upstream

        –  sends traffic status to OLT in order to enable DBA computation

 Payload: Payload data, may be a data frame or DBA status report,Payload=(DBA Report+Pad)/(Gem Header+Gem Frame)

GPON Upstream Framing structure

GPON Upstream Framing structure

GEM introduction

Unlike ATM cells, GEM(GPON Encapsulation Modedelineated frames may have any length,any number of GEM frames may be contained in the GEM partition.ONUs accept GEM frames based on 12b Port-ID in GEM header 

  • GEM is generic – any packet type (and even TDM) supported
  • GEM supports fragmentation and reassembly 

GEMGPON Encapsulation Mode is based on GFP, and the header contains the following fields:

PLIPayload Length Indicator – payload length in Bytes

Port ID :Identifies the target ONU

PTI:Payload Type Indicator (GEM OAM, congestion/fragmentation indication)

HEC:Header Error Correction field (BCH(39,12,2) code+ 1b even parity) 

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